Author: B. A. CheadlePublisher:
ISBN:
Category :
Languages : en
Pages : 0
Book Description
Assessment of possible delayed hydride cracking and fracture in kanupp pressure tubes
Author: B. A. CheadleInitiation of delayed hydride cracking in pressure tubes : review of progress and programs
Author: M. P. PulsInitiation of Delayed Hydride Cracking in Zr-2.5Nb Micro Pressure Tubes
Author: Ravi Kumar SundaramoorthyPublisher:
ISBN:
Category :
Languages : en
Pages : 280
Book Description
Pressure tubes pick up hydrogen while they are in service within CANDU reactors. Sufficiently high hydrogen concentration can lead to hydride precipitation during reactor shutdown/repair at flaws, resulting in the potential for eventual rupture of the pressure tubes by a process called Delayed Hydride Cracking (DHC). The threshold stress intensity factor (KIH) below which the cracks will not grow by delayed hydride cracking of Zr-2.5Nb micro pressure tubes (MPTs) has been determined using a load increasing mode (LIM) method at different temperatures. MPTs have been used to allow easy study of the impact of properties like texture and grain size on DHC. Previous studies on MPTs have focused on creep and effects of stress on hydride orientation; here the use of MPTs for DHC studies is confirmed for the first time. Micro pressure tube samples were hydrided to a target hydrogen content of 100 ppm using an electrolytic method. For DHC testing, 3 mm thick half ring samples were cut out from the tubes using Electrical Discharge Machining (EDM) with a notch at the center. A sharp notch with a root radius of 15 mu m was introduced by broaching to facilitate crack initiation. The direct current potential drop method was used to monitor crack growth during the DHC tests. For the temperature range tested the threshold stress intensity factors for the micro pressure tube used were found to be 6.5-10.5 MPa.m1/2 with the value increasing with increasing temperature. The average DHC velocities obtained for the three different test temperatures 180, 230 and 250oC were 2.64, 10.87 and 8.45 x 10-8 m/s, respectively. The DHC data obtained from the MPTs are comparable to the data published in the literature for full sized CANDU pressure tubes.
Overload Fracture of Flaw Tip Hydrides in Zr-2.5Nb Pressure Tubes
Author: GK. ShekPublisher:
ISBN:
Category : Crack initiation
Languages : en
Pages : 30
Book Description
CANDU Zr-2.5Nb pressure tubes are susceptible to a crack initiation mechanism known as Delayed Hydride Cracking (DHC), which is a process that involves hydrogen diffusion, hydride precipitation, hydride region formation, and fracture at a flaw tip. An overload occurs when the hydrided region is loaded to a stress higher than that at which this region is formed. Service-induced flaws are present in some pressure tubes, which can act as crack initiation sites. Most experimental data to assess DHC initiation are obtained under constant loading conditions in which hydride formation and fracture occur at the same load, and therefore they are not suitable to assess crack initiation under overload condition. A series of step-wise increasing load experiments was performed on unirradiated Zr-2.5Nb pressure tube samples to determine the fracture stress of hydrides formed at notches with 15 ?m root radius under different hydride formation stresses and thermal histories. Crack initiation in the overload tests was detected by the acoustic emission technique. The notch tip hydride morphologies were examined by optical and scanning electron microscopy. Test results indicated that the resistance to overload fracture was dependent on the hydride formation stress and thermal histories, which affected the notch tip hydride size, density, and distribution. Overload tests were performed at different temperatures, and a transition temperature to high resistance to overload fracture was observed.
Threshold stress intensity factor for delayed hydride cracking at 250 degrees c in zr-2.5nb pressure tube material supplied by cezus
Author: A. K. JarvineDelayed hydride cracking in russian rbmk zr-2.5 nb pressure tubes
Author: B. A. CheadleMetallographic observations of delayed hydride cracking from simulated flaws in zr-2.5nb pressure tube during thermal cycling
Author: Z. PanProgress on Probabilistic Assessments of Reactor Cores for Pressure Tube Cracking Due to Hydride Blister Formation
Author: Publisher:
ISBN:
Category :
Languages : en
Pages : 57
Book Description
Detailed description of the computer model used for probabilistic assessments of the numbers of tubes in a reactor core with hydride blisters large enough to initiate delayed hydride cracking. This model has been under development since 1985 and has undergone several significant changes, particularly the development of the concept of a critical blister and a description of its use. This computer model has recently been used to assess the state of the Pickering Unit 4 core based upon inspection information. The report outlines the assumptions and limitations of the model, how inputs to the model are derived and used, and describes checks of the performance of key subroutines.
Growth, Fracture, and Nondestructive Evaluation of Hydride Blisters in Zr-2.5 Nb Pressure Tubes
Author: Léger (M.)Publisher:
ISBN:
Category : Fracture
Languages : en
Pages : 16
Book Description
Rupture of a cold-worked Zircaloy-2 pressure tube in Pickering Unit 2 in 1983 occurred when a crack developed from an array of hydride blisters. These had formed on the outside surface of the pressure tube where it contacted the surrounding calandria tube. Fol-lowing this event, a comprehensive research program was initiated by Ontario Hydro. Its objective was to determine the consequences of pressure tube-calandria tube contact for channels in other reactors with Zr-2.5 Nb pressure tubes. The purpose of this paper is to present some of the results that have been obtained in the areas of blister growth, fracture, and nondestructive evaluation and to show how these results may be applied to Canada Deuterium Uranium (CANDU) reactor inspection.
Author: A. K. Jarvine