Derivation Methods of Clearance Levels for Nuclear Reactors

Abstract

The Nuclear Safety Commission (NSC) derived the unconditional clearance levels for concrete and metal arising from the operation and dismantling of nuclear reactors. The Japan Atomic Energy Research Institute conducted technical analyses to support the discussion by NSC. The clearance levels of 20 radionuclides were derived from 10μSv/y of individual doses by deterministic approach. In this approach, calculation models were established to assess individual doses resulting from 73 exposure pathways related to disposal and recycle/reuse, and realistic parameter values were selected considering Japanese natural and social conditions. The derived clearance levels of most radionuclides (e. g. γ-ray emitters such as ⁶⁰Co and α-ray emitters such as ²³⁹Pu) are nearly same as those shown in IAEA-TECDOC-855. However, some β-ray emitters such as ⁹⁹Tc and ¹²⁹I are smaller than those shown in IAEA-TECDOC-855.