Simplified Method for Quantification of Multi-Unit STC

When multiple NPPs were constructed in Korea, the safety of the site had been assured by the domestic technical criteria based on the IAEA standards. However, the existing criteria for multi-unit sites are difficult to satisfy the public demands in the current status. Thus it is necessary to develop a clear and comprehensive method for assessing the multi-unit safety. To perform multi-unit PSA, we should consider a lot of combinations between the units. So, it is necessary to reduce the number of combinations to appropriate level. For this, we aim to suggest a simplified method to quantify multi-unit STC combinations in this paper. In this paper, the simple method to quantify multi-unit STC has been suggested. Without additional multi-unit Level 2 PSA, the proposed method can quantify the combinations of STC using the results of single-unit Level 2 PSA. However, this method is efficiently used under the assumptions that all units at the same site are identical at full power, and independent from each other. In the real world, various types and operation modes of the units are operated at the same site. In addition, it may be difficult to apply the considerations in terms of site level such as dependency between the units because the quantification using the proposed method is simply performed by multiplying each STC fraction.