A Sodium-Cooled Thermal-Spectrum Fission Battery

We propose a low-enriched-uranium, thermal-neutron-spectrum sodium-cooled reactor with a peak sodium temperature of 700°C coupled to an air-Brayton power cycle for electricity and heat. Three low-enriched-uranium, thermal spectrum sodium-cooled reactors were built in the 1960s and 1970s; but there has been no examination of such systems for many decades. We develop a pre-conceptual design based on “new” enabling technologies since the 1970s including yttrium hydride as the high-temperature neutron moderator, commercial gas turbines and secure decay heat removal systems. We define the reactor as a sodium hydride reactor (SHR). The initial application is as a fission battery. The concept of the fission battery (FB) is a “plug and play” nuclear reactor defined by multiple characteristics: economics enabled by factory fabrication of large numbers of identical units, easy installation and removal, unattended operation and highly reliable operations. FBs are designed to be a low-carbon replacement for fossil fuels by industrial and commercial companies that require energy to produce some product (manufactured goods, chemicals, education, data centers, ship transportation, etc.). The reactors may be owned or leased by the company. The SHR is at an early stage of development.

Candidate Core Designs for the Transformational Challenge Reactor

Early cycle activities under the Transformational Challenge Reactor (TCR) program focused on analyzing and maturing four reactor core design concepts: two fast-spectrum systems and two thermal-spectrum systems. A rapid, iterative approach has been implemented through which designs can be modified and analyzed and subcomponents can be manufactured in parallel over time frames of weeks rather than months or years. To meet key program initiatives (e.g., timeline, material use), several constraints—including fissile material availability (less than 250 kg of HALEU), component availabilities, materials compatibility, and additive manufacturing capabilities—were factored into the design effort, yielding small (less than one cubic meter in volume) cores with near-term viability. The fast-spectrum designs did not meet the fissile material constraint, so the thermal-spectrum systems became the primary design focus. Since significant progress has been made on advanced moderator materials (YHx) under the TCR program, gas-cooled thermal-spectrum systems using less than 250 kg of HALEU that occupy less than 1 m3 are now feasible. The designs for two of these systems have been evolved and matured. In both thermal-spectrum design concepts, bidirectional coolant flow is used. Coolant flows down through YHx moderator elements and is reversed in a bottom manifold and core support structure, and then flows up though or around the fuel elements. The main difference between the two thermal-spectrum design concepts is the fuel elements—one uses traditional UO2 ceramic fuel, and the other uses UN-bearing TRISO fuel particles embedded inside a SiC matrix. Core neutronics and thermal performance for these systems are assessed and summarized herein.