The Long-Life Gas Turbine Fast Reactor Matrix Core Concept

A fast reactor version of the modular HTGR-GT is proposed which has good potential to satisfy the Gen IV goals of competitive economy, enhanced nuclear safety, plus reduced proliferation risk and nuclear waste. Good economy is pursued through a modular design of 300 MWe rating, a direct cycle and a simple balance of plant using a supercritical CO{sub 2} Brayton cycle. The power rating is sufficiently high to capitalize on economy of scale within the constraints imposed by modularity. This plant design facilitates achievement of short construction schedules, high plant net thermal efficiency and maintenance requirements simpler than a steam Rankine cycle, thus leading to reduced capital and operation and maintenance cost. Enhanced safety is achieved by introduction of a solid fueled matrix penetrated by coolant channels. This matrix approach eliminates core compaction scenarios and provides sufficient thermal storage and conductivity to dissipate decay heat in coolant depressurization events, and provides negative reactivity feedbacks that lead to inherent shutdown in accidents with temperature rise. To enhance proliferation resistance on-site fuel movement and access to the core is eliminated through the use of a long-life core. Finally, the proposed core reduces waste inventory by fissioning plutonium obtained from spent LWR fuel.more » The key challenges in the reactor core design involve the selection of core geometry and materials capable of passively removing decay heat in loss of coolant events, achieving sufficiently high specific powers to minimize fuel cycle cost, attaining very long core life with small reactivity swing and overcoming reactivity increase upon loss of coolant in the hard-spectrum core. Various matrix materials have been explored. It has been found that the decay heat can be removed from an 8 m-tall annular core with power densities comparable to those of its thermal reactor counterpart MHR-GT (600 MWth core), and dissipated to water-cooled panels in the cavity wall. Burnup calculations confirm that a core life of {approx}50 years is feasible at power densities compatible with decay heat removal constraints. However, the small cross sections of fissile isotopes in this hard spectrum core require high heavy metal loadings resulting in a low specific power and consequent increased fuel cycle cost. Alternative core configurations are explored to increase specific power. Even though the CO{sub 2} coolant is neutronically transparent, it provides significant moderation in a hard spectrum core and coolant loss results in a reactivity increase, in particular for metallic, plutonium fuels. This reactivity increase can be reduced by using carbide or oxide fuels, and reflector and matrix materials that increase the absorption cross section upon spectrum hardening. (authors)« less