You would think that by now, in discussing the future of Japan’s plutonium stockpile, one fact would be incontrovertible: Commercial plutonium — often called reactor-grade plutonium — can be used as an effective nuclear explosive material in weapons. We are not talking about simple or primitive nuclear weapons, but modern weapons comparable in sophistication and performance to those held in the arsenals of the major nuclear powers.
Yet despite the availability of public information and repeated statements by knowledgeable officials, the advocates of commercial plutonium use as fuel still refuse to acknowledge the point. The respected Council for Nuclear Fuel Cycle (CNFC) prominently displays on its website an article that dismisses concerns expressed by nuclear experts over stockpiles of Japanese plutonium separated from power reactor fuel. The Tokyo-based CNFC specifically criticizes expert statements at meetings in Japan in 2015. As we were among those experts expressing concern at those meetings, we think it is important to explain why CNFC is wrong.
It is understandable that CNFC defends commercial use of plutonium. The organization believes that plutonium use is essential to long-term reliance on nuclear energy. It has been devoted for many years, in its own words, to “promotion of peaceful uses of plutonium.” It has relied on the assumption that plutonium from Japan’s nuclear power reactors — of the so-called light water reactor (LWR) type — cannot be used for bombs. The fact that it is now clear such plutonium is useful for bombs threatens the foundation of CNFC’s thinking. It is difficult to convince the public that a plan to use many tons of nuclear explosives to fuel power plants is an entirely peaceful one when 1 ton could be used to produce over 100 nuclear warheads. The usability of reactor-grade plutonium for weapons thus threatens the whole nuclear fuel-cycle concept of CNFC. This includes not only extraction of plutonium by reprocessing and recycling it in LWRs, but also the planned use of plutonium from LWRs to fuel a future generation of fast breeder reactors — the ultimate goal of plutonium advocates.
CNFC is naturally looking for some way to protect its traditional position on the necessity to use plutonium fuel in the face of undeniable facts about plutonium’s weapon usefulness. The council has been forced to concede that it is indeed possible to use reactor-grade plutonium for a nuclear “device.” But it seizes on the difference between weapon-grade plutonium and reactor-grade plutonium, the latter coming from spent fuel that has been irradiated for a much longer time than weapon-grade plutonium produced in military production reactors. The reactor-grade material contains an admixture of undesirable plutonium isotopes (other forms of plutonium). CNFC insists the use of it for an explosive device poses difficult technical problems. Such a device, in its view, would be too heavy and bulky and dangerous to be a practical weapon. No country has created an arsenal of such weapons, from which CNFC concludes it would be “absurd” to think any country would do so in the future. It goes on to flatly predict: “Nuclear weapons will never be made from plutonium extracted from LWR fuels.”
The problem is that CNFC’s thinking regarding the technical characteristics of nuclear weapons is 70 years out of date, and simplistic as a result. The additional plutonium isotopes in reactor-grade plutonium increase the radioactivity, and therefore also the heat output, of the material. But nuclear- weapon designers have found ways to keep the devices from overheating, without significantly adding to the weight. And fabricators can easily cope with the additional radioactivity.
Some of the additional isotopes spontaneously release neutrons. In the first nuclear- weapon designs this neutron background would tend to initiate a chain reaction too early and thus tend to reduce the yield of the explosion and make it less predictable. But this is an irrelevant consideration for the weapons use of this material by an industrially advanced country.
Quoting from the U.S. Department of Energy Publication — Nonproliferation and Arms Control Assessment of Weapons-Usable Fissile Material Storage and Excess Plutonium Disposition Alternatives dated January 1997: “Advanced nuclear weapon states such as the United States and Russia, using modern designs, could produce weapons from reactor-grade plutonium having reliable explosive yields, weight, and other characteristics generally comparable to those of weapons made from weapons-grade plutonium.”
Until now, CNFC has apparently been unaware of this. This should make CNFC aware of the essential equivalence of reactor grade and weapons grade plutonium for modern nuclear weapons use. One of us, having extensive experience in nuclear explosives design, can attest to the truth of this U.S. government statement.
We would urge CNFC and others who hold similar views to reflect on this and to reconsider their position on the weapon usability of reactor-grade plutonium. It may have been tenable years ago, but no longer. It would be a shame if those who guide Japan’s nuclear energy policy disregarded this fact out of suspicion that it is presented for political purposes. It is undeniable that reactor-grade plutonium — extracted from spent reactor fuel by reprocessing — can be used for effective and powerful nuclear weapons.
Victor Gilinsky was a member of the Nuclear Regulatory Commission under U.S. Presidents Gerald Ford, Jimmy Carter and Ronald Reagan. Bruce Goodwin is associate director at Lawrence Livermore National Laboratory and a leading nuclear-weapon designer. Henry Sokolski directs the Nonproliferation Policy Education Center and served as a senior official in the U.S. Defense Department.