GB2040971A - Radioactive waste solidifying prepolymers and method of solidifying radioactive waste by using such prepolymers - Google Patents

Abstract

A radioactive waste solidifying prepolymer comprises resorcinol compound units, phenol compound units and formaldehyde units, and a method of solidifying a radioactive waste characterized in that a radio active waste, paraformaldehyde and filler are added to the radioactive waste solidifying prepolymer, and the resulting mixture is condensed.

Description

SPECIFICATION Radio active waste solidifying prepolymers and method of solidifying radioactive waste by using such prepolymers FIELD OF THE INVENTION This invention relates to a radioactive waste solidifying prepolymers and a method of solidifying radioactive waste. More particularly, it relates to a radioactive waste solidifying prepolymer comprising resorcinol compound units, phenol compound units and formaldehyde units, and it relates to a method of solidifying and thereby disposing of radioactive waste which is released from the plants where nuclear power is utilized, such as for example nuclear power stations.

DESCRIPTION OF THE PRIOR ART: For treatment of radioactive waste from nuclear power stations, for example in the case of waste water, it is required to process almost all of waste water in a way to allow recycling of water and to subject the ion exchange resin used for treatment of concentrated wastes, waste sludge, waste liquid, etc. (hereinafter referred to comprehensively as radioactive waste) to a solidification treatment.

There are available the following methods for solidification said radioactive waste.

(a) Solidification with cement.

(b) Solidification-with asphalt.

(c) Soiidification with plastic using a urea-formaldehyde copolymer.

However, the above-said method (a), for solidification with cement involves the risk of seepage of the radioactive nuclide which has been set in the cement block, while the method (b), for solidification with asphalt, has the danger of causing a fire or evolution of noxious gas and mercaptan gas as high temperature is required for the solidification operation. The method (c), for solidification with plastic by use of an urea-formaldehye copolymer, involves the problem of fragility of the set mass and also has the danger of causing hydrolysis upon contact with water.

In view of these circumstances, the present inventors have made further studies on the plasticusing set mass having high strength and no likelihood of hydrolysis and found that a condensate obtained from a combination of a specific prepolymer and a specific filler can ideally set the radioactive substance. This invention was completed on the basis of such finding.

SUMMARY OF THE INVENTION: It is an object of the present invention to provide a radioactive waste solidifying prepolymer, and a method of solidifying a radioactive waste characterized in that a radioactive waste, paraformaldehyde and a filler are added to a radioactive waste solidifying prepolymer and the resulting mixture is condensed.

DETAILED DESCRIPTION OF THE INVENTION: The present invention is intended to provide à method of solidifying radioactive waste characterized in that radioactive waste, paraformaldehyde and at least one filler selected from calcium carbonate, calcium sulfate, calcium phosphate, basic magnesium carbonate, silicic acid anhydride, magnesium silicate, calcium silicate, barium sulfate, manganese borate, sodium borate, colemanite, kaolin, bentonite, zeolite, active clay, dolomite, fly ash, diatom earth, sand, earth, rock and slag, or said filler and wood chips or a-cellulose, are added to a radioactive waste solidifying prepolymer consisting of resorcinol compound units, phenol compound units and formaldehyde units, wherein the resorcinol compound reside : phenol comppund residue molar ration is over 0.6 1.0 and the forma!dehyde residue : resorcinol compound residue and phenol compound residue molar ratio is 0.5-0.9 1.0, and also containing more than 50% by weight of nonvolatiles, and the resulting mixture is condensed.

The prepolymer used for the solidification of radioactive waste in this invention may be prepared by a known method in which a resorcinol compound, g phenol compound panda formaldehyde compound are condensed in the presence of an alkaline catalyst, and usually it is only required that a substantial portion of the formaldehyde compound existing in the reaction system be reacted.

Said reaction may be accomplished by mixing the materials all at one time or by adding them in two or more portions. For instance, there may be employed a two-stage reaction method in which first a phenol compound, a formaldehyde compound and a catalyst are mixed and reacted at 90-950C for approximately 60-90 minutes, and then a resorcinol compound and a catalyst are added to perform further reaction at 90--9 5 OC for 120-1 80 minutes.

In the above reaction, water may be added at need, but as the prepolymer used in this invention is required to contain nonvolatiles in an amount of more than 50% by weight, preferably more than 70% by weight, the impurities in the materials (for example water in formaldehyde) which are to become nonvolatiles in the prepolymer may be previously calculated so that the nonvolatile content in the reaction product (prepolymer of this invention) will become more than 50% by weight, preferably more than 70% by weight, or the nonvolatile content may be adjusted into said required range by a suitable operation such as distillation under reduced pressure after completion of the reaction.

It is also possible to obtain a desired prepolymer by mixing or by reacting two or more different prepolymers at suitable proportions. For instance, a resorcinol-formaldehyde resin and a phenolformaldehyde resin or a resorcinol-phenol-formaldehyde resin may be mixed and/or reacted in a suitable ratio.

In the preparation of a prepolymerto be used in this invention, the molar ratio of the resorcinol compound to the phenol compound is peferably over 0.6 and the molar ratio of the formaldehyde compound to the resorcinol and phenol compounds is within the range of 0.5-0.9.

The resorcinol compound used in this invention may be resorcinol or alkyl resorcinol which can be obtained by dry-distilling oil shale.

Examples of the phenol compounds usable in this invention are phenol, cresol, xylenol and the like.

The formaldehyde compound used in this invention is of the type which produces a formaldehyde residue after coupling, and formaldehyde and paraformaldehyde may be cited as examples of such compound. It is preferable to use formalin which is an aqueous solution of formaldehyde.

Preferred examples of the catalyst used in this invention are the alkali metal hydroxides such as sodium hydroxide or potassium hydroxide.

We will now described the method of solidification for the radioactive waste by using a prepolymer obtained in the manner described above.

Briefly, the method of this invention comprises adding to said prepolymer to the radioactive waste, paraformaldehyde and at least one filler selected from calcium carbonate, calcium sulfate, calcium phosphate, basic magnesium carbonate, silicic acid anhydride, magnesium silicate, calcium silicate, barium sulfate, manganese borate, sodium borate, colemanite, kaolin, bentonite, zeolite, active clay, dolomite, fly ash, diatom earth, sand, earth, rock and iron slag, or said filler and wood chips or acellulose, and condensing the resulting mixture.

When the radioactive waste and filler or said filler and wood chips or a-cellulose (hereinafter referred to representatively as filler) are mixed in said prepolymer, the mixture begins to solidify gradually even at room temperature and the solidified mass becomes solid and stout as time elapses. If such solidification or setting is performed under heating, the reaction is so much promoted to allow obtainment of the solid and strong set mass with ease and in a short period of time.

The order of addition of the materials is free to choose.

According to this invention, paraformaldehyde is mixed in an amount of 5 to 40 weight parts, preferably 10 to 30 weight parts, while the filler is mixed in an amount of 5 to 1 50 weight parts, preferably 10 to 1 0 weight parts, per 100 weight parts of the prepolymer, and if the blend of said prepolymer, formaldehyde and filler is in an amount of 80 to 400 weight parts, preferably 100 to 300 weight parts, per 100 weight parts of the radioactive substance to be treated, a solid set mass of the mixture can be obtained.

The radioactive waste that can be treated according to this invention include all types of radioactive materials such as solids or aqueous solutions of the single materials or compounds of tritium, carbon, phosphorus, sulfur, chromium, manganese, iron, cobalt, nickel, tellurium, iodine, cesium and the like, or ion exchange resins which have adsorbed ions produced from said materials.More definitely, they include waste ion exchange resin from the purification desalting apparatus used for removal of radioactive substance- in the nuclear reactor coolant, waste ion exchange resin from the desaiting apparatus for disposal of waste material produced from various machines and floor drains, filter sludge, evaporation-thickened version of waste liquid of regenerated ion exchange resin, waste ion exchange resin derived from the spent nuclear fuel pool desalting apparatus, waste borate solutions (or concentrated version thereof) released from the pressurized water reactors, waste sulfate solutions (or concentrated version thereof) released from the boiling water reactors, laundry, waste water, and solids such as ash, aqueous solutions or slurries produced from incinerators or stoves.

The radioactive waste solidifying method according to this invention involves no risk of seepage aic radioactive nuclide that might take place in the cement method, no danger of causing a fire or evolution of noxious gas as often experienced in the asphalt method, and no problem of fragility inherent to the plastic method using a urea-formaldehyde copolymer. Further, even in case the radioactive waste to be treated is an aqueous solution, there is produced no separated water (generally called free water) in the solidifying operation, and even in the case of an ion exchange resin-water slurry, it can be set without causing separation of any free water. Moreover, the set mass formed according to the method of this invention is very solid and strong, so that the method of this invention finds effective applications for treatment of various types of radioactive materials.

The invention is now described in further detail by way of some typical examples thereof, but it may be understood that the scope of this invention is not limited by these examples.

EXAMPLE 1 Phenol, 48% formalin, paraformaldehyde and 45% sodium hydroxide for first addition were fed into a three-necked flask furnished with a stirrer, a reflux cooler and a thermometer, and the mixture was reacted over a water bath at 950C for one hour. Then resorcinol was further added thereto and the reaction temperature was lowered down to 600 C. The mixture was then added with the second portion of 45% sodium hydroxide and further reacted at 900C for 1 80 minutes, and this was followed by cooling to normal temperature to form a prepolymer.

The viscosity and nonvolatile content of the thus obtained prepolymer are shown in Table 1 in the column of "Properties".

To 100 g of this prepolymer were added 20 g of 88% paraformaldehyde, 60 g of calcium carbonate and 79 g of a 12% boric acid and 50 ppm cesium solution containing 0.5 fllCi of cesium as radioactive substance, and the mixture was stirred sufficiently. The mixture was then cast into a mold with an inner diameter of 40 mm and a height of 200 mm and hardened. The resultantly obtained set mass has incorporated water entirely therein, allowing no hangover or separation of free water. Also, the set mass was uniform throughout its structure and the uniaxial compression strength thereof was 140 kg/cm2. No noticeable change in external appearance took place when the set mass was allowed to stand as it was for one month.

EXAMPLE 2 The same materials were mixed in same amounts as in Example 1 and reacted similarly to Example 1 to obtain a prepolymer having the viscosity and nonvolatile content shown in Table 1. Then 100 ml nitric acid solution of a 10 ppm lanthanum (pH 0.5) containing 1 ,uci of lanthanum as radioactive nuclide was passed, at flow rate (SV) of 2 he~', through a 10 mm inner diameter glass-made column filled with 20 ml of Diaion SK-1 B (H type, and wetted cation exchange resin) to obtain a bastion exchange resin adsorbed with 1 alCi of lanthanum as radioactive nuclide.Likewise, 100 ml nitric acid solution of 30 ppm nitric acid solution (pH 5.0) containing 0.5 ,uci of radioactive strontium was passed as SV = 1 hr-t through the same type of glass column filled with the same cation exchange resin (H type, wetted) as said above to obtain a cation exchange resin adsorbed with 0.5 ,uci of strontium as radioactive nuclide. The thus formed ion exchange resins were extracted from the column and mixed in a beaker to prepare a 50% aqueous slurry of ion exchange resin.

To 100 g of the previously obtained prepolymer were added 18 g of 88% paraformaldehyde, 20 g of calcium carbonate, 10 g of calcium phosphate, 10 g of powdered wood chip and 87 g of said 50% slurry of the lanthanum adsorbed resin and strontium adsorbed resin mixture, and the blend was stirred sufficiently.

Then the mixture was cast into a mold with an inner diameter of 40 mm and a height of 200 mm and hardened. The thus obtained solidified mass has perfectly incorporated water therein, allowing no hangover or separation of free water. The solidified mass was uniform in its entire structure and the uniaxial compression strength thereof was 1 55 kg/cm2. Aiso, two-month standing of this solid caused no change in its external appearance.

EXAMPLE 3 A prepolymer was produced by mixing the materials shown in Table 1 in amounts also shown in Table 1 and reacting them similarly to Example 1. The viscosity and involatile content of the obtained prepolymer were as shown in Table 1.

30 ml of Diaion SA-1 OA (OH type, wetted) (an anion exchange resin) was added to 1 50 g of an aqueous solution (500 Mci) containing 2.5 g of phenol labeled with radioactive carbon 14C, and the mixture was stirred for one hour to prepare specimen slurry I as radioactive substance to be treated in this experiment.

To 1 00 g of said prepolymer were added 28 g of 88% paraformaldehyde, 75 g of calcium sulfate 1/2 hydrate, 147 g of specimen slurry 1, 10 g of wood chips (powder) and 10 g of a-cellulose, and the mixture was stirred sufficiently. This mixture was then cast into a mold with an inner diameter of 40 mm and a height of 200 mm and hardened.

The thus obtained solidified mass was uniform in its structure and has taken up water entirely therein with no hangover or separation of free water, and the uniaxial compression strength thereof was 164kg/cm2. No change in external appearance was noted in one-month standing of the set mass.

Diaion SK-1 B and Diaion SA--1OA are manufactured by Mitsubishi Chemical Industries Limited and "Diaion" is tradename of Mitsubishi Chemical Industries Limited.

EXAMPLE 4 A prepolymer was produced by mixing the same materials and in same amounts as in Example 3 and reacting them after the manner of Example 1, the obtained prepolymer having the viscosity and nonvolatile content shown in Table 1.

30 ml of Diaion SK-1 B (H type, wetted) was added to 1 50 g of an aqueous solution (200 Mci) containing 2.5 g of triallylamine labeled with radioactive carbon 14C, and the mixture was stirred for one hour to prepare specimen slurry II as radioactive substance for this experiment Said prepolymer was mixed with 1 74 g of said specimen slurry II and other materials shown in Table 1 (in amounts also shown in Table 1), and the mixture was hardened in the same way as described above. The thus obtained solid has incorporated the whole amount of water therein, allowing no hangover or separation of free water Said solidified mass was also uniform structurally and the uniaxial compression strength thereof was 1 31 kg/cm2.When said solid was allowed to stand as it was for one month, no change in appearance took place.

COMPARATIVE EXAMPLES 1 and 2 As Comparative Example 1, a prepolymer was prepared from a blend shown in Table 1, and this prepolymer was added with 88 g of an aqueous solution of boric acid containing 0.5 jaci of cesium and other materials shown in Table 1, and the mixture was hardened into a solidified mass in the same way as Example 1. As Comparative Example 2, an urea-formaldehyde prepolymer was prepared from a blend shown in Table 1, and this prepolymer was mixed with 106 g of a mixed slurry of said lanthanum adsorbed resin and strontium adsorbed resin and other materials shown in Table 1, and the mixture was made into a set mass after the manner of Example 2. The solidified mass of Comparative Example 1 caused no hangover of free water but its uniaxial compression strength was as low as 26 kg/cm2, while the set mass of Comparative Example 2 caused hangover of 5.1% of free water and its uniaxial compression strength was also as low as 12 kg/cm2.

TABLE 1

Comparative Comparative Note 3 Example 1 Example 2 Example 3 Example 4 Example 1 Example 2 Phenol 1,500 1,500 1,364 1,364 2,657 Urea 1,800 #1 245 #2 Resorcinol 1,760 1,760 1,917 1,917 396 Formalin 5,840 #1 (37%) 519 #2 Formalin (48%) 1,360 1,360 1,016 1,016 1,354 Ammonia 153 water (25%) Paraformaldehyde (88%) - - 186 186 Sodium (45%) 48 #1 48 #1 48 #1 48 #1 47 #1 (Note 1) 359 #2 359 #2 359 #2 359 #2 356 #2 R/P 1.0 1.0 1.2 1.2 0.127 F/U = 2.4 # 2.3 F/(R+P) 0.68 0.68 0.68 0.68 0.68 (NaUH/R+P) 0.143 0.143 0.143 0.143 0.143 Viscosity, poises (25 C) 25.0 25.0 95.0 95.0 24.5 Nonvolatiles (%) 74.3 74.3 75.8 75.8 73.5 72.0 Prepolymer 100 100 100 100 100 100 Paraformaldehyde (88%) 20 18 28 25 20 NaHSO4, 20 (40%) CaCO3 60 20 - 15 40 Urea 22 CaSO4 1/2H2O - - 75 - 5 50 Setting agent composition (wt parts) Proper- Molar ratio ties (Note 2) Raw materials (g) TABLE 1 (Continued)

Comparative Comparative Note 3 Example 1 Example 2 Example 3 Example 4 Example 1 Example 2 Ca3(PO4)2 - 10 - - - MgCO3Mg(OH)2 - - - 70 - SiO2 - - - - - Diatom earth - - - - - Wood chips - 10 10 10 10 α-cellulose - - 10 15 - Radioactive substance 79 87 147 174 88 106 Radioactive substance/setting agent 0.44 0.55 0.66 0.74 0.50 0.55 Free water (%) None None None None None 5.1 Uniaxial compression strength (kg/cm) 140 155 164 131 26 12 Proper- Radioties of active Setting agent set substance composition mass (wt parts) (wt parts) Note 1: Sodium hydroxide in the "Materials" was added in two portions as indicated by #1 and #2 in the table.

Note 2: R represents resorcinol,P represents phenol and F represents formaldehyde.

Note 3: Comparative Example 2 is the case using a urea resin, and the encircled numbers #1 and #2 in the sections of "Urea" and "Formaline" indicate addition of each said material in two portions as generally employed in the production of urea resin.

EXAMPLE 5 A prepolymer was produced by blending the materials shown in Table 2 and reacting them similarly to Example 1. As properties of this prepolymer; its viscosity and nonvolatile content were shown in Table 1.

The lanthanum adsorbed resin and strontium adsorbed resin obtained in Example 2 were mixed in a beaker to use the mixture as radioactive substance.

To 100 g of said prepolymer were added 1 8 g of 88% paraformaldehyde, 33 g of calcium silicate powder for plastic filler, 5 g of powdered wood chips and 100 g of said mixture of lanthanum adsorbed resin and strontium adsorbed resin, and the whole mixture was stirred sufficiently. This mixture was then cast into a mold with an inner diameter of 40 mm and a height of 200 mm and hardened. The thus obtained solidified mass had uniform structure and uniaxial compression strength of 169 kg/cm2. Also, no change in external appearance took place upon 2-month standing of the set-mass.

EXAMPLE 6 A prepolymer was produced by mixing the materials shown in Table 2 and reacting them after the manner of Example 1, and the obtained prepolymer was added with water in an amount shown in Table 2 to adjust its nonvolatile content.

79 g of a 1296 boric acid solution added with 50 ppm of cesium (containing 0.5 Mci of cesium) was neutralized to pH 7.2 with 30% sodium hydroxide and then evaporated to dryness on an evaporating dish under heating to form a borate, and the latter was pulverized.

To 100g of said prepolymer were added 15 gof 88% paraformaldehyde, 5 g of powdered wood chips and 50 g of said cesium-added borate powder, followed by sufficient stirring, and the mixture was then cast into a mold with an inner diameter of 40 mm and a height of 200 mm and hardened. The thus obtained solidified mass had uniform structure and its uniaxial compression strength was206 kg/cm2.

Although this set mass was allowed to stand as it was for 2 months, no change in external appearance was seen.

EXAMPLE 7 A prepolymer was prepared by mixing the materials shown in Table 2 and reacting them according to Example 1, and this prepolymer was added with water in an amount shown in Table 1 to adjust the nonvolatile content thereof.

30 ml of Diaion SA--1OA (OH type, wetted) was added to 150 y of an aqueous solution (500 juci) containing 2.5 g of phenol labeled with radioactive carbon 14C, and the mixture was stirred for one hour to prepare specimen slurry I. This specimen I was filtered by a glass filter (Buchner's type 25G1) to obtain an anion exchange resin which has adsorbed 500 loci of phenol as radioactive nuclide.

To 100 g of said prepolymer were added 20 g of 88% paraformaldehyde, 5 g of barium sulfate, 6 g of powdered wood chips, 80 g of said phenol-adsorbed resin and 30 g of cesium-added borate obtained in Example 6, and the mixture was stirred sufficiently. This mixture was them cast into a mold with an inner diameter of 40 mm and a height of 200 mm and hardened. The thus obtained solidified mass was uniform throughout its structure and its uniaxial compression strength was 172 kg/cm2.

When allowed to stand for 2 months, the set mass produced no change in external appearance.

EXAMPLE 8 The materials shown in Table 2 were blended in amounts also shown in Table 2 and reacted after the fashion of Example 1 to obtain a prepolymer of which the viscosity and nonvolatile content were as shown in Table 2.

To 100 g of the thus obtained prepolymer were added 20 g of 88% paraformaldehyde, 10 g of slag produced from iron manufacture, 10 g of powdered wood chips, 55 g of 12% boric acid solution and 50 ppm cesium solution containing 0.5,uni of cesium as radioactive nuclide and 55 g of the phenol adsorbed resin used in Example 7, and the mixture was stirred sufficiently. This mixture was then cast into a mold with an inner diameter of 40 mm and a height of 200mm and hardened. The thus obtained set mass has incorporated the entirety of water thereinto, allowing no hangover or separation of free water. Also, the set mass was uniform in structure and had uniaxial compression strength of 1 57 kg/cm2. No noticeable change in external appearance was caused when the set mass was allowed to stand as it was for 2 months.

EXAMPLE 9 A prepolymer was produced by blending the materials shown in Table 2 and reacting them in the same way as Example 1, and the prepolymer was added with water in an amount shown in Table 2 to adjust the nonvolatile content thereof.

There was also prepared 1 50 g of an aqueous solution (200 *4ci) containing 2.5 y of triallylamine labeled with radioactive carbon 14C.

To 100 g of said prepolymer were added 25 g of 88% paraformaldehyde, 42 g of colemanite, 12 g of powdered wood chips and 66 g of said triallylamine solution, followed by sufficient stirring, and the mixture was cast into a mold with an inner diameter of 40 mm and a height of 200 mm and hardened.

The thus obtained solidified mass has taken up the whole of water thereinto, allowing no hangover or separation of free water. The solidified mass was also uniform throughout its structure and had uniaxial compression strength of 148 kg/cm2. No change in extemal appearance took place when the set mass was allowed to stand as it was for 2 months.

TABLE 2

Example 5 Example 6 Example 7 Example 8 Example 9 phenol 1,344 1,344 1,344 1,500 1,653 Resorcinol 1,888 1,888 1,888 1,760 1,586 Methylresorcinol - - - - 200 (Note 2) Formalin (48%) 1,336 1,336 1,336 1,360 2,076 (Note 3) Sodium hydroxide (45%) (Note 1) 152 2256 152 2256 152 2256 148 (2)359 148 2359 Water 1 1,200 800 - 1,350 R/P 1.2 1.2 1.2 1.0 F/(R+P) 0.68 0.68 0.68 0.68 (NaOH/R+P) 0.11 0.11 0.11 0.143 Viscosity, polses (25 C) 7.2 2.3 6.5 25.0 2.8 Nonvolatiles (%) 72.9 58.3 63.4 74.3 53.1 Prepolymer 100 100 100 100 100 Paraformaldehyde (88%) 18 15 20 20 25 Calcium silicate 33 - - - Kaolin - 5 - - Barium sulfate - - 5 - Zeolite - - - 23 Setting agent composition Pro- Molar ratio (wt parts) Raw materials (g) perties (Note 4) TABLE 2 (Continued)

Example 5 Example 6 Example 7 Example 8 Example 9 Slag from iron manufacture - - - 10 Colemanite - - - - 42 Wood chips 5 5 6 10 12 Radioactive substance 100 50 110 110 66 Radioactive substance/setting agent 0.64 0.40 0.84 0.66 0.37 Free water - - - None None Uniaxial compresion strength (kg/cm) 169 206 172 157 148 Radio Setting agent Pro- active composition perties of substance (wt parts) set mass (wt parts)

Claims (10)

1. A radioactive waste solidifying prepolymer comprising resorcinol compound units, phenol compound units and formaldehyde units, wherein the resorcinol compound residue :phenol compound residue molar ratio is over 0.6:1.0 and the formaldehyde residue: resorcinol compound residue and phenol compound residue molar ratio is 0.5--0.9: 1.0, and also containing more than 50% by weight of nonvolatiles.

2. A radioactive waste solidifying prepolymer as claimed in Claim 1, wherein the nonvolatile content is more than 70% by weight

3. A method of solidifying a radioactive waste characterized in that a radioactive waste, paraformaldehyde and at least one filler selected from calcium carbonate, calcium sulfate, calcium phosphate, basic magnesium carbonate, silicic acid anhydride, magnesium silicate, calcium silicate, barium sulfate, manganese borate, sodium borate, colemanite, kaolin, bentonite, zeolite, active clay, dolomite, fly ash, diatom earth, sand, earth, rock and slag, or said filler and wood chips or n-celtulose, are added to a radioactive substance setting prepolymer consisting of resorcinol compound units, phenol compound units and formaldehyde units, wherein the resorcinol compound residue ::phenol compound residue molar ration is over 0.6:1.0 and the formaldehyde residue: resorcinol compound residue and phenol compound residue molar ratio is 0.54.9 :1.0, and also containing more than 50% by weight of nonvolatiles, and the mixture is condensed.

4. A method of solidifying a radioactive waste according to Claim 3, wherein the nonvolatile content in the radioactive waste setting prepolymer is more than 70% by weight.

5. A method of solidifying a radioactive waste according to Claim 3, wherein the radioactive waste is an aqueous solution.

6. A method of solidifying a radioactive waste according to Claim 3, wherein the radioactive waste is one adsorbed in an ion exchange resin.

7. A method of solidifying a radioactive waste according to Claim 3, wherein the radioactive waste is an aqueous slurry containing an ion exchange resin.

8. A method of solidifying a radioactive waste according to Claim 3, wherein the radioactive waste is solid.

9. A radioactive waste solidifying prepolymers substantially as hereinbefore described in any of the Examples 1 to 9 disclosed herein.

10. A method of solidifying radioactive waste substantially as ,hereinbefore described with reference to any one of the Examples 1 to 9 disclosed herein;