6.2 - Nuclear Energy

Nuclear Energy

Nuclear energy, also called atomic energy, is released during radioactive decay, nuclear fission and nuclear fusion.
Fusion of hydrogen nuclei in the Sun’s core releases nuclear energy, which reaches the Sun’s surface as light and heat.
Nuclear research in Malaysia began with the establishment of the Tun Ismail Atomic Research Centre (PUSPATI) on 19 September 1972. The centre became the Malaysian Nuclear Agency (ANM).

Nuclear fission splits a heavy nucleus into two or more lighter nuclei and releases a large amount of energy.
In the uranium-235 example:
1. A neutron bombards a uranium-235 nucleus.
2. An unstable uranium-236 nucleus forms.
3. It splits into barium-141, krypton-92 and three neutrons, releasing energy.

_{92}^{235} U +_{0}^{1} n \to_{92}^{236} U \to_{56}^{141} Ba +_{36}^{92} Kr + 3_{0}^{1} n + energy

Nuclear fusion combines small, light nuclei into a heavier nucleus and releases a large amount of energy.
Fusion requires extremely high temperature and pressure.
Deuterium, $_{1}^{2} H$ , and tritium, $_{1}^{3} H$ , fuse to produce helium-4 and one neutron:

_{1}^{2} H +_{1}^{3} H \to_{2}^{4} He +_{0}^{1} n + energy

Atomic masses are very small, so the atomic mass unit (amu) provides a relative measure using a carbon-12 atom as the reference.
Carbon-12 is the reference because carbon occurs in many compounds on Earth. The Avogadro number, $N_{A}$ , is the number of atoms in one mole of carbon-12.
One carbon-12 atom has a mass of 12 amu. Therefore, 1 amu equals one-twelfth of the mass of a carbon-12 atom.

1 amu = 1.66 \times 1 0^{- 27} kg

Mass defect, $m$ , is the decrease in total mass during a nuclear reaction or radioactive decay: the products have less total mass than the initial particles.
Include all particles, including incident and emitted neutrons, in the mass totals.

m = total mass before reaction - total mass after reaction

For the uranium-235 fission example, the neutron mass is 1.00867 amu, uranium-235 mass 235.04392 amu, barium-141 mass 140.91441 amu and krypton-92 mass 91.92611 amu.

Mass before Mass after m = 1.00867 + 235.04392 = 236.05259 amu = 140.91441 + 91.92611 + 3 (1.00867) = 235.86653 amu = 236.05259 - 235.86653 = 0.18606 amu

E = m c^{2}

$E$ : total energy released in joules; $m$ : mass defect in kilograms; $c$ : speed of light in vacuum, $3.00 \times 1 0^{8} m s^{- 1}$ .
Convert the mass defect from amu to kg before substituting into $E = m c^{2}$ .
Nuclear energy can also be expressed in megaelectronvolts (MeV):

1 MeV = 1.60 \times 1 0^{- 13} J

_{88}^{226} Ra \to_{86}^{222} Rn +_{2}^{4} He

m E = 226.54 - (222.018 + 4.003) = 0.519 amu = 0.519 (1.66 \times 1 0^{- 27}) = 8.6154 \times 1 0^{- 28} kg = (8.6154 \times 1 0^{- 28}) (3.00 \times 1 0^{8})^{2} = 7.75 \times 1 0^{- 11} J

Deuterium–tritium fusion: using deuterium 2.014 amu, tritium 3.016 amu, helium-4 4.003 amu and neutron 1.009 amu:

m E = (2.014 + 3.016) - (4.003 + 1.009) = 0.018 amu = 0.018 (1.66 \times 1 0^{- 27}) = 2.988 \times 1 0^{- 29} kg = (2.988 \times 1 0^{- 29}) (3.0 \times 1 0^{8})^{2} = 2.69 \times 1 0^{- 12} J

Uranium-235 fission and the ensuing chain reaction produce heat in the reactor core.
Water pumped through the core absorbs the heat. The steam generator (heat exchange system) transfers heat to water to produce high-pressure steam.
High-pressure steam flows to and rotates the turbine.
The turbine rotates the magnet or coil of the generator, producing electrical energy. Steam condenses back into water in the condenser.
Electrical energy reaches consumers through the power supply transmission system.

The system includes water pumps, a condenser and a cooling tower for its water and cooling circuits.
TRIGA PUSPATI (RTP) in Bangi is a research reactor for nuclear science and education. Malaysia has no nuclear reactors for electricity generation.

In the illustrated fission reaction, one uranium-235 nucleus produces two daughter nuclei, three fast-moving neutrons and energy.
The neutrons bombard other uranium-235 nuclei, causing further fission and releasing more neutrons. This continuing process is a chain reaction.
The chain reaction in the reactor core must be controlled, and the structure must prevent radioactive radiation from leaking into the surroundings.

Reactor component	Function and material
Control rods	Absorb excess neutrons to control the reaction rate; made of boron or cadmium.
Moderator	Slows fast-moving neutrons so further fission can occur; made of graphite or water.
Uranium rods	Fuel that releases nuclear energy through fission.
Water coolant	Absorbs heat from the chain reaction for steam production and controls reactor temperature.
Thick concrete walls	Prevent radioactive radiation from escaping to the surroundings.

Coal, natural gas and water are sources used for electricity generation in Malaysia. Nuclear energy is used for electricity generation in countries including the United States, Japan, France, India and China.
Nuclear energy offers an alternative for meeting increasing electricity demand and reducing reliance on fossil fuels.
The suitability of nuclear, coal and hydropower plants depends on these factors:
- Construction, operating and maintenance costs.
- Location of the power plant.
- Effects on ecosystems and carbon footprint.
- Safety and health issues.
- Available technology and expertise.
- Waste management issues.