| Containment vessel is the last barrier to prevent the release of radioactive substances.In addition to defending human destruction and natural disasters,it also has the safety function to withstand exterior crashes.All the nuclear reactors in operation,under construction or proposed to be constructed are designed with containment vessel which mainly serves as a barrier to prevent the release of radioactive substances,however,not every of them are designed to withstand exterior crashes and to release heat from the core with no personal emergency interference.Containment vessel of AP1000 Passive Pressurized Water Reactor can meet such requirements in adverse conditions.As a new containment vessel,AP1000 Steel Containment Vessel was designed by ANSALDO per ASME standard and built from new material.Based on ASME B&PVC,Section III,Subsection NE 2001&2002 Addenda and construction technical practices in the construction of AP1000 Steel Containment Vessel,material application,shell construction,hatches and penetrations installation,pneumatic test and so forth were systematically summarized in this paper.It provides technical references for the construction of steel containment vessels in China,and contributes to the construction of steel containment vessels in similar following-up nuclear power plants in China.Firstly,during the plate forming of steel containment vessel,improved impact toughness shall be guaranteed after hot forming,welding and postweld heat treatment.Steel containment vessel was composed of formed plates.The plates of the elliptical heads were heated up to 550℃-600℃ in furnace and then formed by large hydraulic pressing machine and mold.The plates of cylindrical shell were rolled to take shape after being heated to180℃-200℃.Secondly,the tolerance requirements of steel containment vessel stipulated in ASME B&PVC,Section III,Subsection NE shall be met.When the formed plates machined to the designed size,each layer in the elliptical heads and the cylindrical shells shall reserve an adjustable plate for site assembly,except the first layer in the elliptical heads that consists of two plates.The bevel of compensation plate shall be machined per site curve condition instead of the general requirements of butt welding.This helped to prevent curve discontinuous near the joint after welding.Thirdly,as to installation of hatches and penetrations,mockup shall be performed and holes then drilled accordingly.For the hole drilling of equipment hatches,status of insert plates,deviation of shell installation,and deformation of stress release from hole drilling shall be taken into consideration.Survey and hole drilling shall never be barely based on simulation and calculation,it is preferred that mockup shall be done on site using equipment hatches and temporary reinforcement shall be set up for hole drilling.This can minimize the hole drilling deviation and optimize the assembling&welding preparation of insert plates.With respect to the construction of penetrations which involves cross work,communication among different disciplines shall be maintained and detailed construction logic shall be prepared.Fourthly,the structural integrity of the containment vessel shall be guaranteed during pneumatic test.Safety function of radioactive substances containing was proved by integrated leakage test. |
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