Shohachiro Miyazono

Ductile fracture behavior of circumferentially cracked type 304 stainless steel piping under bending load

Abstract A ductile pipe fracture test program has been conducted in Japan Atomic Energy Research Institute (JAERI) to investigate the ductile fracture behavior of circumferentially cracked pipes and to demonstrate the validity of the leak before break concept in LWR pipings. In the paper are described the scope of the pipe test program and current test results for 6-inch diameter type 304 stainless steel pipes. Test pipes with a through-wall or a part-through crack in the circumferential direction were bent under low or high compliance condition, and stable or unstable pipe fracture behavior was investigated. J based tearing instability criterion and the net section collapse criterion are compared with the pipe test results, and the validity of these fracture criteria is discussed. Furthermore, geometries of acceptable flaws in pipes are evaluated considering the leak before break condition.

Measurement of leak-rate through fatigue-cracks in pipes under four-point bending and BWR conditions

Abstract Leak-rate tests were performed using 114 mm and 165 mm (4 and 6 in) diameter, schedule 80 pipes made of austenitic stainless steel SUS304 and carbon steel STS42. Each pipe contained a through-wall fatigue crack and was mounted on a four-point bending machine of 400 kN maximum loading. Tests were done under a pressure of 7 MPa, with a subcooling temperature. The leak rate was measured by a Venturi flow meter and a differential pressure transducer attached to the pressure vessel. Comparisons of the effect of pipe material, diameter and crack angle were made. This paper shows that from a Leak-Before-Break viewpoint, the stainless-steel pipe is superior to the carbon-steel one, and that the pipe with the larger diameter is better than the one with the smaller diameter. No unstable fracture was observed in the tests.

Experimental study of jet discharging test results under BWR and PWR loss of coolant accident conditions

Abstract This report describes the results of the jet discharging experiments conducted at the Japan Atomic Energy Research Institute. The tests were done under BWR and PWR Loss of Coolant Accident conditions using 4 inch, 6 inch and 8 inch test pipes, and varying distance between the pipe exit and the target plate. Simple and practical experimental formulae to estimate the maximum pressure on the target plate and maximum pressure distribution are given. Further, relations between pipe reaction thrust forces and jet impingement forces are described.

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 neutron irradiation embrittlement of heavy section nuclear reactor pressure vessel steels in terms of elastic-plastic fracture toughness

The fracture toughness degradation due to neutron irradiation was examined for the evaluation of the structural integrity of a nuclear reactor pressure vessel using four kinds of currently used heavy section manganese-molybdenum-nickel low alloy steels, which included the welded joint as well as the base metal. Neutron irradiation was conducted up to 2to 7×1019 n/cm2 > 1 MeV at 290°C in JMTR, and the embrittlement was mainly evaluated by the Charpy and fracture toughness tests using small three point bend specimens. From the results, the following can be pointed out: 1. (1) The elevations of the transition temperature of steels used, which are evaluated by 41 J of the Charpy absorbed energy, are within 50°C, and a quite high resistance against neutron irradiation embrittlement is observed. 2. (2) The JIC fracture toughness and J - R curve of irradiated materials as well as unirradiated ones are successfully determined by a dc electrical potential method using a single specimen. 3. (3) At the transition region, the increase of transition temperature (ΔRTNDT) at the 41 J level of the Charpy impact test is nearly equal to the shift at the 100 MPa m12 level of the fracture toughness test.

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.

Structural analysis of Japanese PWR steel containment vessel under internal pressure loading

Abstract Elastic—plastic structural analyses of a typical Japanese PWR steel containment vessel under static or dynamic internal pressure loading representing conditions of a typical severe accident were performed using the finite-element analysis code “ADINA”. In the analysis, static pressure was applied up to 1 MPa, simulating the conditions of a severe accident. Dynamic pressure loadings were assumed, such as a triangular pressure pulse with 10 ms duration and 1 or 2 MPa peak pressure, representing dynamic conditions of hydrogen burn or steam explosion in a containment. It was found in the present analysis that the containment behaves elastically as a whole up to 0.8 MPa in the statically applied loading.

Fatigue and fracture behavior of straight pipe with flaws in inner surface

Abstract Fatigue and fracture tests of piping models with flaws in the inner surface were carried out to investigate the fatigue crack growth, coalescence of multiple cracks and fracture behavior. Two straight test pipes with and without weldment in the test section of AISI type 304L stainless steel were tested under almost the same test conditions by imposing moment loads. Three artificial defects were machined in the inner surface of the test section of the test pipes and the fatigue test was performed until the cracks coalesced and grew through the thickness. Subsequently, a static load was imposed on the test pipe which contained a large crack in the test section. The fatigue test results are compared with an analytical crack growth behavior predicted by the method described in the Section XI of ASME Code, and show slower crack growth than that of the prediction. From the fracture test results, it is found that the test pipes can endure considerably high load.

Structural analysis of a Japanese BWR MARK-I containment under internal pressure loading

Abstract This paper describes the elastic-plastic analysis of the Japanese BWR MARK-I steel containment vessel under pressure loadings by a general purpose finite element method code ADINA. The present study is focused on the entire deformation of the vessel rather than the stress or strain concentrations around the structural singularities such as penetrations. Elastic deformation limits, displacements and equivalent stress distributions are discussed.