Citation

Prošek A, Mavko B. Sci. Technol. Nucl. Install. 2010; 2010: 1-12.

Copyright

(Copyright © 2010, Hindawi Publishing)

DOI

10.1155/2010/797193

PMID

unavailable

Abstract

The experience accumulated in the last few decades has shown that human factors play a significant role in the risk of system failures and accidents, throughout the life cycle of a system. This explains significant focus on human reliability analysis (HRA) and on its full integration within systematic risk analysis and reliability assessment procedures. A major problem in meeting this growing importance of HRA is the lack of empirical plant specific data needed for assessment of human reliability. In general, there are several information requirements for HRA, including the available time for diagnosis and correct execution of a tasks, steps, and actions (i.e., time window for action). This information comes from the deterministic analysis.

The time window for human action actually represents the success criteria for the action. It represents the time interval in which operators have to perform the action in order that the plant is put in a safer state, that is, the plant is put into a scenario that leads to a safe state and not to an accident state.

To estimate the success criteria time windows of operator actions the conservative approach was used in the conventional probabilistic safety assessment (PSA). The current PSA standard recommends the use of best-estimate codes. The purpose of the study was to estimate the operator action success criteria time windows in scenarios in which the human actions are supplement to safety systems actuations, needed for updated HRA. For calculations the RELAP5/MOD3.3 best estimate thermal-hydraulic computer code and the qualified RELAP5 input model representing a two-loop pressurized water reactor, Westinghouse type, were used. The results of deterministic safety analysis were examined what is the latest time to perform the operator action and still satisfy the safety criteria. The results showed that uncertainty analysis of realistic calculation in general is not needed for human reliability analysis when additional time is available and/or the event is not significant contributor to the risk.