Stabilising boiling water reactors by optimising the position of the feedwater sparger

The influence of changing the position of the feedwater sparger on the thermal-hydraulic stability of natural-circulation boiling water reactors (BWRs) is investigated. Frequency-domain, linear stability analysis is applied using a reduced-order dynamic model. It is found that the phase with which the temperature oscillations, created at the feedwater sparger, reach the core inlet has a significant influence on the stability. This phase is influenced by the position of the sparger. It is shown that moving the sparger to the core inlet has a stabilising influence. Similar result is found using the thermal-hydraulic code MONA.