Ongoing and planned fuel safety research in NEA member states - Compiled from SEGFSM Members' Contributions

This report is in response to an action placed on SEGFSM members to compile ongoing and planned fuel safety research in NEA member states with the aim of providing CSNI an overview on related R and D international programmes and projects, along with the identification of current and future needs and priorities. A questionnaire was distributed to SEGFSM members on 18 October 2000, requesting them to identify fuel safety research programmes and to provide information on achievements and future plans. The questionnaire required respondents to provide information on the ongoing R and D programmes under the following headings: Title; Research Laboratory/Sponsor(s); Objectives/Goals; Status of Work; Brief description/presentation of the main results achieved; Future plans; References. Replies were received from organizations in the following countries: Belgium, Canada, Czech Republic, France, Germany, Hungary, Japan, Korea, Norway (Halden Reactor Project), Sweden, Switzerland, United Kingdom, USA. The report is based on the information provided in the replies received, as a consequence it cannot be viewed as comprehensive; programmes may well be in progress in addition to those detailed here. It is also possible that the detailed results of some programmes may remain proprietary and therefore not available in the short term. The report is organized in topic sections relating to: fuel and clad studies, integral fuel rod tests and PIE, LOCA and RIA studies including whole rods and bundles as well as single effects studies of fuel and cladding, code development for both steady state and transient fuel behaviour, thermal hydraulics, reactor physics codes and finally severe accident studies. The main issues for the current generation of reactors are those of high burn-up performance in normal operations, LOCA and RIA conditions and the main goal for the industry is to consolidate the safety issues to bring all countries up to a licensed discharge burn-up of ∼60 MWd/kg in assembly average and possibly 65 MWd/kg. The principal issues requiring attention can be broken down as follows: Normal operation: - fission gas release and rod over-pressure, - properties of the High Burn-up Structure (HBS) at the pellet rim, its effect on thermal performance and fission gas release, - cladding oxidation, hydriding and embrittlement. Loss of Coolant Accidents (LOCA) - the possibility of fuel slumping into the ballooned region; the effect of fuel-clad bonding at high burn-up, - increase of pressure in the ballooned region due to fission gas release from slumped fuel, - response of irradiation hardened and hydride embrittled cladding. - review of the 17% Equivalent Clad Reacted (ECR) criterion, Reactivity Initiated Accidents (RIA) - PCMI (Pellet-Clad Mechanical Interaction) loading mechanism(s) on the cladding, the effect of the HBS at the pellet rim, - effect of HBS on fuel dispersal, - response of embrittled cladding to transient PCMI. In addition to these, for those countries that load both MOX and UO2 fuelled assemblies, there is a requirement to bring the MOX database to the same level as that for UO2 fuel with the aim of treating MOX indistinguishably from that of UO2 as far as safety is concerned. The survey of international research programmes outlined in the report demonstrates the large element of activity to address these issues. When put together, the individual programmes add up to a tremendous effort in both time and money and will ultimately lead to a much better understanding of materials and component behaviour in a wide range of postulated scenarios