R E G U L A T O R Y M A L P R A C T I C E: NRC’S “Handling” of the PWR Containment Sump Problem

The report alleges that the NRC has failed to enforce 10 CFR 50.46, allowing 68 of 103 U.S. nuclear reactors to operate with a known vulnerability to containment sump clogging. This issue, which can lead to core meltdown and containment failure during a loss-of-coolant accident (LOCA), has been resolved in dozens of PWRs globally but remains unaddressed in the U.S. The author contends that the NRC selectively uses risk-based probability arguments to justify inaction while ignoring its own regulations and the evidence provided by pseudo-plant-specific analyses from Los Alamos National Laboratory. The report calls for Congressional hearings to reform the NRC's enforcement and resolution processes for generic safety issues.

• The containment sump problem affects 68 of the 103 nuclear reactors operating in the United States, increasing the likelihood of a meltdown with containment failure.
• Los Alamos National Laboratory's parametric analysis estimated that the core damage frequency (CDF) for the operating fleet of 69 PWRs increased by a factor of 100 when debris clogging was considered, rising from 3.3E-06 to 1.5E-04.
• The NRC has failed to enforce 10 CFR 50.46, which requires evaluation models to realistically describe reactor behavior during a loss-of-coolant accident, despite evidence that sump clogging is 'very likely' for about half of operating PWRs.
• While the NRC has not required plant-specific fixes for the operating fleet, it revised Regulatory Guide 1.82 to ensure that no future PWR would be licensed without a plant-specific evaluation of debris-blockage potential.
• The Davis-Besse nuclear plant in Ohio serves as a case study proving that plant-specific analyses of sump clogging are possible and that the NRC can review them to determine compliance with 10 CFR 50.46.
• International regulatory bodies have been more proactive than the NRC; at least 25 PWRs outside the U.S. have increased sump screen sizes and at least 23 have replaced fibrous insulation to resolve the problem.
• The NRC is accused of arbitrarily using probability arguments to justify inaction on the sump problem while ignoring similar probability logic to mandate immediate security upgrades following terrorist threats.

APA

Lochbaum, D. (2003). R E G U L A T O R Y M A L P R A C T I C E: NRC’S “Handling” of the PWR Containment Sump Problem. Union of Concerned Scientists. https://www.ucs.org/sites/default/files/2019-10/20031029-ucs-regulatory-malpractice.pdf

Chicago

Lochbaum, David. R E G U L A T O R Y M A L P R A C T I C E: NRC’S “Handling” of the PWR Containment Sump Problem. Union of Concerned Scientists, 2003. https://www.ucs.org/sites/default/files/2019-10/20031029-ucs-regulatory-malpractice.pdf.

Wikipedia

{{cite report |last1=Lochbaum |first1=David |title=R E G U L A T O R Y M A L P R A C T I C E: NRC’S “Handling” of the PWR Containment Sump Problem |publisher=Union of Concerned Scientists |date=29 October 2003 |url=https://www.ucs.org/sites/default/files/2019-10/20031029-ucs-regulatory-malpractice.pdf |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{lochbaum2003nrcs, author = {Lochbaum, David}, title = {{R E G U L A T O R Y M A L P R A C T I C E: NRC’S “Handling” of the PWR Containment Sump Problem}}, institution = {Union of Concerned Scientists}, year = {2003}, month = oct, url = {https://www.ucs.org/sites/default/files/2019-10/20031029-ucs-regulatory-malpractice.pdf}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }