Sensitivity Analysis on Safety Functions of Engineered and Natural Barriers for Fuel Debris Disposal
- PDF / 274,935 Bytes
- 6 Pages / 432 x 648 pts Page_size
- 20 Downloads / 185 Views
Sensitivity Analysis on Safety Functions of Engineered and Natural Barriers for Fuel Debris Disposal Taro Shimada1, Yuki Nishimura1 and Seiji Takeda1 1 Nuclear Safety Research Center, Japan Atomic Energy Agency, 2-4 Shirakata, Tokai-mura, Ibaraki, 3191195, JAPAN. ABSTRACT A disposal measure for fuel debris generated at the accident in the Fukushima Daiichi Nuclear Power Station has been studied so far. However, physical and chemical properties of the fuel debris located in reactor containment vessels have not yet been obtained. In order to investigate the safety function of barriers required for disposal of fuel debris, sensitivity analysis for radionuclide migration was carried out, considering with uncertainty of the properties. As a result, it is indicated that it was important for evaluation of fuel debris disposal to obtain the physical and chemical properties of 14C and 129I during release to groundwater, in addition to 238 U. INTRODUCTION A disposal measure for fuel debris generated at the accident in the Fukushima Daiichi Nuclear Power Station has been studied so far. Samples of the fuel debris located in reactor containment vessels in unit 1, 2 and 3 have not been obtained, while the investigation inside the containment vessel has been tried using some robots with remote controlled. Some data on leaching ratio of actinide elements and fission products from simulated fuel debris into seawater were obtained [1, 2]. However, physical and chemical properties of the actual fuel debris have not yet investigated. In order to investigate the safety function of barriers required for disposal of the fuel debris, sensitivity analysis for uncertainties of properties of the fuel debris was carried out under the geological disposal conditions the same as high-level vitrified radioactive wastes (HLW), because the disposal measure was unknown. METHODOLOGY The procedure of sensitivity analysis of radionuclides migration to investigate the barrier function necessary for fuel debris disposal consisted of two parts. Firstly, temporal changes of migration fluxes at the boundaries of engineered barrier and natural barrier for a standard case were calculated by GSRW-PSA [3] using the parameters determined for the fuel debris, engineered barrier and natural barrier. Next, sensitivity analysis was carried out considering with the uncertainties of leaching behavior of radionuclides in the waste form, the design of engineered barrier, and migration parameters in comparison of max values of migration fluxes for representative radionuclides such as 238U, 79Se, 135Cs, 14C and 129I. In this study, the leaching behavior of radionuclides from the fuel debris was treated as follows. At the accident fuel debris was generated after UO2 pellet, clad, control rods and reactor internals were melted, mixed and solidified by cooling. It was considered that nuclides in the fuel debris existed in inhomogeneous media such as porous configuration. Nuclides in the solidified matrix may be gradually released into groundwater controlled by dissolution of
Data Loading...
