Development and Application of Monte Carlo Neutronics Methodologies for Safety Studies of Current Operating Reactors (Analisi neutronica con Metodi Monte Carlo di Impianti Nucleari Tipo PWR)

Within the framework of safety analysis of currently operated nuclear power reactors, innovative Monte Carlo methods have been developed to perform both fixed source and eigenvalue simulations; taking advantage of variance reduction techniques for in-core and ex-core responses. The activity is carried out within the present work, dealing with a benchmarking with two different nuclear systems. A close collaboration is carried on with IRSN (French Institute for Radiation Protection and Nuclear Safety). In fact, two complementary sample problems were adopted: TAPIRO, a small fast research reactor and the large GEN-III PWR model employed before the TIHANGE model for the calculation of neutron and gamma detectors in and outside the pressure vessel well. The TAPIRO model provided a good benchmark, while Tihange offered a case study for ex-core detector analysis through the deep shield in the reactor well. First approach has been eigenvalue calculation during which the fission source is sampled and then wrote to a file. Secondarily, DSA is employed in fixed source simulation. In addition, in-core or ex-core local responses are added to in-core global responses to utilize DSA variance reduction technique directly in an eigenvalue simulation – thanks to the multi-response capability. Finally, a simple experimental benchmark is used to check nuclear data utilized and methodology consistency: PCA-Replica is selected for this purpose.