An Adaptive Algebraic Multigrid for Reactor Criticality Calculations

An effective algorithm for reactor criticality calculations has been developed, based on shift-and-invert iterations with an algebraic multigrid solver and Wachspress rebalancing. Use of rebalancing makes it possible to transform the system into the “natural” basis in which a sequence of levels and intergrid operators are effectively calculated. The main problem is to make such a procedure robust with respect to the error of approximation of the main eigenfunction without loss of efficiency. This is achieved by coordinating the shift value with the value of the error of the current approximation of the main eigenfunction used in the rebalancing procedure.