Between 1971 and 1974, a group of 15 States - some already parties to the Nuclear Non-Proliferation-Treaty (NPT), others prospective parties - held a series of informal meetings in Vienna chaired by Professor Claude Zangger of Switzerland. As suppliers or potential suppliers of nuclear material and equipment, their objective was to reach a common understanding on:
(a) the definition of what constituted "equipment or material especially designed or prepared for the processing, use or production of special fissionable material" (as it was not defined anywhere in the Treaty);
(b) the conditions and procedures that would govern exports of such equipment or material in order to meet the obligations of article III, paragraph 2 of the NPT, on a basis of fair commercial competition.
The group, which came to be known as the Zangger Committee, decided that its status was informal and that its decisions would in themselves not be legally binding upon its members. Decisions of the Committee are taken by consensus.
In 1972, the Committee reached consensus on basic "understandings" contained in two separate memoranda. These memoranda form the guidelines of the Zangger Committee today. Each memorandum defines and provides for procedures for the export of materials and equipment described in article III, paragraph 2; the first memorandum on source and special fissionable material (article III, para. 2 (a)), the second on equipment and material especially designed or prepared for the processing, use or production of special fissionable material (article III, para. 2 (b)).
The Zangger Committee Understandings reflect the requirements laid down in article III, paragraph 2. There are three conditions of supply:
(a) For exports to non-nuclear-weapon States, source or special fissionable material either directly transferred, or produced, processed, or used in the facility for which the transferred item is intended, shall not be diverted to nuclear weapons or other nuclear explosive devices;
(b) For exports to non-nuclear-weapon States, such source or special fissionable material, as well as transferred equipment and non-nuclear material, shall be subject to safeguards under an agreement with the International Atomic Energy Agency (IAEA);
(c) Source or special fissionable material, and equipment and non-nuclear material shall not be re-exported to a non-nuclear-weapon State unless the recipient State accepts safeguards on the re-exported item.
The understandings were formally accepted by individual States members of the Committee in an exchange of notes among themselves. These amounted to unilateral declarations that the Understandings would be given effect through respective domestic export control legislation. In parallel with this procedure, most member States wrote identical letters to the Director General of the IAEA informing him of their decision to act in conformity with the conditions set out in the Understandings and asking him to communicate their decision to all States members of the IAEA. He did so in INFCIRC/209, dated 3 September 1974.
The two memoranda became known as the "trigger list", since the export of listed items "triggers" IAEA safeguards.
Attached to the trigger list is an annex "clarifying", or defining, the equipment and material of memorandum B in some detail. The passage of time and successive developments in technology have meant that the Committee is periodically engaged in considering possible revisions to the trigger list, and the original annex has thus become increasingly detailed. To date, eight clarification exercises have taken place. Clarifications are conducted on the basis of consensus, using the same procedure followed in the adoption of the original understandings.