Abstract
Recent interest in compact nuclear reactors for applications in space or in remote locations drives innovation in nuclear fuel design, especially non-oxide ceramic nuclear fuels. This work details neutronic modeling designed to support the development of a new nuclear fuel concept based on a mixture of thorium and uranium nitride. A Monte Carlo N-Particle Version 6.2 (MCNP-6) model of a compact 10 MWe reactor design which incorporates (ThxU1−x)N fuel is presented. In this context, a “compact” reactor is a completely assembled reactor which may be emptied of coolant and transported by specialized commercial vehicle, deployed by a C130J aircraft, or launched into space. Core geometry, reflector barrels, and the heat exchange zones are designed to support reduction of overall reactor volume of core components while maintaining criticality with a fixed total fuel mass of 4500 kg. Dense mixed nitrides of thorium nitride (ThN) additions in uranium nitride (UN) in 5 wt.% increments between 0.05 le x le 0.5 have been considered for calculation of k_{infty } and k_{{{text{effective}}}}. ThN additions in UN results in a slight increase in the magnitude of the temperature coefficient of reactivity, which is negative by design. The isotopic distribution of the principal actinide inventory as a function of burnup, time, and initial fuel composition is presented and discussed within the context of the proliferation risk of this core design.
Highlights
Energy abundance in remote locations could enable a broad mission space, yet such technologies require significant investment and development
The neutronic performance of (ThxU1Àx)N from 0:05 x 0:5 was presented and discussed within the framework of both an infinite reactor and in the specific application of a compact reactor design under development by Los Alamos National Laboratory. k1 calculations for the infinite core model were determined as a function of atom fraction of thorium in (ThxU1Àx)N in increments of 5 at.%, from 0 to 70 at.%
The infinite model remains critical from 0 x 0:58, which indicates that uranium nitride (UN) is fairly insensitive to thorium addition
Summary
Energy abundance in remote locations could enable a broad mission space, yet such technologies require significant investment and development. Kg, and an explosively compressed mass would be considerably smaller.[38,39] Another key advantage is that plutonium can be readily chemically separated from uranium by PUREX processing.[40] reactor-produced 239Pu is rarely suitable for use in a weapon, since it is generally formed with an appreciable quantity of 240Pu. The high rate of spontaneous fission ð1030 neutrons=s Á gÞ in 240Pu makes it unsuitable for use in nuclear weapons, and separation of 239Pu from 240Pu is not practical.[41] The definition of weapons-grade plutonium allows no more than 6 at.% 240Pu as an impurity in 239Pu. While it is possible to accommodate higher levels of impurities of 240Pu, such designs would be very sophisticated, implosion-type devices.[42] From the perspective of proliferation assessment, it is assumed that countries which have access to such. Isotopic separation of 235U from 238U is a mature technology and would be considerably easier to apply, as opposed to attempting to produce parallel methods on such a diverse, highly radioactive mixture
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