Vacation matrix method for fission source convergence in Monte Carlo criticality calculations

Joshua P Finch, Purdue University

Abstract

Fission source convergence in Monte Carlo criticality calculations can be difficult for some types of problems, particularly those with weak neutron communication between different regions of the problem. Several attempts to solve this problem have met with limited success. The Fission Matrix method has been the method of choice for the acceleration of convergence of the fission source distribution to the fundamental eigenmode, or steady-state distribution. A new approach is introduced to circumvent the statistical noise of the estimated fission matrix and to make the physical model amenable to improvement by engineering means. The new Vacation Matrix method achieves the correct fission source distribution by identifying the key variables that contribute to the noise of the solution. It determines which of these variables are independent of one another and can be altered without changing the real system but, instead, by changing only the spatial binning used to define the solution matrix geometry---these variables are the leakage probability and the vacated source probability. The said variables, and their associated noise, are strategically removed from the system model, leading directly to the vacation matrix model. The Vacation Matrix method is a new way of looking at an old problem.

Degree

Ph.D.

Advisors

Choi, Purdue University.

Subject Area

Nuclear physics

COinS