Plutonium, an element with the atomic number 94, named after Pluto, has six isotopes, or, brothers and sisters, plutonium-238, 239, 240, 241, 242, and 244. Of these, the most famous is plutonium-239, which was used in the atomic bomb dropped on Nagasaki and has still been used in a number of nuclear weapons today.
In the reactor of a nuclear power plant, non-fissile uranium-238 absorbs neutrons emitted from nuclear fission of uranium-235 and transmutes into uranium-239, then neptunium-239, and finally plutonium-239. This plutonium-239 undergoes nuclear fission in the reactor, generating heat, which accounts for about 30% of total electricity produced in the nuclear power plant. In a nuclear reactor, not only plutonium-239 is produced; but also its brothers and sisters, plutonium-238, -240, -241, and -242 are produced naturally. As the degree of the burnup of uranium fuel increases, so does the percentage of these siblings.
Besides plutonium-239, plutonium-238 also has other practical applications. In deep outer space where no sunlight reaches, plutonium-238 has been used as a material that makes up a fuel cell in space probes. In the U.S., plutonium-238 had played an important role in medicine: It had been used as a battery source of heart pacemakers until high-performance lithium batteries replaced them.
Technically, it is very difficult to isolate each species of plutonium spawned from uranium fuel in the reactor; so, we must deal with them as a non-separable family of plutonium. To increase the percentage of plutonium-239, in other words, to produce plutonium suitable for the use in nuclear weapons, you must have another small uranium burning reactor dedicated for the production of weapon-grade plutonium. You cannot simply extract what you want from the fuel burnt in the reactor for four years for generating electricity. All nuclear-weapon states have such weapon-grade plutonium production reactors.
In the 61st Pugwash Conference on Science and World Affairs held in Nagasaki in November 2015, some nuclear disarmament experts expressed concerns over plutonium in the fuel spent in light water reactors (LWRs). Before that, at the First Committee of the United Nations General Assembly held in the UN Headquarters in New York on October 20, 2015, Chinese Ambassador for Disarmament Affairs in his speech also expressed concerns over plutonium contained in the fuel spent in Japan's LWR nuclear power plants. Furthermore, in a public hearing held by the U.S. Senate Foreign Relations Committee on March 17, 2016, the U.S. Assistant Secretary of State expressed concerns over plutonium extracted in reprocessing the spent fuel of Japan's nuclear power plants. These remarks were addressed to Japan by nuclear disarmament experts, the disarmament ambassador of the nuclear-weapon state which possesses as many as 250 nuclear weapons under the Nuclear Non-Proliferation Treaty (NPT), and the high-ranking government official of the state which knows everything about the properties of uranium and plutonium, having conducted as many as 1,032 nuclear tests in the atmosphere, undersea, and underground. These remarks were not necessarily made for the first time – some of them were old but restated. Even the nuclear weapons and national defense experts did not seem to understand the properties of reactor-grade plutonium; or if they did understand the properties correctly, they probably gave these statements for political reasons. We do not know the background of the statements for certain; but in either case, statements of these kinds from such experts and politicians were really surprising.
The U.S. conducted a nuclear test in 1962 at Nevada Test Site, using reactor-grade plutonium, that is, plutonium extracted from nuclear power plants. The U.S. made public the results of the test on June 27, 1994, nearly 30 years after that. It is more realistic to conceive that all nuclear-weapon states conducted similar tests rather than to consider that only the U. S. did this kind of nuclear test; and, that country made public the fact, either based on the federal Freedom of Information Act (enacted in 1967) or with some political intention toward nuclear non-proliferation.
The publicized information revealed the result of the successful underground nuclear test, which confirmed the feasibility of manufacturing nuclear explosives with the yield of less than 20 kilotons using reactor-grade plutonium. Furthermore, it states that this fact had been declassified as early as in July 1977, which was 15 years after the nuclear test, suggesting that the information had been considered not as important as that must be kept classified indefinitely.
This publicized data also recorded the question and answer sessions with mass media held on June 27, 1994 upon this announcement. A spokesperson for the U.S. Department of Energy, responding to a question from the media, told them that the U.S. government regarded plutonium containing no more than 7% plutonium-240 as weapon-grade, which had been actually used in making nuclear weapons. The radioactivity of reactor-grade plutonium (this announcement did not contain any information about the specific content; but, it seemed to indicate plutonium containing greater than 20% plutonium-240) was extremely high, which made it hard to design and manufacture weapons as well as to store it. It was expected to increase radiation exposure to military service personnel, requiring much larger facilities for remote handling, etc. For these reasons, it concluded that reactor-grade plutonium was not suitable for the use in nuclear weapons.
The spokesperson did not disclosed the composition of plutonium used in this test in view of concern over nuclear non-proliferation, but mentioned the supply source; the plutonium used in this test was provided by the UK. The nuclear power plants in operation in the UK before 1962, the year in which this test was conducted, were Calder Hall Nuclear Power Station (60 MW x 4 reactors) and Chapelcross Nuclear Power Station (60 MW x 4 reactors). They both had a type of reactor called Magnox, which was a carbon dioxide cooled, graphite moderated reactor, fueled with natural uranium. These two were built as military facilities, to produce electricity using heat generated while producing plutonium for nuclear weapons (both stations were shut down in 2003-2004).
The U.S. is believed to have conducted this underground nuclear test using plutonium of these Magnox reactors provided by the UK. Since then, the country did not seem to have conducted nuclear tests using plutonium extracted from LWRs. Perhaps the U.S. government have considered further tests unnecessary.
It is estimated that at present, the five nuclear weapon-states designated under the NPT -the U.S., Russia, China, the UK, and France- possess close to 10,000 nuclear warheads in total and the other de facto nuclear weapon-states possess about 300 nuclear warheads. To maintain the prestige of being nuclear weapon-states, they must keep a large number of nuclear weapons with great care in a safe management in the future as well. On top of that, they will also have to bear an enormous amount of associated cost and work, such as those for periodical maintenance and material and parts replacement, in order to ensure the safety of nuclear materials and related complicated devices.
If you are lavish of time and money, you will probably be able to build “devices” that induce nuclear explosions even with reactor-grade plutonium; however, such devices will likely to be bulky ones equipped with secure radiation protection and cooling devices that are rarely found in general nuclear weapons. Moreover, reactor-grade plutonium, containing a great amount of plutonium-240, which undergoes spontaneous fission, is likely not only to deteriorate more precious plutonium-239 but also to destruct itself by self-detonation. No country or organization has ever been willing to make such bulky and potentially dangerous devices and keep them for a long time; and we do not expect to see countries willing to do such an absurd thing in the future as well. Reactor-grade plutonium can only be re-used as fuel for generating electricity – or rather, we should use our technology to transmute non-fissile uranium-238, which accounts for 99.3% of natural uranium resources, into fissile fuel plutonium and then use it for generating electricity. This is the foundations of peaceful uses of nuclear energy.
Nuclear weapons will never be made from plutonium extracted from LWR fuels. This principle was manifested by the US-DPRK Agreed Framework signed in October 1994, where North Korea agreed to freeze and dismantle its graphite-moderated reactor which was constructed in its homeland. Within this framework, the Korean Peninsula Energy Development Organization (KEDO) was established in March 1995 jointly by Japan, U.S., and South Korea, and in return for the above-mentioned obligation, the construction of two LWRs with a capacity of 1,000 MW each was started in North Korea. This framework also provided annual 500,000 tons of crude oil for North Korea until the completion of the construction. However, as you know, following the declaration of the possession of nuclear weapons by North Korea in February 2005, KEDO in November 2005 suspended the LWR construction, 34.5% of which work had been advanced by then. If nuclear weapons can be made from plutonium extracted from the spent fuels of LWR, the U.S. should not have entered into the agreement of building the LWRs in North Korea in the first place.
While coping with the increasing world population, we have to tackle with economic development, opportunity of education, and improvement of healthcare and welfare services in developing countries. And it is essential to maintain stable energy supply more than ever for these purposes. Besides that, to alleviate global warming, which has been becoming obvious along with increased consumption of fossil fuels, and to prevent overconsumption of oil, a fair share of which should be left for our future generations, the utilization of nuclear power and renewable energy sources must be increased. The nuclear power development policy must not be shortsighted; that is, the energy policy must not be chosen by the preference of some groups of people in advanced industrialized countries, because of anti-nuclear power movement, or for the benefit of particular political parties.
Necessity of nuclear power not only comes from the energy policy. To accomplish the abolishment of nuclear weapons, which has long been the hope of mankind, various measures must be taken, including the bestowment of the Nobel Peace Prize. Ultimately, fissile materials of dismantled nuclear weapons must be eliminated in one way or another. The most efficient method for eliminating fissile materials is to consume them as fuels in nuclear power stations. Nuclear power stations in the U.S. have already implemented a project that consume Russian fissile materials as fuels.
To promote future global energy policy and accomplish the abolishment of nuclear weapons, uses of present LWRs must be promoted. The advocacy that nuclear weapons can be made from plutonium extracted from electricity generating power reactors would be a too innocent notion; and it would be a shame to take advantage of such oversimplified non-nuclear logic and use it as a political agenda. We must end this kind of nonsense. Nuclear disarmament experts and politicians in nuclear-weapon states should have already known what we say here.