Research and Application of Influence of Black Rod and Gray Rod on Control Rod Drop Time in Nuclear Power Plant

In order to achieve more accurate and detailed drop time of control bank in nuclear power plant, based on the force analysis of control rod assembly in Chinese Pressurized Reacter 1000 MW (CPR1000) and Advanced Chinese Pressurized Reactor 1000 MW (ACPR1000⁺) nuclear power units and the test results of 11 units, it is found that the influence of core flow distribution difference on the drop time of control rod assembly is negligible during the commissioning and start-up of the units, but the influence of mass difference due to different materials of black rod and gray rod on the drop time is obvious. The average drop time of gray rod is about 4.6% longer than that of black rod because the mass of gray rod is 8.5 kg less than that of black rod. The test results are consistent with the theoretical expectation. Accordingly, it is suggested that the drop time consistency check of black rod and gray rod should be considered separately, and the acceptance criterion of drop time consistency check with 5 times standard deviation is put forward for the first time, which can achieve more accurate and detailed drop time consistency valuation than the original acceptance criterion.