Can/Could/Will/Would

Can please explain to me why is it could/would here and not can/will ? ( I use could to talk about the past only ( like Could lift heavy things we I was young now I can't anymore ) , but here the reactor probably still can produce plutonium so why could and not can ? )

(Source radio)

Jeffrey says our best chance to stop this was probably in the late '90s. This was before North Korea had nuclear bombs. Jeffrey points out it's always easier to get someone to give up something that they don't have yet. The US-- this was the Clinton administration-- and North Korea had negotiated something called the Agreed Framework.

North Korea would shut down its nuclear reactor that could produce plutonium for bombs. In exchange, they would get two new nuclear power plants, a different type that would make electricity and would be harder to get plutonium out of for bombs. North Korea would also get fuel oil to tide them over until the new reactors could be built. And we'd try to resume normal economic and diplomatic relations. But some Republican members of Congress felt like we were appeasing what was a brutal regime, so ending sanctions was a nonstarter. We were slow in fulfilling our part of the deal. Oil shipments were late. There were also delays building the new reactors, which were to be paid for mostly by South Korea and Japan.

Thank you.