Helium Level Research Articles

Geochemical characteristics of He and CO2 from the Ordos (cratonic) and Bohaibay (rift) basins in China

According to the compositional and isotopic analyses of He, CO2 and CH4 of 95 gas samples from the Ordos Basin and 76 gas samples from the Bohaibay Basin in China, this study carried out a detailed investigation on the geochemical characteristics of helium and CO2 from the cratonic and rift basins, especially the cratonic Ordos Basin and rift Bohaibai Basin in China. Compared to the rift Bohaibay Basin, the cratonic Ordos Basin has lower level of helium and CO2, lower R/Ra ratio and lower δ13CCO2 maximum value. When the content of CO2 is <10%, both cratonic and rift basins have organic CO2 associated with the hydrocarbon generation process and inorganic CO2 from the thermal decomposition of carbonates or dissolution of organic acid. Rift basin can also have CO2>20% and δ13CCO2 of −6±2‰ or −4‰–−9‰, which is of volcanic-magmatic or mantle-derived origin, while cratonic basin has no such type of CO2. The cratonic basins (Ordos, Sichuan) have CO2<5% and relatively smaller variation range of δ13CCO2, i.e., 25.6‰ (−0.8‰–−26.4‰). The rift basins have higher level of CO2, R/Ra ratios and δ13CCO2 values. The content of CO2 can reach 100%, the R/Ra ratio can be up to 6.45 and the variation range of δ13CCO2 is 34‰ (7‰–−27‰). Bigger variation range of δ13CCO2 implies stronger tectonic activities, which is not favorable for the gas accumulation. While smaller variation range means more stable structure, which is favorable for the discovery of large gas fields. Sample in the cratonic basin in China generally has CH4/3He of 109–1012 and R/Ra<0.1 and in the rift basin it has CH4/3He of 105–1013 and R/Ra of 0.1–6.45. It is concluded that methane with CH4/3He≤108 is of inorganic origin and methane with CH4/3He≥1011 is of organic origin. The regression equation for the CH4/3He-R/Ra in the cratonic basin is: y=3E+11e−46.28x and it is: y=4E+10e−1.791x in the rift basin. Both Ordos and Bohaibay basins found gas wells with He>0.05%, which has significant commercial values and provides a clue for the exploration of helium-rich gas fields. Traps with R/Ra>2 is a favorable clue for the discovery of CO2 gas fields. Seven CO2 gas fields have been found in the Bohaibay Basin, but no systematic development has been carried out and only some liquid CO2 has been injected for tight oil from the Huagou CO2 gas field.

Chlorine Stable Isotope and Helium Isotope Studies Contributing to the Understanding of the Hydrogeochemical Characteristics of Old Groundwater

Chlorine stable isotope and helium isotope data were integrated in order to study the chemical and isotopic characteristics of old groundwater in the Pannonian Basin. Former studies showed groundwater is of meteoric origin, based on oxygen and deuterium isotopes, which have isotopic signatures of formation waters from the deeper part of the basin. Depletion of the heavier 37Cl isotope can be observed along the flow paths. Despite the fact that most of the sampled groundwater contains high helium levels, indicating a crustal helium origin, their 3He content is also high. The 3He/4He ratios (expressed in R/Rac) with values between 0.4 and 1.2 shows that helium of mantle origin must also be a component in the groundwater along the flow paths. The presence of mantle origin helium could be detected not just in the deeper part of the basin, but even in the Quaternary sediments.

Design, Development & Functional Validation of Magnets system in support of 42 GHz Gyrotron in India

A multi institutional initiative is underway towards the development of 42 GHz, 200 kW gyrotron system in India under the frame work of Department of Science and Technology, Government of India. Indigenous realization comprising of design, fabrication, prototypes and functional validations of an appropriate Magnet System is one of the primary technological objective of these initiatives. The 42 GHz gyrotron magnet system comprises of a warm gun magnet, a NbTi/Cu based high homogenous superconducting cavity magnet and three warm collector magnets. The superconducting cavity magnet has been housed inside a low loss cryostat. The magnet system has been designed in accordance with gyrotron physics and engineering considerations respecting highly homogenous spatial field profile as well as maintaining steep gradient as per the compression and velocity ratios between the emission and resonator regions. The designed magnet system further ensures the co-linearity of the magnetic axis with that of the beam axis with custom winding techniques apart from a smooth collection of beam with the collector magnet profiles. The designed magnets have been wound after several R & D validations. The superconducting magnet has been housed inside a low loss designed cryostat with in-built radial and axial alignment flexibilities to certain extent. The cryostat further houses liquid helium port, liquid nitrogen ports, current communication ports, ports for monitoring helium level and other instrumentations apart from over-pressure safety intensive burst disks etc. The entire magnet system comprising of warm and superconducting magnets has been installed and integrated in the Gyrotron test set-up. The magnet system has been aligned in both warm and when the superconducting cavity magnet is cold. The integrated geometric axes have been experimentally ensured as well as the field profiles have been measured with the magnets being charged. Under experimental conditions, all magnets including the superconducting magnet have been charged to their nominal values with appropriate protection measures against the quench. This is the first time in India that a gyrotron specific magnet system with superconducting magnet has been realized.

An experimental study of helium diffusion and helium induced microstructural evolution in ion implanted polycrystalline titanium nitride

In this paper, the behavior of helium and its influence on the microstructure in polycrystalline titanium nitride (TiN) is studied by ion implantation technique, coupled with post-implantation annealing experiments between 1273 and 1873 K. The samples were implanted at room temperature with helium up to ∼2.2, 0.25 and 0.07 at. % at the implantation peak, respectively. Helium induced bubble microstructure was characterized using transmission electron microscopy (TEM) which revealed the effect of annealing temperature and helium concentration on the evolution of the bubbles in the material. TEM analysis also revealed that no amorphisation occurred up to the maximum dose level of 0.8 dpa at room temperature, corresponding to the highest implantation level. The technique of nuclear depth profiling using nuclear reaction analysis (NRA) revealed the helium diffusion and retention behavior in the material at different annealing temperatures and helium concentration levels. A sharp increase in helium loss from TiN occurred after annealing beyond 1373 K for the highest helium level, whereas no loss occurred for the lowest implanted helium level. The effective activation energies of helium diffusion and release were estimated utilizing Fick's law of diffusion and 1st order kinetic law, respectively. A novel method of estimating pressure inside bubbles is discussed by utilizing the high-density equation of state, incorporating the experimentally determined helium density, deduced from coupling the result of helium concentration measurement from NRA and vacancy concentration measurement from the experimentally determined size and number density of bubbles from TEM. These results reveal that such kind of calculation technique can be utilized for bubbles formed at higher annealing temperatures.

Progress in the Development and Construction of a 32-T Superconducting Magnet

The 32-T superconducting magnet is envisioned as a 15-T low-temperature superconductor (LTS) magnet combined with a separately powered REBCO high-temperature superconductor (HTS) insert configured as two coil stacks generating 17 T. Progress was made in all aspects of this project and is reported in this work. The design concept, which has been quite stable, is presented, as well as key elements from recent developments such as increased voltage standoff requirements. In both factory testing and installation at the NHMFL, the 15-T/250-mm-bore outer magnet built by Oxford Instruments met all specifications, including a ramp time of 1 h to full field. The test protocol included a deliberately induced full-field quench, releasing 7 MJ. After the helium level recovered, the magnet was ramped again in 1 h to full field, demonstrating full recovery. Helium boiloffs during normal operation and quench were observed, as well as the current and field decay during quench. The latter information serves as one of many inputs for the numerical quench code developed specifically to model quench in coupled LTS-HTS coils. Results from the 32-T quench analysis and implications for quench protection are summarized. All HTS conductor lengths were subjected to an extensive quality assurance (QA) protocol, and SuperPower has now delivered all required conductor lengths within specifications. A summary of the QA data and its implications are presented. The prototype coils, which are very similar in design to the 32-T REBCO coils but of reduced height, have now been impregnated with paraffin to address winding motion observed in previous testing. The prototype test protocol includes a study of the effectiveness of the quench heaters in the HTS coils in both a constant background field as provided by the actual 15-T LTS outer magnet for 32 T and, uniquely, in case the outer magnet is deliberately quenched.

The crystal structure, orientation relationships and interfaces of the nanoscale oxides in nanostructured ferritic alloys

The capability of nanostructured ferritic alloys (NFAs) to manage high levels of transmutation product helium will help resolve one of the grand challenges to transforming the promise of C-free fusion energy into a reality. NFAs are dispersion strengthened by an ultrahigh density of Y-Ti-O nano-oxides (NOs), which result in both high strength and temperature limits, as well as unique irradiation tolerance. Here, aberration-corrected high-resolution transmission electron microscopy was used to characterize the NOs in four NFA conditions, including following severe deformation and extreme neutron radiation exposure. Fast Fourier Transform analysis of focal series images revealed the NO crystal structure, including the smallest at < 2 nm in diameter, to be Y2Ti2O7 pyrochlore in all cases, consistent with both exit wave analysis and scanning transmission Z-contrast imaging of the atomic columns in a larger feature. The faceted NOs exhibit a quasi-epitaxial orientation relationship with the ferrite matrix: [110]YTO||[100]Fe and [001]YTO||[010]Fe, forming a 5 × 7 near coincidence site interface. The NOs also exhibit size-dependent strains in both the oxide and matrix ferrite phases.

The Unreasonable Accuracy of Moore's Law [Historical

In 1960, three years before receiving the Nobel Prize in Physics, Hungarian-born American theoretical physicist and mathematician Eugene Wigner (1902?1995) published a paper, ?The Unreasonable Effectiveness of Mathematics in the Natural Sciences.? In it, he argued about the surprising precision with which mathematical equations can describe physical phenomena [1]. He considered Newton?s second law, which states that the gravitational force acting on a falling body is proportional to its mass and no other parameter of that body. Newton brought this law into relation with the motion of the moon, noting that the parabola of a thrown rock and the circle of the moon's path in the sky are particular cases of the same mathematical object, the ellipse, deducing the universal law of gravitation. Initially, this law was supported by a single and rough coincidence with an accuracy of a mere 4%, but subsequent observations proved that it held to an accuracy of 0.001%. Wigner also examined other laws, such as quantum mechanics that, when formulated in the form of matrix mechanics to calculate the lowest energy level of helium, matched experiments to a relative error of 10?7.

Experimental and numerical study of light gas dispersion in a ventilated room

The objective of this study is to validate the ANSYS CFX version 12 computational code on the basis of light gas dispersion tests performed in two ventilated rooms. It follows an initial study on heavy gas dispersion carried out by Ricciardi et al. (2008). First, a study of sensitivity to various numerical parameters allows a set of reference data to be developed and the influence of the numerical scheme of advection to be revealed. Second, two helium (simulating hydrogen) dispersion test grids are simulated for the two rooms studied, and the results of the calculations are compared with experimental results. The very good agreement between these results allows the code and its dataset to be validated for this application.In future, a study with higher levels of helium (on the order of 4% vol at equilibrium) is envisaged in the context of safety analyses related to the hydrogen risk, these levels representing the lower explosive limit (LEL) of hydrogen.

Use of double and triple-ion irradiation to study the influence of high levels of helium and hydrogen on void swelling of 8–12% Cr ferritic-martensitic steels

In accelerator-driven spallation (ADS) devices, some of the structural materials will be exposed to intense fluxes of very high energy protons and neutrons, producing not only displacement damage, but very high levels of helium and hydrogen. Unlike fission flux-spectra where most helium and hydrogen are generated by transmutation in nickel and only secondarily in iron or chromium, gas production in ADS flux-spectra are rather insensitive to alloy composition, such that Fe–Cr base ferritic alloys also generate very large gas levels. While ferritic alloys are known to swell less than austenitic alloys in fission spectra, there is a concern that high gas levels in fusion and especially ADS facilities may strongly accelerate void swelling in ferritic alloys. In this study of void swelling in response to helium and hydrogen generation, irradiation was conducted on three ferritic-martensitic steels using the Electrostatic Accelerator with External Injector (ESUVI) facility that can easily produce any combination of helium to dpa and/or hydrogen to dpa ratios. Irradiation was conducted under single, dual and triple beam modes using 1.8 MeV Cr+3, 40 keV He+, and 20 keV H+. In the first part of this study we investigated the response of dual-phase EP-450 to variations in He/dpa and H/dpa ratio, focusing first on dual ion studies and then triple ion studies, showing that there is a diminishing influence on swelling with increasing total gas content. In the second part we investigated the relative response of three alloys spanning a range of starting microstructure and composition. In addition to observing various synergisms between He and H, the most important conclusion was that the tempered martensite phase, known to lag behind the ferrite phase in swelling in the absence of gases, loses much of its resistance to void nucleation when irradiated at large gas/dpa levels.

The Effect of Quantum-Mechanical Interference on Precise Measurements of the n = 2 Triplet P Fine Structure of Helium

For many decades, improvements in both theory and experiment of the fine structure of the n = 2 triplet P levels of helium have allowed for an increasingly precise determination of the fine-structure constant. Recently, it has been observed that quantum-mechanical interference between neighboring resonances can cause significant shifts, even if such neighboring resonances are separated by thousands of natural widths. The shifts depend in detail on the experimental method used for the measurement, as well as the specific experimental parameters employed. Here, we review how these shifts apply for the most precise measurements of the helium 23P fine-structure intervals.

Hydrogen Permeation through Dense BaCe0.8Y0.2O3-δ - Ce0.8Y0.2O2-δ Composite-Ceramic Membranes

This report presents hydrogen permeation measurements through dense composite-ceramic membranes. The high-temperature operation of ceramic hydrogen-separation membranes makes them suitable in many hydrogen-production applications, such as catalytic partial oxidation of methane (CPOX), steam reforming of methane, the gasification of carbonaceous materials, and methane dehydroaromatization (MDA). Hydrogen permeation is measured through BaCe0.8Y0.2O3-δ–Ce0.8Y0.2O2-δ (BCY-YDC) membranes fabricated by solid-state reactive sintering with 1 wt.-% NiO and standard ceramic-processing methods. Hydrogen gas is incorporated into the membrane as protonic defects; proton transport must be compensated by electron transport in order for protons to re-associate into hydrogen gas on the opposite side of the membrane. BCY serves as the proton conductor, and YDC serves as the electronic conductor. For hydrogen-permeation testing, the composite-ceramic membranes are hermetically sealed inside of a ceramic manifolding assembly utilizing a spring-compression system with vermiculite seals. Hydrogen and helium (for leak detection) are fed to the permeant (feed) side of the membrane using high-precision mass flow controllers, while argon is fed to the permeate (sweep) side of the membrane. All gases are humidified using a room-temperature bubbler, which results in ~3 mol.-% steam. The permeate gas composition is continuously measured using a gas chromatograph calibrated for low levels of hydrogen, helium, nitrogen, and oxygen (balance argon). The hydrogen-permeation rate is quantified through the hydrogen mole fraction measured in the permeate exhaust. Hydrogen permeation rates are measured as a function of temperature and the hydrogen partial-pressure gradient. The permeation rate is found to increase exponentially with increasing temperature, and linearly with an increasing hydrogen partial-pressure gradient. The hydrogen permeation rate through a BCY-YDC membrane over several days is shown in Figure 1. No degradation in performance is observed at 900 °C and a 0.1 atm hydrogen partial-pressure gradient. However, when the gradient is increased to 0.5 atm, the permeation rate is found to decrease over time. Following testing, grain-boundary fractures and metallic nano-particles are observed in scanning electron micrographs of the membrane. This, in addition to performance degradation, may indicate that the materials are not stable in highly reducing environments. However, X-ray diffraction patterns of the membrane after testing do not reveal the formation of tertiary phases. Figure 1: Hydrogen permeation through a BCY-YDC membrane at 900 °C with a 0.1 and a 0.5 atm hydrogen partial-pressure gradient. Figure 1

Effect of pre-implanted helium on void swelling evolution in self-ion irradiated HT9

Void evolution in Fe++-irradiated ferritic-martensitic alloy HT9 was characterized in the temperature range of 400–480°C between doses of 25 and 375 displacements per atom (dpa) with pre-implanted helium levels of 0–100appm. A systematic study using depth profiling in cross-section samples was conducted to determine a valid region of analysis between 300 and 700nm from the surface, which excluded effects due to the injected interstitial and the surface. Pre-implanted helium was found to promote void swelling at low doses by shortening the nucleation regime and to retard void growth at doses in the transient regime by enhancement of nucleation of small voids. Swelling was found to peak at a temperature of 460°C. The primary effect of temperature was on the nucleation regime; nucleation regime was the shortest at 460°C compared to that at 440 and 480°C. The growth rate of voids was temperature-invariant. Steady state swelling was reached at 460°C between 188 and 375dpa at a rate of 0.02%/dpa.

Characterizing the recovery of a solid surface after tungsten nano-tendril formation

Recovery of a flat tungsten surface from a nano-tendril surface is attempted through three techniques; a mechanical wipe, a 1673K annealing, and laser-induced thermal transients. Results were determined through SEM imaging and elastic recoil detection to assess the helium content in the surface. The mechanical wipe leaves a ∼0.5μm deep layer of nano-tendrils on the surface post-wipe regardless of the initial nano-tendril layer depth. Laser-induced thermal transients only significantly impact the surface morphology at heat loads of 35.2MJ/m2s1/2 or above, however a fully flat or recovered surface was not achieved for 100 transients at this heat load despite reducing the helium content by a factor of ∼7. A 1673K annealing removes all detectable levels of helium but sub-surface voids/bubbles remain intact. The surface is recovered to a nearly flat state with only some remnants of nano-tendrils re-integrating into the surface remaining.

Fast Sensitive Ultra-Low Power Micro Thermal Conductivity Gas Sensor

A miniature, ultra-low power, sensitive, microbridge-based thermal conductivity gas sensor has been developed. The batch fabrication of the sensors was realized by CMOS compatible processes and surface micromachining techniques. Doped polysilicon was used as the structural material of the suspended sensing element with critical dimension of 500 nm. To understand the design of the sensors, a model of the suspended element was simulated in COMSOL that couples electrical and thermal physics together and includes minimal simplifications. Modeling results coincide with experimental data in predicting resistance changes. The sensor was tested with nitrogen, carbon dioxide, helium and methane.An electronic circuit was developed to measure very fine changes in the signal output and to keep the signal to noise ratio such that ppm detection is possible, while exciting the sensor at minimal power levels. The sensor was able to detect ppm levels of helium, methane, or carbon dioxide in nitrogen at room temperature. The sensor can make a measurement in less than 2 ms consuming only 5 nJ or power per reading.The transient as well as steady state response was investigated as potential indicator of gas thermal capacity; as thermal conductivity and thermal capacity are independent properties of a gas, this new approach may enable MicroTCD sensors to make detections in gas mixtures by thermal analysis [1].[1]U.S. Patent 8,426,932 B2, April 23, 2013, Apparatus and Method for Microfabricated Multidimensional Sensors and Sensing Systems, Joseph R. Stetter.

Bohr’s molecular model and the melding of classical and quantum mechanics

Anatoly Svidzinsky, Marlan Scully, and Dudley Herschbach have illustrated well how the molecular theory might have looked had quantum mechanics not been invented. It’s worth noting that Niels Bohr was not alone in his attempts to extend semiclassical mechanics to systems more complex than the hydrogen atom. From 1913 to 1925, many semiclassical models of two-electron systems were proposed.As we see from the authors’ figure 3a, Bohr assumed that electrons in hydrogen molecules move around the molecular axis out of phase. It is a remarkable fact that Werner Heisenberg put forward in 1922 a two-electron atomic model that had electrons moving similarly out of phase and that ascribed a fractional quantum number (½) to the bending mode of the configuration.11. G. Tanner, K. Richter, J.-M. Rost, Rev. Mod. Phys. 72, 497 (2000). https://doi.org/10.1103/RevModPhys.72.497 Although Heisenberg’s model predicted the ground-state helium level, which was in excellent agreement with the spectroscopic data, Bohr opposed the model, since a noninteger quantum number was considered sacrilege. For the same reason, Bohr never published his own results. However, the asynchronous two-electron atomic model turned out to be the fertile one, though the corresponding classical configurations can have very complex structure.22. P. Grujic, N. Simonovic, J. Phys. B 28, 1159 (1995). https://doi.org/10.1088/0953-4075/28/7/011REFERENCESSection:ChooseTop of pageREFERENCES <<1. G. Tanner, K. Richter, J.-M. Rost, Rev. Mod. Phys. 72, 497 (2000). https://doi.org/10.1103/RevModPhys.72.497, Google ScholarCrossref, ISI2. P. Grujic, N. Simonovic, J. Phys. B 28, 1159 (1995). https://doi.org/10.1088/0953-4075/28/7/011, Google ScholarCrossref, ISI© 2014 American Institute of Physics.

Programmable System-on-Chip (PSoC) Embedded Readout Designs for Liquid Helium Level Sensors

This article reports the development of programmable system-on-chip (PSoC)-based embedded readout designs for liquid helium level sensors using resistive liquid vapor discriminators. The system has been built for the measurement of liquid helium level in a concave-bottomed, helmet-shaped, fiber-reinforced plastic cryostat for magnetoencephalography. This design incorporates three carbon resistors as cost-effective sensors, which are mounted at desired heights inside the cryostat and were used to infer the liquid helium level by measuring their temperature-dependent resistance. Localized electrical heating of the carbon resistors was used to discriminate whether the resistor is immersed in liquid helium or its vapor by exploiting the difference in the heat transfer rates in the two environments. This report describes a single PSoC chip for the design and development of a constant current source to drive the three carbon resistors, a multiplexer to route the sensor outputs to the analog-to-digital converter (ADC), a buffer to avoid loading of the sensors, an ADC for digitizing the data, and a display using liquid crystal display cum light-emitting diode modules. The level sensor readout designed with a single PSoC chip enables cost-effective and reliable measurement system design.

Demonstration of Transfer of Liquid Helium Using a Pump System with MgB2 Wires

An electric pump composed of an MgB2 motor is combined with a superconducting level sensor using a thin CuNi-sheathed MgB2 wire to demonstrate the transfer of liquid helium. An impeller is attached to the lower end of a rotating shaft of the MgB2 motor and covered with an outer casing to form a kind of centrifugal pump. After that, the MgB2 motor with the impeller is located vertically inside a cryostat with an infill of the liquid helium. Another glass Dewar vessel is also prepared to receive the liquid helium transferred from the cryostat containing the MgB2 motor. The MgB2 sensor is used not only to detect the level of the liquid helium but also to control the electric pump on the basis of its pre-estimated calibration curve. By using the assembled pump system, the liquid helium is successfully transferred from the cryostat to the glass Dewar vessel via a transfer tube. The transfers of liquid hydrogen with the identical pump system will be carried out in the near future.

Molecular dynamics simulation of cascade-induced ballistic helium resolutioning from bubbles in iron

Molecular dynamics simulations have been used to assess the ability of atomic displacement cascades to eject helium from small bubbles in iron. This study of the ballistic resolutioning mechanism employed a recently-developed Fe–He interatomic potential in concert with an iron potential developed by Ackland and co-workers. The primary variables examined were: irradiation temperature (100 and 600K), cascade energy (5 and 20keV), bubble radius (0.5 and 1.0nm), and He-to-vacancy ratio in the bubble (0.25, 0.5 and 1.0). Systematic trends were observed for each of these variables. For example, ballistic resolutioning leads to a greater number of helium atoms being displaced from larger bubbles and from bubbles that have a higher He/vacancy ratio (bubble pressure). He resolutioning was reduced at 600K relative to 100K, and for 20keV cascades relative to 5keV cascades. Overall, the results indicate a modest level of He removal by ballistic resolutioning. The results may be particularly relevant to fusion irradiation conditions which produces high levels of helium by transmutation. They can be used to provide initial guidance in selection of a “resolution parameter” that can be employed in kinetic models to predict the bubble size distribution that evolves under irradiation.

Liquid nitrogen level meter for high-temperature superconductor (HTS)

Many kinds of high temperature superconductor (HTS) power machines such as HTS cable, HTS fault current limiter and HTS magnet are cooled by liquid nitrogen. The level of liquid nitrogen should be monitored and controlled to ensure the thermal stability and the dielectric strength as well. To measure the level, capacitance method and differential pressure method are usually used. However, each method has installation difficulties and measurement errors for unsteady state operation with varying system pressure. A new liquid level meter using a 2G HTS conductor is described, which has similar structure with the liquid helium level meter with NbTi filament. The level meter is fabricated with a parallel connected heater, which helps the separation of the superconducting region and normal region, considering the critical temperature, large heat capacity of conductor and cooling characteristics. The level of liquid nitrogen can be obtained from the measured voltage signal along the 2G HTS conductor. Design, fabrication and test results of the new liquid nitrogen level meter are presented.

On-line monitoring of control rod integrity in BWRs using a mass spectrometer

Surveillance of fuel and control rod integrity in the core of a boiling water reactor is essential for maintaining a safe and reliable operation. Control rods of a boiling water reactor are mainly filled with boron carbide as a neutron absorber. Due to the irradiation of boron with neutrons, a continuous production of lithium and helium will occur inside a control rod. Most of the created helium will be retained in the boron carbide lattice; however a small part will escape into the void volume of the control blade. Therefore the integrity of control rods during operation can efficiently be followed by on-line measurements of helium concentration in the reactor off-gas system using a mass spectrometer. Since helium is a fill gas in fuel rods, the same method is a useful early warning system for primary fuel failures. In this paper, we introduce an on-line helium detector system which is installed at the nuclear power plant in Leibstadt. Furthermore the measuring experiences of control rod failure detection at the plant are presented. Different causes of increased helium levels in the off-gas system have been distinguished. There are spontaneous helium releases as well as helium releases caused by changed conditions in the reactor (power reduction, control rod movement, etc.). Helium peaks can also be characterized according to the released amount of helium, the peak shape and the duration of the release, which leads to different interpretations of the release mechanisms. In addition, the measured amount of released helium from a 50 days period (280l) is also compared to the calculated amount of produced helium from the washed out boron during the same time period (190l).