Use of the Phenomena Identification and Ranking Table (PIRT) in the assessment of Source Term (ST) phenomena

Abstract of the technical paper/presentation presented at:

OECD-NEA CSNI Working Group on Analysis and Management of Accidents
January 21–22, 2019

Prepared by:
Mounia Berdaï and Quanmin Lei
Canadian Nuclear Safety Commission

Abstract

Source term (ST) designates releases of fission products from containment into the environment during a nuclear accident. It involves various complex phenomena that are influenced by many factors and physical processes, and which are not fully understood and require more experimental tests. Since these experimental tests are very costly in terms of financial and human resources, it is more rational to optimize their number and determine the best ways to carry them out. This prioritization can be achieved by applying the Phenomena Identification and Ranking Table (PIRT).

In this presentation, we intend to determine whether all of the main ST phenomena have been covered by the available PIRT studies and whether they are properly ranked. We will also identify the main knowledge gaps in the ST area.

Based on our literature review, it appears that data from the Fukushima Daiichi accident provide the best opportunity to fill knowledge gaps related to ex vessel core debris spreading and debris coolability. Some studies highlight the effect of human performance, and instrumentations on Severe Accident (SA) progression and thus on ST generation. In these studies, it appears that there are differences in the identified ST gaps that could be caused by the PIRT process itself.

This study also revealed a significant increase in the understanding of some SA and ST phenomena. However it is still not clear how they can be classified according to their respective impacts on ST. Therefore, it is recommended that further research be carried out to address this shortcoming.

Keywords: PIRT, Source Term, Severe Accident

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