Japanese Nuclear Power Plants Research Articles

Accident Sequence Precursor Analysis of an Incident in a Japanese Nuclear Power Plant Based on Dynamic Probabilistic Risk Assessment

Probabilistic risk assessment (PRA) is an effective methodology that could be used to improve the safety of nuclear power plants in a reasonable manner. Dynamic PRA, as an advanced PRA, allows for more realistic and detailed analyses by handling time-dependent information. However, the applications of this method to practical problems are limited because it remains in the research and development stage. This study aimed to investigate the possibility of utilizing dynamic PRA in risk-informeddecision-making. Specifically, the author performed an accident sequence precursor (ASP) analysis on the failure of emergency diesel generators that occurred at Unit 1 of the Tomari Nuclear Power Plant in Japan using dynamic PRA. The results were evaluated by comparison with the results of simplified classical PRA. The findings indicated that dynamic PRA may estimate lower risks compared with those obtained from classical PRA by reasonable modeling of alternating current power recovery. The author also showed that dynamic PRA can provide detailed information that cannot be obtained with classical PRA, such as uncertainty distribution of core damage timing and importance measure considering the system failure timing.

Study for the optimization of the decommissioning project of nuclear facilities

Basically, decommissioning of nuclear facilities is a project that does not generate new profit because it is carried out with the reserve funds from operation, etc. Therefore, its cost should be minimized with optimization by shortening the process and minimizing the waste, etc. Meeting the requirements of exposure risk (safety) also affects the optimization. In this study, we decided to integrate these evaluation methods to develop a comprehensive optimization evaluation method. In this study, we established an average process for the current decommissioning plans of Japanese nuclear power plants and developed a cost evaluation method including sensitivity analysis. As a result of examining the feasibility of the deferred dismantling strategy using the above calculation method, it became clear that although there is a reduction in disposal and dismantling costs due to the natural decay of radioactive materials, the maintenance and management costs during the safe storage period account for a large proportion of the costs, and for this reason, immediate dismantling is unconditionally advantageous, at least in Japan. The components of optimization described above are naturally subject to various uncertainties and risks. For example, there are regulatory risks, and the location of waste disposal site is subject to social acceptance, so there is a great deal of uncertainty. In the future, these factors will be incorporated into the evaluation and studied, and the optimal strategy for decommissioning and what kind of uncertainty should be focused on will be clarified quantitatively.

Radiation exposure to the lens of the eye for Japanese nuclear power plant workers

In Japan, the radiation-dose limit for the lens of the eye was revised in April 2021. Consequently, for workers, the numerical values of the equivalent dose to the lens of the eye are equal to those of the effective dose. Radiation workers, radiation safety officers and licensees must comply with regulations related to radiation protection and optimize protection. The new guidelines on dose monitoring of the lens of the eye developed by the Japan Health Physics Society recommend for the dose to be estimated near the eye for accurate estimation, when the dose to the lens approaches or exceeds the management criteria. However, there is limited information regarding the non-uniform exposure of nuclear power plant workers. In this study, the dose equivalents of high-dose-rate workplaces and the personal doses of 88 workers were estimated at four Japanese commercial nuclear power plant sites (RWR: 3 units and BWR: 3 units) and the dose to the lens of the eye and the exposure situations of the workers were analyzed.

КОНЦЕПТУАЛІЗАЦІЯ РИЗИК-МЕНЕДЖМЕНТУ У СИСТЕМІ КОРПОРАТИВНОГО УРЯДУВАННЯ БАГАТОНАЦІОНАЛЬНИХ ПІДПРИЄМСТВ

The purpose of the article is to summarize and present the fundamental trends of the last decade related to the formation of the role and place of risk management in the system of corporate governance of multinational enterprises (MNEs). The analysis is based on the latest research by leading international researchers, such as American scientists Warren Bennis, Bert Nanus, Hugh Grove and Lorenzo Patelli, British scientists Mingzhui Wang, Elizabeth Kelan and Kevin Crowley, international organizations Basel Committee on Banking Supervision, Group of Thirty, Institute of international finance and the Organization for Economic Cooperation and Development. The conducted analysis clearly indicates that failures in MNEs risk management over many years led to catastrophic losses in various industries, when such failures, as in the energy sector, led not only to financial, but also to significant environmental consequences. Among the most significant incidents, we can highlight the accidents on the oil platform "Deepwater Horizon" of the British oil and gas company BP in 2010 in the Gulf of Mexico and the Japanese nuclear power plant Fukushima-1 in 2011. Often these failures also contributed to failures in corporate governance, where boards of directors did not fully consider the risks that MNEs were taking and/or imperfect risk management systems. Thus, the conceptualization of risk management in the system of corporate governance of MNEs becomes an important component of achieving medium and long-term strategic goals of MNEs in conditions of growing macroeconomic and geopolitical uncertainty.

SELECTION OF LARGE-SCALE NUCLEAR POWER PLANT BASED ON ECONOMIC AND RELIABILITY ASPECTS IN INDONESIAN POWER SYSTEM

Choosing the Indonesia's power systems that are suitable with the large-scale nuclear power plant (NPP) and the NPP's vendor country are crucial problems faced by Indonesian government. Therefore, this research analyzes the NPP impact on the power system reliability to choose the suitable power systems and the NPP economics of each possible vendor country to choose the optimal vendor that provides minimize cost. This research uses two electricity price scenarios: electricity production cost (scenario 1) and adjustment tariff (scenario 2). The results show that only Sumatra and Java-Bali system can be connected with the NPP. For both of these systems, Japanese NPP is not economical to be developed because it provides a levelized unit electricity cost (LUEC) of 0.116 USD/kWh, which is higher than the electricity prices. Meanwhile, Chinese and South Korean NPP is economical to be developed in both systems. For the Java-Bali system, Chinese NPP is the best choice in scenario 1 with a LUEC of 0.036 USD/kWh. In scenario 2, South Korean NPP that has a LUEC of 0.058 USD/kWh becomes the best choice because it has better public perception than Chinese. For the Sumatra system, South Korean NPP is the best choice in both scenarios.Keywords: Large-scale NPP selection, Indonesia power system, Reliability, Minimize cost, Electricity priceJEL Classifications: D21, D22, E39DOI: https://doi.org/10.32479/ijeep.11107

Nuclear Hydrogen Production: Modeling and Preliminary Optimization of a Helical Tube Heat Exchanger

Hydrogen production is a topical issue in an energy scenario where decarbonization is a priority, especially with reference to the transport sector that has a great weight on global emissions. Starting from this consideration, GIF (Generation-IV International Forum) investigated the possibility to produce hydrogen by nuclear energy. The “classic” strategy is based on the use of nuclear as energy source for the electrolysis; but on the medium-long term, a more sustainable and smart approach could be founded on the use of thermochemical processes (e.g., I-S) that require a direct coupling of a chemical plant to a nuclear reactor. In order to develop this strategy, it is mandatory to design and optimize all the key components involved in this complex plant. In this study, we developed the 3D-CAD and CFD models of the intermediate heat exchanger (IHX) installed in the Japanese HTTR nuclear power plant. This component is extremely important for both the safety of the two plants and the stability of the whole hydrogen production plant. Initially, our model (developed by AutoCAD 3D and implemented in Star CCM+) was validated on the basis of experimental data available in literature; then, an initial optimization of the IHX testing innovative materials, such as Alloy 617 and ODS–MA754, and a different primary coolant (supercritical CO2) was performed.

Major Outcomes through Recent ROSA/LSTF Experiments and Future Plans

Many experiments have been conducted on accidents and transients of pressurized water reactor (PWR) employing the rig of safety assessment/large-scale test facility (ROSA/LSTF). Recent research activities concerned with the OECD/NEA international joint projects included experimental investigation via the ROSA and ROSA-2 Projects, and counterpart testing with thermal-hydraulic integral test facilities under collaboration of the PKL-2, PKL-3, ATLAS, and ATLAS-2 Projects. Major results of the related integral effect tests (IETs) with the LSTF were reviewed to experimentally identify thermal-hydraulic phenomena involved, regarding the PWR accident sequences in accordance with the new regulatory requirements for the Japanese light-water nuclear power plants. Future separate effect test using the LSTF is planned to simulate loss of emergency core cooling system (ECCS) recirculation functions in a large-break loss-of-coolant accident (LOCA). Key results of the recent IETs utilizing the LSTF and future plans were presented relevant to multiple steam generator tube rupture accident with recovery operation, small-break LOCA with accident management measure on core exit temperature reliability, and small-break LOCA with thermal stratification under cold water injection from ECCS into cold legs. Also, main outcomes of the LSTF IETs were indicated for wide spectrum LOCA with core uncovery and anticipated transient without scram following small-break LOCA under totally failed high-pressure injection system.

Grain-boundary phosphorus segregation in highly neutron-irradiated reactor pressure vessel steels and its effect on irradiation embrittlement

Reactor pressure vessel (RPV) steels for pressurized water reactors (PWRs) with bulk P contents ranging from 0.007 to 0.012wt.% were subjected to neutron irradiation at fluences ranging from 0.3 to 1.2 × 1020 n/cm2 (E > 1 MeV) in PWRs or a materials testing reactor (MTR). Grain-boundary P segregation, which was analyzed using Auger electron spectroscopy (AES) on intergranular facets, increased with increasing neutron fluence. A rate theory model based on four diffusion-reaction equations for substitutional P atoms, octahedral interstitial P atoms, vacancies, and self-interstitial atoms was also used to simulate the increase in grain-boundary P segregation for RPV steels with a bulk P content up to 0.020wt.%, using parameters optimized by the present AES data. The increase in grain-boundary P segregation in RPV steel with a bulk P content of 0.015wt.%, which is the maximum P concentration in RPV steels used in Japanese nuclear power plants intended for restart, was estimated to be less than 0.1 in monolayer coverage at 1 × 1020 n/cm2 (E > 1 MeV). A comparison of the PWR data with the MTR data, including that from the literature, showed that neutron flux had no effect upon grain-boundary P segregation for A533B steels. The relationships of the ductile-brittle transition temperature (DBTT) shifts to grain-boundary P segregation and to yield strength were also discussed. A linear relationship between the yield strength and the DBTT shift with a slope of 0.63 was obtained for RPV steels with a bulk P content up to 0.026wt.%, which is higher than that of most U.S. A533B steels. It is concluded that the intergranular embrittlement is unlikely to occur for RPV steels irradiated in PWRs.

ESTIMATION OF PHOTON ENERGY AND DIRECTION DISTRIBUTIONS AT JAPANESE NUCLEAR POWER PLANTS BASED ON LITERATURE SURVEY FOR J-EPISODE STUDY.

In order to reconstruct organ-absorbed dose from recorded dose for risk estimation in nuclear worker cohort, the preceding study of the International Agency for Research on Cancer (IARC) 15-Country Collaborative Study estimated the organ dose conversion factor from the recorded dose of Hp(10) under the assumption that on average, in the nuclear power plants (NPPs), 10% of the dose received by workers was due to photon energies ranging from 100 to 300 keV and 90% from photon energies ranging from 300 to 3000 keV, with the average geometry being 50% in the antero-posterior geometry and 50% in the isotropic geometry. Similar examination was conducted at the Japanese Epidemiological Study on Low-Dose Radiation Effects (J-EPISODE).Literature survey disclosed that Japanese electric power companies had jointly conducted the research on energy distribution and incidence direction distribution of gamma rays in working environments during periodical inspection and maintenance as well as during operation in the 1980s. The analysis of the survey results on photon energy and geometry distribution of Japanese NPPs demonstrated appropriateness in applying the IARC study assumption for nuclear workers in Japan and reconstructing organ-absorbed dose in the J-EPISODE. These results in Japan also provide strong evidence to support the robustness and generality of the IARC study assumption, which was estimated based on the judgment of experts at nuclear facilities around the world.

Effectiveness of a Basic Education Program on RadiationRelated Health Concerns for Nurses of Public Health and School Health in Japan

Background: After the Japanese nuclear power plant disaster in 2011, many residents became concerned about health effects of radiation. We aimed to evaluate the effectiveness of a training program for public health and school health nurses to improve their skills and expertise for better support to residents and students. Methods: This was a quasi-experimental study using single-group and pre-post comparison in 2016 in Hiroshima, Kagoshima and Hyogo prefectures of Japan. The educational evaluation was conducted through each sub-item of Bloom’s attainment goals. The evaluation of effectiveness was surveyed among 61 participants before and immediately after the workshop, and at 1-week and 1-month later. The analysis compared initial scores obtained before the workshop with subsequent responses. Where a significant difference was observed among three-group or more in the Friedman test, the Wilcoxon signed-rank test was used for two-group comparisons across the time periods. The significance level was set at P<0.05. Results: Data of 54 participants were analyzed. The knowledge based on Bloom’s taxonomy was increased as the number of correct responses increased significantly after the workshop (P<0.001). Cognitive domain was significantly increased after 1-week and 1-month (P<0.001). Affective and psychomotor performances were also increased compared with prior. Participants increased vocabulary related to radiation and developed confidence in radiation disaster recovery measures. Conclusion: Each sub-item of the Bloom’s attainment (goal, cognitive, affective, psychomotor) has almost been reached and the effect was maintained even after 1-month. By learning concrete words, they could explain accurately. Participants improved their confidence after receiving the training to respond and clarify the radiation anxieties to the community people.

Japan’s Energy Policy towards the SCO Member States: Current Situation and the Perspectives

The Shanghai Cooperation Organization is undoubtedly an important economic and geopolitical player in the Central, East and South Asia regions, bringing together countries of different size and potential. This is primarily about the economy and energy sectors, but the military-strategic partnership within the framework of the association shouldn’t be ignored too. Japan does not have a coherent policy towards the SCO as a single structure, at least it is not reflected in official documents, but individual member States are of significant interest. These are mainly Russia and China, and Russia is considered as one of the chief energy resources suppliers, which contributes to the implementation of the Japanese concept of energy security, aimed at maximum diversification of supply geography. China is regarded as one of the largest buyers of Japanese high-tech industrial products and an exporter of coal. The countries of the Central Asian region, which are rich in energy resources and do not have sufficient financial and technological capabilities to explore them, are also attracting more and more attention from Japan, but there is great competition with Chinese companies. India and Pakistan, that joined the SCO in 2017, are important for Japan as a counterweight to China’s expansion in South Asia and also markets for Japanese nuclear power plant construction technologies and various types of renewable energy generators. All in all, Japanese energy policy towards the SCO member States is balanced and flexible, but the presence of certain geopolitical contradictions with the founders of the organization still hinders the building of a meaningful multilateral dialogue, although options for involving Japan in the Shanghai Cooperation Organization periodic work, for instance, in the observer status, have been repeatedly voiced.

Crack Growth Evaluation for Cracked Stainless and Carbon Steel Pipes Under Large Seismic Cyclic Loading

Abstract Some Japanese nuclear power plants have experienced several large earthquakes beyond the design basis ground motion. In addition, cracks resulting from long-term operation have been detected in piping systems. Therefore, to assess the structure integrity and to evaluate the fragility of cracked pipes taking the occurrence of large earthquakes into account, it is very important to establish a crack growth evaluation method for cracked pipes that are subjected to large seismic cyclic response loading. In our previous study, we proposed an evaluation method for crack growth during large earthquakes through experimental study using small size specimens and investigation using finite element analyses. In the present study, to confirm applicability of the proposed method to pipe, crack growth tests were conducted on both stainless and carbon steel pipe specimens with a circumferential through-wall crack, considering large seismic cyclic response loading with complex waveforms. The predicted crack growth values are in good agreement with the experimental results and the applicability of the proposed method was confirmed.

Nuclear Power Plants and Terror Attacks in Japan

The operation of several Japanese nuclear power plants has been halted because the Nuclear Regulatory Committee (NRC) reported that these nuclear power plants are not sufficiently prepared for potential terror attacks. It is unclear how the Japanese judiciary exercises judicial review for this NRC decision regarding terror attack protection measures. Japanese courts previously avoided the constitutionality of defense and peace statutes by using political questions. The attitude of the Japanese judiciary toward national defense is symbolic in several cases for Article 9, the pacifism provision of the Japanese constitution. Japanese administrative agencies are authorized to exercise discretion in the scope of power that is vested in them by the statutes passed in the parliament, or Diet. Under the Administrative Case Litigation Act (ACLA), which was revised in 2004, Japanese courts can review administrative discretion according to several principles such as fact-finding, purpose, timing, equal principles, constitutional rights infringement, and unconstitutional motives. The Judiciary has reviewed administrative agencies’ decision under under ACLA. Under ACLA, Japanese courts maintain arbitrary and capricious administrative discretion but not the political validity and policy judgement capability of administrative agencies. Judiciary defers to administrative agency decisions for its expertise. Citizens may take action toward administrative agencies regarding its validity by the Administrative Appeal Act (AAA). The AAA provides an avenue that is simpler than ACLA and yields a more rapid response, but it is not as fair as the ACLA because agencies themselves conduct an internal review on the validity of its decisions. In the famous Ikata nuclear power plant case of 1992, the Japanese Supreme Court deferred to the administrative agency decision for its expertise but did not use the term “discretion.” This may have been because nuclear power plants are related to Japanese energy policy, thus affecting Japan as a whole. This paper argues that in general, the judiciary does not thoroughly review public records and the reasoning behind administrative decisions but may identify unconstitutional motives. The Japanese court has not yet reviewed the NRC decision of halting nuclear power plant operation due to possible terror attacks. The statute for terror attacks was passed soon after the Great East Japan Earthquake in 2011. Terror attacks may provide an avenue for the Japanese judiciary to avoid conducting a judicial review of the administrative agency’s decision. It is unclear whether the Japanese judiciary will carefully examine this issue or defer to the NRC as terrorist protection overlaps with the field of national defense, which is stipulated in Article 9. This paper argues that national defense and nuclear power plant safety in the event of natural disasters both differ and overlap. Japanese administrative law scholars must analyze the expertise of the administrative agency in giving deference to the Japanese judiciary.

Ensuring the safety of Japanese nuclear power plant

Ensuring the safety of Japanese nuclear power plant

Ensuring the safety of Japanese nuclear power plant

Ensuring the safety of Japanese nuclear power plant

An analysis of the historical trends in nuclear power plant construction costs: The Japanese experience

In this study, we collected Japanese nuclear power plant construction cost data from official documents submitted by the electric utilities and conducted a quantitative analysis of the past trends. We found that the unit construction cost of Japanese nuclear power plants rose during the period from 1975 to 1980, when the “improvement and standardization” programs took place, and did not increase or decline significantly after that. We also observed significant economies of scale, even if we take into account interest during construction, as well as the so-called overnight cost. As far as we know, this study is the first attempt to analyze the total history of Japan's nuclear power generation until the Fukushima accident from the cost perspective. The findings could contribute to a better understanding of the economics of nuclear power, as similar studies in the United States and France tend to exhibit different results. The analyses in this study appear to reinforce the reliability of the cost estimation by the Japanese government, which has been used as the numerical basis for the current energy policies in Japan.

Текущие тенденции на мировом рынке ядерной энергетики

The review of the nuclear energy technologies market, namely the main processes of the initial and final stages of the nuclear fuel cycle (NTC) was shown. The authors reveal key players in the markets of natural uranium mining, conversion, enrichment, fabrication of nuclear fuel, direct disposal, and reprocessing as well as determine their market shares. The article shows the fundamental factors influencing the development trends of the global nuclear power market such as: units’ commissioning in China, India, the Republic of Korea and other countries, the restart of the Japanese nuclear power plants, growth of uranium supplies long-term contracting planned for the period up to 2025, volatility of world prices of the NFC initial and final stages, political, economic and environmental reasons for the nuclear power generation choice. The article presents the results of analyses of Russian and world prices on the NFC initial and final stages main processes’ allowing to draw a conclusion about the current competitiveness of Russian nuclear energy technologies

放射性ヨウ素吸着剤AgRとAgXについて

Rasa-AgX as an adsorbent of radioactive organic iodine has been commercialized and is being used in filtered venting system at Japanese nuclear power plants (NPPs) as their countermeasures of severe accidents. However, as the venting conditions vary in different NPPs, the adsorbents with matched characteristics are demanded. For this reason, a new radioiodine adsorbent, AgR, has been developed. Although the Ag content is as low as 10%, AgR still shows the adsorption efficiency of 99.5% even if dew point distance (DPD) is 0K (Residence time is 0.24 sec.). Furthermore, since AgR exhibits a weak reactivity with hydrogen, it can work very well in the atmosphere with the concentration of 10% hydrogen. In addition, AgX shows excellent long-term storage stability and water resistance under high humidity.

Nuclear Energy Security: Emerging Trends and Pakistan

The demand for nuclear energy has increased in recent years mainly in the developing countries of the Asia-Pacific. Despite the Japanese (Fukushima) nuclear power plant accident in 2011, the nuclear power industry is expected to inflate exponentially in the coming decade to maintain the delicate balance between sustainable socioeconomic development and environmental fortification. Therefore, an overwhelming majority of states are inclined to add nuclear power plants to their national grids. India and Pakistan, neither party to the Nuclear Non-Proliferation treaty (NPT) nor members of the Nuclear Supplier Group (NSG), are included in the list of new contenders. These two institutional arrangements forbid nuclear cooperation with states that have unsafeguarded facilities and are not party states to the NPT. Besides, India has been mainstreamed in international nuclear commerce whereas Pakistan is deprived of similar rights despite the fact that energy deficiency plagues its socioeconomic developments. The study finds that the existing, ambiguous construct that promotes peaceful uses of nuclear technology and simultaneously opposes nuclear proliferation is not consistent with 21st century's realities. Therefore, the non-proliferation construct necessitates revisions in order to meet the contemporary demands to address developing states' energy needs based on a renewed framework.

Geoneutrinos and Hydridic Earth (or primordially hydrogen-rich planet)

Geoneutrino is a new channel of information about geochemical composition of the Earth. We alnalysed here the following problem. What statistics do we need to distinguish between predictions of Bulk Silicate Earth model and Hydridic Earth model for Th/U signal ratio? We obtained the simple formula for estimation of error of Th/U signal ratio. Our calculations show that we need more than $22 kt \cdot year$ exposition for Gran-Sasso underground laboratory and Sudbury Neutrino Observatory. We need more than $27 kt \cdot year$ exposition for Kamioka site in the case of stopping of all Japanese nuclear power plants.