Seismic Walkdown (Task 4)

Task Overview

Objective

The objective is to walkdown the SSCs in the seismic equipment list to assess their vulnerability in a seismic event. Potential seismic interactions and operator access pathways are also evaluated during a walkdown.

Purpose

This section describes a process for examining SSCs on the SEL via plant walkdown. It is suggested that all items on the initial PRA components list be physically examined for seismic vulnerabilities, if possible, and their locations recorded. The suggested emphasis is on evaluations against screening cautions, anchorage and attachment of subassemblies and parts, and seismic spatial systems interactions, including the potential for seismically induced fires and floods. Items on the initial list may be subdivided or combined, as appropriate, for further assessment.

Guidance

The following steps are often included for the plant walkdown task.

1. Review the equipment list prepared by the systems analysts.
2. Prepare walkdown sequence. This step usually involves coordination with plant operations to lay out a schedule and route that minimize any effect on plant operations or maintenance.
3. Conduct the walkdown. During the walkdown, SSCs are examined to accomplish the following:

• Assess seismic failure modes.
• Verify anchorage capacities.
• Identify potential spatial systems interactions (such as fire and flooding sources, potential for actuation of fire-suppression systems, block walls, displacements that cause impacts, and so on).
• Take field dimensions and document the SSCs with photographs and sketches as appropriate.

Supplemental Guidance

Related Element of ASME/PRA Standard

Part 5, Seismic Plant Response (SPR)

EPRI Guidance

Seismic Fragility and Seismic Margin Guidance for Seismic Probabilistic Risk Assessments (3002012994)

A Methodology for Assessment of Nuclear Power Plant Seismic Margin, Revision 1 (NP-6041-SLR1)

Generic Implementation Procedure (GIP) for Seismic Verification of Nuclear Power Plant Equipment, Seismic Qualification Utility Group (SQUG)

• EPRI provides SQUG Walkdown Screening and Seismic Evaluation Training through EPRI|U.

Other Guidance

(none noted)