Helium Pipe Research Articles

Mitigation of Helium Leakage Risks Within the Cryostat of ITER Including Diagnosing the Occurrence of Stress Corrosion Cracking Within the Thermal Shield Cryogenic Helium Pipes

Mitigation of Helium Leakage Risks Within the Cryostat of ITER Including Diagnosing the Occurrence of Stress Corrosion Cracking Within the Thermal Shield Cryogenic Helium Pipes

Design Study of a Superconducting Quadrupole Magnet System Sustainable Under Dark Current Heating in ILC Main Linac

The International Linear Collider (ILC) main linac comprises a series of 12 m-long cryomodules. The cryomodule contains eight 9-cell superconducting (SC) RF (SRF) cavities and an SC quadrupole magnet combined with dipole correctors to focus and steer electron and positron beams. The magnets are installed between the SRF cavity string and at the longitudinal center of a common cryomodule/cryostat. These magnets are conductively cooled by pure aluminum channels thermally connected to a 2 K two-phase helium pipe for cooling the SRF cavities. A recent study shows that field-emitted electrons, so-called “dark current” initiated in the SRF cavities, are transmitted through the SRF cavity string and reach the SC magnet. The energy is inevitably absorbed in the SC coil due to the magnetic field, resulting in risks of a quench caused by the coil heating. We are investigating alternate magnet designs by using Nb <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{3}$</tex-math></inline-formula> Sn or <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{MgB}_{2}$</tex-math></inline-formula> SC and by adding the dark current absorber surrounding the beam-pipe to realize sustainable magnet operation under the dark current heating. We report the design study of the magnet system and interfaces to the cryomodule accommodating it with the SRF cavities.

Numerical study on suppression of thermoacoustic oscillation in cryogenic helium pipeline system

Suppression of gas oscillation is essential to realize the stable operation of the cryogenic helium piping systems. In the current study, a structural solution, that is, a tube is connected to the main pipe as an adjustment accessory to control unfavourable gas oscillations. The model with dual temperature gradients is developed by introducing an adjustment tube. The effects of the parameter sensitive to the distribution of the dual temperature gradients on the thermoacoustic oscillation (TAO) characteristics are revealed. The results demonstrate that the asymmetry of the temperature distribution and a large frequency deviation makes it easier to achieve the oscillation-free operation of the system. At the initial start-up stage, the phase relationship between the acoustic waves is shown. As the cold length to warm length ratio decreases, the phase difference between sound waves increases, and the oscillation-free operation is accomplished when the cold length to warm length ratio is 0.11. Therefore, an approach of adjusting the length ratio in the adjustment tube can control thermoacoustic oscillations of cryogenic fluid.

Final Design of the CFETR Central Solenoid Model Coil

The central solenoid model coil (CSMC) for China Fusion Engineering Test Reactor (CFETR) is being developed in the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP). The maximum magnetic field is 12 T in the bore of the Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn coils. It has a 1.5 T/s changing rate under 47.65 kA operating current. It was designed as a hybrid superconducting magnet with Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn and NbTi coils to reduce cost. The detailed structure of the CSMC has been designed, it mainly including Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn coils, NbTi coils, preload structure, coil buffer zone, joints, supports, feeder throughs, helium pipes and pipe supports. The preload structure consisting of 15 preload beams, 30 preload rods and support plates. And a 75 MN preload force will be applied on the preload structure at room temperature. This paper describes the final design of the Central Solenoid Model Coil. And the mechanical analysis results show that the final design is reasonable and feasible.

Identification of nonlinear characteristics of thermoacoustic oscillations in helium piping systems

Insufficient dynamic information on helium piping systems limits our ability to understand and identify thermoacoustic oscillation (TAO) phenomena in these systems. In this study, we investigate the associated oscillation behaviours and the effects of the temperature distribution steepness, S, and the inflection point position, x0, on the TAO characteristics through numerical simulations. The results indicate that x0 has a greater impact on the oscillation behaviour and is a decisive factor for oscillation-free operation. It is found that oscillation-free operation can be achieved when x0 = 0.9 m. To identify the nonlinear dynamic characteristics related to TAO, the original pressure time series are unfolded in phase portraits and Poincaré maps. In contrast to the period-1 and period-2 limit circle oscillations at other positions, the trajectory at x0 = 0.9 m displays a transition from limit circles to a fixed point (zero amplitude), corresponding to a series of points including the point (0,0) in the Poincaré map. Therefore, an approach of adjusting the inflection point position can be used to control the state of the TAO, and the transition in the nonlinear dynamic characteristics can be identified, which can also provide guidelines for designers to mitigate unfavourable TAO.

Measurement of the energy spectra and of the angular distribution of the Transition Radiation with a silicon strip detector

We plan to develop an advanced Transition Radiation Detector (TRD) for hadron identification in the TeV momentum range, based on the simultaneous measurement of the energies and of the emission angles of the Transition Radiation (TR) X-rays with respect to the radiating particles. To study the feasibility of this project, we have carried out a beam test campaign at the CERN SPS facility with 20 GeV/c electrons and muons up to 300 GeV/c. To detect the TR X-rays and the radiating particles, we used a 300 μm thick double-sided silicon strip detector, with a strip readout pitch of 50 μm. A 2 m long helium pipe was placed between the radiators and the detector, in order to ensure adequate separation between the TR X-rays and the radiating particle on the detector plane and to limit the X-ray absorption before the detector. We measured the double-differential (in energy and angle) spectra of the TR emitted by several radiators. The results are in good agreement with the predictions obtained from the TR theory.

Thermal performance assessment of cryogenic transfer line with support and multilayer insulation for cryogenic fluid

Cryogenic transfer lines are very important to transport cryogenic fluid in the fields of fusion energy and hydrogen energy. The main aim of this work is to assess and minimize heat leakage of cryogenic transfer line. A three-channel coaxial liquid helium pipe with three support structures and typical multilayer insulation (MLI) materials was designed. Cryogenic transfer lines installed three support structures and MLI with different layer density & number of layer were studied based on a horizontal cryogenic transfer line test platform with liquid nitrogen. Thermal performance including heat leakage and temperature distribution of straight and elbow pipe have been numerically and experimentally analyzed for boundary temperature 77 K–293 K. By comparing simulated results with experimental heat leakages of supports, MLI and cryogenic transfer lines, the largest deviations are less than 10%, 10.7% and 6.6%, respectively. Based on above analysis, the minimal heat leakages of two-plate support and MLI with 50 layers and 25 layers/cm are 0.200 W and 0.488 W, respectively. Furthermore, the minimal heat leakages of straight pipe and elbow pipe were acquired as the values of 0.688 W and 0.858 W with two-plate support and MLI under 50 layers and 25 layers/cm. The results have been successfully applied in 250 W@4.5 K helium cryogenic refrigerator. The new and useful assessment method could also be applied to minimize heat leakage of cryogenic transfer lines with different size, support and MLI, etc, and then to improve the energy efficiency of system.

Experimental Study of Minimizing Heat Leakage of Cryogenic Transfer Lines

In this paper, a three-channel coaxial liquid helium pipe with three support structures and typical MLI materials was designed. Heat leakage of cryogenic transfer lines has been experimentally analyzed for MLI with different layer density & number of layer and three support structures, based on an experimental cryogenic transfer lines test platform. The experimental results show that the minimal heat leakage of MLI was 0.488 W/m under the conditions of MLI with 50 layers and 25 layers cm-1.The heat leak of two-plate support structure is 0.200 W per one, which decreases by more than 54% comparing to triangle support. After optimization, the total heat leakage of liquid helium cryogenic transfer line was reduced to 0.688 W/m, which has been successfully applied in 250 W @ 4.5 K helium cryogenic refrigerator.

Thermometric chains for ITER superconductive magnets

High environmental constraints are applied on the ITER magnets and therefore on their cryogenic thermometric chains. Accurate and reliable temperature measurements of the ITER magnets and their cooling circuits is of fundamental importance to make sure they operate under well controlled and reliable conditions. Therefore, thermometric chains shall reach a high operation reliability. In this paper, we present the full thermometric chain installed on the ITER magnets and their helium piping as well as the associated components production.The thermometric chain is described from the signals conditioning electronics, to the sensor and its on-pipe assembly. The thermometric block design is based on the CERN's developed one for the LHC, which has been further optimized thanks to thermal simulations carried out by CEA to reach a high quality level for an industrial production. The ITER specifications are challenging in terms of accuracy and call for severe environmental constraints, in particular regarding irradiation level, electromagnetic immunity and distance between the sensors and the electronic measuring system. A focus will be made on this system, which has been recently developed by CEA. It is based on a lock-in measurement and amplification of small signals, and provides a web interface and a software to monitor and record the temperatures. This measuring device provides a reliable system for resistive temperature sensors between a few ohms and 100 kOhms.During last two years, around 2600 thermo-blocks and nearly 50 crates of five boards, with eight channels each, have been produced and tested at CEA low temperature laboratory. All these developments and tests have been carried out thanks to three test benches built up at CEA Grenoble and in one industrial electronics laboratory. Test benches results on the entire production are presented.

A PC-based high temperature gas reactor simulator for Indonesian conceptual HTR reactor basic training

In planning for nuclear power plant construction in Indonesia, helium cooled high temperature reactor (HTR) is favorable for not relying upon water supply that might be interrupted by earthquake. In order to train its personnel, BATAN has cooperated with Micro-Simulation Technology of USA to develop a 200 MWt PC-based simulation model PCTRAN/HTR. It operates in Win10 environment with graphic user interface (GUI). Normal operation of startup, power maneuvering, shutdown and accidents including pipe breaks and complete loss of AC power have been conducted. A sample case of safety analysis simulation to demonstrate the inherent safety features of HTR was done for helium pipe break malfunction scenario. The analysis was done for the variation of primary coolant pipe break i.e. from 0,1% - 0,5 % and 1% - 10 % helium gas leakages, while the reactor was operated at the maximum constant power of 10 MWt. The result shows that the highest temperature of HTR fuel centerline and coolant were 1150 °C and 1296 °C respectively. With 10 kg/s of helium flow in the reactor core, the thermal power will back to the startup position after 1287 s of helium pipe break malfunction.

Dynamic simulation of relief line during loss of insulation vacuum of the ITER cryoline

The ITER cryoline (CL) system consists of 37 types of vacuum jacketed transfer lines which forms a complex structured network with a total length of about 5 km, spread inside the Tokamak building, on a dedicated plant bridge and in the Cryoplant building/area. One of them, the low pressure relief line (RL) recovers helium discharged from process safety relief valves of the different cryogenic users and is sent it back to the Cryoplant via heater and recovery system. The process pipe diameters of the RL vary from DN 50 to DN 200 and the length is more than 1500 m. Loss of insulation vacuum (LIV) of a CL is one of the worst scenarios apart from LIV in Auxiliary Cold Boxes (ACBs). The Torus and Cryostat CL is chosen to simulate the virtual LIV and to study the anticipated behavior of the RL. Both helium LIV (LIV due to leak in helium pipe) and air LIV (LIV due to air ingress in outer vacuum jacket of the cryoline) with and without fire) have been simulated during this study. After the brief description of the CL system, the paper will describe the EcosimPro® model prepared for the dynamic study. The paper will also describe the results like minimum temperature of RL, mass flow and maximum pressure in the RL which are essentially used to choose the type and location of safety relief devices to protect the CL process pipes.

Cryopump development of the 5 MW neutral beam injector system on HL-2M tokamak.

In order to carry out the long pulse and high power neutral beam injector (NBI) heating experiment on the HL-2M tokamak and satisfy its high vacuum pumping speed in the NBI, two built-in cryopumps with large area and based on a three-stage adsorption structure have been developed. The design idea and size of the three stage structure, the manufacturing technique, and the test experiment for cryopumps have been described in this paper. The experimental result shows that the cooldown time of liquid nitrogen pipes and liquid helium pipes are 1.5 h and 10 min, respectively. With activated charcoal bonded on the condensation plates, the pumping speed reaches 1.13 × 106 l/s, and the consumption of liquid helium is 2.53 g/s and 3.11 g/s for the 4-component pump and the 5-component pump, respectively. The conductance probability of the pump inlet is 0.25 for hydrogen.

Cryogenic instrumentation for ITER magnets

Accurate measurements of the helium flowrate and of the temperature of the ITER magnets is of fundamental importance to make sure that the magnets operate under well controlled and reliable conditions, and to allow suitable helium flow distribution in the magnets through the helium piping. Therefore, the temperature and flow rate measurements shall be reliable and accurate. In this paper, we present the thermometric chains as well as the venturi flow meters installed in the ITER magnets and their helium piping.The presented thermometric block design is based on the design developed by CERN for the LHC, which has been further optimized via thermal simulations carried out by CEA. The electronic part of the thermometric chain was entirely developed by the CEA and will be presented in detail: it is based on a lock-in measurement and small signal amplification, and also provides a web interface and software to an industrial PLC. This measuring device provides a reliable, accurate, electromagnetically immune, and fast (up to 100 Hz bandwidth) system for resistive temperature sensors between a few ohms to 100 kΩ.The flowmeters (venturi type) which make up part of the helium mass flow measurement chain have been completely designed, and manufacturing is on-going. The behaviour of the helium gas has been studied in detailed thanks to ANSYS CFX software in order to obtain the same differential pressure for all types of flowmeters. Measurement uncertainties have been estimated and the influence of input parameters has been studied. Mechanical calculations have been performed to guarantee the mechanical strength of the venturis required for pressure equipment operating in nuclear environment. In order to complete the helium mass flow measurement chain, different technologies of absolute and differential pressure sensors have been tested in an applied magnetic field to identify equipment compatible with the ITER environment.

Design, Test, and Validation of Thermometric Chains for ITER Magnets

The accurate measurement of the temperature of ITER magnets is of fundamental importance, to make sure that the magnets operate under well-controlled and reliable conditions, and allows suitable flow distribution in the magnets through the helium piping. Therefore, the temperature measurements shall be reliable and accurate. In this paper, we present the full thermometric chain of ITER magnets, from the sensor and its attachment, to the electronic conditioning of the signals. The thermoblock is based on a CERN design, which has been further optimized due to thermal simulations carried out by CEA. The electronic system is based on a lock-in measurement and amplification of small signals and provides a web interface and a software to monitor and record temperatures. This device allows the reliable, accurate, electromagnetically immune, and fast (100-Hz bandwidth) measurement of resistive temperature sensors between a few ohms to 100 k $\Omega$ . Measurements are also available through Profinet and Modbus TCP fieldbus for process automation. The cryogenic test bench for validation of the full thermometric chain is described, with a particular attention to the accuracy of the measurement. First results of this qualification are presented, which give good confidence in the reliability and accuracy of the thermometric system for ITER magnets.

Design guidelines for avoiding thermo-acoustic oscillations in helium piping systems

Thermo-acoustic oscillations are a commonly observed phenomenon in helium cryogenic systems, especially in tubes connecting hot and cold areas. The open ends of these tubes are connected to the lower temperature (typically at 4.5 K), and the closed ends of these tubes are connected to the high temperature (300 K). Cryogenic instrumentation installations provide ideal conditions for these oscillations to occur due to the steep temperature gradient along the tubing. These oscillations create errors in measurements as well as an undesirable heat load to the system. The work presented here develops engineering guidelines to design oscillation-free helium piping. This work also studies the effect of different piping inserts and shows how the proper geometrical combinations have to be chosen to avoid thermo-acoustic oscillations. The effect of an 80 K intercept is also studied and shows that thermo-oscillations can be dampened by placing the intercept at an appropriate location. The design of helium piping based on the present work is also verified with the experimental results available in open literature.

Experimental Study on Paschen Discharge in Helium for High Voltage Cryogenic Insulation Material

According to the requirements of large superconducting components, all the solid superconducting insulation of current leads, magnets, cooling and measurement pipeline at high potential should withstand 80–300 K thermal cycles. If helium leak or pipe leak taken place, and insulation has been formed some flaws, Paschen discharge would be occur. The experimental program aimed at analyzing the low-temperature electro-physical performance of solid superconducting insulation, which was designed with different configuration such as thickness, material structure and so on. The dielectric performance of both pre-preg cryogenic insulation and the wet wrap cryogenic insulation were studied. Both of the dielectric strength of the two type insulation is in the range from 11 to 23 kV/mm at 80 K helium condition. Besides, both of the two type insulation samples of 3 and 5 mm thickness can withstand 30 kV under various helium pressures at 80 K.

Corrosion in water supply pipe stainless steel 304 and a supply line of helium in stainless steel 316

A corrosion spreading throughout the 304 stainless steel tubing of a water system to supply various buildings was observed, and also leaks were detected in welding zones. The same place is also crossed by a gas distribution network, with a helium pipe 316 of stainless steel that required periodic repairs more or less every two years, due to the presence of leaks. The tests showed that both types of stainless steel have suffered localized corrosion induced by hypochlorite ion, in a mechanism of dry/wet, and that the welding procedure performed on the 304 stainless steel is unacceptable. Some immediate procedures were undertaken to keep systems running, but recommendations were given for a final resolution of the problems.

ICONE19-43223 DESIGN OF HIGH TEMPERATURE HELIUM PIPE FOR THE PHASE II OF HTR-10

In the phase II of HTR-10, it will focus on experimental studies of helium turbine cycle. Secondary helium pipe with temperature 750℃ and internal pressure 1.2MPa should be designed in the second design. This paper will introduce the design of high-temperature secondary helium pipe. First, the design principle for this kind pipe is presented. The performance of resistance to elevated temperature and pressure are taken into consideration separately. Then, the key parts of the high-temperature pipe, which includes pipe, bellows compensator, penetration assembly, are introduced in detail. After heat transfer and structural analysis, it is shown that the high temperature pipe could satisfy the requirements of the phase II of HTR-10.

Safety evaluation on the depressurization accident in the gas turbine high temperature reactor (GTHTR300)

Japan Atomic Energy Agency has been developing a gas turbine high temperature reactor (GTHTR300) with electric power of approximately 300 MW. One of the unique safety design concepts of this system is that events with frequency of occurrence of higher than 10 −8/reactor-year are evaluated as design basis events in order to show that the frequency of large amount of FP release is less than 10 −8/reactor-year. According to this concept, a depressurization accident by a large break of helium piping is postulated as a design basis event. This accident is one of the most serious accidents in the high-temperature gas-cooled reactors from the viewpoint of loss of coolability. The safety evaluation on the accident was conducted based on the actual design of the system. The short-term and long-term behaviors of fuel temperature after occurrence of the accident, internal pressure of the reactor building, oxidation behavior of fuels and graphite structures were evaluated and exposure dose of general public was also estimated using the results of evaluation of fuel temperature and fuel failure by oxidation. All of the evaluation results meet the safety criteria and feasibility of the GTHTR300 was shown by this study.

Behavior of a superconducting magnet, with the conductor built into plates, during quench and subsequent fast discharge

In the paper the difference between a 1D and a 3D heat conduction model is investigated during quench of a single pancake. It was found that heat conduction between adjacent turns stabilizes the reversed flow at the cable inlet. Then the 3D model is used to investigate quench in a four pancake stack of the Toroidal Field Model Coil (TFMC). The analysis covers also the Helium piping outside the coil. It is found that inter pancake heat conduction can be neglected for transients lasting only 10–20 s. Pancake to pancake quench propagation can take place in this time span via the inter pancake joints and the inlet manifold.