Pipe Rupture Accident Research Articles

高温ガス炉(GTHTR300)システムの空気浸入挙動解析(NP3 新型炉技術)

Japan Atomic Energy Research Institute (JAERI) has been carrying out a design and developmental program for the gas turbine high temperature reactor of 300Mwe nominal-capacity, the GTHTR300 (Gas Turbine High Temperature Reactor 300). The objective of this study is to clarify safety characteristics of the GTHTR300 for the pipe rupture accident. A numerical analysis of heat and mass transfer fluid flow with multicomponent gas mixture was performed to obtain the air ingress phenomena and the onset time of natural circulation of air. From the results obtained in this analysis, it was found that the duration time of the air ingress by molecular diffusion would increase due to the existence of the recuperator in the GTHTR300.

水冷却型試験・研究炉の炉心冠水維持装置サイフォンブレーク弁の性能評価法

A siphon break valve has been installed as a core covering system in water-cooled test and research reactors in order to prevent the core damage by keeping the core covered with water in case of a primary coolant pipe rupture accident. In this study, a program to evaluate the performance of a siphon break valve as the core covering system was developed and its applicability to water-cooled test and research reactors was studied experimentally. In order to analyze the effect of air inhaled from a siphon break valve on the primary cooling water flow-out phenomenon, the program adopted a liquid-gas separation model assuming that the air completely separates from the primary cooling water in the pipe. It was verified that this model could evaluate certainly the performance of siphon break valve. And, it was found that the onset of air-entraining vortex should be considered in order to analyze accurately the primary coolant water flow-out phenomenon in a primary coolant pipe rupture accident with very large water flow-out rate.

高温ガス炉の１次冷却系主配管破断事故時の空気浸入挙動，（ＩＩ） 炉心の黒鉛流路管温度が非均一の場合

A primary pipe rupture accident is one of the design-basis accidents of a High-Temperature Gas Cooled Reactor (HTGR). When the primary pipe rupture accident occurs, air is expected to enter the reactor core from the breach and oxidize in-core graphite structures. During the accident a complicated multi-component gas flow is expected to occur in the reactor vessel. This paper deals with experimental study on the process of air ingress into an apparatus simulating the HTGR during the 1st stage of the accident. Present study focuses on investigating the density change of the gas mixture, concentration change of each gas species, and duration of the 1st stage of the accident when the temperature of the central flow path is higher than that of the peripheral ones and when the temperature of the reactor simulator decreases with time after the pipe rupture accident. It was found that the cooling rate of the reactor core temperature for preventing natural circulation of air existed. The results of the density and concentration changes in the non-uniform temperature case are almost the same as those in the uniform temperature case if natural circulation does not occur in the reactor core flow paths.

高温ガス炉の１次冷却系主配管破断事故時の空気浸入挙動 （Ｉ） 炉心の黒鉛流路管温度が均一の場合

A primary pipe rupture accident is one of the design-basis accidents of the High-Temperature Engineering Test Reactor (HTTR), which is now under construction at Japan Atomic Energy Research Institute. When the primary pipe rupture accident occurs, air is expected to enter the reactor core from the breach and oxidize in-core graphite structures. During the accident a complicated multi-component gas flow is expected to occur in the reactor vessel. This report deals with experimental study on air ingress process in the 1st stage of the accident. The experiments are carried out with a test model simulating the HTGR. Temperature of the simulated reactor core is varied from about 400-1, 050°C.

A Study of Plateout Fission Product Behavior During a Large-Scale Pipe Rupture Accident in a High-Temperature Gas-Cooled Reactor

In high-temperature gas-cooled reactors, a small amount of fission products (FPs) are released from fuel elements during normal operation, and condensable FPs plate out on the inner surface of prim...

69 ヘリウム―空気置換流の流速分布計測および可視化

This paper presents the experimental results of visualization into the buoyancy-driven exchange flows between helium and air through a vertical pipe. This type flow might be caused by a pipe rupture accident in a high temperature gas cooled reactor. The exchange flows induced by density difference are complicated by Kelvin-Helm-holtz instability arising on internal contact surface.The exchange flows formed in the vertical pipe connecting between the helium vessel and ambient air are visualized by means of the laaer-light-sheet illumination technique. The results obtained show the transient process of flow development in the pipe, and unsteady, three dimensional structure of the flows.

70 密度の異なる気体を静止空気中に噴出する層流円形噴流の数値解析、LDV測定と流れの可視化

In a High Temperature Gas-Cooled Reactor(HTGR), air ingress after pipe rupture accidents causes corrosion of the graphite structures in a pressure vessel. To prevent this phenomenon, injection of inert gas might be very effective. We have done the transient and steady numerical analyses on the code based on the SIM-PLEST algorithm to study the flow behavior and mass transfer. Experimentally we have measured the velocity fields by LDV and we have suceeded the flow visualization by using the smoke tracer of the joss sticks and a slit light.As the result, the followings were obtained. The jet is accelerated by the gravity force. The velocity fields by the LDV experiments agree with those by the numerical calculations. And it becomes evidence by the flow visualization that the width of the jet decreases due to the acceleration of the jet and the jet entrains ambient air near the jet outlet.

円管内混合気体層流における黒鉛酸化時の物質伝達

Experiments and numerical analyses on mass transfer in a gas mixure laminar flow through a circular graphite tube accompanied with graghite oxidation were performed to clarify characteristics of graphite corrosion in connection with the primary cooling pipe rupture accident in a high temperature gas cooled reactor. In the experiment, inlet Reynolds numbers ranged from 16 to 320, graphite temperatures from 600 to 1, 050°C and inlet oxygen mass fractions from 10 to 50%. IG-110 and PGX graphites were used. The mass transfer coefficients in the experiment at a high temperature were less than those obtained on the basis of analogy between heat and mass transfer. It was found from the numerical analysis that the reduction of mass transfer coefficient resulted from the injection flow from the wall. The mass fractions of carbon monoxide and carbon dioxide in the experiment were well predicted on the basis of the one-dimensional numerical analysis in which graphite oxidation and carbon monoxide combustion were taken into consideration.

密度の異なる気体を静止空気中に噴出する層流円形浮力噴流の過渡数値解析と流れの可視化

Air ingress after pipe rupture accidents causes corrosion of the graphite structures in a pressure vessel in a High Temperature Gas-Cooled Reactor (HTGR). Injection of inert gas might be very effective to prevent this phenomenon. We have carried out the transient numerical analysis on the code based on the SIMPLEST algorithm to study the flow behavior and mass transfer. Experimentally we have visualized the mass fraction of inert gas by using the Mach-Zehnder interferometer and compared the results with those from numerical calculations.As the results, the head of the jet is pushed out to radial direction by impinging against the stagnant air at the first stage of the discharging. The flow patern reaches a steady state after 0.5s of gas injection.

ヘリウム-空気置換流の流速分布計測および可視化

In this paper, experimental results of visualization and velocity measurements of the buoyancy-driven exchange flows through the small opening are described. This type flow might be caused by a pipe rupture accident in a high temperature gas cooled reactor.After helium gas had been filled in the test cylinder, the cap covered the top of the opening was abruptly removed. Then an ascending helium current issuing from the opening and an entering air current into the test cylinder were occurred. The ascending flows seeded with fine particles were illuminated by sweeping beam scanned by a polygon mirror in vertical and horizontal planes. And multi-exposure specklegrams of the flows were recorded on the films. The velocity vector diagrams of the helium current were obtained from the specklegrams by means of Young's fringe method.Experimental results show that maximum velocity of helium current depends on the shapes of the opening with/without throat.

A study of the rapid depressurization of hot water and the dynamics of vapour bubble generation in superheated water

Liquid can be brought to a superheated state by means of very rapid depressurization. Such situations are typical for pipe rupture accidents, which can occur in processing equipment and have to be taken into account, for example, in the design of nuclear power plants with water-cooled reactors. An experimental investigation was carried out using a horizontal pipe attached to a pressure vessel. Rapid depressurization was achieved with the use of a rupture disc assembly. The paper describes the most important test results, a method for calculating the pressure undershoot below the saturation pressure and a simplified model of expansion wave propagation with vapour bubble generation in superheated liquid. On the basis of this model, the density of nucleation sites and the evolution of pressure and void fraction in the two-phase mixture can be estimated.

A116 安定な密度成層を形成する湧き出し流れの濃度分布の可視化

An experimental study has been performed to investigate the behavior of flowand mass transfer in gaseous slow jet in which buoyancy force opposed the flowforming stably stratified field. The study has been performed to understand thebasic features of air ingress phenomena at pipe rupture accident of the hightemperature gas-cooled reactor. A displacement fringe technique was adopted inMach-Zehnder Interferometer to visualize the mole fraction distribution. As theresult, the followings were obtained:(1) The stably stratified fields were formed in the vicinity of the outlet of theslow bet. The penetration distance of the stably stratified fields increased with Froude number.(2) Mass fraction distributions in the stably stratified fields were well correlatedwith the present model using the ramp mole velocity profile.

Study on diffusion and natural circulation of two component gases. (1st Report, Experiment and analysis with a reverse U-shaped pipe).

When a primary coolant pipe of a high temperature gas-cooled reactor (HTGR) ruptures, air is expected to ingress into the reactor core from the broken part by natural circulation and diffusion. In order to study the basic features of the air ingress during the early stage of the primary pipe rupture accident in a high temperature gas-cooled reactor, the conjugate problem of natural circulation and diffusion of the He-N2 two-component gas was studied experimentally and analytically. The study was performed on the phenomenon in a reverse U-shaped round pipe with one pipe heated and the other cooled. The analytical and experimental results were in good agreement on gas concentration change in the tube and initiation time of natural circulation of N2 single component gas.

『本誌』特集“サリー原発事故”への藤村氏コメントに答える

『本誌』特集“サリー原発事故”への藤村氏コメントに答える

Numerical Analysis of Two-Phase Jet Impingement by Homogeneous Flow Model

A two-dimensional homogeneous equilibrium model is developed in order to evaluate impingement load caused by discharge of a two-phase mixture in postulated pipe rupture accidents of light water reactors. The present analysis differs from previous studies mainly in that a backward expansion around the pipe exit is taken into account. As a result: (1) it is confirmed that the backward expansion occurs around the pipe exit in a super-sonic two-phase flow; (2) when the dimensionless position of an impingement wall z/D is larger than 2.0, the present calculations predict the pressure distribution on the impingement wall within an error of 10%, while the previous calculations, which did not take the backward expansion into account, overestimated the pressure by 25%; (3) existence of jet core and occurrence of shock waves in the two-phase jet are obtained and (4) a supersonic state of the jet is illustrated by comparing the velocity with the sonic velocity.

Numerical and experimental study of two-phase jet impingement

A two-dimensional homogeneous equilibrium model is developed in order to evaluate impingement load caused by discharge of a two-phase mixture in postulated pipe rupture accidents of light water reactors. The present analysis differs from previous studies mainly in that a backward expansion around the pipe exit is taken into account. Visualization tests are conducted to observe the Mach disc in an air-water two-phase jet, followed by comparison of the results with those from the newly developed computer code. As a result: (1) the backward expansion is found around the pipe exit in a supersonic two-phase flow; (2) when dimensionless position of an impinged wall, z/D, is longer than 2.0, the present calculations predict the pressure distribution on the impinged wall within an error of 10% while the previous calculations, which did not take the backward expansion into account, overestimated the pressure by 25%; (3) calculations show the same qualitative behavior for the Mach disc as the observations.

サリー原子力発電所の配管破断事故

On December 9, 1986, in the feed water piping for No.2 plant in the Surry Nuclear Power Plant, Virginia Electric and Power Company, a pipe rupture accident occurred. The outline of the accident and the results of analysis and evaluation from the viewpoint of the design, material, water flow, water chemistry, fractography and so on of the piping have been published. In this report, on the basis of the published data and information on this accident, the experience of the piping reliability verifying test carried out by Japan Atomic Energy Research Institute, and the results of inspection and maintenance of pipings in Japanese nuclear power stations, the results of investigation, examination and evaluation of this accident are described. As the contents of this report, the outline of No.2 plant in the Surry Nuclear Power Station, the accident sequence the situation and cause of the accident, the analysis of the rupture, the analysis of the pipe whipping, and the response after the accident in USA are included. Moreover, the situation of the inspection and maintenance of the piping in the same system in Japanese nuclear power stations is reported. The No.2 plant is a three-loop type PWR plant of 775,000 kW, and the place of rupture was an 18 in elbow on the inlet side of a main feed pump. The cause of rupture was the decrease of wall thickness due to erosion-corrosion. (Kako, I.).

Numerical analysis of two-phase jet impingement by homogeneous flow model.

A two-dimensional homogeneous equilibrium model is developed in order to evaluate impingement load caused by discharge of a two-phase mixture in postulated pipe rupture accidents of light water reactors. The present analysis differs from previous studies mainly in that a backward expansion around the pipe exit is taken into account. As a result: (1) it is confirmed that the backward expansion occurs around the pipe exit in a super-sonic two-phase flow; (2) when the dimensionless position of an impingement wall z/D is larger than 2.0, the present calculations predict the pressure distribution on the impingement wall within an error of 10%, while the previous calculations, which did not take the backward expansion into account, overestimated the pressure by 25%; (3) existence of jet core and occurrence of shock waves in the two-phase jet are obtained and (4) a supersonic state of the jet is illustrated by comparing the velocity with the sonic velocity.

Analytical Studies of Blowdown Thrust Force and Elastic-Plastic Behavior of Pipe at Pipe Rupture Accident

When high-temperature and high-pressure water is ejected from pipe, a blowdown thrust force will act on the pipe and it will cause pipe movement. The analytical methods of blowdown thrust force and pipe movement are presented in the paper. The equation of momentum conservation is used to calculate the blowdown thrust force, together with the results of the thermal-hydraulic analysis code RELAP4/MOD6. The finite element method is used to calculate the dynamic movement of pipe. The equations for calculating the maximum strain at the outer surface of pipe are derived by assuming the static equilibrium condition. The analytical results are compared with experimental ones to verify the analytical methods presented here.

An Experimental Study of Blowdown Thrust and Jet Forces for a Pipe under Boiling Water Reactor Loss-of-Coolant Accident Conditions

Blowdown thrust and jet impingement forces are simultaneously examined in jet discharge tests relating to an instantaneous pipe rupture accident. Tests were performed with a 6-in. pipe under boiling water reactor loss-of-coolant accident conditions. The initial pressure of the hot saturated water was 6.86 MPa. The time history of the blowdown thrust force just after the break, the jet thrust parameter of the pipe, the jet impingement force, the pressure and temperature distributions of the impinging jet, and the relationship between the thermal-hydraulic quantities and the thrust forces are examined.