US3120435A - Regeneration of fission-products-containing magnesium-thorium alloys - Google Patents

Regeneration of fission-products-containing magnesium-thorium alloys Download PDF

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US3120435A
US3120435A US19999862A US3120435A US 3120435 A US3120435 A US 3120435A US 19999862 A US19999862 A US 19999862A US 3120435 A US3120435 A US 3120435A
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    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21C—NUCLEAR REACTORS
    • G21C19/00—Arrangements for treating, for handling, or for facilitating the handling of, fuel or other materials which are used within the reactor, e.g. within its pressure vessel
    • G21C19/42—Reprocessing of irradiated fuel
    • G21C19/44—Reprocessing of irradiated fuel of irradiated solid fuel
    • G21C19/48—Non-aqueous processes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E30/00—Energy generation of nuclear origin
    • Y02E30/30—Nuclear fission reactors
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W30/00—Technologies for solid waste management
    • Y02W30/50—Reuse, recycling or recovery technologies

Definitions

  • This invention deals with the regeneration of neutronbombarded magnesium thorium alloys, and in particular with the removal of fission products therefrom.
  • Fission-products-containing magnesium-thorium alloys are obtained in the processing of so-called thorium blankets used in nuclear breeder reactors, for instance by the process that is the subject matter of US. patent No. 2,990,273, granted to Premo Chiotti on June 27, 1961.
  • the neutronbombarded thorium metal is reacted with magnesium at from 800 to 900 C. whereby a liquid magnesiumthorium-fission products alloy anda solid metal predominantly consisting of uranium and protactinium form.
  • the instant process deals with the regeneration of this magnesium-thorium-fission product alloy.
  • the fission products usually present in the magnesiumthorium alloy are alkali metals, alkaline earth metals, lanthanide rare earths (hereinafter referred to simply as rare earths), and yttrium. Apart from fission products, the alloy also contains trace amounts of protactinium and uranium.
  • magnesium chloride is a selective oxidizing agent for the alloy to be processed, since it chlorinates most of the fission products enumerated above, but does not appreciably chlorinate thorium, uranium or protactinium. This finding is utilized in the process of this invention.
  • the process of this invention broadly comprises adding to the molten magnesium-thorium alloy potassium chloride-lithium chloride-magnesium chloride, whereby the fission products, such as alkali metals, alkaline earth metals, rare earth metals, including samarium and yttrium, and a minor fraction of the thorium, are chlorinated and taken up by a salt phase, while practically all protactinium and minor fraction of calcium, cerium and lanthanum remain in a metal phase; separating the salt and the metal phases from each other; scrubbing the salt phase with a binary zinc alloy containing a small amount of magnesium, whereby the chlorides of cerium, yttrium, rare earths (except samarium), uranium and thorium are reduced to the metals and taken up by a magnesium-zinc phase, while the alkali metal chlorides, alkaline earth metal chlorides and samarium chloride, SmCl are retained in a chloride phase; and
  • the magnesium-thorium alloy is preferably, although not necessarily, the eutectic which contains about 58% by weight of magnesium and melts at 582 C.
  • the mixture of potassium chloride-lithium chloridemagnesium chloride preferably contains the eutectic of the potassium and lithium chlorides (44.4% LiCl; melting point 354 C.) and magnesium chloride in a concentration of from to 25% by weight.
  • a quantity of from 400 to 500 grams of this salt mixture per one kilogram of magnesium-thorium alloy to be treated was found satisfactory; however, a greater quantity can be used.
  • the operating temperature preferably ranges between 600 and 650 C.
  • the separation of the salt phase from the metal phase can be carried out by customary means, for instance by cooling for solidification of one phase and decantation.
  • the magnesium-zinc alloy that is added to the salt phase can have a magnesium content of between 2 and 4%, the preferred concentration being about 3%. A quantity of between and 250 grams for 500 grams of salt is adequate.
  • the magnesium-zinc phase is separated from the chloride phase and either discarded, or it is purified by distillation of the zinc and magnesium away from the fission products, whereby the latter are obtained in a concentrated, compact form ready for disposal.
  • the chloride phase can be recycled until it has an undesirably high radioactive content of alkali and alkaline earths.
  • the metal phase obtained in the treatment with magnesium chloride and containing thorium and the bulk of the protactinium can be treated for recovery of thorium.
  • One way of accomplishing this is by reaction with hydrogen at between 650 and 675 C. and atmospheric pressure whereby thorium hydride, ThH precipitates from the metal to form a magnesium solution containing a remainder of about 8% by weight of thorium.
  • the precipitated thorium hydride is separated by customary means and then subjected to vacuum distillation at about 700 0, whereby both hydrogen and magnesium are volatilized, and a magnesium-free thorium sponge is obtained. This process of hydriding the magnesiumthorium phase per se is not part of this invention.
  • Example 1 To 2000 grams of a magnesium-thorium alloy containing 40% by weight of thorium and also 0.100 each of yttrium, cerium, neodymium and samarium, 500 grams of a potassium chloride-lithium chloride eutectic containing 15% by weight of magnesium chloride are added. The mixture is heated in a tantalum crucible and maintained therein in an argon atmosphere at a temperature of between 600 and 625 C. for four hours; during the entire period the mixture is stirred. The mass is then allowed to settle for one hour, the salt and metal phases are separated from each other and analyzed.
  • the salt phase contains 0.26% of yttrium, 0.15% of cerium, 0.15% of neodymium, 0.4% of samarium and 0.074% of thorium.
  • the magnesium-thorium metal phase contains 0.035% of yttrium, 0.062% of cerium, 0.063% of neodymium and 0.0008% of samarium.
  • the salt is then transferred to another tantalum container and contacted there, by stirring, with 250 grams of a binary zinc-magnesium alloy containing 3% by Weight of magnesium at a temperature of 600 C. After four hours of equilibration and one hour of settling, the salt and zinc-magnesium metal phases are separated from each other and analyzed.
  • the zinc contains, in solution or as precipitated metal, 0.45% of yttrium, 0.25% of cerium, 0.29% of neodymium, 0.024% of samarium and 0.15 of thorium; the salt contains 0.035% of yttrium, 0.0045% of cerium, 0.0049% of neodymium, 0.40% of samarium and 0.001% of thorium.
  • This cycle of treatment with potassium chloride-lithium chloride-magnesium chloride, phase separation, treatment with zinc-magnesium alloy and subsequent phase separation is repeated two more times, each time using the same zinc-magnesium alloy, and the same charge of the chloride mixture.
  • the magnesium-thorium alloy contains 0.0083% of yttrium, 0.029% of cerium, 0.033% of neodymium and 0.0008% of samarium, which amounts to a removal of 92, 71, 67 and 99.2% of these respective contaminants in the three cycles.
  • the total amount of thorium that is transferred to the zinc-magnesium alloy is only 1.1 grams.
  • the zinc-magnesium metal after the third cycle, contains 0.65% of yttrium, 0.55% of cerium, 0.52% of neodymium, 0.026% of samarium and 0.43% of thorium.
  • the salt obtained after the third equilibration with the zinc-magnesium alloy contains 0.035% of yttrium, 0.0045% of cerium, 0.0049% of neodymium, 0.40% of samarium and 0.001% of thorium; these are the same contents as those obtained after the first equilibration, which is due to the fact that the zinc-magnesium alloy becomes saturated in the first equilibration with respect to yttrium, cerium, neodymium, Samarium and thorium.
  • a process of regenerating a magnesium-thorium alloy containing fission products and residual amounts of protactinium and uranium comprising adding to the molten alloy molten potassium chloride-lithium chloridemagnesium chloride, whereby the fission products, such as alkali metals, alkaline earth metals, rare earth metals, yttrium and minor fractions of the thorium and uranium, are chlorinated and taken up by a salt phase, while practically all protactinium and minor fractions of calcium, cerium and lanthanum remain in a metal phase; separating the salt and the metal phases from each other; scrubbing the salt phase with a molten binary zinc-magnesium alloy containing from 2 to 4% by weight of magnesium, whereby the chlorides of cerium, yttrium, trivalent rare earths, uranium and thorium are reduced to the metals and taken up by a magnesium-zinc phase, while the alkali metal chlorides, al
  • the potassium chloride-lithium chloride-magnesium chloride mixture contains potassium chloride and lithium chloride in about the eutectic composition and magnesium chloride in a quantity of from 10 to 25% by weight and wherein a reaction temperature of between 600 and 650 C. is maintained.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • General Engineering & Computer Science (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Manufacture And Refinement Of Metals (AREA)

Description

United States Patent Ofi ice 3,120,435 Patented Feb. 4, 1964 3,120,435 REGENERATION OF FISSION-PRODUCTS-CON- TAINING MAGNESIUM-THORIUM ALLOYS Premo Chiotti, Arnes, Iowa, assignor to the United States of America as represented by the United States Atomic Energy Commission No Drawing. Filed June 4, 1962, Ser. No. 199,998
5 Claims. (Cl. 7584.1)
This invention deals with the regeneration of neutronbombarded magnesium thorium alloys, and in particular with the removal of fission products therefrom.
Fission-products-containing magnesium-thorium alloys are obtained in the processing of so-called thorium blankets used in nuclear breeder reactors, for instance by the process that is the subject matter of US. patent No. 2,990,273, granted to Premo Chiotti on June 27, 1961. In the first step of that patented process the neutronbombarded thorium metal is reacted with magnesium at from 800 to 900 C. whereby a liquid magnesiumthorium-fission products alloy anda solid metal predominantly consisting of uranium and protactinium form. The instant process deals with the regeneration of this magnesium-thorium-fission product alloy.
The fission products usually present in the magnesiumthorium alloy are alkali metals, alkaline earth metals, lanthanide rare earths (hereinafter referred to simply as rare earths), and yttrium. Apart from fission products, the alloy also contains trace amounts of protactinium and uranium.
It was found that magnesium chloride is a selective oxidizing agent for the alloy to be processed, since it chlorinates most of the fission products enumerated above, but does not appreciably chlorinate thorium, uranium or protactinium. This finding is utilized in the process of this invention.
The process of this invention broadly comprises adding to the molten magnesium-thorium alloy potassium chloride-lithium chloride-magnesium chloride, whereby the fission products, such as alkali metals, alkaline earth metals, rare earth metals, including samarium and yttrium, and a minor fraction of the thorium, are chlorinated and taken up by a salt phase, while practically all protactinium and minor fraction of calcium, cerium and lanthanum remain in a metal phase; separating the salt and the metal phases from each other; scrubbing the salt phase with a binary zinc alloy containing a small amount of magnesium, whereby the chlorides of cerium, yttrium, rare earths (except samarium), uranium and thorium are reduced to the metals and taken up by a magnesium-zinc phase, while the alkali metal chlorides, alkaline earth metal chlorides and samarium chloride, SmCl are retained in a chloride phase; and separating the magnesiumzinc phase from the chloride phase.
The magnesium-thorium alloy is preferably, although not necessarily, the eutectic which contains about 58% by weight of magnesium and melts at 582 C.
The mixture of potassium chloride-lithium chloridemagnesium chloride preferably contains the eutectic of the potassium and lithium chlorides (44.4% LiCl; melting point 354 C.) and magnesium chloride in a concentration of from to 25% by weight. A quantity of from 400 to 500 grams of this salt mixture per one kilogram of magnesium-thorium alloy to be treated was found satisfactory; however, a greater quantity can be used. The operating temperature preferably ranges between 600 and 650 C. The separation of the salt phase from the metal phase can be carried out by customary means, for instance by cooling for solidification of one phase and decantation.
The magnesium-zinc alloy that is added to the salt phase can have a magnesium content of between 2 and 4%, the preferred concentration being about 3%. A quantity of between and 250 grams for 500 grams of salt is adequate. The magnesium-zinc phase is separated from the chloride phase and either discarded, or it is purified by distillation of the zinc and magnesium away from the fission products, whereby the latter are obtained in a concentrated, compact form ready for disposal. The chloride phase can be recycled until it has an undesirably high radioactive content of alkali and alkaline earths.
The reduction of the rare earth chlorides with and their extraction into the magnesium-zinc alloy could not be predicted or expected from thermodynamical considerations.
The metal phase obtained in the treatment with magnesium chloride and containing thorium and the bulk of the protactinium can be treated for recovery of thorium. One way of accomplishing this is by reaction with hydrogen at between 650 and 675 C. and atmospheric pressure whereby thorium hydride, ThH precipitates from the metal to form a magnesium solution containing a remainder of about 8% by weight of thorium. The precipitated thorium hydride is separated by customary means and then subjected to vacuum distillation at about 700 0, whereby both hydrogen and magnesium are volatilized, and a magnesium-free thorium sponge is obtained. This process of hydriding the magnesiumthorium phase per se is not part of this invention.
In the following an example is given to illustrate the process of this invention.
Example To 2000 grams of a magnesium-thorium alloy containing 40% by weight of thorium and also 0.100 each of yttrium, cerium, neodymium and samarium, 500 grams of a potassium chloride-lithium chloride eutectic containing 15% by weight of magnesium chloride are added. The mixture is heated in a tantalum crucible and maintained therein in an argon atmosphere at a temperature of between 600 and 625 C. for four hours; during the entire period the mixture is stirred. The mass is then allowed to settle for one hour, the salt and metal phases are separated from each other and analyzed. The salt phase contains 0.26% of yttrium, 0.15% of cerium, 0.15% of neodymium, 0.4% of samarium and 0.074% of thorium. The magnesium-thorium metal phase contains 0.035% of yttrium, 0.062% of cerium, 0.063% of neodymium and 0.0008% of samarium.
The salt is then transferred to another tantalum container and contacted there, by stirring, with 250 grams of a binary zinc-magnesium alloy containing 3% by Weight of magnesium at a temperature of 600 C. After four hours of equilibration and one hour of settling, the salt and zinc-magnesium metal phases are separated from each other and analyzed. The zinc contains, in solution or as precipitated metal, 0.45% of yttrium, 0.25% of cerium, 0.29% of neodymium, 0.024% of samarium and 0.15 of thorium; the salt contains 0.035% of yttrium, 0.0045% of cerium, 0.0049% of neodymium, 0.40% of samarium and 0.001% of thorium.
This cycle of treatment with potassium chloride-lithium chloride-magnesium chloride, phase separation, treatment with zinc-magnesium alloy and subsequent phase separation is repeated two more times, each time using the same zinc-magnesium alloy, and the same charge of the chloride mixture. After the three cycles the magnesium-thorium alloy contains 0.0083% of yttrium, 0.029% of cerium, 0.033% of neodymium and 0.0008% of samarium, which amounts to a removal of 92, 71, 67 and 99.2% of these respective contaminants in the three cycles. The total amount of thorium that is transferred to the zinc-magnesium alloy is only 1.1 grams.
The zinc-magnesium metal, after the third cycle, contains 0.65% of yttrium, 0.55% of cerium, 0.52% of neodymium, 0.026% of samarium and 0.43% of thorium. The salt obtained after the third equilibration with the zinc-magnesium alloy contains 0.035% of yttrium, 0.0045% of cerium, 0.0049% of neodymium, 0.40% of samarium and 0.001% of thorium; these are the same contents as those obtained after the first equilibration, which is due to the fact that the zinc-magnesium alloy becomes saturated in the first equilibration with respect to yttrium, cerium, neodymium, Samarium and thorium.
These results show that a good decontamination of the magnesium-thorium alloy from the fission products is obtained by the process of this invention.
It will be understood that the invention is not to be limited to the details given herein but that it may be modified within the scope of the appended claims.
What is claimed is:
1. A process of regenerating a magnesium-thorium alloy containing fission products and residual amounts of protactinium and uranium, comprising adding to the molten alloy molten potassium chloride-lithium chloridemagnesium chloride, whereby the fission products, such as alkali metals, alkaline earth metals, rare earth metals, yttrium and minor fractions of the thorium and uranium, are chlorinated and taken up by a salt phase, while practically all protactinium and minor fractions of calcium, cerium and lanthanum remain in a metal phase; separating the salt and the metal phases from each other; scrubbing the salt phase with a molten binary zinc-magnesium alloy containing from 2 to 4% by weight of magnesium, whereby the chlorides of cerium, yttrium, trivalent rare earths, uranium and thorium are reduced to the metals and taken up by a magnesium-zinc phase, while the alkali metal chlorides, alkaline earth metal chlorides and Samarium chloride are retained in a chloride phase; and separating the magnesium-zinc phase from the chloride phase.
2. The process of claim 1 wherein the magnesiumthorium alloy has about the composition of the eutectic.
3. The process of claim 1 wherein the potassium chloride-lithium chloride-magnesium chloride mixture contains potassium chloride and lithium chloride in about the eutectic composition and magnesium chloride in a quantity of from 10 to 25% by weight and wherein a reaction temperature of between 600 and 650 C. is maintained.
4. The process of claim 3 wherein the magnesium chloride content is about 15% by weight.
5. The process of claim 1 wherein the magnesium content is about 3% by weight.
References Cited in the file of this patent UNITED STATES PATENTS 2,914,399 Dwyer et al. Nov. 24, 1959 2,968,547 Lyon et al Jan. 17, 1961 2,990,273 Chiotti June 27, 1961 3,053,650 Teitel Sept. 11, 1962 3,063,830 Martin et al. Nov. 13, 1962 FOREIGN PATENTS 610,220 Canada Dec. 6, 1960

Claims (1)

1. A PROCESS OF REGENERATING A MAGNESIUM-THRORIUM ALLOY CONTAINING FISSION PRODUCTS AND RESIDUAL AMOUNTS OF PROTACTINIUM AND URANIUM, COMPRISING ADDING TO THE MOLTEN ALLOY MOLTEN POTASSIUM CHLORIDE-LITHIUM CHLORIDEMAGNESIUM CHLORIDE,WHEREBY THE FISSION PRODUCTS, SUCH AS ALKALI METALS, ALKALINE EARTH METALS, RARE EARTH METALS, YTTRIUM AND MINOR FRACTIONS OF THE THORIUM AND URANIUM, ARE CHLORINATED AND TAKEN UP BY A SALT PHASE, WHILE PRACTICALLY ALL PROTACTINIUM AND MINOR FRACTONS OF CALICUM, CERIUM AND LANTHANUM REMAIN IN A METAL PHASE; SEPARATING THE SALT AND THE METAL PHASES FROM EACH OTHER; SCRUBBING THE SALT PHASE WITH A MOLTEN BINARY ZINC-MAGNESIUM ALLOY CONTAINING FROM 2 TO 4% BY WEIGHT OF MAGNESIUM, WHEREBY THE CHLORIDES OF CERIUM, YTTRIUM, TRIVALENT RARE EARTHS, URANIUM AND THORIUM ARE REDUCED TO THE METALS AND TAKEN UP BY A MAGNESIUM-ZINC PHASE, WHILE THE ALKALI METAL CHORIDES, ALKALINE EARTH METAL CHLORIDES AND SAMARIUM CHLORIDE ARE RETAINED IN A CHLORIDE PHASE; AND SEPARATING THE MAGNESIUM-ZINC PHASE FROM THE CHLORIDE PHASE.
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Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3147109A (en) * 1963-05-03 1964-09-01 James B Knighton Separation of plutonium, uranium, americium and fission products from each other
US3152887A (en) * 1963-05-03 1964-10-13 Lawroski Stephen Americium-curium separation
US3218160A (en) * 1964-11-10 1965-11-16 James B Knighton Regeneration of nuclear fuel
US3271133A (en) * 1965-06-29 1966-09-06 James B Knighton Purification of molten salts
US3282681A (en) * 1966-02-08 1966-11-01 James B Knighton Separation of uranium and plutonium values
US3284190A (en) * 1966-02-08 1966-11-08 James B Knighton Separation of uranium from noble and refractory metals
WO1992017887A1 (en) * 1991-03-27 1992-10-15 The Dow Chemical Company Process for selectively concentrating the radioactivity of thorium containing magnesium slag

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2914399A (en) * 1958-08-20 1959-11-24 Orrington E Dwyer Removal of certain fission product metals from liquid bismuth compositions
CA610220A (en) * 1960-12-06 B. Knighton James Method for purifying uranium
US2968547A (en) * 1959-12-18 1961-01-17 Ward L Lyon Production of plutonium metal
US2990273A (en) * 1959-08-28 1961-06-27 Chiotti Premo Uranium recovery from metallic masses
US3053650A (en) * 1959-07-02 1962-09-11 Dow Chemical Co Process for recovering uranium values
US3063830A (en) * 1961-07-14 1962-11-13 Allan E Martin Separation of uranium, plutonium and fission products from neutron-bombarded uranium

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CA610220A (en) * 1960-12-06 B. Knighton James Method for purifying uranium
US2914399A (en) * 1958-08-20 1959-11-24 Orrington E Dwyer Removal of certain fission product metals from liquid bismuth compositions
US3053650A (en) * 1959-07-02 1962-09-11 Dow Chemical Co Process for recovering uranium values
US2990273A (en) * 1959-08-28 1961-06-27 Chiotti Premo Uranium recovery from metallic masses
US2968547A (en) * 1959-12-18 1961-01-17 Ward L Lyon Production of plutonium metal
US3063830A (en) * 1961-07-14 1962-11-13 Allan E Martin Separation of uranium, plutonium and fission products from neutron-bombarded uranium

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3147109A (en) * 1963-05-03 1964-09-01 James B Knighton Separation of plutonium, uranium, americium and fission products from each other
US3152887A (en) * 1963-05-03 1964-10-13 Lawroski Stephen Americium-curium separation
US3218160A (en) * 1964-11-10 1965-11-16 James B Knighton Regeneration of nuclear fuel
US3271133A (en) * 1965-06-29 1966-09-06 James B Knighton Purification of molten salts
US3282681A (en) * 1966-02-08 1966-11-01 James B Knighton Separation of uranium and plutonium values
US3284190A (en) * 1966-02-08 1966-11-08 James B Knighton Separation of uranium from noble and refractory metals
WO1992017887A1 (en) * 1991-03-27 1992-10-15 The Dow Chemical Company Process for selectively concentrating the radioactivity of thorium containing magnesium slag
US5223181A (en) * 1991-03-27 1993-06-29 The Dow Chemical Company Process for selectively concentrating the radioactivity of thorium containing magnesium slag

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