How much nuclear energy does the UK use in a year?

As of 2011, the UK produces about 19% of its power (roughly 10 GW) via nuclear means.

Using the above metric that nuclear plants produce about 10 GigaWatts, that means the total yearly energy production of the those plants is about 87,600 GigaWatt-hours, or 315.36 TeraJoules.