Nuclear energy contributes a very small amount of emissions into the atmosphere which can cause many environmental problems such as global warming. Uranium is not burned in a nuclear power plant as coal is so there are no emissions from it.
Info on the 2017 USPS Postage Rate Increase. The U.S. Postal Service (USPS) will implement new postage rates for several mailing and shipping products on Sunday, January 22, 2017. Summary of the 2017 Postage Rate Increase: First Class Mail Letters (1 oz.) rates will increase from $0.47 to $0.49 when purchased at the Post Office. Each additional ounce will cost $0.21.
According to the US Post Office postage calculator (link attached to this answer) the current cost for the most basic postage, first class letter to from the US to the UK, is 94 cents. If you don't want to go to the post office to get the exact postage you need, three first class stamps would do it. You'd be overpaying, though.