Helium construction materials

Probably the biggest problem with helium leak detector use comes from the construction material of the vacuum system or apparatus being tested. If the materials within the tested piece readily absorb helium, a false and/or confusing reading will exist for a considerable time afterward and will remain until the helium has left the piece. 

Production rates of total hydrogen and total helium are important parameters in the evolution of the microstructure during the irradiation of solids, especially for fission and fusion reactor construction materials. These data can be measured by using a vacuum furnace equipment connected to a mass spectrometer for the detection of H and He gases produced in an irradiated bulk sample. 

The liquid hydrogen was contained in the flight-type tank shown in Fig. 1. The tank was about 23 ft long and 30 in. in diameter and had a capacity of about 450 gal. The construction material, type 302 stainless steel, was covered with a 2-in.-thick Styrofoam insulation. Resin-impregnated Fiberglas was placed on the outer shell. A positive helium gas pressure was used in the insulation space to prevent condensation of air around the outside of the tank. 

The integration of the optics within the stress rheometer allows the simultaneous acquisition of optical and mechanical properties of the sample, which can be important for determining the relationship between a material s microstructure and its rheological response. The particular rheometer used here has an open construction that easily accommodates the insertion of an optical train for the purpose of birefringence and dichroism measurements. The optical train consisted of a helium-neon light source with a (P/RII)/)(,G... 

Such are the goals that justify the construction of a machine as expensive and as complex as the SSC. But a key question continues to nag the people who would build the supercollider and the physicists who would use it would it not be better to wait until the high-temperature superconductivity materials are perfected and use them instead of the older liquid-helium-cooled windings for the magnets ... 

Relative Construction Time. It is the consensus that a plant like this could be built in from two to three months less time than the lower powered helium cooled plants now under consideration, would involve less vital material and would require only a fraction of the total external power for the same power output. 

Gaseous helium is noncorrosive and inert, and may consequently be contained in systems constructed of any common metals and designed to safely withstand the pressures involved. At the temperature of liquid helium, ordinary carbon steels and most alloy steels lose their ductility and are considered unsafe for liquid helium service. Satisfactory materials for use with liquid helium include Type... 

Markova et al. (1967) constructed a phase diagram for the dysprosium-yttrium system utilizing thermal analyses, X-ray diffraction, metallography, hardness and electrical resistance measurements. Their starting materials were distilled yttrium and dysprosium of 99.6 to 99.7(wt )% purity. Both metals contained gaseous impurities as well as the metals Ca, Fe, Cu, Y, Gd, Dy and Ta. Alloys were prepared at approximately 10 at% intervals, arc-melted under purified helium and annealed at 850°C for 70 hr. The structure of all specimens was single phase with the hep lattice. A continuous series of solid solutions between isomorphic modifications was observed. 

The primary gas envelope can also be considered a barrier against radionuclide release. However, for the short-lived fission gases, the dominant removal mechanism is radioactive decay. For the condensable fission products, the dominant removal mechanism is deposition or plate-out on the various helium wetted surfaces in the primary circuit. The primary pressure boundary, consisting of conventional steel pressure vessels, is designed to ASME Section HI. Through-wall cracks are considered unlikely. The chemically inert helium coolant minimizes corrosion and eliminates the complications associated with internal cladding, and only materials for which extensive data exist are to be used in the construction of the vessels. 

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