World powers have been working for years to limit Iran's nuclear activities. But news reports often fail to provide details of the nuclear negotiations. Today we explore some of the issues that the negotiators have been discussing.

Iran agreement targets machinery

Western countries have targeted the equipment that Iran needs to produce plutonium and enriched uranium. Both materials are needed to make a nuclear weapon.

Not just any uranium can be used. The metal must be purified, or enriched. It is first changed into a gas. Workers then place the gas into a machine called a centrifuge. The centrifuge makes the gas spin at very high speeds. The spinning creates the enriched uranium required at nuclear power centers. But if the gas is put in centrifuges for long periods, it becomes enriched at a much higher level. This highly-enriched uranium can be used in nuclear weapons.

Under the agreement, Iran will still have the ability to make fuel for its nuclear reactors. But it will not be permitted to enrich uranium for use in nuclear weapons.

In April, Iran agreed to a limit of about 6,000 centrifuges. Iran also said it would only enrich uranium at very low levels -- under five percent. The country promised to store no more than 300 kilograms of this "low-enriched" uranium.

The April agreement limited research on ways to improve centrifuge designs. It also covered Iran's ability to produce plutonium, the other bomb-making material. It required the redesign of a nuclear reactor, so that it can use natural uranium, instead of the enriched kind.

Natural uranium is nearly all U238, the heavier form of the element. When a neutron strikes this form of uranium, the atom will change into plutonium. This "heavy-water" reactor can produce radioactive chemicals used to treat cancer. When the redesign is completed, it will still make those chemicals, but produce much less plutonium.

The plutonium formed in the reactor must still be separated from the rest of the fuel. Iran says it will ship "spent" fuel out of the country.

Under the new deal, Iran has agreed to increased international inspections of its nuclear activities. The country is also required to provide detailed information on all its nuclear activities within three months. Western powers have agreed to lift trade restrictions on Iran. They will also return control of billions of dollars to Iran as soon as it meets the requirements of the agreement.

US officials react to the deal

In Washington, President Barack Obama said on Wednesday that the agreement stops Iran from building a nuclear weapon. He said it will make the United States, its allies and the world, "safer and more secure."

Some members of Mr. Obama's party do not support the agreement. And most of his political opponents strongly oppose it. When members of Congress are given the agreement, they will have 60 days to decide whether to reject it. The president has said if they do, he will veto the rejection. The votes of at least two-thirds of lawmakers are needed to cancel his veto.

I'm Christopher Jones-Cruise.

This story was based on reports from VOA science correspondents Steve Baragona and George Putic. Christopher Jones-Cruise adapted their stories for Learning English. George Grow edited this report.

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spin – v. to turn or move around in circles

reactor – n. a device that produced nuclear energy

radioactive – adj. possessing or producing radiation

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