Stainless Steel as a Replacement for Beryllium as Braze Material

Abstract

Beryllium is currently used as the filler metal for brazing appendages on CANDU® fuel elements. Because of its toxicity, occupational exposure limits for Be have been reduced to very low levels. To address this significant challenge, the CANDU Owners Group initiated the Be Replacement Test Program with the objective of identifying a filler material to replace Be that meets the established technical requirements for CANDU fuel. Based on out-reactor testing of a number of candidate materials, stainless steel (SS316) was chosen to advance to the irradiation testing phase. Several fuel elements brazed with either SS316 or Be were manufactured for irradiation testing in NRU. After achieving burnups of 180 MWh/kgHE, the elements were subjected to post-irradiation examination, which showed that the performance of the SS316-brazed elements was similar to that of the Be-brazed elements. A higher rate of hydrogen pickup was observed for the SS316-brazed joints, however, mechanical testing of the irradiated joints indicated that this does not constitute a fuel performance issue. Therefore, this program has demonstrated that SS316 is a suitable replacement braze filler material to Be.