Steam Generator and Preheater Tube ID Fouling and the Impact on Reactor Inlet Header Temperature and Eddy Current Inspections

Abstract

Materials selection is an important consideration in new build and refurbishment of Heavy Water Reactors (HWR). This paper will focus on the impacts of the deposit of magnetite on the tube ID of steam generators and preheater. Bruce Power OPEX is being shared to illustrate the importance of materials selection.The deposit of magnetite on the tube ID of steam generators (SG) and preheater (PH) has two significant impacts that will be presented. Firstly, the degradation in SG and PH thermal performance causes a rise in the reactor inlet header temperature (RIHT). This rising trend continues unabated as long as deposits on the tube ID continues. If not managed this may result in loss of production due to the RIHT limits being reached. Mitigating actions such as tube ID cleaning is only a temporary solution as it does not stop the root cause which is feeder flow accelerated corrosion (FAC).Secondly, deposit of magnetite on the tube ID of steam generators (SG) and preheater (PH) has an impact on tube inspections as required by CSA N285.4. There are two impacts on SG and PH inspections. ID deposits reduces the clearance for eddy current probes in the tubes and make it more difficult to acquire inspection data. Additionally, tube ID deposits can reduce the effectiveness to detect and size flaws in the SG and PH tubes. Both issues make eddy current inspection a challenge for the utilities.These impacts affect the operation and inspection and maintenance of CANDU nuclear power plants at Bruce Power. Where possible these issues should be addressed in any future new build or refurbishment of HWR power plants.