INCREASING ELECTRICAL OUTPUT OF BRUCE POWER UNITS BY CONTROLLING THE RISE IN REACTOR INNER ZONE INLET HEADER TEMPERATURE

Abstract

The Reactor Inlet Header temperature has been increasing more rapidly in most CANDU units, compared to the original aging predictions. The Reactor Inlet Header temperature is monitored and high temperature alarms are required to prevent operation outside the safe operating envelope as supported by the safety analysis. Operating adjustments to prevent high Reactor Inlet Header temperature alarms include reducing pressure in the steam generators, followed by reduction of unit reactor power resulting in loss of production.

Multiple design modification alternatives were assessed for Bruce Power units based on their suitability, risk, economics and effectiveness in reducing the Reactor Inlet Header temperature with minimum system level impacts. PEPSE based model was used to evaluate the effect of design alternatives on the thermal cycle efficiency and possible increase in production. External bypass of high pressure feedwater heaters (tube side) was selected as the best design alternative and the modification has been operational for several years in two Bruce A units. It has also been recently implemented in one Bruce B unit and is being commissioned. Implementation of the high pressure feedwater heaters bypass design change allowed an increase of over 100 kPa in steam generator pressure and up to 2.5% increase in reactor power.