Potential failure of steam generator tubes following a station blackout
The U.S. Nuclear Regulatory Commission is considering changes to pressurized water reactor (PWR) requirements relating to steam generator tube plugging and repair criteria, including leakage monitoring. The proposed changes are known as the alternate tube plugging criteria (APC) and are intended to permit PWRs to operate with through-wall cracks in steam generator tubes subject to meeting a specified limit on predicted primary to secondary leakage under accident conditions. To assess the consequences of the alternate plugging criteria, analyses were performed for a station blackout sequence in which the reactor core melts while the reactor coolant system (RCS) remains at high pressure. Evaluations were conducted to investigate the potential for tube failure with and without secondary system depressurization. The excessive heat coupled with the high-pressure differentials across the steam generator tubes could result in creep rupture failure of the tubes during a severe accident, which could lead to a radiological release directly to the environment. In order to assess the safety significance of the APC, it is important to identify the level of steam generator tube leakage that can occur without challenging the previous study conclusions that steam generator creep failure will not occur prior to a surge line or hot-leg failure. To assess the effect of leakage on steam generator tube integrity during a core melt sequence with the RCS at high pressure and the secondary side of the steam generators pressurized and depressurized, an analysis was performed for a core melt event resulting from an unmitigated station blackout to identify the total steamenerator and tube leakage flow rates that could induce tube ruptures prior to other RCS boudary faliures that could depressurize the RCS.
- OSTI ID:
- 89347
- Report Number(s):
- CONF-941102--
- Journal Information:
- Transactions of the American Nuclear Society, Journal Name: Transactions of the American Nuclear Society Vol. 71; ISSN 0003-018X; ISSN TANSAO
- Country of Publication:
- United States
- Language:
- English
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