This question may be suggesting (I am assuming without certainty), a total lack of knowledge regarding the type of explosion that can occur in a nuclear power plant.
The explosions that are possible to happen are of order
thermal, never nuclear
. In Chernobyl, the worst example, from a project that would never be approved in the West, what happened was a thermal explosion, aggravated by the absence of the barriers that the plants like Angra have and by the fact that, in Chernobyl, graphite is used as a moderator in the reactor, instead of water. Among other problems, graphite catches fire, not water.
The Angra project foresees the construction of several buildings and support structures,
The Reactor Building, formed by the internal structure (UJA) and the external structure (Reactor-Annulus – UJB), is made of reinforced concrete with an external diameter of 60.40 m and a thickness of 0.60 m, which surrounds the containment sphere and houses the core’s emergency cooling system. The building is designed to provide a biological barrier to ionizing radiation during normal plant operation and in case of accident, as well as to protect the containment sphere from windstorms, storms, explosion pressure waves and earthquakes.
The sphere was designed to withstand the 5.3 bar pressure at 145ºC, which would develop in the event of a rupture of a pipe in one of the reactor cooling circuits, followed by vaporization of all the water contained in the primary and secondary circuits. This situation is known as an accident with loss of coolant and designated by the acronym LOCA, of Loss-Of-Coolant Accident.
The containment sphere completely surrounds the reactor, the steam generation system, the pool of used fuel elements and the tank of new fuel elements, as well as the concrete biological shield, 1.2 to 2 m thick, which surrounds the reactor pressure vessel, as can be seen in the Figure.
What may occur (in the PWR reactor) is a steam explosion, which may eventually spread radioactive material into the environment. But there are a number of safety procedures to prevent such an explosion from occurring. Therefore, it is very unlikely, but that does not mean it is impossible.
If something does occur, the system relies on successive containment barriers so that the radioactive material does not spread to the outside environment. In plants like Angra, the number of these containment barriers is higher than in Chernobyl.
With regard to Fukushima, no engineering work has been designed to withstand such a great event. Most of the buildings and industrial facilities with risks of explosion and release of toxic products to the environment, such as oil refineries, fuel depots, thermal power plants and chemical industries, located in the affected region collapsed immediately, with thousands of deaths.
But after Fukushima, the nuclear industry has analyzed the failures that have occurred to prevent them from occurring again, and to this end they are designing what have been called 4th generation reactors.
What is considered to be 4th generation nuclear power does not deviate much from what exists in terms of the basic fission technology of core elements such as Uranium, Thorium, Plutonium, but focuses its attention on four main aspects:
Sustainability: Generation IV nuclear power reactors will provide sustainable energy generation that meets the goals of clean air and promotes the long-term availability of systems and the efficient use of fuel for global energy production. Such nuclear power reactors are expected to minimize and manage their nuclear waste, significantly reduce the long-term management burden, improve public health and environmental protection, and improve resource utilization and nuclear waste generation ;
Economy: Generation IV nuclear power reactors are expected to have a clear life cycle cost advantage over other energy sources and a level of financial risk comparable to other energy projects;
Safety and reliability: Generation IV nuclear reactor operations are expected to outperform other nuclear reactor projects in safety and reliability aspects and will have a very low probability and degree of reactor core damage. Generation IV nuclear power reactors are also expected to eliminate the need for external emergency response.
Proliferation resistance and physical protection: Generation IV nuclear power reactors are expected to increase the assurance that they are a very unattractive and less desirable route for diversion or theft of weapons-usable materials and will provide greater physical protection against acts of terrorism.