Compared to disruptions, the thermal effects from runaway electrons are confined to a much smaller area, but the localized damage is expected to be more severe and can cause severe melting/vaporization in virtually all materials and can lead to surface spallation. These events have been observed to cause severe damage to graphite tiles in present day tokamaks. While the beryllium in the strike region will probably be severely melted, the most critical issues for runaway electron damage and VDE are damage of coolant pipes with resulting risk of water spillage. Because of the deep

penetration and large spatial dispersion of the high — energy electrons, a thick armor may be required to avoid overheating of the coolant channels with subsequent coolant leakage. As thicker armor implies higher surface temperatures, the best solution may be local regions that are either uncooled or with thick armor that receives low heat flux during normal opera­tions. Typically a runaway electron energy deposition transient of 50MJm~2 over 0.3 s on the Be first-wall modules results in a maximum heat flux to the coolant of ~7.4MW m~ , a maximum Cu alloy temperature ^640 °C, and a Be melt layer thickness ~1.8mm.2 A reduction of the armor thickness will lead to an increase in the maximum Cu alloy temperature and could lead to the damage of joints.