nuclear energy chapter 12. nuclear fuel cycle uranium mines and mills u-235 enrichment fabrication...

Nuclear Energy

Chapter 12

Nuclear Fuel Cycle

Uranium mines and mills

U-235 enrichment

Fabrication of fuel assemblies

Nuclear power plant

Uranium tailings

Depleted uranium tails

Factory wastes

Low-level wastes

Spent fuel stored on-site

Deep geological disposal

Spent fuel reprocessing

Politics

Enrichment

Enrichment Methods:

• Gaseous & Centrifuge• Both require repeated steps• UF6 (Uranium Hexaflouride) is uranium of all weights mixed with flourine gas

U235 is enriched to 3-5% from 0.7%Enriched U-235 (1 pellet) containing uranium enriched to 3% = one ton of coal

Centrifuges

Georgia Power

Vogle +2Georgia’s Electrical GenerationCoal 74%Nuclear 18% - France 75%Oil & Gas <6%Hydro <3%Renewable

Introduction to the Nuclear Process• Fission – nuclear energy released when atom split• Fusion – nuclear energy released when atoms fused

Fuel Assembly

A fuel assembly consists of a square array of 179 to 264 fuel rods, and 121 to 193 fuel assemblies are loaded into an individual reactor - numbers vary greatly

Fuel Assembly

Nuclear FissionHow Electricity is Produced from Conventional Nuclear Fission

Primary/Secondary/Tertiary water circuits?

Vogtle Power Plant

Cooling Towers

Cooling Towers

Cooling water absorbs heat in the condenser and is pumped to the cooling towers where the water pours over a horizontal grid. Upward airflow cools it off. A minor part of the cold cooling water flows back into the river.

Spent Fuel Storage

Pu-239 Breeder Reactor

• U-235 <1% of worlds uranium• Most available U-238

Issues:•Pu- 239 extremely carcinogenic•Half-life 24,000 years• Sodium coolants are explosively reactive

The plutonium-239 core is surrounded by a layer of uranium-238 – which becomes or is “bred” into U-239

U-235 could run for 200 years at current rates of consumption.

Breeder reactors could match today's nuclear output for 30,000 years

Pros and Cons of Nuclear Energy

Impact Coal Nuclear

Land use 17,000 ac 1,900 ac

Daily fuel requirement

9,000 tons/day 3 kg/day

Air pollutionModerate to severe

Low

Radioactive emissions

1 curie 28,000 curies

Risk from catastrophic accidents

Short-term local risk

Long-term risk over large area

Accidents Can Happen

Three Mile Island

1979, Three Mile Island plant in PAthe most serious nuclear reactor accident in the USA -human error (cooling system failed) -50% meltdown of reactor core

Luckily, containment building kept radioactivity from releasing into the countryside

What caused 3 miles island?

1. Minor malfunction in cooling causes Emergency shutdown

1. Steam relief valve opens but does not close as it should

1. Instruments indicate valve had closed

1. Coolant levels dropped and reactor heated up

1. Later that day hydrogen gas build-up threatened an explosion

Chernobyl Disaster

1986, Ukraine (former Soviet Union)

Worst accident ever (?) to occur at a nuclear power plant

Safety Issues in Nuclear Power Plants

Radioactive fallout from Chernobyl:

What caused Chernobyl?

1. Plant operators ran a safety test of back-up safety systems - specifically the generators that would power coolant

2. Control rods were removed and when “SCRAM” was initiated

1. Control rods jammed 1/3 of the way in as fuel rods warped

1. Explosion was from steam pressure followed y fire as oxygen mixed with heated graphite

Impact• Fire broke out and explosions spread radioactive waste

• 350,000 people relocated

• 4,000 Deaths

• 2 million acres of farmland lost

• 1,700,000 acres of forest lost

•Resurgent animals?•http://www.cnn.com/2011/WORLD/europe/01/14/chernobyl.nature.radiation.debate/index.html

Japan

Tsunami: http://www.youtube.com/watch?feature=player_detailpage&v=w3AdFjklR50

The Future of Nuclear Power

Issues:

• Making nuclear power safer

• Standardizing power plant designs

• Decommissioning Nuclear Power Plants

• Lowering construction costs

• Securing Long Term Waste Storage

• Monitoring storage - weapons