Step 3:Predict error rates for each human operation or group of operations. Errors likely to be made in each task or subtask must be identified. Errors that are not significant in terms of system operation are ignored. This step includes estimating the likelihood of each error occurring and the likelihood of an error not being detected.

For this step, use the Event Tree (PDF) Download Event Tree (PDF)provided to fill in the error rates.

Determine the basis human error probability (HEP) based on the event tree provided. You will be using data found in the NRC: Handbook of Human Reliability Analysis with Emphasis on Nuclear Power Plant Applications (PDF)Links to an external site.(NUREG/CR-1278). Go to Chapter 20 to see how to use the THERP tables to locate probability values.

For this case, the data sources in the NUREG/CR-1278 tables are shown for each action in the table below. Given that the operators omitted a procedural step from a long (>10 items) list of procedures, what should the Basic Human Error Probability (HEP) for each action be?

Reference

NUREG/CR-1278, "Handbook of Human Reliability Analysis with Emphasis on Nuclear Power Plant Applications - Final Report." (nrc.gov)