Flood Penetration Seal Testing Protocol Research (NUREG-2240)
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Manuscript Completed: August 2021
Date Published: February 2022
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001
Flood protection features are commonly incorporated into nuclear power plants (NPPs). The most common flood protection features are seals for penetrations in external and internal walls of safety related structures that allow cables, conduits, cable trays, piping, etc. to pass through the walls. Other common flood protection features include water-tight doors, as well as temporary flood barriers (e.g., temporary walls, stop-logs). The potential safety significance of NPP flood penetration seal performance during internal or external flooding events has long been recognized. The U.S. Nuclear Regulatory Commission (NRC) issued Information Notices (INs) related to flood barrier performance in 1988 and 2007. In a 1999 external flooding event at the French Le Blayais NPP, flood barrier failures resulted in underground rooms containing safety-related equipment being flooded. More recently, in the aftermath of the 2011 Fukushima Dai-ichi accident, walkdowns of licensing-basis flood protection features conducted by U.S. NPP licensees found examples of degraded or nonconforming flood protection features, including penetration seals. Inspections by NRC staff resulted in a number of findings related to flood penetration seals and barriers that were evaluated through the NRC’s Significance Determination Process (SDP). Subsequently, in 2015, NRC issued another IN discussing degraded barrier ability to mitigate flooding events.
Although there is abundant operational experience indicating the potential safety significance of flood penetration seal performance, quantitative risk information is lacking. Both industry and the NRC have appropriate analysis tools for addressing the risk-significance of flood barrier performance (i.e. PRA models), but basic performance/reliability data on in-service components is not available. This is due, in part, to the lack of a widely recognized standard or protocol for evaluating flood penetration seal performance. For example, during the post-Fukushima flood protection walkdowns, flood penetration seals were assessed mainly through ad-hoc visual inspection.
As part of the Probabilistic Flood Hazard Assessment (PFHA) research program, the NRC's Office of Nuclear Regulatory Research conducted a research project to investigate how flood penetration seal performance might be evaluated. The research comprised three steps: (1) profiling of flood penetration seals currently used in U.S. NPPs, (2) developing an ex situ performance testing protocol, and (3) evaluating and refining the testing protocol by using it in limited testing of several seal types and applications. It is hoped that this initial research effort can be further refined or adapted by appropriate standards-making organizations (e.g., ANS, ASME, ASTM) in order to support development of basic performance/reliability data for flood penetration seals and, subsequently, quantitative risk information.
The first step in this research project comprised reviewing NRC documents, licensee submittals, and other sources of penetration seal information. The review included NPP licensee post-Fukushima flood protection walkdown reports, licensee responses to NRC requests for additional information, licensee event reports, fire seal testing literature, information available from seal vendors, and NRC-generated documents, such as NUREGs, information notices, and inspection reports. This review summarized seal types and seal materials, as well as penetration shapes, penetration sizes, and penetrants used in NPPs.
In the second step of this project, researchers developed a draft protocol for ex situ (i.e., laboratory-based) flood penetration seal performance testing. This testing protocol was designed for evaluating the flood mitigation performance of penetration seals installed to protect openings in barriers (e.g., internal and external walls, floors, ceilings). The protocol focuses on pressure testing. It includes the definition of terms, test scope, the significance and use of the test procedures, the test specimens and test equipment, test conduct, and proposed documentation of the testing procedures. The draft protocol was published for public comment in 2018, and revisions were made based up on comments received from stakeholders (e.g., Nuclear Energy Institute, Electric Power Research Institute).
In the third part of this project, researchers assessed the effectiveness of the revised draft testing protocol by conducting a limited series of penetration seal performance tests using a number of seal types and penetrants, as well as various penetration types, shapes, and sizes. The results of this test series largely confirmed the viability of the test protocol and its applicability to flood penetration seal performance testing. The testing protocol was further revised to incorporate lessons learned from the limited test series.
A draft of this report was published for public comment in 2020. This final report includes revisions made in response to stakeholder comments. It includes a summary of information derived from the review performed step 1, the proposed testing protocol initially developed in step 2 and revised based on the limited performance testing series conducted in step 3 and stakeholder comments, as well as overall lessons learned from the testing series.
The performance testing protocol developed in this project provides NRC staff and other interested parties with information on how to measure flood penetration seal performance in a controlled laboratory setting. Note that the data and observations from the limited testing series conducted in this project were designed to exercise the test protocol and should not be interpreted as qualifying or disqualifying any specific flood penetration seal or installation design.
Overall, insights developed from this research project could be used to inform future NRC activities related to flood penetration seals (e.g. inspection procedures, guidance development). This initial research effort can be further refined or adapted by appropriate standards-making organizations in order to advance development of basic performance/reliability data for flood penetration seals and support development of quantitative risk information and risk insights.
Page Last Reviewed/Updated Friday, February 18, 2022