ZINC INJECTION IMPLEMENTATION PROCESS AT EDF: RISK ANALYSIS, CHEMICAL SPECIFICATIONS AND OPERATING PROCEDURES

摘要

Zinc's ability to replace cobalt from oxides of primary circuit surfaces has provided the first motivation for implementing the zinc addition in BWRs since the mid-1980s. The beneficial results regarding dose reductions have been demonstrated; therefore, this practice has been extended to PWRs since the 1990s, not only for radiation fields' considerations, but also for reducing PWSCC. From the beginning of the 2000s, further reasons to inject zinc associated with the fuel management process have been identified (e; g; power increase, high burn-up, and/or cycle length increase). These evolutions must be accompanied by an adapted chemistry program in order to mitigate the crud deposition on fuel assemblies and the consequent AOA/CIPS or localized clad corrosion risks. The source term reduction (due to the decrease of the general corrosion rate of several materials) and the absence of negative impact on alloy cladding in the presence of zinc in the primary coolant are the main reasons for selecting zinc injection as a reliable option for preventing and/or mitigating the effects of fuel deposits.These three PWR motivations (field radiation, components performance, and fuel reliability) are also the major objectives of CANDU®1, WWER, and new reactors (EPR, AP1000), where the zinc injection feasibility analyses are in progress in order to improve the safety of their operating conditions.With the purpose of achieving the optimal results of zinc injection, the process's implantation in a unit must be conducted with an appropriate risk analysis, covering all possible domains affected by this primary coolant chemistry modification : safety, fuel and component performance, radioprotection, waste, environment, human and installation security, human and material resources, staff formation, and documentation.EDF has performed a complete analysis of this enlarged scope, relying upon theoretical and experimental results as well as NPP feedback. This paper describes EDF's strategy and the different measures adopted by EDF to provide the necessary tools to the French units : zinc injection procedures, risk analysis, chemistry -radiochemistry surveillance programs, and chemical specifications. This work can be useful for other utilities, assisting them in optimizing and/or implementing the zinc injection in the most suitable conditions, which would help to obtain the expected results in the current and the future reactors.