Significance of the resonance self-shielding in fissile breeding blankets

It is shown that neglect of resonance self-shielding of fertile materials causes gross overestimation of fissile breeding in fission—fusion hybrids and threatens unexpected criticality of water cooled spallation target/blanket assemblies even at low enrichments. In the latter case the spallator's task, i.e. fissile breeding cannot be fulfilled. The importance of resonance self-shielding is fully confirmed in the performed calculations, primarily in soft spectrum blankets. Consequently, the necessity of consideration of the resonance self-shielding effects is proven and the resignation of use of moderators in fissile breeding systems is suggested.