As described in a prior blog post, the Unit 3 reactor at the Palo Verde Generating Station had one of two emergency diesel generators (EDGs) explode during a test run. The license issued by the Nuclear Regulatory Commission (NRC) allowed the reactor to remain running for up to 10 days with one EDG unavailable. Fixing the heavily damaged EDG would require far longer than 10 days, so the plant’s owner submitted requests to the NRC for its permission to run the reactor for up to 21 days and then up to 62 days with only one EDG available.
As described in a followup blog post, NRC staffer(s) filed formal opposition to the agency’s approval of the owner’s requests by initiating Differing Professional Opinions (DPOs). Under the NRC’s DPO process, a DPO panel is formed to review the issue and to document its findings and conclusions in a report to the NRC senior manager who makes the final decisions. In this matter, that individual was the Director of the Office of Nuclear Reactor Regulation (NRR). The DPO originator(s) can nominate one individual to serve on the DPO panel. (The DPO process requires a minimum of three persons on the DPO panel, ensuring that the panel won’t have a majority of members sympathetic to the originator(s)’s concerns.)
The DPO panel issued its report on June 5, 2017, and the NRR Director issued his decision on June 28, 2017. The NRC made the DPOs, the DPO panel report, and the NRR Director’s decision publicly available on July 21, 2017.
The DPO Originator
Troy Pruett originated both of the DPOs in the Palo Verde EDG case. Mr. Pruett is the Director of the Division of Reactor Projects in NRC Region IV. Among other things, Mr. Pruett oversees the NRC’s resident inspectors at all of the nuclear power plants operating in Region IV, including Palo Verde. Mr. Pruett has worked for the NRC for nearly a quarter century—long enough to know the agency’s regulations and procedures intended to protect nuclear plant workers and the American public inside and out (Fig. 1).
The DPO Originator’s Position
In his DPOs, Mr. Pruett contended that the owner’s requests to operate Palo Verde Unit 3 for up to 21 and later up to 62 days with one emergency diesel generator unavailable should not have been approved because they departed from the agency’s regulations, procedures, and practices.
The DPO Panel’s Conclusion
Quoting from their report: “The DPO Panel was not unanimous in concluding that Palo Verde License Amendments 199 and 200 should have been approved by the staff.”
One of Mr. Pruett’s candidates was appointed to the DPO Panel. NRC management selected three other members, assuring they’d have a majority. And sure enough, a majority of the NRC management-appointed panel sided with NRC management.
The DPO Panel’s 18 Observations
The DPO Panel’s report contained 18 Observations about the processes used (and not used) en route to the Palo Verde EDG approvals:
(1) The owner submitted two licensing requests to the NRC: one to operate for up to 21 days and the second to operate for up to 62 days with one EDG unavailable. The overwhelming majority of the hundreds of licensing requests submitted to the NRC each year are not bifurcated in this way and the agency’s procedures for reviewing licensing requests do not address such “split” requests. The DPO panel recommended that additional guidance be provided in LIC-101, the NRC’s procedure for handling such reviews, if the practice becomes more frequent.
(2) The DPO Panel noted that the staff’s reasoning for the two-step approach could have been made clearer in the first approval in the interest of transparently providing a complete record of the staff’s decision basis to the public.
(3) The DPO Panel observed that there may be opportunities to more effectively communicate with the public, including the use of less formal communications tools, during emergency requests, and suggests that guidance and training be considered in this area.
(4) The second approval issued by the NRC staff contained an explicit requirement to shut down Unit 3 if workers found the cause of the EDG’s failure could also disable the surviving EDG. The DPO Panel noted that no formal regulatory commitment existed in the first approval. During interviews, the NRC staff was not able to provide a sufficient basis as to why a similar condition was not included.
(5) The DPO Panel observed that the Safety Evaluation issued by the NRC staff in support of the first approval lacked sufficient documentation to objectively identify the staff’s decision basis in several key areas, including how the potential for common cause failure of the surviving EDG was evaluated and the basis for a 21 day EDG outage time. In other words, the NRC staff failed to ask and answer all the relevant safety questions.
(6) The DPO Panel concluded that the use of a zero test and maintenance assumption (i.e., no other safety equipment would fail or be unavailable while the EDG was broken) in the owner’s probabilistic risk assessment (PRA) model was not consistent with Regulatory Guide 1.177 guidance and the regulatory commitment put in place for the second approval for the conduct of routine maintenance and surveillance was not consistent with PRA assumptions.
In other words, when the EDG was unbroken, the owner’s risk assessment assumed that there was a small, but non-zero, chance that the highly reliable emergency equipment would not perform needed safety functions during an accident. But when evaluating the risk during the 62 days the reactor would operate with a broken EDG, the owner’s risk assessment assumed that all emergency equipment would function perfectly. The DPO Panel found this assumption unrealistic, non-conservative, and contrary to longstanding NRC expectations.
(7) Additional guidance should be evaluated with respect to defense-in-depth, the adequacy of long duration equipment outage periods, and whether there should be a backstop (i.e., maximum outage period).
(8) The DPO Panel concluded that the Branch Technical Position 8-8 guidance was not strictly adhered to for the two approvals. The DPO Panel recommended that deviations from established guidance should be documented and justified. The Branch Technical Position explicitly stated that the NRC staff should not even review a request to operate for longer than 14 days with one EDG unavailable; in this case, the NRC staff not only reviewed such a request, they approved it without explaining why they dismissed the 14-day maximum duration.
(9) The DPO Panel confirmed that the NRC’s safety evaluation supporting the first approval did not include an independent verification of the owner’s risk evaluations.
(10) The DPO Panel identified that the second approval used the three risk-informed tiered review approach outlined in Regulatory Guide 1.177. The DPO Panel pointed out this approach was inconsistent with Standard Review Plan 16.1 guidance, which states that Regulatory Guide 1.177 only applied to permanent (as opposed to temporary or “one-time”) changes. In other words, the NRC staff used an approach not allowed by the agency’s procedures.
(11) The DPO Panel found no discernible differences between the DC Cook request for a 65-day EDG outage in June 2015 and the Palo Verde request. However, the staff appears to have arrived at entirely different conclusions, based upon different interpretations of the deterministic guidance of Branch Technical Position 8-8. Cook’s owner sought the NRC’s permission to operate Unit 1 for up to 65 days with one of two EDGs unavailable. The NRC said no to Cook’s owner and yes to Palo Verde’s owner, citing Branch Technical Position 8-8 for each of the entirely opposite decisions.
(12) In the DPO Panel’s opinion, the Palo Verde risk evaluation warranted closer scrutiny. However, interviews of the NRC staff identified that there is no guidance for when to use the agency’s SPAR models for independent verification and it appears to be at the discretion of the reviewer(s).
(13) Section 4.2 of the NRC’s procedure for reviewing licensing requests, LIC-101, states that, “Decisions to not apply specific precedents, especially precedents cited by a licensee, should be clearly explained in the SE [NRC’s Safety Evaluation] (to avoid the appearance of being arbitrary and/or inconsistent).” The DPO Panel observed that neither of the Safety Evaluations prepared by the NRC staff for the two approvals addressed the licensee’s referenced precedents. In other words, the NRC staff did not follow the procedure they purportedly used to make the approvals.
(14) The DPO Panel found that both of the Safety Evaluations prepared by the NRC staff for its approvals included Branch Technical Position 8.8 in the list of regulatory guidance documents reviewed. The Safety Evaluations stated that Branch Technical Position 8.8 required more defense-in-depth for station blackout scenarios than for loss of coolant accident scenarios because of a higher likelihood of occurrence. But the DPO Panel found no such statement or implication about design basis accident likelihoods in the Branch Technical Position. In other words, the NRC staff departed from the regulatory guidance document it purportedly used to justify the approvals.
(15) The DPO Panel determined that there is no established guidance for how NRC staff should judge the adequacy of risk evaluations provided by plant owners. The good news is that the NRC staff cannot depart from non-existent guidance; the bad news is that the NRC staff can, and has, wandered all over the map since it lacks proper directions.
(16) The DPO Panel identified a lack of clarity in the existing review guidance and related inconsistencies in the understanding between the NRC departments regarding who is responsible for reviewing what in licensing requests.
(17) The DPO Panel recommended additional guidance be developed for the NRC staff when reviewing requests for extended periods of safety equipment unavailability.
(18) The DPO Panel recommended that a lessons learned review be conducted after significant or first of a kind licensing actions to determine if the action should be used as future precedent and/or whether there should be specific attributes identified that future staff should evaluate before using the precedent.
Grading on a (Mobius) Curve
If you read these observations, and the more voluminous supporting text in the report, before reading the conclusion, you’d likely think that the entire panel agreed with Mr. Pruett.
After all, Mr. Pruett contended that the requests departed from regulations and the DPO Panel’s Observations 5, 6, and 14 confirm that contention and several others support it.
Mr. Pruett contended that the requests departed from the agency’s procedures. The DPO Panel’s Observations 1, 8, and 13 confirm that contention and several others support it.
Mr. Pruett contended that the requests departed from the agency’s practices. The DPO Panel’s Observations 9, 10, and 11 confirm that contention and several others support it.
But nooooo. The DPO Panel disagreed with Mr. Pruett.
You might ask why the DPO Panel could possibly have disagreed with Mr. Pruett.
If you do ask and someone gives you a straight answer, please forward it to me. I’ve monitored the NRC for nearly two decades and I cannot fathom how the DPO Panel could assemble so many reasons why Mr. Pruett was right, and yet conclude he was wrong.
It’s like a 19 chapter mystery novel with the first 18 chapters describing how the upstairs maid committed crime after crime only to have the butler—mentioned for the first time—arrested for the crimes.
Perhaps that explains it: the DPO Panel report is an intriguing work of fiction. Or maybe it only needed a non-fictional final chapter.