Core Technology Of Nuclear Power Spring Loaded Steam Pressure Relief Valve

As one of the most important accessories to ensure the safe operation of nuclear power plant,the pressure relief valve(PRV)plays an important role in the design and operation of nuclear power plants.The dynamic simulation of steam PRV under high temperature and high pressure,high lift,critical flow and seismic conditions is an important way to optimize the design and improve the reliability of PRV.However,few reports can be found on the dynamic simulation,thus leading to long period and high cost in the development of nuclear steam PRV.In addition,the existence of the surface damage of the moving parts during the pop-up of PRV would affect the dynamic performance of PRV.To address these issues,steam PRV performance test facility and methods,dynamic simulation and surface strengthening were investigated in this thesis as follows:1.A steam PRV test facility in accordance with ASME standards was designed and built.The methods of grid pre-deformation,moving mesh,domain decomposition and external virtual large container were used for the dynamic simulation on PRV performance.The dynamic characteristics of the valve disk was described by using the two-order differential equation.The dynamic simulation on large caliber spring loaded steam PRV used under high temperature and high pressure condition was accomplished.The simulation results are in good agreement with the experimental ones.For the high temperature and high pressure steam pressure relief valve(HTHPPRV),the flowrate increases with the increase of the ratio of the curtain area to the throat area,and the flowrate reaches the maximum value when the ratio reaches 1.18.The region of high Maher number in the flow field changes with the change of the lift of the HTHPPRV.There are three regions of high Maher number in the stable discharge process of the HTHPPRV.The re-seating pressure of the HTHPPRV is overestimated if compressed air is used as an alternative.The degree of superheat ranging from 0? to 100? has a negligible effect on the dynamic performance of HTHPPRV.A roughly linear increase in the re-seating pressure can be observed for a HTHPPRV with the rise in the upper adjusting ring position.In contrast,the re-seating pressure slightly decreases with the rise in the lower adjusting ring position.For the HTHPPRV,the rated lift to throat diameter equaled to 0.25 and 0.35 have the higher blowdown than that of 0.3.The decrease in spring stiffness can significantly reduce the re-seating pressure but has little effect on the opening time.2.The dynamic simulation of the nuclear power main steam pressure relief valve(NPMSPRV)with back pressure chamber was carried out.The simulation results are verified by experimental ones.It was found that the back pressure chamber has a great influence on the dynamic performance of NPMSPRV.The pressure rise in the back pressure chamber lags behind in the opening process of the NPMSPRV,which has little effect on the pop-up of NPMSPRV.In the re-seating process,the pressure drop in the back pressure chamber lags behind,which is helpful for the quick re-seating of NPMSPRV.The adjusting sleeve in the back pressure chamber has a big influence on the blowdown of the NPMSPRV.The blowdown increases linearly by 0.163%with the value of E(the distance between the top of the adjusting sleeve and the upper of the cover of the back pressure chamber)increasing per millimeter from 35 to 62 mm.The complex influence of the position of upper adjusting ring,lower adjusting ring,adjusting sleeve and adjusting screw on blowdown of NPMSPRV was studied by response surface method.It was found that the position of upper adjusting ring has the greatest impact on the blowdown,followed by the adjusting sleeve,the position of adjusting screw and lower adjusting ring.The interaction between the four parts has weak effect on the blowdown of NPMSPRV.3.The dynamic simulation of the fluid-solid coupling of the spring loaded PRV was carried out.The influence of the longitudinal seismic wave on the dynamic performance of the PRV was investigated by imposing a sine wave on the PRV.The results showed that the oscillation amplitude of the spring decreases with the increase in the Numerical Damping coefficient,which is beneficial to the stable discharge of the PRV.The fluttering is triggered when a vertical sine wave is imposed.The blowdown is affected by the phase and frequency of the sine wave.4.WC/Ni flexible cloth composite coating was developed to avoid the deterioration of the performance of PRV caused by the erosion damage and the scratch between the moving parts of PRV.Results showed that the metallurgical bonding was formed between the 304-stainless steel substrate and the coating.The Ni species infiltrated into the WC particles,which enhanced the binding force between the WC particles and the Ni matrix.The experimental results showed that the addition of WC particles can improve wear resistance of the coating greatly.The volume wear rate of WC/Ni flexible cloth composite coating with 59.80 wt.%WC particles is 1/328 of the 304-stainless steel.Two-body abrasive wear,three-body abrasive wear and fatigue wear all exist in the wear process of the WC/Ni flexible cloth composite coating.The erosion resistance of the WC/Ni flexible cloth composite coating with 59.80 wt.%WC particles is about 1.4 times that of the 304-stainless steel when the erosion angle is 30°.With the erosion angle of 30°,the failure mechanism of the coating mainly includes micro cutting and micro furrow caused by the erosion particles.With the erosion angle of 90°,hammer effect is the main failure mechanism.