Jeffrey LewisSpecial Fissionable Materials

Only very rarely do I receive e-mail that makes me say: “Wow, that is an obscure question.”

Eric Hundman from CDI e-mailed me to ask whether the term “special fissionable materials”—which appears in the NPT—had a specific definition. I dimly recalled something about the Zangger Committee, the 1970s, pet rocks and bell bottoms. I pointed him in the direction of several individuals who might have possessed one or both of the latter items, as well as the answer.

Eric tracked down the evolution of the term, which provides an interesting story.

Caution: only for the wonkiest of wonks, those who drool over definitions like “source materials,” “States party,” or “instruments of ratification.”

Earlier this summer I was reading through the (surprisingly short) text of the Nonproliferation Treaty, when I came upon some terms that puzzled me:

Each State Party to the Treaty undertakes not to provide: (a) source or special fissionable material, or (b) equipment or material especially designed or prepared for the processing, use or production of special fissionable material, to any non-nuclear-weapon State for peaceful purposes, unless the source or special fissionable material shall be subject to the safeguards required by this article (emphasis mine).

These terms are not defined anywhere else in the text of the NPT, so a quest ensued to track down their origins. The actual definitions, quoted later in this post, are enshrined in the Statute of the International Atomic Energy Agency, but the route they took to get into the NPT was –- in typical diplomatic fashion –- long and winding.

In 1955, a year after Eisenhower’s Atoms for Peace initiative and the passage of the Atomic Energy Act, the United States began drafting statutes for the organization that would soon become the IAEA. The first draft was finished by the US alone; the text was then circulated to seven other nations: Australia, Belgium, Canada, France, Portugal, South Africa, and the United Kingdom. Comments and concerns from these countries –- states which had been instrumental in the development of the bomb –- were incorporated into a new draft. That text was submitted to the Soviet Union for consideration in 1955.

A debate on the proposal ensued at the United Nations. Eventually, the member states decided to hold an international conference the following year (1956) to debate and hopefully finalize the Statute of the IAEA.

Meanwhile, the US held a “drafting session” from February to April 1956 –- the eight countries originally consulted on the text were invited again, but this session also included Brazil, Czechoslovakia, India, and the Soviet Union.

At the Conference in the fall of 1956, France and India joined in an attempt to exempt “source materials” from the Agency’s proposed controls. The attempt failed, ultimately, and the language on inspections and controls was passed with only slight revisions. The Conference ended with the signing of the IAEA Statute, which incorporated the following definitions of “special fissionable material” and “source material:”

ARTICLE XX: Definitions

As used in this Statute:

1. The term “special fissionable material” means plutonium-239; uranium-233; uranium enriched in the isotopes 235 or 233; any material containing one or more of the foregoing; and such other fissionable material as the Board of Governors shall from time to time determine; but the term “special fissionable material” does not include source material.

2. The term “uranium enriched in the isotopes 235 or 233” means uranium containing the isotopes 235 or 233 or both in an amount such that the abundance ratio of the sum of these isotopes to the isotope 238 is greater than the ratio of the isotope 235 to the isotope 238 occurring in nature.

3. The term “source material” means uranium containing the mixture of isotopes occurring in nature; uranium depleted in the isotope 235; thorium; any of the foregoing in the form of metal, alloy, chemical compound, or concentrate; any other material containing one or more of the foregoing in such concentration as the Board of Governors shall from time to time determine; and such other material as the Board of Governors shall from time to time determine.

Straightforward enough, I suppose. The NPT, though, entered into force in 1970 without a comparable definition of “special fissionable materials.”

In 1971, fifteen states began meeting in Vienna to clarify vague phrases in the treaty text; one that they specifically hoped to define was “equipment or material especially designed or prepared for the processing, use, or production of special fissionable material.” The fifteen states, while not all parties to the treaty, were either suppliers or potential suppliers of nuclear material and equipment. The meetings where chaired by Professor Claude Zangger of Switzerland, and the group eventually came to be known as the Zangger Committee (it persists today to help interpret certain portions of the NPT).

The members of the Zangger Committee reached agreement in 1974 on, among other things, the NPT’s definition of “special fissionable material!” Apparently without drama, they simply decided to adopt the definition laid forth in the IAEA statute. Boring, perhaps, but eminently pragmatic.

To enact their decision, the states on the Committee, essentially, declared that they would each implement national legislation according to the agreement. Then, they asked the Director General of the IAEA to convey their decision to all members of the Agency. He did so in a document titled, dully, INFCIRC/209 –- eventually it was called by a slightly sexier name, the “trigger list.”

Subsequent NPT review conferences slowly incorporated the trigger list as part of the NPT canon. The final document of the 1975 Review Conference referenced the Zangger Committee’s work, but did not mention the Committee itself by name. The 1990 Review Conference did not adopt a final document, but the States party to the treaty were urged by the Committee to adopt the trigger list (which by that time had gone through several revisions).

So, 20 years after it entered into force, the NPT gained a working definition of “special fissionable materials.” If you’ve read this far, give yourself a pat on the back: you’ve waded even deeper into wonkhood.


  1. Robot Economist (History)

    When I first stepped up to the history of the NPT and Zangger Committee, the “special fissionable material” term was a little alien at first.

    It made sense pretty quickly though. The States-Parties needed a way to distinguish between uranium ore, enriched uranium, and plotonium. I imagine this was mostly to define the boundaries of IAEA activity.

    I imagine that the Kennedy administration made reference to the term when drafting the NPT out of convenience.

  2. Alex (History)

    The AEA of 1946 refers only to “fissionable materials,” whereas the AEA of 1954 uses “special nuclear material” to refer to Pu, U-235, and U-233. It’s interesting that “special” became used there whereas it is not in the AEA of 1946 — it is not really a new word to be using in terms of atomic energy; the “S” in the “S-1 Committee” (the designation of the Uranium Committee inside of the NDRC during World War II, pre-OSRD), stood for “special” as well. But why it vanished from the AEA of 1946 and re-appeared later I have no idea. At first I thought it would be used to differentiate weapons-grade from reactor-grade material, but the only differentiation I see is between “source” and “special nuclear.”

    According to “Atoms for Peace and War”: “To reflect recent accomplishments in developing thermonuclear weapons, the committee substituted the words ‘special nuclear materials’ for the more limited phrase ‘fissionable materials’ wherever it appeared in the bill. The revised languge of Section 51 would permit the Commission to declare other materials such as tritium or deuterium to be special nuclear materials of it so desired.”

    So why back away from that definition to the more limited “fissionable,” while preserving the “special”? Very odd.

    On the subject of language, I stumbled across a fairly entertaining article awhile back on the difficulties of translating the word “warhead” into Russian (it can mean the entire front of a missile in Russian, not just the explosive charge, which has obvious effects for interpreting dismantlement treaties). I thought it was fairly interesting—somewhere at the bottom of it there is some (empty) Derridean point to make about language, though lord knows I’m not the one who is going to make it. For the interested, “Just what exactly is a warhead?” (1998) is online at:

  3. luca (History)

    As I recall, the Russian euphanism is “battle block”

  4. Andrew Foland (History)

    In the world of contraband screening & detection the term “special nuclear material” is nearly always used in preference to “fissionable”, but the list is the same.

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