Should California reverse its 2018 decision to close the aging reactors by 2025?

"Reactor Vessel Head" by NRCgov is licensed under CC BY-NC-ND 2.0.





Should California reverse its 2018 decision to close the aging reactors by 2025?

A briefing for the citizens of California, the Legislature, and the Governor

on important new data and analyses since passage of S.B. 846

San Luis Obispo Mothers for Peace

December 14, 2023


INTRODUCTION. This briefing paper by San Luis Obispo Mothers for Peace (MFP) provides current data and high-level expert analysis to answer key questions posed by the California Legislature in 2022 when it passed S.B. 846, emergency legislation to allow continued operation of the Diablo Canyon nuclear plant (DCPP) for five years or more past their expiration dates of 2024 (Unit 1) and 2025 (Unit 2). And it explains why today’s decision by the California Public Utilities Commission (CPUC) to approve continued operation is contradicted by new data and analyses showing that continued operation of DCPP is not necessary, cost-effective, or safe; and furthermore, that it would undermine the State’s goal of a 100% renewable electric energy economy.

BACKGROUND. S.B. 846 reversed a 2018 decision by the CPUC to approve Pacific Gas & Electric’s (PG&E’s) proposal to close DCPP on the reactors’ retirement dates in favor of less expensive and more modern power sources. Concerned by power shortages caused by abnormal weather and fire conditions in 2021-22, the Legislature passed S.B. 846 to preserv[e] the option of continued operation of the Diablo Canyon powerplant for an additional five years beyond 2025.” The Legislature also offered a $1.4 billion forgivable loan for the project.

As directed by S.B. 846, during the summer/fall of 2023, the CPUC conducted a rulemaking and took evidence and legal briefing on issues related to the prudency or imprudency of continuing to operate DCPP. MFP submitted detailed expert evidence on the following questions:

  1. Is extended operation of DCPP prudent or imprudent?

  2. Is DCPP extended operation needed to avoid summer blackouts?

  3. Is extended operation of DCPP consistent with the State’s goal of reaching a 100% renewable electric energy economy?

  4. What will DCPP cost Californians in comparison to alternative zero carbon electricity sources? And who will pay?

  5. Is safety assured during extended operation of DCPP? And if so, what will it cost?

As demonstrated in this briefing paper, new data and analyses, not considered by the CPUC, show that these questions cannot be answered in the affirmative. Therefore, continued operation of DCPP is imprudent and unjustified.




  1. Is extended operation of DCPP prudent or imprudent?

Answer unknown. See Attachment 1, THE PRUDENT COURSE ON CONTINUED OPERATION OF DIABLO CANYON NUCLEAR POWER PLANT: TAKE THE OFFRAMP NOW a report by Peter Bradford, CEO of Bradford Brook Associates.

Astonishingly, the CPUC has failed to answer this question. Never in the history of U.S. utility regulation has a regulated project of this multi-billion dollar magnitude (to say nothing of major safety issues affecting a significant area of the state) been allowed to go forward without the requisite finding of the relevant regulatory agency.

There is only one actual CPUC determination about the prudency of operating DCPP, and that determination was made in 2018 by the CPUC to approve the on-time retirement of the reactors. The CPUC agreed with PG&E’s prediction that the continued operation of Diablo Canyon beyond 2025 would exacerbate over-generation, requiring curtailment of renewable generation. The CPUC also agreed with PG&E that there is no need to replace Diablo Canyon in order to maintain system reliability.

From 2016 until today, PG&E never deviated from that conclusion. It has yet to notify the CPUC that it has changed its 2016 conclusion, and it has yet to file any studies that would support such a changed conclusion. If the Company had changed its view in light of the weather and fire-driven stresses to its system before mid-2022, it would have been under a clear duty to inform the CPUC. It did not do so. This evidence as to what a prudently managed utility in PG&Es circumstances would have done could not be clearer.

  1. Is extended operation of DCPP necessary to avoid blackouts?

No. See Attachment 2, WE HAVE ENOUGH POWER TO KEEP THE LIGHTS ON WITHOUT DCPP, a report by Rao Konidena, Rakon Energy LLC, former Midcontinent ISO (MISO) Principal Advisor for Policy Studies.

California has enough power to keep the lights on without the 2,200 MW generated by DCPP – even during extreme heat events. Data from the CPUC and California Energy Commission (CEC) show that the California Independent System Operator (CAISO) now has more than 8,500 MW of energy storage capacity (with more being added each year), plus up to 5,000 MW of demand response – more than sufficient to ensure grid reliability during extreme weather conditions. Inexplicably, while the CPUC has acknowledged the significant growth in renewables and the significant quantity of available demand response, it arbitrarily chose to rely on smaller estimates.

Further, running DCPP 24/7 for an additional 5 years would actually increase the risk of blackouts. This is illustrated by the 2022 rolling blackouts, when CAISO had to keep 2,200 MW in reserve just in case DCPP unexpectedly went offline during the two-hour peak demand. This 2,200 MW was in addition to the 6% reserve margin that CAISO must maintain at all times, putting a great strain on the CAISO system and increasing the likelihood of blackouts. Because reserve requirements are determined by the size of the largest potential power loss on the system, reliance on the large range of smaller, flexible, low-cost renewable and storage energy sources that are now available in ample supply would reduce blackout likelihood.

  1. Is extended operation of DCPP cost-effective? And who will pay?

No. See Attachment 3, EXTENDED OPERATION OF THE DIABLO CANYON NUCLEAR PLANT: WHAT WILL IT COST AND WHO WILL PAY FOR IT? a report by Mark Cooper, President of Citizen Research

California is slouching toward an economic mistake of epic proportions. The CPUC has followed the lead of Governor Newsom and the Legislature in reversing its decision to replace DCPP with an assortment of less costly resources far more compatible with a 21st century electric power grid. Running DCPP for an additional 5 years harms customers immediately, and each dollar wasted on keeping DCPP online also makes California’s goal of transitioning to a carbon-free, reliable and safe grid more difficult and expensive.

Consumers and ratepayers will bear a significant cost. The cost to customers of continuing to operate the Diablo Canyon nuclear power plant past the reactors’ operating license expiration dates in 2024 and 2025 are significant, even taking into account a $1.4 billion taxpayer subsidy from state and federal funds. The CPUC has stated that while complete costs are unknown, they are expected to exceed $6 billion.

The estimated $6 billion minimum cost of continued operation of DCPP exceeds $500 for every family of four in the state -- a sobering sum. The CPUC has said that all customer classes will bear a part of this cost burden, although the CPUC lacks the information needed to calculate its basic responsibility, i.e., what the bill impacts will be. Some of the costs will of course show up in the price of goods and services rather than in electric bills. PG&E ratepayers will certainly be harmed. The cost burden will also be spread to other (non-PG&E) ratepayers, but exactly how large their share will be is also unclear.

Given the potentially large size of the costs of running DCPP for another 5 years or more, it is irresponsible to make a decision to go ahead without reckoning with those costs. In any event, it is clear today that adding significant total costs to ratepayer bills and consumer pocketbooks is unjustified now -- and will raise costs in the future by curbing the growth of cheaper renewables.

  1. Is extended operation of DCPP consistent with the State’s goal of reaching a 100% renewable electric energy economy?

No. See Attachment 2 (Konidena Report) and Attachment 3 (Cooper Report). Keeping DCPP online will crowd out and slow down the development of alternatives (wind, solar, storage, efficiency, demand response). And it will depress the State’s growing renewable market, thus causing collateral economic effects and undermining the State’s goal of converting to an entirely renewable energy budget. Thus, each dollar that is wasted in keeping DCPP online also makes the eventual transition to renewables more difficult and expensive.

  1. Is safe operation of DCPP assured during extended operation?

No. Significant questions about seismic safety and the integrity of the Unit 1 pressure vessel remain unaddressed. Upgrades could cost millions of dollars – and if the risks go unaddressed, the effects of a radiological accident could cost more.

See Attachment 4, PG&E SIGNIFICANTLY UNDERESTIMATES SEISMIC RISK TO DCPP, a report by Dr. Peter Bird, Professor of Geophysics and Geology, Emeritus at the University of California at Los Angeles.

As explained by Dr. Bird, California residents should be greatly concerned about the significantly underestimated risk of an earthquake-caused accident at DCPP during extended operation. Seismic studies by PG&E fail to consider recent data and analyses by well-respected experts showing that seismic risk to DCPP is considerably greater than estimated by PG&E.

See also Attachment 5, EMBRITTLEMENT OF REACTOR PRESSURE VESSEL AT DIABLO CANYON UNIT 1 POSES AN UNACCEPTABLE SAFETY RISK DURING CURRENT AND EXTENDED OPERATION, a report by Dr. Digby Macdonald, Professor in Residence, Departments of Nuclear Engineering, University of California at Berkeley.

Dr. Macdonald concludes that the current operation and proposed extended operation of DCPP Unit 1 pose an unreasonable risk to public health and safety due to serious indications of an unacceptable degree of embrittlement in the reactor pressure vessel (RPV), coupled with a lack of information to establish otherwise. In Dr. Macdonald’s expert opinion, the reactor should be closed unless and until PG&E obtains and analyzes additional data demonstrating that Unit 1 is safe to operate. But so far, neither PG&E nor the federal regulator, the U.S. Nuclear Regulatory Commission, has taken any steps to assess the current condition of the Unit 1 RPV.

CONCLUSION. Instead of approving continued operation of DCPP, the CPUC should order that the reactors should be retired on schedule and that the State should proceed with replacement of DCPP with renewable energy sources as approved by the CPUC in 2018.