The Dual Fluid Reactor

atw Vol. 65 (2020) | Issue 3 ı March The Dual Fluid Reactor – An Innovative Fast Nuclear-Reactor Concept 145 with High Efficiency and Total Burnup Jan-Christian Lewitz, Armin Huke, Götz Ruprecht, Daniel Weißbach, Stephan Gottlieb, Ahmed Hussein and Konrad Czerski 1 Introduction In the early decades of nuclear fission power technology development, most of the possible implementations were at least considered in studies and many were tested in experimental facilities as have been most of the types of the Generation IV canon. Uranium enrichment and fuel reprocessing with the wet chemical PUREX process for today’s reactors originated from the Manhattan project in order to gain weapons-grade fissile material. The use of fuel elements in light water with respect to the EROI-measure and capability and best neutronic proper- reactors originated from the propul- to passive safety standards according ties. sion systems of naval vessels like to the KISS (keep-it-simple-and-safe) Pure molten Lead has low neutron submarines and carriers. principle and with attention to capture cross-sections, a low modera- A sound measure for the overall current- state technology in mechani- tion capability, and a very suitable efficiency and economy of a power cal, plant and chemical engineering liquid phase temperature range. For plant is the EROI (Energy Return on for a speedy implementation. the fuel, it is possible to employ RESEARCH AND INNOVATION Investment). The known problem of There was a gap in the reactor undiluted fissionable material as solid fuel elements in power reactors concepts of the past with a high opposed to a MSFR that works with is fission product accumulation during development potential for the present less than 20 % actinide fluoride, see operation requiring heavy safety and the future. A DFR power plant Sec. 4 for details. Consequently, a DFR measures to avoid a core meltdown. could exploit the potential of nuclear has increased power density, small These measures reduce the EROI for fission power with an EROI two orders core volume and very hard neutron today’s Pressurized Water Reactors of magnitude higher than fossil fired spectrum that further improves the (PWRs) to values of about 75 (Sec. 9) power plants. neutron economy. Additional benefits which is only a factor of 2 higher than of liquid metal coolant comprise the for fossil-fired power plants. This is 2 Basic principle application of magneto hydrodynamic in fact surprisingly low compared The Dual Fluid Reactor (DFR) is a techniques both for pumping and, with the possible maximum EROI for heterogeneous fast reactor with a possibly in the future, direct elec tricity nuclear energy of 10,000 (Sec. 9). liquid fuel and a liquid coolant generation because of the high con- Unfortunately, most Generation IV whereby both flow through the centration of charge carriers. reactor concepts except the Molten reactor core. Separation of cooling Furthermore, the reactor core and Salt Fast Reactor (MSFR, see below) and fuel supply function is achieved primary coolant loop can operate at are again based on solid fuel tech- by an interconnected array of fuel normal pressure which allows for nology. For the probably most inten- conduits immersed in the coolant simple and cost regressive size- scaling. sively developed breeder technology, liquid. Both cycles can now be opti- Figure 1 explains the synergetic the Sodium-Cooled Fast Reactor SFR mized for their respective purpose. effects. The Dual Fluid Principle opens (or the Traveling-wave variant, Terra- This has many advantages to a MSFR, the possibility of a liquid fuel with power’s TP-1), sodium has been cho- where both functions must be satis- high actinide concentration in com- sen as the coolant. It has aggressive fied by one liquid in a trade-off bination with a coolant with high chemical reactivity with air, water and between high-temperature fuel, low- heat transfer capability, which leads structural materials as well as a high temperature cooling, and an accept- to a high-power density. Liquid fuel neutron reaction cross section with able heat capacity. like in a MSR already reduces the the possibility of a temporary positive The coolant liquid should have the consumption of structural materials void coefficient. These properties highest possible heat transportation compared with solid fuel reactors, require a reactor pressure vessel, double- walled piping, and an inter- mediary cooling cycle. In effect, all this sums up to expenses which double the electricity production costs of the SFR relative to a PWR as calculated for the Superphénix class. Hence Generation III and most of Generation IV nuclear power plants are in danger of losing competition against fossil fired power plants, especially in the advent of the shale gas exploitation. | Fig. 1. The Dual Fluid Reactor (DFR) The flow chart shows the advantages of the Dual Fluid principle partially depending on each other. It is essential for the understanding of the synergetic effects. concept presented here is designed Research and Innovation The Dual Fluid Reactor – An Innovative Fast Nuclear-Reactor Concept with High Efficiency and Total Burnup ı J.-C. Lewitz, A. Huke, G. Ruprecht, D. Weißbach, S. Gottlieb, A. Hussein and K. Czerski atw Vol. 65 (2020) | Issue 3 ı March but the power density is limited. In the DFR, both positive properties can be combined which leads to a 146 massive reduction of structural materials. At high operating temperatures (needed when using an undiluted salt, see Sec. 7), corrosion of core structural materials limits the choices of such materials. However, corrosion resistant materials at high temperatures do exist, but they are quite expensive. Using such materials in a DFR design has little effect on its economy due to its small size, low material inventory, and the absence of | Fig. 2. any parts that need be to replaced Possible power plant based on the DFR, with the nuclear part including the core, the pyro-processing unit (PPU), disposal and decay heat dump (left hand side) and the conventional part with the heat periodically. exchanger and turbines (right hand side). The compactness allows for a subterranean installation. On the other hand, the use of such expensive corrosion resistant ma terials in a MSR has adverse economic effects due to its high inventory of structural material. Thus, the temperature of a RESEARCH AND INNOVATION MSR is limited and the MSR research was focused in the past on finding suitable eutectic salt mixtures, also compli- cating the production and reprocessing techniques. For the DFR, very simple state-of-art techniques can be applied, see Sec. 4.2. Another comparison can be made with the Generation IV concept of the Lead-cooled Fast Reactor, LFR. Again, due to economic reasons, the wall material of the exchangeable fuel rods must be cheap, which focused the research on finding suitable steel alloys. They yet have a higher lead corrosion susceptibility than the expensive materials intended for the DFR design, | Fig. 3. therefore also limiting the operating DFR fuel and cooling loop. The fuel circulates between the PPU (which is also connected to the short-li- temperature. Due to these material ved fission products storage) and the core whereas the coolant loop connects the fissile zone to the conventional part, also cooling the fission product storage. PPU, core and fission product storage are equip- restrictions, both, LFR and MSR, ped with a fuse plug. are not able to achieve operating tem peratures suitable for economic As a result, a new concept not electric grid of industrialized coun- hydrogen production from water. fitting into one of the Generation-IV tries. But also, power-sizes even down These restrictions do not exist for reactor developments has been in- to approx. 35 M GWe are possible, the DFR. vented. It foresees a compact core with depending on markets demands. Due Contrary to a MSFR, DFR’s liquid a very high power density, an operating to its compact size, the nuclear part fuel is not limited to actinide salts, temperature of about 1,000 °C, in- can reside in a sub terranean bunker but it is the current reference design. herits MSFR’s passive safety features, that can withstand high magnitude However, an alternative could be a and has hard neutron spectrum. The earthquakes, direct aircraft impacts solder-like melt of a metal alloy made abundant neutron excess can be used and non-concen trated conventional up of actinides and, if necessary, met- for multiple transmutation purposes, military attacks. The conventional als with low melting points in order to like nuclear waste incineration, and part can utilize supercritical water or 238 232 reduce the solidus temperature of the breeding for U and Th cycles. supercritical CO2 (see Sec. 8.1) and is alloy and gain a pumpable fluid. The All this produces a nuclear power not fortified for economic reasons, but advantage would be an even higher plant with an outstanding economic fortification to any desired degree can power density due to better heat competitiveness. easily be achieved. transportation capability, and a possible higher operating temperature due 3 System overview 3.1 Fuel and coolant loop to the lower corrosive potential of the Figure 2 shows how a DFR reference Since the cooling function is separated metal alloy. The basic design, then, al- power plant might look like. The from the liquid fuel, the circulation lows for a high degree of possibilities reference design has a power output of the fuel can be adjusted to nuclear which can be trimmed to a specific of 3 GWth and an electric output of purposes like maximum burn-up, purpose. These concepts will be dis- 1.5 GWe which is currently the typical transuranic incineration, isotope pro- cussed briefly in Sec.

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