Pacific Gas & Electric Company; Diablo Canyon Power Plant, Unit Nos. 1 and 2; Petition

SUPPLEMENTARY INFORMATION:

On March 4, 2024, the petitioners filed a petition requesting that the NRC exercise its supervisory authority to order the immediate closure of Diablo Canyon due to “the unacceptable risk of a seismically induced severe accident.” An order was issued on March 12, 2024, referring the request to the enforcement petition process under section 2.206 of title 10 of the Code of Federal Regulations (10 CFR), “Requests for action under this subpart.”

The specific concerns expressed in the March 4, 2024, petition, as supplemented on June 7, 2024, now include:

1. Thrust faulting is neglected by Pacific Gas & Electric Company's (PG&E's) 2012 Seismic Source Characterization (SSC) model, because the model assumes that a majority of large earthquakes affecting Diablo Canyon are strike-slip and disregards the significant contribution of thrust faulting earthquake sources under the Diablo Canyon site and the adjacent Irish Hills. In addition, PG&E did not use a hanging-wall term for the modeling of potential ground motions from the Los Osos and San Luis Bay thrust faults.

2. The January 2024 magnitude 7.5 (moment magnitude) earthquake centered in the Noto Peninsula (Japan), with an average slip of 2 meters on the fault, is analogous to future potential thrust mechanism earthquakes beneath Diablo Canyon. Based on the slip rate of the Irish Hills adjacent to Diablo Canyon and the slip of the Noto earthquake, large thrust fault earthquakes will occur, on average, every 715 years near the Diablo Canyon site.

3. PG&E's 2012 SSC model does not account for an inferred offshore thrust fault that has a slip rate of 2.8 millimeters per year (mm/yr) and the potential for producing a magnitude 7.5 earthquake.

4. Seismic core damage frequency estimated by PG&E in 2018 to be 3 × 10⁻⁵, should be 1.4 × 10⁻³ per year (about once every 715 years) based on this higher recurrence rate for thrust earthquakes.

The NRC staff assembled a Petition Review Board (PRB) in accordance with NRC Management Directive (MD) 8.11, “Review Process for 10 CFR 2.206 Petitions,” and its associated Directive Handbook 8.11, Section III. In an email dated May 15, 2024, the petition manager informed the petitioners that the PRB's initial assessment was to not accept the petition for review. The PRB's position was that the petition did not meet the criteria in MD 8.11 for accepting petitions under 10 CFR 2.206 because “the issues raised have previously been the subject of a facility specific or generic NRC staff review . . .” and the petition does not provide significant new information that the staff did not consider in a prior review.

On May 15, 2024, along with the initial assessment, the petition manager offered the petitioners an opportunity to address the PRB in a public meeting, which was accepted by the petitioners.

The June 7, 2024, supplement to the petition responded to the PRB's initial assessment.

The NRC then held the public meeting on July 17, 2024. During the meeting, the petitioner's presentation discussed and expounded on information from the supplement dated June 7, 2024, and included graphics to represent their position. The transcript of that meeting is considered a supplement to the petition.

Following the public meeting, the PRB met to consider what had been presented during the meeting. The PRB determined that the concerns as previously described in this notice, which were raised in the original petition and supplements, meet the criteria in MD 8.11, Sections III.C.1(a) and (b) and will be accepted into the 10 CFR 2.206 process for further review by the PRB in accordance with MD 8.11. The PRB also determined that there is no imminent safety concern that warrants immediate shutdown of Diablo Canyon. On August 22, 2024, the petition manager informed the petitioners of this outcome.

Availability of Documents

The documents identified in the following table are available to interested persons through ADAMS.