3 octobre 2013
Le 10 août 2013, un conteneur de déchets radioactifs, dont la protection neutronique est constituée par de l’eau déminéralisée, a été découvert insuffisamment rempli de cette eau.
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Les personnels travaillant à proximité du conteneur défaillant étaient équipés d’appareils de mesure de neutrons et n’auraient pas dépassé les limites réglementaires.
Le 3 octobre 2013, le problème a été déclassé car l’Autorité de sûreté nucléaire américaine a jugé que, dans cette configuration précise, la déclaration n’était pas légalement nécessaire !
Les personnels exposés aux neutrons issus du conteneur défaillant seront surpris d’apprendre qu’ils ont des droits inférieurs aux travailleurs d’autres secteurs pour qui la défaillance de cet élément majeur mérite un classement.
Ce conteneur peut renfermer jusqu’à 61 assemblages combustibles de réacteurs à eau bouillante.
Independent Spent Fuel Storage Installation Event Number : 49263 Licensee : PPL SUSQUEHANNA LLC - City : ALLENTOWN - State : PA - County : LUZERNE
Event Date : 08/10/2013 - Event Time : 04:30 -
Emergency Class : NON EMERGENCY 10 CFR Section : 72.75(c )(2) - SPENT FUEL, HLW OR RX-REL GTCC RED. EFECT 72.75(d)(1) - SFTY EQUIP. DISABLED OR FAILS TO FUNCTION
Event Text
DEGRADED NEUTRON SHIELDING FOR A SPENT FUEL CASK
"PPL Susquehanna, LLC became aware of a reduction in the effectiveness of a spent fuel confinement system at 0430 [EDT] on Saturday August 10, 2013. One of the safety barriers in a spent fuel cask is the water filled volume of the cask which provides neutron shielding. This volume is normally filled with approximately 670 gal of demineralized water. It has been determined that the neutron shielding volume was not completely filled. The cask neutron shield volume is currently being filled. The loaded spent fuel canister is currently located in the reactor building on the refuel floor and has been located there for the duration of the event. Investigation is currently in progress concerning personnel radiation exposure. The lack of neutron shielding represents a significant reduction in the effectiveness of a spent fuel storage cask confinement system which is an 8 hour reportable condition under 10CFR72.75(c)(2). This also represents a dry fuel storage safety system that was disabled or failed to function which is a 24 hour reportable condition under 10CFR72.75(d)(1)."
The cask was a TransNuclear NUHOMS-61BTH. Personnel on the refuel floor were equipped with neutron dosimetry.
The licensee notified the NRC Resident Inspector and will notify the Commonwealth of Pennsylvania.
* * * RETRACTION AT 1609 EDT ON 10/3/2013 FROM DOUG LAMARCA TO MARK ABRAMOVITZ * * *
"At the time the original ENS notification was made, PPL Susquehanna, LLC had determined that a significant reduction in the effectiveness of a spent fuel storage confinement system had occurred, and that spent fuel equipment important to safety was disabled or failed to function as designed. This conclusion was reached because a loaded dry fuel storage transfer cask’s neutron water shield was found partially drained down.
"Subsequent to this event, an investigation concluded that the identified condition is not reportable in accordance with 10 CFR 72.75(c)(2) or 10 CFR 72.75(d)(1). Transnuclear’s Final Safety Analysis Report (FSAR), Chapter K.7 defines the 61BT dry fuel storage ’confinement system’ as those components which make up the dry shielded cask (DSC) and not the transfer cask. Therefore, the transfer cask neutron shield is not part of the confinement system and the reporting requirements of 10 CFR 72.75(c)(2) do not apply. In addition, Transnuclear FSAR drawing number NUH-03-8002-SAR, Rev. 8, Sheet 1 ’General License NUHOMS� ISFSI Onsite Transfer Cask Inner & Outer Shell Assembly’ defines the neutron shield components as ’not important to safety.’ Therefore, the TC neutron shield is not part of the dry fuel storage safety system and the reporting requirements of 10 CFR 72.75(d)(1) do not apply.’"
No personnel exposures exceeded regulatory limits.
The licensee notified the NRC Resident Inspector and will notify the state.
https://www.nrc.gov/reading-rm/doc-collections/event-status/event/2013/20131004en.html
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