MET 401 Chapter 8 -_nuclear_power_plant

NUCLEAR POWER PLANT

MET401 POWERPLANT ENGINEERING

CONTENT

Nuclear fission & neutron energies

Radioactive decay and half life

Temperature distribution, Heat transfer and fluid flow in nuclear reactor

Types of reactor Pressurized water reactor (PWR) Boiling water reactor (BWR) Gas cooled reactor Liquid metal fast breeder reactor Heavy water reactor Fusion power reactor

Nuclear Fission

Nuclear Fission energy is released when a very heavy atomic nucleus absorbs a neutron and splits into two lighter fragments. The energy release in this process is enormous. It is 10 million times greater than the energy released when one atom of carbon from a fossil fuel is burned.

There are 3 nuclear isotopes of importance to nuclear power that exhibit this behavior. 235U (Uranium-235) 239Pu (Plutonium-239) 233U (Uranium-233)

Of the 3, only 235U is found naturally on Earth. Natural Uranium found on Earth consists of 99.3 % 238U and 0.7% 235U. The two other isotopes, 239Pu and 233U can be created from the far more abundant 238U and Thorium nuclei via advanced Nuclear techniques.

Nuclear fission video

Radioactive decay and half life

An atom that is radioactive will decrease its radioactivity in time and eventually decay.

How fast the radioactivity decreases depends on the half-life.

The half-life is defined as the time it takes for half of the radioactivity to decay.

Hence an isotope with a short half-life will decay quickly. The half-life is also inversely proportional to the intensity of radioactivity. Therefore the higher the intensity of radioactivity the shorter the half-life.

Half life of some radioactive isotopes

Isotope Half-life

Strontium-90 28 years

Caesium-137 30 years

Plutonium-239 24,000 years

Caesium-135 2.3 million years

Iodine-129 15.7 million years

World statisticCountry No. of nuclear

powerplantCapacity in MWe

Sweden 11 9401Ukraine 13 11358India 14 2446South Korea 16 12990Germany 19 21072Canada 20 13601Russia 30 20739United Kingdom 32 12427Japan 54 44394France 59 63113United States 104 95622TOTALS 447 355542

Locations

Types of nuclear reactors

Pressurized Water Reactors

Pressurized Water Reactors (PWR's) are by far the most common type of Nuclear Reactor deployed to date.

Ordinary water is used as both neutron moderators and coolant. It is separate from the water used to generate steam and to drive a turbine.

In order to efficiently convert the heat produced by the Nuclear Reaction into electricity, the water is contained at pressures 150 times greater than atmospheric pressure.

Boiling Water Reactors

In a Boiling Water Reactor (BWR), ordinary light water is used as both a moderator and coolant,

there is no separate secondary steam cycle. The water from the reactor is converted into steam and used to directly drive the generator turbine. These are the second most commonly used types of reactors.

Liquid-Metal Fast-Breeder Reactor

In the LMFBR, the fission reaction produces heat to run the turbine while at the same time breeding plutonium fuel for the reactor.

High Temperature Gas Cooled Reactors

High Temperature gas cooled reactors operate at significantly higher temperatures than PWRs and use a gas as the primary coolant.

The nuclear reaction is mostly moderated by carbon. These reactors can achieve significantly higher efficiencies than PWRs but the power output per reactor is limited by the less efficient cooling power of the gas.

Heavy Water Reactors

Heavy Water reactors are similar to PWRs but use water enriched with the deuterium isotope of Hydrogen as the moderator and coolant.

The "heavy water" and makes up about 0.022 parts per million of water found on Earth.

The advantage of using Heavy water as the moderator is that natural, un-enriched Uranium can be used to drive the nuclear reactor.

Evolution of nuclear power plant

Fukushima incident

watch video