Pressure Tube Research Articles

Anisotropy and variability in thermal creep behaviour of Zr-2.5Nb pressure tube

The Zr-2.5Nb alloy pressure tubes of Indian Pressurized Heavy Water Reactors were manufactured from double melted ingots initially and subsequently from quadruple melted ingots to reduce impurities such as chlorine, phosphorus and carbon. In the current investigation, creep tests were carried out in the stress range of 0.7–0.9 times the yield strength and the temperature range of 350 °C–450 °C to characterize the thermal creep behaviour of Zr-2.5Nb alloy pressure tubes fabricated from double and quadruple melted ingots. The rupture time, minimum creep rate, stress exponent, activation energy and threshold stresses were obtained by carrying out the creep tests of the samples fabricated with their axis parallel to the axial and transverse directions of the pressure tubes. Experimental analysis revealed that the rupture time for double melted tube was 2–3 times lower than that of quadruple melted tubes, whereas no significant change in minimum creep rate was observed. Stress exponent values were obtained in the range of 3–5 signifying dislocation creep as the dominant creep mechanism. To predict the long-term creep properties, the master curves employing the Larson-Miller and Monkman-Grant methods were also evaluated. The effect of microstructural anisotropy, alloying elements and impurities on the thermal creep behaviour of Zr-2.5Nb pressure tube has been investigated.

Abstract 15532: Pressure Measurement From a Peripheral Iv Correlates Well With Invasive Central Venous Pressure Measurement

Introduction: Despite its importance in cardiac patients, accurate central venous pressure (CVP) estimation remains a challenge. Noninvasive methods, such as jugular venous pressure measurement, are highly dependent on examiner experience, and the gold-standard invasive methods require procedures that carry risk of complication. Recent studies suggest that pressure measurement directly from a patient’s peripheral intravenous (IV) catheter, termed peripheral venous pressure (PVP), appears promising as an accurate and noninvasive method for CVP estimation. Methods: To be included in the study, patients were either receiving right heart catheterization (RHC) or had an existing pulmonary artery catheter (PAC) in place. CVP was measured using standard technique either during RHC or at bedside from the PAC. The same pressure tubing was then connecting to the patient’s existing IV, regardless of the location or catheter gauge, for measurement of the PVP. Results: Seventeen patients were prospectively enrolled. The majority (70.6%) had their CVP and PVP measured during RHC. In the overall cohort, 35.3% were on mechanical circulatory support, and 29.4% were on inotropes at the time of measurement. CVP and PVP measurements were significantly correlated with one another (Pearson’s r = 0.73, p < 0.001; Figure 1A). Sensitivity analysis was performed to exclude one notable outlier, which strengthened the correlation (Pearson’s r = 0.91, p < 0.001; Figure 1B). Conclusions: This data suggests that PVP is a promising and simple method for the noninvasive estimation of CVP.

Deuterium concentration profiles at the rolled joints of CANDU fuel channels

A diffusion model is proposed to explain high concentrations of hydrogen isotopes seen in some rolled joints of CANDU reactors. Predicted concentration profiles emanating from the rolled joints into the Zr-2.5Nb pressure tubes suggest an early ingress event happens within the first six months of operation in some tubes. This event is consistent with gettering of hydrogen from the 403 stainless steel end-fittings by the pressure tubes.

Divergence instability in an air-conveying soft tube: Analysis of static zig-zag shapes

This work is devoted to the characterization and modeling of surprising stable states appearing in air-conveying soft tubes. A soft tube differs from a flexible tube by its very thin walls which allows it to fold with a sharp angle. When the upper end of a soft tube is fixed to an air pump while the bottom end is left free, the system exhibits a divergence instability which develops under the form of “zig-zag” shapes constituted by three roughly straight segments. We characterize each stable shape by the lengths and angles of these three segments. We observe, for example, that the intermediate segment is limited to short lengths because its inclined direction with respect to the vertical increases the gravitational torque on the upper fold. In order to theoretically reproduce the zig-zag shapes, we use a model of three articulated straight rigid tubes conveying airflow. The torque exerted by the pressurized tube on a folded part of the pipe is modeled by a nonlinear torsional spring. This model shows that the system can stabilize into zig-zag states qualitatively similar to experimental observations.

Uniform oxidation in steam and nodular corrosion in gas phase of Zr-2.5Nb pressure tube material - effect of nature of initial oxide

Oxide layers of similar starting thicknesses were grown on Zr-2.5Nb pressure tube material in air at 400 °C and in steam at 400 °C and 10 MPa. Both types of oxides were subjected to (a) further long term exposure up to 85 days in steam at 400 °C and 10 MPa and (b) nodular corrosion in a gas mixture of CO2 and O2 in presence of a contaminant, HCl at 350 °C. The air oxidized material gave an advantage of no hydrogen pick-up to start with as against steam oxidized material. Both types of oxides exhibited similar uniform oxidation and hydrogen pick up behaviour during long term exposure in steam at 400 °C and 10 MPa. On the other hand, the air-formed oxide was found to be more resistant to nodular corrosion in a gas mixture of CO2 and O2 at high temperature in presence of hydrochloric acid. The superior nodular corrosion resistance was attributed to a thicker impervious layer in the oxide rendering better protection from local oxide damage. This has been explained through the global mechanism for nodular corrosion in gas phase. The usefulness of air oxidation in the final steps of pressure tube fabrication has been discussed as well.

Designing hetero-structured ultra-strong and ductile Zr-2.5Nb alloys: Utilizing the grain size-dependent martensite transformation during quenching

• A heterogeneous structured Zr-2.5Nb alloys were fabricated successfully utilizing the grain size-dependent martensite transformation. • The present Zr-2.5Nb alloys manifest the highest yield strength (∼710 MPa), together with a high ultimate tensile strength (∼844 MPa) and good ductility (∼17.1%). • A model based on the grain-size-dependent critical resolved shear stress for dislocation slip and twinning has been proposed to explain the α' martensite substructures transition at a critical grain size d c = 3.3 μm. To further improve the service performance of Zr-2.5Nb alloy worked as pressure tubes in pressurized heavy water reactors, more investigation about the microstructure and thermomechanical processing route of Zr-2.5Nb alloy need to be conducted. In this work, a hetero-structured Zr-2.5Nb alloy was prepared by applying a novel technique. Microstructure analysis reveals that the alloy exhibits a grain size-dependent martensite substructure transition during post-rolling quenching. The hetero-structure consists of equiaxed primary α grains and the lamellae groups containing both parallel α' dislocation martensite and α' twin martensite. Compared with the previously reported Zr-Nb alloys, the present Zr-2.5Nb alloys manifest the highest yield strength (∼710 MPa), together with a high ultimate tensile strength (∼844 MPa) and good ductility (∼17.1%). The enhanced mechanical properties are found to arise from the properly controlled fraction/size of the two types of martensite, which not only significantly strengthens the alloy but also contributes to a stronger strain hardening. A model based on the grain-size-dependent critical resolved shear stress for dislocation slip and twinning has been proposed to explain the α' martensite substructures transition at a critical grain size d c = 3.3 μm. Below this size, the critical resolved shear stress (CRSS) for twinning is higher than that for the <c + a> slip. Thus, the α' dislocation martensite is more favorable to form. Otherwise, the α' twin martensite would exhibit a high activity. The present work indicates that making use of the grain size-dependent martensite transformation to tailor the hetero-structure in Zr alloys is an effective strategy to overcome the strength–ductility trade-off in the material.

An explosively driven launcher capable of $$10\,\mathrm{km\,s}^{-1}$$ projectile velocities

Launching large (> 1 g) well-characterized projectiles to velocities beyond 10 km/s is of interest for a number of scientific fields but is beyond the reach of current hypervelocity launcher technology. This paper reports the development of an explosively driven light-gas gun that has demonstrated the ability to launch 8 mm diameter, 0.36 g magnesium projectiles to 10.4 km/s. The implosion-driven launcher (IDL) uses the linear implosion of a pressurized tube to shock-compress helium gas to a pressure of \SI{5}{\giga\pascal}, which then expands to propel a projectile to hypervelocity. The launch cycle of the IDL is explored with the use of down-bore velocimetry experiments and a quasi-one-dimensional internal ballistics solver. A detailed overview of the design of the 8 mm launcher is presented, with an emphasis on the unique considerations which arise from the explosively driven propellant compression and the resulting extreme pressures and temperatures. The high average driving pressure results in a launcher that is compact, with a total length typically less than a meter. The possibility to scale the design to larger projectile sizes (25 mm diameter) is demonstrated. Finally, concepts for a modified launch cycle which may allow the IDL to reach significantly greater projectile velocities are explored conceptually and with preliminary experiments.

Relationship between pressure drop and tube deformation in a reformer furnace: a case study

Relationship between pressure drop and tube deformation in a reformer furnace: a case study

Numerical modeling of the thermal behavior of a severely damaged core of PHWR under accident condition

Under the accident condition, the loss of the continuous flow of coolant through the channel and the associated oxidative clad-steam chemical reaction causes an increase in the temperature of the fuel assemblies. If the moderator subcooling margin is insufficient, the channel may overheat to the point where the bundle assembly is jeopardized, and the fuel elements collapse onto the bottom of the Pressure Tube (PT). The present study aims to perform the numerical modeling of a severely degraded channel under steam flow condition from the thermal point of view. The configuration and the parameters employed in the study have been taken from the experiment. The energy equation incorporates all types of heat transfer, as well as secondary heat generated during the clad-steam oxidation reaction. The axial and circumferential temperature distribution has been obtained for the cladding, PT and Calandria Tube (CT), and compared with the experimental data. The predicted results are found to be in line with the experimental results, with the exception of the temperature excursion in the Fuel Bundle simulator (FBS) downstream of the coolant.

Dislocation density evolution in cold-rolled Zr-2.5%Nb pressure tubes under thermal treatments by high energy XRD and neutron TOF diffraction peak profile analysis

Diffraction line profile analysis was done to characterize the change in the dislocation density at different stages of the processing route of a Zr-2.5%Nb pressure tube. Two diffraction experiments were carried out: High Energy X-Ray Diffraction (HE-XRD) and Neutron Time of Flight Diffraction (TOF-ND). On samples in the extruded, cold-rolled and post-annealed conditions, the HE-XRD experiment in transmission geometry allows a detailed characterization of the dependence of the line shape on the direction of the scattering vector. Important variations of the FWHM (Full Width at Half Maximum) were observed, which was interpreted as the non-uniform distribution of dislocations among grains with different orientations. Average values of the dislocation density and subgrain size were obtained after applying the Warren-Averbach method.The effect of post deformation annealing for soaking temperatures from 400° to 450°C was studied using TOF-ND. Peak profile analysis was performed on in-situ neutron time-of-flight diffractograms to obtain peak positions and widths to calculate residual stresses and dislocation densities. The results show that the dislocation density decreases largely at early times and it is followed by a slow diminution over time. Dislocation density decreases from ∼8 × 1014 m−2 for the cold-rolled sample to values close or under 2 × 1014 m−2. A remnant dislocation density after long annealing times was detected, with a value that decreases as the soaking temperature increases. Dislocation type was also characterized. It was found that dislocations with 〈a〉 Burgers vectors represent approximately 90% of the population, while the other 10% are 〈c+a〉. An empirical recovery kinetics model was proposed where dislocation mobility is assumed as a thermally activated mechanism. This model can be used as a processing tool to estimate the dislocation density expected for different soaking temperatures and times. The effect of residual stresses on peak broadening was also discussed. It was estimated that this contribution represents around 10–20% to the observed physical line broadening.

A plate theory for inflatable panels

An inflatable panel is an airtight membrane structure whose envelope has two parallel flat sides when pressurized. It acquires load-carrying capacity due to its internal pressure. While pressurized tubes have been studied extensively over the past decades, panels were less investigated. In this work, a model of inflatable panels including shear effects is proposed. The nonlinear equations of motion are derived from the principle of virtual power within the framework of finite deformations and exhibit the essential pressure terms that allow for the correct prediction of the panel behavior. The equations are then linearized around the pre-stressed reference configuration and solved for a simply-supported circular panel subjected to a uniform load. The solution is found to be in good agreement with 3D finite element results.

Physics Assessment of the Impact of Modified End Pellets on Axial Power Peaking for Advanced/Nonconventional Uranium-Based Fuels in Pressure Tube Heavy Water Reactors

Abstract Axial power peaking is a phenomenon with safety implications for pressure tube heavy water reactors (PT-HWRs). Since PT-HWRs use shorter (∼50 cm) bundles, there are small axial gaps, which expose the ends of the fuel elements to more neutron flux, and therefore results in higher power density levels occurring in the ends of the fuel elements. Power peaking has the potential to cause fuel damage and failure, if the local linear element rating (LER) exceeds 57 kW/m, and may be of greater concern for advanced, higher burnup fuels. Earlier studies have been done using three-dimensional mcnp models of a PT-HWR fuel bundle with slightly enriched uranium; they demonstrated that ThO2 could be used to reduce axial power peaking in fresh fuel. This result was achieved by replacing some of the UO2 with ThO2 in the last 3 cm of fuel pellets at each end of a fuel bundle. This study extends the previous work by performing 3D neutronics and burnup calculations using serpent, to evaluate how power peaking changes with burnup. In addition, alternative dilution materials (such as depleted UO2, ZrO2, and MgO) were also evaluated. It was found that axial power peaking can be significantly reduced by using the ThO2 dilution material for fresh fuel, while ZrO2 or MgO are even more effective at higher burnup levels. Dilution materials have little impact (less than 2%) on the exit burnup of the fuel.

Investigating various factors affecting neutron spectrum in the pressure tube in pressurized heavy water reactor design

The fuel bundles in the pressurized heavy water reactor design (PHWR), such as the CANDU (Canada Deuterium Uranium), are placed inside horizontal fuel channels. Each fuel channel consists of concentric tubes called the pressure tube (PT) and the calandria tube (CT). Due to continuous exposure to extreme neutronics and thermal hydraulics conditions, the PTs undergo physical deformations in both the axial and radial directions, as the reactor ages. The deformations include diametral creep, wall thinning, sag, and axial elongation. One of the contributing factors to these deformations is the neutron spectrum in the PT, especially neutrons with energy greater than 1 MeV. In this paper, the sensitivity of the neutron spectrum in the PT to various operating conditions of a PHWR is evaluated. Sensitivity assessments have been completed on several parameters namely the coolant purity, coolant temperature, moderator purity, moderator temperature, and pressure tube diametral creep (PTDC). Since the deformations are inevitable, identifying parameters that have the greatest impact on the population of neutrons with energy greater than 1 MeV in the PTs would be important for fine-tuning the operational conditions which are conducive to reducing the rate of deformation. From this study, it is concluded that the coolant temperature and PTDC are the two variables having the most impact on the fast energy neutron population in the pressure tubes.

Calcination and desulfurization characteristics of calcium carbonate in pressurized oxy-combustion

Pressurized oxy-combustion is one of the most promising and efficient CO2 capture technologies for coal-fired power plants, which could reduce energy consumption for carbon capture. However, due to the effects of pressurization and flue gas recirculation, the partial pressure of sulfur oxides (SOx) in pressurized oxy-combustion is significantly higher than that of air-combustion, which leads to the corrosion risks and environment hazards. It is essential to investigate the SOx control in pressurized oxy-combustion. In this paper, the in-furnace calcination and desulfurization characteristics of calcium carbonate in pressurized oxy-combustion were carried out in a pressurized drop tube furnace. The findings show that the sulfation reaction in pressurized oxy-combustion is direct sulfation and the sulfation rate increases with the increase of temperature and pressure. The desulfurization efficiency in pressurized oxy-combustion is lower than that in atmospheric air atmosphere below 950 °C, but it reverses above 950 °C, indicating that the minimum desulfurization temperature in the furnace of the pressurized oxy-combustion is higher than that of atmospheric air atmosphere. Therefore, limestone can still be used as a sorbent in the pressurized oxy-combustion furnace. This study could contribute to the design of dry desulfurization systems in pressurized oxy-combustion combustors that use fossil fuel energies with high efficiency and low SOx emissions.

Experimental study on the structure and reactivity of char in pressurized O2/H2O atmosphere

Pressurized O2/H2O combustion is regarded as a promising high-efficiency CCS technology. In this study, char combustion in a pressurized O2/H2O atmosphere was performed with a pressurized horizontal tube furnace. The effects of pressure (0.1–1.3 MPa) and H2O concentration (0–60%) on char conversion, char physicochemical structure and reactivity were investigated by means of XPS, Raman, temperature-programed desorption and TGA tests. The results show that both pressurization and H2O can promote char conversion and facilitate the formation of carbon‑oxygen bonds on the char surface. Pressure mainly affects the consumption and generation of micropores, while the effect of H2O on the pore structure has no obvious selectivity. Pressurization reduces the relative content of CC, while H2O has the opposite effect. At low pressure (0.1–0.7 MPa) and low H2O concentration (0–40%), pressurization and H2O can promote the formation of C(O) on the surface of char. The reactivity of char first decreased and then increased with increasing pressure and increasing H2O concentration.

Effect of metallurgical variables on hydride precipitation behavior in Zr-2.5Nb micro pressure tubes

The effect of manufacturing routes (heat treatment done by a conventional β-quenching (BQ), or slow cooling (SC) prior to hot extrusion), and location along the tube (front end (FE) and back end (BE) emerging from the press) on hydride precipitation behavior in Zr-2.5Nb micro pressure tubes were evaluated. After being hydrided to 100 wppm H, stepped micro pressure tube samples with three kinds of microstructure (BQ-BE, SC-FE, SC-BE) were pressurized to obtain nominal hoop stresses ranging from 65 MPa to 350 MPa. All the samples were heated to 350°C to dissolve all of the hydrogen, followed by cooling under stress to allow hydride reorientation to occur. Almost complete reorientation was observed in the BQ-BE sample at stress levels of above 100MPa, while the SC-FE and BE samples showed stronger resistance to reorientation. After subsequent reheating to 350°C for 1 hour or 24 hours and cooling without stress, little memory effect was found for the re-orientated hydrides in the BQ-BE sample. However, a clear memory effect was observed in the SC-FE and SC-BE sample in the range of angles where hydrides were naturally present.

A study on the effect of residual stresses on hydride assisted crack in Zr-2.5Nb pressure tube material using XFEM

Residual stresses in the Zr-2.5Nb pressure tube (PT) significantly affect its resistance to hydride embrittlement. This work aims to study the influence of residual stresses on hydride embrittlement using a model formulated for the delayed hydride cracking (DHC) mechanism. The DHC model includes transient hydrogen diffusion and hydride precipitation. The model is implemented using the extended finite element method (XFEM) that is validated with the analytical and numerical solutions available in the literature. Two different variations of residual stresses at different locations of PT available in the literature are used for this study. The results show that high tensile residual stresses in the PT help hydride growth and reduce the failure time.

Numerical investigations on boiling of moderator during PT/CT contact in 220 MWe IPHWR under postulated accidental scenario

For an Indian pressurised heavy water reactor, a numerical investigation was performed to study the boiling of moderator in a fully voided single nuclear channel during Pressure tube- calandria tube contact condition by applying variable heat flux. The setup included calandria tube, moderator, pressure tube, fuel bundle and an enclosure. It was observed that because of the contact between calandria tube and pressure tube, a notable variation in the circumferential temperature distribution of calandria tube and pressure tube were observed pointing out that contact condition drastically affects the temperatures of top and bottom portion of the tubes. It was also observed that upon increasing the heat flux, the top to bottom temperature variation decreases for pressure tube but increases for calandria tube. The phenomenon of boiling of moderator started when 1650 W/m2 heat flux was given to the system as input and the rate of boiling increased as the heat flux was increased which resulted in increasing moderator vapour fraction in the enclosure and decrease in average moderator density. The film thickness of the moderator vapour on the outer circumference of the calandria tube varied with time, following a cycle of increasing and decreasing thickness. The result showed that upto 4950 W/m2 heat flux, the moderator acted as an efficient heat sink. If the heat flux is increased further, the moderator can fail to act as a good heat sink and eventually lead to fuel channel failure.

Computational fluid dynamic investigations of flow bypass through an aged CANDU pressure tube

Single-phase, isothermal computational fluid dynamics simulations of a whole CANada Deuterium Uranium (CANDUTM) channel with twelve simplified CANDU 37M fuel bundles were performed with Hydra. Both as-received and aged pressure tubes were considered in this work. The aged pressure tube geometry considered asymmetric sag and diametral expansion profiles with a maximum sag of 57 mm and a maximum diametral expansion of 5.2%. The predicted fluid velocity and turbulent kinetic energy obtained from the two cases were compared in order to predict the impact of pressure tube deformation (sag and diametral expansion) on coolant flow. The boundary conditions and material properties are representative of normal operating conditions in a high-powered channel of the Darlington Nuclear Generating Station. It has been determined that pressure tube deformation has a significant impact on coolant flow behaviour, whereby up to 27% of flow bypasses the fuel.

Determination of relative sensitivity factor, sputtering rate, and detection limits of deuterium in deuterium ion‐implanted Zircaloy‐4 using secondary ion mass spectrometer

Zirconium‐based alloys are extensively used in the nuclear industry as materials for reactor core components. These alloys are used in fuel cladding and pressure tubes with 1H2O or 2H2O as the primary heat exchange fluid. Continuous usage of pressure tubes and fuel cladding inside the reactor results in heavy ingress of hydrogen (1H) or deuterium (2H), which gives rise to the formation of hydrogen (or deuterium) precipitates in the host of zirconium matrix. This is called hydrogen (or deuterium) embrittlement phenomenon. Therefore, determination of hydrogen or deuterium concentration periodically in zirconium alloy pressure tubes and cladding are crucial for safe operation of nuclear reactors. Hence, in this work, secondary ion mass spectrometry (SIMS) has been utilized to determine the relative sensitive factor (RSF), sputtering rate, and detection limits of 2H in 2H+ ion‐implanted Zircaloy‐4 sample. SIMS analysis has been carried out using O2+ and Cs+ primary ion beams. Depth profiles of various elemental and molecular secondary ions have been monitored to determine the RSF values and detection limits of 2H in the sample under different primary ion beam analysis conditions. Sputtering rate under different analysis conditions has also been determined from the correlation between the projected range of 2H+ ions in Zircaloy‐4 sample determined from Stopping and Range of Ions in Matter (SRIM) software and the depth of the crater formed by primary ion beam bombardment process. The projected range of 2H+ ions in Zircaloy‐4 was estimated to be ~524.2 nm using the simulation carried out by SRIM software. The projected range, evaluated by SRIM software, was utilized for depth scale calibration of SIMS sputtered time profiles. The SIMS depth profiles were also calibrated by determining the depth of the SIMS crater by using optical depth profilometer. The values of range estimated by SRIM as well as optical profilometer were found to be in good agreement, within instrument uncertainty.