Abstract
The double-ended guillotine break (DEGB) of the horizontal coaxial gas duct of a high-temperature gas-cooled reactor is an extremely hypothetical accident, which could cause the air to enter into the primary circuit and react with graphite in the reactor core. The performance of the HTR-PM plant under this extremely hypothetical accident has been studied by the system code TINTE in this work. The results show that the maximum fuel temperature will not reach the temperature design limitation, and the graphite oxidation will not cause unacceptable consequences even under some conservative assumptions. Moreover, nitrogen and helium injected from the fuel charging tube were studied as the possible mitigation measures to further alleviate the consequences of this air ingress accident. The preliminary results show that only the flow rate of nitrogen injected reaches a certain value, which can effectively alleviate the consequences, while for helium injection, both high and small flow rate can prevent or cut off the natural circulation and alleviate the consequences. The reason is that helium is much lighter than nitrogen, and the density difference between the coolant channel and the reactor core is small when helium is injected. Considering the injection velocity, the total usage amount, and the start time of gas injection, helium injected with a small flow rate is suggested.
Highlights
At the end of 2012, the 200 MWe High-Temperature gascooled Reactor Pebble-bed Module (HTR-PM) which is designed by the Institute of Nuclear and New Energy Technology (INET) of Tsinghua University was started to be constructed in Rongcheng, Shandong Province, China
Ere are two kinds of scenarios which are being researched extensively by researchers: one is the simultaneous rupture of both upper and lower pipes connected to the primary loop, which could cause air ingress due to the chimney effect [3]; the other is the double-ended guillotine break (DEGB) of the horizontal coaxial gas duct, which could result in air ingress into the primary circuit. ese two kinds of air ingress accident are both regarded as Beyond Design Basis Accident (BDBA) of the High-Temperature gas-cooled Reactor (HTR)-PM
Juelich Research Center has studied the air ingress accident of HTRs from the 1970s and found that the consequences of double-ended guillotine break (DEGB) of coaxial gas duct are more severe than the simultaneous rupture of the upper and lower pipe connected to the primary circuit [4]
Summary
Horizontal coaxial gas duct e second aspect is that the graphite oxidation affects the integrity of the fuel element and the bottom reflector. (3). E fuel temperature design limitation of the HTR-PM is 1620°C under accident conditions. Under 1620°C, the SiC layer of the coated fuel particles can maintain the integrity and its capability of retaining fission products will not be damaged. The SiC layer of the coated fuel particles can maintain integrity even under higher temperature according to the results of the high-temperature irradiation experiment. It presents that the maximum fuel temperature during the air ingress accident is about 1462°C. Erefore, even considering the uncertainty effect, the maximum fuel temperature is 1542°C which still has a margin of the temperature design limitation According to the recent results [28], the effective conductivity of pebble-bed and the decay heat contribute the most uncertainty in the maximum fuel temperature analysis, and the uncertainty of maximum fuel temperature is smaller than ±80°C under a two standard deviation (2σ). erefore, even considering the uncertainty effect, the maximum fuel temperature is 1542°C which still has a margin of the temperature design limitation
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