Use of fission gas release characteristics to identify type of fuel element failure in LMRs

The performance of liquid-metal reactor (LMR) metal fuel elements has been studied at the Experimental Breeder Reactor II (EBR-II) for >25 yr and valuable fission gas (FG) data have been accumulated from the very occasional fuel element failure. In addition, the run-beyond-clad-breach (RBCB) performance of metal fuel has been specifically studied since 1986. From May 1986 to the present, archived data were obtained from the data acquisition system at EBR-II with the specific intention of studying the FG release behavior of different types of metal fuel breaches. The slope of natural logarithm of release to birth ratio versus the logarithm of decay constant of seven FG isotopes (i.e., {sup 85m}Kr, {sup 87}Kr, {sup 88}Kr, {sup 133}Xe, {sup 135}Xe, {sup 135m}Xe, {sup 138}Xe) as a function of time along with their activity were calculated and plotted and distinct characteristics were observed for different types of failure, e.g., upper plenum versus fuel column failures. A description of the analytical methods used and a comparison of the FG release behavior of these type types of breach are presented in this paper.