Safety analysis of engineered barrier in geologic disposal of high-level waste

In this report, the performance analysis for an engineered barrier system for high level radioactive waste disposal is described. The analysis was carried out by using simulation codes, CRANP, STARG 4 and GESPER/RAPRAN for overpack, waste glass and buffer material, respectively. GRANP indicated the life of general corrosion of a 25 cm thick carbon steel overpack is more than 10,000 years. The life of 1,000 years is set for later simulation. STRAG 4 showed the time of the complete dissolution of waste glass is more than a million years. GESPER indicated the migration rate of Np-237 in oxidized condition was much faster than that in reduced condition. RAPRAN showed the dominant nuclides were Am-243 and long-lived fission products of Cs-135 and Se-79. Comparative calculation was carried out to indicate the performance of the engineered barrier system. The normalized hazard at the edge point of geosphere having the migration length of 500 m was calculated for both cases of natural barrier only and having an engineered barrier system in addition. The peak hazard of Np-237, Cs-135, Tc-99 and Se-79 was reduced by the effect of an artificial barrier. (K.I.)