Reactor grade plutonium nuclear test

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The reactor grade plutonium nuclear test was a low-yield underground nuclear test using non-weapons-grade plutonium, conducted at the US Nevada Test Site in 1962.

Some information regarding this test was declassified in July 1977 under instructions from President Jimmy Carter as background to his decision to prohibit the nuclear reprocessing of spent nuclear fuel.

The plutonium used was manufactured in a Magnox reactor in the United Kingdom, and provided to the US under the 1958 US-UK Mutual Defence Agreement. Its isotopic composition has not been disclosed, other than the description reactor grade. However the DOE definition of reactor grade changed in 1976, and it has not been disclosed which definition was used in describing the material for this test as reactor grade.

Up until 1976, two grades were recognised:
- Weapons grade, less than 7% Pu-240.
- Reactor grade, 7% or more Pu-240.

From 1976, three grades were recognised:
- Weapons grade, less than 7% Pu-240.
- Fuel grade, 7% to 19% Pu-240.
- Reactor grade, more than 19% Pu-240.

The difference is important in assessing the significance of the test in the context of nuclear proliferation. Fuel grade plutonium is not recovered by the proposed reprocessing of spent PWR and BWR fuel, while reactor grade material (as defined since 1976) is.

To overcome the ambiguity of the term reactor grade, some authorities describe the test as being of non-weapons-grade plutonium.