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Emerging Advanced Reactor Concepts

The eight concepts received from industry spanned a range of reactor types and coolant selections. The concepts included five fast reactors and three thermal reactors. As to reactor coolants, there were three sodium-cooled reactors, two gas-cooled reactors, one light water-cooled reactor, one lead-bismuth-cooled reactor and one salt-cooled reactor. Four reactors use uranium oxide or uranium metal fuel, one proposes use of uranium nitride fuel and three would use thorium fuel. The concepts also varied considerably in level of design maturity. Five of the concepts have power levels less than 300 MWe.

The objective of the TRP process was to evaluate the viability of the concepts, gain an understanding of their R&D needs and prioritize research that supports the commercialization of those concepts. The report identifies concept specific needs and needs of multiple concepts. The report then identifies priorities for advanced reactor R&D activities. The overall outcome of the TRP process is a listing of R&D needs and priorities that would be beneficial to industry and DOE. This information will be used to inform Office of Nuclear Energy reactor technology funding decisions.

Interaction through this process can lead to an R&D program that has greater insight into industry, university, and national laboratory perspectives and potential opportunities for collaborative R&D projects.

Use of thorium in ADS

Accelerator-driven systems (ADSs) are investigated for long-lived fission product transmutation and fuel regeneration. The aim of this paper is to investigate the nuclear fuel evolution and the neutronic parameters of a lead-cooled accelerator-driven system used for fuel breeding. The fuel used in some fuel rods was for  production.

In the other fuel rods was used a mixture based upon Pu-MA, removed from PWR-spent fuel, reprocessed by GANEX, and finally spiked with thorium or depleted uranium. The use of reprocessed fuel ensured the use of  without the initial requirement of  enrichment. In this paper was used the Monte Carlo code MCNPX 2.6.0 that presents the depletion/burnup capability, combining an ADS source and kcode-mode (for criticality calculations). The multiplication factor () evolution, the neutron energy spectra in the core at BOL, and the nuclear fuel evolution during the burnup were evaluated. The results indicated that the combined use of  and reprocessed fuel allowed  production without the initial requirement of  enrichment.

In recent years great interest has been given to accelerator-driven systems (ADSs). This is mainly because of their inherent safety features, their waste transmutation potential, and their capability to breed the required 233U when the thorium fuel is used. ADSs are useful for recycling of americium, curium, neptunium, and plutonium. A great number of works on the ADS and the relative neutronics have been reported in the scientific literature.

Both critical reactors and subcritical accelerator-driven systems are potential candidates as dedicated transmutation systems. Critical reactors, however, loaded with fuel containing large amounts of MA have safety problems caused by unfavorable reactivity coefficients and small delayed neutron fraction. Nevertheless, subcritical systems present criticality and safety advantages: they operate with a neutron source rate that can be increased to compensate for the negative reactivity or any variation during the operation. Therefore, research interest in spent nuclear fuel transmutation has focused on both accelerator-driven systems and fusion-driven systems.

Another fuel proposed for using in ADS is the thorium-based fuel. There are many reasons for the resurgence of interest in the thorium fuel cycle nowadays. The thorium’s abundance is about three times more than uranium abundance. Thorium-fueled reactor is also an attractive tool to produce long-term nuclear energy with low radiotoxicity waste. The main issue verified in the usage of this fuel in subcritical systems is the need of initial enrichment (), since the use of natural thorium () is not feasible due to the very low values of achieved criticality.

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