On-line power monitoring in CANDU using PMFD

The use of digital computers in the on-line control of the spatial power distribution has been well established in CANDU reactors. The instantaneous spatial power distribution in a CANDU reactor is calculated on-line, once every two minutes, by the Flux mapping program. This program synthesizes the global reactor power distribution using a least-squares fit to a set of measured flux detector readings to find amplitudes for a subsequent expansion of a precalculated set of flux harmonics. The reactor control program compares the mapped power shape with the reference power shape. The difference between these two power shapes is minimized by the appropriate deployment of the zone control system. The higher fissile content and the higher fuel burnup of SEU reactors can result in higher power ripples than those in the CANDU natural uranium reactors. Also, concerns of fuel performance at high burnup require accurate on-line monitoring of individual rippled channel and bundle powers. The present Flux Mapping program cannot meet the requirements of Highly Advanced CANDU reactors. The power mapping finite difference (PMFD) program is specifically designed to supplement or replace the Flux Mapping program in the spatial control system of CANDU SEU reactors. It solves the system of three-dimensional, two-energy group neutron diffusion equations on-line. A unique feature of PMFD is its ability to use measured detector fluxes as internal boundary conditions in the flux solution. The resulting flux shape satisfies both the distribution of material properties and the measured flux values