Investigations of Two-phase Natural Circulation Loop with Artificial Seawater

Description

Nuclear power, with zero direct emissions during operation, is a very effective option to reduce greenhouse gas emissions. Indeed, nuclear power plays an important role in the energy sector for many countries. In particular, nuclear power is still growing in China. The safety of nuclear power reactors would have been significantly enhanced, if a passive heat removal system were adopted. The proposed project will investigate the thermofluid characteristics of 3.5 wt% artificial seawater in a two-phase natural circulation loop, which is simple, inherently safe and of high heat transfer capability. The studies in the literature and our recent works indicate that bubbles in seawater usually do not merge each other; consequently, the two-phase flow structure in a boiling loop of seawater can be very different from that of de-ionized water. This may significantly influence the two-phase flow pressure drop and hence the characteristics of two-phase natural circulation loop using seawater as working fluid. At atmospheric pressure, the mass flow rates versus heating power at different inlet subcooling, which reflects the performance of the two-phase natural circulation loop using artificial seawater, will be acquired. The corresponding mechanisms will be analyzed based on the studies of heat transfer coefficients and void fraction in the heated section and riser. Moreover, it is well known that two-phase natural circulation loop is quite unstable with de-ionized water. Seawater, which inhibits bubble coalescence, may behave differently. The proposed study will construct the marginal stability map for the two-phase natural circulation loop of seawater on the plane of inlet subcooling number versus phase change number. Furthermore, the nature of instabilities in artificial seawater will be examined. The stability map and oscillation characteristics are important issues and firstly explored for seawater in the proposed study. The results of the proposed study will be of significant fundamental interest as well as potential for the enhancement of nuclear safety. The results of the proposed study together with the outcomes of PI’s previous works on seawater will enrich our knowledge on seawater and enable seawater as an alternative emergency coolant to promote the safety of nuclear power plants located at sea coast. If natural seawater can be employed as an effective alternative emergency coolant with confidence, the nuclear power plants at sea coast, which account for about half of nuclear power units in the world, will be secured with plenty of emergency coolant to enhance their safety.