VIENNA, Feb 26 (Reuters) - Iran's surprise announcement it will have to remove fuel from its first nuclear reactor suggests a new setback for its atomic ambitions, but the reason for the unusual step and how long it may take remain unclear.
"It is significant. Unloading unspent fuel is a rare occurrence in the nuclear industry," said a senior Western diplomat familiar with the issue.
The U.N. nuclear watchdog said in a report obtained by Reuters on Friday it had been informed by Iran that it would take fuel assemblies out from the core of the Russian-built Bushehr reactor, just a few months after they were loaded.
The International Atomic Energy Agency (IAEA) did not give details in its document, which came a month after Russia warned that an attack by a computer virus known as Stuxnet could have triggered a Chernobyl-style disaster at Bushehr.
Experts said the fuel measure may cause further delays for the plant, a flagship project which Iran has said would start producing electricity early this year and which it says is proof of the peaceful nature of its nuclear programme.
"Unloading fuel from a reactor core which has already reached the stage of criticality is unusual, pointing towards possible problems with the fuel itself," Olli Heinonen, former head of IAEA inspections worldwide, told Reuters.
If the issue was caused by a leaking fuel assembly and this was known, it would not take much time, he said.
"But if it turns out to be a quality problem or if other vital equipment is broken or malfunctioning, it may take a long time," Heinonen, now at Harvard University, said.
MONTHS OF DELAY?
Iran’s nuclear envoy Ali Asghar Soltanieh told the ISNA news agency that Russian engineers had advised the fuel be unloaded for tests, and that it would later be put back. The head of the plant said it was happening for safety reasons.
Last week, state media quoted Iranian Foreign Minister Ali Akbar Salehi as saying that the 1,000 megawatt reactor on Iran’s Gulf coast was undergoing tests and that "everything is ready to produce electricity in the near future".
Bushehr was begun by Germany’s Siemens in the 1970s, before Iran’s Islamic revolution. Russia later took over the $1 billion project and supplied the fuel for the reactor, which has yet to start injecting power onto Iran’s national grid.
Mark Hibbs, a nuclear expert at the Carnegie Endowment for International Peace, said Bushehr may have a problem with equipment in its primary cooling circuit.
"At Bushehr there is a critical interface in this area between equipment supplied by German industry and equipment supplied by the Russians," Hibbs said.
"If there is a problem in that equipment … that could delay the start-up of the unit for a few months."
A senior Iranian atomic energy official said earlier this month the country should investigate claims that the Stuxnet computer worm, which security analysts suspect targeted Iran’s nuclear programme, had caused major harm to Bushehr.
That came after a senior Russian official warned that Stuxnet could have triggered a nuclear disaster on the scale of Chernobyl, referring to the 1986 nuclear accident at a plant in Ukraine, then part of the Soviet Union.
SAFETY PROBLEMS?
Many analysts believe Stuxnet was a cyber attack by the United States and Israel aimed at disabling Iran’s nuclear equipment and slowing down a programme they suspect is aimed at making nuclear weapons, something Tehran denies.
Iranian officials have confirmed Stuxnet hit staff computers at Bushehr but said it did not affect major systems.
But the Institute for Science and International Security, a Washington-based think-tank, said it did not believe the Bushehr fuel issue was related to Stuxnet.
Instead, it said the fuel development possibly confirmed reports of "safety problems or equipment failures at the reactor, which could significantly delay its start".
Experts say that firing up Bushehr will not take Iran any closer to building a nuclear bomb since Russia will supply the enriched uranium for the reactor and take away the spent fuel that could be used to make weapons-grade plutonium.
A Vienna-based official with knowledge of the Iran nuclear issue predicted that the unloading of the fuel would take place in the next few days.
Heinonen, who stepped down from his IAEA post in August, said the issue could be embarrassing for the Russian operator of Bushehr, Rosatom.
Full responsibility for the plant is only "supposed to be turned over to the Iranians after the first refuelling which is estimated to take place perhaps two years from now", he said.
