SAFETY ANALYSIS OF INCREASE IN HEAT REMOVAL FROM REACTOR COOLANT SYSTEM WITH INADVERTENT OPERATION OF PASSIVE RESIDUAL HEAT REMOVAL AT NO-LOAD CONDITIONS

GE SHAO,XUEWU CAO 한국원자력학회 2015 Nuclear Engineering and Technology Vol.47 No.4

The advanced passive pressurized water reactor (PWR) is being constructed in China andthe passive residual heat removal (PRHR) system was designed to remove the decay heat. During accident scenarios with increase of heat removal from the primary coolant system,the actuation of the PRHR will enhance the cooldown of the primary coolant system. Thereis a risk of power excursion during the cooldown of the primary coolant system. Therefore,it is necessary to analyze the thermal hydraulic behavior of the reactor coolant system(RCS) at this condition. The advanced passive PWR model, including major components inthe RCS, is built by SCDAP/RELAP5 code. The thermal hydraulic behavior of the core isstudied for two typical accident sequences with PRHR actuation to investigate the corecooling capability with conservative assumptions, a main steam line break (MSLB) eventand inadvertent opening of a steam generator (SG) safety valve event. The results showthat the core is ultimately shut down by the boric acid solution delivered by Core MakeupTank (CMT) injections. The effects of CMT boric acid concentration and the activation delaytime on accident consequences are analyzed for MSLB, which shows that there is noconsequential damage to the fuel or reactor coolant system in the selected conditions.

Experimental study on hydrogen behavior and possible risk with different injection conditions in local compartment

Liu Hanchen,Tong Lili,Cao Xuewu 한국원자력학회 2020 Nuclear Engineering and Technology Vol.52 No.8

Comparing with the large containment, the gas can not flow freely within the local compartment due to the small volume of the compartment in case of serious accident, which affects the hydrogen flow distribution, and it will determines the location where high concentration occurs in compartment. In this paper, hydrogen distribution and possible hydrogen risk in the vessel under the different conditions are investigated. The results show that when the initial gas momentum is increased, the ability of gas enters into the upper region of the vessel will be strengthened, and the hydrogen volume fraction in the upper region of the vessel is higher. Comparing with horizontal source direction, when source direction is vertically towards upper space, hydrogen is more likely to accumulate in the upper region of the vessel. With the increasing of steam mass flow, the dilution effect of steam on the hydrogen volume fraction will be strengthened, while the pressure in the vessel is also increased. When steam flow is decreased, the hydrogen explosion risk is higher in the vessel. The experiment data can provide technical support for the validation of the CFD software and the mitigation of hydrogen risk in the containment compartment

Investigation of aerosol resuspension model based on random contact with rough surface

He Liwen,Tong Lili,Cao Xuewu 한국원자력학회 2023 Nuclear Engineering and Technology Vol.55 No.3

Under nuclear reactor severe accidents, the resuspension of radioactive aerosol may occur in the containment due to the disturbing airflow generated by hydrogen combustion, hydrogen explosion and containment depressurization resulting in the increase of radioactive source term in the containment. In this paper, for containment conditions, by considering the contact between particle and rough deposition surface, the distribution of the distance between two contact points of particle and deposition surface, rolling and lifting separation mechanism, resuspension model based on random contact with rough surface (RRCR) is established. Subsequently, the detailed torque and force analysis is carried out, which indicates that particles are more easily resuspended by rolling under low disturbing airflow velocity. The simulation result is compared with the experimental result and the prediction of different simulation methods, the RRCR model shows equivalent and better predictive ability, which can be applicable for simulation of aerosol resuspension in containment during severe accident

Condensation oscillation characteristic of steam with non-condensable gas through multi-hole sparger at low mass flux

Zhang Dandi,Tong Lili,Cao Xuewu 한국원자력학회 2023 Nuclear Engineering and Technology Vol.55 No.2

To study oscillation characteristic of steam and non-condensable gas direct contact condensation through multi-hole sparger at low mass flux, a series of experiments of pure steam and mixture gas condensation have been carried out under the conditions of steam mass flux of 20e120kg/m2s, water temperature of 20e95 C and mass fraction of non-condensable gas of 0e5%. The regime map of pure steam condensation through multi-hole sparger is divided into steam chugging, separated bubble, aggregated bubble and escaping aggregated bubble. The bubbles behavior of synchronization in the same hole columns and desynchronized excitation between different hole columns can be found. The coalescence effect of mixture bubbles increases with water temperature and non-condensable gas content increasing. Pressure oscillation intensity of pure steam condensation first increases and then decreases with water temperature increasing, and increases with steam mass flux increasing. Pressure oscillation intensity of mixture gas condensation decreases with water temperature and non-condensable gas content increasing, which is significantly weaker than that of pure steam condensation. The oscillation dominant frequency decreases with the rise of water temperature and non-condensable gas content. The correlations for oscillation intensity and dominant frequency respectively are developed in pure steam and mixture gas condensation at low mass flux.

Study on dryout heat flux of axial stratified debris bed under top-flooding

Wenbin Zou,Lili Tong,Xuewu Cao Korean Nuclear Society 2024 Nuclear Engineering and Technology Vol.56 No.2

The coolability of the debris bed with a simulant of solidified corium is experimentally studied, focusing on the effects of the structure of the axial stratified debris bed on the dryout heat flux (DHF). DHF was obtained for the four structures with different particle sizes for the axial stratified debris bed under top flooding. The experimental results show that the dryout position of the axial stratified debris bed is formed at the stratified interface indicated by the temperature rise, and the DHF of the axial stratified bed is much lower than that of the homogeneous bed packed with the upper small particles. To predict the dryout heat flux of the stratified debris beds, by considering the properties of the mixed area, a one-dimensional dryout heat flux model of the porous medium is derived from a water and vapor momentum equation for porous medium, two-phase permeability modifications, interfacial drag, and the correlation between capillary pressure and liquid saturation and verified with the experimental data. The modified model can give reasonable results under different structures.

Preliminary numerical study on hydrogen distribution characteristics in the process that flow regime transits from jet to buoyancy plume in time and space

Di Wang,Lili Tong,Luguo Liu,XUEWU CAO,Zhiqiang Zou,Lingjun Wu,Xiaowei Jiang 한국원자력학회 2019 Nuclear Engineering and Technology Vol.51 No.6

Hydrogen-steam gas mixture may be injected into containment with flow regime varying both spatiallyand transiently due to wall effect and pressure difference between primary loop and containment insevere accidents induced by loss of coolant accident. Preliminary CFD analysis is conducted to gain informationabout the helium flow regime transition process from jet to buoyancy plume for forthcomingexperimental study. Physical models of impinging jet and wall condensation are validated using separatedeffect experimental data, firstly. Then helium transportation is analyzed with the effect of jetmomentum, buoyancy and wall cooling discussed. Result shows that helium distribution is totallydominated by impinging jet in the beginning, high concentration appears near gas source and wallwhere jet momentum is strong. With the jet weakening, stable light gas layer without recirculating eddyis established by buoyancy. Transient reversed helium distribution appears due to natural convectionresulted from wall cooling, which delays the stratification. It is necessary to concern about hydrogenaccumulation in lower space under the containment external cooling strategy. From the perspective ofexperiment design, measurement point should be set at the height of connecting pipe and near the wallfor stratification stability criterion and impinging jet modelling validation.