Fundamentals of Nuclear Power

Nuclear Power Plants Nuclear power is generated using Uranium, which is a metal mined in various parts of the world. Some military ships and submarines have nuclear power plants for engines Nuclear power produces around 11% of the world's energy needs, and produces huge amounts of energy from small amounts of fuel, without the pollution that you'd get from burning fossil fuels.

How it Works The main bit to remember : Nuclear power stations work in pretty much the same way as fossil fuel-burning stations, except that a "chain reaction" inside a nuclear reactor makes the heat instead.

Nuclear Power Nuclear power is produced by controlled (i.e., non-explosive) nuclear reactions. Commercial and utility plants currently use nuclear fission reactions to heat water to produce steam, which is then used to generate electricity.nuclear reactionsnuclear fissionsteamelectricity In 2009, 13-14% of the world's electricity came from nuclear power.[1] Also, more than 150 naval vessels using nuclear propulsion have been built.[1]nuclear propulsion

Nuclear Fission Simple diagram of nuclear fission. In the first frame, a neutron is about to be captured by the nucleus of a U-235 atom. In the second frame, the neutron has been absorbed and briefly turned the nucleus into a highly excited U-236 atom. In the third frame, the U-236 atom has fissioned, resulting in two fission fragments (Ba-141 and Kr-92) and three neutrons, all with large amounts of kinetic energy.

A slow moving neutron induces fission in Uranium 235

Expanding Chain Reaction The fission reaction produces more neutrons which can then induce fission in other Uranium atoms.

Linear Chain Reaction Obviously, an expanding chain reaction cannot be sustained for long (bomb). For controlled nuclear power, once we reach our desired power level we want each fission to produce exactly one additional fission

Tricks of the trade Slow moving (thermal) neutrons are more effective at inducing fission, but, fissions produce fast moving electron. We need to slow neutrons down. Fissions typically produce several neutrons but a linear chain reaction only needs one. We need to get rid of a good fraction of our neutrons.

Moderator Neutrons are slowed down by having them collide with light atoms (Heavy Water in reactors). Highest level of energy transfer occurs when the masses of the colliding particles are equal (ex: neutron and hydrogen)

Control Rods Control rods are made of a material that absorbs excess neutrons (usually Boron or Cadmium). By controlling the number of neutrons, we can control the rate of fissions

Basic Idea The Uranium is both the fuel and the source of neutrons. The neutrons induce the fissions The Water acts as both the moderator and a heat transfer medium. Control rods regulate the energy output by “sucking up” excess neutrons

Practicalities Processing of Uranium Each ton of Uranium ore produces 3-5 lbs of Uranium compounds Uranium ore is processed near the mine to produce “yellow cake”, a material rich in U 3 O 8. Only 0.7% of U in yellow cake is 235 U. Most of the rest is 238 U which does not work for fission power.

Enrichment To be used in reactors, fuel must be 3-5% 235 U. Yellow cake is converted into UF 6 and this compound is enriched using gaseous diffusion and/or centrifuges. There are some reactor designs that run on pure yellow cake.

NOTE: A nuclear bomb requires nearly 100% pure 235 U or 239 Pu. The 3% found in reactor grade Uranium CANNOT create a nuclear explosion!

Fuel Pellets The enriched UF 6 is converted into UO 2 which is then made into fuel pellets. The fuel pellets are collected into long tubes. (~12ft). The fuel rods are collected into bundles (~200 rods per bundle ~175 bundles in the core

Cladding The material that the fuel rods are made out of is called cladding. It must be permeable to neutrons and be able to withstand high heats. Typically cladding is made of stainless steel or zircaloy.

Controlling the chain reaction depends on Arrangement of the fuel/control rods Quality of the moderator Quality of the Uranium fuel Neutron energy required for high probability of fission

Two common reactor types: Boiling Water Reactor and Pressurized Water Reactor. BWR: P=1000 psi T=545  F PWRP=2250 psi T=600  F PWR is most common and is basis of marine nuclear power.

Reactor is inside a large containment building

Other Options Other countries use different reactor designs. Some use heavy water (D 2 O) as a moderator. Some use Graphite as a moderator. Some are designed to use pure yellow cake without further enrichment Liquid metal such as sodium or gasses such as Helium are possibilities to use for coolants

Nuclear Power Plant in Pakistan In Pakistan, nuclear power makes a small contribution to total energy production and requirements, supplying only 2.34% of the country's electricity. Total generating capacity is 20 GWe and in 2006, 98 billion kWh gross was produced, 37% of it from gas, 29% from oil. The Pakistan Atomic Energy Commission (PAEC) is responsible for all nuclear energy and research applications in the country. Its first nuclear power reactor is a small (125 MWe) Canadian pressurized heavy water reactor (PHWR) which started up in 1971 and which is under international safeguards - KANUPP near Karachi, which is operated at reduced power.

Nuclear Power Plant in Pakistan The second unit is Chashma-1 in Punjab, a 325 MWe (300 MWe net) pressurised water reactor (PWR) supplied by China's CNNC under safeguards. The main part of the plant was designed by Shanghai Nuclear Engineering Research and Design Institute (SNERDI), based on Qinshan-1. It started up in May 2000 and is also known as CHASNUPP-1. Construction of its twin, Chashma-2, started in December It is reported to cost PKR billion (US$ 860 million, with $350 million of this financed by China). A safeguards agreement with IAEA was signed in 2006 and grid connection is expected late in 2010 or in 2011.