Enhancement of the moderator subcooling margin using glass-peened calandria tubes in CANDU reactors

One of the important design features present in CANDU reactors is the cool heavy water moderator surrounding the assembly of horizontal fuel channels. The effectiveness of the moderator heat sink to ensure fuel channel integrity after pressure tube/calandria tube contact during postulated accident events in safety analysis is influenced primarily by the moderator subcooling at the time the contact would occur. Through the research and development program, AECL has developed an improved feature of the calandria tube: glass-peening the outside surface of the calandria tube. With an assessment of several full scale qualification contact boiling experiments using glass-peened calandria tubes, the better understanding of the contact boiling test results were achieved. Following that, the moderator subcooling required to ensure fuel channel integrity was derived, and the enhancement of the moderator subcooling margin using glass-peened calandria tubes in CANDU reactors was concluded. (author)