Component Qualification Procedures in Relation to Large Fire Scenarios in Nuclear Installations

The new European Commission Direct Action SONIS addresses the R&D in relation to operational safety of nuclear installations. One of the most relevant task is covering the engineering programs and in particular fire safety. In fact, despite of the many efforts spent by operators, consultants and researchers, fire still is the main accident initiator and in the new reactor design it is going to play a major role in the overall safety assessment of the plants, as the internal events are better controlled by the innovative design features. Moreover, large fire scenarios are often requested to be evaluated in relation to the design basis of new plants and in the assessment of current installations. In fact, all nuclear facilities are designed in relation to accidental fires; even so, they need to be assessed in relation to a broader selection of fire scenarios, including also the sabotage induced ones. This need is due to the special characteristics of such scenarios, not addressed by the current engineering practice for the design of nuclear installations. In fact conventional fire hazard analysis is based on the hypothesis of the presence of combustible materials in the buildings and limited number of contemporaneous sources of fire. In addition, conventional fire safety assessment relies upon the presence of mitigation measures and fire related operational procedures. Also the implementation of emergency planning should be reviewed to take account of this concern. In conclusion, conventional assessment techniques are not applicable to such scenarios where a significant portion of the site is affected by fire ignited either on-site or off-site. Therefore safety strategies for a safe plant shutdown have to be developed and assessed. The R&D carried out in the new EC action addresses deterministic and probabilistic safety assessment of SSC (structure, systems and components) capacity to withstand large fires ignited at the site by both internal and external sources. The first step is the identification of the fire related parameters associated to the design basis scenarios for both accidental and malevolent events. Next, the research identifies the SSCs where fire vulnerabilities are important for the overall safety evaluation of the plants. Detailed analysis of the potential scenarios at the component level induced by fire are being carried out. Last, a comparison of available qualification procedures for fire relevant effects is carried out. For components and equipment where either no data or procedures are available, the project is planning the development of new qualification procedures, based on the outcome of the analysis of the current practice for component qualification. This paper gathers state-of-the-art experience developed in some Countries, which represents the background information for the development of the research in this field. The paper reviews how the current design practice for nuclear installations can cope with an enlarged selection of fire scenarios and provides preliminary results from the research on going on how to address these issues in a reasonable framework and with suitable component qualification procedures.

CONTRI Paolo;  BRUYNOOGHE Christiane; 

DUCHAC Alexander; 

2008-01-29

CNSC

JRC37217

https://publications.jrc.ec.europa.eu/repository/handle/JRC37217,