It as never been illegal to perform nuclear research in Sweden. Between 1988 and 2006 it was illegal to perform preparatory actions for building nuclear power plants (in addition to actually building them, after the 1980 referendum vote). It was commonly referred to as "tankeförbudet" (a pejorative term, close to "illegal thoughts"). The law was removed 2006, one of the reason was this common misconception.

However, ABB created and exported (among others) the BWR90+ during the nineties, proving your statement wrong. You can read about it in the newspaper about how it iw popular to study nuclear power again (article from 2010). http://www.dn.se/nyheter/politik/karnkraft-hett-pa-universit...