Leak Rate Test Research Articles

Microencapsulated phase change materials based on graphene Pickering emulsion for light-to-thermal energy conversion and management

The superior thermal behavior and light-to-thermal energy conversion performance are crucial for microencapsulated phase change materials (microPCMs) in thermal energy management. In this work, a series of paraffin@graphene/melamine-formaldehyde microPCMs based on graphene Pickering stabilizer were prepared by in-situ polymerization. Graphene was served as a Pickering stabilizer. We have undertaken a comprehensive study of the effects of different graphene concentrations and core/shell ratio on the microPCMs. The leakage rate test showed that the leakage rate of the microPCMs with 0.2 wt% of graphene is decreased by 93.20% than that of the microPCMs without graphene. Graphene promotes light-to-thermal conversion efficiency of microPCMs, which reaches to 90.7%. Additionally, the optical microscope (OM) and scanning electron microscope (SEM) were used to characterize the morphology of the Pickering emulsion droplet and microPCMs, respectively. Thermal properties of microPCMs were evaluated by differential scanning calorimetry (DSC) and thermal conductivity test. The results indicated that the latent heat of the microPCMs with core/shell ratio of 4/1 is 204.0 J g−1 and thermal conductivity of that is 0.707 W m−1 K−1. Furthermore, because of the leakage prevention performance, thermal conductivity and light-to-thermal conversion performance of microPCMs, it may be forecast that microPCMs possess significant applications in thermal energy storage management.

Performance of Geosynthetic Clay Liner with Polymerized Bentonite in Highly Acidic or Alkaline Solutions

The hydraulic behavior of a polymerized bentonite (PB) and the self-healing capacity of a geosynthetic clay liner (GCL) using the PB as core material (PB-GCL) in corrosive solutions (pH ranging from 1 to 13) were investigated through a series of laboratory tests [i.e., free swelling index, swelling pressure, permeability (k) (consolidation), and leakage rate tests]. The test results indicate that the PB had a higher swelling capacity than that of the corresponding untreated bentonite (UB). Particularly, for pH greater than 12.5 solutions, PB had a higher free swelling index (FSI), higher swelling pressure, and lower k value than that of the PB with deionized water. PB-GCL with a damage hole had lower permittivity for the damage hole (ψhole) and a higher self-healing capacity than that of the GCL using UB as the core (UB-GCL). Based on the test results, it is suggested that PB-GCL can be used as an effective barrier material to contain acidic and alkaline liquids.

Comparison of Measured and Calculated Data for NPP Krško CILR Test

Containment is the last barrier for release of radioactive materials in the case of an accident in the nuclear power plant (NPP). Its overall integrity is tested during a containment integrated leak rate test (CILRT) at the design pressure, at regular intervals. Due to applied risk based licensing, the test intervals can be increased up to once in 10 years and beyond. Taking that into account it is important to prepare the test properly and to use obtained results to assess the real status of the containment. The test can be used to verify existing containment calculation models. There is a potential benefit of verified computer models usage for the explanation of some test results, too. NPP Krško has performed CILRT during the plant outage in 2016. The paper presents a comparison between measured data and results calculated using a multivolume GOTHIC (Generation Of Thermal Hydraulic Information For Containment) model. The test scenario was reproduced using limited available data up to the end of the pressurization phase. The depressurization phase is calculated by the code and measured leakage rate is implemented in the model. Taking into account the necessary adjustments in the model, overall prediction of the measured results (in terms of pressure, temperature and humidity) is very good. In the last phase of the test some non-physical behavior is noticed (without influence on overall test results), probably caused by the combination of air redistribution within the containment and influence of heat transfer to plant systems that were in the operation during the test. GOTHIC model was used to check sensitivity of the predicted pressure (leak rate) to different heat inputs and to investigate the influence that operation of only one reactor containment fan cooler (RCFC) train during pressurization can have on the mixing of air within the containment. In addition, the influence of currently used weighting factors (weighting of measured temperature, relative humidity and pressure data) on the used test methodology is investigated. The possible non-conservative direction of the influence (currently used weighting factors are giving lower leakage rate) was demonstrated and a new set of weighting factors is proposed too.

Validation of the MELCOR input model for a CANDU PHWR containment analysis by benchmarking against integrated leakage rate tests

Abstract In an effort to overcome limitations when validating a code input model for the containment of a nuclear power plant, two integrated leakage rate tests (ILRTs) performed at a CANDU 6 plant were simulated with a MELCOR input model consisting of 51 control volumes. Leakages were assumed to occur at the volumes enclosed within the containment wall. The initial conditions were set to the measurements at the time when the atmosphere stabilization phase was started. The analysis was then carried out until the end of the main test phase. The analysis results show reasonable agreement with the measurements of temperature and vapor pressure, whereas they show deviations with regard to pressure and local temperatures in the middle and lower regions. In addition, a sensitivity analysis of the effects of the heat structure model and the manner by which thermodynamic variables can be lumped was carried out. This study revealed that the ILRT is useful for validating the containment input model. However, available data with which to verify the appropriateness of modeling flow paths and heat structures are limited. Based on the insights obtained, we suggest that an elaborate ILRT be carried out during the commissioning stage with more detailed test provisions and analysis methods to allow this specific application.

A Low-Reflectivity Vacuum Window for Rectangular Hollow Waveguides

The design and performance of a broadband and low-reflectivity millimeter-wave vacuum window for rectangular hollow waveguides are presented. A reflectivity below −15 dB is achieved over almost the full ${W}$ -band. The vacuum window is sufficiently compact, so that two separate channels fit into a single ConFlat CF-35 vacuum flange. The proposed vacuum window utilizes a well-known circuit concept based on two-quadrature hybrid couplers together with two identical vacuum barriers (similar to a balanced amplifier). Due to the dielectric discontinuity at the vacuum barrier, a part of the incident wave is transmitted and another part is reflected. A hybrid lattice network recombines the transmitted signals and reroutes all reflected power to absorbers. The proposed low-reflectivity vacuum window has been fabricated in the WR10 waveguide technology. Broadband branch-guide couplers enable an operational frequency range of 75–105 GHz. Ultrahigh vacuum compatibility is verified by a helium leak rate test, and electrical measurements show good agreement with full-wave simulations.

Research on the Total Leakage Rate Test of the Spacecraft and its Uncertainty Evaluation

Leak testing is the major type of non destructive testing for spacecrafts and the sealing performance of the spacecraft is an important parameter to evaluate the quality of the spacecraft. So it is necessary to study the total leakage rate test of the spacecraft and its uncertainty evaluation. In this paper, the basic principle of the total leakage rate test of the spacecraft was analyzed firstly from the theoretical aspect. Secondly, the various influencing factors on the results of total leakage rate test had been systemically analyzed. Finally, through the uncertainty evaluation theory, the uncertainty components induced by these influencing factors were respectively quantified and combined. And the expanded uncertainty of the result of total leakage rate test was given.

Graphene oxide-modified microencapsulated phase change materials with high encapsulation capacity and enhanced leakage-prevention performance

Novel microencapsulated phase change materials (MEPCMs) with high encapsulation capacity and enhanced leakage-prevention performance were prepared by in situ polymerization. For these MEPCMs, paraffin and melamine-formaldehyde resin (MF) are respectively used as core and shell, and graphene oxide (GO) nanosheets, which can be seen as extra protective screen, are situated at the interface between the core and the shell. Effects of GO on morphology, microstructure and properties of MEPCMs were characterized by scanning electronic microscopy (SEM), laser diffraction particle analyzer, atomic force microscopy (AFM), Fourier transformation infrared spectroscopy (FTIR), X-ray diffractometry (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TG) and paraffin leakage rate test. The results show that the fabricated MEPCMs with GO nanosheets have gradual increasing average diameters from 6.32 to 15.89μm with an increase content of GO, while the size of MEPCMs without GO is 5.63μm. When the time of leakage rate test is 50h, the MEPCMs prepared with 0.5mg/mL GO aqueous dispersion have considerably high encapsulation ratio of 93.9wt.%, and the leakage rate is reduced by 93.1% compared with those without GO. The high encapsulation capacity and enhanced leakage-prevention performance might be highly attractive for the application of MEPCMs.

Evaluation of CANDU NPP containment structure subjected to aging and internal pressure increase

The objective of this study is to investigate the long-term performance of a typical CANDU®1®Registered trademark of Atomic Energy of Canada Ltd. (AECL) used under exclusive license by Candu Energy Inc., a Member of the SNC-Lavalin Group.1 containment structure. A three-dimensional nonlinear finite element model was built to realistically evaluate the performance of the structure under service load as well as a hypothetical beyond-design level internal pressure. Consideration is given to the time-dependent effects, such as shrinkage, creep, and relaxation of prestressing tendons, over a 60-year timeframe. In addition, the sensitivity of the response of the containment structure against support condition, internal temperature profile and temporary construction openings was also investigated. The accuracy of the numerical model was validated against structural measurements made during a routine leak rate test. The analysis results show that the containment structure would develop a ductile mechanism if the internal pressure significantly exceeded the design pressure. The pressure-deformation relationship of the structure is sensitive to the considered time-dependent parameters.

Probabilistic finite element investigation of prestressing loss in nuclear containment wall segments

The main function of the concrete containment structures is to prevent radioactive leakage to the environment in case of a loss of coolant accident (LOCA). The Canadian Standard CSA N287.6 (2011) proposes periodic inspections, i.e., pressure testing, in order to assess the strength and design criteria of the containment (proof test) and the leak tightness of the containment boundary (leakage rate test). During these tests, the concrete strains are measured and are expected to have a distribution due to several uncertainties. Therefore, this study aims to propose a probabilistic finite element analysis framework. Then, investigates the relationship between the concrete strains and the prestressing loss, in order to examine the possibility of estimating the average prestressing loss during pressure testing inspections. The results indicate that the concrete strain measurements during the leakage rate test may provide information with respect to the prestressing loss of the bonded system. In addition, the demonstrated framework can be further used for the probabilistic finite element analysis of real scale containments.

원전 격납건물 국부누설률시험에서의 압력감소법을 이용한 과다누설 측정 방법

원전 격납건물 국부누설률시험에서의 압력감소법을 이용한 과다누설 측정 방법

중수로 원자로건물 총누설감시계통 시험 중지에 따른 리스크 영향 평가

Wolsong Unit 2,3&4 has been performing a containment integrity test during power operation. This test could impact to the safe operation during test. If an accident occurs during pressure dropping phase, reactor trip can be delayed because of the increased pressure difference which causes a time delay to reach the trip set-point. On the contrary, if an accident occurs during pressure increasing phase, reactor trip could be accelerated because the pressure difference to the trip set-point decrease. Point Lepreau nuclear power plant, which installed GCLMS (Gross Containment Leakage Monitoring System) in 1990, has discontinued the test since 1992 due to these adverse effects. Therefore, we evaluated the risk to obviate the GCLMS test based on PWR's ILRT (Integrated Leak Rate Test) extension methodologies. The results demonstrate that risk increase rate is not high in case of performing only ILRT test at every 5 years instead of doing GCLMS test at every 1.5 years. In addition, the result shows that GCLMS test can be removed on a risk-informed perspective since risk increasement is in acceptable area of regulatory acceptance criteria.

Measurement and analysis of the leak tightness of reactor containment vessels: experiences and results

The reactor containment vessel consisting of a reinforced concrete structure with an internal steel liner in the drywell and wetwell is designed to prevent the uncontrolled release of radioactivity to the environment. As the allowable leakage area by which this test passes is small, the containment leakage rate test is crucial not only for periodic but also for pre-operational tests. This paper presents a measurement system as well as a leakage rate analysis program for the test. The experiences for leakage examination are presented and several break holes are then identified thanks to the permeability of concrete and the localization property for gas leakage from inside to outside of the containment vessel. After repairing the leakage holes, the test is conducted and the result is satisfactory.

Experimental investigation on the friction and sealing characteristics of narrow end-face seal ring with spiral grooves for wet clutch

Purpose – The purpose of this paper is to investigate the friction and sealing characteristics of narrow end face seal ring with spiral grooves for wet clutch by experiment. Design/methodology/approach – The shallow spiral grooves are machined in the end face of narrow seal ring by laser, and all of other parameters of specimens are the same with the actual production. The investigation of friction and sealing characteristics are carried out by comparing the experiment results of end face seal ring with spiral grooves with the conventional seal ring without spiral grooves through friction coefficient test, volume leakage rate test and pv value test. Findings – Comparing with conventional seal ring without spiral grooves, seal ring with spiral grooves experiences boundary lubrication, mixed lubrication and fluid film lubrication with the increase of rotation speed, whereas the conventional seal ring only experiences mixed lubrication. Besides this, the volume leakage rate is slightly larger, but the pv value is much larger than that of conventional seal ring. Originality/value – Effect of spiral grooves on the friction and sealing characteristics of narrow end face seal ring for wet clutch is investigated. The improved lubrication performance can be achieved by shallow spiral grooves even if the distance of radius difference used to machine grooves is very small.

Low-Temperature Solid-State Bonding Using Hydrogen Radical Treated Solder for Optoelectronic and MEMS Packaging

Many optoelectronic and MEMS devices require hermetic sealing for protection of the optoelectronic elements and movable fragile parts to ensure stable and reliable performance characteristics. Most commonly used bonding techniques for hermetic sealing are glass-frit bonding, anodic bonding, solder bonding, and eutectic bonding. For many applications, low temperature bonding is desirable because the temperature sensitive materials or components degrade and thermally induced stresses can be created during bonding. Furthermore, since the hermetic sealing is typically the final processing step in device fabrication, bonding method that is tolerant to surface roughness is desirable.In this study, a low-temperature solid-state bonding process at bonding temperature lower than 200 °C using hydrogen radical treated Sn-3.0Ag-0.5Cu (wt%) solder without flux is investigated for potential application as hermetic packaging. The interfacial reaction between solder and Au is studied by means of scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX). The bonding quality is evaluated by means of die-shear test and leak rate test.The re-oxidation of hydrogen radical treated Sn was studied by X-ray photoelectron spectroscopy (XPS). Fig. 1 shows the typical XPS spectra of Sn plate (purity: 5N) treated with hydrogen radicals (a) and argon fast atom beam (FAB) (b). The XPS Sn (3d2/5) spectra have been used to follow the surface oxide growth on Sn surfaces as a function of exposure time to air after removal of surface oxide. Two peaks are due to the presence of Sn metal and SnOx. The surface of Sn plate treated with Ar FAB contained a large amount of SnOxthan that with hydrogen radicals after exposure time to air of over 20 h. These results indicate differences between the removal of surface oxide by chemical reaction of hydrogen radicals and that by physical bombardment using fast atom beams. The inhibitory effect of re-oxidation of hydrogen radical treated solder [1] was confirmed by XPS measurement.Fig. 2 shows the process flow of the low-temperature solid-state bonding. Sn-Ag-Cu solder paste (melting point: 217 °C) is deposited by screen printing technique. Then, the surface oxides of Sn-Ag-Cu particles in the paste are reduced by hydrogen radical treatment at 180 ºC. After that, the solder is reflowed at 230 °C for 90 s with additional hydrogen radical treatment for 3 sec. During the reflow process, the Sn-Ag-Cu particles completely coalesce and solder pattern is formed on the wettable metal parts of the substrate [2]. Then, the Sn-Ag-Cu patterns are exposed to air and bonded with Au films without flux at temperatures below the melting point.Successful bonding was obtained at a bonding temperature above 150 °C for 10 min. Fig. 3 shows the SEM image and EDX map of the cross section of the bonded interface under the application of a bonding pressure of 150 MPa and held at 170 °C for 30 min. The Sn-Ag-Cu solder pattern was deformed to achieve enough contact with Au thin film (thickness: 500 nm) and Au-Sn intermetallic compounds were formed during bonding process as shown in Fig. 3(b). No clear interface corresponding to the original Au surfaces is visible. To evaluate the bonding strength, die-shear test was performed and the die shear strength was over 30 MPa. Fracture mainly occurred in the inside of solder layer, which indicates that solder layer was well bonded with Au.The Sn-Ag-Cu sealing ring pattern (width: 100 μm, size: 2.4 mm × 2. 4 mm, thickness: 5-10 μm) was formed on a glass substrate (2.8 × 2.8 mm2) by hydrogen radical reflow process for hermetic leak rate testing. The cavity structure (cavity volume: 1.9 × 10-3 cm3) with Ti (thickness: 50 nm)/Au (thickness: 500 nm) sealing ring was also fabricated on a Si substrate. Hermeticity was evaluated by measuring the resonance characteristics of photothermally excited microcantilevers inside the cavity [3]. The samples bonded at the low temperature of 170 °C under the application of a bonding pressure of 150 MPa showed leakage rates of less than 1.0 × 10−9 Pa·m3 s−1, which is the rejection limit defined by the MIL-STD-883G specification.In conclusion, hydrogen radical treated Sn-Ag-Cu solder patterns were bonded with Au thin films at a lower temperature than the melting point of Sn-Ag-Cu without flux. This process is expected to be applicable for chip-size packaging of optoelectronic and MEMS devices.

In-service Inspection and Structural Health Monitoring for Safe and Reliable Operation of NPPs

In nuclear power plants, continuous efforts are made to ensure that plants are operated in safe, reliable and economical manner. While utmost care is taken during design, construction and commissioning of the structures, systems& components (SSCs), continued healthiness has to be ensured during operation phase in accordance with the design intent. This is primarily achieved through the establishment of a comprehensive life management programme of surveillance, condition monitoring, periodic In-service inspections (ISI) and maintenance, the purpose of which is to ensure that required safety margins are maintained for all important SSCs throughout plant service life. In any industry, the important mechanisms which lead to SSCs degradation are general corrosion, Flow accelerated corrosion, erosion, thermal effects, fatigue and mechanical wear & fretting. In a Nuclear Power Plant, in addition to these, degradation also occurs due to irradiation and creep. Therefore SSCs need to be designed with due consideration of all such degradation mechanisms. During operation phase, the limiting conditions for operation and requirements of surveillance & condition monitoring for all components important to safety are documented in Technical Specification. A plant specific ISI manual defines and elaborates the ISI internal inspection methods and acceptance criteria. The ISI requirements are decided taking into account best industry practices and operational experience and meet the requirements of existing codes and standards. Both these documents are approved by AERB. In pressurized heavy water reactors, major components covered in ISI programme are coolant channels, feeder pipes, steam generators, heavy water heat exchangers, pressure boundary components, relief valves etc. The inspection methods adopted include use of UT, ECT, DPT and visual inspection. In addition to functional checks for some of the components, ferrography, vibration monitoring and thermography etc are also utilized for rotating equipment. The SSCs where unacceptable indications are revealed by ISI are repaired, replaced or isolated. The base line data generated during Pre-Service inspection is used for comparing and trending of observations. The observations made during ISI are subjected to thorough review and analysis by qualified experts to obtain assurance that unacceptable degradation in component quality is not occurring and it remains fit for service. The containment system of a NPP plays a crucial role in minimizing dose to the public in case of an accident situation. The integrity of Primary and Secondary Containment is assessed by conducting integrated leak rate tests in every Biannual Shut Down. The concrete structure is also subjected to NDT checks on a specified frequency to ensure continued healthiness. Indian nuclear power plants have accumulated an operating experience of more than 380 reactor years of operation. Over the years, the programmes for surveillance, condition monitoring and in-service inspections have been improved significantly and match with best in the industry. As a result, there has been no major age related failure in any of the important SSCs and thus continued safe and reliable operation of NPPs is assured. This paper brings out the ISI & health monitoring methodology adopted at Indian NPPs, to ensure safe and reliable operation.

Structural Monitoring and Response Analysis of Prestressed Concrete Primary Containment of a Nuclear Power Plant

Before commissioning, Pressurised Heavy Water Reactor (PHWR) containments are tested for their integrity at proof pressure and Loss-of-Coolant Accident (LOCA) pressure. During operation, as per the current practice for Indian PHWR containments, in-service Integrated Leakage Rate Test (ILRT) is done once in two years at about one third of LOCA based test pressure. Kaiga Generating Station unit-2 (KGS-2) has been in operation for more than 11 years. For the first time, a periodic ILRT at LOCA pressure (0.86 kg/cm2 (g)) was conducted at KGS-2. During this ILRT, structural monitoring of pre-stressed concrete primary containment was carried out. The deflection and strains at critical locations in the IC were recorded during ILRT mainly to compare the same with the values obtained from analytical study and with those observed during the first ILRT. The strain and deflection measurements were taken using vibrating wire strain gauges (VWSG) and high precision dial gauges respectively connected to data-logger. This technical paper highlights the structural behaviour of KGS-2 primary containment after 11 years of operation.

Over-pressure test on BARCOM pre-stressed concrete containment

Bhabha Atomic Research Centre (BARC), Trombay has organized an International Round Robin Analysis program to carry out the ultimate load capacity assessment of BARC Containment (BARCOM) test model. The test model located in BARC facilities Tarapur; is a 1:4 scale representation of 540MWe Pressurized Heavy Water Reactor (PHWR) pre-stressed concrete inner containment structure of Tarapur Atomic Power Station (TAPS) unit 3&4. There are a large number of sensors installed in BARCOM that include vibratory wire strain gauges of embedded and spot-welded type, surface mounted electrical resistance strain gauges, dial gauges, earth pressure cells, tilt meters and high resolution digital camera systems for structural response, crack monitoring and fracture parameter measurement to evaluate the local and global behavior of the containment test model.The model has been tested pneumatically during the low pressure tests (LPTs) followed by proof test (PT) and integrated leakage rate test (ILRT) during commissioning. Further the over pressure test (OPT) has been carried out to establish the failure mode of BARCOM Test-Model. The over-pressure test will be completed shortly to reach the functional failure of the test model. Pre-test evaluation of BARCOM was carried out with the results obtained from the registered international round robin participants in January 2009 followed by the post-test assessment in February 2011. The test results along with the various failure modes related to the structural members – concrete, rebars and tendons identified in terms of prescribed milestones are presented in this paper along with the comparison of the pre-test predictions submitted by the registered participants of the Round Robin Analysis for BARCOM test model.

Self healing capacity of geosynthetic clay liners and influencing factors

Self-healing capacities of geosynthetic clay liners (GCLs) have been investigated using laboratory leakage rate tests. Two types of GCL were tested. The first type was a geomembrane supported GCL (GM-GCL) and the second type was geotextile encased GCL (GT-GCL). The diameters of the defects investigated ranged from 5 to 50 mm. Overburden stress (σ) varied over the range 0–200 kPa. Tap water, a solution of 10 g/l of NaCl in tap water and a solution of 100 ml/l ethanol in tap water were used as the liquid permeants. The test results indicate that for both GM-GCL and GT-GCL, defects with diameters less than 30 mm can be self-healed providing the liquid is tap water or the ethanol and tap water solution. Factors that tend to reduce the thickness of the diffusive double layer around particles of bentonite tend to reduce the self-healing capacity of a GCL, and the free swelling index of bentonite used in a GCL can be used to evaluate the self-healing capacity. The applied stress has two possible effects on self-healing capacity. One is the squeezing of hydrated bentonite into the damage hole and another is limiting the amount of hydration-induced expansion of the bentonite. For the conditions tested, the self-healing capacity increased with increasing applied stress.

La–Sr–Fe–Co oxygen transport membranes on metal supports deposited by low pressure plasma spraying-physical vapour deposition

Dense La0.6Sr0.4Fe0.8Co0.2O3−δ (LSFC) membranes were successfully prepared on NiCoCrAlY metal supports by low pressure plasma spraying-physical vapour deposition. He leakage rate tests and microstructural analysis by SEM of the as-deposited films showed that a gas-tight membrane layer is achieved. Membrane thicknesses are between 40 and 65µm. The oxygen permeation flux was determined at atmospheric pressure in an air-Ar gradient at different temperatures between 700 and 950°C and compared with 1mm thick LSFC pellet. Although leakage was detected, noteworthy oxygen permeation rate of the supported membranes (∼0.3mlcm−2min−1 at 885°C) is reported.

Leak behavior of steam generator tube-to-tubesheet joints under creep condition: Experimental study

To address concerns regarding excessive leakage from throughwall cracks in steam generator tube-to-tubesheet joints under severe accident conditions, leak rate testing was conducted using tube-to-collar joint specimens. The tube interior and the interface between tube and collar (crevice) were pressurized independently using nitrogen gas. The leak rate through the crevice was almost zero when the specimens were pressurized at ∼500 °C; this low leak rate is attributed to thermal mismatch effects preventing much leakage. The near zero leak rate was maintained until the onset of large leakage at higher temperatures. The leak rate behavior after the onset of the large leakage was not much affected by the crevice length or heat-to-heat variation of Alloy 600 tubes. This suggests that once the crevice gap opens, the creep rate of the low alloy steel collar becomes dominant. Specimens with different tube diameters behaved essentially the same way. To simulate a flawed steam generator tube in the tubesheet, the crevice region was pressurized through a hole in the tube. This simulation resulted in essentially the same behavior as those specimens whose tubes and crevices were pressurized independently. Oxidation of low alloy steel collars in air tests can increase the flow resistance, and thus tests using nitrogen gas would provide more conservative leak rate data.