| Fukushima nuclear accident in Japan becomes the most seriousnuclear disaster after the Three Mile Island nuclear accident in the UnitedStates, the Chernobyl nuclear accident in the former Soviet Union. Aftersumming up the lessons, it is obvious that relying solely on accidentprevention in real conditions has been unable to meet the higher securityneeds. Severe accident mitigation needs greater emphasis. In-VesselRetention strategy is an important passive safety strategy in China’sintroduction, digestion and absorption of the AP1000, which is the thirdgeneration of advanced pressurized water reactor. External reactor vesselcooling is one of the important strategy of IVR. The cooling water shouldbe injected into the space between RPV and containment in severe accident.If all the decay heat can be taken through the cooling water by naturalcirculation, RPV may be cooled sufficiently effective and the moltenmaterial is retained. RPV keeps integral. One of the most critical requirements to ensure the decay heat fully brought out by the coolingwater is that the heat flux on the wall of RPV can t exceed the limits of theexternal cooling which is also called critical heat flux, CHF.In this paper we design facility and carry out tests to get betterunderstand of the impact factors of the two-phase natural circulation flowprocess and CHF values in IVR-ERVC process. The experiment can alsoprovide some experience and inspiration for the CAP1400the IVR-ERVCof verification test. Experiments are performed for demineralized water atdifferent degree of subcooling with inclination angle of7.5°,37.5°,67.5°and condenser height of5.5m,6.5m in~2m radius and90°arc,150mm×150mm flow channel to analyse the boiling heat transfer and CHFcharacteristics on a downward facing curved heating surface. In the presentstudy, CHF on a downward facing curved heating surface raises withincreasing of the degree of subcooling and inclination angle. CHF is alsoinfluenced by form and rate of the flow. |
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