Improvements relating to neutron-absorbing bodies for use in nuclear reactors

A solid neutron-absorbing body is made by powder-metallurgical methods and comprises a discrete phase dispersed in a matrix, the discrete phase being composed of particles of a neutron-absorbing element (in elemental or combined form) that are large enough to be retained on a 200 mesh B.S.S. screen, but preferably should pass through a 60 mesh screen, and both the matrix and the discrete phase being stable up to 900 DEG C. The matrix may be of copper and the discrete phase boron carbide, titanium boride or zirconium boride, or the matrix may be nickel or iron and the discrete phase gadolinium oxide or europium oxide. In one example 15% by weight of boron carbide powder is mixed with electrolytic copper powder, compacted, sintered for half an hour at 900 DEG C. in a hydrogen atmosphere, and reduced in thickness by 50% by cold rolling. The body may be provided with a covering or stainless steel or other corrosion-resistant alloy and used as a control rod for a nuclear reactor or as a shield for auxiliary equipment associated with a reactor.