VARIATIONAL ESTIMATES FOR USE WITH THE IMPROVED QUASI-STATIC METHOD FOR REACTOR DYNAMICS

A new variational estimate for dynamic reactivity that accounts for de layed neutron hold-back is introduced and adapted for use with the imp roved quasistatic (IQS) method. Numerical tests on a large light water reactor model indicate that the computational effort required with th e IQS method can be reduced by a factor of 3 to 4 by using this new va riational estimate of dynamic reactivity. With comparable computationa l effort, the accuracy of the standard IQS method, which uses the flux shape interpolation/recomputation procedure and a first-order estimat e of static reactivity, can be improved by using a standard variationa l estimate without the flux shape interpolation/recomputation procedur e, and it can be further improved by using the new variational estimat e of dynamic reactivity.