13 mars 2013
Des réservoirs de stockage de liquide de veille (SLC) avaient été jugés capables de résister à un séisme : il a été établi qu’ils ne résisteraient à un séisme qu’à la condition d’être... vides !
1ère divergence : février 1974 - 774 MW net - Type : BWR-MARK 1
Available in english only.
Facility : COOPER - State : NE - Unit : [1] RX Type : [1] GE-4
Event Date : 03/13/2013 - Event Time : 17:26
Emergency Class : NON EMERGENCY 10 CFR Section : 50.72(b)(3)(v)(C) - POT UNCNTRL RAD REL 50.72(b)(3)(v)(D) - ACCIDENT MITIGATION Initial PWR : 100 % Current PWR : 100 %
Event Text
LOSS OF REASONABLE ASSURANCE OF OPERABILITY FOR STANDBY LIQUID CONTROL TANK
"Information Notice IN 2012-01 on seismic qualification of Standby Liquid Control (SLC) tanks was evaluated in 2012 to assess immediate operability of the SLC system based on SLC Test Tank and Mixing Tank not being qualified to Seismic Class 1S. Based on calculation NEDC 12-015 in response to IN 2012-01, [Cooper Nuclear Station] CNS concluded that SLC was still operable with the test tank full. Long-term actions from the 2012 condition were completed by issuance of calculation NEDC 13-010 and evaluation EE 13-009. NEDC 13-010 concludes that the SLC storage tank is qualified when full and the test tank and mixing tank are qualified when empty.
"No procedure step existed in the SLC surveillances to ensure the test tank is drained prior to restoration of SLC to an operable status to ensure it remained fully qualified to its NEDC 13-010 design. Further, no Caution Order or Standing Order existed to ensure short-term control until a procedure change could be implemented. So, as a short-term action, CNS implemented a Standing Order to establish positive control of the test tank. The Standing Order directs that SLC be declared INOPERABLE if the Test Tank is filled.
"Initially, this was thought to be a conservative measure only, because CNS judged that reasonable assurance of OPERABILITY remained due to conservative assumptions in NEDC 13-010. However, on 3/19/13 at 2146 CDT, the Prompt Operability Determination was changed to credit the Standing Order as a compensatory measure needed to maintain or enhance OPERABILITY of SLC. Therefore, CNS had lost reasonable assurance of OPERABLITY as of 03/13/2013 at 1726 CDT when the Control Room was notified that NEDC 13-010 concluded the test tank and mixing tank had to be empty to preserve the required seismic qualification, and an 8-hour report should have been made prior to 0126 CDT on 03/14/2013.
"Currently the SLC Test Tank is drained and SLC is OPERABLE."
The licensee has notified the NRC Resident Inspector.
https://www.nrc.gov/reading-rm/doc-collections/event-status/event/2013/20130329en.html
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