Toward a safe development of the energy amplifier systems. Self-protected against time reactivity enhancement thermal and fast nuclear fuels

The principal objective of the present investigation is aimed at a safe development proposal of Energy Amplifier system (E.A.s) devices. In the context of this matter previous results demonstrate a clear time reactivity enhancement (more than safe criticality thresholds), in the case of thermal irradiation of ThO2 fuel based E.A.s. From nuclear criticality point of view such cumbersome effect represents a further system complexity. To find remedy for the increasing neutron multiplication factor K (due to the delayed fissile U233 content buildup), new types of nuclear fuel have been envisaged for both thermal and fast option advancement of the E.A.s. based innovating devices. Now, the contemporary demand of high sub-critical K factor values (of the order of 0.95), typical requirement of E.A.s. based configuration operating, along with attainable power levels leading to proper breeding performances doesn''t meet further problems of supervening over-criticality. In other words, the new fuels at issue, in terms of selectively graded components as well as their specific neutron properties, are endowed with reactivity invariability, i.e. time stability of the K factor at established periods of irradiation cycles. (author)