Power Plant Engineering MCQ Questions & Answers | Mechanical Engineering

A boiling water reactor (BWR) uses demineralized water as a coolant and neutron moderator.
Heat is produced by nuclear fission in the reactor core, and this causes the cooling water to boil, producing steam.

The moderator, which is of importance in thermal reactors, is used to moderate, that is, to slow down, neutrons from fission to thermal energies.
Commonly used moderators include regular water , solid graphite and heavy water

Pressurized water reactor is designed To prevent the water coolant from boiling in the core
Pressurized water reactor is a nuclear reactor in which the fuel is uranium oxide clad in zircaloy and the coolant and moderator is water at high pressure so that it does not boil at the operating temperature of the reactor.

The efficiency of a nuclear power plant is generally less than that of a conventional thermal power plant because of the inherent limitations in its operating temperature and thermodynamic cycle.

In a nuclear power plant, the heat energy is produced by nuclear fission within the reactor core. However, the maximum temperature inside the reactor is limited due to the constraints imposed by fuel element materials, coolant properties, and reactor safety considerations.

Typically, the steam temperature and pressure in a nuclear plant are much lower than those achievable in a conventional coal-fired thermal plant. As a result, the thermal efficiency of a nuclear power plant usually ranges between 30% and 35%.

On the other hand, a conventional thermal power plant using coal or oil can operate at much higher steam temperatures and pressures, achieving an efficiency of about 35% to 42% or even higher with modern supercritical technologies.

Hence, due to the lower operating temperature and pressure of the working fluid in a nuclear plant, its efficiency is comparatively lower than that of a conventional thermal plant.

Therefore, the correct answer is Option C: Less.

Moderators are made from materials with light nuclei which do not absorb the neutrons but rather slow them down by a series of collisions.
Carbon in the form of graphite is a material used for moderators as is heavy water which is Deuterium an isotope of Hydrogen with an atomic mass of 2 bonded to Oxygen.

Isotopes of same elements have Same chemical properties but different atomic numbers

Boiling water reactor uses the following as moderator, coolant and working fluid and Ordinary fluid

Gas cooled reactor uses following materials as moderator and coolant Graphite, CO₂.

Amongst the following, the fissionable materials are U₂₃₃ and Pu₂₂₉.

Control rods are used in nuclear reactors to control the fission rate of uranium and plutonium. They are composed of chemical elements such as boron, silver, indium and cadmium that are capable of absorbing many neutrons without themselves fissioning.