In this study, the results of surveys conducted over the past 30 years were analyzed. The surveys include continuous opinion polls conducted by seven organizations, those conducted by eight news media one year after the Fukushima Daiichi accident, and those conducted by INSS fourteen times from 1993 to December 2011. The results were as follows: (1) Negative opinions toward nuclear power generation (NPG) suggesting “abolition or reduction”, which used to be 20-30% over the past 30 years, increased to 70% from four to six months after the accident, when there was also much news about renewable energy. (2) Even after the accident, 60% regarded NPG as “inevitable”, but many opposed future replacement or new construction of NPG facilities. (3) After the accident, recognition of the usefulness of NPG and concerns about electric power shortages in the near future remained unchanged, while anxiety and distrust toward NPG increased significantly. When considering power generation options, people now tend to focus on accident risks. (4) Nevertheless, people are neither aware of various possible problems caused by reducing NPG nor willing to accept a significant increase in electricity rate caused by the shift to renewable energy.
As the first step of inspection of the applicability of the PRODIA Code for dismantling activities in the decommissioning of FUGEN, manpower needs for dismantling activities in FUGEN conducted in 2008 were calculated with conventional calculation formulas developed from the data obtained from the JPDR decommissioning program. In this inspection, it was found that the actual data for the dismantling of feedwater heaters show the following two characteristic profiles: 1) the actual data were significantly smaller than the results of the conventional calculation formulas and 2) the actual data for the dismantling of the 3rd feedwater heater were two times larger than those for the dismantling of the 4th one, although both data were almost of the same weight. In order to use the PRODIA Code for further dismantling activities in the decommissioning of FUGEN, the origin of these results was investigated. This investigation showed that both of the differences in the work description between FUGEN and JPDR and between the 3rd feedwater heater of FUGEN and the 4th one produce these characteristic profiles. Since this means that the conventional calculation formula for the dismantling of feedwater heaters has no applicability, it was considered necessary to construct a new calculation formula reflecting the work description of the dismantling of feedwater heaters in FUGEN. It was found that the calculation results with this new formula showed good agreement with the actual data of both the 3rd and 4th feedwater heaters. Based on these findings, some case studies for the dismantling of feedwater heaters were conducted.
The probabilistic fracture mechanics analysis code PASCAL3 has been developed at JAEA to support the validation of the codes and standards that provide the structural integrity assessment method for reactor pressure vessels (RPVs) during pressurized thermal shock. The previous version of PASCAL2 has many functions including the evaluation method for an embedded crack, the PTS transient database, nondestructive inspection models. This code has been improved mainly focusing on the cladding on the inner surface of RPV. Using PASCAL3, the effects of the initiation and growth model for a surface flaw have been analyzed to determine the standard condition of PASCAL3. Deterministic and probabilistic evaluations using PASCAL3 for a current structural integrity assessment method for RPV have also been conducted. The results show that the consideration of the warm prestress effect decreases the conditional probability of failure by less than one-tenth.
Gamma-ray pulse-height distributions from widely distributed Cs-134 and Cs-137 calculated using the EGS5 Monte Carlo code with the transformation of a system consisting of a plane isotropic source and a unit sphere detector into a system consisting of a point isotropic source and a plane detector were compared with measured ones. Results agree well in terms of both spectrum shape and absolute value. Spectra at a height of 1 m from widely distributed I-131, Cs-134 and Cs-137 were studied by EGS5 calculation. It was clarified that the contribution of scattered gamma rays is dominant within the total gamma-ray flux. The contributions of the scattered gamma rays to ambient dose equivalents and effective dose were also studied.
In this paper, we propose a new methodology of identifying important research problems to be solved to improve the performance of some specific scientific technologies by the phenomena identification and ranking table (PIRT) process, which has been used as a methodology for demonstrating the validity of the best estimate simulation codes in USNRC licensing of nuclear power plants. It keeps the fundamental concepts of the original PIRT process but makes it possible to identify important factors affecting the performance of the technologies from the viewpoint of the figure of merit and problems associated with them, which need to be solved to improve the performance. Also in this paper, we demonstrate the effectiveness of the developed method by showing a specific example of the application to physical events or phenomena in objects having fatigue or SCC crack(s) under ultrasonic testing and eddy current testing.
This technical report shows the situation of the dismantling of the main equipment in the radiation-controlled area of a uranium refining and conversion plant. The dismantling was carried out at the beginning of the uranium refining and conversion plant decommissioning project. We started the dismantling in April 2008 and finished it in 29 September 2011. The dismantled waste and equipment were stored in 200 small drums. All the contaminated devices were sealed and kept in this stage. The radioactivity inventory of the uranium refining and conversion plant did not change in this stage. However, the risk of contamination due to the deterioration of this facility with time became remarkably small. Moreover, we were able to get many information and experience about dismantling. Then, we began decommissioning. We were in a new stage from April 2012. We are going to dismantle or tightly close the fluidization media storage underground tank, the neutralization and precipitation system of a waste fluid with fluorine, and the uranium and ventilation system in about three years from now on.