* Radiation may be detectable in Europe in a week
* Background radiation adds premium to pre-1945 steel By Alister Doyle, Environment Correspondent
OSLO, March 18 (Reuters) - Harmless traces of Japan's nuclear accident may reach Europe in a week's time, part of a normally ignored background of radiation whose effects include a premium for pre-1945 steel such as in old shipwrecks. Fallout from the 1945 U.S. bombings of Hiroshima and Nagasaki and nuclear tests, along with accidents such as at Chernobyl in 1986, have spread a pervasive background of radiation around the globe.
"We expect that maybe in seven days from now we could detect some atoms, with very, very exact instruments here in Sweden," Klas Idehaag, reactor inspector at the Swedish Radiation Safety Authority, said on Friday.
"But it will be no effect on the environment or for people," he said.
Low-level leaks of radiation from the Fukushima plant in Japan, crippled by an earthquake and tsunami a week ago, have been detected on the U.S. west coast after crossing the Pacific, diplomatic sources said in Vienna on Friday.
Background radiation means that low-radiation steel made before 1945 is favoured for uses such as in sensitive medical equipment or geiger counters. Steel made since 1945 absorbs extra radiation from the atmosphere during production.
Major sources of old steel have included the German fleet scuppered in 1919 after World War One off Scotland.
"It has had a number of applications, including in measuring minute amounts of radiation," said Jude Callister, custodian of the Scapa Flow Visitor Centre and Museum in Scotland. After 1945 "the German steel acquired a premium".
In June 1919, the German naval commander ordered the scuppering of the interned High Seas Fleet to avoid capture by the British after World War One. Most of the 74 ships sank.
On Thursday, U.S. President Barack Obama said that he did not expect harmful levels of radiation to reach the United States from Japan. U.S. fear about the leak has pushed up demand online for potassium iodide antidotes and Geiger counters.
A major accident at the reactors, where workers are trying to cool crippled reactors, could spew dangerous radioactivity in Japan but is unlikely to end up as a global threat.
"We believe it won't have any health consequences for any countries except for Japan," said Ole Reistad of the Norwegian Radiation Protection Authority.
The International Atomic Energy Agency says that people also pick up radiation from sources such as x-rays, cancer therapy and from natural sources such as rocks containing thorium or unanium. Many homes have detectible amounts of radon.
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(Editing by Sonya Hepinstall)