The companies are initially required to examine the reactor vessels, and decide whether the reactor vessels need to undergo further testing, and then submit a report to authority covering the outcome of their review and an assessment on any testing that might be needed by June 30, 2015.

The decision is a consequence of the manufacturing flaws discovered at two Belgian nuclear power reactors Doel 3 and Tihange 2 the summer of 2012.

Swedish Radiation Safety Authority section head Lars Skanberg said the defects at the Belgian reactors are due to flaws from manufacturing the material used in the reactor vessels.

"Now we want the power companies to investigate whether similar flaws are present in the material used to manufacture O3 and F3," Skanberg added.

Meanwhile, Ringhals which operates the third nuclear power plant in Sweden, has not been issued an order by the Authority since the company has already performed a review of manufacturing documentation in addition to testing of Ringhals 2.

The company is also planning to examine and test the Ringhals 3 and 4 reactor vessels.