Power Plant Engineering — Part 1 MCQs with Explanations

Reactors for propulsion applications refer to nuclear reactors used to power moving systems such as submarines, naval ships, and aircraft carriers . These reactors are designed to produce high power in a compact system that can operate continuously for several years without the need for frequent refueling. The fuel used in such reactors is a crucial factor because it determines the reactor’s efficiency, lifespan, and safety. In propulsion reactors, the fuel is generally uranium , which may be used in different forms — either as natural uranium or enriched uranium — depending on the specific design and power requirements of the reactor. 1. Natural Uranium: Natural uranium contains about 0.7% of the fissile isotope U-235 and the rest is mostly U-238. It can be used as fuel in reactors that employ heavy water (D₂O) or graphite as moderators, which allow the chain reaction to be sustained with low enrichment levels. However, for propulsion systems, this type of reactor is generally too large and heavy to be practical, though it is technically possible. 2. Enriched Uranium: Most naval propulsion reactors (such as those in nuclear submarines and aircraft carriers) use enriched uranium fuel . Enrichment increases the proportion of U-235 (typically 20% or even higher in naval applications), allowing the reactor to be smaller, more efficient, and capable of long-term operation without refueling — an essential feature for submarines that must operate underwater for months or even years at a time. Therefore, propulsion reactors are designed to operate using any form of uranium fuel depending on their design constraints and performance needs. This flexibility in fuel type ensures adaptability to different reactor designs, ranging from pressurized water reactors (PWRs) to liquid metal–cooled fast reactors used in advanced naval systems. 3. Clarifying the Other Options: Option A: Natural uranium – While natural uranium can be used in some types of reactors, it is not the most common fuel for propulsion reactors because enriched uranium provides much better efficiency and compactness. Option B: Molten lead – Molten lead is not a fuel; it is sometimes used as a coolant or heat transfer medium in certain advanced reactor types (like lead-cooled fast reactors), but it does not act as a fissile material. Option D: Thorium – Thorium is a fertile material, not a fissile one, meaning it must be converted into uranium-233 before it can sustain a chain reaction. It is still in experimental use and not employed in propulsion reactors. 4. Conclusion: The type of uranium fuel used depends on the reactor’s design and intended performance. Both natural uranium and enriched uranium can be utilized, making the most comprehensive and technically accurate answer: Option C: Any form of uranium Hence, for examination and professional understanding, Option C is the correct and most defensible answer.

Reactors designed for propulsion applications are designed for Enriched uranium

Reactors designed for propulsion applications are designed for Enriched uranium

When the atom-splitting reactor of a nuclear power plant is operating normally, it is said to be “critical” or in a state of “criticality.” Criticality means that a reactor is controlling a sustained fission chain reaction, where each fission event releases a sufficient number of neutrons to maintain an ongoing series of reactions. This is the normal state of nuclear power generation.

Breeder reactor is a nuclear reactor that produces more fissionable material than it consumes to generate energy. This special type of reactor is designed to extend the nuclear fuel supply for electric power generation. It produces more fuel than it consumes It requires highly enriched fuel It requires liquid sodium metal as moderator

A fast-breeder nuclear reactor produces more fuel than it consumes, while generating energy. Conventional reactors use uranium as fuel and produce some plutonium. Breeders produce much more plutonium, which can be separated and reused as fuel

fast breeder reactors are Operate at extremely high power densities and liquid metal cooled and it Produce more fuel than they consume

In a thermal power plant, coal from the coal handling plant is moved to the boiler bunker through a Belt conveyor

Nuclear chain reactions are series of nuclear fissions (splitting of atomic nuclei), each initiated by a neutron produced in a preceding fission. A fission chain reaction in uranium can be developed by increasing the contents of U 235 and by slowing down fast neutrons so that U 235 fission continues by slow neutron.

The efficiency of a nuclear power plant in comparison to conventional and nuclear consideration is lower temperature and pressure conditions. Typical nuclear power plants achieve efficiencies around 33 - 37%, comparable to fossil fueled power plants. Higher temperature nuclear reactors could potentially reach above 45% efficiency.

Most commercial nuclear reactors use normal water (also called light water) as a neutron moderator. Some reactor designs, such as the CANDU reactor, use heavy water. A heavy water molecule contains deuterium (Hydrogen-2), which is an isotope of hydrogen that has a neutron in its nucleus in addition to the proton.

A schematic nuclear fission chain reaction. 1. A uranium-235 atom absorbs a neutron and fissions into two new atoms (fission fragments), releasing three new neutrons and some binding energy

When the reactor is in operation, a large amount of radioactivity is generated. The materials used to build this shield are concrete, water and lead.

When the reactor is in operation, a large amount of radioactivity is generated. The materials used to build this shield are concrete, water and lead.

An atom is the smallest constituent unit of ordinary matter that has the properties of a chemical element. Every solid, liquid, gas, and plasma is composed of neutral or ionized atoms. Atoms are extremely small; typical sizes are around 100 picometers.

An electron is a negatively charged subatomic particle. It can be either free or bound to the nucleus of an atom. The invariant mass of an electron is approximately 9.109×10−31 kilograms,

A moderator, in nuclear power plants, is a medium introduced into the fuel mass in order to slow down the speed of fast moving neutrons. 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.

A reflector is a region of unfueled material surrounding the core. Its function is to scatter neutrons that leak from the core, thereby returning some of them back into the core. Reflector in nuclear power plants decreases neutron leakage.

1 curie = 3.7 x 10 10 radioactive decays per second [exactly]. 1 becquerel = 1 radioactive decay per second = 2.703 x 10 -11 Ci.

One gram of uranium will produce energy equivalent to approximately 4.5 tonnes of high grade coal

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, CO 2 .

Amongst the following, the fissionable materials are U 233 and Pu 229 .

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.

Each fission of U 235 produces on the average 2.46 fast neutrons as a product of reaction.

Enriched uranium is required as a fuel in a nuclear reactor, if light water is used as moderator and coolant, because light water has Low moderating efficiency

an induced nuclear fission event where a slow-moving neutron is absorbed by the nucleus of a uranium-235 atom, which fissions into two fast-moving lighter elements (fission products) and additional neutrons

Criticality means that a reactor is controlling a sustained fission chain reaction, where each fission event releases a sufficient number of neutrons to maintain an ongoing series of reactions. This is the normal state of nuclear power generation.

The fuel needed, with reflector in nuclear power plant, in order to generate sufficient neutrons to sustain a chain reaction, would be Less

A power plant giving least running cost of production of electrical power is Nuclear power plant

Breeder reactors are possible because of the proportion of uranium isotopes that exist in nature A fast breeder reactor uses 90% U 235 .

Fast breeder reactor uses Double circuit system of coolant cycle fast reactor uses a coolant that is not an efficient moderator, such as liquid sodium, so its neutrons remain high-energy. This plutonium isotope can be reprocessed and used as more reactor fuel or in the production of nuclear weapons.

In order to have constant chain reaction to produce a constant rate of heat output, the value of ratio of the number of neutrons in one generation to the number of neutrons in the immediately preceding generation must be Equal to 1.0

Boiling water nuclear reactor does not need a heat exchanger for generation of steam.