Long-term storage of spent nuclear fuel -Survey and recommendations

摘要

The group discussions were held under the perspective of extensions to existing storage periods and both UO_2 and MOX fuel reaching higher burnup by means of advanced materials. Up to now, the nuclear industry worldwide has accumulated significant fuel storage operating experience over the past 50 years. This experience is mainly based on wet storage systems, which have been found to be safe and effective. Wet fuel storage is now considered to be a mature technology. In comparison, dry storage is an evolving technology, which has been developed over the past 20 years. Under present boundary conditions, dry storage can also be regarded as an established technology. Unlike wet storage, dry storage can be more sensitive to fuel design changes and burnup increase because of higher storage temperatures; which give rise to thermally activated processes. The results of the group discussions can be summarized as follows: 1. In wet storage there exist no urgent questions to be solved with regard to increasing operating life times. However, some recommendations e.g. in the area of monitoring or technical optimization were made. 2. In dry storage, there also exists a certain amount of supporting technical data covering the burnup of the fuel loaded and the performance of the systems to date. For high burnup and MOX fuel an extension of the knowledge on the creep behavior of future cladding materials is needed. Additionally, a surveillance program could demonstrate the long time behavior of cask and fuel. For the development of advanced dry storage systems further R&D activities are needed such as system performance for the perceived duty. 3. The regulatory objectives are very similar for all member states. Regulatory concerns were identified in a number of areas; examples include: 1) How to handle technology changes, 2) Extrapolation of material behavior or performance for increasing storage duration.