Thermosyphoning capability, also known as the natural circulation is an important nuclear safety indicator in NPP. In the absence of any forced circulation of the NPP primary system, the cooling of the fuel to remove the decay heat can be provided by thermosyphoning to the steam generator (SG).
Based on the theory of natural circulation and simulated test, this paper will further identify thermosyphoning capability of Qinshan III PHWR (CANDU6). Analysis shows that, the ultimate reactor heat sinks are SGs and related safety valves in case of loss main pumps. Thermosyphoning capability was confirmed as effective and acceptable.
Furthermore, loss of Power accident happened during Qinshan III Unit#1 normal operating condition. We will investigate the impact of reactor core cooling and validate thermosyphoning as the capability of Qinshan III PHWR heat sink on accident.
Finally, this paper will give some suggestions to NPP operator’s actions issues with reactor core temperature difference, reactor inlet headers sub-cooling margin, reactor outlet header temperatures, and others. Meanwhile, paper also discuss on the improvement of CANDU future design.