Determination of the liquid eutectic metal fuel dual fluid reactor (DFRm) design – steady state calculations

Abstract

Summary The dual fluid reactor (DFR) is a novel concept of a very high‐temperature (fast) reactor that falls off the classification of generation 4 international forum (GIF). DFR makes best of the two previous designs: molten salt reactor (MSR) and lead‐cooled fast reactor (LFR). In this paper, we present a new reactor design Dual Fluid Reactor metallic (DFRm) with the liquid eutectic U‐Cr metal fuel composition and the lead coolant of which general idea was patented recently. By performing the first steady state neutronic calculations for such a reactor (the neutron flux density as a function of energy, the burnup, the effective multiplication factor/reactivity), we show that this 250‐MWth reactor is critical, and that it can operate almost 20 years without refuelling. We also optimise the geometry (reflector thickness, fuel tubes pin pitch) with respect to the multiplication factor. The optimisation together with some other opportunities for the liquid metal fuel design (eg, the use of electromagnetic pumps to circulate the medium) allows DFRm to be of a small size. This rises economy of the construction as expressed nicely in terms of the energy return on invested (EROI) factor, which is even higher than for the molten salt fuel design (DFRs). Last but not least, we show that DFRm has all the (fuel, coolant, reflector) temperature coefficients negative, which is an important factor of the passive safety.

Dual Fluid Reactor as a long‐term burner of actinides in spent nuclear fuel

“…Our starting point was the DFRm with the enriched uranium fuel 1 as presented in Table 2. As one could see, the fissile material was mainly 235 U and one used an eutectic of Uranium with Chromium in the following weight proportions: 235 U − 12.80%, 238 U − 82.42%, 52 Cr − 4.78%.…”

“…Our first attempt was to keep the fuel composition as close as in our previous work 1 regarding the U‐Cr eutectic composition, so that we added some fraction of the natural Uranium into the typical composition of SNF as given in Table 3. It is important that we keep the same proportions of the actinides with Chromium.…”

“…Whereas MSRs need diluted eutectic salts for proper operation, the Dual Fluid Reactor (DFR) which was patented by the group from Institut für Festkörper Kernphysik Berlin 2,3 offers a possibility to use undiluted fuel at high operating temperatures (above 1000°C and up to 1300°C in the upper core). This includes the feasibility of using liquid metal fuel with very high actinide fractions 1,4 . In fact, the Liquid Metal Fuel Reactors were already discussed in the early days of nuclear power, 5‐7 but they were not accompanied by the liquid metal coolant as in the DFR.…”

“…A detailed description of the DFR, though initially in its molten salt fuel version DFRs, can be found in introductory publications 3,8 . The metallic version—DFRm 1 —consists of a cylindric fission zone with Uranium‐Chromium (U‐Cr) eutectic liquid metal fuel in the centre surrounded by a thick Lead coolant reflector. The structural material is assumed to be dense silicon carbide (SiC) although Zirconium Carbide, Titanium Carbide or compositions of the latter two (ZrC, TiC, ZrC‐TiC), at least with some adoption of Y 2 O 3 , are better known for its corrosion resistance against the metallic fuel 9 .…”

“…First Monte Carlo calculation results of a Dual Fluid Reactor metallic (DFRm) core with 250 MW thermal power including special liquid metal eutectic fuel consisting of 80 mol% actinides with fissile 235 U and 20 mol% of chromium have been introduced in a prior publication 1 . It showed a very high neutron economy and a very hard neutron spectrum while maintaining a fair fuel temperature reactivity coefficient.…”