My first guess was this was somehow related to environmental groups, but Swedish news is full of speculation and much talk about former terrorist usages of TATP. Two people have been arrested and OKG is reviewing the man's history in their employment.
A Swedish contractor was arrested on Wednesday when traces of highly explosive material were found on him as he was about to enter a nuclear power plant in southern Sweden, police and the plant said.
"At 8am we received a call from the nuclear plant at Oskarshamn. They told us one worker was stopped in the control. He had explosive material in his bags," Sven-Erik Karlsson of the Kalmar county police told AFP.
The company that operates the Oskarshamn plant, OKG, meanwhile said the man's bags contained "no visible illegal substances" but routine tests at the entrance to the plant "detected traces of explosives."
"We can see that our security routines functioned properly," the managing director of OKG, Lars Thuring, said in a statement, adding that the plant was collaborating with police.
Karlsson said the man, who was being interrogated by police, was a welder hired for temporary purposes, but could provide no further details on his age nor his background.
"The explosive material has been taken care of by ... police and apparently it is highly explosive, probably TATP," Karlsson said.
TATP is relatively easy to make and has surfaced in a number of recent terrorism investigations, including bombings in the Middle East and the London bombings in July 2005.
Source: The Local (English), h/t Tundra Tabloid
Two welders have been arrested, though not many details are being released. The men were born in 1955 and 1962. They had entered the nuclear plant several times in the past and moved about freely there. It is unclear whether they had managed to bring in explosives in to the plant in the past.
One of the men is registered by the police, but both had gone through security police checks before starting to work at the plant.
Source: Expressen , Aftonbladet (Swedish)