| Nuclear energy, as one of important energy, because of its outstanding environmentalbenefit and economical efficiency, is the key object of the development of many countries, butradioactive is produced in the process of nuclear reaction, so security is especially importantin the use of nuclear energy. Pressurized water reactors are mostly chosen for nuclear powerplant throughout the world. They take up60%of the reactors being used in the world. InChina, up to87%of the nuclear reactors are pressurized water reactors. The two importantfactors of PWR core and the primary circuit system: core thermal and primary circuit waterhammer are made a deep theoretical research and numerical calculation. The results not onlyprovide theory basis for the design and safety, but also provide theoretical reference foreliminating or reducing the harm of water hammer of PWR.Based on the900MW PWR core as simulation object, using the COBRA-IV subchannelmodel reactor core analysis software, the core fuel assembly and the coolant flow channelsection were divided into subchannel from inner to outer; and considering the blend ofadjacent subchannel coolant mass and momentum, the reactor’s thermal analysis was carriedout. Reaching the coolant mass flow distribution of each subchannel in different axial heightand different section; Each of the coolant’s subchannel axial temperature distribution were gotby using the quality, energy, momentum, and the discrete equations; According to the heatconduction model of core, each subchannel fuel rod cladding surface axial temperaturedistribution and each subchannel fuel pellets axial temperature distribution at different heightswere calculated, and verified if it reaches the thermal design criteria of the required standards.The core’s DNBR value at every point could be got by each subchannel critical heat fluxdensity and the actual heat flux, and analyzed the safety margin of reactor core as well. At last,the results were compared with the practical running results, to verify the accuracy of thecalculation results. Based on the method of characteristic line, a set of mathematic expressions withreasonable boundary conditions of the integral reactor primary circuit has been established.Pump-valve start-up and trip formula are set up respectively according to the Suter curve,waterhead balance, valve flap motion curve, etc. A program has been developed inFORTRAN programming languages based upon all these models above. Numericalcalculation is carried out on the check valve-induced water hammer phenomena in a threepumps paralleled feed water system during the alternating startup process of parallel pumps,and get the pressure transient time, amplitude, the flow transient, etc. Results found two mainkinds of water hammer process and two kinds of pressure vibration. The two water hammeroccurs while the valve is closed, its intensity mainly depends on the pump start-up mode, andpresents trend of attenuation; The two obvious pressure vibration phenomenon: the first timeis happened after6seconds to switch between pump, the flow will be a short rise but todecline in the pump branch. During to the bypass of stopping the pump is still in the fullyopen position, and it does not cause a shock change of pressure in the branch, while thechange of flow convey to the branch that does not start, because the bypass of the branch isnot open, causing a severe pressure fluctuations; Another pressure vibration occurred at6seconds later, when the pressure fluctuation occurs because of the full opening of the branch. |
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