Fuel burn up

Aprile 9th, 2021 | by Marcello Colozzo |

Appunti ed esercizi di Fisica del Reattore nucleare elaborati dell'ing. Giorgio Bertucelli.

A nuclear fission supplies an average total energy of about 200MeV , a useful nember to remember. The complete fission of 1g of U²³⁵ thus produces a quantity of energy equal to

This relates to fuel burn up. Maximum theoretical burn up would therefore be

This figure applies only if the fuel were entirely composed of fissionable nuclei (U²³⁵, Pu²³⁹, U²³³) and if these nuclei were all fissioned. Reactor fuel, however, contains other uranium or thorium isotopes. Also, the fissionable isotopes in it cannot be all fissioned because of absorbtion stopping the chain reaction. The meaning of fuel is all uranium, plutonium and thorium isotopes; it does not include alloying or other chemical compouns or mixtures. The term used fuel material is to refer to fuel plus other materials.

Problem
Consider the following case of fuel burn up:
a) 2000MW d/ton with metallic uranium. Compute the per cent fuel that has fissioned.

Solution