Additional Information Concerning Underground Nuclear Weapon Test ofReactor-Grade Plutonium

U.S. Department of Energy, Office of the Press Secretary, Washington, DC20585

Additional Information Concerning Underground Nuclear Weapon Test ofReactor-GradePlutonium

Table of Contents

Who Are the Key Stakeholders?
Questions and Answers

The Department of Energy is providing additional information related toa 1962 underground nuclear test at the Nevada Test Site that usedreactor-grade plutonium in the nuclear explosive.


  • A successful test was conducted in 1962, which used reactor-gradeplutonium in the nuclear explosive in place of weapon-grade plutonium.
  • The yield was less than 20 kilotons.


  • This test was conducted to obtain nuclear design informationconcerning the feasibility of using reactor-grade plutonium as thenuclear explosive material.
  • The test confirmed that reactor-grade plutonium could be used tomake a nuclear explosive. This fact was declassified in July 1977.
  • The release of additional information was deemed important toenhance public awareness of nuclear proliferation issues associated withreactor-grade plutonium that can be separated during reprocessing ofspent commercial reactor fuel.
  • The United States maintains an extensive nuclear test data baseand predictive capabilities. This information, combined with theresults of this low yield test, reveals that weapons can be constructedwith reactor-grade plutonium.
  • Prior to the 1970's, there were only two terms in use to defineplutonium grades: weapon-grade (no more than 7 percent Pu-240) andreactor-grade (greater than 7 percent Pu-240). In the early 1970's, theterm fuel-grade (approximately 7 percent to 19 percent Pu-240) came intouse, which shifted the reactor-grade definition 19 percent or greaterPu-240.


  • As part of the Secretary of Energy's Openness Initiative, theDepartment of Energy is providing additional information regarding a1962 underground nuclear test that used reactor-grade plutonium. As aresult, the American public will have information that is important tothe current debate over nonproliferation issues associated withreactor-grade plutonium that can be separated during spent fuelreprocessing and the importance of international safeguards. Therelease of this information should encourage other nations to declassifysimilartestinformation.
  • This information will be useful in the international arena indefining the nonproliferation regime for separated reactor-gradeplutonium. It will be useful in confirming and underpinning therequirements for international safeguards.
  • This information will correct erroneous statements made elsewhereabout the potential use of reactor-grade fuel for nuclear weapons.

Who Are the Key Stakeholders?

  • The Public. This information will be useful to nonproliferationpublic interest groups who are debating nuclear proliferation issues.
  • Public Interest Organizations. Stakeholders includeenvironmental, safety and health groups, historians, archivists,researchers, scientists, and industrial workers, as well as State andFederal personnel. Those interested in oversight of nuclear weaponstesting related activities will have additional information regardingthe nuclear test of reactor-grade plutonium. Public interestorganizations which have expressed such an interest include (but are notlimited to): Energy Research Foundation, Environmental InformationNetwork, Friends of the Earth, Greenpeace, Institute for Science andInternational Security, League of Women Voters, Military ProductionNetwork, National Association of Atomic Veterans, National SecurityArchive, Natural Resources Defense Council, Nevada Desert Experience,Nuclear Control Institute, Physicians for Social Responsibility,Plutonium Challenge, Sierra Club, University of Sussex/England, and theWestern States Legal Foundation.
  • Environmentalists. With this declassification, those interested inenvironmental oversight of plutonium related activities will haveadditional information regarding the utility of reactor-grade plutonium.Those interested include Greenpeace, Institute for Science andInternational Security, Nuclear Control Institute and the University ofSussex, England.


U.S. Department of Energy
Office of Public Affairs
Contact: Sam Grizzle
(202) 586-5806

U.S. Department of Energy, Office of the Press Secretary, Washington, DC20585


Q. Why wasn't the exact yield of the event released?

A. Revelation of the yield was determined to be of value to certainproliferants.

Q. What was the quantity of reactor-grade plutonium used in the test?

A. In this circumstance, specific information would be of benefit tocertain proliferants and is not releasable.

Q. What is the grade of plutonium used in U.S. nuclear weapons?

A. The United States uses weapon-grade plutonium. Weapon-gradeplutonium is defined as plutonium containing no more than 7 percentplutonium-240.

Q. Why is weapon-grade plutonium better than reactor-grade plutonium inweapons?

A. Reactor-grade plutonium is significantly more radioactive whichcomplicates its use in nuclear weapons.

Q. If this was a successful test as you indicate, why didn't the UnitedStates use reactor- grade plutonium in nuclear weapons?

A. Reactor-grade plutonium is significantly more radioactive whichcomplicates the design, manufacture and stockpiling of weapons. Use ofreactor-grade plutonium would require large expenditures for remotemanufacturing facilities to minimize radiation exposure to workers. Reactor-grade plutonium use in weapons would cause concern overradiation exposure to military service personnel. In any event, PublicLaw 97-415 prohibits United States defense use of plutonium produced inlicensed facilities, i.e., commercial reactors.

Q. What was the source of the reactor-grade plutonium?

A. The plutonium was provided by the United Kingdom under the 1958United States/United Kingdom Mutual Defense Agreement.

Q. What was the actual plutonium isotopic composition used in thistest?

A. It is the policy not to reveal the actual isotopic composition ofplutonium used in specific weapons or tests to prevent releasinginformation which may be of assistance to proliferants.

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