[geijoenr]

It depends on the mass of the ship, but yes; quite a bit.

https://www.quora.com/How-much-energy-does-it-take-to-accele...

I don't think that means is unfeasible if the energy source allows for that.

[credit_guy]

No, actually it does not depend.

The rocket equation says that the fuel mass of a rocketship is higher than the cargo mass by exp(delta_v/v_exhaust).

When the final velocity is relativistic, delta_v should be replaced with delta_rapidity. In our case this would introduce a factor of 2.65, but the results are so ridiculous that we can ignore that.

So, let's simply say that delta_v is the speed of light, or 300000 km/s.

The exhaust velocity for a nuclear thermal rocket is about 9 km/s.

The ratio between delta_v and the exhaust velocity is about 33000. The exponential of that is roughly speaking 1 followed by 15000 zeros.

There are less than 10^100 atoms in the known universe.

So, even if you want to accelerate just one single atom to 99% of the speed of light, you would need more fuel than the entire universe. Many, many, many times more.