The Arak heavy water nuclear reactor in Iran will be capable of producing two nuclear bombs' worth of weapons grade plutonium a year and will be capable of producing the material by next summer, according to a Wall Street Journal report on Monday that cited US, UN and EU officials.
Progress at Arak could complicate international efforts to negotiate with Iran on its suspected nuclear arms program and it also "heightens the possibility of an Israeli strike on the site," the report stated, citing officials.
According to the report, US and the West has been focused mainly on Iran's program to enrich uranium and that the issue of plutonium, that can also serve as a material for an explosive devise, took some officials by surprise.
Regarding the capabilities of the Arak reactor, the report quoted an official based at the IAEA's Vienna headquarters who said that it "really crept up on us."
The Wall Street Journal report stressed that a site like Arak was more vulnerable to attack compared to Iran's other enrichment facilities at Natanz and Qom.
"There's no question that the reactor and its heavy water are more vulnerable targets than the enrichment plants," the report quoted Gary Samore as saying, a former top adviser on nuclear issues to US President Barack Obama.
"This could be another factor in [Prime Minister Binyamin] Netanyahu's calculations in deciding how long to wait before launching military operations," Samore added.
The report cited current and former US officials who said an Israeli strike on Arak would likely have to take place prior to Iran introducing nuclear materials into the facility, in order to prevent an enormous environmental disaster.
Echoing this concern about the consequences of attacking a nuclear facility was a senior Israeli security official.
"Whoever considers attacking an active reactor is willing to invite another Chernobyl," former Israeli military intelligence chief Amos Yadlin said last month, referring to the 1986 Soviet reactor accident which sent radioactive dust across much of Europe. "And there is no one who wants to do that."
In May, Netanyahu said that Iran's work on a heavy-water reactor to build a plutonium-based bomb and its nuclear enrichment program was "the biggest challenge of our time.”
The Islamic Republic claims its nuclear program is peaceful, and insists it will use the Arak facility to make isotopes for medical and agricultural use.
Reuters and Tovah Lazaroff contributed to this report.
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