Improvement of biosphere model for performance assessment of geological disposal system (II)

Ikeda, Takao*; Yoshida, Hideji*

In the safety assessment of the high level radioactive waste (HLW) disposal system, it is inevitable to evaluate the radiological effects to human in the biosphere. This is because the biosphere is a field through which repository-derived radionuclides would migrate by several processes and those radionuclides would finally have an effect to human. The Japan Nuclear Cycle Development Institute (JNC) has so far developed the robust and comprehensive model / analytical code and surveyed the relevant data applicable to the assessment of several kinds of biosphere condition based on the survey and review of the "Reference Biosphere Methodology" developed and enhanced in the International Programme on Biosphere Model validation Study (BIOMOVS) and the International Programme on on Biosphere Modelling and Assessment Methods (BIOMASS). In the study of the last year, the biosphere model developed so far has been revised and refined, and using this new model the migration and accumulation of radionuclides and those effects to human has been evaluated, in order to reflect the results to the H12 assessment for HLW disposal in Japan. Thus this study, a specific reference biosphere has been developed using an approach, which is consistent with the above mentioned reference biosphere methodology. For FY97 consideration was given to groundwater release to a deep well. For FY98 consideration is being given to groundwater releases to river and inter-tidal geosphere-biosphere interfaces. The key sequential stages of the approach are listed below. (1)Development of the assessment context. (river and inter-tidal zone) (2)Description of the biosphere system. (3)Identification and initial screening of Features, Events and Processes (FEPs). (4)Identification of FEP relationships and development of conceptual model. (5)Specification of mathematical model and associated parameters values. (6)Implementation of analyses.