NUREG-1749, Implications From the Phenomenon Identification and Ranking Tables (PIRTs) and Suggested Research Activities for High Burnup Fuel

Phenomenon identification and ranking tables (PIRTs) were developed by an international group of fuel experts for three postulated accident types that are important in plant safety analysis. Rankings were determined with regard to cladding damage and fuel dispersal for high-burnup fuel rods. Developing PIRTs is a structured way of obtaining expert opinions to help improve computer codes and to conduct experimental programs related to the accidents being considered. The PIRT tables and associated information are documented in three large reports, but those reports do not contain conclusions because of the way the activity was structured. In the present report, conclusions are reached based on rankings and rationales in the PIRT documents, transcripts from the PIRT meetings, and notes. Implications of the phenomenon rankings are discussed, and methods of resolving issues related to fuel damage limits are outlined. Resolution of these issues for approved fuel types and the current burnup limit of 62 GWd/t are expected to be completed in the 2003-2005 time frame within NRC's confirmatory research program. This report was prepared by NRC's Office of Nuclear Regulatory Research and does not necessarily represent the views of any individual PIRT expert or the group as a whole.