The advantages over a fission reactor are comparatively huge for magnetic containment fusion reactors, of which tokamak, ITER, and the new Lockheed CFR all are. I don't have any more training in regards to the engineering of fusion reactors than most of you (i.e. non-research articles) but I've been in nuclear fission reactor design for 7 years, now, so I can speak to those designs.
All fission designs currently operating and permitted to operate, run on essentially the concept of controlling a runaway fission reaction of low enrichment metals. These include all Gen II, III, and III+ designs. Even theoretical so-called Gen IV designs which are mostly fast fuel breeding heavy metal or gas cooled, share this design paradigm. In order to achieve criticality and "useful" levels of heat, a substantial amount of scale is required. That makes the reactor vessel itself large and heavy which means opening it to refuel it (although heavy water reactors get around this limitation, somewhat) is not economical as it is slow and inefficient to reach 100% power. Thus, the operating philosophy for these designs revolve around putting in as much fuel as possible and operating at 100% power for very long times without going offline. Indeed, most designs are analyzed and safest when running at 100% power rather than any transient condition. It is the ultimate locomotive in terms of time to reach full speed, time and dynamics to go to hot shutdown (emergency procedure), and magnitude of things going wrong when the train runs the tracks.
The best analogy I can think of between a fission reactor and the proposed magnetically contained fusion reactor designs is being on top of a hill with a huge boulder versus being on top of a hit with the same boulder broken into thousands of hand size pieces. A fission reactor puts the massive boulder in motion restrained by a team of workers with a rope. At any moment, if he rope breaks, if too many workers lose their grip, if it starts to rain and the hill becomes slippery etc. the boulder will run down the hill out of control. A fusion reactor of the proposed design allows control for how much fuel is inside the reactor/containment at a time. Unless it's in containment, it will not react, as it needs the precisely stabilizing conditions of the magnetic flux to achieve fusion. One person can stand atop the hill and throw the rocks down one at a time with little or no consequence.
The unintuitive consequences of fission reactor design can also be eliminated. If you haven't ever stepped foot inside a 1,000+ megawatt unit, you might be surprised at how much **** is actually in there. There are thousands of huge pipes, pumps, motors, associated electrical switchgear, and other components which have nothing to do with generation. Many are redundant safety coolant injection systems, which require massive pumps/motors to run, which themselves require support cooling and lubrication systems necessitating their own use of pumps, motors and valves. The balance of systems are chemical treatment systems of one type or another for processing leaked and recovered coolant, or to maintain the chemical composition of the nuclear coolant/working fluid, itself. The amount of energy diverted from generation back into the plant to run all these systems is not trivial.
Furthermore, plant operators have to know exactly which procedure to follow to know which combination of valves, instruments, switchgear/breaker cubicles to manipulate in response to any of the thousand of hypothetical scenarios and sub-variations of scenarios which might occur. One might say this environment is prone to human error. As you can imagine, in an industry where mistakes are politicized, even if benign on their own, for a design and philosophy built around defense-in-depth, where the ultimate risk to radioactive release to the public is measured in probability, there is simply a lot of bullshit going on with corrective measures.
This is the average looking control room for an operating plant.
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All of that goes away with a small, inherently safe, reactor design. This proposed Lockheed design, if their literature is true, is more of a power generator than a power plant. That is indeed, game changing.