Problem Description

Abstract

Gobstopper.inp is a test problem that is designed to be a nice middle-of-the-road problem that balances work done in tracking and collisions. It is domain decomposed to stress particle communication between domains while in the tracking phase. This is an eigenvalue problem that is forced to run for 25 cycles with 10,000 particles per cycle. The final eigenvalue (keff) should be around 0.998 with some uncertainty reported. The cross sections are stored in a 230 energy multigroup fashion, but the collisions use continuous energy physics. The geometry is 1,000 nested spheres made of random materials from the list of materials found in a reactor. The shells are uniformly spaced up to 10 centimeters. However, 80% of the shells are made of highly enriched uranium found in the Godiva criticality experiment. This was to push the criticality eigenvalue (keff) closer to 1.0. The material compositions may be found in the material section. The densities are all the same for each material and can be found in the cell description. The geometry is further decomposed into 64 (4 X 4 X 4) cube domains. The problem is initially sourced in the first cycle with particles uniformly over a 10 cm sphere. Their energy spectrum is represented by the outgoing fission spectrum from U-235 nucleus hit by a 1.5 MeV neutron. The tallies are mostly turned off except for the balance, eigenvalue and spectrum tallies. The spectrum and eigenvalue tallies are written out to the .plt file. The balance and eigenvalue tallies are written to the .out file.