An accelerated characteristics method including a spatial polynomial expansion for cross sections

This paper deals with the spatial polynomial treatment for cross sections recently introduced in the 3D method of characteristics solver of the APOLLO3 neutron transport code. The adaptation of the DPN synthetic acceleration method to the new approach is presented, showing how the acceleration coefficients are reformulated to take into account the polynomial description of media properties. An adaptive quadrature technique for the evaluation of the resulting transmission integrals is also addressed. The results of the depletion sequence of a 7x7 PWR assembly are presented, proving the clear advantage of using the polynomial method over the traditional step-constant one. (authors)