High levels of radiation resulting from the Chernobyl disaster are detected at Forsmark Nuclear Power Plant in Sweden, leading Soviet authorities to publicly announce the accident.

On 26 April 1986, the no. 4 reactor of the Chernobyl Nuclear Power Plant, located near Pripyat, Ukrainian SSR, Soviet Union, exploded. With dozens of direct casualties, it is one of only two nuclear energy accidents rated at the maximum severity on the International Nuclear Event Scale, the other being the 2011 Fukushima nuclear accident. The response involved more than 500,000 personnel and cost an estimated 18 billion rubles. It remains the worst nuclear disaster and the most expensive disaster in history, with an estimated cost of US$700 billion.

Forsmark Nuclear Power Plant is a nuclear power plant in Forsmark, Sweden that provides 14% of Sweden's total electricity output, and also the site of the Swedish Final repository for radioactive operational waste. It is operated by a company mainly owned by Vattenfall.

April 28 is the 118th day of the year in the Gregorian calendar; 247 days remain until the end of the year.