The physical properties of beryllium are summarized in Table 2, which is taken from ITER MPH.128 These properties have been used for design and performance assessments. In addition to its low atomic number, beryllium has several excellent ther­mal properties that make it well-suited for heat removal components. The thermal conductivity is comparable with that of graphite or CFC at low and high temperatures but, in contrast to C-based mate­rials, is not significantly degraded as a result of neutron-irradiation. The specific heat of beryllium exceeds that of C-based materials typically by a factor of 2 over the temperature range of interest for operation. However, Be has poor refractory

properties, such as low melting temperature and high vapor pressure. The high heat capacity and good thermal conductivity of Be can be used to maintain low surface temperatures in PFCs during normal operation, but its low melting temperature and high vapor pressure cause great design difficul­ties from the standpoint of survivability from off — normal events such as vertical displacement event (VDE), ELMs, disruptions, and runaway electron impact (see Section 4.19.6.2).

For the beryllium hexagonal close packed crystal structure, the main physical properties, such as the coefficient of thermal expansion, elastic modulus etc. have some anisotropy. However, for the polycrystal­line grades these properties could be, in the first approximation, considered as isotropic. Some anisot­ropy is also typical for the highly deformed grades. The physical properties (thermal conductivity, spe­cific heat, elastic modulus, etc.) in first approximation are the same for beryllium grades with similar BeO and other impurity content and they are produced by the same fabrication method.