Correct Answer - Option 2 : boiling water
Explanation:
Pressurized water reactor (PWR)
- A pressurized water reactor (PWR) is a type of light-water reactor.
- In a PWR, the primary coolant (water) is pumped under high pressure to the reactor core where it is heated by the energy released by the fission of atoms.
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The heated, high pressure water then flows to a steam generator, where it transfers its thermal energy to lower pressure water of a secondary system where steam is generated. The steam then drives turbines, which spin an electric generator.
Boiling water reactor (BWR)
- A boiling water reactor (BWR) is a type of light water nuclear reactor used for the generation of electrical power.
- The main difference between a BWR and PWR is that in a BWR, the reactor core heats water, which turns to steam and then drives a steam turbine. In a PWR, the reactor core heats water, which does not boil. This hot water then exchanges heat with a lower pressure water system, which turns to steam and drives the turbine.
- So, the risk of radioactive hazard is higher with BWR than PWR.
Gas-cooled reactor (GCR)
- A gas-cooled reactor (GCR) is a nuclear reactor that uses graphite as a neutron moderator and a gas (carbon dioxide or helium) as coolant.
- The risk of radioactive hazard is lower with GCR than BWR as, in a BWR, the reactor core heats water, which turns to steam and then drives a steam turbine which have less control.
liquid metal cooled nuclear reactor, liquid metal fast reactor (LMFR)
- A liquid metal cooled nuclear reactor, liquid metal fast reactor or LMFR is an advanced type of nuclear reactor where the primary coolant is a liquid metal.
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Metal coolants remove heat more rapidly and allow much higher power density. This makes them attractive in situations where size and weight are at a premium, like on ships and submarines.
- Additionally, the high temperature of the liquid metal can be used to produce vapour at higher temperature than in a water-cooled reactor, leading to a higher thermodynamic efficiency.
To improve cooling with water, most reactor designs are highly pressurized to raise the boiling point, which presents safety and maintenance issues that liquid metal designs lack. So, among all above reactors, the risk of radioactive hazard is greatest in the turbine with BWR.
