JP3809045B2 - Co-solidification method for low-level radioactive wet waste generated from boiling water nuclear power plants - Google Patents

Description

[0001]
(Technical field)
The present invention relates generally to radioactive waste treatment technology, and in particular, the present invention relates to a method for solidifying radioactive wet waste. More specifically, the present invention relates to a method for co-solidifying low level radioactive wet waste resulting from boiling water nuclear power plants.
[0002]
(Background of the Invention)
During operation, in a boiling water reactor (BWR) used in a boiling water nuclear power plant, high-concentration sodium sulfate waste liquid, powdered used ion exchange resin, sludge waste, and other wet waste are generated. These wet wastes are radioactive, and therefore must be solidified, chemically and physically stable solids, and finally discarded as a normal safety measure for radioactive waste. Don't be.
[0003]
At present, there are three solidification methods for low-level radioactive wet waste. A cement solidification method, a resin solidification method, and a tar solidification method. Among these solidification methods, the cement solidification method has the lowest volumetric efficiency. Therefore, even if the work is the simplest of these three solidification methods and the product cemented waste has the required long-term stability, it will be reflected in the final disposal procedure. Due to the high cost, the cement solidification method is hardly regarded as an attractive method.
[0004]
The resin solidification and tar solidification methods use an organic material for the solidifying agent, and any of these methods has a high volumetric efficiency. However, regarding the tar solidification method, tar solidified waste has low compressive strength and is flammable. Once in Germany, such solidified waste has exploded and burned during the tar solidification process. A few years ago, one of Japan's tar solidification systems exploded, causing a major radioactive accident and raising concerns around the world. Since then, many European countries have banned tar solidification. And, even in other countries, the tar solidification systems and plants, is where you are closing one by one in the order people.
[0005]
While this is a very controversial issue regarding the use of resin solidification methods, new resin solidification systems are still emerging despite the problems. Those who oppose it argue that because the resin ages, the stability of the waste of the resin solidification process is very dangerous and unreliable. In most European countries, the treatment of radioactive wet waste no longer allows resin solidification, but this method is still widely used in other countries because of its volumetric efficiency advantage. Yes.
[0006]
The main direction of research on low-level radioactive wet waste solidification methods under these circumstances is non-recognized with the hope that any method may change the organic method as soon as possible. It is suitable for increasing the volumetric efficiency of organic solidifying agents.
[0007]
The cement solidification performed so far is just an organic method. A problem often encountered in this process is that in the solidification process of sulfate waste, the sulfate reacts with tricalcium aluminate (3CaOAl ₂ O ₃ ) to gradually form a low density solid called ettringite, which is generally This means that volume expansion causes strain and sometimes even cracks in the solidified waste. There are two known precautions against this problem. That is, (1) reducing the ratio of sulfate to cement, and (2) reducing the tricalcium aluminate content in the cement. The former is of no interest at all because it results in a considerable amount of solidified waste, resulting in a considerable cost in the final disposal procedure. The latter, on the other hand, is not only because cement with low tricalcium aluminate content is not readily available, but also because of the very slow formation of ettringite, It is far from satisfactory because it is a process where stability is highly questionable.
[0008]
U.S. Pat. No. 04,804,498 proposes a method for eliminating the aforementioned problems caused by sodium sulfate which is very fast and easily dissolves. Sodium sulfate is reacted with sodium hydroxide to produce barium sulfate and barium hydroxide, then these two materials are separated, barium sulfate is solidified and sodium hydroxide is recycled for reuse. Since barium sulfate is highly stable and very low in solubility, the solidified waste produced in this way is very stable and avoids the troubles often encountered in the solidification method of sodium sulfate waste liquid. That said, if one problem is solved, another new problem will soon arise. Because the separated sodium hydroxide takes up most of the radioactive elements, further decontamination work must be done before recycling for reuse. Normally, recycled chemicals rapidly increase in their pollutant content, and therefore lose their effectiveness rapidly when recycled two or three times. Therefore, in the end, the solidification process must still be restored.
[0009]
Japanese Unexamined Patent Publication No. 62-126,400 reports a solidification method related to the disclosed contents of the present application. In this patent, the sodium sulfate waste liquor is dried to a powder, and then the powder is mixed with a compound of barium hydroxide and glassy water to produce water, sodium hydroxide, insoluble barium sulfate, Silicon dioxide and a solidifying agent are introduced to promote solidification. The high energy costs associated with the use of evaporation dryers are the main drawbacks of this method, as well as several technical issues such as solid-solid reactions, stirring and heat transfer. It is necessary to overcome.
[0010]
In another solidification method disclosed in Japanese Patent Laid-Open No. 04-128,699 , a barium sulfate and sodium hydroxide liquid mixture is produced in the same manner as in the aforementioned US patent, and only in this case, these can be separated. After that, the mixture is condensed by heating and then silicon dioxide and cement are introduced to solidify the wet waste. It is known that the quality of waste from cement solidification processes is highly dependent on the amount of sodium hydroxide present in the waste. Sodium hydroxide and silicon dioxide react to produce sodium silicate and glassy water. Glassy water reacts with calcium ions resulting from the cement's hydrolysis reaction to form silicon calcium gel hydrated products. Therefore, it is clear that the quality of the waste produced by the solidification method is considerably related to the amount of silicon dioxide used and the type and quality of cement. An example of a particular approach to this problem is Japanese Unexamined Patent Publication No. 62-278,499 , where the silicon to sodium ratio is used when trying to solidify radioactive wet waste with the help of glassy water. Suggests that it should be kept within the range of 0.5 to 1.0. This is because it has been found that when the sodium hydroxide content exceeds 8% by weight, the compressive strength of the solidified waste is lower than 50 kg / cm ² . This means that even after the sodium sulfate effluent has been converted to barium sulfate and sodium hydroxide, the quality of the waste from the cement solidification process depends on the type and amount of solidifying agent used, of course, It clearly shows that it also depends on the solidification conditions.
[0011]
Regarding solidification of powdered spent ion exchange resin, most boiling water nuclear power plants solidify this kind of waste with cement. Usually, there is 20% by weight of used ion exchange resin in such solidified waste. As such, the ion exchange resin content can reach as much as 30% of the total weight of the solidified waste, such solidified waste being treated with sodium hydroxide, As shown in Japanese Patent Application Laid-Open No. Sho 62-238,499 in which blast furnace slag powder is added and solidified, it still has a sufficiently high compressive strength.
[0012]
Some of the solidification methods described above can produce solidified waste with sufficient compressive strength, but all of these prior arts are one type of radioactive wet waste with very limited volumetric efficiency. It would be better to stress that
[0013]
(Summary of Invention)
Therefore, the solidification method of the present invention disclosed in this specification employs a method of solidifying waste with waste, in which a concentrated sodium sulfate waste liquid and a used ion exchange resin can be solidified together.
[0014]
The procedure and principle of this solidification method are as follows. First, when the sodium sulfate waste liquid is reacted with barium hydroxide, the waste liquid is converted into a slurry of barium sulfate and sodium hydroxide. Next, when spent ion exchange resin that reacts immediately with sodium hydroxide is added to the slurry, this reaction can increase the stability of the waste by reducing the ion exchange activity of the resin. Third, the slurry is thoroughly mixed with a solidifying agent consisting of cement, fine silica gel particles, pozzolanic materials (eg, blast furnace slag powder and fly ash), silicate esters, phosphates, and the like.
[0015]
This new radioactive wet waste solidification method immediately co-solidifies both sodium sulfate waste liquor and spent ion exchange resin, providing the following advantages. One is to convert chemically very unstable sodium sulfate to barium sulfate with very high stability. This not only ensures the stability of the solidified waste, but also results in a waste volume reduction due to the high density of barium sulfate (4.5). Second, during the solidification process, barium sulfate functions as a fine agglomerated material that increases the strength of the solidified waste. Third, by reacting the spent ion exchange resin with sodium hydroxide, the activity of the ion exchange resin is significantly reduced, so that the problem with solidified waste volume expansion no longer exists. Fourth, all of the converted waste is solidified together without producing secondary waste and without the complexity of waste recycling. Fifth, by properly preparing the solidifying agent, sodium hydroxide together with the solidifying agent forms an insoluble solidified material, which solidifies the wet waste by sealing. Is to become. This technique not only reduces the amount of solidifying agent used, but also achieves the goal of producing solidified waste.
[0016]
(Detailed description of the invention)
In the following, the inventors use several laboratory examples to illustrate in detail the co-solidification method as well as the preparation of the solidifying agent. These examples of the invention, including the procedures, conditions and results thereof, are only partly indicative of the scope of the invention, and are not intended to represent the full scope of the invention. Should not be regarded as a thing.
Example I :
[0017]
920 parts (all parts given below are parts by weight) of 98 wt% sodium hydroxide solution and 2760 parts of barium sulfate are prepared and mixed in a stirrer, while slowly 2300 parts of deionized. Add water. Stirring is continued until the sodium hydroxide is completely dissolved, then wait until the solution cools down to 30 ° C. and maintain this temperature. Prior to addition to the solidifying agent, the solution is weighed and added to an appropriate amount of 30 ° C. deionized water to correct for water loss due to evaporation during the stirring process.
[0018]
Type-2A slurry-shaped solidifying agent (product of Taiwan cement company), pozzolanic material (including blast furnace slag powder and fly ash) and silicate, phosphate, calcium phosphate, magnesium phosphate powder mixed together A homogeneous powder solidifying agent is prepared by grinding. The main components of this solidifying agent are, according to chemical analysis, 27.14% SiO ₂ , 6.86% Al ₂ O ₃ , 46.29% CaO, 1.71% Fe ₂ O ₃ , 2.14. % MgO, 7.71% P ₂ O ₅ , and 5.57% SO ₃ . Next, this homogeneous powder solidifying agent is added to the sodium hydroxide / barium sulfate mixed solution. At the same time, it is vigorously stirred until the slurry is visually homogeneous. The weight ratio of solidifying agent to slurry is 0.54. In this experiment, stirring is continued for 10 minutes or more immediately after the last particles of solidifying agent are added to the agitator. The slurry is then poured immediately into a number of cylindrical polyethylene molds. Each mold has an inner diameter of 5 cm and a height of 11 cm. The mold is then sealed and placed at room temperature for a period of 30 days for curing and solidification. Next, the solidified waste is taken out from the mold, and five of them are selected, and the raw ends are cut off to form five standardized cylindrical samples (length 10 cm). A compressive strength test is performed on these five samples following the ASTM-C39 test procedure in accordance with the requirements of the US Nuclear Regulatory Commission (USNRC). It has been found that the average compressive strength of these five samples is 50 kg / cm ² . In addition, when tested according to the standard test procedure specified by the Taiwan Nuclear Energy Council for Low Level Radioactive Waste Quality Control, the average water resistant compressive strength of these samples (ie, 90 days immersion in water) Later sample compressive strength) was 81 kg / cm ² and was placed in a weather test chamber at an average weathering compressive strength (ie 30 cycles of −10 ° C. to + 60 ° C., 60% to 95% relative humidity 40). The later sample compressive strength was found to be 48 kg / cm ² .
[0019]
Example II :
373 parts of 98 wt% sodium hydroxide solution is dissolved in 2038 parts of water, then 1167 parts of powdered latex (powder) is added and mixed vigorously for 30 minutes to form a homogeneous slurry. A powdered solidifying agent is prepared according to the method described in Example I. The main components of this solidifying agent are, according to chemical analysis, 23.2% SiO ₂ , 4.59% Al ₂ O ₃ , 61.19% CaO, 3.79% Fe ₂ O ₃ , 2. 88% MgO, 2.2% P ₂ O ₅ , and 1.58% SO ₃ . Then, the same solidification method as described above is applied. Only in this case the weight ratio of solidifying agent to slurry is 0.887. Prepare solid waste samples in the same way as already described in the previous example, and select five for testing. These samples have an average compressive strength of 59 kg / cm ² , an average water resistant compressive strength of 113 kg / cm ² , and an average weather resistant compressive strength of 72 kg / cm ² .
[0020]
Example III :
482 parts of sodium hydroxide are dissolved in 1800 parts of water, 1418 parts of barium sulfate and 1354 parts of powder are added and they are vigorously mixed to form a homogeneous slurry. A powdered solidifying agent is prepared according to the method described in Example I. The main components of this solidifying agent are 36.05% SiO ₂ , 5.72% Al ₂ O ₃ , 61% CaO, 1.43% Fe ₂ O ₃ , 1.79% MgO, 9.61. % P ₂ O ₅ , and 4.65% SO ₃ . To apply the same solidification method as previously mentioned base. In this case, the weight ratio of solidifying agent to slurry is 0.425. Prepare solid waste samples in the same way as described earlier, choose 5 of them and test. These samples have an average compressive strength of 58 kg / cm ² , an average water resistant compressive strength of 111 kg / cm ² and an average weather resistant compressive strength of 64 kg / cm ² .
[0021]
Example IV:
580 parts of sodium hydroxide are dissolved in 2346 parts of water, then 1285 parts of barium sulfate and 1449 parts of powder are added and mixed vigorously to form a homogeneous slurry. A powdered solidifying agent is prepared in the same manner as shown in Example I. Major component of the solidifying _{agent, 30.72% SiO 2, 3.08%} Al 2 O 3, 41.02% CaO, 2.54% of Fe ₂ O _3, 1.93% of MgO, 19. 28% P ₂ O ₅ and 2.54% SO ₃ . To apply the same solidification method as previously mentioned base. In this case, the weight ratio of solidifying agent to slurry is 0.389. Prepare the solidified waste samples in the same way as before and select five of them to test. These samples have an average compressive strength of 39 kg / cm ² , an average water resistant compressive strength of 53 kg / cm ² and an average weather resistant compressive strength of 56 kg / cm ² .
[0022]
Example V:
Collect 2765 parts of 20 wt% sodium sulfate effluent from Taiwan Nuclear Plant II. Next, this is gradually mixed with 1226 parts of barium hydroxide powder and Ba (OH) ₂ 8H ₂ O to form a barium sulfate / sodium hydroxide mixed solution. The solution is heated slowly and 1745 units of water are removed by evaporation. Next, 864 parts of the powder are mixed to form a homogeneous slurry. Wait until the temperature of the slurry cools down to 30 ° C. and add to the same powdered solidifying agent as in Example III. In this experiment, the solid weight of solidifying agent to slurry is 0.389. The sample preparation and compressive strength test procedures are again the same as above. These samples have an average compressive strength of 43 kg / cm ² , an average water resistant compressive strength of 46 kg / cm ² and an average weather resistant compressive strength of 46 kg / cm ² . Furthermore, the ANSI 16.1 test method showed that the average filtration index of Co-60, Cs-134 and Cs-137 were 8.34, 6.27 and 6.32, respectively.
[0023]
While the invention has been shown and described in connection with the foregoing embodiments, those skilled in the art will recognize that other modifications can be made in broader aspects without departing from the spirit and scope of the invention.

Claims (5)

Sulfate sodium waste that is part of the radioactive waste and spent ion-exchange resins to a method for co-solidifying, (1) by reaction with the barium hydroxide and sodium sulfate waste, sodium hydroxide and barium sulfate pozzolan comprising a step of converting the slurry, (2) forming a mixed waste solution of this slurry was mixed with the ion exchange resin scan rally form, the (3) cement, blast furnace slag powder and fly ash A powder solidifying agent comprising a material, one or several species of divalent or higher metal oxides or salts is prepared, and the powder solidifying agent is mixed with the mixed waste solution obtained in the step (2). after uniformly mixed, a method characterized in that it comprises coagulation, and curing.   2. The method according to claim 1, wherein the metal salt of the components of the solidifying agent used is a borate, silicate ester, phosphate or silicate compound.   2. The method according to claim 1, wherein the metal oxide or salt of the components of the solidifying agent used is an oxide or salt of calcium, silicon, magnesium, aluminum, iron, titanium or zirconium. .   2. The method according to claim 1, wherein the pozzolanic material of the components of the solidifying agent used is silica fume, blast furnace slag powder or fly ash. The method of claim 1, wherein the temperature during mixing of the scan rally-like mixed waste solution and the solidifying agent is characterized in that at 90 ° C. or less.