Reactor-grade plutonium and nuclear weapons: exploding the myths

Nuclear Monitor Issue: 

Many Nuclear Monitor readers will have heard the argument before: reactor-grade plutonium (RGPu) produced in the normal course of operation of a reactor cannot be used for weapons production and thus claims about the connections between peaceful and military nuclear programs amount to anti-nuclear scuttlebutt.

The premise is false − RGPu can be used in weapons, and has been used in weapons ‒ and in any case the connections between peaceful and military nuclear programs are manifold.

The debate over the weapons-usability of RGPu has been going on for decades and has been covered in Nuclear Monitor (e.g. #787, 6 June 2014). It has essentially been solved: there is no doubt that RGPu can be used in weapons ‒ yet some nuclear industry insiders and lobbyists persist with the fiction that it cannot.

Gregory S. Jones has written a 170-page on the book on the topic, published by the Nonproliferation Policy Education Center and available online at no cost. Jones is a defense policy analyst with 44 years experience. He was part of the research team whose findings prompted the US government in 1976 to reveal, for the first time, the weapons-usability of RGPu.

Jones' book ought to be the last word on the matter; but of course the nuclear lobby will keep lying. For example, Jones' detective work proved beyond any reasonable doubt that a much-debated 1962 US weapon test did indeed use RGPu. That research was published in 2013 yet it has been largely ignored and many still claim the 1962 test used weapon-grade or fuel-grade plutonium.

Likewise, one prominent advocate of the nuclear industry's line of argument claims that a British weapon test in South Australia in 1953 used RGPu and it must have been unsuccessful (or at least underwhelming) since the UK subsequently used weapon grade plutonium in its bombs. But in fact there is compelling evidence that weapon grade plutonium was used in the 1953 test.

The book covers the technical debates in detail, and Jones explains the issues in simple terms. Take for example the most glaringly stupid aspect of the pro-nuclear position ‒ even if we accepted the fiction that RGPu cannot be used in weapons, reactors can nonetheless produce weapon-grade or near-weapon-grade plutonium simply by shortening the irradiation time. Jones writes:

"In late 2012, Iran abruptly discharged all of the fuel from its Bushehr PWR. After some months the fuel was reinserted, but the reason for this discharge was never explained. As I have written elsewhere, Iran (or any country with a LWR) has the option of producing near weapon-grade plutonium by simply discharging the fuel in the outermost part of the reactor core after just one irradiation cycle instead of the normal three. The country could cite safety concerns as the reason for the early discharge. Since countries such as Iran plan to produce their own reactor fuel, it would not be hard for them to deliberately introduce flaws into the fuel that they produce so that early discharge would be required.

"It is sometimes said that to use a power reactor in this manner would be uneconomical but there is no prohibition against operating a nuclear power reactor in an uneconomical fashion. After all, it is universally acknowledged that the use of plutonium containing fuels in LWRs (mixed oxide fuel, MOX) is uneconomic but the practice continues in countries such as France and Japan. Therefore, even if the International Atomic Energy Agency (IAEA) were to detect the production of low burnup fuel at a nuclear power reactor, it would have no basis for taking any action to prevent it."

The list of chapters gives some indication of the breadth of the book:

1. Why Countries Might Choose Reactor-Grade Plutonium for Their First Weapon

2. A Short History of Reactor-Grade Plutonium and Why the Nuclear Industry Is Wrong to Downplay Its Dangers

3. The Different Kinds of Plutonium

4. Predetonation and Reactor-Grade Plutonium: No Impediment to Powerful, Reliable Nuclear Weapons

5. Heat from Reactor-Grade Plutonium: An Outdated Worry

6. Radiation and Critical Mass: No Barriers to Reactor-Grade Plutonium Use in Nuclear Weapons

7. How Sweden and Pakistan Planned and India May Be Planning to Use Reactor-Grade Plutonium to Make Weapons

8. Did the U.S. and the British Test Reactor-Grade Plutonium in Nuclear Weapons?

9. Conclusions

Appendix: How Much Pu-240 Has the U.S. Used in Nuclear Weapons: A History

Jones' book concludes:

"All things being equal, weapon-grade plutonium is preferred over reactor-grade plutonium for the production of nuclear weapons. However, today, unlike the 1940s and 1950s, all things are not equal. A non-nuclear weapon state would find it difficult to build a plutonium production reactor without being subjected to enormous international pressure and, as Syria found out in 2007, the reactor could be bombed before it even began operation. In contrast, nuclear power reactors are readily available and, as part of the continuing legacy of the myth of denatured plutonium, half a dozen non-nuclear weapon states have large quantities of separated plutonium. Japan currently has several metric tons of plutonium in the form of pure plutonium nitrate solution or pure plutonium dioxide. In 13 years, after the Comprehensive Joint Plan of Action expires, Iran will be permitted to reprocess spent fuel to obtain pure plutonium nitrate.

"For countries today, the choice is not between weapon-grade plutonium and reactor-grade plutonium for nuclear weapons but rather between reactor-grade plutonium and no nuclear weapons at all. In the past, both Sweden and Pakistan at one time based their nuclear weapon programs on reactor-grade plutonium when weapon-grade plutonium was unavailable. That neither country would eventually produce reactor-grade based nuclear weapons does not change these facts. In the case of Pakistan, its failure to produce nuclear weapons using reactor-grade plutonium had nothing to do with the properties of such weapons. Rather, the United States recognized the dangers of reactor-grade plutonium and applied pressure to France to block the sale of the reprocessing plant needed to produce separated reactor-grade plutonium. Today, India may have deployed nuclear weapons using reactor-grade plutonium.

"It has been claimed that nuclear weapons manufactured using reactor-grade plutonium would be "unreliable," "unpredictable," "bulky," and "hazardous to bomb makers." None of this is true. The entire 270 metric ton current world stockpile of separated plutonium can be used to produce nuclear weapons by simply using a reduced amount of plutonium that is only 60% of a critical mass and coating the core with a half a centimeter of uranium. Employing early 1950s U.S. unboosted implosion technology and modern high explosives, these weapons would have the same predetonation probability as that of the same type of weapon using weapon-grade plutonium and a near critical core. The weapons would be the same exact size and weight as ones using weapon-grade plutonium, and they would require no special cooling. The gamma radiation from the core would be significantly less than that of an unshielded weapon-grade plutonium core. The only difference would be that while the weapon-grade plutonium weapon would produce a yield of 20 kilotons, the reactor-grade plutonium weapon would produce a yield of only 5 kilotons, though its destructive area would still be about 40% that of the 20 kiloton weapon. Further, boosting technology appears to be becoming more readily available to early nuclear weapon states. Boosted weapons produce the same yield regardless of whether weapon-grade or reactor-grade plutonium is used.

"Many claims about so-called denatured plutonium relate to reactor-grade plutonium produced by spiking reactor fuel with either neptunium or americium. However, this spiking has not been done nor is it likely to ever be done since this would greatly increase the costs and technical difficulty of using plutonium as nuclear reactor fuel. Even then, the plutonium could be used to produce nuclear weapons though in this case some special effort would be needed to cool the core by expanding the size of the core to improve heat dissipation and using thermal bridges to conduct the heat away from the core.

"The obvious solution to the nuclear weapon dangers posed by reactor-grade plutonium is to deny non-nuclear weapons states easy access to this material by banning all reprocessing and plutonium recycling, including unirradiated MOX fuel, from such countries. This was the conclusion of the analysis that I participated in at Pan Heuristics over 40 years ago. Our conclusion led to the Carter Administration to end commercial reprocessing in the United States and to try to prevent it in non-nuclear weapon states as well. The intervening years have only reinforced the wisdom of this recommendation. In the 1970s, those in the nuclear industry objected that such a policy would retard the growth of nuclear power which they believed was destined to be a major if not the main source of electricity generation. The nuclear industry expected that uranium resources would be insufficient to support such a large nuclear industry and only plutonium fuel in breeder reactors could power the large number of reactors that they expected.

"Today there are no commercial breeder reactors and none are in sight. Nuclear power did not grow to become anywhere as important as was predicted and uranium resources have proven to be no constraint on nuclear power. The use of plutonium based reactor fuels is universally acknowledged to be uneconomic. Nuclear energy faces stiff competition from natural gas and renewable energy sources.

"Though plutonium reprocessing in nuclear weapon states poses little proliferation risk, it is clearly uneconomic and unnecessary given the 270 metric ton stockpile of separated plutonium that already exists. Reprocessing should be ended in these countries as well to prevent this unnecessary plutonium stockpile from growing even larger."

Gregory S. Jones, April 2018, 'Reactor-Grade Plutonium and Nuclear Weapons: Exploding the Myths', Nonproliferation Policy Education Center,

Full book (PDF):

(Written by Nuclear Monitor editor Jim Green.)