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Sat Oct 28, 2017, 01:03 PM

Industrial drawbacks to the use of neptunium in existing nuclear reactors.

I personally believe that nuclear energy is the last best hope for humanity to address the environmental issues now before us; and in fact, nuclear power represents the last best hope to prevent nuclear war, and in fact, all wars, inasmuch as most wars are resource related.

In the 20th century, beginning notably with the Second World War, the resource that drove most, if not all wars, was oil; in the coming century it is more likely to be water. The Second World War killed people at a rate of about 10 million people per year on average, making the practice of that war even worse than modern air pollution - about which we do little other than issue platitudes - which kills people at a rate of 7 million people per year.

This is noted in an interesting review I read that was mostly concerned with the physical chemistry of water, which although it was a scientific paper contained a quasi-political note:

Despite water’s abundance, its distribution is increasingly problematic for the world’s growing populations; see Figure 1 and Appendix A.3. The availability of drinking water is limited, and it is shrinking worldwide. By the year 2030, the world’s 8.5 billion people9 will consume 6 trillion cubic meters (6000 km3 ) of water per year.10 While today 11% of the global population lives with poor access to clean drinking water,11 it is estimated that in 2030 half the world’s population will be living under severe water stress.12 It is increasingly challenging to get clean water to where it is needed. Early civilizations settled near rivers. But now, clean water is increasingly provided through water purification, desalination, 4,13,14 and transport. Therefore, clean water increasingly requires access to energy. Also, water distribution increasingly poses technical challenges, requiring advances in separating water from salts and oils at low energy costs, for example.

Water conflict is a term used to describe a clash between countries, states, or groups over access to water resources. While traditional wars have rarely been waged over water alone,15 water conflicts date back at least to 3000 B.C.16 The U.S. Dust Bowl drought of the 1930s, which covered nearly 80% of the United States at its peak, drove mass migration. More recent droughts occurred in the southwestern United States in the 1950s, and in California and the southern United States in just the past few years. Water has been regarded as a component of conflicts in the Middle East,17 in Rwanda, and in the Sudanese war in Darfur. Eleven percent of the world’s population, or 783 million people, are still without access to good sources of drinking water.11 Increased water scarcity can compound food insecurity, and put pressure on human survival.

How Water’s Properties Are Encoded in Its Molecular Structure and Energies (Dill et al[, Chem. Rev. 2017, 117, 12385−12414)

The current nuclear infrastructure is actually overall a huge consumer of fresh water for cooling purposes, but wise use of waste heat could transform nuclear energy into a water source, a point I made elsewhere in this space: Two Interesting Papers On the Utilization of Low Grade Heat.

Similarly, as a generator of gamma radiation, many fission products, most notably Cs-137, especially in the form of certain insoluble titanates (although fission product based substances others might also fill the bill) represents a real opportunity to deal with one of the most intractable (and from my perspective frightening) issues in water pollution, halogenated organic molecules, as well as intractable pharmaceutical metabolites and personal care products, since gamma radiation blows otherwise stable molecules to pieces, something we need to happen for airborne and water borne otherwise highly stable pollutants like PFOS and other polyfluorinated, polychlorinated, and polybrominated pollutants.

The point of all of the above, is that nothing that is useful can or should be considered "waste."

From my perspective, another key to realizing the full potential of nuclear energy to save us from ourselves is very much connected with the minor actinides neptunium and americium, elements that have long been considered - foolishly - to be so called "nuclear waste." In fact, if these two elements were in fact, discarded rather than utilized, they would be considered highly problematic because the most stable form of neptunium (into which amercium-241 decays) is the neptunate (V) ion, an oxyanion with a negative charge and three oxygens which forms water soluble salts. I have no doubt that they could be stored for millions of years in a way that would have no major environmental impact, but the question remains, "why do so?"

I elaborated on how I think Neptunium should be used to denature plutonium - to make it unsuitable for use in nuclear weapons - elsewhere: On Plutonium, Nuclear War, and Nuclear Peace

These ideas - which I generally refer to as the "Kessler solution" because one of the most prominent scientists to advance the argument in detail is the German nuclear scientist Günther Kessler, A new scientific solution for preventing the misuse of reactor-grade plutonium as nuclear explosive (Kessler et al, Nuclear Engineering and Design 238 (2008) 3429–3444) - are actually not new, and were not new in 2008, when Kessler wrote the first paper I read on the subject, but hardly the first paper ever written. Here, for example, is a discussion of the same topic dating to 1980: A Uranium-Plutonium-Neptunium Fuel Cycle to Produce Isotopically Denatured Plutonium (P. Wydler, W. Heer, P. Stiller & H. U. Wenger (1980) A Uranium-Plutonium-Neptunium Fuel Cycle to Produce Isotopically Denatured Plutonium, Nuclear Technology, 49:1,115-120). Kessler's paper is still very worthwhile, since it discusses in considerable detail the design of nuclear weapons and shows why nuclear weapons with a considerable heat load would be impractical.

However, the utility of these ideas does not mean that they are immediately practical, as a paper I will no cite discusses with particular attention to nuclear reactor engineering, wherein the neptunium were used in reactors that, by far, dominate all operating reactors on earth, that is thermal reactors.

A paper written the same year as the Kessler paper just referenced addresses the problems associated with utilizing the uranium/neptunium/plutonium cycle and is written by French scientists, who unlike German scientists have direct practical industrial experience both with recycling nuclear fuel and, regrettably, building nuclear weapons.

That paper is here: Neptunium in the Fuel Cycle: Nonproliferation Benefits Versus Industrial Drawbacks (Selena Ng, Dominique GrenÉche, Bernard Guesdon, Richard Vinoche, Marc
Delpech, Florence Dolci, HervÉ Golfier & Christine Poinot-Salanon (2008) Nuclear Technology, 164:1, 13-19)

Some excerpts from that paper:

AREVA, as a major industrial actor in the nuclear energy sector, is firmly committed to proliferation resistance efforts in the civilian fuel cycle. This commitment is even more important in the present context of worldwide development of nuclear power, coupled with recent geopolitical events placing proliferation at the forefront of concerns with the continued use of civil nuclear energy. The realization that a worldwide resurgence in nuclear power will require more sustainable management of its fuel resource and optimization of final repository use has recently turned the spotlight on civilian used fuel treatment-recycling plants. We believe that proliferation resistance should be approached “holistically,” that is, using a combination of technical or intrinsic! and institutional or extrinsic measures that take into account the context in which the system is placed, an aspect that is reflected in the integrated safeguards concept. Industry can boast an excellent track record in that no plutonium has been diverted from commercial treatment-recycling activities to date...

This paper will examine yet another suggestion, which is to add actinides—such as neptunium—at various points in the fuel cycle in order to reduce the attractiveness of the material containing the plutonium for proliferation purposes, or to increase its detectability should the material be diverted. Plutonium is undeniably a material of potential interest to state or non-state actors for nuclear explosive devices. But not all plutonium is equal. A high concentration of the isotopes 238Pu or 240Pu is particularly undesirable to potential proliferators because of their very high rates of radiation and decay heat, which complicate handling and manufacturing, and of spontaneous neutron emissions, which can affect the reliability and overall yield of the ultimate device. Table I, based on calculations using the depletion code CESAR, presents the plutonium isotopic composition 1 yr after reactor discharge of used uranium oxide UOX fuel and used mixed oxide MOX fuel according to burnup. Table I clearly shows that with increasing burnup, fissile plutonium content 239Pu and 241Pu decreases while the concentration of the undesirable plutonium isotopes 238Pu + 240Pu increases. Moreover, it is worth noting that discharged MOX fuel even at 45 GWd0t contains plutonium with an isotopic composition even more degraded than that of UOX fuel at the higher burnup of 60 GWd/t...

...One might then ask how the plutonium contained in discharged UOX fuel could be further degraded. One efficient route could be to add neptunium to fresh fuel, because 237Np—effectively the only neptunium isotope present in used fuel—produces 238Pu by neutron capture in the reactor core via 238Np with a half-life of 51 h!. This proposal, sometimes referred to as the “238Pu heat spike concept,” has been suggested several times in the past 3– 6 a and is still considered today as a possible option to enhance proliferation resistance in the nuclear fuel cycle. The remainder of this paper will examine the industrial feasibility and effectiveness of this proposal...

After a discussion that is highly technical (and also economic, owing to the costs of changing enrichments), and involves reactor physics and safety margins in thermal reactors - these place practical issues as to the amount of neptunium that can be added to the fuel without compromising safety margins owing to the hardening of the neutron spectrum and thus the worth of control rods and boron poisons, they then raise an important technical point that is discussed in many other places where incorporation of neptunium is discussed in these terms, that neptunium itself, generally monoisotopic as the 237 isotope is itself a weapons grade material of unusually high purity:

A brief examination of the physical properties of 237Np shows that it presents a non-negligible proliferation risk in comparison to that presented by highly enriched uranium or 239Pu. Its critical mass bare sphere is similar to that of pure 235U, neptunium in metal form is easier to compress than highly enriched uranium, and it presents insignificant heat generation and spontaneous neutron emission barriers for use in an explosive device. The only drawback it presents compared with 235U or 239Pu is its gamma-ray emission 1 mSv/h{kg 1 at 1 cm, but this can be overcome. It is in fact largely recognized today14 that neptunium could be used to fabricate a nuclear explosive device and that some states may already have tested a nuclear explosive based on neptunium.

Well then...


Does this mean that the incorporation of neptunium into the fuel cycle is a bad idea?

I don't think so.

Neptunium has been been isolated for a number of years, and is still being isolated and the number of nuclear wars that has resulted as a result is zero. Much of the success of the American space program, most notably the recently completed Cassini mission has relied precisely on this technology, the Apollo missions, the Mars Rovers, the Cassini mission, the Pioneers, and the Voyager missions all, among others, relied on the isolation of neptunium and its conversion into plutonium.

It is also worth noting that the French discussion relies on thermal reactors - France has many of them - but fast reactors represent quite a different story. In the fast nuclear cycle it is possible, at least in theory, to utilize pure neptunium as a nuclear fuel - more likely diluted with, say, depleted uranium, of which we have a great deal. Most importantly, in the fast nuclear cycle there is a nuclear reaction which takes place the 237Np[n,2n]236Np reaction that is not appreciable in thermal reactors other than in the fast fission fraction. The cross section of this reaction for fast (1-2 MeV) neutrons is just shy of 1 barn.

Neptunium 236 is a fairly stable isotope; it's half life is about 154,000 years. What makes it useful is that it decays about 12% of the time into plutonium-236, which in turn, with a half life of roughly 2.9 years into uranium-232. Uranium-232's decay series is the reason that thorium based nuclear fuels are considered proliferation resistant, because of the intense gamma radiation associated with its decay product Thallium-208. (In addition 236Pu itself generates even a larger amount of heat than does 238Pu.)

Thus the use of neptunium in fast reactors is extremely proliferation resistant, since it is possible to denature neptunium itself. I have often noted in various places around the internet that the fast neutron cycle is superior to all other fuel cycles since it represents the only opportunity, given the large amounts of depleted uranium - along with the thorium dumped to provide materials for the useless and ineffective wind industry - to put an end to all energy mining for several centuries, no coal, no oil, no gas, fewer lanthanides (many important lanthanides are side products of nuclear fuel recycling, notably praseodymium and neodymium).

We need to wake up and smell the air, which is increasing polluted and degraded precisely because of the fear and ignorance directed against our last best hope.

As I noted in the link I produced above to a post on another website, we can never make nuclear war impossible, since the nuclear cat is out of the bag and as long as uranium exists - and it will always exist - it will always be possible to make nuclear weapons. But the key to making nuclear war less likely is not to ban nuclear power, but rather to embrace it, in particular in the fast cycle, since this cycle makes it possible to denature all potential nuclear materials, including those which occur naturally, specifically, uranium.

Have a nice weekend.

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