# Clarifying Geometric and Material Buckling

1. Apr 21, 2009

### Szymanski

Hello everyone,

I am studying for an upcoming exam and have become somewhat confused as to exactly what geometric and material buckling represent. Are they representative of the shape of the neutron flux distribution in the reactor? Are these quantities related to the structural deformation of the fuel due to temperature gradients?

As far as I have been able to determine, these quantities are useful to determine conditions for criticallity, but I would still like to understand them better, and all the copies of Stacey are checked out of the library!

Any insights or explanations would be appreciated.

2. Apr 22, 2009

### QuantumPion

Geometric buckling is a measure of the curvature of the neutron flux distribution of a reactor at equilibrium due to its geometry. For a slab reactor, Bg^2 = (pi/a)^2 where a is the extrapolation distance where flux is zero.

Material buckling is a description of the characteristics of the fuel material in an infinite medium. Bm^2 = n*Sf-Sa / D (neutron production rate minus absorption rate divided by the neutron diffusion coefficient)

A reactor is critical if the geometric buckling equals the material buckling.

3. Apr 22, 2009

Thank you.