This report is a continuation of two submitted last year (PAR2011). One concerned the collaboration between ENEA and IRSN (Institut de Radioprotection et de Sûreté Nucléaire) dealing with safety issues related to the thick steel reflector of a typical large size GEN III+ reactor design. The other dealt with developments in Monte Carlo algorithms for eigenvalue calculations. These developments partially fed off the PWR modelling, some of which is at the limit of current methodologies and computer capacity. As far as the PWR modelling is concerned, focus was on the phenomenon of flux tilt. Monte Carlo calculations were run on a 2-dimensional model of a NEA benchmark using the same water density variation as previously (±1.50% change in water density in the outer assemblies of opposite quadrants). Results were obtained for the power variation in the whole quadrants for four situations: heavy steel reflector and conventional baffle+water reflector, with and without flux tilt. Also in all four cases the power distribution per assembly was calculated. These calculations were in support of extensive deterministic calculations carried out at IRSN. As far as the Monte Carlo algorithms were concerned, the development was continued from the PAR2011 report. At that stage, superhistories had been inserted in MCNP. The next stage of modifying the fixed source DSA patch to work in the eigenvalue mode and then combining the result with the superhistory patch had been proposed but not realized. The algorithm has now been finished and includes some new options (tallying and variance reduction according to which fission generation it is) as well as a variable number of fission generations per superhistory and the option of varying the v–value to ensure a reasonable supply of children at each normalization. The algorithm has been tested on some realistic thermal and fast fission problems, with both in– and ex–core tallies.

Use of Monte Carlo in State-of-the-Art PWR Design: Study of Tilt in the NEA UAM PWR Benchmark and Development and Testing of New Algorithms within Monte Carlo Eigenvalue Calculations employing the Source-Iteration Method

Burn, Kenneth William
2013-09-10

Abstract

This report is a continuation of two submitted last year (PAR2011). One concerned the collaboration between ENEA and IRSN (Institut de Radioprotection et de Sûreté Nucléaire) dealing with safety issues related to the thick steel reflector of a typical large size GEN III+ reactor design. The other dealt with developments in Monte Carlo algorithms for eigenvalue calculations. These developments partially fed off the PWR modelling, some of which is at the limit of current methodologies and computer capacity. As far as the PWR modelling is concerned, focus was on the phenomenon of flux tilt. Monte Carlo calculations were run on a 2-dimensional model of a NEA benchmark using the same water density variation as previously (±1.50% change in water density in the outer assemblies of opposite quadrants). Results were obtained for the power variation in the whole quadrants for four situations: heavy steel reflector and conventional baffle+water reflector, with and without flux tilt. Also in all four cases the power distribution per assembly was calculated. These calculations were in support of extensive deterministic calculations carried out at IRSN. As far as the Monte Carlo algorithms were concerned, the development was continued from the PAR2011 report. At that stage, superhistories had been inserted in MCNP. The next stage of modifying the fixed source DSA patch to work in the eigenvalue mode and then combining the result with the superhistory patch had been proposed but not realized. The algorithm has now been finished and includes some new options (tallying and variance reduction according to which fission generation it is) as well as a variable number of fission generations per superhistory and the option of varying the v–value to ensure a reasonable supply of children at each normalization. The algorithm has been tested on some realistic thermal and fast fission problems, with both in– and ex–core tallies.
Reattori nucleari ad acqua leggera;PWR;Metodi Monte Carlo;Neutronica
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/20.500.12079/7570
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