Reaction rates were determined for fully dense and porous 88% dense beryllium in steam between 600 and 1230-degrees-C. These materials could represent high or low quality plasma-sprayed beryllium on plasma-facing components (PFCs) in a fusion reactor. Reaction rates for the porous material were 200 times higher than those for solid material at comparable temperatures. The porous material also developed self-sustaining reactions at temperatures as low as 600-degrees-C. First wall temperatures calculated for the international thermonuclear experimental reactor (ITER) during a worst-case loss of coolant accident (LOCA) indicate that 2 mm thick layers of either dense or porous beryllium would completely react. The generation of over 640 kg of hydrogen and aerosols containing 68 kg of beryllium presents serious safety concerns. The poor thermal stability of porous beryllium, which could also represent blanket material, suggests that a more stable form or compound of beryllium should be used for these applications.