Atomic Energy Society Of Japan Research Articles

Current Progress in Standardization of Shielding Concrete Composition for Japanese Facility Design

The working group on shielding materials under the Standards Committee of the Atomic Energy Society of Japan has been studying the standard composition of shielding concrete that has a clear basis for use in the design of Japanese facilities. The policy for determining the composition, the procedure of study, the results obtained to date, and future tasks are described. Concrete is broadly classified into silicon type and calcium type depending on the aggregate. The reference mix design and composition were selected from the Japanese recommendation, and minor elements in the composition were replaced with silicon and calcium while preserving their weight in order to reduce regional differences. However, the penetration dose calculation for 235U thermal fission neutrons indicated that iron and carbon should be retained. The penetration dose calculations for photons from 235U prompt fission and radioisotopes showed that the attenuation ratios of silicon-type and calcium-type concretes differ in the energy region where electron pair production becomes dominant. The water content of concrete was found to vary with thickness as a result of moisture migration analysis over time. Finally, a draft composition of silicon-type concrete by thickness was determined using the residual water content at 60 years after placement. A method for correcting the elemental content under different mix conditions was also proposed.

Bayesian-estimation-based method for generating fragility curves for high-fidelity seismic probability risk assessment

ABSTRACT This paper presents a Bayesian-estimation-based seismic fragility assessment method that can significantly reduce the computational burden. The likelihood function and prior distribution used in the Bayesian estimation were enhanced. A probability density function of the seismic capacity was adopted as the likelihood function, although previous studies have generally used the fragility curve. Further, the prior distribution was assumed based on the seismic capacity obtained by incremental dynamic analysis. A sophisticated parametric study was additionally conducted, and we obtained information on the unknown parameters of the prior distribution to establish the initial values. Preliminary investigations show that these enhancements reduced the required number of seismic simulations to approximately 1/5 of that of the conventional Bayesian method. Then, the method was applied to a reinforced-concrete water intake system, which is a critical component of the core-cooling system in nuclear power plants (NPPs). The results revealed that the fragility curves determined using the proposed method with 12 repetitions of the simulations were comparable to those using a detailed method developed by the Atomic Energy Society of Japan with 500 repeated simulations. Therefore, we concluded that the proposed method could be applied to high-fidelity structures to substantially reduce the computational burden.

The Efforts for Engineer Ethics Education at the Atomic Energy Society of Japan

The Efforts for Engineer Ethics Education at the Atomic Energy Society of Japan

PWR secondary water chemistry guidelines in Japan - Purpose and technical background

In the more than 40 years of operational history of pressurized water reactors (PWRs) in Japan, sustainable development of water chemistry technologies has resulted in the world's highest secondary system component integrity; additionally, secondary system components, especially steam generator (SG) tubing, with excellent material integrity have been developed to prevent leakage of radioactive contamination from the primary to the secondary system and to maintain the heat removal function of the secondary system. Although reasonable control and diagnostic parameters for water chemistry are utilized by each PWR owner, the specific values are not shared.To ensure reliable PWR operation and to achieve the highest safety level, relevant members of the Standards Committee and the related committee organized by the Atomic Energy Society of Japan (AESJ) decided to establish water chemistry guidelines for PWRs. The Japanese PWR secondary water chemistry guidelines provide strategies for improving material integrity and the heat removal function. The guidelines also provide reasonable “action levels” for control parameters and “control values” and “diagnostic values” for multiple parameters, and they stipulate the responses when these levels are exceeded. Specifically, “conditioning parameters” are adopted in the guidelines. Good operational practice conditions are also discussed with reference to long-term experience.This paper introduces the purpose, technical background and framework of preliminary secondary water chemistry guidelines for Japanese PWRs. Addition, the differences in bases of parameter settings between the Japanese and overseas guidelines are discussed.

Automatic plume episode identification and cloud shine reconstruction method for ambient gamma dose rates during nuclear accidents

Ambient gamma dose rate (GDR) is the primary observation quantity for nuclear emergency management due to its high acquisition frequency and dense spatial deployment. However, ambient GDR is the sum of both cloud and ground shine, which hinders its effective utilization. In this study, an automatic method is proposed to identify the radioactive plume passage and to separate the cloud and ground shine in the total GDR. The new method is evaluated against a synthetic GDR dataset generated by JRODOS (Real Time On-line Decision Support) System and compared with another method (Hirayama, H. et al., 2014. Estimation of I-131 concentration using time history of pulse height distribution at monitoring post and detector response for radionuclide in plume. Transactions of the Atomic Energy Society of Japan 13:119–126, in Japanese (with English abstract)). The reconstructed cloud shine agrees well with the actual values for the whole synthetic dataset (1451 data points), with a very small absolute fractional bias (FB = 0.02) and normalized mean square error (NMSE = 2.04) as well as a large correlation coefficient (r = 0.95). The new method significantly outperforms the existing one (more than 95% reduction of FB and NMSE, and 61% improvement of the correlation coefficient), mainly due to the modification for high deposition events. The code of the proposed methodology and all the test data are available for academic and non-commercial use. The new approach with the detailed interpretation of the in-situ environment data will help improving the ability of off-site source term inverse estimation for nuclear accidents.

Severe Accident Research in Japan after the Fukushima Daiichi Nuclear Power Station Accident

After the accident at the Fukushima Daiichi nuclear power station in March 2011 (Fukushima accident), several investigation committees in Japan issued reports with lessons learned from the accident, including some recommendations on severe accident research. The review of specific severe accident research issues began after the Fukushima accident in the Atomic Energy Society of Japan (AESJ). AESJ has recently developed a new Thermal Hydraulics Safety Evaluation Fundamental Technology Enhancement Strategy Roadmap (TH-RM) for light water reactor safety improvement and development after the Fukushima accident by thoroughly revising the first version of the Roadmap (TH-RM-1) prepared in 2009. The revision was made by considering the lessons learned from the Fukushima accident. At the same time, the Research Expert Committee on Evaluation of Severe Accident, which was established by AESJ in 2012, has published phenomena identification and ranking tables (PIRTs) for both thermal hydraulics and source term issues in severe accidents based on findings from the Fukushima accident utilizing PIRT methodologies. The present paper reviews severe accident research before the Fukushima accident, lessons learned about severe accident research from the Fukushima accident, severe accident research issues reviewed after the Fukushima accident by AESJ, and current severe accident research activities mostly based on the two above-mentioned AESJ reviews after the Fukushima accident in Japan.

BWR water chemistry guidelines and PWR primary water chemistry guidelines in Japan – Purpose and technical background

After 40years of light water reactor (LWR) operations in Japan, the sustainable development of water chemistry technologies has aimed to ensure the highest coolant system component integrity and fuel reliability performance for maintaining LWRs in the world; additionally, it aimed to achieve an excellent dose rate reduction. Although reasonable control and diagnostic parameters are utilized by each boiling water reactor (BWR) and pressurized water reactor (PWR) owner, it is recognized that specific values are not shared among everyone involved.To ensure the reliability of BWR and PWR operation and maintenance, relevant members of the Atomic Energy Society of Japan (AESJ) decided to establish guidelines for water chemistry. The Japanese BWR and PWR water chemistry guidelines provide strategies to improve material and fuel reliability performance as well as to reduce dosing rates. The guidelines also provide reasonable “control values”, “diagnostic values” and “action levels” for multiple parameters, and they stipulate responses when these levels are exceeded. Specifically, “conditioning parameters” are adopted in the Japanese PWR primary water chemistry guidelines. Good practices for operational conditions are also discussed with reference to long-term experience.This paper presents the purpose, technical background and framework of the preliminary water chemistry guidelines for Japanese BWRs and PWRs. It is expected that the guidelines will be helpful as an introduction to achieve safety and reliability during operations.

Review of CFD Guidelines for Dispersion Modeling

This is the review of CFD (Computational Fluid Dynamics) guidelines for dispersion modeling in the USA, Japan and Germany. Most parts of this review are based on the short report of the special meeting on CFD Guidelines held at the International Symposium on Computational Wind Engineering (CWE2014), University of Hamburg, June 2014. The objective of this meeting was to introduce and discuss the action program to make worldwide guidelines of CFD gas-dispersion modeling. The following six gas-dispersion guidelines including Verification and Validation (V&V) schemes are introduced by each author; (1) US CFD guidelines; (2) COST/ES1006; (3) German VDI (Verein Deutscher Ingenieure) guidelines; (4) Atomic Energy Society of Japan; (5) Japan Society of Atmospheric Environment; (6) Architectural Institute of Japan. All guidelines were summarized in the same format table shown in the main chapters in order to compare them with each other. In addition to the summary of guidelines, the overview of V&V schemes and many guidelines of CFD modeling in the USA are explained.

Application of Probabilistic Tsunami Hazard Analysis for the Nuclear Power Plant Site

The tsunami hazard analysis is performed for testing the application of probabilistic tsunami hazard analysis to nuclear power plant sites in the Korean Peninsula. Tsunami hazard analysis is based on the seismic hazard analysis. Probabilistic method is adopted for considering the uncertainties caused by insufficient information of tsunamigenic fault sources. Logic tree approach is used. Uljin nuclear power plant (NPP) site is selected for this study. The tsunamigenic fault sources in the western part of Japan (East Sea) are used for this study because those are well known fault sources in the East Sea and had several records of tsunami hazards. We have performed numerical simulations of tsunami propagation for those fault sources in the previous study. Therefore we use the wave parameters obtained from the previous study. We follow the method of probabilistic tsunami hazard analysis (PTHA) suggested by the atomic energy society of Japan (AESJ). Annual exceedance probabilities for wave height level are calculated for the site by using the information about the recurrence interval, the magnitude range, the wave parameters, the truncation of lognormal distribution of wave height, and the deviation based on the difference between simulation and record. Effects of each parameters on tsunami hazard are tested by the sensitivity analysis, which shows that the recurrence interval and the deviation dominantly affects the annual exceedance probability and the wave heigh level, respectively.

The Impact of the Great East Japan Earthquake and Fukushima Daiichi Nuclear Accident on People's Perception of Disaster Risks and Attitudes Toward Nuclear Energy Policy

Multiple nationwide opinion surveys, carried out by the government (cabinet office), major media (national newspapers and NHK), the National Institute for Environmental Studies, and the Atomic Energy Society of Japan, have revealed that the Fukushima nuclear accident has heightened people's perception of disaster risks, fear of nuclear accidents, and increased recognition of pollution issues, and has changed public opinion on nuclear energy policy. The opinion gap on nuclear energy policy between specialists and lay people has widened since the disaster. The results of the Japanese General Social Survey data show that objections to the promotion of nuclear energy are strong among females, and weaker among young males and the supporters of the LDP. These findings are similar to the data collected after the Chernobyl accident. People who live in a 70km radius of nuclear plants tend to evaluate nuclear disaster risks higher. Distance from nuclear plants and the perception of earthquake risk interactively correlate with opinions on nuclear issues. Among people whose evaluation of earthquake risk is low, those who live nearer to the plants are more likely to object to the abolishment of nuclear plants. It was also found that the nuclear disaster has changed people's behavior; they now try to save electricity. The level of commitment to energy saving is found to relate to opinions on nuclear issues.

Development of the source term PIRT based on findings during Fukushima Daiichi NPPs accident

Research Expert Committee on Evaluation of Severe Accident of AESJ (Atomic Energy Society of Japan) has developed thermal hydraulic PIRT (Phenomena Identification and Ranking Table) and source term (ST) PIRT based on findings during the Fukushima Daiichi NPPs accident. These PIRTs aim to explore the debris distribution and the current condition in the NPPs with high accuracy and to extract higher priority from the aspect of the sophistication of the analytical technology to predict the severe accident phenomena by the analytical codes. The ST PIRT is divided into 3 phases for time domain and 9 categories for spatial domain. The 68 phenomena have been extracted and the importance from the viewpoint of the source term has been ranked through brainstorming and discussions among experts. The present paper describes the developed ST PIRT list and summarizes the high ranked phenomena in each phase.

B241 軽水炉の安全性向上に資する熱水力技術戦略マップ(OS3 軽水炉・新型炉・原子力安全(6))

New version of the Thermal-Hydraulics Safety Evaluation Fundamental Technology Enhancement Strategy Roadmap (TH-RM) was developed by the Atomic Energy Society of Japan (AESJ) for LWR safety improvement and development. The 1st version of TH-RM was prepared in 2009 under collaboration of utilities, vendors, universities, research institutes and technical support organizations (TSO) for regulatory body. The revision was made by three sub-working groups (SWGs) by considering the lessons learned from the Fukushima Daiichi Accident. The "safety assessment" SWG pursued development of computer codes for safety assessment. The "fundamental technology" SWG pursued safety improvement and risk reduction via accident management (AM) measures by referring the technical map for severe accident (SA) established by the "severe accident" SWG. Phenomena and components for counter-measures and/or proper prediction are identified by going through SA progression in both reactor and spent-fuel pool of PWR and BWR. Twelve important technology development subjects were identified, which include melt coolability enhancement to maintain integrity of containment vessel. Fact Sheet was developed to describe each of identified and selected R&D subjects. External hazards are also considered how to cope with from thermal-hydraulic safety point of view. This paper summarizes the revised TH-RM with several examples and future perspectives.

B244 安全向上策に関わる技術課題3 : 圧力容器の健全性(OS3 軽水炉・新型炉・原子力安全(6))

Core damage and melt progression behavior due to loss of core cooling function is one of the important factors in the severe accident. After TMI-2 accident, some integral severe accident analysis codes have been developed; however, the core damage behaviors, the relocation behavior of molten core debris and failure modes of reactor pressure vessel have still large uncertainty. The Atomic Energy Society of Japan (AESJ) developed a new thermal-hydraulics safety evaluation fundamental technology enhancement strategy roadmap (TH-RM) for LWR safety improvement and development after Fukushima Daiichi NPP accident. This paper describes the major technical issues and activities to secure the integrity of reactor pressure vessel which are discussed in the TH-RM developing process.

Validation of MAAP model enhancement for Fukushima Dai-ichi accident analysis with Phenomena Identification and Ranking Table (PIRT)

The Modular Accident Analysis Program (MAAP) model enhancement items to improve the simulation capability for molten corium behavior in the accidents at the Fukushima Dai-ichi nuclear power plants were validated with the Phenomena Identification and Ranking Table (PIRT). The importance ranks of the identified phenomena were evaluated for each time phase through brainstorming and discussion with the experts in the Atomic Energy Society of Japan and the members of the MAAP model enhancement project. When the current MAAP evaluation models were reviewed with the PIRT, it is found that 95 of the 386 high-ranked phenomena were not considered in MAAP 5.0.1. While 62 of these phenomena will have been addressed in the MAAP enhancement project and 25 others are not suitable to be analyzed by MAAP, 8 important phenomena should be considered in post-MAAP enhancement project with additional experiments or fundamental studies.

Generation and evaluation of gamma-ray buildup factors prepared as the standard data in the Atomic Energy Society of Japan

c A data set of gamma-ray buildup factors for point isotropic sources has been generated by the method of invariant embedding. Specific features of the data set as compared with the ANSI/ANS-6.4.3 standard published by the American Nuclear Society are 1) the data corresponding to effective dose with AP and ISO irradiation geometries, and ambient dose equivalents are added, 2) the distance from the source is extended up to 100 mean free paths (mfp) from 40 mfp in the ANS data, 3) the method of invariant embedding and the photon cross section PHOTX are used consistently for all materials, and 4) treatment of bremsstrahlung is improved by using the bremsstrahlung production data calculated by the EGS4 code. The accuracy of the transport calculations for exposure buildup factors by the IE method was evaluated quantitatively by works including 1) comparison of buildup factors with those obtained by the moments method in the ANS data, 2) comparison of the buildup factors with those obtained by the EGS4 code, and 3) self evaluation of influence of mesh width in space, energy and angle in the numerical solution of transport equation by the IE method. It is concluded that the magnitude of error in the present data is estimated about 10% or less up to 40 mfp.

Status of standard data on shielding calculation in standard committee of the Atomic Energy Society of Japan

In radiation shielding calculations, fluence-to-dose conversion coefficients are necessary to estimate dose rate. This standard gives effective dose conversion coefficients based largely on the ICRP recommendations in 1990. However, original values based on research conducted in Japan have been retained primarily with respect to the extension of energy range and multigroup-wise data. The gamma-ray buildup factor is defined by the ratio of gamma-ray dose included scattered gamma-ray contribution to dose of unscattered gamma-ray which has no experience of collision from source point to evaluation point. 20 years have passed since publication of standard data by the standard committee of America Nuclear Society at 1991, the extension of data is needed for the evaluation of effective dose and ambient dose equivalent in the shielding calculations, and the codes were also advanced for the evaluation of buildup factors. In the new report, buildup factors obtained by the Invariant Embedding (IE) method and its Geometrical-Progression (GP) fitting formula parameters appeared for 28 materials.

The 14th Nuclear Symposium hosted by Nuclear Senior Network, Atomic Energy Society of Japan

The 14th Nuclear Symposium hosted by Nuclear Senior Network, Atomic Energy Society of Japan

Recent activities in the field of General Issues

The Journal of Nuclear Science and Technology and the Transactions of the Atomic Energy Society of Japan (in Japanese) consist of 11 classified areas of expertise which include a wide range of topi...

JENDL: Nuclear databases for science and technology

It is exactly 50 years since the Japanese Nuclear Data Committee was founded both in the Atomic Energy Society of Japan and in the former Japan Atomic Energy Research Institute. The committee promoted the development of Japan’s own evaluated nuclear data libraries. As a result, we managed to produce a series of Japanese Evaluated Nuclear Data Libraries (JENDLs) to be used in various fields for science and technology. The libraries are categorized into general-purpose and special-purpose ones. The general-purpose libraries have been updated periodically by considering the latest knowledge on experimental and theoretical nuclear physics that was available at the time of the updates. On the other hand, the special-purpose libraries have been issued in order to meet the needs for particular application fields. This paper reviews the research and development for those libraries.

Water chemistry technology – one of the key technologies for safe and reliable nuclear power plant operation

Water chemistry control is one of the key technologies to establish safe and reliable operation of nuclear power plants. Continuous and collaborative efforts of plant manufacturers and plant operator utilities have been focused on optimal water chemistry control, for which, a trio of requirements for water chemistry should be simultaneously satisfied: (1) better reliability of reactor structures and fuel rods; (2) lower occupational exposure and (3) fewer radwaste sources. Various groups in academia have carried out basic research to support the technical bases of water chemistry in plants. The Research Committee on Water Chemistry of the Atomic Energy Society of Japan (AESJ), which has now been reorganized as the Division of Water Chemistry (DWC) of AESJ, has played important roles to promote improvements in water chemistry control, to share knowledge about and experiences with water chemistry control among plant operators and manufacturers and to establish common technological bases for plant water chemistry and then to transfer them to the next generation of plant workers engaged in water chemistry. Furthermore, the DWC has tried and succeeded arranging R&D proposals for further improvement in water chemistry control through roadmap planning. In the paper, major achievements in plant technologies and in basic research studies of water chemistry in Japan are reviewed. The contributions of the DWC to the long-term safe management of the damaged reactors at the Fukushima Daiichi Nuclear Power Plant until their decommissioning are introduced.