Fusion bomb engine spacecraft?

Let's say we one day manage to build a light weight combustion chamber which is capable of containing a a nuclear explosion (up to 50 megatons of tnt) like the Tsar Bomba....and we mange to harness 100% of the energy of that 50 megaton blast and eject it out the back of the nozzle like a rocket....how fast will this make the spaceship go if fitted on one uming that this 50 megaton ejection is continuous throughout the journey....