A high temperature W2B–W composite for fusion reactor shielding

Abstract

We have developed a new material for neutron shielding applications where space is restricted. W 2 B is an excellent attenuator of neutrons and gamma-rays, due to the combined gamma attenuation of W and neutron absorption of B. However, its low fracture toughness (∼3.5 MPa) and high melting point (2670 • C) prevent the fabrication of large fully-dense monolithic parts with adequate mechanical properties. Here we meet these challenges by combining W 2 B with a minor fraction (43 vol.%) of metallic W. The material was produced by reaction sintering W and BN powders. The mechanical properties under flexural and compressive loading were determined up to 1900 • C. The presence of the ductile metallic W phase enabled a peak flexural strength of ∼950 MPa at 1100 • C, which is a factor of 2-3 higher than typical monolithic transition-metal borides. Its ductile-brittle transition temperature of ∼1000 • C is typical of W-based composites, which is surprising as the W phase was the minor constituent and did not appear to form a fully continuous network. Compression tests showed hardening below ∼1500 • C and significant elongation of the phase domains, which suggest that by forging or rolling, further improvements in ductility may be possible.

Tungsten boride shields in a spherical tokamak fusion power plant

“…Theoretical densities are taken from reference [10]. The densities are at 98% of the theoretical values, based on data on W 2 B-based materials in reference [11], which included 2% porosity. The last column gives densities measured by x-rays for this paper [16], multiplied by 0.98. neutron energy is therefore appreciably reduced but there will be a new gamma flux leading to its own transmitted energy and needing extra gamma shielding.…”

“…It has been shown that the inclusion of boron within a tungstenbased shield is advantageous, with its high neutron absorption cross section at lower energies [4]. Various practical efforts to fabricate and test the properties of such materials have begun [10][11][12][13] but the search is on to find the optimal boroncontaining material, and optimal parameters for a tokamak shield of specified lifetime.…”

“…For tungsten the total (black), elastic (green, dashed), inelastic (red, dash-dot), (n, 2n) (blue, dotted) and (n, γ) (yellow) cross sections are shown. For boron the minority (20%)10 B isotope (black) and the majority11 B isotope cross section (blue dashed) are shown. Below 10 keV the 10 B cross section follows an inverse velocity increase with decreasing neutron energy as show in the curve labelled 10 B abs .…”

Materials challenges for successful roll-out of commercial fusion reactors

“…This includes the use of Li-containing components, such as Li 2 TiO 3 [9], and neutron-multiplying materials containing isotopes of Be and Pb [10]. Efficient thermal neutron absorber materials based upon borides (for example, tungsten borides [11]), are being considered alongside other high-neutron cross-section materials and gamma shielding materials with high Z values.…”

Magnezyotermik indirgeme ile sentezlenen Lantanyum hekzaborür (LaB6) ve Seryum hekzaborür (CeB6) malzemelerinin gama zırhlama özelliklerinin Monte Carlo simülasyonu

“…[22] B2O3-Pb3O4-ZnO camlarının nükleer zırhlama özelliklerini, Athanasakis vd. [23] Füzyon reaktör zırhlama malzemesi olarak yüksek sıcaklıklı W2BeW kompozitin özelliklerini çalışmışlardır. Song vd.…”