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Nuclear Event – RCS leakage (Emergency Declared): Prairie Island Nuclear Power Plant – Unit 1, Minnesota

2016/08/15

North America – USA | State of Minnesota, Welch, Prairie Island Nuclear Power Plant
Location: 44°37’18.0″N 92°37’59.0″W
Present Operational Age: ~44 years
Event: UNUSUAL EVENT – EMERGENCY DECLARED

Nuclear Event in USA on Saturday, 13 August, 2016 at 23:59 [CDT].

UNUSUAL EVENT DECLARED DUE TO EXCESSIVE REACTOR COOLANT SYSTEM LEAKAGE

Prairie Island Unit 1 declared an Unusual Event at 2359 CDT on 8/13/2016 based on Reactor Coolant System (RCS) identified leakage being greater than 25 gpm. The RCS leakage was 40 gpm for three (3) minutes. The RCS leakage was stopped when letdown flow was isolated. Minimum charging flow has been established and Excess Letdown was placed in service. Prairie Island Unit 1 is currently stable and continues to operate at 100 percent power. There was no impact on Prairie Island Unit 2.

“CV-31339 (Letdown Line Containment Isolation Valve) failed closed. VC-26-1 (Regenerative Heat Exchanger Letdown Line Outlet Relief to Pressurizer Relief Tank [PRT]) lifted with 40 gallons per minute to the PRT for three (3) Minutes. Operators entered procedure 1C12.1 AOP3, Loss of Letdown Flow to VCT. Letdown was isolated per 1C12.1 AOP3, relief valve VC-26-1 reseated and leakage to the PRT stopped. Charging flow was reduced to one (1) charging pump at minimum speed (16 GPM). Excess letdown was placed in service to maintain pressurizer level between 32 – 34 percent. The cause for CV-31339 closing has not yet been determined.

“The NRC Resident Inspector has been notified.”

Notified DHS SWO, FEMA Ops Center, DHS NICC. Notified FEMA National Watch and Nuclear SSA via E-mail.

* * * UPDATE FROM PAUL FINHOLM TO DONALD NORWOOD AT 0525 EDT ON 8/14/2016 * * *

“At 0329 CDT the Notice of Unusual Event was terminated based on confirmation that conditions meet all termination criteria. RCS conditions are stable. RCS leakage is less than Technical Specification limits. The current value [of RCS identified leakage] is 0.038 gpm. No classification criteria is currently met.

“The NRC Resident Inspector has been notified.”

Notified R3DO (Kozak), NRR EO (Miller), and IRD (Stapleton). Notified DHS SWO, FEMA Ops Center, DHS NICC. Notified FEMA National Watch and Nuclear SSA via E-mail.

Source: NRC  Event Number: 52178

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