Feasibility and risk analysis for control rod insertion test of TNPS at MOL

In order to clarify whether there are any control rod drop time overruns at the middle of cycle (MOL), TNPS (Tianwan Nuclear Power Station) commissioned CNPE (China Nuclear Power Engineering Co., LTD.) to launch a manual control rod insertion test for feasibility and risk analysis. The test consisted of control rods insertion and withdrawn sequence, test time interval, and test procedures, etc. The test may cause the changes in reactivity, power distribution and other core parameters. It is shown that when the core power is under 90% nominal power, the test is feasible, both core reactivity and power distribution are manageable. But there may be some control rod stuck during the test. The stuck position varies and it is hard to predict and enumerate, so it is a risky test. In addition, the successful test does not mean that the control rod won't be stuck any more during the operation period, so the test is not recommended. (authors)