Risk communication about high-level radioactive waste (HLW) disposal is necessary for public acceptance of the HLW disposal program in Japan. To support risk communication, we developed the Online Risk Communication Assistant Tool (ORCAT) system on the World Wide Wed (WWW). In this research, we analyzed the changes in participants' attitudes to HLW disposal through the test operation of the ORCAT system. We carried out the test operation of the ORCAT system from Oct. 29 to Dec. 12, 2005. One hundred fifty nonexpert participants, five experts, and two facilitators participated in this operation. To measure the changes in participants' attitudes to a HLW disposal program, we carried out web questionnaires before and after the test operation. Consequently, we found that most of the participants exhibited on increased level of concern about HLW as well as increased understanding regarding the necessity of HLW disposal. Nonetheless, they did not necessarily reduced their perceived risk of HLW disposal. In addition, we also found that the active participants drew conclusions based on thorough review of the information that experts posted on the ORCAT system, while the inactive participants made decisions primarily based on the context of the information presented on the ORCAT system.
The computer code PARC was developed in Japan Atomic Energy Agency, in order to predict the behavior of uranium, plutonium, neptunium, and several fission products in a reprocessing plant for spent nuclear fuel. This code has several useful calculation functions, i.e., PARC can deal with both mixer settlers and pulsed columns simultaneously, and new equations for chemical reaction, reaction constant, and distribution ratio can be easily inputted to PARC without the recompilation of the program. Therefore, it is expected to be widely used for basic solvent extraction study, separation process design, plant management, and safety analysis for future reprocessing. In the present paper, the outlines of an extractor model and several chemical reaction models used in PARC are introduced, and results of calculations for uranium and plutonium behaviors in the U/Pu separation process in PUREX are shown, which enable the elucidation of the effect of the increase in Pu concentration in the feed solution and the importance of the selection of Pu oxidation/reduction reaction models.
A solvent including tributyl phosphate (TBP) has been used for extraction of uranium (U) and plutonium (Pu) from nuclear spent fuel at Tokai Reprocessing Plant (TRP). TBP is said to be degraded by radiolysis, hydrolysis, and reactions catalyzed by extracted elements. One of the problems caused by TBP degradation is transfer of Pu into U stream caused by strong chemical binding between Pu and dibutyl phosphate (DBP), which is a degradation product of TBP. TBP degradation kinetic equations were developed based on degradation experiments using Pu samples with different alpha-ray emission rates that were taken from actual processes at TRP. The influence of degradation on Pu stripping characteristics was investigated. Diluted nitric acid alone could not readily strip Pu when DBP concentration was on the order of 103 mg/L, but a reduction agent, i.e., U (IV) with hydrazine, drastically improved the efficiency of Pu stripping. TRP has recently started to reprocess mixed oxide (MOX) spent fuel from the heavy water reactor FUGEN that includes Pu with higher alpha-ray emission. However, DBP concentration was still sufficiently low for stable solvent extraction operation. In addition, even after retention of Pu in the solvent for 20 days during a temporary suspension of the solvent extraction process, no Pu transfer into U stream was observed.
Nuclear energy has a great potential to improve energy security. Meanwhile, because of various kinds of risk nuclear power programs of advanced nations do not follow the same course to reach the goal of fuel recycling, which is the most valuable advantage of nuclear energy. This study analyzes the past trend and prospect of energy security levels of advanced nations by assessing their levels on several indexes of energy security. The quantitative analysis of the past trend shows that Japan has improved its level mainly by diversifying its energy supply sources. This study also leads to scenario planning on nuclear power with probable risks as scenario drivers, such as accident, moratorium, weak industrial capability, and uranium resource constraints. The quantitative prospect with the scenario planning shows that the nations without nuclear power programs would stay at lower levels, while the others including Japan would keep their levels beyond the average. A case study shows that an aggressive program has suppressive impact on the improvement, which is also observed in a French case. These outcomes suggest that a nuclear power program should pursue an appropriate portion in an energy supply structure from the viewpoint of energy security.
The behavior of Cs in the U crystallization of an advanced aqueous reprocessing system was investigated. A beaker-scale U crystallization experiment was carried out with a certain simulated dissolver solution. Results show that the possibility of the generation of CsNO3, Cs2UO2(NO3)4 or Cs-FP complex salt is small. A precipitation experiment of Cs-U(IV) complex salts was also carried out with a nitrate solution of U(IV) and Cs. It was found that Cs2U(NO3)6 precipitates at an acidity higher than 5 mol dm−3. It is considered that Cs2Pu(NO3)6 precipitates can be generated in a U crystallization process under a specific solution condition.
Fission product (FP) aerosol trapping along the leakage paths of degraded containment penetrations during a severe accident (SA) was investigated. Typical actual electrical penetration assemblies (EPAs) and several actual hatch flange gaskets, were degraded under prototypical severe accident conditions in a reactor containment. No leakage was observed for any test pieces under the Japanese accident management (AM) conditions, that is, a containment ambient temperature less than 200°C and a pressure less than twice the design pressure. Beyond AM conditions, a small leakage was observed from 266 to 324°C for the low-voltage module and from 279 to 349°C for the flange gasket. The temperature condition rather than the pressure condition dominates the failure criteria. The safety margin for temperature was evaluated to be more than about 70°C. The average equivalent leak area of the test piece was around 6 mm2 per 1 unit module for the low-voltage module and around 13 mm2 per 1 m gasket length for the flange gasket. There was no leak for the high-voltage module. The total leak area of a typical BWR plant during SA was estimated at about 2.5×103 mm2 and the value was about one order of magnitude smaller than the value used in current severe accident analysis codes.
A novel alpha radioactivity monitor using ionized air transport technology has been developed for future constitution of “clearance level” for uranium and TRU radioactive waste. This technology will bring paradigm shift on alpha-ray measurement, such as converting “closely contacting and scanning measurement” to “remotely contacting measurement in the block”, and drastically improve the efficiency of measurement operation. In this article, the origin and chronicle of this technology were simply explained and our newest accomplishment was described. Furthermore, using measurement data obtained in our development process, measurement and evaluation examples of alpha radioactivity were shown for practical operations as informative guides. We hope that this technology will be widely endorsed as a practical method for alpha clearance measurement in the near future.
“Guideline for Regulatory Agencies in Evaluating Contents of Root Cause Analysis by Operators” was enacted as the policy for a new inspection system in Japan. The objective is to indicate the viewpoint to verify the appropriateness of the corrective and preventive actions implemented by operators based on root cause analysis and its analysis results. This guideline leads to taking four points into special consideration for adequate application. They are encouragement of further activities of operators, flexible interpretation of the intention, versatility of analysis methods and concepts, and consideration of no blame culture. Moreover, a viewpoint for regulatory agencies indicates with special emphasis that neutrality of the analyzing party, objectivity of analysis results, and logicality of the analysis method used are ensured. This guideline shall be continuously reviewed through integration of lessons learned from active use in the future.