Generating debate on issues surrounding the venting of containment in the event of LOCA to ensure an optimised safe outcome

Following the incidents at the Japanese Fukushima Nuclear facility, when three units experienced LOCA, the consequences of those events have caused ripples across the world. Regulators around the world are examining the need to prevent excessive pressurisation of NPP Containment, and safely evacuate the gaseous consequences of LOCA, there is a need to return to fundamental principles and examine each putative set of data derived from the various models describing the consequence of LOCA and other events, a LOCA being a 'Loss Of Coolant Accident', and represents the outcome from a range of incidents ranging from fuel pellets being exposed to cooling (heat exchange) water, to a complete melt down of the fuel load with consequence evaporation of the concrete structures of the reactor containment buildings. Clearly it would be highly desirable in both economic and safety terms to minimise the external impact of these events inside the containment. Since one of the results of a LOCA is the pressurisation of the internal space of the containment building, regulators and the industry are looking at the mandatory installation of suitable vent systems to vent the pressure building up inside the containment, whilst ensuring the minimum impact on the surrounding environment. This is clearly a filtration/separation/recombination issue, and as an expert engineering company in the nuclear industry, Porvair has concerns that the issues of Containment Venting are not being addressed by expert filter companies, but by expert nuclear engineering companies with only a superficial knowledge of the complexities and nuances on filtration processes. The paper will describe in depth and detail the individual consequences of each particular aspect of the modelled data. Looking at flowing conditions (pressure, temperature, gas constituents including water vapour and Caesium and Iodine compounds), vent pressure philosophy, deposition of solids (size, type and quantity), decay heat accommodation/removal, maximum temperature limitations in terms of metallurgy and the melting point of deposited materials (for instance, the melting of CsOH at 273 Celsius) as well the consequences of water condensation on pressure loss, solids removal efficiency and the blinding of the medium, and the structural design of the equipment to make it capable of withstanding the worst case pressure loss (a fully blocked system with full containment pressure across it). Extensive work done in the author's company shows clearly that no two event models coincide, to the extent that the company is concerned that there is an assumption in the NPP industry that a 'product' exists which will simply meet any need, taking account of solids load, temperature limits, pressure profiles, decay heat deposition and the gross condensation of water vapour. It is clear, and will be demonstrated, that no single catch-all solution will meet the myriad of needs examined by the company, and the company finds itself in a position where it feels it is compelled to at least present the argument to the industry, so that the industry can then at least have its deliberations informed by supported and fundamental fact. The purpose of the paper is to (hopefully) generate debate to ensure that solutions being provided to meet this most challenging and important of applications, meet the real need, and that the real need is properly modelled. The company has worked on several CV applications in the past years and can say with certainty that no two have been at all similar, suggesting that either the event modelling is wrong, or 'One Size Fits All' is definitely not the case where Containment Venting is concerned. (authors)