Ontario based power utility engaged Promation Nuclear to design and build the first-of-a-kind CANDU reactor permanent start-up instrumentation (PSUI) that would be used to replace the traditional temporary start-up instrumentation used to date.
Deployed from the Reactivity Mechanism Deck (RMD), the instrumentation and PSUI mechanism would be exposed to some of the harshest environments of any instrumentation in the reactor monitoring and control inventory, but it would need to meet a service life of 40 years and provide high reliability. The technical challenges were significant, due to very tight spatial constraints for the instrumentation mechanism, which also forms part of the CSA N285.0 Class 2 pressure boundary. The instrumentation used to measure reactor power during start-up is extremely sensitive and cannot remain in the reactor core during normal full-power operation; therefore, the mechanism would need to provide a means of raising and lowering the instrumentation in and out of the reactor core as required, all while passing the extremely faint signal through the mechanism to the amplifier on the RMD.
Promation Nuclear designed a robust mechanism that could raise and lower the instrumentation within one of the existing vertical flux detector guide tubes, and precisely position it in the reactor. The instrument could also be fully withdrawn from the reactor core so that it would not get damaged during normal full power reactor operation. The main mechanism housing was registered as a Class 2 category H fitting and was seismically qualified in accordance with N289.1. The mechanism underwent reliability testing, and key components were tested in a hot cell to determine radiation resistance and overall life.
Ontario based power utility will benefit greatly from a permanently installed start-up instrumentation by removing the need to install and remove the temporary instrumentation for each start-up, thus reducing the overall outage duration and the additional radiation dose accumulated by the control maintenance personnel.