On 26 April, a disastrous nuclear power plant accident at the Chernobyl site in the USSR destroys unit-4 of the reactor, causes deaths and injuries, and releases radiation across national boundaries; it is first internationally detected and reported by experts in Sweden and Finland. In August, the IAEA becomes the site for post-accident review conference, which provides the world's first authoritative account of the accident. The IAEA's Laboratories are mobilized to analyze and assess Chernobyl's radiological impact. In September, following work of preparatory groups of experts, IAEA Member States adopt two international safety conventions on early notification of a nuclear accident and emergency assistance and response, and endorse an expanded nuclear safety programme. An Emergency Response System is set up in support of the conventions. In December, the Rarotonga Treaty enters into force, for establishing a nuclear-weapon-free zone in the South Pacific and requiring IAEA safeguards.