2-D 2-group neutron noise simulator and its application to anomaly localisation

Paper in proceeding, 2001

This paper presents a so-called neutron noise simulator, essentially an algorithm to calculate the dynamic transfer function, and its use in a procedure allowing to locate a noise source from the neutron detector readings. The noise simulator relies on the two-group diffusion approximation in 2-D. Benchmarking of this calculator versus analytical solutions showed that the finite difference discretisation scheme used in the simulator was accurate in case of homogeneous cores and a central noise source. The localisation algorithm was found to give correct results as long as one single noise source exists in the core and when the transfer function from the removal cross-section noise to the thermal neutron noise was used. Applying this localisation procedure to the Forsmark-1 BWR (Sweden) when a local instability event occurred (cycle 16) pointed out, via the use of an appropriate set of detectors, a region close to where an unseated fuel element was discovered.