As long as you can do the physical part of the job, the pacemaker is not an issue from a nuclear standpoint. I am assuming you are asking if working in a nuclear plant will affect the operation of the implanted device... the answer is no. You are in more danger from a microwave oven than an operating nuclear plant.
However... depending on what you do and where you work, a nuclear plant can be very hot and the work can get quite physical, so you have to decide what kind of physical work you can do. There is also some equipment that operates on (or emits) radio frequencies that may interfere with the pacemaker, depending on its age. Most of the newer ones are less sensitive, but you should check with your doctor or the manufacturer to see what sensitivities your particular device may have.
The amount of ionizing radiation that you would be exposed to should not be an issue.