Evaluation of activated corrosion products in primary coolant circuit of AP-1000 under grid frequency stability mode

The AP1000 is a strong candidate to participate in grid frequency stability because of its better transient response capability. The investigations are essential to sort the behavior of activated corrosion products (ACPs) under frequency control induced power transients. This paper seeks to assess the variation of ACPs in the primary coolant circuit of AP-1000 under base-load as well as grid frequency stability modes. The computer program CPA-AP1000 is modified to incorporate frequent power fluctuations. The simulation results depicted that short-lived ACPs (⁵⁶Mn, ²⁴Na) build up fairly rapidly whereas long-lived ⁵⁹Fe, ⁹⁹Mo, ⁵⁸Co and ⁶⁰Co exhibited slow rise, under customized base-load mode. All of the ACPs are noticed to attain a saturation value of specific activity after several hours of the reactor operation. The corresponding ACPs (⁵⁶Mn, ²⁴Na, ⁵⁹Fe, ⁵⁸Co, ⁹⁹Mo and ⁶⁰Co) in the primary coolant under frequency fluctuation mode, are noted to be governed by the rise and fall in operating power level. The investigations are extended to compare the variation in the behavior of ⁵⁶Mn, ²⁴Na, ⁵⁸Co, and ⁶⁰Co in primary coolant and on the inner walls of piping and core structure, under the grid frequency stability mode. The activity due to corresponding ACPs is the highest inside the core followed by the coolant and piping structure. The results revealed that activity associated with ACPs with shorter half-lives is more susceptible to power oscillations, as compared to those having longer half-lives. The post-fluctuation activity of corresponding ACPs is also explored and found to be significantly dependent on the final and post-fluctuated power levels. The long-term dose of ACPs with longer half-lives is found to be more significant, because their activity holds for an extended spell. This study provides a good insight into on-power accessibility of the primary coolant circuit for recurrently happening operating scenarios.