Conventional Nuclear Fission nuclear fuel cycle producing uranium

Conventional Nuclear Fission • nuclear fuel cycle: producing uranium ore used in nuclear reactors & disposing of radioactive wastes

Uranium Ore • substantial deposits are found in Australia, Kazakhstan, SW United States, Canada, and South Africa • contains 3 isotopes • U-235 is used in conventional fission, but only makes up 0. 71% of uranium ore • uranium enrichment: the refining process which increases the concentration of U-235 to about 3% in ore • can be very energy intensive • *about 20% U-235 in a bomb UNCONTROLLED

What is Done with Enriched Uranium? processed into pellets of uranium dioxide each contains the energy of a ton of coal pellets placed in fuel rods (closed pipes) fuel rods are grouped into square fuel assemblies typical reactor contains ~250 fuel assemblies

How Do We Get Energy Out of U-235? • U-235 is bombarded with neutrons • becomes unstable and splits into two smaller atoms and ejects 2 -3 neutrons • new neutrons collide with other U-235 atoms chain reaction • heat released is used in a nuclear power plant to transform water into steam used to generate electricity • production of electricity is possible because fission is controlled • reactions can be started or stopped, increased or decreased

How Electricity is Produced from Fission #1 #2 #3 #4

#1 – Reactor Core • where fission occurs • contains the fuel assemblies • above each fuel assembly is a control rod (made of a metal alloy capable of absorbing neutrons) • when the control rod is out of the fuel assembly • when the control rod is lowered into the fuel assembly

#2 – Steam Generator • where heat produced by nuclear fission is used to produce steam from liquid water • the primary water circuit heats water to ~ 293 °C • circulates water under high pressure through the reactor core pressure keeps superheated water liquid • very hot water circulates to the steam generator, where it boils water held in a secondary water circuit produces steam

#3 - Turbine • uses steam to generate electricity • steam turns the turbine spins a generator to produce electricity

#4 - Condenser • cools the steam, converting it back to liquid • the tertiary water circuit provides cool water to the condenser cools steam in the secondary water circuit • water in the tertiary water circuit gets heated moves to a lake/cooling tower (to be cooled before circulating back to the condenser)

Safety Features of a Nuclear Power Plant • reactor vessel: a huge steel pot-like structure that surrounds the reactor core • designed to prevent accidental release of radiation • containment building: houses the reactor vessel and steam generator • has steel-reinforced concrete walls

Nuclear Power Plant Revisited

Three Mile Island • PA, 1979 • most serious accident in the U. S. • human error after the cooling system failed 50% meltdown of the reactor core

Effects of Three Mile Island Meltdown • the containment building kept most of the radioactivity from escaping • environmental damages? • human casualties? • cancer rates?

Effects of Three Mile Island Meltdown continued • elevated public apprehension • 12 years + $1 billion for repair and reopening • prompted construction delays and cancellations of several new nuclear power plants • reduced complacency • new safety regulations more frequent inspections, new risk assessments, improved emergency and evacuation plans

Chernobyl • Ukraine, 1986 • worst accident ever to occur at a nuclear power plant • an explosion ripped a nuclear reactor apart and expelled large quantities of radioactive material into the atmosphere

Two Causes of the Chernobyl Meltdown 1. the reactor was not housed in a containment building and was extremely unstable at low power 2. human error – what went wrong?

Immediately Dealing with the Damage • 170, 000 people had to permanently abandon their homes • radiation had to be cleaned up • damaged reactor building was encased in concrete • radioactive soil was removed • buildings and roads were scrubbed down to remove radioactive dust

Long-Term Problems • mostly affect Ukraine • farmland forests still cannot be used • residents cannot drink the water or consume locally produced milk, meat, fish, or produce • mothers do not nurse their babies • ~400, 000 adults and more than 1 million children receive government aid for health problems • increase in frequency of birth defects • increased incidence of leukemia and thyroid cancer in kids

Spread of Radiation • no predictability of the course of spreading radiation

Fukushima • Following a major earthquake, a 15 -metre tsunami disabled the power supply and cooling of three Fukushima Daiichi reactors, causing a nuclear accident on 11 March 2011. All three cores largely melted in the first three days. • The accident was rated 7 on the INES scale, due to high radioactive releases over days 4 to 6 • After two weeks, the three reactors (units 1 -3) were stable with water addition and by July they were being cooled with recycled water from the new treatment plant. Official 'cold shutdown condition' was announced in mid-December. • Apart from cooling, the basic ongoing task was to prevent release of radioactive materials, particularly in contaminated water leaked from the three units. This task became newsworthy in August 2013. • There have been no deaths or cases of radiation sickness from the nuclear accident, but over 100, 000 people were evacuated from their homes to ensure this. Government nervousness delays the return of many. • Official figures show that there have been well over 1000 deaths from maintaining the evacuation, in contrast to little risk from radiation if early return had been allowed.

Nuclear Waste Policy Act (1982) • puts the burden of developing permanent sites for civilian and military high-level radioactive wastes on the federal government • required the first site to be operational by 1998 (was postponed to 2010)