1er mai 2018
Avec le réacteur à l’arrêt en mode 5, à 15 h 51 le 5/1/2018, un signal de surpression de niveau 1 de cuve de réacteur ( Reactor Pressure Vessel : RPV) a été reçu alors qu’il n’y a pas eu de changement effectif du niveau d’eau. Ce niveau resté correct a permis le maintien des opérations de rechargement en combustible.
Le signal intempestif a entrainé le démarrage du groupe électrogène diesel.
La pompe d’extraction de chaleur résiduelle, qui était en mode de refroidissement, a été perdue pendant la tombée du bus électrique. Elle a été réalimenté par la réalimentation de ce bus.
Lors du problème de perte de refroidissement à l’arrêt, il y a eu une augmentation de température d’environ 5 degrés Fahrenheit.
L’origine du signal intempestif fait l’objet d’une enquête.
▸ Type : BWR Mark3 - Puissance : 3 898 MWth - Première divergence : 08 / 1982 -
Available in english only
Event Number : 53374
Facility : GRAND GULF - State : MS Unit : [1] - RX Type : [1] GE-6
Event Date : 05/01/2018 - Event Time : 15:51 [CDT]
Emergency Class : NON EMERGENCY 10 CFR Section : 50.72(b)(2)(iv)(A) - ECCS INJECTION 50.72(b)(3)(iv)(A) - VALID SPECIF SYS ACTUATION 50.72(b)(3)(v)(B) - POT RHR INOP
Initial PWR : 0 % Current PWR : 0 %
Event Text
PLANT RECEIVED DIVISION ONE REACTOR PRESSURE VESSEL LEVEL 1 SIGNAL
"At 1551 hrs [CDT] on 5/1/2018, with the plant in Mode 5, a division one Reactor Pressure Vessel (RPV) Level 1 signal was received ; however there was no actual change in RPV level.
RPV Level remained at High Water Level supporting refuel operations.
This caused an actuation of division one Load Shed and Sequencing system that shed and then re-energized the 15 bus. Division one diesel generator started from standby.
Residual Heat Removal pump ’A’, which was in shutdown cooling mode, was lost during the bus shed, and was re-sequenced upon re-energization of the 15 bus.
Upon restoration of shutdown cooling, the RHR pump discharged into the RPV. RCS temperature increased approximately 5 degrees Fahrenheit as a result of the loss of shutdown cooling. The cause of the actuation signal is under investigation. In accordance with NUREG 1022, Event Reporting Guidelines, this event is conservatively reported under 10 CFR 50.72(b)(2)(iv)(A) as an event that results in emergency core cooling system discharge into the RCS as a result of a valid signal, under 10 CFR 50.72(b)(3)(iv)(B)(8) as an event that results in the actuation of emergency ac electrical power systems, and under 10 CFR 50.72(b)(3)(v)(B) as an event or condition that at the time of discovery could have prevented the fulfillment of a safety function (remove residual heat)."
The licensee notified the NRC Resident Inspector.
https://www.nrc.gov/reading-rm/doc-collections/event-status/event/2018/20180501en.html
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