Research On Hydrogen Behavior In Large Containment Under Loss Of Coolant Accident

It is because that the large containments of PWR have a large free volume and also have a good capacity of loading high pressure that people generally considered that it is no overall hydrogen risk in the containment.However,the compartment of the containment is relatively complex.Hydrogen can easily to be accumulated and ignited in the local place of the containment,which will further case an explosion.As a result,the hydrogen risk of local place in the containment still exists,which will lead to serious accidents.In the paper,a three dimensional calculation fluid dynamic program GASFLOW was used to establish the model of API 000 NPP's containment.Firstly,the transport and distribution of hydrogen in the containment of API 000 NPP is researched which was under the sequence of LOCA(the break was happened at the cold leg of loop one).Secondly,the impact of passive containment cooling system(PCCS)on the transport and distribution of hydrogen in the containment has also studied.Finally,according to the scaling analysis method which was used to study the transport and distribution of hydrogen in the scaling facility,the experimental study has also been happened which was used to verified the phenomenon of accumulation,backflow,stratification and homogenization.Through the numerical simulation of the transport and distribution of hydrogen,it was found that:1,at these spaces of 1#SG room(where the break located)and over it,the hydrogen concentration is high.The phenomenon of accumulation was happened inside the 1#SG room and this room has the highest hydrogen concentration.2.because the backflow happened over the rooms of PRZ and 2#SG,the mixture which contained high hydrogen concentration flowed into these rooms and stratified within this region seriously.Compared to this region,the stratification at the upper space of containment was week,the hydrogen concentration tend to be homogenized.3,at the period of high release rate of hydrogen(the release rate of stream was low),there was a large difference between the density of inject fluid from the break and the surrounding's,at the same time,the hydrogen density is small,which was easily decelerated by damping,so,under the action of thermal diffusion,the inject fluid could easily move in the radial direction.The effect of PCCS on hydrogen behavior was studied by the presence of different gas components and the height of vapor-rich layer within the API 000 NPP's containment.It is found that:1,high water vapor concentration could inhibit the value of hydrogen concentration within the containment as a whole,but it could also cause hydrogen to accumulate in the 1#SG room(where the break was),and it would be more obvious when the content of hydrogen in the inject fluid was high.High water vapor concentration would slow down the rise of hydrogen,which was advantageous for the mixing in the radial direction,so that,the hydrogen concentration in the upper space of containment could be more uniform and the stratification was less likely happen 2,the effect of the height of water vapor-rich layer on the distribution and transport of hydrogen was mainly reflected in the accumulation near the inject fluid and the bottom of water vapor-rich layer.The experimental study was based on the analysis of evolution of the fields of temperature and hydrogen(replaced by nitrogen)concentration in the containment at the period of mixed injection.The experimental method has well verified the phenomena of'accumulation','backflow','stratification' and 'homogenization'.