UPSC IES -Nuclear Tech Solved Questions

Past IES Questions –Nuclear Tech (Solved)

With Detailed explanations and notes which I prepared for my exam. Keep reading, keep testing.

24. The energy produced by 4-5 tons of high grade coal is equivalent to the energy produced

by

(A) 1 kg of Uranium (B) 1 gram of Uranium

(C) 100 grams of Uranium (D) 10 grams of Uranium

Fact: A kilogram of uranium-235 (U-235) converted via nuclear processes releases approximately three million times more energy than a kilogram of coal burned conventionally (7.2 × 10¹³ joules per kilogram of uranium-235 versus 2.4 × 10⁷ joules per kilogram of coal).^[

25. Enriched Uranium is one in which

(A) Percentage of U235 has been artificially increased

(B) Percentage of U238 has been artificially increased

(C) Percentage of U234 has been artificially increased

(D) Extra energy is pumped from outside

26. Which one of the following statements is not correct ?

(A) Fusion is the combination of heavy nuclei of elements resulting in the release of heat energy

(B) Neutron bombardment is the most common and practiced method of initiation of reaction in fission materials

(C) When the multiplication factor is greater than 1, the chain reaction is uncontrollable

(D) The reactor produces , , and neutron radiations. Of all these radiation is the

most dangerous

27. The reflectivity in a reactor depends upon

(A) Geometry of the reflector (B) Energy of neutrons (C) Properties of reflector (D) All of these

28. Shielding in a nuclear power plant is done

(A) To protect against neutron and gamma rays

(B) To absorb excess neutrons

(C) To slow down the speed of fast moving neutrons

(D) To return the neutrons back into the core of the reactor

Q Moderator in nuclear power plant is used to : slow down the fast moving neutrons

Q With natural Uranium : Heavy Water , solid Graphite & Beryllium are used as moderators

Q Radiations against which shielding is to be given are (in nuclear plant)  : neutron & gamma

Q Moderator : Beryllium & Heavy Water

Q Fertile : U233, Atomic No –No of protons, Mass defect: binding energy, scattering: new born fission neutron have energy varying between 0.075 to 17Mev. During travel, they collide with other nuclei and slow down. This is scattering.

Q Energy released during fission of U235 is 193 MEV (say 200Mev)

Q. Gas cooled reactor: CO2 as Coolant & Graphite as moderator  [ both enriched & natural uranium used]

For fast reactors : best coolants are liquid metals such as sodium. Added advantage they can be used unpressurized as their boiling pt at atm pressure are very high.

CANDU type reactors use Heavy water as moderator

Q Fissile material: Pu-239, Pu-241, U-233,235,239 etc

    Fertile : Th-232, U-234,238,Pu 238,Pu240, Cadmium : Poison

·       Poison Fact: In other reactors the coolant acts as a poison by absorbing neutrons in the same way that the control rods do. In these reactors power output can be increased by heating the coolant, which makes it a less dense poison. Poison; Boron in the form of boric acid

·       A neutron poison (also called a 'neutron absorber' or a 'nuclear poison') is a substance with a large neutron absorption cross-section in applications, such as nuclear reactors^[1]. In such applications, absorbing neutrons is normally an undesirable effect. However neutron-absorbing materials, also called poisons, are intentionally inserted into some types of reactors in order to lower the high reactivity of their initial fresh fuel load..

·       The capture of neutrons by short half-life fission products is known as reactor poisoning; neutron capture by long-lived or stable fission products is called reactor slagging.

·       Light water reactors (BWR, PWR) and heavy water reactors (HWR) operate with "thermal" neutrons, whereas breeder reactors operate with "fast" neutrons.

·       Control Rods: Silver (80%) , Indium (15%) & Cadmium (5%) alloys.

·       Liquid Metal Fast Breeder Reactor (LMFBR)  :This is a reactor design that is cooled by liquid metal, totally unmoderated, and produces more fuel than it consumes. They are said to "breed" fuel, because they produce fissionable fuel during operation because of neutron capture.

·        Moderators: Water, Heavy water, Graphite, Beryllium, Lithium.

·       In a nuclear reactor, the neutron population at any instant is a function of the rate of neutron production (due to fission processes) and the rate of neutron losses (via non-fission absorption mechanisms and leakage from the system). When a reactor’s neutron population remains steady from one generation to the next (creating as many new neutrons as are lost), the fission chain reaction is self-sustaining and the reactor's condition is referred to as "critical". When the reactor’s neutron production exceeds losses, characterized by increasing power level, it is considered "supercritical", and; when losses dominate, it is considered "subcritical" and exhibits decreasing power.

Q  CANDU  type reactor using natural uranium finds extensive use because:

·       Heavy water used both as coolant and moderator

·       Cost of fuel is much lower than in pressurized water or boiling water reactor,

·       Small leakage of heavy water does not affect the performance of the reactor substantially,

·       Fuel consumption is low coz of use of heavy water.

Q U-233 –prepared fuel, U-235: primary fuel, graphite: moderator, control rod: cadmium

Q In gas cooled thermal reactor: CO2 used as coolant and Graphite used as moderator

Fast reactors using enriched uranium fuel donot require a moderator

In fast reactors, liquid sodium is used as coolant

Q Thermal efficiency of a nuclear power plant using boiling water reactor is higher than of a plant using pressurized water reactor

R: in former, steam is directly allowed to be generated in the reactor itself, in latter steam is generated in a separate boiler by heat exchanger device using water of primary circuit which absorbs the fission energy.

CANDU advantages:

§ The main advantage of heavy water moderator over light water is reduced absorption of the neutrons that sustain the chain reaction

§ The low ²³⁵U density in natural uranium also implies that less of the fuel will be consumed

§ CANDU most of the moderator is at lower temperatures than in other designs, reducing the spread of speeds and the overall speed of the moderator particles. This means most of the neutrons will end up at a lower energy and be more likely to cause fission, so CANDU not only "burns" natural uranium, but it does so more effectively as well.

§ Major advantage to the heavy water design; it not only requires less fuel, but as the fuel does not have to be enriched, it is much less expensive as well.

§ A further unique feature of heavy-water moderation is the greater stability of the chain reaction. This is due to the relatively low binding energy of the deuterium nucleus (2.2 MeV), leading to some energetic neutrons and especially gamma rays breaking the nuclei apart and producing extra neutrons