Three months before the recent upsurge in tension with Tehran over its nuclear program, an Israeli think tank simulated fallout from what many here consider the unthinkable: an Iranian nuclear explosive test.

The results of the simulation, published this week, are not the Middle East doomsday that some here have warned of.

Rather than use the weapon to attack the Jewish state – as many Israeli leaders fear – the experts playing Iran leveraged the newly unveiled military power as a bargaining chip with the US and Europe. Those representing Israel played down the new threat.

"It doesn’t mean immediate war, and this can be a surprise," says Yoel Guzansky, a fellow at the Institute for National Security Studies, a think tank affiliated with Tel Aviv University. "The sky won't fall."

The simulation reflects an effort to grapple with "the day after," a taboo scenario that many Israeli leaders have suggested should by preempted by a military strike because it would mean an intolerable situation for Israel, which is a sworn enemy of Iran and lies within range of its missiles.

In the simulation, a role-playing exercise used to think through national security questions, Israel was played by a former national security adviser and former deputy foreign minister, while Iran was played by experts from the university and the intelligence community.

Meir Javedanfar, an Iranian expert based in Tel Aviv, says the simulation adds to a relatively new but growing idea among Israeli experts in a society where fears of a nuclear Iran have long dominated.

"It's becoming more acceptable that Iran acquiring a nuclear bomb will be like driving in Tel Aviv: It could be very dangerous but precautions can be taken to reduce the danger,’’ says Mr. Javedanfar.

But plenty of concerns remain. Just today, military planning division chief Maj. Gen. Amir Eshel warned of a "global nuclear jungle" if Iran acquired a nuclear weapon, an event he suggested would set off a global arms race.

The general also said that a nuclear Iran could also deter Israel from striking at Hamas and Hezbollah.

Escalating tensions

In recent weeks, concerns about the standoff have heightened as Iran threatened to close the Strait of Hormuz to oil-tanker traffic and an Iranian nuclear scientist was assassinated on the streets of Tehran.

That triggered Iranian accusations against Israel and pledges of retaliation against Israeli targets. In an apparent effort to defuse tension, Israel said on Monday that a missile-defense drill to be carried out jointly with the US planned for the coming weeks had been postponed.

There is little if any discussion in public that Israel, an undeclared nuclear power, might be compelled to become accustomed to a situation of mutual deterrence with Iran. Statements by Iranian President Mahmoud Ahmedinejad that Israel will be wiped off the map have prompted Israeli Prime Minister Benjamin Netanyahu and others to draw comparisons between Iran and Nazi Germany.

However, many consider this to be an inaccurate view of the Iranian leadership. The recently resigned chief of Israel's Mossad, Meir Dagan, recently suggested that Iranian strategy is not irrational and that its leaders might be sufficiently deterred from an attack by Israel’s capability to strike back.

'Game-changing' step

But the results of the simulation do suggest a "game change" for the Middle East, as had been expected.

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In the simulation, Saudi Arabia moved to acquire its own nuclear weapon. Israel considered for the first time a formal defense pact with the US, while keeping the option open of a military strike against a nuclear Tehran. Iran decided to use its new status to get economic sanctions lifted in return for a promise not to use the weapon.

"It’s a political tool," says Mr. Guzansky. "I think that Iran is rational, although it’s a different type of rationality than ours."