It bears having a written answer that fusion reactors absolutely cannot synthesize heavy isotopes, if the synthesis can only happen during fission. That is to say, some heavy isotopes can be made by using a fusion reactor for neutron bombardment, like Cobalt-60, but other things like Cesium 137 can only be effectively produced by fission of uranium.
That being said, keeping large piles of heavy isotopes around is generally not a great idea. Cesium 137 is only industrially useful when you need to bathe something like a warship in enough energy to take an x-ray of its hull, but Cobalt 60 is actually better at that, and more stable. Cs-137 also reacts easily forming water soluble salts that your body can transport, making it deadly to consume, but useful in radiation therapy.
If you really have an easy time of all of this nuclear power stuff, I'll tell you where you might still see fission, and that's as a black-start power source, because it usually takes power to make power.
Black-start is the ability of a generating station to bring itself back online and place itself on the grid without that grid currently being energized. Currently not a lot of stations actually have this ability, and you may or may not have personally experienced slightly longer power outages because of this. What happens is that the stations that CAN black start have to power up to bootstrap adjacent stations until all the stations are ready to restore power to all the loads that will get turned back on, and it's a real pain when something like the Great Northeast Blackout happens.
Obviously, this point simply may not apply to your given level of technology. Maybe you have unobtainium batteries that can kick over a fusion generator; but if you don't, and if your shielding is good, it is entirely possible to build a fission reactor that can be started entirely by hand, with only a limited amount of power for instrumentation. Also, terrifyingly, reactors have been built this way in the past, with varying degrees of bad results, and the general consensus is that we should try not to do that again.