BeH ₂ as a Moderator in Minimum Critical Mass Systems

TL;DRAbstract

BeH2 could serve as an effective moderator in reducing critical masses in minimum critical mass systems on account of its (n,2n) reactivity bonus and the possibly higher hydrogen atomic density. A parametric study of the variation of keff and critical mass with BeH2 moderator density in the range of 600 to 1000 kg/m3 for the three main fissile nuclides of 235U, 233U, and 239Pu in small spherical thermal assemblies indicates that for 0.40-m-thick BeO-reflected spherical systems with BeH2 moderator of density ≥680 kg/m3 the critical masses are lower than with any other known moderator (such as H2O or CH2). With a moderator of crystalline BeH2 having a density of 780 kg/m3, critical masses are found to be lower than with CH2 by about 15%.

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