Highly enriched uranium is used in US and UK navy nuclear reactors, not just for weapons

It is also used in some civilian ones. Iran could be telling the truth when they say their enrichment program is for peaceful uses. 

S9G reactor - Wikipedia

Rolls-Royce PWR - Wikipedia

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The reactor fuel was highly enriched uranium (HEU) enriched to between 93% and 97%. Each nuclear core had a life of about 10 years, so had to be refueled about twice during the lifetime of a submarine.

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Weapons-grade nuclear material - Wikipedia

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 Highly enriched uranium is considered weapons-grade when it has been enriched to about 90% U-235.

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