Determination of burnup limit for CANDU 6 fuel using Monte-Carlo method

• Published in: Nuclear engineering and technology 2021, 53(3), , pp.901-910
• Main Author: Lee, Eun-ki
• Format: Article
• Language: English
• Subjects: 37 M; 95/95; Burnup limit; CANDU-6; Monte-Carlo; 원자력공학
• ISSN: 1738-5733; 2234-358X
• DOI: 10.1016/j.net.2020.07.033

KHNP recently has obtained the approval for the commercialization of the modified 37-element (or 37 M) fuel bundle and now is loading the 37 M fuel bundles in CANDU-6 reactors in KOREA. One of the main issues for approval was the burnup limit. Due to CANDU design and neutronic characteristics, there was no specific burnup restriction of a fuel bundle. The absence of a burnup limit does not mean that a fuel bundle can stay in the CANDU reactor without a time limit. However, the regulator requested traditional design values as well as the burnup limit reflecting the computer code uncertainty. The method for the PWR burnup limit was not applied to the CANDU fuel bundle. Since there was no approved methodology to build the burnup limit with uncertainties, KHNP introduced a Monte-Carlo method coupled with a 95/95 approach to determine the conservative burnup limit from the viewpoint of the centerline temperature, internal pressure, strain measurement deviation. Moreover, to consider the uncertainties of various computing models, a converted power uncertainty was introduced. This paper presents the methodology and puts forward the limits on burnup, evaluated for each of the existing and modified fuel bundles, in consideration of the pressure tube aging condition.