ML22172A164

Response to Public Follow-up Question Regarding Unit 1 Reactor Vessel Neutron Embrittlement Coupon Testing - June 21, 2022

ML22172A164
Person / Time
Site:	Diablo Canyon
Issue date:	06/21/2022
From:	Patricia Vossmar NRC/RGN-IV/DORS
To:
Vossmar P
References
Download: ML22172A164 (1)

Text

Follow-up Question: You stated that PG&E had withdrawn several coupons from Unit 2; specifically, enough to estimate embrittlement through 60 years of operation. But they haven't withdrawn a coupon from Unit 1 since 2002, twenty years ago. The reason given was that the coupon drawn in 2002 is enough to predict embrittlement up through 2024.

However, Diablo Canyon's Unit 1 reactor vessel was determined by the NRC to be the third most embrittled reactor vessel in the whole fleet, only outpaced by Palisades and Point Beach. I can't understand why the NRC wouldn't require MORE surveillance of a reactor vessel that was deemed to be embrittled, rather than less.

PG&E has withdrawn multiple coupons from Unit 1 but no coupons from Unit 1 since 2002. Why? This does not make sense to me.

Answer: The coupon removed from Unit 1 in 2002 was exposed to neutron irradiation levels that allowed PG&E through analysis to assess the future condition of the reactor vessel wall through 40 years of operation. This analysis took into account the actual state and rate of embrittlement of the Unit 1 reactor vessel. The results provided confidence that the Unit 1 vessel would continue to maintain its integrity, and that it was safe to operate through the end of the operating license in 2024 with no additional coupons needing to be withdrawn. For reference, ML13108A336 provides background on the options that PG&E will have available if they decide to pursue license renewal and the Unit 1 vessel begins to approach embrittlement screening thresholds.