EPR - Flamanville 3 and Olkiluoto 3: Chemistry challenges during commissioning phases and the beginning of operation - T07-3

Since the end of the Hot Functional Testing (HFT) at Flamanville 3 (FA3) in February 2020, several significant commissioning steps have been performed with an essential role of the chemistry: -Delivery of first Fuel Assemblies into the Spent Fuel Pool (SFP). -Additional tests under Cold Functional configuration with reactor vessel open (CFTRVO) and Hot Functional Test (HFT) conditions with the objective of verifying and requalifying the equipment and systems following material modifications and requirement evolutions. -Additional hydraulic tests for secondary side and steam generators -Specific individual system tests as TEG/GWPS (Gaseous Waste Processing System) delay beds with radioactive gas and TEP/CSTS (Coolant Storage and Treatment System) evaporator for boron recycle. In parallel, at Olkiluoto 3, the last Commissioning phases have been successfully achieved: - Fuel Core loading with the application of a specific chemistry surveillance in the reactor and fuel pools to ensure the boron criteria and to limit the impurity concentrations. - Pre-critical Tests at Cold and Hot conditions enabling to verify the improvements included in some systems for chemistry objectives as for instance the RCV/CVCS (Chemical and Volume Control System) modifications for depleted zinc injection. - First Criticality and Power Escalation Tests with evolution of chemical and radiochemical conditions and application of appropriate actions to limit risks. For instance: -the hydrogen and lithium injection in order to accomplish the OTS (Operational Technical Specifications) requirements due to the nuclear reaction. - The depleted zinc injection in order to reduce the material corrosion, the term source activation and to inhibit the cobalt/nickel deposition on primary surfaces. -The control of the main radionuclides in order to limit the potential impacts on dose exposure and radioactive waste (liquid/gas effluents and solid wastes): fission products (coming from fuel failures and fuel tramp contamination), activation/corrosion products (coming from the activation of chemistry elements, impurities and material components present in the primary circuit). EDF and TVO collaboration is established since the beginning of EPR Project, and it has been reinforced since 2018 during OL3 HFT. This collaboration will be continued to ensure the chemistry conditions during OL3 power operation and the following FA3 commissioning phases. Chemistry role has always to be kept at high level due to its multiply interfaces (safety, hazards protection, material integrity, radioprotection, environment). The key insights and lessons drawn from FA3 and OL3 are analyzed in this paper to provide essential inputs for the next challenges of nuclear industry (EPR-Hinkley Point C, construction of new reactors as EPR2). (authors)