A natural-uranium graphite lattice absorbs a fraction of its thermal neutrons in the fuel

PHYSICS · Subjective · Fermi University Physics · Nuclear Physics · Fission, fusion and nuclear energy · Fission, fusion and nuclear energy

Energy from Physics, Ch The critical reactor: neutron diffusion, buckling and the size of a core

Problem

A natural-uranium graphite lattice absorbs a fraction

f = 0.85

of its thermal neutrons in the fuel. Pure graphite has a diffusion area

L_M^2 = 3500\,\mathrm{cm^2}

. Using

L^2 \approx L_M^2(1-f)

, estimate the thermal neutron diffusion length

L

of the lattice.