The development of a nuclear chemical plant human reliability management approach: HRMS and JHEDI

Abstract

In the late 1980's, amidst the qualitative and quantitative validation of certain Human Reliability Assessment (HRA) techniques, there was a desire for a new technique specifically for a nuclear reprocessing plant being designed. The technique was to have the following attributes: it should be data-based rather than involving pure expert judgement; it was to be flexible, so that it would allow both relatively rapid screening and more detailed assessment; and it was to have sensitivity analysis possibilities, so that Human Factors design-related parameters, albeit at a gross level, could be brought into the risk assessment equation. The techniques and literature were surveyed, and it was decided that no one technique fulfilled these requirements, and so a new approach was developed. Two techniques were devised, the Human Reliability Management System (HRMS), and the Justification of Human Error Data Information (JHEDI) technique, the latter being essentially a quicker screening version of the former. Both techniques carry out task analysis, error analysis, and Performance Shaping Factor-based quantification, but JHEDI involves less detailed assessment than HRMS. Additionally, HRMS can be utilised to determine error reduction mechanisms, based on the way the Performance Shaping Factors are contributing to the assessed error probabilities. Both techniques are fully computerised and assessments are highly documentable and auditable, which was seen as a useful feature both by the company developing the techniques, and by the regulatory authorities assessing the final output risk assessments into which these two techniques fed data. This paper focuses in particular on the quantification process used by these techniques. The quantification approach for both techniques was principally one of extrapolation from real data to the desired Human Error Probability (HEP), based on a comparison between Performance Shaping Factor (PSF) profiles for the real, and the to-be-assessed, task or scenario. The extrapolation process therefore required a set of PSF profiles for a number of real and representative data-based scenarios, and empirically-derived rules to extrapolate to new but similar scenarios. Using existing nuclear chemical plant human error and other data, a PSF profiling and extrapolation system was developed, which could assess most HEPs required for nuclear chemical risk assessments. The two techniques were then employed in a major risk assessment, with HRMS being utilised for approximately twenty high risk scenarios, and JHEDI being used to calculate well over five hundred HEPs for a large range of tasks and scenarios, by a number of assessors.