Jiejuan Tong

Safety margins confidence estimation for a passive residual heat removal system

For licensing purposes, safety cases of nuclear power plants (NPPs) must be presented at the Regulatory Authority with the necessary confidence on the outcomes of the models used to analyze the plant safety behavior. In the present work, we consider the problem of providing a quantitative indication of the confidence in the safety margin estimation by a model with uncertain inputs giving in output the maximum outlet water temperature of the residual heat removal system (RHRs) in accident scenarios of the high temperature reactor-pebble modular (HTR-PM). The quantitative evaluation is carried out by means of a computational procedure of literature, based on order statistics (OS). The procedure is analyzed with respect to some of its key parameters defining the sample size and the number of uncertain inputs.

An integrated modeling approach for event sequence development in multi-unit probabilistic risk assessment

To obtain a complete site risk profile for multi-unit nuclear power plants (NPPs), the existing single-unit probabilistic risk assessment (PRA) model needs to be upgraded to address both intra-unit and inter-unit dependencies. The high temperature gas cooled reactor-pebble bed module (HTR-PM), with two reactor-steam generator modules and one shared steam turbine-generator set, is a ready-in-hand pilot for multi-unit PRA (MUPRA) studies. In this paper, a general framework for MUPRA is firstly developed based on HTR-PM PRA methodology. An Integrated Modeling (IM) approach is then proposed for multi-unit event sequence modeling. The approach is discussed in detail and illustrated with a loss of offsite power (LOOP) case study. Also, the limitations of the current analysis are put forward for open discussion.

Identifying key performance shaping factors in digital main control rooms of nuclear power plants: A risk-based approach

Abstract Various human reliability analysis (HRA) methods use performance shaping factors (PSFs) to model operator performance. The tendency in HRA is to increase the number of PSFs. However, using many PSFs may negatively affect the quality of HRA outcomes. An elite-set PSF model with key PSFs is lacking. We therefore suggest a risk-based approach for identifying the key PSFs by ranking their risks to operator performance. In this approach, we elicit nuclear power plant (NPP) operators’ perceptions of the frequency and impact of PSF indicators in main control rooms (MCRs), quantify the perceived risk scores of PSFs by multiplying their perceived frequency and impact, and classify PSF risk levels according to the suggested PSF risk matrix. Licensed operators (N = 33) from a digital NPP MCR participated in our survey. The top-ranked PSFs in terms of perceived risk score and the PSFs at the High Risk level were identified as the key PSFs from the surveyed NPP MCR. A comparison with other studies indicates that the importance of these key PSFs has been previously recognized, implying that the risk-based approach can yield meaningful results for ranking and identifying the key PSFs.

Identifying Macrocognitive Function Failures from Accident Reports: A Case Study

Reliable macrocognitive functions are important for maintaining system safety. Few studies were conducted to investigate macrocognitive function failures in a complex system. NUREG-2114 proposes a cognitive framework connecting macrocognitive function failures, proximate causes, failure mechanisms, and performance influencing factor (PIFs). This model can serve as a model for analyzing human failure events in human reliability analysis (HRA). This study investigated macrocognitive function failures in a complex environment and also examined the usability of the cognitive framework in the HRA qualitative analysis. A total of 103 investigation reports of incidents and accidents from a petrochemical plant in China were involved. It was found that 35 % of the incidents and accidents could be attributed to human errors. Failures of action implementation and team coordination were the dominant failures. This study also gave the information of proximate causes, failure mechanisms, and PIFs for each macrocognitive function failure. The usability issue of the cognitive framework in NUREG-2114 was discussed. It seems that the current cognitive framework needs to be improved to inform HRA.

Operating Events in Chinese Nuclear Power Plants: A Preliminary Analysis

Operating event reporting is important for continuously improving the safety level of nuclear power plants (NPPs). This paper presents the preliminary analysis results based on the data of the licensee operating events (LOEs) occurred in Chinese NPPs during 1991–2015. A total of 805 LOEs were collected. Trends of the number of LOEs and reactor units are presented. It is found that the number of LOEs per unit declined gradually. There were 50% of all LOEs related to human factors and 48% related to equipment factors. More than 50% of human-related LOEs were associated with Personal Work Practices and Written Procedures and Documents. The differences in operating events between conventional and advanced NPPs were analyzed. These results and lessons learned from these LOEs will be helpful for operator error prevention and human reliability analysis in NPPs.