Study of the methods for modelling incomplete assemblies in pools for criticality calculations
Sánchez Agostini, Paula (2025)
Diplomityö
2025
School of Energy Systems, Energiatekniikka
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Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi-fe2025050838434
https://urn.fi/URN:NBN:fi-fe2025050838434
Tiivistelmä
The presents work focuses on the methods to evaluate the criticality of incomplete assemblies; where the absence of an unknown number of fuel rods (the so-called “Missing Fuel Rods”) can lead to an increase in reactivity in the spent fuel storage pool.
Different methods to model the effect of the Missing Fuel Rods spatial distribution on criticality have been proposed in the last years. The aim of this work is to study and implement the so-called “contact surface method”, and to compare it with the method of generational Genetics Algorithms. The contact surface, a geometric parameter of the Missing Fuel Rods pattern, should be able to parametrize the reactivity of the assembly.
The method has been applied to several study cases of a PWR assembly. Three environments have been studied: the isolated assembly, the assembly surrounded by two sides of water and two sides of concrete, and the array of assemblies. To evaluate the method, the Metropolis-Hastings algorithm has been put in place to create the configurations of interest. For the criticality calculations, the Monte Carlo code SERPENT2 has been used.
Results proved that the contact surface parameter gathers together configurations with similar keff, with more or less precision for the different study cases. Some of the patterns generated by means of Metropolis-Hastings algorithm have been found to be more reactive than patterns obtained by other methods, such as the generational Genetics Algorithms. This gives further evidence of the pertinence of the method.
Different methods to model the effect of the Missing Fuel Rods spatial distribution on criticality have been proposed in the last years. The aim of this work is to study and implement the so-called “contact surface method”, and to compare it with the method of generational Genetics Algorithms. The contact surface, a geometric parameter of the Missing Fuel Rods pattern, should be able to parametrize the reactivity of the assembly.
The method has been applied to several study cases of a PWR assembly. Three environments have been studied: the isolated assembly, the assembly surrounded by two sides of water and two sides of concrete, and the array of assemblies. To evaluate the method, the Metropolis-Hastings algorithm has been put in place to create the configurations of interest. For the criticality calculations, the Monte Carlo code SERPENT2 has been used.
Results proved that the contact surface parameter gathers together configurations with similar keff, with more or less precision for the different study cases. Some of the patterns generated by means of Metropolis-Hastings algorithm have been found to be more reactive than patterns obtained by other methods, such as the generational Genetics Algorithms. This gives further evidence of the pertinence of the method.