Post-Fire Human Reliability Analysis (Task 12)

Task Overview

Background

This task considers operator actions for manipulation of plant components. The analysis task procedure provides structured instructions for identification and inclusion of these actions in the Fire PRA. The procedure also provides instructions for estimating screening human error probabilities (HEPs) before detailed fire modeling results (e.g., fire growth and damage behaviors) have been developed. Estimating HEP values with high confidence is critical to the effectiveness of screening in a Fire PRA. This report does not develop a detailed fire HRA methodology. There are a number of HRA methods that can be adopted for fire with appropriate additional instructions that superimpose fire effects on any of the existing HRA methods, such as SHARP, ATHEANA, etc. This would improve consistency across analyses i.e., fire and internal events PRA.

Purpose

This document describes the procedure for evaluating the impact of fire scenarios on the human actions addressed in the base PRA study (i.e., the Internal Events PRA or original Fire IPEEE analysis) used to create the Fire PRA Model, as well as how to identify and quantify new actions to be performed as part of the plant fire mitigation plans and procedures. Evaluating the reliability for these human actions supports the Fire PRA Model for calculating such metrics as CDF, CCDP, LERF, and CLERP for fire-induced initiating events. The initial quantification of these metrics makes use of screening probabilities for human failure events (HFEs) where appropriate. As necessary, more detailed best estimate analyses of some human actions will be needed to obtain more realistic assessments of fire risk.

Scope

Task 12 addresses a process for performing both screening and detailed analysis of post-fire human actions identified in accident sequences initiated by a fire. The main focus is to foster the process for assessing the impact of location-specific fires on the human actions taken in response to a fire-induced initiating event, thus preventing core damage and mitigating releases. This task procedure covers three essential elements of most human reliability analysis (HRA) studies.

• Identification of the HFEs to be included in the Fire PRA.
• The assignment of screening human error probabilities for the identified HFEs to assist in focusing the modeling and fire risk analysis to those scenarios and human actions most important to the overall risk results.
• Considerations for the detailed best-estimate quantification of the more important HFEs to properly consider the fire effects on human performance.

In covering the above scope, it is important to stress that this procedure focuses on those unique fire considerations that need to be included in performing a HRA for the Fire PRA using whatever method (e.g., ASEP [12.1], etc.) is chosen by the analyst. It is therefore equally important to stress what this procedure does not do. This procedure is not a handbook or a similar stand-alone manual for doing a Fire HRA, in that it does not attempt to duplicate all the typical activities in carrying out a HRA like that specified by the ASME Standard ASME-RA-S2002 [12.2]. Nor does this procedure attempt to provide a new or particularly prescriptive method for assessing the HEPs in a Fire PRA, since introducing such a method would be a research project far beyond the intended boundaries and resources for producing these fire procedures. Use of this procedure and the unique fire-related considerations that it covers is expected to be used in concert with already-available HRA techniques and calculation tools by an experienced HRA analyst(s) to perform a defensible and realistic HRA for a Fire PRA.

Notably, the scope of this procedure does not include pre-initiator human failure events specifically related to fire systems, barriers, or programs. Undetected pre-initiator human failures such as improperly restoring fire suppression equipment after test, compromising a fire barrier, or incorrectly storing a transient combustible can all affect the fire risk. Tasks 6, 8, and 11 make use of industry-wide data that within it contains contributions from such human failures. Hence to that extent, these pre-initiator failures are treated within the Fire PRA. Nevertheless, no specific steps are provided here for performing a plant-specific review of the potential for such human failures and thus influencing the use of the industry-wide data. This does not preclude the expectation that pre-initiator human failure events from the Internal Events PRA (i.e., not specifically related to fires) should remain in the Fire PRA Model covering their contribution to component unavailability for safe shutdown systems within the PRA model structure.