CL-36 IN NUCLEAR WASTE-DISPOSAL .1. ASSESSMENT RESULTS FOR USED FUEL WITH COMPARISON TO I-129 AND C-14

Chlorine-36 in used fuel arises from the activation of Cl-35. Unlike I -129 and C-14, it was not immediately clear that Cl-36 would be presen t in significant quantities in used fuel, because Cl-35 would be prese nt only as a contaminant and little was expected because of the volati lity of Cl during the high-temperature sintering used in fuel producti on. With more intensive elemental analysis of reactor metals, Cl was o bserved, and the analyses were extended to include used fuel. Chlorine -36 was found. It was expected to behave much like I-129 and C-14; rap idly released from the wasteform, mobile in geological materials and b iologically important. This study assessed the impact of Cl-36 in nucl ear fuel waste and results are presented here relative to the other ra dionuclides. For radiological dose to humans and for chemical toxicity effects, Cl-36 has 20-fold less impact than I-129. For radiological d ose to non-human biota, Cl-36 exceeds I-129 for plants because of the markedly higher soil-to-plant transfer. Large isotopic dilution in the surface environments is the most important feature of dose estimation for Cl-36. All th, predicted impacts, however, are very small for the disposal concept for Canadian nuclear fuel waste. Crown Copyright (C) 1997 Published by Elsevier Science Ltd.