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Journal Articles

Burning of MOX fuels in LWRs; Fuel history effects on thermal properties of hull and end piece wastes and the repository performance

Hirano, Fumio; Sato, Seichi*; Kozaki, Tamotsu*; Inagaki, Yaohiro*; Iwasaki, Tomohiko*; Oe, Toshiaki*; Kato, Kazuyuki*; Kitayama, Kazumi*; Nagasaki, Shinya*; Niibori, Yuichi*

Journal of Nuclear Science and Technology, 49(3), p.310 - 319, 2012/03


 Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)

The thermal impacts of hull and end piece wastes from the reprocessing of MOX spent fuels burned in LWRs on repository performance were investigated. The heat generation rates in MOX spent fuels and the resulting heat generation rates in hull and end piece wastes change depending on the fuel histories including the burn-up of UO$$_{2}$$ spent fuels, the cooling period before reprocessing, the storage period of fresh MOX fuels. The heat generation rates of hull and end piece wastes from the reprocessing of MOX spent fuels with any of those histories are significantly larger than those from UO$$_{2}$$ spent fuels with burn-ups of 45 GWd/THM. If a temperature below 80$$^{circ}$$C is specified for cement-based materials used in waste packages after disposal, the allowable number of canisters containing compacted hull and end pieces in a package for 45 GWd-MOX needs to be limited to a value of 0.7 to 1.6, which is significantly lower than the value of 4.0 for 45 GWd-UO$$_{2}$$.

Journal Articles

Study on improvement of reliability on inventory assessment in vitrified waste for long-term safety of geological disposal

Ishikawa, Masumi*; Kaneko, Satoru*; Kitayama, Kazumi*; Ishiguro, Katsuhiko*; Ueda, Hiroyoshi*; Wakasugi, Keiichiro*; Shinohara, Nobuo; Okumura, Keisuke; Chino, Masamichi; Moriya Noriyasu*

Nihon Genshiryoku Gakkai Wabun Rombunshi, 8(4), p.304 - 312, 2009/12

Since quality control issues for vitrified waste are defined mainly with the focus on the transport and storage of the waste rather than the long-term safety of geological disposal, they do not cover inventories of long-lived nuclides which are of most interest in the safety assessment of geological disposal. Therefore we suggest a flow chart for assessment of inventories of long-lived nuclides in the vitrified waste focusing on measured value. We started a programme to examine the applicability as well as to improve reliability of nuclide generation/decay code and nuclear data library using liquid waste from spent fuel with clear irradiation history. To solve the issue of quality control for vitrified waste, comprehensive study is needed in aspects not only of geological disposal field but also of operation of nuclear power plant, reprocessing of spent fuel and vitrification of liquid waste. This study is a pioneering study to integrate them.

JAEA Reports

Discussion on sealing performance required in disposal system; Preliminary study on hydraulic analysis of disposal panel

Sugita, Yutaka*; Takahashi, Yoshiaki*; Uragami, Manabu*; Kitayama, Kazumi*; Fujita, Tomoo; Yui, Mikazu

JAEA-Research 2007-023, 70 Pages, 2007/03


The sealing performance of a repository is very important for the safety assessment of the geological disposal system for high-level radioactive waste. NUMO and JAEA set up a technical commission to investigate sealing technology in a repository in 2004 following a cooperation agreement between these two organisations. The objectives of this commission were to present a concept of sealing performance required in the disposal system and to direct future R&D for design requirements of closure components (backfilling material, clay plug, etc.). Hydraulic analyses on tunnel intersections were carried out during the first year in 2004. This was expanded into a hydraulic analysis of a complete disposal panel with all tunnels during the second year in 2005. Since the model structure in 2005 was more complicated than the one used in 2004, the concept of equivalent permeability was adopted in and around each tunnel in the hydraulic analyses. Parameters used in the hydraulic analyses were installation positions of clay plugs, permeability of the backfilling material, permeability of disposal tunnel and directions of hydraulic gradient to estimate influences to the analytical results preliminary. Analytical results showed that flow rate in a disposal tunnel was influenced by directions of hydraulic gradient, installation of the clay plug at the both ends of each disposal tunnel and permeability of the main tunnel.

Journal Articles

EBS modelling for the development of repository concepts tailored to siting environments

Ishiguro, Katsuhiko*; Ueda, Hiroyoshi*; Wakasugi, Keiichiro*; Sakabe, Yasushi*; Kitayama, Kazumi*; Umeki, Hiroyuki; Takase, Hiroyasu*

Engineered Barrier Systems (EBS) in the Safety Case; The Role of Modelling, p.167 - 180, 2007/02

Japanese siting approach calls for volunteer host municipalities for an HLW repository and places particular emphasis on design flexibility. The repository concept should be developed to be tailored to the given siting environments. Starting from the H12 repository concept, NUMO has been examining a range of possible repository design options including EBS. The requirements and strategy of model development for performance assessment and process understanding have been discussed taking into account the step-wise, iterative process of development of repository concepts. The areas further to develop the models and databases in the long-term R&D programme have been identified as a wish list in order to evaluate a range of potential repository concepts, focusing on the near-field for the early stages of development process. Among the issues in the list, NUMO has started the development of a flexible computer code for three-dimensional mass transport model to evaluate various design options and components of the EBS. This tool has been applied for the analysis of the barrier effects of the tunnel plugs placed in fractured rock media.

Journal Articles

The Japanese approach to developing clay-based repository concepts; An Example of design studies for the assessment of sealing strategies

Sugita, Yutaka; Fujita, Tomoo; Takahashi, Yoshiaki*; Kawakami, Susumu; Umeki, Hiroyuki; Yui, Mikazu; Uragami, Manabu*; Kitayama, Kazumi*

Physics and Chemistry of the Earth, 32(1-7), p.32 - 41, 2007/00

 Times Cited Count:6 Percentile:20.97(Geosciences, Multidisciplinary)

The H12 repository concept for vitrified high-level radioactive waste was developed based on a multi-barrier system with the emphasis on robust engineered barrier performance to ensure its feasibility for a wide range of geological conditions typically observed in Japan. The buffer is clay-based and plays a very important role in the engineered barrier system (EBS). The decision to use a volunteer siting process requires maximum flexibility of the repository concept to allow it to be adapted to potential sites and hence a wide range of variants of the basic H12 repository design has been developed. In order to evaluate the feasibility and the applicability of different repository options to specific siting environments, NUMO has established a set of "design factors" which classify the aspects that need to be considered when evaluating the pros and cons of different repository options. A Na-type bentonite from Japan is used as the reference material for all clay-based repository components (buffer, backfill, clay plug, etc.). The characteristics of this bentonite (thermal, mechanical, chemical, hydraulic) have been examined with consideration of various practical constraints (limitation on the repository footprint, the influence of saline water, the interaction of hyperalkaline leachates and practical working environment, etc.). Clay-based seals, which close off the tunnels after emplacement of the EBS, may also be key components for assessment of the repository. Full analyses considering all engineered barrier components (buffer, backfill, clay plug, concrete lining, tunnel, concrete plug, host rock) that may be used in a repository will be an essential future task. As a first step towards this goal, a numerical analysis focusing on hydraulic behaviour at the intersections of the disposal tunnels and the main tunnel is presented to illustrate how the design requirements of clay-based seals can be determined.

Journal Articles

Alternative repository design concepts for HLW disposal; Challenges and initiatives

Masuda, Sumio*; Kawamura, Hideki*; McKinley, I. G.*; Kitayama, Kazumi*; Umeki, Hiroyuki

Proceedings of Radioactive Waste Management; The Next Step: Confidence, Safety and Implementation, 8 Pages, 2006/06

Many of the "standard" designs for deep geological radwaste repositories were developed decades ago and have altered little since. Changing boundary conditions - both technical and socio-economic - are driving increasing interest in the consideration of alternatives, particularly for disposal of higher activity and longer-lived wastes. This was particularly the case in Japan, following the decision by NUMO to proceed with site selection based on a volunteering process. The work by NUMO to examine alternatives provides a good illustration of the range of possibilities which are available to allow flexible tailoring of design to fit both the characteristics of volunteer sites and the desires of local communities. On an even larger scale, however, the 21st century can be expected to bring challenges that will affect the future nuclear power generation at both national and global levels. As repository project are planned and implemented over timescales of many decades, such uncertainties should be taken into account to ensure that waste disposal projects initiated now remain appropriate to the future generations who will build, operate and close them.

Journal Articles

Judging compliance of ${it ambiguous}$ PA results against safety criteria with inherent ${it vagueness}$

Umeki, Hiroyuki; Naito, Morimasa; Kitayama, Kazumi*; Takase, Hiroyasu*

Proceedings of 10th International Conference on Environmental Remediation and Radioactive Waste Management (ICEM '05) (CD-ROM), 6 Pages, 2005/09

In this paper, ambiguity of our knowledge required toundertake PA and vagueness associated with the judgment of compliance to safety criteria are characterised through a seriesof expert elicitations. Furthermore optimisation of the way ofpresenting PA results with uncertainties is discussed in the light of the generalised safety margin that is defined based onpossibility theory.

Journal Articles

A Structured approach for stepwise tailoring of repository concepts to volunteer sites

Kitayama, Kazumi*; Umeki, Hiroyuki; Ueda, Hiroyoshi*; Mckinley, I. G.*; Kaku, Kenichi*

Proceedings of 10th International Conference on Environmental Remediation and Radioactive Waste Management (ICEM '05) (CD-ROM), 5 Pages, 2005/09

NUMO has been developing a structured approach to the entire stepwise repository development process. This includes both a bottom-up procedure for analysing the applicability of particular repository components (or sub-systems) within the range of expected site characteristics and a top-down multi-attribute analysis approach for comparing alternative disposal concepts or siting options.

Journal Articles

Status of Disposal Technology Development for High-Level Radioactive Waste Repository

Kitayama, Kazumi*; Yui, Mikazu

Nihon Genshiryoku Gakkai-Shi, 45(12), p.787 - 797, 2003/00

 Times Cited Count:1 Percentile:10.94(Nuclear Science & Technology)

The report introduces the engineering technologies for geological disposal of high-level radioactive waste. The contents of the report are current status of the technologies on design and assessment of long-term behavior of the engineered barrier, and design, construction, operation and closure of a repository, based on the concept of geological disposal.

Journal Articles

Microstructural Modeling of Compacted Sodium-Bentonite and Application of Unified Molecular Dynamics/Homogenization Analysis for Diffusion Process

Suzuki, Satoru; Fujishima, Atsushi; Ueno, Kenichi; Ichikawa, Yasuaki*; Kawamura, Katsuyuki*; Fujii, Naoki*; Shibata, Masahiro; Sato, Haruo; Kitayama, Kazumi*

Nendo Kagaku, 41(2), p.43 - 57, 2001/12


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