Major concerns about nuclear Fission power
Potential for possibly severe radioactive contamination by accident. As we saw earlier accidents do happen and Chernobyl disaster was not the only nuclear accident in history. Another meltdown occured in the second reactor of the Three Mile Island power plant in 1979, being the most significant accident in the history of the America, and even though it resulted in no deaths or injuries to plant workers or members of the nearby community - there is no such thing as zero radioactivity in practice.
Nuclear proliferation and use of waste byproduct as a weapon. Nuclear proliferation is the spread of nuclear weapons and it's known that reactors could be used for weapons-development purposes — the first nuclear reactors were developed for exactly this reason — as the operation of a nuclear reactor converts U-238 into plutonium. An additional concern is that if the by-products of nuclear fission — the nuclear waste generated by the plant — were to be unprotected it could be used as a radiological weapon, colloquially known as a "dirty bomb."
Vulnerability of nuclear power plants to sabotage and attack. Nuclear power plants are designed to withstand threats deemed credible at the time of licensing. Land attacks are relatively difficult to achieve but an attack from the air is a more problematic concern. The most important barrier against the release of radioactivity in the event of an aircraft strike is the containment building and its missile shield. However, as weapons evolve it cannot be said unequivocably that within the 60 year life of a plant it will not become vulnerable. In addition, the future status of storage sites may be in doubt. Sabotage of nuclear power plants may be the greatest domestic vulnerability in the US today.
Differences of nuclear Fusion power
Accident potential and safety during abnormal operation. The likelihood of a catastrophic accident in a fusion reactor in which injury or loss of life occurs is much smaller than that of a fission reactor. The primary reason is that the fuel contained in the reaction chamber is only enough to sustain the reaction for about a minute, whereas a fission reactor contains about a year's supply of fuel. The density of the plasma is extremely low and the total amount of fusion fuel in the chamber is very small. If the fuel supply is closed, the reaction stops within seconds. Furthermore, fusion requires very extreme and precisely controlled conditions of temperature, pressure and magnetic field parameters. If the reactor were damaged, these would be disrupted and the reaction would rapidly extinguish.
Nuclear proliferation and waste management. Although fusion power uses nuclear technology, the overlap with nuclear weapons technology is very small. The half-life of the radioisotopes produced by fusion tend to be less than those from fission, so that the inventory decreases more rapidly. Furthermore, there are fewer unique species, and they tend to be non-volatile and biologically less active. Unlike fission reactors, whose waste remains dangerous for thousands of years, most of the radioactive material in a fusion reactor would be the reactor core itself, which would be dangerous for about 50 years, and low-level waste another 100. By 300 years the material would have the same radioactivity as coal ash.
Fusion power as a sustainable energy source. Large-scale reactors using neutronic fuels (e.g. ITER) and thermal power production (turbine based) are most comparable to fission power from an engineering and economics viewpoint. Both fission and fusion power plants involve a relatively compact heat source powering a conventional steam turbine-based power plant, while producing enough neutron radiation to make activation of the plant materials problematic. The main distinction is that fusion power produces no high-level radioactive waste (though activated plant materials still need to be disposed of). There are some power plant ideas which may significantly lower the cost or size of such plants; however, research in these areas is nowhere near as advanced as in a tokamak pictured below.
Click this link to watch the best video documentary online about Chernobyl disaster and read the current debate on fission energy.