Boron Carbide as High-Energy Radiation Shielding Material for ITER

Abstract

Boron carbide (B4C) has emerged as a potential material, which can be used for high-energy radiation shielding in International Thermonuclear Experimental Reactor (ITER). This is one of the hardest ceramic materials with required properties, such as low density, high hardness, high toughness, high melting point, chemical inertness, outstanding thermal–electrical characteristics, and most importantly having a high cross section for the absorption of neutrons. Recently, ITER-India, Institute for Plasma Research (IPR) initiated prototype activities for the development of hot-pressed B4C blocks/pellets. ITER-India with support from an Indian Industry has demonstrated the manufacturing capability for large-scale, vacuum-hot-pressed blocks with machining feasibility for the final product (shielding block). Development activities have been carried out as per ASTM C750 (Nuclear Grade B4C Powder), ASTM C751 (Nuclear Grade B4C blocks/pellets), and other stringent requirements of ITER. The B4C blocks/pellets have been fabricated in a vacuum at the high-temperature range of 2050 °C–2100 °C and high pressure of ~30 MPa. To qualify this material as per ITER requirements, its chemical composition, mechanical, and physical properties are studied and validated. Scanning electron microscopy (SEM) studies were conducted to calculate the grain size in the microstructure. As this material is to be used in an ultrahigh vacuum (UHV) environment in ITER ports and systems, the outgassing rate of B4C is also determined. We ascertained outgassing rate <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\le1\,\,\times \,\,10^{-8}$ </tex-math></inline-formula> Pam <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{3}\text{s}^{-1}\text{m}^{-2}$ </tex-math></inline-formula> at 100 °C of B4C as per the ITER vacuum handbook (IVH) as well as ITER-derived requirements for ports. The main reason to achieve this outgassing rate is the process of fabrication used as it does not include any sintering aids and additives; hence, it is a unique hot-pressing technique, which is better suited for nuclear applications. This article describes the details of the study related to B4C blocks/pellets development and toward the qualification as per shielding material requirements for ITER.