抄録
From the early 1990s, both loop dose rate index and annual collective dose of the French PWR fleet have significantly decreased. This positive evolution is mainly linked to the progress made in source term reduction and worker exposure limitation during maintenance operation. As one of the bases of the current radiation protection system is related to the assumption of a linear dose-response without a threshold, the so-called Linear-no-Threshold (LNT) hypothesis, maintaining the radiation protection improvement remains a challenge. This is an aim, not only for the operating French fleet, but also for the new build reactors. To achieve that goal, regarding the source term topic, we need to perform more accurate analyses in the fields of chemistry, material composition, surface state, component design, and component replacement, in order to identify the optimal values of key parameters. Complementarily to Operating Experience data study, the OSCAR code, which last version (v1.4) has been released in December 2017, can be an effective tool to perform such analyses. This paper focuses on the assessment using the OSCAR v1.4 code of the impact of 3 coordinated chemistries on the cobalt 58 surface contamination of the steam generators (SG). The simulation uses as input data set the characteristics of a French 3 loop PWR with 690 TT alloy SG. The impact of the B/Li coordination is studied for 10 cycles of 283 Equivalent Full Power Days (EFPD) each. The results show that: - The production of Ni-58 in the primary coolant is mainly due to both dissolution/precipitation of the inner and outer oxide/deposit and erosion/deposition of the deposit/outer oxide mechanisms, the first one being directly influenced by the pHT and the second one indirectly. - The production of Co-58 by activation of Ni-58 in the core is primarily linked to the precipitation mechanism on the hotter part of the core and to the deposition mechanism on the colder part of the core. - The erosion/deposition mechanism is the main mechanism involved regarding the presence of Co58 in the coolant and the out-of-flux contamination phenomenon. - The antagonistic effect for the dissolution/precipitation mechanisms identified for the SG surface contamination (increase of the contamination in the inner oxide and decrease of the contamination in the outer oxide/deposit, when the pH decreases) is less decisive in the case of the Co-58 contamination than in the Co-60 one.
