High energy pipeline fracture is a condition that must be considered in the design process of nuclear power plants. Shan Yu's high-energy pipelines have high slamming energies after breaking, so they may cause great harm and even affect nuclear safety. Many nuclear power plants built in the past have set up a large number of components and structures for this purpose to prevent the fracture hazard of high-energy pipelines. With the application of the leakbeforebreak (LBB) technology, the high-energy pipelines in the AP1000 nuclear island do not need to consider the condition of complete breakage, and the anti-sloshing components and structures have been eliminated. The analysis of pipeline fracture is extremely important.
1 The engineering background 50 requires the design of pipeline damage protection. In the event of a rupture of high-energy and medium-energy pipes in the power plant, sufficient measures need to be set to ensure that important structures, systems, and components protect the nuclear island side from the adverse effects of the pipe-breaking accident. Non-safety-related systems do not need to protect against the dynamic and environmental effects associated with hypothetical pipe breaking accidents.
The guidelines for the assessment of pipeline damage protection in the AP1000 nuclear power plant basically comply with the guidelines of the National Nuclear Regulatory Commission (NRC), including the Standard Review Program (SRP), NUREG-1061, and other relevant technical standards. There are several types of hypothetical tube-breaking effects involved in the AP1000 nuclear power plant. The dynamic effects on the hypothetical tube-breaking accident are mainly limited to the rupture area and the consequences of the dynamic effects caused by pipeline rupture, such as jet impact effect, pipeline slamming, compartment overpressure and fluid System buck. High-energy pipelines are those system pipelines or some system pipelines whose maximum normal operating temperature exceeds 93.33 ° C (200 ° F) or whose maximum normal operating pressure exceeds 1.896MPa (275psi). Pipeline systems subject to high energy pressure or temperature are considered to be medium energy when the operating time of the system exceeds 23.3% or 1.896MPa at 2% or less, or the operating time of the power plant is less than 1 ° /. The high-energy pipeline system in the AP1000 nuclear power plant includes steam generator blowdown (BDS), chemical and volume control (CVS), main feed water and start-up feed water (FWS), main steam (MSS), primary loop sampling (PSS), passive core Cooling (PXS), reactor coolant (RCS), steam generator (SGS), main control room habitability (VES), heated water (VYS); medium energy pipeline fluid system including compressed and instrumented air (CAS), Equipment cooling water (CCS), waste water removal of demineralized water (RNS), spent fuel pool cooling (SFS), central chilled water (VWS), liquid waste (WLS), radioactive drainage (WRS).
The high-energy pipeline systems related to conventional islands are: main water supply and start-up water supply (FWS), main steam (MSS), steam generator blowdown (BDS), heated water (VYS): medium energy pipeline system with compressed and instrumented air ( 0 å…« 5), equipment cooling water, central chilled water, fire fighting (FPS), etc.
The diameters of the system pipes are 100 and 200mm, which are much smaller than the main steam pipe (1067mm) and the main water supply pipe (508mm). Seen from the conventional island structure layout. As long as the problems of the main steam and main water supply pipelines are resolved, the effects of other high-energy and medium-energy pipeline fractures can be basically eliminated. Therefore, this article focuses on the main steam and main water supply pipeline. 2 is a three-dimensional layout of the main steam and main water supply pipeline in a conventional island of an AP1000 project.
Main steam pipeline Fig. Main water supply pipeline Fig. 2 2 Analysis of pipeline fracture position The conventional high-energy pipelines in the island are non-nuclear-grade power pipelines. The judgment of pipeline fracture position 1 mainly involves two methods.
(1) Method 丨 is the stress analysis method: report the actual conditions of the project to determine the boundary conditions or assumptions of the pipeline fracture analysis, conduct seismic analysis of the pipeline, and analyze the main steam and main water supply under different load combinations Perform stress calculation and analysis based on the stress of the pipeline. Find out where fractures may occur. According to the judgment criteria given by ANSI / ANS-58.2-1998, the hypothetical pipeline rupture location occurs in pipeline stress. S exceeds 0.8 (1 + 10 points. S is the stress under the combination of thermal expansion, continuous load and accidental load (including seismic load) is the load under pressure, weight, other continuous load and accidental load (including seismic load) Allowable stress under combination; y is the allowable stress of thermal expansion stress.
(2) Method 2 is the specific location method: According to the judgment criteria given by ANSI / ANS-58.2-1998, it is assumed that the fracture location occurs at the end of the pressure-bearing part of the pipe network and the intermediate position where there may be high stress or high fatigue, such as pipe fittings , Valves, flange base welding accessories. One by one, analyze the possible impact on the nuclear island after the rupture, and determine the location of the pipeline that endangers the nuclear safety system or components.
3 Calculation of pipeline fracture load The fluid released from the circumferential or longitudinal fracture of a high-energy pipeline will cause a significant change in the flow characteristics of the pipeline system. The reaction force that can cause dynamic excitation of the pipeline is generated, causing the pipeline to flutter. The fluid force acting on the damaged pipeline is a function of time and space, which depends on the state of the fluid in the pipe before the damage, the flow area of ​​the breach, the friction loss, the power plant system Characteristics, geometric characteristics of the piping system and other factors. In the sense of engineering design, it mainly focuses on the initial jetting force, steady-state jetting force and plastic bending moment of the pipe after the pipe breaks.
3.1 The initial jet force after the split circumferential fracture of the pipeline, according to the principle of fluid injection, the initial jet force P after the pipeline breaks is that according to formula (1), the main steam pipeline of a conventional island of an AP1000 project breaks, and the steam pressure in the pipeline is > = 5.7MPa, the area where the pipeline breaks. 4 = 0.72m: so that the initial jetting force = 4 100kN; for the conventional island main water supply pipeline breakage, the water supply pressure in the pipeline = 7.2MPa, the area of ​​the pipeline breakage 4 = 0.15m2, so that the initial Injection 3.2 Steady state injection force When the fluid is injected for a certain period of time and reaches a steady state, the steady state injection force at this time is determined by factors such as pressure, temperature, and characteristics of the piping system.
For an AP1000 project where the conventional island main steam pipe breaks, the steady-state impact coefficient C = 0.65, so that the steady-state injection force P, = 2700kN: for the conventional island main water supply pipe break, the steady-state impact coefficient C = 1.19, so that The steady-state injection force P, = l 3.3 is obtained. 3.3 Plastic bending moment The sloping bending moment is related to the characteristics of the pipeline itself. The formula is according to formula (3). The plastic bending moment of the main island ’s steam pipeline for an API000 project is 11800 IcNtti. The plastic bending moment of the water supply pipe is 420kN.m. 4 The geometric characteristics of the spray after the pipe breaks. After the pipe is broken in the ring direction, the fluid is ejected from the break. When the jet hits the target, it will affect the target in the spray area. Causes damage, so it is important to judge the geometry of the spray after the pipeline breaks. Pipeline circumferential fractures are divided into two conditions: unrestricted ends and restricted ends. The fracture is similar.
4.1 Unconstrained ends The geometric characteristics of an AP1000 project's conventional island main steam pipeline after unrestricted end circumferential fractures are shown below.
Coldness.
The distance of the crack plane.
Area.
4.2 Constrained end The geometric characteristics of the API Island project's conventional island main steam pipeline with constrained end fractures are shown below.
The length of the core of the ring-shaped fracture with restricted ends: the degree of supercooling at the fracture.
The distance of the crack plane.
(11) L is the distance from any section in the region 3 to the fracture plane.
5 Conclusion Through calculation and analysis, it is known that the load and spray influence range of the conventional island high-energy pipeline is very large. After judging the location of the high-energy pipeline fracture, you can analyze the possible damage after the fracture. If it affects the nuclear safety items, you need to carry out anti-slash design and other protective designs to eliminate this effect. The design basis is the pipeline after the fracture Various loads: The specific project design still needs to consider the effects of compartment boosting effect, environmental effect and flooding in combination with the characteristics of the project.
API000 nuclear power plant conventional island high-energy pipeline fracture analysis is closely related to the layout of pipelines and structures. Reasonable pipeline and structure design can simplify pipeline fracture analysis and anti-flutter structure design, which can not only ensure safety but also be economical and reasonable. The AP1000 nuclear power plant conventional island high-energy pipeline fracture analysis is a design content related to nuclear safety within the scope of the conventional island design and has very important significance.
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