Probabilistic risk assessment method development for high temperature gas-cooled reactors, 2; Development of accident sequence analysis methodology

Matsuda, Kosuke*; Muramatsu, Ken*; Muta, Hitoshi*; Sato, Hiroyuki; Nishida, Akemi; Ohashi, Hirofumi; Itoi, Tatsuya*; Takada, Tsuyoshi*; Hida, Takenori*; Tanabe, Masayuki*; et al.

Proceedings of 2017 International Congress on Advances in Nuclear Power Plants (ICAPP 2017) (CD-ROM), 7 Pages, 2017/04

This paper proposes a set of procedures for accident sequence analysis in seismic PRAs of HTGRs that can consider the unique accident progression characteristics of HTGRs. Main features of our proposed procedure are as follows: (1) Systematic analysis techniques including Master Logic Diagrams are used to ensure reasonable completeness in identification of initiating events and classification of accident sequences, (2) Information on factors that govern the accident progression and source terms are effectively reflected to the construction of event trees for delineation of accident sequences, and (3) Frequency quantification of seismically-initiated accident sequence frequencies that involve multiplepipe ruptures are made with the use of the Direct Quantification of Fault Trees by Monte Carlo (DQFM) method by a computer code SECOM-DQFM.

Parametric survey for benefit of partitioning and transmutation technology in terms of high-level radioactive waste disposal

Oigawa, Hiroyuki; Yokoo, Takeshi*; Nishihara, Kenji; Morita, Yasuji; Ikeda, Takao*; Takaki, Naoyuki*

Journal of Nuclear Science and Technology, 44(3), p.398 - 404, 2007/03

https://doi.org/10.3327/jnst.44.398

Benefit of implementing Partitioning and Transmutation (P&T) technology was parametrically surveyed in terms of high-level radioactive waste (HLW) disposal by discussing possible reduction of the geological repository area. The results showed that, by recycling minor actinides (MA), the placement area could be reduced by 17-29% in the case of UO-LWR and by 63-85% in the case of MOX-LWR in comparison with the conventional PUREX reprocessing. This significant impact in MOX fuel was caused by the recycle of Am which was a long-term heat source. Further 70-80% reduction of the placement area in comparison with the MA-recovery case could be expected by partitioning the fission products (FP) into several groups for both fuel types.

Parametric survey on possible impact of partitioning and transmutation of high-level radioactive waste

Oigawa, Hiroyuki; Yokoo, Takeshi*; Nishihara, Kenji; Morita, Yasuji; Ikeda, Takao*; Takaki, Naoyuki*

Proceedings of International Conference on Nuclear Energy System for Future Generation and Global Sustainability (GLOBAL 2005) (CD-ROM), 6 Pages, 2005/10

The benefit of implementing Partitioning and Transmutation (P&T) of high-level wastes was parametrically surveyed. The possible reduction of the geological repository area was estimated. By recycling minor actinides (MA), the repository area required for unit spent fuel was reduced significantly in the case of MOX-LWR. This effect was caused by removal of Am which is a long-term heat source. By partitioning the fission products, in addition to MA recycling, further 70-80% reduction from the MA-recovery case can be expected for both UO and MOX. This significant reduction was independent of the cooling time before the partitioning process.

Improvement of Biosphere Assessment Methodology for Performance Assessment of Geological Disposal Facility (IV)

Oyamada, Kiyoshi*; Ikeda, Takao*

JNC TJ8400 2004-006, 199 Pages, 2004/02

JNC-TJ8400-2004-006.pdf:8.87MB

This report presents results on trial study of methodology to identify Geosphere-biosphere Interface (GBI), and examination in consideration of overseas trend of long-term biosphere assessment.

Systematization and Sophistication of a Comprehensive Sensitivity Analysis Program (Phase 2)

Oyamada, Kiyoshi*; Ikeda, Takao*

JNC TJ8400 2003-095, 243 Pages, 2004/02

JNC-TJ8400-2003-095.pdf:4.06MB

This study developed minute estimation by adopting comprehensive sensitivity analytical program for reliability of TRU waste repository concepts in a crystalline rock condition. We examined each components and groundwater scenario of geological repository and prepared systematic bases to examine the reliability from the point of comprehensiveness. Models and date are sophisticated to examine the reliability. Based on an existing TRU waste repository concepts, effects of parameters to nuclide migration were quantitatively classified. Those parameters, that will be decided quantitatively, are such as site character of natural barrier and design specification of engineered barriers. Considering the feasibility of those figures of specifications, reliability is re-examined on combinations of those parameters within a practical range. Future issues are ; (1)Comprehensive representation of hybrid geosphere model including the fractured medium and permeable matrix medium. (2)Sophistication of tools to develop the reliable combinations of parameters. It is significant to continue this study because the disposal concepts and specification of TRU nuclides containing waste on various sites shall be determined rationally and safely through these studies.

Systematization and Sophistication of a Comprehensive Performance Assessment Program

Miki, Takahito*; Oyamada, Kiyoshi*; Ikeda, Takao*

JNC TJ8400 2003-053, 386 Pages, 2003/02

JNC-TJ8400-2003-053.pdf:10.69MB

This study developed analytical programs and procedures based on a method of stochastic radionuclide migration to estimate the feasibility of disposal concepts and to define design specifications, considering the variety of scenarios and disposal concepts divided by depth of repository for TRU nuclides containing waste.

Improvement of Biosphere Assessment Methodology for Performance Assessment of Geological Disposal Facility (III)

Miki, Takahito*; Ikeda, Takao*

JNC TJ8400 2003-017, 342 Pages, 2003/02

JNC-TJ8400-2003-017.pdf:5.64MB

This report contains results on study of method of identification of Geosphere-Biosphere Interface (GBI), toxicological impact of non-radioactive contaminants contained in radioactive waste disposal facility and consideration of climate change in long-ter

A Comprehensive study on nuclide migration using scenario exploration method (3)

Miki, Takahito*; Oyamada, Kiyoshi*; Ikeda, Takao*

JNC TJ8400 2002-050, 217 Pages, 2002/02

JNC-TJ8400-2002-050.pdf:2.66MB

In this study, for the mid-depth disposal system for TRU wastes, asset of stochastic simulations covering uncertainties corresponding to variety of scenarios, models and parameter values were conducted to; (1)indicate measures to reduce potential exposure based on the knowledge of sensitivity structure (2)introduce new methodology for clarify the requirement of repository system (3)show guidelines of disposal system development by clarifying conditions in system specification for achieving a target which is well below the dose constraint for base scenarios (4)identify scenarios and conditions that could lead to a radiological impact greater than the dose constraint for alternative scenarios In the course of geological disposal for TRU waste, improvement of assessment methodology for the alternative scenarios was carried out.

Improvement of biosphere assessment methodology for performance assessment of geological disposal facility (II)

Miki, Takahito*; Yoshida, Hideji*; Ikeda, Takao*

JNC TJ8400 2002-009, 338 Pages, 2002/02

JNC-TJ8400-2002-009.pdf:8.57MB

This report contains results on study of Geosphere-Biosphere Interface (GBI), development of biosphere assessment model for gaseous and volatile radionuclides, review of biosphere assessment and research on safety indicators. Regarding study of Geosphere-Biosphere Interface (GBI), FEP database for the Geosphere-Biosphere Transitions Zone (GBTZ) were compiled. Furthermore, release scenarios were identified from the FEP database, and review of conservativeness and robustness of the conceptual and mathematical models developed previously by JNC were undertaken. Regarding development of biosphere assessment model for gaseous and volatile radionuclides, the conceptual and mathematical models were developed, and it was confirmed that the impact of the exposure pathway regarding gas release to flux-to-dose conversion factor is small. Regarding review of biosphere assessment data, the parameters which were used on JNC second progress report were reviewed and classified using the biosphere data protocol categories. Furthermore, the data for key parameter(important but poorly characterized parameters) were revised. Regarding research on safety indicator, some kinds of safety indicators, especially for the non-radioactive contaminant and for the non-human biota, are reviewed.

Biosphere modeling with climate changes for safety assessment of high-level radioactive waste geological isolation

Kato, Tomoko; ; Suzuki, Yuji*; ; Ishiguro, Katsuhiko; Ikeda, Takao*; Richard, L.*

JNC TN8400 2001-003, 128 Pages, 2001/03

JNC-TN8400-2001-003.pdf:6.09MB

In the safety assessment of a high-level radioactive waste (HLW) disposal system, it is required to estimate radiological impacts on future human beings arising from potential radionuclide releases from a deep repository into the surface environment. In order to estimate the impacts, a biosphere model is developed by reasonably assuming radionuclide migration processes in the surface environment and relevant human lifestyles. Releases from the repository might not occur for many thousands of years after disposal. Over such timescales, it is anticipated that the considerable climatic change, for example, induced by the next glaciation period expected to occur in around ten thousand years from now, will have a significant influence on the near surface environment and associated human lifestyles. In case of taking these evolution effects into account in modeling, it is reasonable to develop several alternative models on biosphere evolution systems consistent with possible future conditions affected by expected climatic changes. In this study, alternative biosphere models were developed taking effects of possible climatie change into account. In the modeling, different climatic states existing in the world from the present climate condition in Japan are utilized as an analogy. Estimation of net effects of the climatic change on biosphere system was made by comparing these alternative biosphere models with a constant biosphere model consistent with the present climatic state through flux to dose conversion factors derived from each one.