Environment & Energy

NNadir

(38,308 posts) Tue Apr 21, 2026, 08:27 PM Tuesday

Some Aspects of the Fuel for the Energy Device with the Lowest Carbon Intensity Known.

The paper I'll discuss in this post, a long paper that I can only find time to discuss briefly, is this one:

Matthews, C., Unal, C., Galloway, J., Keiser, D. D., & Hayes, S. L. (2017). Fuel-Cladding Chemical Interaction in U-Pu-Zr Metallic Fuels: A Critical Review. Nuclear Technology, 198(3), 231–259.

The paper touches on two fission products I have discussed in earlier posts, one on ⁹³Zr, which I discussed here:

Recent Advances in Cladding Material Extraction from Fuels in Nuclear Fuel Cycles...

...and...

¹⁰⁷Pd which I discussed here:

Improved efficiency of selective photoionization of palladium isotopes via autoionizing Rydberg states.

Because of the very high fuel utilization the reactor whose fuel is discussed here, a fast neutron reactor, has the lowest carbon dioxide intensity of any energy device, 1 gram CO₂/kWh.

The comparison between the carbon intensity of energy devices is given in this figure, figure 1 of the paper:

Very few fast neutron breeder reactors now operate in the world, the two most successful examples being Russian reactors, BN-600, commissioned in 1980 and licensed to operate until 2040, and the BN-800, a larger version, commissioned in 2016.

These are sodium cooled reactors with two sodium heat exchangers, one of which is radioactive (containing traces of radioactive ²⁴Na, with a half-life just under 15 hours and ²³Na, the natural isotope, and one containing only the natural isotope of sodium, ²⁴Na). These reactors produce more fissionable nuclear fuel than they consume: They are breeders.

India recently brought, earlier this month, its own breeder reactor to criticality. It is designed to produce plutonium and the fissile isotope ²³³U - which does not occur naturally, from thorium.

The information in this paper is based on the performance of the US EBRII, which operated from 1964 until 1994 at Argonne National Lab, powering the facility with about 20 MWe, and 65M(th) power having been built at a cost of $327 million dollars in 2025 dollars, ($32M in 1964 dollars).

The successor IFR program was cancelled in 1994, a damned shame.

From the text:

As the global goal of reducing carbon emissions continues to motivate technological advances in energy production, the base-load capabilities provided by nuclear power have sparked renewed interest in innovative reac tor designs.1–5 Based on a report authored by the International Atomic Energy Agency (IAEA), nuclear generated power is among the lowest greenhouse gas emitters per unit of energy produced when the plant’s entire lifecycle is considered.6 If emissions per energy produced are compared between advanced technologies for low carbon emitting energy sources (i.e., solar, wind, hydro, and nuclear technologies), fast breeder reactors (FBR) surpass all other viable types of energy production (Fig. 1), primarily due to the enormous energy output per plant and the avoidance of energy intensive fuel enrich ment that light water reactors (LWR) and gas-cooled reactors (GCR) require. Many reactor designs have been proposed in an effort to address specific problems facing nuclear technology, 231 232 MATTHEWS et al. · FUEL-CLADDING CHEMICAL INTERACTION IN U-PU-ZR METALLIC FUELS Fig. 1. Median values of green-house gas emissions in grams of CO2 equivalence per kilowatt-hour produced over the lifetime of the plant.6 primarily through enhanced safety, reduced cost, and decreased waste. Fast spectrum reactors, of which breeder reactors are a subset, attempt to address these concerns through the use of nonmoderated cores. Although several fast reactor concepts are currently being pursued in both the governmental and private sectors, the sodium fast reactor (SFR) benefits from having the highest technolo gical maturity due to extensive U.S. experience gained through the successful operation of the Experimental Breeder Reactor II (EBR-II) and the Fast Flux Test Facility (FFTF)...

Figure 1 from the text:

https://i.postimg.cc/Sj0GfRW0/NT198(3)-231-259f1.jpg

Zirconium, which is both a manufacturing component and a fission product available from used nuclear fuel is used as diluent for uranium and plutonium in the fuel pellets, which are metallic.

Interestingly, the cladding contained iron, which forms a eutectic with plutonium, an intriguing feature exploited by the LAMPRE reactor which used liquid plutonium fuel in the 1960s, the liquid being an iron plutonium eutectic. (A ternary cobalt/cerium/plutonium eutectic was also considered, but was not tested in the LAMPRE reactor.) I'm fascinated by the LAMPRE, and trying to get it into my son's head, but the eutectic I would advise is the binary plutonium/neptunium eutectic.

The composition of the claddings used are shown in table 2 in the paper, shown here with table 1, giving the reactor properties:

The Pu/Fe eutectic is discussed in the paper:

Fuel-cladding chemical interaction (FCCI) is a phenomenon that occurs at the interface between nuclear fuel and the fuel pin cladding during irradiation. In zirconium based SFRs, FCCI is observed between the stainless steel cladding and the U-Zr and U-Pu-Zr metallic nuclear fuel (hereby represented as U-xPu-yZr for both binary and ternary fuels where x and y are in wt%). As the fuel pin is irradiated, chemical inter diffusion of fuel and cladding constituents can occur, resulting in a complex, multi-phase region that places both the fuel and cladding at risk (Fig. 2). The transport of lanthanide fission-products into the cladding results in a brittle, low-strength “wastage” zone, decreasing the margin to failure via creep-rupture. Correspondingly, iron diffused into the fuel forms a low-temperature eutectic phase with uranium and plutonium, increasing the probability of localized fuel melting during a high temperature transient. Both failure mechanisms have been avoided primarily through administrative controls on peak cladding temperature and fuel pin burnup, which have adequately protected against failures. Unfortunately, fuel lifetime limitations result in increased cost as the total energy produced per pin is reduced.

A figure in the paper considers the migration of lanthanides to the fuel pin periphery onto the cladding, and the simultaneous migration of iron into the fuel:

One possible mechanism to address this problem is doping the fuel with palladium, a fission product I discussed in the earlier post linked above.

Furthermore, advanced FCCI mitigation concepts, such as palladium doped fuel, will benefit from a more physically based model by providing insight into the basic physical phenomena that can be manipulated. Last, future metallic fuel experiments that are essential to bolster the sparse U-xPu-yZr can be informed and guided through calculations with a more robust model, maximizing the effectiveness of each experiment and ultimately reducing the total cost required to qualify the fuel.

This approach, were it to prove valuable would provide an excellent opportunity to expand the use of the odd palladium isotopes, ¹⁰⁷Pd and ¹⁰⁵Pd potentially isolated by exploiting Rydberg states described in my previous post. During this process, ¹⁰⁷Pd would be transmuted into non-radioactive ¹⁰⁸Pd; however new ¹⁰⁷Pd would be generated by fission.

Interestingly, it appears that an issue with the fuel is the migration of lanthanide fission products to the edge of the fuel pellets; the solubility of cerium is discussed therein, as is the accumulation of neodymium. I can certainly imagine several benefits of this behavior, although it is clear from the paper that this migration was considered problematic.

There's quite a bit to ponder in this wonderful paper, but regrettably I won't have time for further discussion of the many interesting points therein.

I only have time to give a flavor.

The cancellation of the IFR program thirty years ago was a very bad mistake; unfortunately as American science is being decimated by ignoramuses, it will be difficult to correct that mistake in the next several years.

Have a nice evening.