Voluntary Offer Agreements are bilateral agreements between a nuclear weapons state and the IAEA. Each of the five nuclear weapons states has concluded a VOA with the IAEA. In a VOA, the NWS is able to essentially delineate non-military facilities and materials to be under IAEA safeguards. The specified facilities and materials are subject to inspections, similar to those in NNWS. 

"The five NPT nuclear-weapon States have concluded safeguards agreements covering some or all of their peaceful nuclear activities. Under the Voluntary Offer Agreements (VOAs), facilities are notified to the IAEA by the State concerned and offered for the application of safeguards. The IAEA applies safeguards under VOAs to nuclear material in selected facilities."

Source: IAEA

Voluntary Offer Agreements with NPT Declared Nuclear Weapon States
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