Reactor Design: WIMS10 & PANTHER - Queries

[Syed Alam]

I am currently using WIMS and PANTHER for reactor design. I have some queries:

WIMS10
1. Why does WIMS10 use 172 energy group?
2. Why does it collapse energy group to 11 energy group for calculation?

PANTHER
1.Why does PANTHER use 2 energy group for calculation? Is it possible to cover all the energy ranges by only 2 energy group?

 

[Astronuc]

I am currently using WIMS and PANTHER for reactor design. I have some queries:

WIMS10
1. Why does WIMS10 use 172 energy group?
2. Why does it collapse energy group to 11 energy group for calculation?

PANTHER
1.Why does PANTHER use 2 energy group for calculation? Is it possible to cover all the energy ranges by only 2 energy group?

WIMS is a lattice code, which models the individual fuel rods in an assembly, and PANTHER is a 3D core simulation code, which uses inputs from WIMS to simulate the depletion and power distribution in a reactor core.

Lattice codes use higher resolution energy groups to treat resonances between fast fission and thermal energies, particularly strong absorption resonances of burnable poisons like Gd 155, 157 and various rare Earth isotopes, e.g., Nd, Sm, Pm, . . . . since some are strong poisons. The 172 groups would be collapsed into 11 groups and further reduced to two groups for a 2 group, neutron diffusion code. Most neutron diffusion codes were written when memory was very limited and the speed of processors was slow compared to today's microprocessor, so the calculations were rather coarse. Such a neutronics code also has a basic thermal hydraulics model, or otherwise, is coupled to a more detailed TH code.

A summary of PANTHER - http://www.answerssoftwareservice.com/panther/Validation of important fission product evaluations through CERES integral benchmarks
http://curie.ornl.gov/system/files/documents/38/ndata07172.pdf

Optimization of energy resources suggests increased fuel residence in reactor cores and hence improved fission product evaluations are required. For thermal reactors the fission product cross sections in the JEF2.2 and JEFF3.1 libraries plus new evaluations from WPEC23 are assessed through modelling the CERES experiment in the DIMPLE reactor. The analysis uses the lattice code WIMS10. Cross sections for 12 nuclides are assessed. The thermal cross section and low energy resonance data for 147,152Sm and 155Gd are accurate to within 4%. Similar data for 109Ag, 143Nd and 149Sm are within 8% while 95Mo, 99Tc, 103Rh, 133Cs and 145Nd are within three benchmark standard deviations at ~12%. The use of the 172 XMAS group scheme is adequate for all nuclides considered except 153Eu.

Evaluated Data Library for the Bulk of Fission Products - a summary of some important radioisotopes.
https://www.oecd-nea.org/science/wpec/volume23/volume23.pdf