Study On Failure Mechanism Of Prestressed Concrete Containments With FRC Following A Loss Of Coolant Accident

In case of loss of coolant accident(LOCA),the containment of nuclear power plant will bear high-temperature and high-pressure loads at the same time.The high-temperature temperature stress will aggravate the risk of early damage to the containment,thus reducing the safety margin provided by the design.Therefore,a comprehensive study of the failure and lifting mechanism of nuclear power plant containment under the coupling action of temperature and internal pressure has become a key scientific problem to be solved.After adding fiber into concrete,fiber reinforced concrete(FRC)shows high post crack strength and toughness and excellent mechanical properties and durability due to the bridging effect of fiber at the crack to prevent the further development of crack.However,the research on the application of FRC to the containment structure of nuclear power plant is very limited.This paper will take the numerical simulation of FRC Containment under temperature internal pressure coupling as the starting point,reveal the failure mechanism of FRC containment,study the influence of different fiber types and fiber parameters on the pressure bearing performance of FRC containment structure under LOCA,preliminarily verify the applicability of fiber concrete in the containment structure,and propose the optimal fiber types and fiber parameters.Provide technical reference for later specification preparation and engineering design.The research content includes the following six parts:(1)A finite element model of containment is established by using the finite element analysis software ABAQUS.The model is mainly divided into two types: temperature model and mechanical model.The constitutive relations of concrete with different types of fibers(including steel fiber,steel polypropylene hybrid fiber and steel polyvinyl alcohol fiber)and different fiber parameters are calculated by using the methods of theoretical derivation,literature review,specifications and numerical calculation.(2)The temperature field analysis model is used to simulate the changes of the temperature field of the containment under normal working conditions and after the LOCA.Ten minutes after the LOCA,the temperature in the containment barrel wall reaches the maximum.On this basis,the structural response under LOCA temperature load is analyzed.Under the action of load,the concrete,buttress column and steel lining at the equipment opening of ordinary concrete containment shell are damaged.(3)The response of ordinary and fiber reinforced concrete containment under LOCA temperature load is compared and analyzed.Compared with ordinary concrete containment,fiber reinforced concrete containment has the advantages of less distribution of concrete cracks and less yield strain of steel lining.When the main tensile strain of steel lining is selected as the index,the performance improvement effect of steel polypropylene reinforced PCCV is the best;When the concrete failure is selected as the index,the performance improvement effect of steel fiber reinforced PCCV is the best.(4)The loss of coolant accident of ordinary concrete containment structure is systematically analyzed,the mechanical properties of the structure under the coupling action of temperature and internal pressure are obtained,and the failure mechanism of the structure under the condition of loss of coolant accident is revealed.Under the condition of water loss,the failure mode of containment is that the cylinder expands outward,the area near the equipment hole shrinks inward,and the high thermal temperature stress makes the containment reach the limit state in advance.(5)The effects of different fiber types on the pressure bearing performance of FRC containment structure under LOCA are compared.Among the three fibers,when the containment performance index is the ultimate internal pressure,the performance improvement effect of steel fiber reinforced concrete containment is the best.When the performance index of the containment is the yield internal pressure of the steel lining,the performance improvement effect of the steel-polyethylene fiber concrete containment is the best.(6)Compared with the failure mode of conventional PCCV,the pressure bearing λvalue of steel fiber and steel polypropylene fiber Containment under different performance standards under LOCA increases with the increase of fiber parameters,but there is no such law in steel polyethylene fiber containment.