Toshikazu Yano

Transient analysis of blowdown thrust force under PWR LOCA

Abstract The analytical results of blowdown characteristics and thrust forces were compared with the experiments, which were performed as pipe whip and jet discharge tests under the PWR LOCA conditions. The blowdown thrust forces were obtained by Navier-Stokes momentum equation for a single-phase, homogeneous and separated two-phase flow, assuming critical pressure at the exit if a crifical flow condition was satisfied. The following results are obtained: 1. (1) The node-junction method is useful for both the analyses of the blowdown thrust force and of the water hammer phenomena. 2. (2) The Henry-Fauske model for subcooled critical flow is effective for the analysis of the maximum thrust force under the PWR LOCA conditions. The jet thrust parameter of the analysis and experiment is equal to 1.08. 3. (3) The thrust parameter of saturated blowdown has the same one with the value under pressurized condition when the stagnant pressure is chosen as the saturated one. 4. (4) The dominant terms of the blowdown thrust force in the momentum equation are the pressure and momentum terms except that the acceleration term has large contribution only just after the break.

Experimental and analytical studies of four-inch pipe whip tests under PWR LOCA conditions

Abstract This paper presents experimental and analytical results of pipe whip tests performed under PWR LOCA conditions using a test pipe of 4-inch diameter and U-shaped restraints. In the tests, the effects of the overhang length on the pipe whip behavior of the pipe-restraints system were studied by measuring the strains and deformations of the test pipe and restraints, and the restraints forces. The equation for predicting the maximum strain at the outer surface of the pipe was derived using a static equilibrium condition. The calculated maximum strains at the outer surface of the pipe agree fairly well with experimental data. The dynamic response analysis of the pipe-restraints system was conducted by the finite element program ADINA. The applicability of the ADINA program to the pipe whip analysis is made clear through this analysis.

TEST RESULTS OF JET DISCHARGE FROM A 4 INCH PIPE UNDER BWR LOCA CONDITIONS

This report describes the result of tests on jet discharge of saturated water through a 4 inch discharge pipe from a pressure vessel having 4 m3 of inner volume, where the initial pressure was 69 kg/cm2 g and the temperature was 283°C. Behind the exit, a 10 ton load cell was installed to measure thrust force due to sudden jet discharge. In front of the pipe exit a 1000 mm diameter target disk was installed. The distance from the pipe exit to the target was 500 mm. Thirteen pressure transducers and 13 thermocouples were mounted on the target disk to measure the pressure and temperature increase due to jet impingement on the target. The following conclusions were reached. 1. (1) Pipe reaction thrust is calculated using a homogeneous flow model at the early stage of blowdown where stagnation quality is low. It agrees closely with the experimental data. 2. (2) Maximum pressure on the target due to jet impingement is 1 kg/cm2 g when the distance from pipe exit to target is 500 mm. 3. (3) Mass flow rate was calculated by RELAP4/MOD5. Agreement between computed and experimental results was reached based on the assumption that CD = 0.63 for a 4 inch discharge pipe.

Experimental studies of 4-inch pipe whip test under BWR loca conditions

Abstract Pipe whip tests or jet discharge tests have been performed at the Japan Atomic Energy Research Institute, which simulate the instantaneous circumferential guillotine break of primary coolant piping in nuclear power plants. The present paper describes the results of the pipe whip tests using test pipes of 4 inch diameter, under the BWR LOCA conditions, which were performed from 1979 to 1981. The tests were carried out at an initial pressure of about 6.8 MPa and an initial temperature of about 285°C. The test pipe was 114.3 mm (4 in) in diameter, 8.6 mm in thickness and 4500 mm in length. The four pipe whip restraints used in the tests were the U-bar type of 8 mm in diameter and fabricated from Type 304 stainless steel. The experimental parameters were the clearance (30, 50 and 100 mm) and the overhang length (250, 400, 550 and 1000 mm). The main purpose of these tests is to investigate the effects of the clearance and the overhang length on the pipe whip behavior. It has been clarified from the test results that a smaller clearance and a shorter overhang length causes the deformation of the pipe and restraints to be minimized, and the test pipe collapses near the setting point of the restraints with the overhang length of 1000 mm.

Evaluation of leak flow rate and jet impingement related to leak before break

Leak flow rate and jet impingement load are experimentally evaluated using very narrow and short artificial slits which simulate a through-wall fatigue crack. The following items are clarified in the experiments under BWR fluid conditions: (1) the leak flow rate from the rectangular slit is experimentally clarified and it agrees well with the analytical result when the estimated thermodynamic nonequilibrium parameter N in the present experiment is introduced; (2) the orifice effects are experimentally evaluated concerning the through-wall fatigue crack, in which the discharge coefficients CD between 0.75 and 0.25 are obtained as a function of the exit to the stagnation area ratio Ae/Ao; (3) when very narrow and short slits are used in the jet impingement experiments, the maximum pressure on the target is higher than that of a large diameter pipe and it increases with the decrease of the flow path length to hydraulic diameter ratio L/D of the slit because of the thermodynamic nonequilibrium effect.

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.

Void fraction measurement by a gamma-ray densitometer under instantaneous pipe rupture

Abstract A high-response gamma-ray densitometer was developed for the measurement of void fraction caused by the flashing vaporization of high-pressure and -temperature water under an instantaneous pipe break accident of a boiling water reactor, BWR. The initial conditions of the water were 6.86 MPa in pressure and saturation temperature. In order to prove the reliability and accuracy, the calibration test by dropping the acrylic void simulators and the air injection test into the cold water filled in the pipe were conducted. The following results are obtained in the experiments: (1) the cone slit method is very useful to increase the measuring accuracy, (2) it is clearly observed that the apparent increase of the void fraction occurs after the rarefaction wave passes, (3) the first maximum of the void fraction occurs with some delay time after break. Secondly, the minimum void fraction concurs with the maximum pressure in the pressure recovering process.

Blowdown thrust force under pipe rupture accident: I. Experimental evaluations of blowdown thrust force and decompression characteristics

Abstract Blowdown thrust forces and decompression characteristics were evaluated concerning the jet discharge or pipe whip tests with a 4-inch or 6-inch diameter pipe under PWR LOCA or BWR LOCA conditions related to pipe rupture accidents in nuclear power plants. This paper presents experimental evaluations of time-dependent and maximum blowdown thrust forces, and evaluations of decompression characteristics under instantaneous pipe rupture conditions. The following items are discussed: the peak value of the blowdown thrust force, the jet thrust coefficient for the maximum blowdown thrust force, the pressure recovery after break, and the relationship between the pressure undershoot of the sudden decompression and the decompression rate.

Blowdown thrust force under pipe rupture accident: II. Analytical evaluations of partial break and ramped opening break

Abstract Blowdown thrust forces of partial break and ramped opening break of a pipe were studied analytically simulating the pipe rupture accident in light water reactor power plants. The analyses were carried out concerning pipe rupture tests with a 4-inch diameter pipe under PWR LOCA conditions which were performed at the Japan Atomic Energy Research Institute. In this paper, the relationship between the partial break and the blowdown thrust force is described. Furthermore, it is also clarified and discussed that the ramped opening break influences the blowdown thrust force just after the break and the maximum blowdown thrust force.