A Broadening Definition in Fast Nuclear Reactor Design: A New Meaning for the Abbreviation "LMFR."

Last edited Sun Jan 12, 2020, 03:02 PM - Edit history (1)

The paper I'll discuss in this brief post is this one: A Review of Molten Salt Reactor Kinetics Models (Wooten and Powers, NUCLEAR SCIENCE AND ENGINEERING · VOLUME 191 · 203–230 · SEPTEMBER 2018.)

The concept of "Molten Salt Nuclear Reactors" generally referred to as MSR's, has enjoyed a resurgence in recent years, and there are a plethora of start up companies devoted to them, some more likely to succeed than others. Even people who have a vague understanding that nuclear energy is the best (and in my opinion "only" ) tool for fighting climate change, but otherwise no deeper understanding of the technology, can generate enthusiasm for the "Liquid Thorium Molten Salt Reactor," about which they've heard, peripherally on the internet is "safer" and "generates less waste" than current nuclear reactors.

This is in spite of the fact that in comparison to all other forms of energy, the existing nuclear fleet is already "safer" and generates "less waste" than all other forms of energy. Combustion waste, approximately equally divided between "renewable" biofuels and dangerous fossil fuels - there is less difference between these two than people think - kills between six and seven million people per year. That is "unsafe." The quantity of combustion waste is in the tens of billions of tons per year, whereas used nuclear fuel accumulates at about ten thousand tons per year. Used nuclear fuel is generally a solid, easy to contain indefinitely, combustion waste is gaseous, impossible (on scale) to contain even briefly. All of the deaths associated with commercial nuclear technology utilized in a period of well more than 60 years, do not match the number of deaths that will take place in the next six days from combustion waste.

Molten salt reactors cannot be "more safe" than pressurized water reactors, because pressurized water reactors have half a century of experience of remarkably safe operation when measured against any other form of energy in terms of DALY/GWh. (DALY = Disability Adjusted Lost Years of life.) Any money spent to make nuclear reactors "safer" is wasted so long as fossil fuels and raw (and even processed) biomass exist, since they are both spectacularly "unsafe."

This said, Molten Salt Reactors are not really bad technologies; they have many features to recommend them, and other features that are may be less desirable, depending on design and chemistry of the working fluids. (The most commonly discussed working fluid is FLIBE, a eutectic mixture of lithium and beryllium fluorides.)

I've lost some of my initial strong enthusiasm for the concept of MSR's for various reasons, although I can't imagine any type of reactor, even an RBMK reactor of the Chernobyl type - no RBMK will ever be built again - that is dangerous as dangerous fossil fuels.

If people start building MSR's all over the world, so much the better for the world.

Most MSR's are built around the utilization of thorium based fuels, with the common isotope of thorium - 233Th - being a fertile rather than a fissile fuel. In recent years, I've been much more interested in plutonium - in the presence of fertile uranium 238 and/or 233 Th - because of certain remarkable features of plutonium metal across which I've come.

The MSR concept is largely based on a reactor built and operated at Oak Ridge National laboratory under the guidance of the great nuclear engineer Alvin Weinberg in the early 1960's. Another type of reactor - which has fascinated me in recent years - also operated around that time at Los Alamos, the LAMPRE, reactor, the "Los Alamos Molten Plutonium Reactor Experiment."

In the modern literature on nuclear reactors almost never discusses the LAMPRE concept, which involved the use of liquid plutonium metal as a eutectic with iron. Most of what I've learned about this reactor is from literature published in the 1960's, although there are some later papers that discuss the properties of liquid plutonium, for example, Properties of plutonium and its alloys for use as fast reactor fuels (Hecker and Stan, Journal of Nuclear Materials 383 (2008) 112–118).

The LAMPRE was not a reactor designed to have flowing fuel - as operated - but the paper above, is the first paper published in decades, to my knowledge - that refers to a new use of the abbreviation of LMFR, "liquid metal breeder reactor" - which refers in general to stationary solid nuclear fuels cooled by a liquid metal, generally and regrettably liquid sodium metal, in a new way, as a "liquid metal fueled reactor," a subtle and important difference.

To wit:

The italics and bold are mine.

I like this new (to my knowledge) generalized abbreviation "CFR" which covers a broad range of possible reactor types.

For the record, my own thinking about liquid metal fueled does not involve flowing liquid fuels; I am interested in the potential of liquid fuels - owing to the metallurgical properties of liquid plutonium based fuels - to spontaneously reprocess some valuable and essential fission products. Some of these fission products were shown to be volatile at Chernobyl and Fukushima, where their uncontrolled volatilization accounted for their health risks, which despite being very real, are dwarfed by the health risks of volatile dangerous fossil fuel and biomass waste, risks humanity stupidly accepts continuously - under the normal operation of combustion equipment (as opposed to being in accidental settings) - without a whimper generally, and more generally with lip service not matched by action.

The paper focuses on MSR type reactors, but the point that it can be generalized is interesting.

The paper is basically about mathematical modeling.

For some flavor of its starting point, here's some more text:



"DNP" here refers to "delayed neutron precursor." Delayed neutrons allow for the control of nuclear reactors, if they flow out of a reactor before emitting neutrons, they can complicate reactivity.

In terms of generalization, for stationary liquid fuels this graphic from the paper interests me, as it touches on a problem about which I think quite often:



Some years ago, there was talk of a "nuclear renaissance" which looked backward to a time where humanity built more than 400 nuclear reactors in a period of about two decades, saving millions of lives that otherwise would have been lost to air pollution (dangerous combustion wastes). It didn't work out, owing to the willful destruction in the 1990's of intellectual and physical nuclear infrastructure by people who have a poor comprehension of basic facts, engineering, scientific or otherwise. This doesn't mean that we shouldn't look back to the life saving success of nuclear reactor engineering in the 1960's and 1970's, briefly continuing into the 1980's. These pressurized nuclear reactors were a spectacular success and they saved lives. The result of this failure of a nuclear renaissance has resulted in the rise of carbon dioxide concentrations by an unbelievable 45 ppm since January of 2000. The rate of the rate of increase, (the second derivative) is increasing, not decreasing as a result of this triumph of ignorance.

The triumph of ignorance is also rising, not falling. Part of this is political, but other factors are clearly involved.

Nevertheless, there are these pockets of knowledge - among them obscure nuclear engineering groups in national labs and universities - that function as monasteries did in the Middle Ages - that may bring future generations a better world, in spite of what we've done to them.

Language is a key to knowledge, and this subtle change of language where the letter "f" represents "flow" as opposed to - or in addition to - "fast" is a wonderful, if subtle, development.

I trust you're having a pleasant weekend.