Defining the Challenges—Identifying the Key Poisoning Elements to Be Separated in a Future Integrated Molten Salt Fast Reactor Clean-Up System for iMAGINE

Abstract

Nuclear fission technologies have the potential to play a significant role in the energy mix of a net-zero and sustainable society. However, to achieve the sustainability goal two significant challenges remain: efficient and sustainable fuel usage and the minimization of long-term nuclear waste. Civil nuclear molten salt systems and technologies offer the opportunity to address both, delivering future reactors at scale for efficient and effective power production and nuclear waste burnup. Potentially, both objectives could be fulfilled in one reactor system, which could significantly improve sustainability indices. The key to this innovation is demand driven development of a significantly reduced fuel cycle with enhanced proliferation resistance which offers further potential for improvement. To achieve these goals, a transformative approach for salt clean-up during molten salt reactor operation is proposed, by concentrating on the detection and removal of key neutron poisoning elements which prevent the reactor from long-term operation. To enable this highly innovative development work, a novel analysis of the evolving elementary fuel composition, their concentrations, and their criticality influence is now provided in this work. This, combined with consideration of the oxidation states of each of these elements then provides the basis for the selection of these key poisons and the development of advanced separation processes and process monitoring. This work also discusses the importance of the effective integration of physics and chemistry when systems modelling in achieving these system development goals.

A HELIOS Based Dynamic Salt Clean-Up Study for iMAGINE

“…Table 1. Fission product elements followed through the HELIOS simulation with the concentrations appearing after different accumulated burnup states of the salt without clean-up and comparison of the results to POLARIS results published in [16]. The criticality effect of the accumulation of each of the followed-up fission product elements of Error!…”

“…The approximations and the use of the HELIOS code package seem to be adequate for the approximation level required for this kind of longterm investigation of isotope accumulation to support the development of a clean-up system. The results of the influence of different elements on the system criticality has been evaluated against earlier publications [15,16].…”

“…In a first step the analysis was based on the criticality effect of the fission products in spent fuel from LWRs [15]. In a second step, the fission product accumulation in the MSFR operation and the related criticality effect was studied [16]. However, all these studies were based on static calculations to a certain burnup and the MSFR study was based on a classical burnup study without considering the release of volatile fission products during operation.…”

A First Step to Zero Waste Nuclear – Advanced Strategic Thinking in the Light of iMAGINE

“…The noble metals have been shown to be the most criticality relevant fission products dissolved in the fuel salt. Thus, their separation will be one of the core challenges [57]. The molten salt turns through the energy production into NaCl -UCl3 -UCl4 -FpCl , where FpCl are the chloride of fission products (Fp), which includes the noble metals (Nm), Tc, Ru, Rh, Pd and other elements such as Ag, Cd, In, Sn and Sb that can precipitate under a reducing atmosphere (e.g.…”

“…Understanding the demand will allow the development of the relevant processes in the most appropriate way to support tailored final disposal solutions e. g. through the specific separation of elements which contain long lived isotopes, or elements which are carrying the isotopes responsible for the major decay heat production. This can be delivered in the same way as identifying the elements which have the major influence on the reactor long term operation [18,57]. This approach has identified elements to be separated through the salt clean-up system e. g. Ru, Mo, Pd, Cs, Nd, Tc [57] using the processes described above while most other fission products will be kept in the salt as long as the solubility limits allow.…”