light-water reactor and plutonium produce !

[magnetar]

In principle, light-water reactor can also produce plutonium from uranium-238 as heavy-water reactor .Plutonium can be used to make nuclear-weapon!
But,Why do we like to offer this kind of power plant to other nations?

[QuantumPion]

LWR's don't just make plutonium in principle. A significant amount of energy produced by commercial LWR's actually does comes from plutonium fission!

While Plutonium-239 is weapons grade, when left in a reactor for more then a few weeks it will absorb another neutron, becoming Pu-240. Pu-240 poisons the fuel as far as weapons are concerned, its presence prevents the material from being used in a weapon.

If you had the technology to separate Pu-240 from Pu-239 then you could have more easily separated U-235 from U-238, which would be far cheaper since the Plutonium isotopes are closer together in mass, and come from radioactive fuel which was in the reactor.

So to answer your question - we aren't worried about other nations being able to make weapons-grade material with LWR's because it really isn't feasible, unless you stop the reactor to refuel it every few weeks instead of running it for 2 years. This kind of activity would not go unnoticed and would be expensive and wasteful compared to conventional methods (e.g. if you had the money to waste on a commercial-sized LWR to operate it with a capacity factor < 50% to refuel it all the time, as well as the fuel processing plant to get the plutonium out of the highly radioactive fuel, you could have afforded a small research reactor to breed plutonium to begin with).

[joelupchurch]

QuantumPion is correct. No one has ever used a commercial reactor to produce Pu-239 for weapons. The easiest route to a weapon doesn't require a reactor at all. You need a source of uranium, such as yellowcake and a gas centrifuge.
http://en.wikipedia.org/wiki/Gas_centrifuge
Also constructing a nuclear weapon with U-235 is easier than Pu-239.