EP0081044A1 - Verfahren zur Behandlung hochradioaktiver flüssiger Abfälle - Google Patents

Verfahren zur Behandlung hochradioaktiver flüssiger Abfälle Download PDF

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Publication number
EP0081044A1
EP0081044A1 EP82108466A EP82108466A EP0081044A1 EP 0081044 A1 EP0081044 A1 EP 0081044A1 EP 82108466 A EP82108466 A EP 82108466A EP 82108466 A EP82108466 A EP 82108466A EP 0081044 A1 EP0081044 A1 EP 0081044A1
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EP
European Patent Office
Prior art keywords
waste liquor
solid
high level
level radioactive
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.)
Granted
Application number
EP82108466A
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English (en)
French (fr)
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EP0081044B1 (de
Inventor
Makoto Kikuchi
Kiyomi Funabashi
Fumio Kawamura
Toshio Takagi
Naohito Uetake
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Hitachi Ltd
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Hitachi Ltd
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Publication date
Priority claimed from JP15768081A external-priority patent/JPS5858499A/ja
Priority claimed from JP1962982A external-priority patent/JPS58137798A/ja
Application filed by Hitachi Ltd filed Critical Hitachi Ltd
Publication of EP0081044A1 publication Critical patent/EP0081044A1/de
Application granted granted Critical
Publication of EP0081044B1 publication Critical patent/EP0081044B1/de
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    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
    • G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
    • G21F9/04—Treating liquids
    • G21F9/06—Processing
    • G21F9/16—Processing by fixation in stable solid media
    • G21F9/162—Processing by fixation in stable solid media in an inorganic matrix, e.g. clays, zeolites

Definitions

  • This invention relates to a method of processing a high level radioactive waste liquor such as a radioactive waste liquor discharged from a nuclear fuel reprocessing step of a nuclear fuel used for atomic power generation.
  • nuclear fission products having long half life such as caesium (Cs) and strontium (Sr) are build up and uranium 235 is consumed so that the fuel becomes gradually difficult to burn.
  • the fuel must be taken out from the reactor and be replaced by a fresh fuel at a suitable timing.
  • nuclear fuel reprocessing has been carried out to extract plutonium that remains in the used fuel that is taken out from the reactor for replacement and to isolate the effective component such as uranium 235 from the fission products by applying chemical treatment to the used fuel.
  • the chemical treatment to be conducted in this nuclear fuel reprocessing step in turn generates a high level radioactive waste liquor containing large quantities of fission products. Because the fission products have long half life, the high level radioactive waste liquor must be safely stored and disposed. The volume of the waste liquor must also be reduced since the waste liquor must be generally stored for an extended period of time.
  • the nuclear fission products such as caesium and strontium must be prevented from being emitted to the environment by evaporation or permeation.
  • the final processing method is preferably flexible sufficiently. From the aspect of safety, volume reduction of the waste and easy handling, the method is preferably flexible such that the waste can be stored intermediately and temporarily at least under the solidified state and if a decision is thereafter made to store the waste in the solid form, the method can change the waste to the final solid or if a decision is made to store the waste in the liquid form, the method can change again the waste from the solid to the liquid.
  • a first characterizing feature of the present invention resides in a method of processing a high level radioactive waste liquor, which method solidifies the waste liquor by mixing the waste liquor with a solidifying agent which reversibly changes from a liquid to a solid and vice versa depending upon a pH value.
  • a second characterizing feature of the present invention resides in a method of processing a high level radioactive waste liquor, which method solidifies the waste liquor while sealing nuclear fission products therein by mixing the waste liquor with a solidifying agent which changes reversibly from a liquid to a solid and vice versa depending upon a pH value and a fixing agent which reacts with nuclear fission products contained in the high level radioactive waste liquor and prevents the permeation or evaporation of the fission products.
  • a third characterizing feature of the present invention resides in a method of processing a high level radioactive waste liquor, which method solidifies the waste liquor to change it into a solid for intermediate storage and heats the solid for intermediate storage to change it into a solid for final storage, whenever necessary, by mixing the high level radioactive waste liquor with a solidifying agent which reversibly changes from a liquid to a solid and vice versa depending upon a pH value.
  • a fourth characterizing feature of the present invention resides in a method of processing a high level radioactive waste liquor, which method solidifies the waste liquor to a solid for intermediate storage and changes again the solid to the liquid by the addition thereto of an acid or an alkali, whenever necessary, by mixing the high level radioactive waste liquor with a solidifying agent which reversibly changes from a liquid to a solid and vice versa depending upon a pH value.
  • a fifth characterizing feature of the present invention resides in a method of processing a high level radioactive waste liquor, which method solidifies the waste liquor to change it to a solid for intermediate storage while sealing therein nuclear fission products, and heats the solid for intermediate storage and changes it to a solid for final storage, whenever necessary, by mixing the high level radioactive waste liquor with a solidifying agent which reversibly changes from a liquid to a solid and vice versa depending upon a pH value and a fixing agent which reacts with the nuclear fission products contained in the waste liquor and prevents the evaporation or permeation of the fission products.
  • a sixth characterizing feature of the present invention resides in a method of processing a high level radioactive waste liquor, which method solidifies the waste liquor to change it into a solid for intermediate storage while sealing therein nuclear fission products, and changes again the solid for intermediate storage to the liquid by the addition thereto of an acid or an alkali, whenever necessary, by mixing the high level radioactive waste liquor with a solidifying agent which reversibly changes from a liquid to a solid and vice versa depending upon a pH value and a fixing agent which reacts with the nuclear fission products contained in the waste liquor and prevents the evaporation or permeation of the fission products.
  • a seventh characterizing feature of the present invention resides in a method of processing a high level radioactive waste liquor, which method solidifies the waste liquor by mixing the waste liquor with a solidifying agent which reversibly changes from a liquid to a solid and vice versa depending upon a pH value and a hardening agent which neutralizes the mixture of the high level radioactive waste liquor and the solidifying agent and promotes hardening.
  • This embodiment primarily deals with a waste liquor which is extracted from the nuclear fuel reprocessing step and contains principally nitric acid, as the high level radioactive waste liquor.
  • Figure 1 shows a typical nuclear fuel reprocessing flow diagram.
  • the used fuel generated in an atomic power plant is stored in a storage basin for several months.
  • the radioactivity of the fuel decays.
  • the cladding of the used fuel is removed mechanically or the fuel rods are cut into pieces as such and are then dissolved by nitric acid inside a dissolving tank.
  • Concentrated nitric acid of 7N to 13N is used.
  • the solid content is removed as a solid waste while gaseous products of nuclear fission such as krypton, xenon and the like are discharged in the off gas.
  • the remaining fuel solution is transferred to the co-decontamination step after the nitric concentration is adjusted to about 3N.
  • the high level radioactive waste liquor containing caesium, strontium and the like is separated and extracted from the organic phase containing uranium and plutonium.
  • the organic phase containing uranium and plutonium which is thus separated from the fission products as described above is distributed to uranium and plutonium in the distribution step and uranium and plutonium are then purified, enriched and then stored for reuse.
  • the solution consisting principally of nitric acid that contains the nuclear fission products and is formed in the co-decontamination step in the fuel reprocessing is the typical example of the high level radioactive waste liquor.
  • FIG. 2 shows the flow of the processing of the high level radioactive waste liquor.
  • the high level radioactive waste liquor containing the fission products such as caesium and strontium is mixed with a solidifying agent for solidifying the high level radioactive waste liquor and with a fission product- fixing agent for stably fixing the fission products contained in the high level radioactive waste liquor in the waste liquor or in the solidified matter.
  • the fission products account for 800 Ci/l.
  • a sodium silicate solution or so-called "water glass" is used as the solidifying agent.
  • water glass contains the water of crystallization of xH 2 0.
  • Copper ferrocyanide or titanium tetrachloride is used as the fixing agent for the fission products. They are expressed by the formulas Cu 2 [Fe(CN) 6 ] and TiCl 4 , respectively.
  • the mixing ratio of the high level radioactive waste liquor and the water glass must be taken into consideration when mixing them together.
  • the proportion of oxides such as the fission products in the solidified matter and the glass component in the water glass is preferably about 1/10. In terms of the mixing ratio of both solutions, this proportion is from about 1/2 to about 1/5, though varying to some extents depending upon the waste liquor and the water glass component.
  • the hardening reaction develops when the high level radioactive waste liquor, the water glass as the solidifying agent and the fixing agent of the fission products are mixed together, forming the solidifed matter.
  • the mechanism why the solidified matter is formed will be explained with reference to Figure 3, which illustrates the change in the behaviour of the water glass depending upon the pH value (hydrogen ion concentration).
  • the abscissa represents the pH value of the water glass and the ordinate does the free water content.
  • the diagram illustrates the proportion of the water of crystallization to the free water. In other words, if the free water content is 0 %, the water glass is a solid and if the free water content is 100 %, the water glass is a liquid.
  • the water glass is solid at the neutral of pH 6 to 8 and the free water content becomes greater on both acidic and alkaline sides so that the water glass gradually changes into the liquid.
  • the present invention makes use of this property of water glass.
  • the high level radioactive water liquor generated from the fuel reprocessing step contains principally the nitric acid solution and is hence acidic.
  • the invention makes use of the neutralizing reaction between the water glass which is alkaline and the waste liquor which is acidic. Both solutions are mixed and are then left standing for two to five days.
  • the hardening reaction expressed by the following formula occurs and a solidified matter having a .sufficient strength is formed:
  • the fixing agent for the fission products will be described.
  • the fission products contained in the high level radioactive waste liquor such as caesium and strontinum are likely to evaporate from the waste liquor together with the vapor or to permeate into the water during storage.
  • Any fixing agents may be employed so long as they incorporate the fission products into the large molecular structure or converting them into substances having low solubility, thereby changing the fission products to stable products.
  • the fixing agents include copper ferrocyanide and titanium tetrachloride. The mechanism of fixing the fission products by these fixing agents will be explained with reference to Figures 5 and 6.
  • solid line represents the change in the evaporation quantity of strontium with the change in the addition amount of titanium tetrachloride contained in the solidified natter when the solidified matter formed in the manner described above is heated at 1-,200°C for 6 hours and dotted line represents the change in the permeation quantity of strontium when the solidified matter is left standing in water for 30 days.
  • solid line in Figure 6 represents the change in the evaporation quantity of caesium with the change in the addition amount of copper ferrocyanide in.the solidified matter when the solidified matter is heated at 1,200°C for 6 hours while dotted line represents the change in the caesium permeation quantity when the solidified matter is left standing in water for 30 days.
  • the effect of the fixing agent is relatively small for strontium because strontium is orginially not easy to evaporate, but a large evaporation inhibiting effect can be seen for caesium because the element is highly easy to evaporate.
  • the fixing agent shows a large permeation inhibiting effect for both strontium and caesium.
  • Copper ferrocyanide and titanium tetrachloride can check the evaporation and permeation of the fission products because they have such characteristics as to selectively take the alkali or alkaline earth metal such as caesium and strontium into their crystal lattice.
  • caesium and strontium are caught into the net-like structure of the macromolecules of (Si0 2 ) n described already.
  • copper ferrocyanide used as the fixing agent, it reacts with caesium as expressed by the following reaction formula:
  • caesium can not easily escape physically from the net-like structure of the water glass and can not easily permeate chemically in water because its solubility with water drops.
  • the fixing agent Since the fixing agent is mixed with the water glass and the high level radioactive waste liquor, the fixing agent reacts with caesium, strontium and the like and forms a non-volatile non- permeable compound. Thus, the solidified matter fixing therein caesium, strontium and the like is formed.
  • the solidified matter thus obtained is stored as the solid for intermediate storage until the final processing method is decided.
  • the optimal treatment of the solid is carried out to change it into a storage body suitable for the final storage.
  • the final processing method is one that stores the waste in the form of liquid, for example, an acid or an alkali is added to the solid for intermediate storage.
  • the form of the water glass changes with its pH value.
  • the solid for intermediate storage remains solid in the pH range of 6 to 8. If the pH value of this solid is changed to at least 10 or below 4, the solid dissolves and again returns to the liquid.
  • Nitric acid which is primarily contained in the radioactive waste liquor is used as the acid while sodium hydroxide or the. like is used as the alkali.
  • the pH value of the solid for intermediate storage may be selected from a range in which the solid is soluble.
  • the solid for storage that is again returned to the liquid is charged into rocks or strata or into tanks in accordance with the final processing method selected.
  • the selected final processing method is one that stores the waste in the solid form
  • the solid for intermediate storage is subjected to treatment which changes it into the solid for final storage.
  • This final treatment will be explained with reference to Figure 7.
  • the diagram of Figure 7 shows the change of the weight of the water glass with respect to the change in the heating temperature.
  • the water glass is 100 % by weight, it contains the water of crystallization and other water contents.
  • the weight drops down to about 80 % and the water of crystallization starts evaporating.
  • the water glass loses the water of crystallization, its weight becomes about 50 % by weight and the glass water changes into a vitreous solid.
  • this embodiment forms the solid for final storage by heating the water glass to about 1,200 o C
  • the solid for final storage may be a vitreous solid which is obtained by heating to about 600°C.
  • the solid for intermediate storage of the high level radioactive waste liquor can be formed by utilizing the property of the solidifying agent whose form changes reversibly between the liquid and the solid by the addition thereto of the acid or alkali. If the solid for intermediate sotrage is formed, the solid is sufficiently flexible to cope with any method of final processing, whether the selected method finally stores the waste in the liquid form or in the solid form.
  • FIG. 8 depictes an apparatus for forming the solid for intermediate storage in accordance with the present invention.
  • Tanks 1, 2 and 3 store therein the high level radioactive waste liquor, the water glass as the solidifying agent and copper ferrocyanide as the caesium-fixing agent and titanium tetrachloride as the strontium-fixing agent, respectively.
  • Flow regulating valves 8, 9 and 10 are disposed at the intermediate portions of pipes 5, 6 and 7 for connecting the tanks 1, 2 and 3 to a mixing tank 4, respectively.
  • the mixture is sufficiently mixed inside the mixing tank 4 by a mixer 11.
  • a pH meter 12 detects the pH value of the mixed solution inside the mixing tank 4 and the openings of the valves 8, 9 and 10 are adjusted so that the pH value of the mixed solution falls between 6 and 8.
  • the mixed solution is transferred to an intermediate storage tank 13, where the mixed solution is left standing for two to five days. After these procedures are completed, a solid 14 for intermediate storage which incorporates therein the fission products as the compound can be formed.
  • this embodiment uses sodium silicate as the solidifying agent, the same result can be obtained by use of alkali silicates such as potassium silicate, calcium silicate and so forth.
  • An organic liquid silica compound such as ethyl silicate may also be used.
  • an aluminum compound such as sodium aluminate can also form the solid for intermediate storage, it is preferred in this case to add glass components such as silica in forming the solid for final storage by heating the solid for intermediate storage.
  • a boron compound such as expressed by B 2 0 3 may also be used either alone or as a mixture with sodium silicate. Since the composition becomes analogous to that of so-called borosilicate glass in this case, a glass solidified matter having excellent weatherability and radiation resistance can be formed.
  • Titanium-containing oxides which are obtained by hydrolyzing these titanium compounds such as a compound of the formula Ti(OH) 4 can also be used but since the compound is solid, it must be mixed in the fine powder form to ensure sufficient homogeneity.
  • Beisdes copper ferrocyanide other metal ferrocyanides such as nickel ferrocyanide can provide the same effect as the caesium-fixing agent but it has been confirmed experimentally that the copper compound reduces the addition amount by 10 to 20 % as compared with other metal compounds.
  • Zeolite can further be used either alone or as a mixture with the metal ferrocyanides.
  • the waste liquor is neutralized with the alkaline fixing agent. If the high level radioactive waste liquor is alkaline, however, an organic phosphoric acid such as Na 3 P0 4 is used for the neutralizing reaction. This acid Na 3 P0 4 has the function of hardening further the solidifying agent and hence, serves as the hardening agent.
  • the high level radioactive waste liquor is mixed with the solidifying agent having the property such that it reversibly changes between the liquid and the solid depending upon the pH value, thereby forming the solid for intermediate storage.
  • the present invention provides the method of processing the high level radioactive waste liquor, which method is flexible such that it can form the liquid or solid for final storage in accordance with the selected final processing method. Since the fixing agent that seals the fission products such as caesium and strontium in the solid for storage under the stable state is added, it is possible to prevent the permeation and evaporation of the fission products.

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  • Chemical & Material Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Solid-Sorbent Or Filter-Aiding Compositions (AREA)
  • Processing Of Solid Wastes (AREA)
EP19820108466 1981-10-02 1982-09-14 Verfahren zur Behandlung hochradioaktiver flüssiger Abfälle Expired EP0081044B1 (de)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
JP157680/81 1981-10-02
JP15768081A JPS5858499A (ja) 1981-10-02 1981-10-02 放射性廃液の処理方法
JP19629/82 1982-02-12
JP1962982A JPS58137798A (ja) 1982-02-12 1982-02-12 高レベル放射性廃液の処理方法

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EP0081044A1 true EP0081044A1 (de) 1983-06-15
EP0081044B1 EP0081044B1 (de) 1986-01-02

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0089580B1 (de) * 1982-03-12 1986-07-23 Hitachi, Ltd. Verfahren zum Verfestigen von radioaktiven Abfallstoffen
FR2615144A1 (fr) * 1987-05-14 1988-11-18 Clextral Procede et installation de preparation en continu de produits constitues d'une charge a base de liquide et d'un liant thermoplastique

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2228938A1 (de) * 1972-06-14 1974-01-03 Nukem Gmbh Verfahren und einrichtung zur verfestigung von festen und fluessigen radioaktiven abfallstoffen, insbesondere von nasschlaemmen
BE812192A (en) * 1974-03-12 1974-07-01 Radioactive or hazardous liquid wastes treatment - to produce solid masses suitable for storage using a silicate carrier soln.
DE2559724A1 (de) * 1975-07-11 1977-10-27 Kernforschungsanlage Juelich Verfahren zum verfestigen von abfallstoffe, wie radioaktive oder toxische stoffe, enthaltenden waessrigen loesungen

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2228938A1 (de) * 1972-06-14 1974-01-03 Nukem Gmbh Verfahren und einrichtung zur verfestigung von festen und fluessigen radioaktiven abfallstoffen, insbesondere von nasschlaemmen
BE812192A (en) * 1974-03-12 1974-07-01 Radioactive or hazardous liquid wastes treatment - to produce solid masses suitable for storage using a silicate carrier soln.
DE2559724A1 (de) * 1975-07-11 1977-10-27 Kernforschungsanlage Juelich Verfahren zum verfestigen von abfallstoffe, wie radioaktive oder toxische stoffe, enthaltenden waessrigen loesungen

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0089580B1 (de) * 1982-03-12 1986-07-23 Hitachi, Ltd. Verfahren zum Verfestigen von radioaktiven Abfallstoffen
FR2615144A1 (fr) * 1987-05-14 1988-11-18 Clextral Procede et installation de preparation en continu de produits constitues d'une charge a base de liquide et d'un liant thermoplastique

Also Published As

Publication number Publication date
EP0081044B1 (de) 1986-01-02
DE3268303D1 (en) 1986-02-13

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