Monte Carlo and deterministic evaluation of pressure tube creep in a CANDU lattice

In the CANDU reactor, the coolant channel diameter increases due to the pressure tube creep resulting from neutron irradiation damage. For two diametric creep (2.5% and 5%) cases in the standard 37-pin CANDU lattice, the pressure tube creep was evaluated from the neutronic point of view with the continuous-energy Monte Carlo depletion code McCARD and the collision probability neutron transport code HELIOS. Impact of the crept pressure tube is evaluated in terms of the lattice reactivity, void reactivity, pin-wise power, atom density of plutonium isotopes, and fuel temperature coefficient. The results show that both McCARD and HELIOS codes provide consistent results and the coolant void reactivity increases noticeably with the crept geometry. (author)