Spatial Power Control in Large CANDU Reactors: The Whys and Wherefores

摘要

The ratio R exp 2 /M exp 2 (reactor core area/neutron interaction area), a measure of reactor core size, has increased by a factor of 6 as the CANDU reactor has evolved from NPD to the proposed PHW-1250 MWe design. Consequently, the various regions of the larger reactor cores are less tightly coupled. Another trend in CANDU design has been an increase in flux flattening in the reactor core, to increase the power form factor and hence power output from a given core size. This also decreases the coupling between core regions. In the early CANDU reactors (e.g. NPD, Douglas Point) little or no spatial control action was necessary. Bulk power control, based on out-of-core flux monitors, was sufficient. However, current CANDU reactors require spatial power control and use in-core flux detectors to provide the information on spatial power distribution required by the control system. In this paper we discuss the evolution of spatial power control in CANDU reactors and outline some of the methods used to assess the spatial controllability of current and future CANDUs. To illustrate the methods, reference is made to a recent assessment of the spatial controllability of a large CANDU-BLW reactor. (Atomindex citation 09:411773)