CA1131004A - Molecular glasses for nuclear waste encapsulation - Google Patents
Molecular glasses for nuclear waste encapsulationInfo
- Publication number
- CA1131004A CA1131004A CA339,896A CA339896A CA1131004A CA 1131004 A CA1131004 A CA 1131004A CA 339896 A CA339896 A CA 339896A CA 1131004 A CA1131004 A CA 1131004A
- Authority
- CA
- Canada
- Prior art keywords
- melt
- glass
- block
- waste
- radioactive waste
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Landscapes
- Glass Compositions (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A molecular glass based upon a phosphate of aluminum, or other trivalent metal, provides significant improvement over prior art glasses for encapsulation of high level radioactive nuclear waste. When containing a controlled amount of those elemental oxides found in a typical nuclear waste, the waste-glass could not be forced to devitrify, exhibited hydrolysis losses lower by an order of magnitude, had higher solvency power for these elemental oxides, exhibited no tendency for in-ternal crystallite formation, and possessed other desirable physical characteristics; all in direct antithesis to the properties of the best prior known glasses used for this application.
A molecular glass based upon a phosphate of aluminum, or other trivalent metal, provides significant improvement over prior art glasses for encapsulation of high level radioactive nuclear waste. When containing a controlled amount of those elemental oxides found in a typical nuclear waste, the waste-glass could not be forced to devitrify, exhibited hydrolysis losses lower by an order of magnitude, had higher solvency power for these elemental oxides, exhibited no tendency for in-ternal crystallite formation, and possessed other desirable physical characteristics; all in direct antithesis to the properties of the best prior known glasses used for this application.
Description
BACKGRO~ND OF THE INVENTION
, .
Radioactive waste has arisen from two major sources: production of nuclear weapons and production of nuclear enërgy. The waste can take at least three forms.
By far the largest volume is liquid waste from commercial nuclear ~nergy ~enexating plants. To recover unused uranium and/or plutonium, the spent fuel rods are dis-solved in nitric acid. After removal of these actinides, the strong acia wastes are neutralized and stored in steal tanks. The problem has been that the tanks corrode with subsequent leakage of high-level radioactive liquids into the biosphere.
One can convert the radioactive liquids to solid oxides but this physical form can also be aispersed fairly easily. These powders are generally referred to as cal-cines. The level of radioactivity from calcine is very high and of the order of 1.5 million rads (R3 per hour as a dosage. After storage for a hundred years, the level will have dropped tb 5800 R per hour but 1000 years storage i5 indicated before an acceptable dose-rate for humans arises. However, the above refers only to sub-uranic, or fission product wastes. I the actinides such as uranium and plutonium are not removed, then the wastes must be kept in secure storage for about 250,000 years before they can be considered safe for human exposure.
The volume of commercial waste (high level waste - HLW~ is enormous. About 74 million gallons have existed, ox will exist once the stored spent-fuel rods are processed.
Because of the lack of a really satisfactory disposal method for HLW, a major part of the spent fuel rods have been st~red under water in underground bunkers. The United States has sufficient uranium stockpiled so that recovery of unused uranium from the spent fuel.rods is not critical.
'' '~ .
~13~)4 Howeve~, this practice cannot continue indefinitelyn Some of the liquid waste already produced has been converted to calcine. There is about 3.9 million (M) cubic feet of unprocessed liquid waste which will form some 585,000 cubic feet of calcine.
The second form of radioactive waste consists of actinide waste which has been separated from HLW and other sources. It amounts to about 1.8 M cubic feet of liquid waste. The third form of radioactive waste, weapons waste, amounts to about 75 M gallons, or about 9.6 M cubic feet. This waste is of lower radioactivity level than that of HLW from reprocessing of commercial fuel rods, but that of separated actinide waste is much high~r in radioacti~i~y emissions level.
The use of glass for containment of high-level rad~oactive waste has been under development for many years. There are many attractive features of this mode of encapsulationO They include a rigid incorporation of the radioactive ions, or species, by dissolving them into the melt to form the glass structure. They are then not free to move as long as the glass st:ru~ture is maintained.
Glass is not subject to grain growth, surface ox~dation, and o-ther factors common to crystalline solids. However, there are six critical properties required for any glass in this application. These include:(l) minimal tendency to devitrify, (2) low hydrolytic leach rate~ ~3) high solvency power, ~4) relatively low melt temperatures, (5) low tendency to form crystals from the added waste com-ponents, and (6) low softening point and viscosity of the melt.
Devitrification refers to the proclivity of an amorphous solid (glass~ to beco~e crystalline. All 'glass will devitrify provided that the internal temperature _5 o~ the glass b~d~ is r~ised to a certain point ca,lled the devitrification temperature. The devitrification process is exothermic; that is, it releases heat, so that when devitrification starts, it is self-sustaining.
The devitrification product COlISiStS of microcrystals so that the mass is friahle and easily dispersed~ It is therefore important to maintain the amorphous state for the HLW encapsulation ~pplication. The problem is that the incorporated HLW is a heat source through natuLal fission pxocesses plus absorption of energy from the em-itted radiation by the glass matrix. 'Internal temperatures of up to 850 C. have been observedO Thus all of the prior glasses used for this application have devitrified when the incorporated HLW has heated the glass to its devitri-! fication temperature during storage. This remains a severe problem for which theie has been no solution heretofore.
Since the HLW-glass is to be stored for prolonged times as a solid mass, the hydrolytic leach rate, as a loss of the surface of the glass bociy, is important,, Ordi-nary window glass has a relatively high leach rate of 5.3 x 10-4 gm/cm2~hr in boilin~water. A good waste~glass must have a value of at least 150 times smaller than this.
Granite, an igneous rock, has a leach rate of about 4~6 x 10-6 gm/cm2/hr while that o marble is about 1.2 x 10 5 gm/cm2/hr. Since the waste-glass is to be stored in under-ground rock vaults, its hydrolytic leach rate ou~ht to be less than the surrounding roc]c.
When the HLW is to be added to the glass melt, all of the components need to be dissolved. Many of them are refractor~ oxides such as CeO~, Zr02 and Ru02. A
high solvency power of the melt is thPrefore needed. In j most glasses, the addition of excess oxides to the glass ~331~4 melt tends to cause formation of insoluble crystallite.s as specific compounds which begin to recrystallize and grow larger. When the rnelt is cask, the crystals, as a second phase, form centers of internal strain, thereby causing the glass to develop cracks and become friable.
Hence it is also desirable if the glass exhihits little or no tendency for internal crystallite formation.
Furthermorel the processing temperatures required for production of glass need to be relatively low for ~uclear waste encapsulation, preferably not over 1400 C. Conservation of energy is one reason for this limitation while another is that the containers intended for actual storage o~ the waste-glass cannot stand process-ing temperatures in excess of this value~ Finally, the glass melt also needs to have a low viscosity so that added waste oxides can be dispersed into the melt more easily.
The best glass known heretofore for the nuclear waste encapsulation application, a zinc borosilicate (ZBS)~
was developed especially for this purpose. A melt is produced at 1400 C. which has a viscosity of less than 200 poise. Up to 45~ by weigh~~of the HLW oxides can be dissolved into the melt. The hydrolytic leach rate is lower by an order of magnitude than most commercial glasses.
Unfortunately, HLW-ZBS ~lass devitrifies at 750 C. and so~tens at 570~ C. Refractory waste oxides such as Ru02, CeO2 and ZrO2 do not dissolve at all well into the melt and crystallites of Zn2SiO4, SrMoO4, NdBSiO5 and Gd2Ti207 are among the crystalline compounds observed to ~orm in the glass or devitrified product.
t ~ ~.31~0~
SUMM7~RY O~ THE INVENTION
I have found the use of a molecular glass, based upon a polymexized phosph~te o~ aluminum (PAPj, indium or gallium and made according to methods already given in U.5~ Patent No. 4,~49,779 and U.S. Patent No. 4,087,511, overcomes all o~ the prior objections to use of glass as a high-level nucleax waste encapsulation agent. ~his ~LW glass product could not be made to devitrify, disso~ved all of the oxides found in calcine, including the difficultly soluble ones~ did not form microcrystallites în the melt or subsequent glass-casting, and possessed a hydrolytic etching xate to boiling water even lower than that of HLW-~B5 slass.
In accordance with the present invention, a pre-cursor compound, M(H2P04)3, is prepared according to methods of U.S. Patent No. 4,049,779, where M is a trivalent metal selec~d f ~ ~e group consisting of aluminum, indium and gallium. Advantageously, the impurity level is carefully controlled so as not to exceed 300 ppm. total. The pre-cursor crys1-als may be washed to remove excess phosphoric acid as desired. HLW is added to the crystals and the mixture is then heated at a co~rolled heating xate to induce solid state polymerization and to form a melt a~
1350 C~ in which the ~W oxides dissolve rapidly. When aluminum was used, the resulting HLW-PAP glass had a hydro-lytic leach rate to boiling water some 15.8 times lower than HL~ZBS glass, The melt dissolved all components of the HLW and no crystallite formation was noted in the melt or in the finished glass form. The softening point of HLW-PAP glass is 650 C. It has a high thermal conductivity, a low thermal expansion which above 350 C. has been observed t~ become negative, possesses a low cross-section for absorption of radiation, and apparently does not re~uire ~r ~3 I,. rmal annealing to relieve internal stress generated during casting ~f the melt to ~orm the glass, like other. ~~
pxior known glasses.
Alternately, the HLW can be mixed with the formed precursor crystals plus phosphoric acid to form H~ phosphate compounds prior to melting the precursor crystals to produce the HLW glass composition. Another method which produces a very stable HLW glass substance involves the preparation of a solid prefire, by firing the precursor rrystals at 1100 C. to form a calcine, to which th~ H~W is added. A melt is then formed at 1350 C., which is subsPquently cast to produce the stable HLW
glass block ~or long term storage. Still another alternate is the formation of the polymexized melt from the pre cursor crystals, follow~d by casting the melt to form a glass, to form a glass frit~ The frit softens at 822 C.
and HLW dissolves into ~he melt at 1150 C. rapidly to form the solidified HLW glass block as a ~inal prodl~ct for prolonged or permanent storage.
.. . . . .
me present invention, in one aspect, ~hen, resides in a nuclear waste block for storage of high level ra~ioactive was~e, said block comprising, in combination:
~olid radioactive waste material dispersed in a polymeric phospha~e glass selected from the group consisting of polymeric phosphate glasses having the general formula M3 P7 22 and polymeric phosphate glasses having the general formula M(PO3)3, wherein M is a trivalent metal selected from the group consisting of aluminum, indium and gallium, and mlxtures of said phosphate glasses.
According to another aspect of the present inv~ntion there is provided a process of using a polymeric phosphate glass selected from the group consisting of polymeric phosphate ylasses having the general fo.rmula M3 P7 22 and polymeric phosphate glasses having the general formula M (PO3)3, wherein M is a trivalent metal selected from the group consisting of aluminum, indium and gallium, and mixtures of said phosphate glasses, said process comprising the steps of:
forming a mel~ o said glass;
dissolving high level radioactive waste in said r~lt; and .
~ ~L3~
- 8a-allowing said nelt incorporating said radioactive ~ -waste to cool and solidify into a block;
said block with its encapsulated radioactive waste being ~uitabl~ for prolonged or permanent storage.
,~
~v~
~3~ 0gL --g . .
.
DESCRIPTIOl~ OF THE PREFERRED l~MBODIMENTS
-I have determined tha~ a high degree of chemical durability of non-silicate glasses, such as those based upon phosphate, sulfate and the like, cannot be attained unless a precursor is first formed as a separate phase, heated to induce solid state polymerization of said phase, to form a melt, to form a polymerized glass. For encapsu-lation of high-level radioactive nuclear waste, a poiymerized phosphate of aluminum is required, possessing a high degree of purity. The precursor compound is prepared by dissolv-ing an aluminum compound in an excess of phosphoric acid.
Al(OH)3 is preferred as a source of aluminum although other aluminum compounds can be employed. It is important to maintain a certain molar ratio of H3P04 : Al in the solu-tion. The minimum is about 6 : 1 mols per mol but 7 : 1 works much better~ and ratios as high as 9 : 1 have been found useful. The higher ratios accelerate Al(OH)3 dis-solution, which may take 3-5 days at the 6 : 1 ratio. After purification of the resulting solution, controlled evapora-tion is employed to obtain the precursor ~rystals, Al(H2PO4)3, with good yield. These crystals, of high crystallinity and regular morphology, are th~n washed with an organic sol~ent such as methyl-ethyl ketone or ethyl acetate, but not'limited to those solvents, to remove excess H3P04 to produce mon~basic crystals uncontaminated by other chemical species or contained impurities, The presence of a large excess o~ H3P0~ during evaporation is essential, during the precursor crystal formation~ to prevent the appearance of other unwanted phosphates of aluminum which will not undergo solid state pol~merization when he~ted to elevated temperatures. Table I shows the analysis of a typical batch of precursor crystals used to prepare my new and improved glass for the nucleax waste encapsulation application.
~3~
T A B L E
Typical Analysis of Precursor Crystals Vsed to Prepare Polymeric Glass Impurity ~ mpurity Mg 10 Pb -~
Si 50 Cr 3 Fe 20 Mn --Cu -- Ca . 50 Al major Na . 100 Ni -- Li 15 Sr 3 K 30 Mo ~ -- Ba --Co ---- V .----The ~lass product prepared by heating the precursor crystals has a novel stoichlometxy not described or known heretofore.
For a typical preparation, the analysis of washed and dried crystals was: 98.38% Al(H2P04)3 0.04% ~3P04 1-58% ~2 ~pon heating the precursor crystals in a suitable container, all of the absorbed water is lost by the ~ime the temperature reaches 17S C. A loss of the three waters of constitution beyins sequentially at 210~ C. and is complete at 700 C., according to the reaction:
(1) m A1(~2P04)3 ~ ~Al(P03)3]m ~ 3 H20~' where m is an initial degree of polymerization, from m = 1 to m = 4. At about 866 C., the small amount of excess phosphoric acid is lost as 7 H3P04 3 H20. If a prefire or calcine is desired, the temperature is held at 1100 -1150D C. for several hours. If the temperature continues to rise, a further loss of P~05 is ~bserved above about 1200 C., according to the reaction:
~2) 3 [Al(P03)3] m ~ A13P7022 ~ m P205 The loss of P205 accelerates above the melting point of 1325 - 1350 C. and is complete by 1500 C. If the temperature is held at the melting point, ~he loss continues until the final stoichiometry given in reaction (2) is attained. This final stoi~iome~ is maintained while further polymeriza-tion continues. If ~he polymerization is allowed ~o continue, the stoichiometry begins to change fur~her and crys~als appear in the melt, according to the reaction:
(3) n A13P7022 ~ 2 [Al(P03)3]n ~ n AlP04~.
Since crystals are unwanted in the HLW-PAP glass application, the polymerization time o~ about 36 hours, required for the appearance o~ AlP04 crystals in the mel~, represents a maxi- ~
mum which can be used. The useful glass composition thus ~:
appears to be: A13P7022. A non-purified, washed precursor, containing about 4000 ppm of impurities, was analyzed to be:
98.23% AltH ~04)3 1.76% H20 0.01% H3P04 Upon heating, it behaved in an identical thermal manner and produced a glass composition, A13P7022, when polymerized for 16 hours. ~n unwashed batch of precursor crystals was analyzed to be.
( 2P04)3 10.37~ H20 21,28% H P04 .,~
,,~,....
Its thermal decomposition behavior was alsv identical t~
that described ahove~ The reac~ion is thus not affected by the degree of impurity level nor by the presence of excess phosphoric acid.
The same nominal glass composition may be formed by precipitatinq Al(P03)3 using metaphosphoric acid , and then ~iring the product. The precipitation reaction is:
(4) Al(NG3)3 ~ 3 ~PO3 3 3~ 3 Although this method is much to be preferred over the methods taught in the prior art, such as that of Hatch, Canadi.an Patents Nos. 449,983 and 504,835, it still suffers ~rom several deficiencies. Althouyh HP03 is very soluble in water, it tends to hydxolyze to ~3P04 rather easily so that the reaction ~4), given above, is difficult to control without introducing other unwanted aluminum p~osphates into the meit. In addit~on, contamination by the anion, in this case nitrate ion N0 , interferes with subsequent reactions.when the Al(P03)3 is isolated, dried, and then heated to form the glass melt. The worst. method to use is the method of Hatch who teahes to combine A1203 and P04 into a solid mass and then to fire the mass to fusion and quickly cool it. The resulting glass is subject to incipient recxystallization and is des~ribed as a ve.ry slowly water soluble dehydrated phosphate useful in water purification procedures. If an intermediate is not isolated, and if said intermediate is not of high purity, in contrast to the prior art, then the improved product o~ my new and improved invention does not result.
The products of the prior art inventions suffer fro... lack of stability to recrystallixation and lack of xesistance to hydrolytic etching by boiling water, which characterize and uniquely set apart the product o~ my new and improved 3L~L3~
invention for encapsulation of high level nuclear waste.
I have determined that it is much better to isolate the monobasic precursor, fire it to the prefire calcine~
and then to form the glass melt. The prior art has taugllt to use 3.00 mols H3P04 per mol of aluminum salt, ~ut even if one uses my improved ratio of 7.00 mol H3P0~ per mol of Al salt and fires ~his mixture, the glass product remains inferior and lacks many of the improved properties of my new and novel invention. Even the properties of the glass obtained from melting the isolated pxecipitated product Al(P03~3, remain inferior to those of my new invention.
Observed physi~al properties of my new improved glass, A13P7022, were determined to be:
glass transition point ~g = 7~2 C.
softening point T = 816 C, devitrification Td = 1053~ C.
melting point TM = 1287 C.
There is an endothermic peak associated with Tsp which is the "heat of softeningl'. For A13P7022' ~H = 0.201 Kcal/
mole. Its thermal conductivit~is high and lS described by the e~uation:
~ 5) ~ = 5.1 x 10 3 T(C.) + 0.0023, where ~ is the thermal conductivity in cal~-cm./C./cm2/sec.
~ increases linearly with temperature and one can calculate that at 750 C., the expected internal temperature for a HLW-glass form, my new glass will dissipate 13.8 Kcal.
per cm2 per hour of energy or 14~9 Kilowatts per square foot of surface per hour. The expansion coefficient o my new glass is low in relation to prior glasses used in this a~plication and more nearly matches that oE the metal con-tainers used for storage. Three parts of the expansion ~L~3~
curve have been determined.
~6) ~1 = 47 x 10 7 in~/in./C. (T - 142 to 285 C.
~2 = zero (T = 285 to 363~ C.); and a3 = 32 x 10 7 in./in./C. (T = 363 to 604 C.3.
In this equation a is the expansion coefficient and remains positive. In another case, I observed a negative value for ~3, vis:
(7) al =! 30 x 10 7 in.~in./C. (T = 78 to 456 C.);
, .
Radioactive waste has arisen from two major sources: production of nuclear weapons and production of nuclear enërgy. The waste can take at least three forms.
By far the largest volume is liquid waste from commercial nuclear ~nergy ~enexating plants. To recover unused uranium and/or plutonium, the spent fuel rods are dis-solved in nitric acid. After removal of these actinides, the strong acia wastes are neutralized and stored in steal tanks. The problem has been that the tanks corrode with subsequent leakage of high-level radioactive liquids into the biosphere.
One can convert the radioactive liquids to solid oxides but this physical form can also be aispersed fairly easily. These powders are generally referred to as cal-cines. The level of radioactivity from calcine is very high and of the order of 1.5 million rads (R3 per hour as a dosage. After storage for a hundred years, the level will have dropped tb 5800 R per hour but 1000 years storage i5 indicated before an acceptable dose-rate for humans arises. However, the above refers only to sub-uranic, or fission product wastes. I the actinides such as uranium and plutonium are not removed, then the wastes must be kept in secure storage for about 250,000 years before they can be considered safe for human exposure.
The volume of commercial waste (high level waste - HLW~ is enormous. About 74 million gallons have existed, ox will exist once the stored spent-fuel rods are processed.
Because of the lack of a really satisfactory disposal method for HLW, a major part of the spent fuel rods have been st~red under water in underground bunkers. The United States has sufficient uranium stockpiled so that recovery of unused uranium from the spent fuel.rods is not critical.
'' '~ .
~13~)4 Howeve~, this practice cannot continue indefinitelyn Some of the liquid waste already produced has been converted to calcine. There is about 3.9 million (M) cubic feet of unprocessed liquid waste which will form some 585,000 cubic feet of calcine.
The second form of radioactive waste consists of actinide waste which has been separated from HLW and other sources. It amounts to about 1.8 M cubic feet of liquid waste. The third form of radioactive waste, weapons waste, amounts to about 75 M gallons, or about 9.6 M cubic feet. This waste is of lower radioactivity level than that of HLW from reprocessing of commercial fuel rods, but that of separated actinide waste is much high~r in radioacti~i~y emissions level.
The use of glass for containment of high-level rad~oactive waste has been under development for many years. There are many attractive features of this mode of encapsulationO They include a rigid incorporation of the radioactive ions, or species, by dissolving them into the melt to form the glass structure. They are then not free to move as long as the glass st:ru~ture is maintained.
Glass is not subject to grain growth, surface ox~dation, and o-ther factors common to crystalline solids. However, there are six critical properties required for any glass in this application. These include:(l) minimal tendency to devitrify, (2) low hydrolytic leach rate~ ~3) high solvency power, ~4) relatively low melt temperatures, (5) low tendency to form crystals from the added waste com-ponents, and (6) low softening point and viscosity of the melt.
Devitrification refers to the proclivity of an amorphous solid (glass~ to beco~e crystalline. All 'glass will devitrify provided that the internal temperature _5 o~ the glass b~d~ is r~ised to a certain point ca,lled the devitrification temperature. The devitrification process is exothermic; that is, it releases heat, so that when devitrification starts, it is self-sustaining.
The devitrification product COlISiStS of microcrystals so that the mass is friahle and easily dispersed~ It is therefore important to maintain the amorphous state for the HLW encapsulation ~pplication. The problem is that the incorporated HLW is a heat source through natuLal fission pxocesses plus absorption of energy from the em-itted radiation by the glass matrix. 'Internal temperatures of up to 850 C. have been observedO Thus all of the prior glasses used for this application have devitrified when the incorporated HLW has heated the glass to its devitri-! fication temperature during storage. This remains a severe problem for which theie has been no solution heretofore.
Since the HLW-glass is to be stored for prolonged times as a solid mass, the hydrolytic leach rate, as a loss of the surface of the glass bociy, is important,, Ordi-nary window glass has a relatively high leach rate of 5.3 x 10-4 gm/cm2~hr in boilin~water. A good waste~glass must have a value of at least 150 times smaller than this.
Granite, an igneous rock, has a leach rate of about 4~6 x 10-6 gm/cm2/hr while that o marble is about 1.2 x 10 5 gm/cm2/hr. Since the waste-glass is to be stored in under-ground rock vaults, its hydrolytic leach rate ou~ht to be less than the surrounding roc]c.
When the HLW is to be added to the glass melt, all of the components need to be dissolved. Many of them are refractor~ oxides such as CeO~, Zr02 and Ru02. A
high solvency power of the melt is thPrefore needed. In j most glasses, the addition of excess oxides to the glass ~331~4 melt tends to cause formation of insoluble crystallite.s as specific compounds which begin to recrystallize and grow larger. When the rnelt is cask, the crystals, as a second phase, form centers of internal strain, thereby causing the glass to develop cracks and become friable.
Hence it is also desirable if the glass exhihits little or no tendency for internal crystallite formation.
Furthermorel the processing temperatures required for production of glass need to be relatively low for ~uclear waste encapsulation, preferably not over 1400 C. Conservation of energy is one reason for this limitation while another is that the containers intended for actual storage o~ the waste-glass cannot stand process-ing temperatures in excess of this value~ Finally, the glass melt also needs to have a low viscosity so that added waste oxides can be dispersed into the melt more easily.
The best glass known heretofore for the nuclear waste encapsulation application, a zinc borosilicate (ZBS)~
was developed especially for this purpose. A melt is produced at 1400 C. which has a viscosity of less than 200 poise. Up to 45~ by weigh~~of the HLW oxides can be dissolved into the melt. The hydrolytic leach rate is lower by an order of magnitude than most commercial glasses.
Unfortunately, HLW-ZBS ~lass devitrifies at 750 C. and so~tens at 570~ C. Refractory waste oxides such as Ru02, CeO2 and ZrO2 do not dissolve at all well into the melt and crystallites of Zn2SiO4, SrMoO4, NdBSiO5 and Gd2Ti207 are among the crystalline compounds observed to ~orm in the glass or devitrified product.
t ~ ~.31~0~
SUMM7~RY O~ THE INVENTION
I have found the use of a molecular glass, based upon a polymexized phosph~te o~ aluminum (PAPj, indium or gallium and made according to methods already given in U.5~ Patent No. 4,~49,779 and U.S. Patent No. 4,087,511, overcomes all o~ the prior objections to use of glass as a high-level nucleax waste encapsulation agent. ~his ~LW glass product could not be made to devitrify, disso~ved all of the oxides found in calcine, including the difficultly soluble ones~ did not form microcrystallites în the melt or subsequent glass-casting, and possessed a hydrolytic etching xate to boiling water even lower than that of HLW-~B5 slass.
In accordance with the present invention, a pre-cursor compound, M(H2P04)3, is prepared according to methods of U.S. Patent No. 4,049,779, where M is a trivalent metal selec~d f ~ ~e group consisting of aluminum, indium and gallium. Advantageously, the impurity level is carefully controlled so as not to exceed 300 ppm. total. The pre-cursor crys1-als may be washed to remove excess phosphoric acid as desired. HLW is added to the crystals and the mixture is then heated at a co~rolled heating xate to induce solid state polymerization and to form a melt a~
1350 C~ in which the ~W oxides dissolve rapidly. When aluminum was used, the resulting HLW-PAP glass had a hydro-lytic leach rate to boiling water some 15.8 times lower than HL~ZBS glass, The melt dissolved all components of the HLW and no crystallite formation was noted in the melt or in the finished glass form. The softening point of HLW-PAP glass is 650 C. It has a high thermal conductivity, a low thermal expansion which above 350 C. has been observed t~ become negative, possesses a low cross-section for absorption of radiation, and apparently does not re~uire ~r ~3 I,. rmal annealing to relieve internal stress generated during casting ~f the melt to ~orm the glass, like other. ~~
pxior known glasses.
Alternately, the HLW can be mixed with the formed precursor crystals plus phosphoric acid to form H~ phosphate compounds prior to melting the precursor crystals to produce the HLW glass composition. Another method which produces a very stable HLW glass substance involves the preparation of a solid prefire, by firing the precursor rrystals at 1100 C. to form a calcine, to which th~ H~W is added. A melt is then formed at 1350 C., which is subsPquently cast to produce the stable HLW
glass block ~or long term storage. Still another alternate is the formation of the polymexized melt from the pre cursor crystals, follow~d by casting the melt to form a glass, to form a glass frit~ The frit softens at 822 C.
and HLW dissolves into ~he melt at 1150 C. rapidly to form the solidified HLW glass block as a ~inal prodl~ct for prolonged or permanent storage.
.. . . . .
me present invention, in one aspect, ~hen, resides in a nuclear waste block for storage of high level ra~ioactive was~e, said block comprising, in combination:
~olid radioactive waste material dispersed in a polymeric phospha~e glass selected from the group consisting of polymeric phosphate glasses having the general formula M3 P7 22 and polymeric phosphate glasses having the general formula M(PO3)3, wherein M is a trivalent metal selected from the group consisting of aluminum, indium and gallium, and mlxtures of said phosphate glasses.
According to another aspect of the present inv~ntion there is provided a process of using a polymeric phosphate glass selected from the group consisting of polymeric phosphate ylasses having the general fo.rmula M3 P7 22 and polymeric phosphate glasses having the general formula M (PO3)3, wherein M is a trivalent metal selected from the group consisting of aluminum, indium and gallium, and mixtures of said phosphate glasses, said process comprising the steps of:
forming a mel~ o said glass;
dissolving high level radioactive waste in said r~lt; and .
~ ~L3~
- 8a-allowing said nelt incorporating said radioactive ~ -waste to cool and solidify into a block;
said block with its encapsulated radioactive waste being ~uitabl~ for prolonged or permanent storage.
,~
~v~
~3~ 0gL --g . .
.
DESCRIPTIOl~ OF THE PREFERRED l~MBODIMENTS
-I have determined tha~ a high degree of chemical durability of non-silicate glasses, such as those based upon phosphate, sulfate and the like, cannot be attained unless a precursor is first formed as a separate phase, heated to induce solid state polymerization of said phase, to form a melt, to form a polymerized glass. For encapsu-lation of high-level radioactive nuclear waste, a poiymerized phosphate of aluminum is required, possessing a high degree of purity. The precursor compound is prepared by dissolv-ing an aluminum compound in an excess of phosphoric acid.
Al(OH)3 is preferred as a source of aluminum although other aluminum compounds can be employed. It is important to maintain a certain molar ratio of H3P04 : Al in the solu-tion. The minimum is about 6 : 1 mols per mol but 7 : 1 works much better~ and ratios as high as 9 : 1 have been found useful. The higher ratios accelerate Al(OH)3 dis-solution, which may take 3-5 days at the 6 : 1 ratio. After purification of the resulting solution, controlled evapora-tion is employed to obtain the precursor ~rystals, Al(H2PO4)3, with good yield. These crystals, of high crystallinity and regular morphology, are th~n washed with an organic sol~ent such as methyl-ethyl ketone or ethyl acetate, but not'limited to those solvents, to remove excess H3P04 to produce mon~basic crystals uncontaminated by other chemical species or contained impurities, The presence of a large excess o~ H3P0~ during evaporation is essential, during the precursor crystal formation~ to prevent the appearance of other unwanted phosphates of aluminum which will not undergo solid state pol~merization when he~ted to elevated temperatures. Table I shows the analysis of a typical batch of precursor crystals used to prepare my new and improved glass for the nucleax waste encapsulation application.
~3~
T A B L E
Typical Analysis of Precursor Crystals Vsed to Prepare Polymeric Glass Impurity ~ mpurity Mg 10 Pb -~
Si 50 Cr 3 Fe 20 Mn --Cu -- Ca . 50 Al major Na . 100 Ni -- Li 15 Sr 3 K 30 Mo ~ -- Ba --Co ---- V .----The ~lass product prepared by heating the precursor crystals has a novel stoichlometxy not described or known heretofore.
For a typical preparation, the analysis of washed and dried crystals was: 98.38% Al(H2P04)3 0.04% ~3P04 1-58% ~2 ~pon heating the precursor crystals in a suitable container, all of the absorbed water is lost by the ~ime the temperature reaches 17S C. A loss of the three waters of constitution beyins sequentially at 210~ C. and is complete at 700 C., according to the reaction:
(1) m A1(~2P04)3 ~ ~Al(P03)3]m ~ 3 H20~' where m is an initial degree of polymerization, from m = 1 to m = 4. At about 866 C., the small amount of excess phosphoric acid is lost as 7 H3P04 3 H20. If a prefire or calcine is desired, the temperature is held at 1100 -1150D C. for several hours. If the temperature continues to rise, a further loss of P~05 is ~bserved above about 1200 C., according to the reaction:
~2) 3 [Al(P03)3] m ~ A13P7022 ~ m P205 The loss of P205 accelerates above the melting point of 1325 - 1350 C. and is complete by 1500 C. If the temperature is held at the melting point, ~he loss continues until the final stoichiometry given in reaction (2) is attained. This final stoi~iome~ is maintained while further polymeriza-tion continues. If ~he polymerization is allowed ~o continue, the stoichiometry begins to change fur~her and crys~als appear in the melt, according to the reaction:
(3) n A13P7022 ~ 2 [Al(P03)3]n ~ n AlP04~.
Since crystals are unwanted in the HLW-PAP glass application, the polymerization time o~ about 36 hours, required for the appearance o~ AlP04 crystals in the mel~, represents a maxi- ~
mum which can be used. The useful glass composition thus ~:
appears to be: A13P7022. A non-purified, washed precursor, containing about 4000 ppm of impurities, was analyzed to be:
98.23% AltH ~04)3 1.76% H20 0.01% H3P04 Upon heating, it behaved in an identical thermal manner and produced a glass composition, A13P7022, when polymerized for 16 hours. ~n unwashed batch of precursor crystals was analyzed to be.
( 2P04)3 10.37~ H20 21,28% H P04 .,~
,,~,....
Its thermal decomposition behavior was alsv identical t~
that described ahove~ The reac~ion is thus not affected by the degree of impurity level nor by the presence of excess phosphoric acid.
The same nominal glass composition may be formed by precipitatinq Al(P03)3 using metaphosphoric acid , and then ~iring the product. The precipitation reaction is:
(4) Al(NG3)3 ~ 3 ~PO3 3 3~ 3 Although this method is much to be preferred over the methods taught in the prior art, such as that of Hatch, Canadi.an Patents Nos. 449,983 and 504,835, it still suffers ~rom several deficiencies. Althouyh HP03 is very soluble in water, it tends to hydxolyze to ~3P04 rather easily so that the reaction ~4), given above, is difficult to control without introducing other unwanted aluminum p~osphates into the meit. In addit~on, contamination by the anion, in this case nitrate ion N0 , interferes with subsequent reactions.when the Al(P03)3 is isolated, dried, and then heated to form the glass melt. The worst. method to use is the method of Hatch who teahes to combine A1203 and P04 into a solid mass and then to fire the mass to fusion and quickly cool it. The resulting glass is subject to incipient recxystallization and is des~ribed as a ve.ry slowly water soluble dehydrated phosphate useful in water purification procedures. If an intermediate is not isolated, and if said intermediate is not of high purity, in contrast to the prior art, then the improved product o~ my new and improved invention does not result.
The products of the prior art inventions suffer fro... lack of stability to recrystallixation and lack of xesistance to hydrolytic etching by boiling water, which characterize and uniquely set apart the product o~ my new and improved 3L~L3~
invention for encapsulation of high level nuclear waste.
I have determined that it is much better to isolate the monobasic precursor, fire it to the prefire calcine~
and then to form the glass melt. The prior art has taugllt to use 3.00 mols H3P04 per mol of aluminum salt, ~ut even if one uses my improved ratio of 7.00 mol H3P0~ per mol of Al salt and fires ~his mixture, the glass product remains inferior and lacks many of the improved properties of my new and novel invention. Even the properties of the glass obtained from melting the isolated pxecipitated product Al(P03~3, remain inferior to those of my new invention.
Observed physi~al properties of my new improved glass, A13P7022, were determined to be:
glass transition point ~g = 7~2 C.
softening point T = 816 C, devitrification Td = 1053~ C.
melting point TM = 1287 C.
There is an endothermic peak associated with Tsp which is the "heat of softeningl'. For A13P7022' ~H = 0.201 Kcal/
mole. Its thermal conductivit~is high and lS described by the e~uation:
~ 5) ~ = 5.1 x 10 3 T(C.) + 0.0023, where ~ is the thermal conductivity in cal~-cm./C./cm2/sec.
~ increases linearly with temperature and one can calculate that at 750 C., the expected internal temperature for a HLW-glass form, my new glass will dissipate 13.8 Kcal.
per cm2 per hour of energy or 14~9 Kilowatts per square foot of surface per hour. The expansion coefficient o my new glass is low in relation to prior glasses used in this a~plication and more nearly matches that oE the metal con-tainers used for storage. Three parts of the expansion ~L~3~
curve have been determined.
~6) ~1 = 47 x 10 7 in~/in./C. (T - 142 to 285 C.
~2 = zero (T = 285 to 363~ C.); and a3 = 32 x 10 7 in./in./C. (T = 363 to 604 C.3.
In this equation a is the expansion coefficient and remains positive. In another case, I observed a negative value for ~3, vis:
(7) al =! 30 x 10 7 in.~in./C. (T = 78 to 456 C.);
2 (T = 456 to 480 C.); and ~ 3 = -6.5 x 10-7 in./in./ C. (T = 480 - 750 C.).
These expansion properties can be controlled somewhat by the polymerization time used. It is quite obvious that a negative expansion is a valuable- property in a glass which becomes reheated by the nuclear waste it contains. While the metal container expands, this glass contracts, thereby obviating external stress which might crack the glass block otherwise.
When a synthetic mixture of chemical oxides was added to the ~13P7022 melt in ~uantities to simulate the HLW additives, I determined two essential factors, which set my new and improved glass apart Erom any prior known glasses used heretofore in the ~ield of nuclear waste en-capsulation. The first is that the HLW-PAP glass would not devitrify under any circumstances employed. This was first observed visually and con~irmed several *imes b~ differential thermal analysis, an analytical method commonly used to determine thermal.behavior of glasses.
This is entirely unexpected and unique since my ~lass is the only one observed to date which does not devitrify when containing ~ILW~ The second is that the hydrolysis loss o~ HLW~PAP glass is related to the pol~erization time.
The relation has been determined to he linear and its the equation:
(8) Wt = 0.0466 t - 0.806, where Wt i~' the weight change observed in 10-6 ~m./cm2/hr.
and t is the polymexization time in hours. At 4 hours polymerization time, a loss of 0.64 x 10~~ gm./cm2/hr~ in boiling water was observed, whereas at 24 hours polymeri-zation time, a galn of 0.36 x 10 6 gm./cm2/hr. was determined.
According to Ithe above equation, a polymerization time of 17.0 hours polymerization time ought to give a zero change in weight. When this was tried, the result was ,a loss, 1.91 x 10 7gm?/cm2/hr~ (4'.6 x 10 gm.,/cm /day~, This is some 15 times lower than that of HL~-ZBS glass. These results were obtained by measuring the physical dimensions of the glass bar and immersing i,t in boiling water f~r 96 hours.
The behavior of my new glass is unusual, especiall~for HLW-PAP glass, as shown in Table II~ These data were obtained for a HLW-PAP glass rod in which the glass had been polymeriæed for 17.0 hours before casting the melt.
T A B L E I I
Effect of ~ryin~ Time on Weight Changes Observed or a 17 Hour Polymerized HLW-PAP Gla~ss Time After Removal ~rom Boiling Weight Gain Water (96 Hour Immersion) ' --6 2 (x 10 gm./cm /h~.) O hour 0.315 O . 510 2 " 0.382
These expansion properties can be controlled somewhat by the polymerization time used. It is quite obvious that a negative expansion is a valuable- property in a glass which becomes reheated by the nuclear waste it contains. While the metal container expands, this glass contracts, thereby obviating external stress which might crack the glass block otherwise.
When a synthetic mixture of chemical oxides was added to the ~13P7022 melt in ~uantities to simulate the HLW additives, I determined two essential factors, which set my new and improved glass apart Erom any prior known glasses used heretofore in the ~ield of nuclear waste en-capsulation. The first is that the HLW-PAP glass would not devitrify under any circumstances employed. This was first observed visually and con~irmed several *imes b~ differential thermal analysis, an analytical method commonly used to determine thermal.behavior of glasses.
This is entirely unexpected and unique since my ~lass is the only one observed to date which does not devitrify when containing ~ILW~ The second is that the hydrolysis loss o~ HLW~PAP glass is related to the pol~erization time.
The relation has been determined to he linear and its the equation:
(8) Wt = 0.0466 t - 0.806, where Wt i~' the weight change observed in 10-6 ~m./cm2/hr.
and t is the polymexization time in hours. At 4 hours polymerization time, a loss of 0.64 x 10~~ gm./cm2/hr~ in boiling water was observed, whereas at 24 hours polymeri-zation time, a galn of 0.36 x 10 6 gm./cm2/hr. was determined.
According to Ithe above equation, a polymerization time of 17.0 hours polymerization time ought to give a zero change in weight. When this was tried, the result was ,a loss, 1.91 x 10 7gm?/cm2/hr~ (4'.6 x 10 gm.,/cm /day~, This is some 15 times lower than that of HL~-ZBS glass. These results were obtained by measuring the physical dimensions of the glass bar and immersing i,t in boiling water f~r 96 hours.
The behavior of my new glass is unusual, especiall~for HLW-PAP glass, as shown in Table II~ These data were obtained for a HLW-PAP glass rod in which the glass had been polymeriæed for 17.0 hours before casting the melt.
T A B L E I I
Effect of ~ryin~ Time on Weight Changes Observed or a 17 Hour Polymerized HLW-PAP Gla~ss Time After Removal ~rom Boiling Weight Gain Water (96 Hour Immersion) ' --6 2 (x 10 gm./cm /h~.) O hour 0.315 O . 510 2 " 0.382
3 " ; 0.330 0.216 25 " 0.161 67 " 0.090 72 !' .0 . 082 ~3~ 0~
This behavior indicates that the surface of the HLW-PAP
glass becomes hydroxylated and that the actual weight loss ~or gain) is really zero (at 17.0 hours polymeriza tion time). This was estimated by fitting the data of Table II to an exponential decay equation, starting with 1 hour drying time. The statistical fit is 96% and the e~uation obtained was:
(9) Wt' = 0.378 exp. - 0.022 t.
~xtrapolating the gain from 72 hours to one week gives a value of 8.9 x 10 9 gm ~cm2/hr.~ that for 2 weeks is 2.1 x 10 10, while the value calculated for 4 weeks is:
Wt = 3.9 x 10 14gm./cm2/hr., as a final weight loss. This illustrates the fact that the gain change observed for the glass rod is xeversible and is caused by the boiling water at the sur~ace of the glass rod. The weight change then reequilibrates, with time, back to its original value.
In other words, only the surface of the glass is affected but it reverts back to its original state once the boiling water is removed. This proves that the change within the glass matrix is actually zero in accordance with the experi-ment~lly determined equation (8) for 17~0 hours polymeriza-ti~n time. ~
~ he changes in weight as related to surface hydroxylation are affected by the methods of J~Ll~-PAP glass preparation ~s shown in Table III.
.
~3~
~ A !'l I, E III
Erfect Or ~ P.~ e.la;s Prc~re~ thsd Upc:~ Rcslst~ncc to Surfr~ce ~Iyarox~,rlntlon !~atDrl~l Ura to E~ess }!370~ ity cr P~ crlzation Welrht ChDJ~e Gbs~rv~d *
M2'~ 1t Pre,~3t ~la~erl~ (10-6 ~m/c.-~/hr) loss ~t 72 hrs.
prcc~rssr cr~stals 20 ~ hlg:h4 hr.... ~~ o.66 --n ~ . n 17 ~. o.o66 - _ n ~ 24 hr . O . ~7 48 hr. 1.38 -- __ w c~ 72 ~ . . 2 . 60 - - _ pref~re ~c~lc~e) 20$ ~ih '72 ~rØ11 -_ t~.l2 n DCrDg 0.20 ___ 0.21 " BoIle ~ ~17 ~- 0.25 -- 0.17 Dcn~ b~. 0.2~
~p hi3h . y hr. 0.21 -~ O.OI7 ,~ _ 95 ~ s ~ ~cili~g-;~'.,er The data in Table IIIshows: (1) the prefire is a better method and a better material with which to make the melt, (2) the convert~on of HLW to phosphates is indicated as a better method to approach zero weight loss, and (3) purification of the precursor crystals gives a ~LW-PAP
glass form with essentially no~weight change, i.e., 1.7 x 10 8 gm./cm /hr. or 4.1 x 10 7 gm./cm /day, as a gain. Undoubtedly, this will revert to zero as the surface continues to dehydroxylate with time.
The molecular glass has other interesting properties in regard to the HLW encapsulation application.
The melt dissol~es all metals includin~ the noble metals (Pt is very slow but Rh and Pd dissolve rapidly). All o~~~des, or compounds which decompose to form oxides, do dissolve, including the re~ractory oxldes, CeO2, ZrO2 and Ru02. No crystal formation has been observed at any time from HLW additives, unless the polymerization time exceeds .
, ~3~4 about 36 hours, when AlP04 crystals appear. The melt has a low viscosity of about 180 poise.
The amount of HLW additives can be varied frorn about 5~ by weight of the glass, ~13P7022, to nearly 45%
by weight. I prefer to use about 20% - 25% by weight of HLW additives, although one is not limited to this, as is well known in the art.
It will be recognized that the instant invention arises from the application of my novel polymerized molecu-lar phosphate ~lass to the encapsulation of high-level radioactive nuclear waste for disposal thereo~. Although I have given data and results which stemmed from the aluminum cationic variety of my new glass, other cations can be employed for the same purpose, using the methods and approaches given herein as applying to my new and impro~ed invention.
Two trivalent cations which may be substituted for the alumi-num are In3~ and Ga3~; however, these materials are considerably more expensive and have a larger cross-section for neutron capture than aluminum. A particular advantage of using aluminum is its low nuclear absorption, as compared with indium and gallium and as compared wtth zinc borosilicate (ZBS) glasses of the prior ar~. rrhis transparency to nuclear particles reduces the possibility of radiation damage to the molecu~ar structure, and ~linimizes the generation of thermal energy.
As examples of the invention, I cite:
Example I
To prepare the precursor compound, measure out 970 ml of reagent grade, 85% H3P04 (specific gra~ity of 1.689 gm/cc), although other, lower grades can be used as well, and add to 1000 ml. of water. Dilute to 2000 ml.
total vo]ume. Weigh out 156.0 gm. of Al(OH)3 and dissolve in ~I3P04 solution. Heating may be necessary to obtain a -19~ O~
clear ~olution. Weigh out 5.0 - 10.0 gm. of ammonium l-pyrrolidine dithiocarbamate (APC) and dissolve in 50 mlc of water. Add to solution. ~ilter oif the dark grey precipitate using a a 45 micron filter. Set up a mercury-pool electrolysis apparatus and electrolyze solution in a nitrogen atmosphere at - 2.90 VDC at Hg pool for several hours to remove residual impurities. A minimum of 2 hours is required be~ore most of the impurities are removed. Evapo-rate the purified solution slowly~ using a hea sc~rce, to obtain precur~or crystals plus a liquid. The liquid con~
tains excess H3P04 plu~ water. The exce~s liquor is decanted and the crystals are washed free o~ exc~ss H3P04, using methyl-ethyl ketone as a washing agent. Assay the washed and dried crystalsO
~ dd 20.0 gm. of HLW add.itives per 96.5 gmO of cry~tals (assuming t~,~ experimental assay to be 83.0%);
the total Yolume used should fill the container used for heating. Heat at a rate of about 10-12 C. per minute to cause initial dehydration and polymerization. As the temperature rises to 1325 C., a melt will form, with a shrinkage o~ about 80~. More HLW-crystal mix is added until the container is filled with meltO This takes about 1 hour..-Hold the melt about 16 hours longer to reach a suitable degree o~ polymerization, and then cast the melt in a suitable mold to form the final HLW-PAP glass slug, ~or long term stora~e thereo~. No annealing is necessary but very large pieces may require a minimal annealing.
Molecular glasses require that annealing be done some 8-1~ C~ above the softening point.
Exam~le 2 .
Alternately~ the methods of Example I are followed except that the HLW is not added at the point of ~ .
3~
initial firing. The precursor rystals are heated separately at a rate of about 10 C. per minute to 1100 C. and then held there for several hours to form a calcine powder. This , powder, which is partially polymerized, is cooled and mixed with HLW at a rate of 0.O gm. of calcine powder to 20.0 gm.
of HLW additives, heated to 1350 C. to ~orm a melt which is held at t~?is temperature for 17.0 houxs to complete polymerizatiGn and then cast in final form for long term storage thereof..
Example 3 Another alternate method is to heat the precursor crystals to induce initial polymerizatio~ and then to obtain the melt. The melt is then cast immediately and c0012d.
The resulting giass is ground to obtain a glass frit which is ~hen used to encapsulate the HLW additives according to methods o Example 2. In this ~ase, the frit sof tens at 822 C. and is liquid at 1150 C. This ~lt is used for the encapsulation of ~LW additives according to methods given aboveO This method has the advantage that much lower tempera~ures can be used when ~he final casting container to be used for long term storage cannot withstand the higher temperatuxes required for producti~n of a direct melt.
Example 4 The procedure given in Example 1 is followed except that the crystals are not washed free of excess H3P04. A portion of the crystals are assayed. The assay is used to calculate the weight of crystals plus phosphoric acid needed to obtain 0.20 HLW - 0.80 PAP glass on a weight basis. ~he HLW, added prior to heating, begins to ~orm phosphates. Upon heating, phosphate ~ormation is accelerated and is complete by the time melt temperature is reached.
The formation of HLW-phosphates accelerates the dissolu-tion of HLW into the melt, and aids dispersion thereof.
Further procedures of Example l are then followed.
Example 5 The procedure of Example 2 is followed to obtain a calcine. Both HLW additives and H3P04 are added at a ratio of 207 mlO of 85% H~P04 per 100 gm. of HLW additives, to form a final composition of 0.20 HLW-0.80 PAP glass by weight. The HLW - H3P0~ mixture is thoroughly blended before it is added to the calcine, and then the final mixture is heated according to the procedures of Example 2 to form the melt, to form the final glass composition of ~.20 HLW -0.80 PAP glass, for storage thereof.
~ . .
Example 6 If a glass frit is to be used, the procedures of Examples 3 and 5 axe followed exc~ept that the H3P0~
is mixed with the HLW additives prior to addition to the glass former, and is gently heated to 100 ~ 150 C.j as required, to induce frothing an~ phosphate ~ormation.
~hen phosphate formation is complete, the HLW-phosphates are added to the PAP glass-frit to Eorm a 0.20HLW-0.80 PAP
glass composition ~ixture, and the mass is heated at a rate of 8 , 10 C. per minute to 825 C. where the frit so~tens. The heating is continued up to 1100-1150 C.
where the melt is held for several hours until the HLW
additives can dissolve and become d;spersed within the melt~
~h* melt is then cast and handled according to procedures already developed in prior examplesO
Example 7 The above examples give methods suitable for HLW
~L3~
encapsulation b~ PAP glass using a static or single con-tainer method. If a continuous method is desired, there are several alternatives. A glass melting furnace capable of operating continuously at 1400 C. is set up and made ready for operation. Such furnaces generally are composed of a preheat chamber, a melt chamber and a holding tank~
It is essential that the inner faces of each chamber be lined with impervious (high density) alumina, which is the only material found to be sufficiently resistant to etching by the very corrosive melt. A mixture of ~LW additives and precursor crystals is added to the preheat chamber to orm a melt. As the volume o~ melt încreases, the melt moves over into the melt chamber and finally to the hold chamber. HLW-phosphates are added simultaneously with the PAP calcine, to form more melt, at a ratio so as to mai~tain a ratio in tlle general range of 0.20 HLW - 0.80 PAP
glass in the final product. It is essential that the throughput of the HLW-PAP glass be about 17.0 hours in order for sufficient polymerization to take place before the glass-casting is formed. Therefore the rate of addi-tion of the HLW - calcine powder must be adjusted according to the size of furnace used so as to obtain about 17.0 hours of poly~erization time.
The addition o,f HLW aaditives can take 'at least two forms, as oxides obtained by drying or calcining the high-level liquid wastes, or as phospha-tes obtained by the addition of H3P04 to the li~uid wastes, followed by separa-tion thereof of the radioactive precipitated wastes as phosphates.
The melt can be formed from precursor crystals (,un~
washed ox 'washed precursor crystals~ or PAP-calcine powder. When HLW calcine is to be used, it is better to 'use unwashed crystals containing excess ~3P04 to convert ~3~0~L
the HLW oxides to phosphates in the preheat chamber of the furnace. If HLW-phosphates are used, then PAP-calcine can be use~ and added simultaneously to the preheat chamber.
The II~W-PAP glass melt is continuously drawn from the holding chamber of the glass furnace, the melt having a residence time of 17.0 houxs before casting into a suitable container for long term storage thereof.
Example 8 When a glass frit is to be used on a continuous casting basis, the method to be employed is somewhat dif-ferent than that of Example 7. The HLW plus glass frit, or-alternatively the HLW-phosphates plus glass frit are mixed together in a ratio of about 0.20 HLW - 0.80 PAP
glass frit, but not to exceed about 0.45 to 0.55, and adcled dir~ectly to a heated container, held at about 1150C. The addition is fairly slow so as to give the melt enough time to form. I~ the cannister i5 stainless steel, the addition rate can be faster then if it is alumina, which has a lower heat transfer rate from the furnace. After the cannister is full, the melt is held at 1150 C. so that the total melt-hold-time is about 17 hours. The cannister is then cooled slowly and made ready for long term storage, as is known in the priox art.
While the invention has been described hereinahove in terms of the preferred embodiments and specific examples, the invention itself is not limited thereto, but rather comphrehends all such modifications of, and variatlons and c~
departures from these embodiments as properly fall within t} - spirit and scope of the appended claims.
This behavior indicates that the surface of the HLW-PAP
glass becomes hydroxylated and that the actual weight loss ~or gain) is really zero (at 17.0 hours polymeriza tion time). This was estimated by fitting the data of Table II to an exponential decay equation, starting with 1 hour drying time. The statistical fit is 96% and the e~uation obtained was:
(9) Wt' = 0.378 exp. - 0.022 t.
~xtrapolating the gain from 72 hours to one week gives a value of 8.9 x 10 9 gm ~cm2/hr.~ that for 2 weeks is 2.1 x 10 10, while the value calculated for 4 weeks is:
Wt = 3.9 x 10 14gm./cm2/hr., as a final weight loss. This illustrates the fact that the gain change observed for the glass rod is xeversible and is caused by the boiling water at the sur~ace of the glass rod. The weight change then reequilibrates, with time, back to its original value.
In other words, only the surface of the glass is affected but it reverts back to its original state once the boiling water is removed. This proves that the change within the glass matrix is actually zero in accordance with the experi-ment~lly determined equation (8) for 17~0 hours polymeriza-ti~n time. ~
~ he changes in weight as related to surface hydroxylation are affected by the methods of J~Ll~-PAP glass preparation ~s shown in Table III.
.
~3~
~ A !'l I, E III
Erfect Or ~ P.~ e.la;s Prc~re~ thsd Upc:~ Rcslst~ncc to Surfr~ce ~Iyarox~,rlntlon !~atDrl~l Ura to E~ess }!370~ ity cr P~ crlzation Welrht ChDJ~e Gbs~rv~d *
M2'~ 1t Pre,~3t ~la~erl~ (10-6 ~m/c.-~/hr) loss ~t 72 hrs.
prcc~rssr cr~stals 20 ~ hlg:h4 hr.... ~~ o.66 --n ~ . n 17 ~. o.o66 - _ n ~ 24 hr . O . ~7 48 hr. 1.38 -- __ w c~ 72 ~ . . 2 . 60 - - _ pref~re ~c~lc~e) 20$ ~ih '72 ~rØ11 -_ t~.l2 n DCrDg 0.20 ___ 0.21 " BoIle ~ ~17 ~- 0.25 -- 0.17 Dcn~ b~. 0.2~
~p hi3h . y hr. 0.21 -~ O.OI7 ,~ _ 95 ~ s ~ ~cili~g-;~'.,er The data in Table IIIshows: (1) the prefire is a better method and a better material with which to make the melt, (2) the convert~on of HLW to phosphates is indicated as a better method to approach zero weight loss, and (3) purification of the precursor crystals gives a ~LW-PAP
glass form with essentially no~weight change, i.e., 1.7 x 10 8 gm./cm /hr. or 4.1 x 10 7 gm./cm /day, as a gain. Undoubtedly, this will revert to zero as the surface continues to dehydroxylate with time.
The molecular glass has other interesting properties in regard to the HLW encapsulation application.
The melt dissol~es all metals includin~ the noble metals (Pt is very slow but Rh and Pd dissolve rapidly). All o~~~des, or compounds which decompose to form oxides, do dissolve, including the re~ractory oxldes, CeO2, ZrO2 and Ru02. No crystal formation has been observed at any time from HLW additives, unless the polymerization time exceeds .
, ~3~4 about 36 hours, when AlP04 crystals appear. The melt has a low viscosity of about 180 poise.
The amount of HLW additives can be varied frorn about 5~ by weight of the glass, ~13P7022, to nearly 45%
by weight. I prefer to use about 20% - 25% by weight of HLW additives, although one is not limited to this, as is well known in the art.
It will be recognized that the instant invention arises from the application of my novel polymerized molecu-lar phosphate ~lass to the encapsulation of high-level radioactive nuclear waste for disposal thereo~. Although I have given data and results which stemmed from the aluminum cationic variety of my new glass, other cations can be employed for the same purpose, using the methods and approaches given herein as applying to my new and impro~ed invention.
Two trivalent cations which may be substituted for the alumi-num are In3~ and Ga3~; however, these materials are considerably more expensive and have a larger cross-section for neutron capture than aluminum. A particular advantage of using aluminum is its low nuclear absorption, as compared with indium and gallium and as compared wtth zinc borosilicate (ZBS) glasses of the prior ar~. rrhis transparency to nuclear particles reduces the possibility of radiation damage to the molecu~ar structure, and ~linimizes the generation of thermal energy.
As examples of the invention, I cite:
Example I
To prepare the precursor compound, measure out 970 ml of reagent grade, 85% H3P04 (specific gra~ity of 1.689 gm/cc), although other, lower grades can be used as well, and add to 1000 ml. of water. Dilute to 2000 ml.
total vo]ume. Weigh out 156.0 gm. of Al(OH)3 and dissolve in ~I3P04 solution. Heating may be necessary to obtain a -19~ O~
clear ~olution. Weigh out 5.0 - 10.0 gm. of ammonium l-pyrrolidine dithiocarbamate (APC) and dissolve in 50 mlc of water. Add to solution. ~ilter oif the dark grey precipitate using a a 45 micron filter. Set up a mercury-pool electrolysis apparatus and electrolyze solution in a nitrogen atmosphere at - 2.90 VDC at Hg pool for several hours to remove residual impurities. A minimum of 2 hours is required be~ore most of the impurities are removed. Evapo-rate the purified solution slowly~ using a hea sc~rce, to obtain precur~or crystals plus a liquid. The liquid con~
tains excess H3P04 plu~ water. The exce~s liquor is decanted and the crystals are washed free o~ exc~ss H3P04, using methyl-ethyl ketone as a washing agent. Assay the washed and dried crystalsO
~ dd 20.0 gm. of HLW add.itives per 96.5 gmO of cry~tals (assuming t~,~ experimental assay to be 83.0%);
the total Yolume used should fill the container used for heating. Heat at a rate of about 10-12 C. per minute to cause initial dehydration and polymerization. As the temperature rises to 1325 C., a melt will form, with a shrinkage o~ about 80~. More HLW-crystal mix is added until the container is filled with meltO This takes about 1 hour..-Hold the melt about 16 hours longer to reach a suitable degree o~ polymerization, and then cast the melt in a suitable mold to form the final HLW-PAP glass slug, ~or long term stora~e thereo~. No annealing is necessary but very large pieces may require a minimal annealing.
Molecular glasses require that annealing be done some 8-1~ C~ above the softening point.
Exam~le 2 .
Alternately~ the methods of Example I are followed except that the HLW is not added at the point of ~ .
3~
initial firing. The precursor rystals are heated separately at a rate of about 10 C. per minute to 1100 C. and then held there for several hours to form a calcine powder. This , powder, which is partially polymerized, is cooled and mixed with HLW at a rate of 0.O gm. of calcine powder to 20.0 gm.
of HLW additives, heated to 1350 C. to ~orm a melt which is held at t~?is temperature for 17.0 houxs to complete polymerizatiGn and then cast in final form for long term storage thereof..
Example 3 Another alternate method is to heat the precursor crystals to induce initial polymerizatio~ and then to obtain the melt. The melt is then cast immediately and c0012d.
The resulting giass is ground to obtain a glass frit which is ~hen used to encapsulate the HLW additives according to methods o Example 2. In this ~ase, the frit sof tens at 822 C. and is liquid at 1150 C. This ~lt is used for the encapsulation of ~LW additives according to methods given aboveO This method has the advantage that much lower tempera~ures can be used when ~he final casting container to be used for long term storage cannot withstand the higher temperatuxes required for producti~n of a direct melt.
Example 4 The procedure given in Example 1 is followed except that the crystals are not washed free of excess H3P04. A portion of the crystals are assayed. The assay is used to calculate the weight of crystals plus phosphoric acid needed to obtain 0.20 HLW - 0.80 PAP glass on a weight basis. ~he HLW, added prior to heating, begins to ~orm phosphates. Upon heating, phosphate ~ormation is accelerated and is complete by the time melt temperature is reached.
The formation of HLW-phosphates accelerates the dissolu-tion of HLW into the melt, and aids dispersion thereof.
Further procedures of Example l are then followed.
Example 5 The procedure of Example 2 is followed to obtain a calcine. Both HLW additives and H3P04 are added at a ratio of 207 mlO of 85% H~P04 per 100 gm. of HLW additives, to form a final composition of 0.20 HLW-0.80 PAP glass by weight. The HLW - H3P0~ mixture is thoroughly blended before it is added to the calcine, and then the final mixture is heated according to the procedures of Example 2 to form the melt, to form the final glass composition of ~.20 HLW -0.80 PAP glass, for storage thereof.
~ . .
Example 6 If a glass frit is to be used, the procedures of Examples 3 and 5 axe followed exc~ept that the H3P0~
is mixed with the HLW additives prior to addition to the glass former, and is gently heated to 100 ~ 150 C.j as required, to induce frothing an~ phosphate ~ormation.
~hen phosphate formation is complete, the HLW-phosphates are added to the PAP glass-frit to Eorm a 0.20HLW-0.80 PAP
glass composition ~ixture, and the mass is heated at a rate of 8 , 10 C. per minute to 825 C. where the frit so~tens. The heating is continued up to 1100-1150 C.
where the melt is held for several hours until the HLW
additives can dissolve and become d;spersed within the melt~
~h* melt is then cast and handled according to procedures already developed in prior examplesO
Example 7 The above examples give methods suitable for HLW
~L3~
encapsulation b~ PAP glass using a static or single con-tainer method. If a continuous method is desired, there are several alternatives. A glass melting furnace capable of operating continuously at 1400 C. is set up and made ready for operation. Such furnaces generally are composed of a preheat chamber, a melt chamber and a holding tank~
It is essential that the inner faces of each chamber be lined with impervious (high density) alumina, which is the only material found to be sufficiently resistant to etching by the very corrosive melt. A mixture of ~LW additives and precursor crystals is added to the preheat chamber to orm a melt. As the volume o~ melt încreases, the melt moves over into the melt chamber and finally to the hold chamber. HLW-phosphates are added simultaneously with the PAP calcine, to form more melt, at a ratio so as to mai~tain a ratio in tlle general range of 0.20 HLW - 0.80 PAP
glass in the final product. It is essential that the throughput of the HLW-PAP glass be about 17.0 hours in order for sufficient polymerization to take place before the glass-casting is formed. Therefore the rate of addi-tion of the HLW - calcine powder must be adjusted according to the size of furnace used so as to obtain about 17.0 hours of poly~erization time.
The addition o,f HLW aaditives can take 'at least two forms, as oxides obtained by drying or calcining the high-level liquid wastes, or as phospha-tes obtained by the addition of H3P04 to the li~uid wastes, followed by separa-tion thereof of the radioactive precipitated wastes as phosphates.
The melt can be formed from precursor crystals (,un~
washed ox 'washed precursor crystals~ or PAP-calcine powder. When HLW calcine is to be used, it is better to 'use unwashed crystals containing excess ~3P04 to convert ~3~0~L
the HLW oxides to phosphates in the preheat chamber of the furnace. If HLW-phosphates are used, then PAP-calcine can be use~ and added simultaneously to the preheat chamber.
The II~W-PAP glass melt is continuously drawn from the holding chamber of the glass furnace, the melt having a residence time of 17.0 houxs before casting into a suitable container for long term storage thereof.
Example 8 When a glass frit is to be used on a continuous casting basis, the method to be employed is somewhat dif-ferent than that of Example 7. The HLW plus glass frit, or-alternatively the HLW-phosphates plus glass frit are mixed together in a ratio of about 0.20 HLW - 0.80 PAP
glass frit, but not to exceed about 0.45 to 0.55, and adcled dir~ectly to a heated container, held at about 1150C. The addition is fairly slow so as to give the melt enough time to form. I~ the cannister i5 stainless steel, the addition rate can be faster then if it is alumina, which has a lower heat transfer rate from the furnace. After the cannister is full, the melt is held at 1150 C. so that the total melt-hold-time is about 17 hours. The cannister is then cooled slowly and made ready for long term storage, as is known in the priox art.
While the invention has been described hereinahove in terms of the preferred embodiments and specific examples, the invention itself is not limited thereto, but rather comphrehends all such modifications of, and variatlons and c~
departures from these embodiments as properly fall within t} - spirit and scope of the appended claims.
Claims (49)
1. A nuclear waste block for storage of high level radioactive waste, said block comprising, in combination:
solid radioactive waste material dispersed in a polymeric phosphate glass selected from the group consisting of polymeric phosphate glasses having the general formula M3 P7 O22 and polymeric phosphate glasses having the general formula M(P03)3, wherein M is a trivalent metal selected from the group consisting of aluminum, indium and gallium, and mixtures of said phosphate glasses.
solid radioactive waste material dispersed in a polymeric phosphate glass selected from the group consisting of polymeric phosphate glasses having the general formula M3 P7 O22 and polymeric phosphate glasses having the general formula M(P03)3, wherein M is a trivalent metal selected from the group consisting of aluminum, indium and gallium, and mixtures of said phosphate glasses.
2. A nuclear waste block for storage of high level radioactive waste, said block comprising, in combination: solid radioactive waste material dispersed in a polymeric phosphate glass having the formula:
M3 P7 O21, where M is a trivalent metal selected from the group consisting of aluminum, indium and gallium.
M3 P7 O21, where M is a trivalent metal selected from the group consisting of aluminum, indium and gallium.
3. The nuclear waste block of claim 2, wherein said metal is aluminum.
4. The nuclear waste block of claim 2, wherein said metal is indium.
5. The nuclear waste block of claim 2, wherein said metal is gallium.
6. A process of using a polymeric phosphate glass selected from the group consisting of polymeric phosphate glasses having the general formula M3 P7 O22 and polymeric phosphate glasses having the general formula M (P03)3, wherein M is a trivalent metal selected from the group consisting of aluminum, indium and gallium, and mixtures of said phosphate glasses, said process comprising the steps of:
forming a melt of said glass;
dissolving high level radioactive waste in said melt; and allowing said melt incorporating said radioactive waste to cool and solidify into a block;
said block with its encapsulated radioactive waste being suitable for prolonged or permanent storage.
forming a melt of said glass;
dissolving high level radioactive waste in said melt; and allowing said melt incorporating said radioactive waste to cool and solidify into a block;
said block with its encapsulated radioactive waste being suitable for prolonged or permanent storage.
7. A process of using a polymeric phosphate glass having the formula:
M3 P7 O22, where M is a trivalent metal selected from the group con-sisting of aluminum, indium and gallium, said process com-prising the steps of:
forming a melt of said glass;
dissolving high level radioactive waste in said melt; and allowing said melt incorporating said radio-active waste to cool and solidify into a block;
said block with its encapsulated radioactive waste being suitable for prolonged or permanent storage.
M3 P7 O22, where M is a trivalent metal selected from the group con-sisting of aluminum, indium and gallium, said process com-prising the steps of:
forming a melt of said glass;
dissolving high level radioactive waste in said melt; and allowing said melt incorporating said radio-active waste to cool and solidify into a block;
said block with its encapsulated radioactive waste being suitable for prolonged or permanent storage.
8. The process of claim 7, wherein said metal is aluminum.
9. The process of claim 7, wherein said metal is indium.
10. The process of claim 7, wherein said metal is gallium.
11. The process of claim 7, further comprising the steps of transporting said block to a permanent storage site and depositing said block at said site.
12. A process of encapsulating high level radio active (nuclear) waste for prolonged or permanent storage, said process comprising the steps of:
forming a melt of a polymeric phosphate glass having the formula:
M3 P7 O22, where M is a trivalent metal selected from the group con-sisting of aluminum, indium and gallium;
dissolving high level radioactive waste in said melt; and allowing said melt incorporating said radioactive waste to cool and solidify into a block.
forming a melt of a polymeric phosphate glass having the formula:
M3 P7 O22, where M is a trivalent metal selected from the group con-sisting of aluminum, indium and gallium;
dissolving high level radioactive waste in said melt; and allowing said melt incorporating said radioactive waste to cool and solidify into a block.
13. The process of claim 12, wherein said metal is aluminum.
14. The process of claim 12, wherein said metal is indium.
15. The process of claim 12, wherein said metal is gallium.
16. The process of claim 12, wherein said melt forming step includes:
preparing precursor crystals having the formula:
M(H2 PO4)3;
adding radioactive waste crystals to said precursor crystals to form a crystal mixture; and heating said crystal mixture to induce solid state polymerization and form said melt.
preparing precursor crystals having the formula:
M(H2 PO4)3;
adding radioactive waste crystals to said precursor crystals to form a crystal mixture; and heating said crystal mixture to induce solid state polymerization and form said melt.
17. The process of claim 16, wherein said melt forming step further includes washing said precursor crystals substantially free of phosphoric acid prior to adding radioactive waste crystals.
18. The process of claim 16, wherein the im-purity level of said precursor crystals does not exceed 300 ppm.
19. The process of claim 16, wherein said mixture is heated to a temperature of approximately 1350° C.
20. The process of claim 16, wherein said crystal mixture includes phosphoric acid.
21. The process of claim 16, further comprising the step of heating said precursor crystals to form a cal-cine prior to adding said radioactive waste crystals.
22. The process of claim 12, wherein said melt forming step includes:
preparing precursor crystals having the formula:
M(H2P04)3;
heating said precursor crystals to induce solid state polymerization and form a first melt;
allowing said first melt to cool;
grinding the cooled glass to form a glass frit;
adding radioactive waste crystals to said glass frit to form a glass-crystal mixture; and heating said glass-crystal mixture to form a second melt.
preparing precursor crystals having the formula:
M(H2P04)3;
heating said precursor crystals to induce solid state polymerization and form a first melt;
allowing said first melt to cool;
grinding the cooled glass to form a glass frit;
adding radioactive waste crystals to said glass frit to form a glass-crystal mixture; and heating said glass-crystal mixture to form a second melt.
23. A nuclear waste block for storage of high level radioactive waste, said block comprising, in combination: solid radioactive waste material dispersed in a polymeric phosphate glass having the formula:
M(PO3)3, where M is a trivalent metal selected from the group consisting of aluminum, indium and gallium.
M(PO3)3, where M is a trivalent metal selected from the group consisting of aluminum, indium and gallium.
24. The nuclear waste block of claim 23, wherein said metal is aluminum.
25. The nuclear waste block of claim 23, wherein said metal is indium.
26. The nuclear waste block of claim 23, wherein said metal is gallium.
27. The nuclear waste block as defined in claim 23, wherein said polymeric phosphate glass further includes a phosphate glass of the general formula M3 P7 O22. wherein M is as defined in claim 23.
28. A process of using a polymeric phosphate glass having a formula:
M(PO3)3, where M is a trivalent metal selected from the group con-sisting of aluminum, indium and gallium, said process comprising the steps of:
forming a melt of said glass;
dissolving high level radioactive waste in said melt; and allowing said melt incorporating said radio-active waste to cool and solidify into a block;
said block with its encapsulated radioactive waste being suitable for prolonged or permanent storage.
M(PO3)3, where M is a trivalent metal selected from the group con-sisting of aluminum, indium and gallium, said process comprising the steps of:
forming a melt of said glass;
dissolving high level radioactive waste in said melt; and allowing said melt incorporating said radio-active waste to cool and solidify into a block;
said block with its encapsulated radioactive waste being suitable for prolonged or permanent storage.
29. The process of claim 28, wherein said metal is aluminum.
30. The process of claim 28, wherein said metal is indium.
31. The process of claim 28, wherein said metal is gallium.
32. The process of claim 28, further com-prising the steps of transporting said block to a permanent storage site and depositing said block at said site.
33. The process of claim 28 or of claim 32 wherein said polymeric phosphate glass further includes a phosphate glass of the general formula M3 P7 O22 wherein M is as defined in claim 28.
34. A process of encapsulating high level radioactive (nuclear) waste for prolonged or permanent storage, said process comprising the steps of:
forming a melt of a polymeric phosphate glass having a formula:
M(PO3)3, where M is a trivalent metal selected from the group con-sisting of aluminum, indium and gallium;
dissolving high level radioactive waste in said melt; and allowing said melt incorporating said radio-active waste to cool and solidify into a block.
forming a melt of a polymeric phosphate glass having a formula:
M(PO3)3, where M is a trivalent metal selected from the group con-sisting of aluminum, indium and gallium;
dissolving high level radioactive waste in said melt; and allowing said melt incorporating said radio-active waste to cool and solidify into a block.
35. The process of claim 34, wherein said metal is aluminum.
36. The process of claim 34, wherein said metal is indium.
37. The process of claim 34, wherein said metal is gallium.
38 . The process of claim 34, wherein said melt forming step includes:
preparing precursor crystals having the formula:
M(H2 PO4)3, adding radioactive waste crystals to said precursor crystals to form a crystal mixture; and heating said crystal mixture to induce solid state polymerization and form said melt.
preparing precursor crystals having the formula:
M(H2 PO4)3, adding radioactive waste crystals to said precursor crystals to form a crystal mixture; and heating said crystal mixture to induce solid state polymerization and form said melt.
39. The process of claim 38, wherein said melt forming step further includes washing said precursor crystals substantially free of phosphoric acid prior to adding radioactive waste crystals.
40. The process of claim 38, wherein the im-purity level of said precursor crystals does not exceed 300 ppm.
41. The process of claim 38 wherein said mixture is heated to a temperature of approximately 1350° C.
42. The process of claim 38 wherein said crystal mixture includes phosphoric acid.
43. The process of claim 38, further compris-ing the step of heating said precursor crystals to form a calcine prior to adding said radioactive waste crystals.
44. The process of claim 34, wherein said melt forming step includes:
preparing precursor crystals having the formula:
M(H2PO4)3;
heating said precursor crystals to induce solid state polymerization and form a first melt, allowing said first melt to cool;
grinding the cooled glass to form a glass frit;
adding radioactive waste crystals to said glass frit to form a glass-crystal mixture; and heating said glass-crystal mixture to form a second melt.
preparing precursor crystals having the formula:
M(H2PO4)3;
heating said precursor crystals to induce solid state polymerization and form a first melt, allowing said first melt to cool;
grinding the cooled glass to form a glass frit;
adding radioactive waste crystals to said glass frit to form a glass-crystal mixture; and heating said glass-crystal mixture to form a second melt.
45. The process of encapsulating as defined in any one of claims 34, 38 or 44, wherein said polymeric phosphate glass further includes a phosphate glass of the general formula M3 P7 O22, wherein M is as defined in claim 34.
46. The process of claim 34, wherein said melt forming step includes the steps of:
precipitating M(PO3)3 by combining a purified solution of a soluble salt with a purified solution of metaphosphoric acid; and heating the M(PO3)3 to form a polymerized melt.
precipitating M(PO3)3 by combining a purified solution of a soluble salt with a purified solution of metaphosphoric acid; and heating the M(PO3)3 to form a polymerized melt.
47. The process of claim 46, wherein said soluble salt is one having the formula M(NO3)3 wherein M is as defined in claim 34.
48. The process of claim 46, wherein the impurity level of said soluble salt does not exceed 300 ppm.
49. The process of claim 46, wherein the impurity level of said metaphosphoric acid does not exceed 300 ppm.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US96412078A | 1978-11-18 | 1978-11-18 | |
| US964,120 | 1978-11-18 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1131004A true CA1131004A (en) | 1982-09-07 |
Family
ID=25508150
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA339,896A Expired CA1131004A (en) | 1978-11-18 | 1979-11-15 | Molecular glasses for nuclear waste encapsulation |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1131004A (en) |
-
1979
- 1979-11-15 CA CA339,896A patent/CA1131004A/en not_active Expired
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4351749A (en) | Molecular glasses for nuclear waste encapsulation | |
| EP0042770B1 (en) | Method of immobilizing nuclear waste in glass | |
| US4422965A (en) | Nuclear waste encapsulation in borosilicate glass by chemical polymerization | |
| CN104844190A (en) | Method for preparing fluorapatite ceramic solidified body | |
| CN103827039A (en) | Process for preparing an oxychloride and/or oxide of actinide(s) and/or of lanthanide(s) from a medium comprising at least one molten salt | |
| Metcalfe et al. | Candidate wasteforms for the immobilization of chloride-containing radioactive waste | |
| US4094809A (en) | Process for solidifying high-level nuclear waste | |
| CA1131004A (en) | Molecular glasses for nuclear waste encapsulation | |
| EP0102153B1 (en) | Process for making cinder aggregates | |
| WO1994001527A1 (en) | Compounds and methods for separation and molecular encapsulation of metal ions | |
| US5875407A (en) | Method for synthesizing pollucite from chabazite and cesium chloride | |
| US3114716A (en) | Method of preparing radioactive cesium sources | |
| Ropp | Molecular glasses for nuclear waste encapsulation | |
| Danilov et al. | Hydrolytic durability of uranium-containing sodium aluminum (iron) phosphate glasses | |
| US5340506A (en) | Method to synthesize dense crystallized sodalite pellet for immobilizing halide salt radioactive waste | |
| US5264159A (en) | Process for treating salt waste generated in dry reprocessing of spent metallic nuclear fuel | |
| US20230139928A1 (en) | Method for dehalogenation and vitrification of radioactive metal halide wastes | |
| US3330889A (en) | Preparation of heat sources for radioisotope heated thermoelectric generators | |
| EP1412950B1 (en) | Encapsulation of waste | |
| Rankin et al. | Microstructures and leachability of vitrified radioactive wastes | |
| US5545797A (en) | Method of immobilizing weapons plutonium to provide a durable, disposable waste product | |
| US3124538A (en) | Certificate of correction | |
| Volkovich et al. | Nano-Materials from Molten Salts: Preparation of Nano-Sized Lanthanide Phosphates from Chloride Melts | |
| GB2157675A (en) | Glass containing radioactive nuclear waste | |
| Vance et al. | Ceramic phases for immobilization of 129 I |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |