The 13th International Conference on Environmental ... - Events

Abstracts
impact of uncertainties in a geological environment model is important to identify and prioritize key issues for further
investigations. <strong>The</strong>refore, a plan for site characterization should be made based on the results of the modeling. <strong>The</strong> aim of
this study is to support the planning of initial surface-based site characterization based on the technical know-how
accumulated from the Mizunami Underground Research Laboratory Project and the Horonobe Underground Research
Laboratory Project. <strong>The</strong>se projects are broad scientific studies of the deep geological environment that are a basis for
research and development for the geological disposal of high-level radioactive wastes. In this study, the work-flow
followed in developing the geological model, one of the geological environment models, and the related technical
know-how acquired from literature data have been summarized.
6) 40039 – <strong>The</strong> long-term stability of geological environments in the various rock types in Japan from the
perspective of uranium mineralization
Eiji Sasao, JAEA (Japan)
Long-term stability of the geological environment is one of the important keys for deep geological disposal of
high-level radioactive waste in the Japanese Islands due to their location in a tectonically active island-arc. Uranium
occurrences in Japan have been subjected to many geological processes inherent to the island-arc setting. Geological
environments associated with uranium mineralization are considered favorable for HLW disposal, because uranium
mineralization is considered a natural analogue of the radionuclides in HLW. Studies on the long-term stability of the
uranium mineralization in Japan can be instructive as these could provide useful information on the long-term stability of
the geological environment. Information on host rock and mode of occurrence of uranium mineralization was compiled
from published data. <strong>The</strong> mineralization occurs in these types of deposits, i.e., sedimentary formations, association with
metallic ore mineralization of magmatic origin and stratiform manganese mineralization, pegmatite, and alluvial placer
deposit. <strong>The</strong> mineralization occurs in various geological settings in Japan. This fact suggests that geological
environments suitable for geological isolation are widely distributed in the Japanese Islands, despite their location in a
geologically active area. This study will support building confidence in HLW disposal in the Japanese Islands.
SESSION D5: Measurement and Estimation
1) 40045 – Improvement of Radioactivity Inventory Evaluation Procedure In Preparatory Tasks for
Decommissioning
Ken-ichi Tanaka, Hidenori Tanabe, Hideaki Ichige, JAPC (Japan)
Preparatory tasks for decommissioning of nuclear power plant start with radiological characterization. Residual
radioactivity inventory evaluation is a main part of the characterization. Reliable information on the inventory is
important for specification for decommissioning plan. Japan Atomic Power Company (JAPC) has already started these
tasks for Tsuruga Nuclear Power Plant Unit 1 (TS-1). We can optimize decommissioning plan using the information. To
obtain the reliable information, we improved an evaluation procedure. <strong>The</strong> procedure is divided into two main steps. First
step is neutron flux distribution calculation and second one is radioactivity distribution calculation. Radioactivity
distribution is calculated using neutron flux distribution. In this work, we improved the evaluation procedure to obtain the
reliable information on the inventory Because of the limitation of computer resource, two-dimension (2D) approximation
model was applied to radioactivity distribution around Reactor Pressure Vessel (RPV). We can calculate reliable 2D
neutron flux distribution by having better understanding of neutron transport phenomena. Neutron flux was measured at
30 locations in TS-1 Primary Containment Vessel (PCV) using activation foils. And in order to understand the neutron
transport phenomenon inside the PCV, we also calculated neutron flux distribution with the three-dimensional (3D)
discrete ordinates method calculation (Sn) code. By consideration about the result of the measurement and 3D calculation,
we could understand the characteristics of the neutron flux distribution inside the PCV. To simulate the neutron flux
distribution well with 2D Sn code, neutron flux behaviors inside the PCV had been investigated with referencing the
measurement values and with observing calculated 3D neutron flux distribution. 2D calculation model had been modified
repeatedly until reliable calculation result was provided. After several model modifications, the reliable 2D calculation
was accomplished and important neutron transport phenomena that are necessary to simulate the neutron flux distribution
well was understood. Network-parallel-computing technique was applied to radioactivity distribution calculation. Using
this technique, we could calculate radioactivity at all space mesh points that were used with 2D Sn code and we obtained
the radioactivity distribution. By using this distribution, we can estimate a quantity of radioactivity around RPV more
accurately and optimize dismantling designs.
2) 40202 – Verification of Source Term Analysis System for Decommissioning Wastes from CANDU Reactor
Dong-Keun Cho, Gwang-Min SUN, Jongwon Choi, KAERI (Korea Rep.);
Donghyeun Hwang, Hak-Soo Kim, Tae-Won Hwang, KHNP (Korea Rep.)
<strong>The</strong>re are now twenty commercial nuclear power reactors operating as of May 2010 in South Korea. As nuclear
capacity becomes higher and installations age, the Korean government and industry have launched R&D to estimate
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