Internal Flooding PSA Capability

Internal flooding hazards can pose a significant threat to plant safety and can often contribute a significant portion of total plant risk. This warrants a detailed probabilistic treatment to identify vulnerabilities and provide insights for design or procedural improvements. Jacobsen Analytics Ltd. (Jacobsen) are highly skilled and experienced in conducting such analyses especially for new reactor designs in support of the various stages of the licencing process within the UK.

Jacobsen are familiar with the expectations for internal flooding PSA to meet modern standards requirements and have recently completed a full scope internal flooding PSA for a new reactor design within the UK. This analysis was conducted according to the guidance contained in EPRI Report 1019194 - Guidelines for Performance of Internal Flooding Probabilistic Risk Assessment. These guidelines are considered to be best practice for Internal Flooding PSA and meets the requirements of all applicable national and international standards including the Part 3 requirements of the ASME/ANS standard and the relevant assessment expectations contained within the ONR Technical Assessment Guide (TAG) for PSA. This analysis was conducted for both at-power and shutdown operating states to obtain a comprehensive understanding of the potential internal flooding risk for different plant operating states and configurations. The analysis underwent international peer review and passed through the ONR review with few comments.

Jacobsen’s approach always seeks to provide the best value for money for clients and as part of that approach we are always looking for innovative ways to make our analysis more realistic and more efficient. An output of this approach was the development of a shared database tool (Jacobsen Analytics Fire and Flooding Database – JAFFdb) (see Figure 1) that can support multiple internal hazard assessments. JAFFdb captures the full range of plant data needed for the internal hazards assessments (e.g. fire and flooding) and performs manipulation of that data according to the guidance for probabilistic assessment of those hazards to create the necessary scenarios for quantification in the PSA model. The software is configured to provide scenarios in the EPRI FRANX software is being modified to suit RiskSpectrum®. The tool can be modified to support different PSA software if required.

Figure 1 - JAFFdb Control Panel View

JAFFdb is a standalone application designed to run in a virtual operating environment with a user-friendly web interface (see Figure 2). The application has been through a comprehensive verification and validation (V&V) process supported by a V&V report.

Figure 2 - JAFFdb Architecture

Jacobsen have also developed additional tools to support internal flooding scenario development that are compatible with general arrangement and layout drawings typically used to develop flood propagation pathways. These tools can be used with files in a PDF format and enable searching and layering of different elevations of a building in a single drawing such that items of interest to flood propagation, e.g. doors and hatches etc. can be readily identified and accounted for in the efficient development of flooding pathways.

For the analysis of detailed internal flooding scenarios, Jacobsen have also used a range of flood height calculation approaches from simpler spreadsheet based models through to use of a state of the art 3D hydrodynamic modelling package which can predict with far greater accuracy the expected submergence levels in different rooms given a source flooding rate and the nature of the interfaces between different rooms. This approach can also account for dynamic flooding effects such as wave action and releases of water following failure of interface elements (e.g. internal doors). In certain configurations, dynamic flood levels are often greater than the steady state flood levels predicted using the more simplistic 1-D approach to flood height calculation.

In summary, Jacobsen can provide a full modern standards internal flooding PSA capability with options to enhance the detail and accuracy of the analysis where appropriate based on the significance of the flooding scenarios to the overall risk. The use of JAFFdb can also significantly enhance the efficiency of the analysis especially when combined with other complementary internal hazard analyses such as internal fire.