That's strange since ENDF should have cross sections for
10B and
11B as does JEFF, and it's the
10B that is key due to it's high thermal neutron capture cross section.
I cannot find a reference to NCOMP, although that appears to refer to the number of compositions, so my question would be, has one properly defined the compositions for the various materials?
Pyrex is complicated since Pyrex is composed of (as percentage of weight): 4.0% boron, 54.0% oxygen, 2.8% sodium, 1.1% aluminum, 37.7% silicon, and 0.3% potassium, in one formulation. Another formulation is: SiO
2 81%, Na
2O 4.0%, K
2O 0.5%, B
2O
3 13.0%, Al
2O
3 2.0%.
https://www.pegasus-glass.com/Portals/0/technical_infopyrex.pdf
One could ignore the K
2O, and make it Na
2O, then make sure the components add to 100%. Also, the isotopic content may be different from natural.
Is one modeling a 17x17 lattice? Are the Pyrex rods rods located in the guide tube positions?