Shape optimization of a sodium cooled fast reactor

¹ EDF R&D, département SINETICS, 1 avenue du Général De Gaulle 92141 Clamart
² École Polytechnique, CMAP, Route de Saclay, 91128 Palaiseau, France
³ École Centrale de Paris, Polytechnique/EDF internship

Abstract

Traditional designs of sodium cooled fast reactors have a positive sodium expansion feedback. During a loss of flow transient without scram, sodium heating and boiling thus insert a positive reactivity and prevents the power from decreasing. Recent studies led at CEA, AREVA and EDF show that cores with complex geometries can feature a very low or even a negative sodium void worth.^{(1, 2)} Usual optimization methods for core conception are based on a parametric description of a given core design⁽³⁾.⁽⁴⁾ New core concepts and shapes can then only be found by hand. Shape optimization methods have proven very efficient in the conception of optimal structures under thermal or mechanical constraints.^{(5, 6)} First studies show that these methods could be applied to sodium cooled core conception.⁽⁷⁾ In this paper, a shape optimization method is applied to the conception of a sodium cooled fast reactor core with low sodium void worth. An objective function to be minimized is defined. It includes the reactivity change induced by a 1% sodium density decrease. The optimization variable is a displacement field changing the core geometry from one shape to another. Additionally, a parametric optimization of the plutonium content distribution of the core is made, so as to ensure that the core is kept critical, and that the power shape is flat enough. The final shape obtained must then be adjusted to a get realistic core layout. Its caracteristics can be checked with reference neutronic codes such as ERANOS. Thanks to this method, new shapes of reactor cores could be inferred, and lead to new design ideas.