Helium In Beryllium Research Articles

Retention behaviour of deuterium and helium in beryllium under single D+ and dual He+/D+ exposure

Beryllium plates were irradiated with single deuterium and dual helium plus deuterium energetic ions with fluences of 1e17ions/cm2 and 5e17ions/cm2, and annealed afterwards in vacuum at 523, 723 and 923K for 10min. The surfaces were analysed with electron microscopy, X-ray diffraction and ion beam techniques. The results are consistent with well-established outcomes arising from helium irradiation, evidencing that the degassing mechanisms depend of the microstructure evolution. They point to a supersaturation of the implanted zone by helium in the samples exposed to fluences of 5e17 He+/cm2. In this case, it is observed a simultaneous release of helium and deuterium at lower temperatures, evidencing the formation of a porous microstructure from primary gas bubbles. In the absence of a porous structure, the helium degassing occurs at a higher temperature range, while it depends on the migration of helium-vacancy clusters. The supersaturation of beryllium was never reached under single deuterium irradiation, being the release of deuterium controlled by ion-induced trap sites.

Vacancy trapping mechanism for multiple hydrogen and helium in beryllium: a first-principles study

The microscopic mechanism for H and He trapping by vacancy defects and bubble formation in a Be host lattice is investigated using first-principles calculations. A single He atom prefers to occupy a vacancy centre while H does not. He can segregate towards the vacancy from the interstitial site much more easily than H. Both H and He exhibit lower diffusion barriers from a remote interstitial to a vacancy with regard to their diffusion barriers inside a perfect Be solid. Up to five H or 12 He atoms can be accommodated into the monovacancy space, and the Be–He interaction is much weaker than Be–H. The physical origin for aggregation of multiple H or He atoms in a vacancy is further discussed. The strong tendency of H and He trapping at vacancies provides an explanation for why H and He bubbles were experimentally observed at vacancy defects in materials. We therefore argue that vacancies provide a primary nucleation site for bubbles of H and He gases inside Be materials.

Pores and cracks in highly neutron irradiated beryllium

Beryllium, irradiated in the SM and BR2 research nuclear reactors at 323–343 K up to neutron fluences of (0.4–14.4) × 10 22 cm −2 ( E > 0.1 MeV), was investigated. The dependences of beryllium swelling, brittle strength and microhardness on fast neutron fluence are presented. Three intervals can be outlined where the swelling has the various rates of increase with the growth of the neutron fluence that is connected with accumulation of radiogenic helium in beryllium and evolution of grain boundaries pores to cracks with the formation of a volume-connected network of cracks. The key points for the crack formation and propagation in beryllium under irradiation are the presence of beryllium oxide particles on boundaries and compression of the hexagonal grains along parameter “ c” owing to radiation growth. The annealing at 1123 K for 5 h results in an increase of the helium amount on grain boundaries and an evolution of the pores to gas bubbles.

Accumulation and diffusion of radiogenic helium in beryllium

Accumulation of radiogenic helium isotope 4He, its diffusion characteristics, and microstructure of beryllium have been studied after irradiation at 70 and 200°C by neutrons with an energy of E > 0.1 MeV to fluences of (1.0–13.3) × 1022 cm−2. Experimental results concerning the concentration of radiogenic helium in beryllium after irradiation and subsequent isothermal annealings for 1 h in a temperature range of 700–1200°C have been obtained. The accumulation of helium corresponds to a linear dependence up to a neutron fluence of ∼6 × 1022 cm−2 (E > 0.1 MeV); at fluences from 6 × 1022 to 13 × 1022 cm−2 (E > 0.1 MeV), a deviation from the linear dependence toward the decrease in the rate of accumulation is observed. The diffusion of radiogenic helium in beryllium at annealing temperatures of 70–200°C is low; intense diffusion and degassing of helium from beryllium start at an annealing temperature of 700°C. At annealing temperatures of 1100–1200°C, virtually all helium escapes from the irradiated beryllium.

The Sibelius experiment: Study of the irradiation behaviour of beryllium/ceramic and beryllium/steel compacts

Sibelius is an in-reactor compatibility test of beryllium and ceramics i.e, Be/Li 2O, Be/LiAlO 2, Be/Li 4SiO 4, Be/Li 2ZrO 3, and beryllium and steels i.e., Be/316L, Be/1.4914 (martensitic steel) conducted in the core of the Siloe reactor at Grenoble. The experiment is run for four cycles ( ~ 80 days) at a temperature of 550°C. Effect of neutron irradiation on compatibility is identified by comparison with out-of-reactor tests carried out in identical conditions. By monitoring the tritium release characteristics from the compatibility specimens and comparing with check samples containing only ceramics, one can quickly obtain information on certain reactions. Extensive post-irradiation examination will be performed in the USA, CEA and KFK laboratories to evaluate: 1. (1) corrosion at the beryllium/ceramic interface; 2. (2) corrosion at the beryllium/steel interface; 3. (3) retention of tritium and helium in ceramics; 4. (4) retention of tritium and helium in beryllium; and 5. (5) swelling of beryllium.