[en] Purpose: To enable effective removal of contaminating tritium while suppressing the dissolution at the surface of stainless steels. Constitution: Upon decontaminating the surface of tritium contaminated stainless steels, tritium at the outermost surface layer of the stainless steels is removed by the surface dissolution using diluted hydrochloric acid. Then, tritium intruded to the grain boundary in the surface layer of stainless steels is removed by dipping into an aqueous sulfuric acid - copper sulfate solution. (Horiuchi, T.)

[en] Purpose: To collect effectively tritium produced by nuclear reaction in coolant water of reactor, by means of transferring tritium to gaseous phase as tritium hydride, in the presence of compound comprising hydrogen whose combining energy is less than 95 Kcal/mol. Constitution: Process of collecting tritium produced by nuclear reaction in light or heavy water moderated and cooled reactor, including a step of adding compound comprising hydrogen atom, the combining energy of said hydrogen atom is less than 95 Kcal/mol, and a step of collecting tritium in the form of tritium hydride from coolant water. (M. K.)

[en] Upon extracting separation of metal elements from nitric acid solution in which spent fuels are dissolved, gaseous inorganic materials which can not be used ordinarily as an extraction medium are maintained in a supercritical state to improve solubilization of materials to be used as an extraction medium. In the extracting method, a supercritical fluid of gaseous inorganic materials such as CO₂, CO, ammonium, sulfur hexafluoride or nitrogen is used as an extractor, to provide an extraction rate for rare earth elements higher than that in an existent extraction method using an organic medium as an extraction medium. In addition, the generation amount of radioactive wastes caused by the medium can be remarkably reduced. (T.M.)

[en] Purpose: To prevent Ce⁴⁺ deposition and improve decontamination coefficient in a method of using sulfuric acid-cerium type solvent as a decontaminant. Method: When dissolving chromium-containing cruds by using a sulfuric acid-cerium type solvent, there has been a problem that Ce⁴⁺ is consumed to reduce the concentration in the course of such treatment thereby reducing the oxidizing power. In the present invention, Ce³⁺ is electrolytically oxidized into Ce⁴⁺ so as to maintain the Ce⁴⁺/Ce³⁺ concentration ratio in the decontaminant to less than 1. By this method, it is possible to improve the decontaminating coefficient while suppressing the metal corrosion rate. (K.M.)

[en] Purpose: To suppress the deposition of Co-60 to primary coolant pipeways in a nuclear reactor. Method: To reduce the accumulation of Co-60 by causing chemical species of extremely similar chemical property with soluble Co-60 to be present together in coolants and replacing the deposition of Co-60 to the primary coolant pipeways in a nuclear reactor with that of the coexistent chemical spacies. Ni or Zn is used as the coexistet chemical spacies of similar chemical property with Co-60. The coexistent amount is from 5 to 10 times of the soluble Co-60 in the primary coolants. Ni or Zn solution adjusted with concentration is poured into and mixed with the coolants from a water feed source by using a high pressure constant volume pump. The amount of Co-60 taken into the pipeways caused by corrosion due to high temperature coolant is reduced to about 1/5 as compared with the case of Co-60 alone if 1 ppb of soluble Co-60 is present in water and 5 ppb of soluble Ni or Zn is added and, reduced to 1/12 if the amount of Ni or Zn is 10 ppb. (Kamimura, M.)

[en] Purpose: To dissolve iron and nickel as well as chromium simultaneously at one step for cruds partially containing chromium, and obtain high decontaminating factor (decontamination factor). Method: Radioactive cruds formed as corrosion products in nuclear reactor primary coolant circuits are subjected to dissolving treatment by using a decontaminating agent composed of cerium sulfate type solution as the dissolving solution. When the treatment is substantially completed, a reducing agent is added to reduce the residual 4-valent cerium into 3-valent cerium. Those having potential lower than the redox potential of cerium are used as the reducing agent so that cerium is not deposited. This can provide high decontaminating factor while preventing the deposition of cerium. (Takahashi, M.)

[en] Release of radioiodine built-up during reactor operations presents a potential problem from the standpoint of environmental safety. Among the chemical forms of radioiodine, depending upon the circumstances, organic iodides cast a most serious problem because of its difficulties in the trapping and because of its stability compared to other chemical forms. Furthermore, pellet-cladding interaction (PCl) fuel failures in LWR fuel rods are believed to be stress corrosion cracks caused by embrittling fission product species, radioiodine. To deal with these problems, knowledge is required on the chemical behaviors of radioiodine in and out of fuels, as well as the release behaviors from fuels. Here a brief review is given of these respects, in aiming at clearing-up the questions still remaining unknown. The data seem to indicate that radioiodine exists as a combined form in fuels. upon heating slightly irradiated fuels, the iodine atoms are released in a chemical form associated with uranium atoms. Experiments, however, as needed with specimen of higher burnup, where the interactions of radioiodine with metallic fission products could be favored. The dominant release mechanism of radioiodine under normal operating temperatures will be diffusion to grain boundaries leading to open surfaces. Radiation-induced internal traps, however, after the rate of diffusion significantly. The carbon sources of organic iodides formed under various conditions and its formation mechanisms have also been considered. (author)

No abstract available

[en] In 2010, as the total supply capacity of primary energy, 666 million liter is anticipated under the measures of thorough energy conservation. The development of energy sources along the energy policy based on environment preservation, safety, the quantity of resources and economy is strongly demanded. The nuclear power generation utilizing nuclear fission has been successfully carried out. As the third means of energy production, the basic research and technical development have been actively advanced on the energy production utilizing nuclear fusion reaction. The main object of the nuclear fusion research being advanced now is D-D reaction and D-T reaction. In order to realize low temperature nuclear fusion reaction, muon nuclear fusion has been studied so far. The cold nuclear fusion reaction by the electrolysis of heavy water has been reported in 1989, and its outline is ixplained in this report. The trend of the research on cold nuclear fusion is described. But the possibility of cold nuclear fusion as an energy source is almost denied. (K.I.)

[en] The adsorption of tritiated water vapor on molecular sieves 5A and 13X, silica gel and activated alumina was investigated in the small column experiments. The results were analyzed by a simple first order kinetic equation. The adsorption characteristics of the adsorbents are rationalized by the two important parameters, maximum adsorption capacity and adsorption rate constant, which were determined at various temperatures for each adsorbents. The column exhaustion experiments were also carried out. An equation was derived to express the correlation between breakthrough time and column length. A reasonable consistency has been noticed between the calculated and the observed results. (author)