Impact of Long Term Injection of Platinum (HWC/OLNC) on Water Chemistry, Crud Behavior and Platinum Deposition

摘要

A good understanding of the impact of On-line NobleChemTM (OLNC) on water chemistry and fuel performance is of great importance to be able to prevent potential negative impact on fuel performance and activity build-up. In November 2008, Kernkraftwerk Leibstadt (KKL) started injection of Pt in the reactor water during power operation (HWC/OLNC). An extensive testing and evaluation program has been performed after NWC before the startup of HWC/OLNC transition as well as following the first and fourth OLNC application in KKL. The results have been analyzed in a joint project between KKL, Westinghouse and EPRI and this paper will present results concerning the impact of long term injection of platinum on water chemistry and crud deposition. Increased levels of Co-60 have been observed at KKL. To reduce radiation dose rates, the Zn injection in the feedwater was increased. The change in Zn injection rate did however not result in the desired increase in reactor water Zn level. This indicates increased Zn deposition on fuel, likely caused by the increased release of Fe from the structural surfaces after HWC/OLNC injection. In addition, the increased Zn deposition on fuel may have increased the observations of crud spalling. After four cycles of OLNC, the crud deposition profile was similar to the profile observed pre-OLNC, indicating the top-peaked profile observed after the first cycle of OLNC to be a transition effect. Nevertheless, there are indications that the transition to a modified crud deposition on the fuel might still be ongoing, even though the feed water iron input has been reduced by plant modifications, such as replacement of low pressure turbines and pre heaters fabricated with improved materials. There has been a concern that Pt, from the OLNC application, if deposited close to the fuel cladding metal, could increase the corrosion and/or hydrogen uptake in zirconium metal. However, the SEM/TEM and crud analysis in this study shows that Pt was mostly found in the outer crud layer and mostly on the hematite crud particles.