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Abstracts
steel. Using the experimental data obtained by previous studies, the pHd was defined as a function of four factors shown
in equation (1), where the activity of proton ion ([H+]) for pHd is assumed to be a linear combination of the logarithms of
the total carbonate concentration (C total), the chloride ion concentration (Cl-), and the limiting current density of
dissolved oxygen diffusion (iO2), and the inverse of absolute temperature of contacting solution (T). The derived
equation fitted well experimental data from previous studies.
20) 40124 – Trends in Scenario Development Methodologies and Integration in NUMO's Approach
Takeshi Ebashi, Katsuhiko Ishiguro,NUMO (Japan); Keiichiro Wakasugi, JAEA (Japan);
Hideki Kawamura, Obayashi Corporation (Japan);
Irina Gaus, Stratis Vomvoris, Andrew Martin, Nagra (Switzerland);
Paul Smith, Safety Assessment Management (UK)
The development of scenarios for quantitative or qualitative analysis is a key element of the assessment of the safety
of geological disposal systems. As an outcome of an international workshop attended by European and the Japanese
implementers, a number of features common to current methodologies could be identified, as well as trends in their
evolution over time. In the late nineties, scenario development was often described as a bottom-up process, whereby
scenarios were said to be developed in essence from FEP databases. Nowadays, it is recognised that, in practice, the
approaches actually adopted are better described as top-down or "hybrid", taking as their starting point an integrated
(top-down) understanding of the system under consideration including uncertainties in initial state, sometimes assisted by
the development of "storyboards". A bottom-up element remains (hence the term "hybrid") to the extent that FEP
databases or FEP catalogues (including interactions) are still used, but the focus is generally on completeness checking,
which occurs parallel to the main assessment process. Recent advances focus on the consistent treatment of uncertainties
throughout the safety assessment and on the integration of operational safety and long term safety.
21) 40137 – Development of Methodology to Construct a Generic Conceptual Model of River-valley Evolution
for Performance Assessment of HLW Geological Disposal
Makoto Kawamura, Kenichi Yasue, Tadafumi Niizato, Shin-ichi Tanikawa, JAEA (Japan)
In order to assess the long-term safety of a geological disposal system for high-level radioactive waste (HLW), it is
important to consider the impact of uplift and erosion, which cannot be precluded on a timescale in the order of several
hundred thousand years for many locations in Japan. Geomorphic evolution, caused by uplift and erosion and coupled to
climatic and sea-level changes, will impact the geological disposal system due to resulting spatial and temporal changes
in the disposal environment. Degradation of HLW barrier performance will be particularly significant when the remnant
repository structures near, and are eventually exposed at, the ground surface. In previous studies, river erosion was
identified as the key concern in most settings in Japan. Here, therefore, we present a methodology for development of a
generic conceptual model for performance assessment based on best current understanding of river erosion in Japan.
Critical considerations that have to be taken into account when interpreting the geological record of past river-valley
evolutions, as preserved in ancient fluvial deposits, include: 1) the spatial variation in the relative significance of erosion
and sedimentation at any time between upper- and lower-reaches of rivers originating in mountainous terrain 2) the
temporal variation in the extent of erosion / sedimentation at any specific location during glacial / interglacial cycles 3)
the balance between uplift and vertical erosion as a result of the hardness of the riverbed rock 4) the balance between
vertical and lateral erosion – ranging from formation of narrow gorges to wide meandering flood plains 5) the varying
duration and intensity (as assessed by sea level change) of past glacial / interglacial cycles.
Interpretation of the impact of such phenomena at relevant locations in Japan has led to development of a generic
conceptual model which contains the features typical of mid-reach rivers. This paper presents the methodology to
develop the conceptual model, identifies the simplifications and uncertainties involved and assesses their consequences in
the context of repository performance. Details of resultant analyses using this conceptual model will be discussed in
another paper presented in ICEM’10 by Miyahara et al.
22) 40176 – Structural Integrity Evaluation Approach for PWR Spent Nuclear Fuel
Yun Seog Nam, Seong Ki Lee, Yong Hwan Kim, Jeon Kyeong Lak,
Choi Ki Sung, Chang Sok Cho, KNF (Korea Rep.)
PWR fuel assembly experiences many changes from the time it is manufactured, loaded in the reactor and
repositioned in the core several times until finally removed from the reactor for the interim storage, reprocessing or final
disposal etc. Under a severe radiation and a thermo-mechanical condition, this mechanism can alter fuel assembly
characteristics such as its mechanical properties, geometrical shape, material characteristics etc. Any of these alterations
which impact spent nuclear fuel (SNF) integrity should be considered to design a cask/canister for its transportation or
intermediate dry storage. Regarding the cask/canister design, there could be a freedom to design a system that mitigates
the forces transmitted to SNF and fuel rods. If the storage cask/canister or transport package design prevents or mitigates
forces transmitted to its contents such that structural integrity is not significantly compromised, the detailed SNF
properties are necessary to make a decision of the elaborated design parameters, assuming other factors (temperature,
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