Calculations of the neutron flux outside BWR 8x8 spent-fuel assemblies and the sensitivity to fuel pin diversion

• Published in: Nuclear technology Vol. 146; no. 1; pp. 58 - 64
• Main Authors: Jansson, P, Hakansson, A, Backlin, A
• Format: Journal Article
• Language: English
• Published: 01.04.2004
• ISSN: 0029-5450

The possibility of detecting replaced fuel rods in a spent-fuel assembly by means of measurement of the emitted neutron- and gamma-ray radiation has been investi- gated by computer simulations. The radiation field outside a boiling water reactor 8 X 8fuel assembly with varying patterns of fuel rods replaced with lead dummies was calculated using a simple model for the source distribution and the Monte Carlo code MCNP-4C for the radiation field. In particular, the sensitivity of the thermal neutron field as measured in a Fork detector to various replacement patterns was investigated. The results suggest a detection limit of 5% of the fuel mass replaced, i.e., 3 out of 63 rods, independently of the pattern of the replaced rods.