Fig. 4-11 Multibarrier concept for HLW disposal The vitrified HLW will be disposed of into a deep, stable rock mass with thick containers and surrounding buffer material. The disposal system consists of a series of engineered and natural barriers that retard radionuclide migrations (multibarrier concept).

Fig. 4-12 Evaluated individual dose The repository is assumed to be constructed in a homogeneous rock mass surrounded by fracture zones. The migration path lengths in the homogeneous rock mass are in the range from 100 to 500 m. In the fracture zones they are 1000 m. The individual dose due to the ingestion of drinking water was calculated. The committed dose equivalent from each radionuclide is on the order of 0.1 micro-Sv. This value is quite low when compared to doses due to natural radiations.

The safety of high-level radioactive waste (HLW) disposal is one of the essential assurances needed to realize the nuclear fuel cycle. High-level radioactive waste will be disposed of into a deep, stable rock mass at a depth of several hundred meters. The disposal system consists of a series of engineered and natural barriers (multibarrier system) that will isolate radionuclides effectively and retard radionuclide migrations to the environment. JAERI has developed an integrated computer code system, GSRW, that evaluates the dissolution of radionuclides from a vitrified HLW, radionuclide migrations through engineered and natural barriers by groundwater flow, transport in the biosphere, and the resulting radiological consequence to the public. Safety analyses were performed on the reference disposal system that involves HLW corresponding to 16,000 MTU of spent fuels. The individual dose due to the exposure pathway of ingesting drinking water was calculated using conservative values of geochemical parameters. This is shown in Fig. 4-12. The committed dose equivalent calculated here is on the order of 0.1micro-Sv. This will be a smaller value in a realistic situation because radionuclides will be fixed on minerals in the geologic media. Thus, the geologic disposal of HLW may be feasible if the disposal conditions assumed here remain unchanged throughout the periods assessed here.

Reference H. Kimura, et al., Safety and Sensitivity Analyses of a Generic Geologic Disposal System for High-level Radioactive Waste, JAERI-Research 94-028 (1994).

Select a topic in left column