Abstract
The emergency operating strategy of design extension conditions (DEC) has become an increasingly important hot topic in the nuclear industry of China. The medium break loss of coolant accident (MBLOCA) with medium head safety injection (MHSI) unavailable is a typical and important condition for emergency operating strategy analysis. As MBLOCA results loss of reactor coolant inventory, the reactor core would be uncover if the inventory can’t be compensated in time, and lead to unacceptable results of emergency operating strategy, such as reactor core damage. Therefore, the inventory complement strategy is a key part of MBLOCA with MHSI unavailable emergency operating strategy. And the LHSI is the primary option in the inventory recovery strategies for MBLOCA with MHSI unavailable accident. However, establishing the flow rate of LHSI requires operator to depressurize/cooldown the primary system in a sharp rate, which will induce a pressure shock to primary system. Meanwhile, the emergency operating strategy should consider the MHSI maintain time, and not initiate the primary system depressurizing action unless there is void in the head of pressure vessel. Above all, the judgment of whether to depressurize/cooldown the primary system is the key of the emergency operating strategy for MBLOCA with MHSI unavailable accident. This paper raises two kinds of emergency operating strategy to deal with this accident. One is inventory complement strategy which is based on the outlet temperature of reactor hot leg judgment, while another is based on vessel level judgment. In order to evaluate the effectiveness of these two emergency operating strategies, a best-estimate calculation program is used to simulate a series size of MBLOCA with MHSI unavailable accidents. According to the calculate results, when the primary system depressurize/cooldown rate is fixed, for some special break size, the strategy which is based on outlet temperature of hot leg is too late to mitigate the reactor core inventory. While the calculate results of the strategy which is based on vessel level show it’s a timely and reasonable inventory restore strategy for MBLOCA with MHSI unavailable accident emergency operating strategy.
