Nuclear energy production is growing rapidly worldwide to satisfy increasing energy demands. Reprocessing of used nuclear fuel (UNF) is expected to play an important role for sustainable development of nuclear energy by increasing the energy extracted from the fuel and reducing the generation of the high level waste (HLW). However, during the reprocessing of Used Nuclear Fuel (UNF) gaseous radioactive nuclides including iodine, krypton, xenon, carbon, and tritium are released into the atmosphere through off-gas streams.The volatile iodine ( 129 I), and krypton ( 85 Kr) gases have long lived-isotopes; which have adverse effects on the environment as well as human health. Consequently, the capture of these two target radionuclides (species) is essential for the enhanced growth of nuclear energy. In this review we discuss several techniques for capture of volatile contaminants iodine, krypton, and xenon, focusing upon adsorption using solid sorbents, which has shown promising results for more than 70 years. Commonly used and recently developed sorbents are summarized in this article along with a short review of the results. Metal-organicframeworks (MOFs), gaining favor in recent years as sorbents for the capture of off-gas contaminants are also discussed. Finally, some considerations of future trends and prospects for investigations of the capture of volatile radionuclides are presented.

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Cover Photos: (left to right) PIX 04135, iStock 22779761, PIX 16933., PIX 15648, PIX 08466, PIX 21205 NREL prints on paper that contains recycled content.iii This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. PrefaceThe U.S. economy is constantly evolving, especially in regard to how energy is generated and used in the electricity, buildings, industrial, and transportation sectors. These changes are being driven by economics and by environmental and energy security concerns. The electricity-sector market share of natural gas and variable-generation renewables, such as wind and solar photovoltaics (PV), continues to grow. The buildings sector is evolving to meet efficiency standards, the transportation sector is evolving to meet efficiency and renewable fuels standards, and the industrial sector is evolving to reduce emissions through efficiency improvements, advanced combined heat and power (CHP), and increased energy storage (DOE 2015a). These drivers provide investment and utilization strategies for innovative energy generation and delivery assets.Nuclear and renewable energy sources are important to consider in the U.S. economy's evolution because both are clean, non-carbon-emitting energy sources. The Idaho National Laboratory (INL) and the National Renewable Energy Laboratory (NREL) are jointly investigating potential synergies between nuclear and renewable energy technologies. A series of workshops since 2011 have brought together experts and stakeholders in both areas to identify collaboration opportunities and to develop research plans to analyze and evaluate the costs and benefits and technical development needs of nuclear renewable energy beyond the electrical power market. Workshop participants identified nuclear-renewable hybrid energy systems (N-R HESs) as one of the potential opportunities and recommended investigating whether N-R HESs could both generate dispatchable electricity without carbon emissions and provide clean energy to industrial processes. They also recommended analyzing the potential for N-R HESs to provide dispatchable capacity to the grid and to investigate whether real inertia provided by thermal power cycles within N-R HESs provides value to the grid.Several categories of N-R HESs have been identified. Tightly coupled N-R HESs are co-located, directly integrated, and co-controlled behind the grid (i.e., they have a single connection to the grid). Thermally coupled N-R HESs have an integrated thermal connection and are co-controlled but may have multiple electrical connections to the grid and subsystems may not be co-located. Loosely coupled, electricity-only N-R HESs only have electrical interfaces and subsystems that can be located separately with multiple connections to the grid, but they are co-controlled so a single management entity dispatches the energy and services they provide to the grid. This report is one in a series of reports that INL and NREL are publishing that address the technical and economic asp...

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Small modular reactors (SMRs) refer to any reactor design in which the electricity generated is less than 300 MWe. Often medium-sized reactors with power less than 700 MWe are also grouped into this category. Internationally, the development of a variety of designs for SMRs is booming with many designs approaching maturity and even in or nearing the licensing stage. It is for this reason that a generalized yet comprehensive economic model for first-of-a-kind (FOAK) through nth-of-a-kind (NOAK) SMRs based upon rated power, plant configuration, and the fiscal environment was developed. In the model, a particular project's feasibility is assessed with regards to market conditions and by commonly utilized capital budgeting techniques, such as the net present value (NPV), internal rate of return (IRR), Payback, and more importantly, the levelized cost of energy (LCOE) for comparison to other energy production technologies. Finally, a sensitivity analysis was performed to determine the effects of changing debt, equity, interest rate, and conditions on the LCOE. The economic model is primarily applied to the near future water-cooled SMR designs in the United States. Other gas-cooled and liquid metal-cooled SMR designs have been briefly outlined in terms of how the economic model would change.

This study defines the design options for a secondary heat exchanger that couples the intermediate loop of a molten-salt-cooled nuclear reactor to a power production process. It is the first of several studies needed to select, develop, and demonstrate a secondary heat exchanger. In particular, it identifies design options affecting the functional and operational requirements of the secondary heat exchanger. The reference reactor design and configuration is a 3,400 MW(t) advanced high temperature reactor with three primary heat transfer loops. Multiple power conversion schemes are analyzed for a reactor outlet temperature of approximately 700°C. The applicability of other high temperature process heat applications that might eventually be coupled to the advanced high temperature reactor is also presented. An evaluation of viable secondary heat exchanger concepts is presented along with the parameters such as materials selection, system configuration, and coolant properties that will affect the secondary heat exchanger design. This study sets the stage for the two evaluations-a comparative analysis study and a feasibility study-that will follow. vi vii SUMMARYThe strategic goal of the Advanced Reactor Concept Program for the advanced high temperature reactor (AHTR) is to broaden the environmental and economic benefits of nuclear energy in the U.S. economy by producing power to meet growing energy demands and demonstrating an AHTR's applicability to market sectors not being served by light water reactors. This study is the first of three that will aid in the development and selection of the secondary heat exchanger (SHX) for power production from the AHTR, supporting large-scale deployment. The study identifies design options that will affect the functional and operational requirements of the SHX, and sets the stage for the comparative analysis and feasibility studies that will follow.Heat in the AHTR will be transferred from the reactor core by the primary liquid-salt coolant to an intermediate heat-transfer loop through an intermediate heat exchanger. The intermediate heat-transfer loop will circulate intermediate liquid-salt coolant through as many as three SHXs to transfer the heat to the power production process. Electric power generation was the principal process considered, but other processes were also evaluated because the heat transfer characteristics of molten salt coolants offer some advantages compared to high temperature gases produced by certain other reactor types.A broad comparison of molten salt coolants identified 11 for more detailed analysis, which led to the selection of three as potential intermediate loop coolants: LiF-NaF-KF (FLiNaK), KF-ZrF 4 , and KCl-MgCl 2 . Previous studies, which identified LiF-NaF-KF and KF-ZrF 4 as promising molten salt coolants, were confirmed. The high neutron cross-sections of KCl-MgCl 2 have generally disqualified it from use in the primary loop of thermal reactors, but do not disqualify its use as a coolant in the intermediate loop. Recent evaluations ...

The purpose of this report is to provide a review of thermophysical properties and thermochemical characteristics of candidate molten salt coolants, which may be used as a primary coolant within a nuclear reactor or heat transport medium from the Very High Temperature Reactor (VHTR) to a processing plant; for example, a hydrogen-production plant. Thermodynamic properties of four types of molten salts, including LiF-BeF 2 (67 and 33 mol%, respectively; also known as FLiBe), LiF-NaF-KF (46.5, 11.5, and 52 mol%, also known as FLiNaK), and KCl-MgCl 2 (67 and 33 mol%), and sodium nitrate-sodium nitrite-potassium nitrate (NaNO 3-NaNO 2-KNO 3 , 7-49-44 mol%, also known as Hitec® salt) have been investigated. Limitations of existing correlations to predict density, viscosity, specific heat capacity, surface tension, and thermal conductivity were identified. The impact of thermodynamic properties on the heat transfer, especially the Nusselt number, was also discussed. Stability of the molten salts with structural alloys and their compatibility with the structural alloys was studied. Nickel and high temperature alloys with dense Ni coatings are effectively inert to corrosion in fluorides, but not so in chlorides. Of the chromium containing alloys, Hastelloy N appears to have the best corrosion resistance in fluorides, while Haynes 230 was the most resistant in chloride. In general, alloys with increasing carbon and chromium content are increasingly subject to corrosion by the fluoride salts FLiBe and FLiNaK due to attack and dissolution of the intergranular chromium carbide. Future research to obtain needed information was identified.