10 mars 2018
Le problème est survenu lors de la fermeture de la soupape d’arrivée de vapeur. Cette vanne, située sur le circuit primaire, a été fermée afin d’isoler une fuite non identifiée. Sa fermeture a fait entrer le réacteur dans des paramètres de limitation de fonctionnement. L’isolation du coeur doit être obtenue sous une heure et la mise à l’arrêt du réacteur pour réparation est prévue pour le lendemain à 12 h. Ce système d’injection étant unique, il met en péril l’accomplissement de fonction de limitation des conséquences d’un accident. Lors du changement d’état de la soupape, la fuite du confinement d’origine non identifiée s’est accrue de 455 litres par heure pour atteindre 1 136 llitres par heure.
Type : Fukushima 1 (BWR Mark 1) - Puissance : 2 419 MWth - Première divergence : 2 / 1974 -
Available in english only
Event Number : 53253
Facility : COOPER - 4 State : NE
Unit : [1] - RX Type : [1] GE-4
Event Date : 03/10/2018 - Event Time : 07:09 [CST]
Emergency Class : NON EMERGENCY 10 CFR Section : 50.72(b)(3)(v)(D) - ACCIDENT MITIGATION
Initial PWR : 100 % Current PWR : 100 %
Event Text
HIGH PRESSURE COOLANT INJECTION SYSTEM DECLARED INOPERABLE
"HPCI [High Pressure Coolant Injection] was removed from service (unplanned) on 3/10/2018 at time 0709 [CST] by closing HPCI-MO-15, STEAM SUPPLY INBOARD ISOLATION. The inboard steam supply isolation valve is inside Primary Containment. The steam supply valve was closed in an effort to isolate [unidentified] leakage to Primary Containment from a suspected packing leak from HPCI-MO-15. After closing the HPCI-MO-15, Reactor Coolant System Leakage parameters returned to within Technical Specification [TS] LCO [Limiting Condition of Operations] 3.4.4 limits.
"Entered into Technical Specification LCO 3.5.1 Condition C - HPCI System Inoperable.
"Required Actions for Condition ’C’ are to verify by administrative means RCIC [Reactor Core Isolation Cooling] System is operable within 1 hour and restore HPCI System to operable status within 14 days. RCIC was verified operable by administrative means concurrent with declaration of HPCI inoperable.
"Normal plant shutdown activities are being planned [for 03/11/2018 at 1200 CDT] to support entry into Primary Containment to initiate any necessary repairs.
"HPCI is a single train safety system. This report is submitted as a condition that at time of discovery could prevent the fulfillment of the safety function of an SSC [System, Structure, or Component] needed to mitigate the consequences of an accident.
"This condition has been entered into the CNS [Cooper Nuclear Station] Corrective Action Program. CR-CNS-2018-01346"
LCO 3.4.4 was entered during unplanned maintenance of the HPCI system. When the HPCI-MO-15 was cycled from closed to open, unidentified leakage in the containment increased above 2 gallons per minute (gpm) in less than a 24 hour period. Also, total unidentified leakage exceeded 5 gpm. The licensee closed the HPCI-MO-15 valve resulting in a decrease in unidentified leakage below TS shutdown limit.
The NRC Resident Inspector was notified.
https://www.nrc.gov/reading-rm/doc-collections/event-status/event/2018/20180312en.html
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