Development of a Simple Computer Code to Obtain Relevant Data on H2 and CO Combustion in Severe Accidents and to Aid in PSA-2 Assessments Fernando Robledo Consejo de Seguridad Nuclear (CSN); Spain

By following Consejo de Seguridad Nuclear (CSN) requirements, all of the Spanish NPP ́s performed plant specific PSA level 2 studies and implemented Severe Accident Management Guidelines during the first years of this century. CSN and contractors made an independent detailed review of these PSA level 2 studies (Khatib-Rahbar 1997 2002). This independent review included the performance of plant specific calculations by using the MELCOR code and some other stand-alone codes and the calculation of the fission product release frequencies for each plant. One of the aspects treated in detail by CSN evaluations was the calculation of the containment failure probability due to the burn of combustible gases generated during a severe accident. It was shown that it would be useful to have a fast running code with capability to provide the most relevant data concerning H2 and CO combustion. Therefore, the Polytechnic University of Madrid (UPM) developed the CPPC code (Martín-Valdepeñas, 2004a) for the CSN. This stand-alone module makes fast calculations on maximum static pressures in the containment building generated from H2 and CO combustion in severe accidents, considering well-mixed atmospheres and includes the most recent advances and developments in the field of H2 and CO combustion. Code input is simple: mass of H2 and CO, initial environmental conditions inside the containment before the combustion and simple geometric data, such as the volume of the building enclosing the combustible gases. The code calculates the containment temperature assuming steam saturated atmosphere and provides the following output: • Combustion completeness (CC). • Adiabatic and isochoric combustion pressure (pAICC). • Chapman-Jouguet pressure (pCJ). • Chapman-Jouguet reflected pressure (pCjrefl).