chapter 4. nuclear power 1.introduction 2.characteristics of fission 3. general features 4....

Chapter 4. Nuclear Power1. Introduction

2. Characteristics of Fission

3. General Features

4. Commercial Reactors

5. Nuclear Reactor Safety

6. Nuclear Reactor Accidents

7. Uranium Mining

Key elements: fuel, neutron moderator, control rod, neutron detector and radioactivity detectors, products

World final energy consumption by source 2005

oil44.5%

coal14.9%

natural gas18.8%

combustible renewables &

waste13.1%

hydro2.6%

other3.6%

nuclear2.5%

Source: IEA (2007)

Delivery

• Construction times for nuclear plants – Global average

• 66 months in mid-1970s • 116 months (nearly 10y) in late 1990s• 82 months (nearly 7y) during 2001-05

Energy

Estimate the energy released by the fission of 1.0 kg of 235U.

(3.15e-11 J) 1000 g

= 8.06e13 J (per kg).

DiscussionThis is a large amount of energy, and it is equivalent to the energy produced by burning tones of coal or oil.

1 mol235 g

6.023e231 mol

235U92 142Nd60 + 90Zr40 + 3 n + Q

Q = (235.043924 - 141.907719 - 89.904703 - 3x1.008665)

= 0.205503 amu (931.4812 MeV/1 amu)

= 191.4 MeV per fission(1.6022e-13 J / 1 MeV)

= 3.15e-11 J

This amount of energy is equivalent to 2.2×1010 kilowatt-hour, or 22 giga-watt-hour. This amount of energy keeps a 100-watt light bulb lit for 25,000 years.


7

Fission Energy Budget

Kinetic energy of fission fragmentsPrompt (< 10–6 s) gamma () ray energy

Kinetic energy of fission neutronsGamma () ray energy from fission products

Beta () decay energy of fission productsEnergy as antineutrinos (ve)

168 MeV757812

Energy (MeV) distribution in fission reactions

The total and fission cross section for 235U based on NJOY-processed ENDF/B (version V) data.

Neutron interactions

The fast fission cross section for three fissionable uranium isotopes based on NJOY processed ENDF/B (version V) data

10

The Cyclotron and Fission Research

Threshold* Energy range (keV)Reaction energy(keV) narrow-energy neutron

51V (p, n) 51Cr2909 5.6-5245Sc (p, n) 45Ti1564 2.36-78657Fe (p, n) 57Co 1648 2-1425__________________________________* The threshold energy is the minimum energy of proton required for the reaction.

Neutrons of desirable energy is required for fission research.

Nuclear Fission 11

The Cyclotron and Fission Research

For neutron sources from the cyclotron, energy can be varied.

Energy dependence of neutron induced fission studied.

The cross section data enabled nuclear reactor design.

fast neutrons - 10 MeV to 10 KeV)

slow neutrons - 0.03 to 0.001 eV for neutron induced fission

Chapter 4. Power From Fission1. Introduction


3. General Features





Simplified schematic layout of a typical reactor power plant.

3.1 A nuclear power plant

Control rods, containing neutron-absorbing elements (boron or cadmium)

pressure vessels must be capable of withstanding internal pressures up to 160 bar.

A biological shield, normally several feet of concrete, surrounds the entire system. Its purpose is to attenuate the intensity and neutron radiations to levels that are safe for humans outside the plant

The coolant is pumped through the core inside the pressure vessel and through heat exchangers outside, where steam is generated and used to drive turbines for generating electric power.

Core: The melting point of uranium is 1403 K, The melting point of UO2 is 3138 K

Optimizing the design

f is a decreasing function and p an increasing function of moderator-to-fuel ratio NM / NF

Uranium ~ graphite assemblies

Diffusion length

the root-mean-square distance a neutron will diffuse in the medium before being absorbed

Diffusion and slowing-down constants for moderators.

R, The reaction probability per unit time for N nuclei; M is the mass of fissile material

if each fission liberates an amount E of recoverable energy, the power output is

Reactor power and fuel consumption

example

calculate the power output, rating and fuel consumption for athermal reactor containing 150 tonnes of natural uranium operating with a neutron flux of

energy per fission E = 200 MeV

3.4 MW/t

Fuel consumption, leading to a loss of 235U, depends on the total 235U absorption cross section

= 5.9 x 1026 /year

one-fifth of the initial amount of 235U

refueling



3. General Features




7. Uranium Mining


Key Reactor Power Terms

• Availability – Fraction of time over a reporting period that the plant is operational– If a reactor is down for maintenance 1 week and

refueling( 补给燃料） 2 weeks every year, the availability factor of the reactor would be(365-3 * 7) / 365 = 0.94

Key Reactor Power Terms

• Capacity – Fraction of total electric power that could be produced– If reactor with a maximum thermal power rating

of 1000 MWt only operates at 900 MWt, the capacity factor would be 0.90

• Efficiency – Electrical energy output per thermal energy output of the reactorEff=W/QR (MWe/MWt) ~33%

Carnot efficiency,

A source of steam is used to produce electricity

The inlet temperature islimited by the water/steam pressure rating of the boiler or reactor vessel in a steam cycle, or by the temperature limitation of the turbine blades in a direct-fired gasturbine.The outlet temperature is usually limited by the ambient temperature ofthe cooling water used in the condenser of a steam cycle


Piecing Together a Reactor

1. Fuel2. Moderator3. Control Rods4. Coolant5. Steam Generator6. Turbine/

Generator7. Pumps8. Heat Exchanger

Simplified schematic layout of a typical reactor power plant

Basic Diagram of a PWR (Pressurized Water Reactor)

http://www.nrc.gov/

two water loops: The water in the primary loop is pumped through the reactor to remove the thermal energy. The loop 2,water is converted to high temperature and high pressure steam that turns the turbo-generator unit.

The great disadvantage of water as a coolant:

must remain in liquid form, steam is a much poorer coolant than liquid water.must be pressurized to prevent boiling at high temperatures(15.5 MPa).

For water, the critical temperature is 375 °C, above which liquid water cannot exist. Typically, coolant temperatures are limited to about 340 °C.

Advantage: small(nature U?)

The steam cycle of a pressurized water reactor. [Westinghouse Electric Corp.

It is about 13 meters tallwith a diameter of about 4 to 6 m. The vessel is built from low-alloy carbon steeland has a wall thickness of about 23 cm

The primary coolant enters the vessel throughtwo or more inlet nozzles, flows downward between the vessel and core barrel

Parameters for a typical 1000 MW(e) PWR sold in the early 1970s.

Boiling-water reactor

a pressurized-water reactor

water is allowed to boil

self-stabilizing behaviour

a direct-cycle, boiling-water reactor

Breeder Reactor增值反应堆

Basic Elements of a Fast Breeder Reactor

Borongraphiteshield

Fuelloadingmachine

Heatexchanger

Core

BREEDER

BLANKET

Magneticpump

The uranium cycle breeder reactors require fast neutrons. Liquid metal and steam may be used as coolants for fast breeding

CANDU reactor

Reactor Generations• Gen I

– Prototypes in 50’s & 60’s• Gen II

– 70’s & 80’s– Today’s Operational Reactors– BWR, PWR, CANDU, …

• Gen III– ABWR, APWR– Approved 90’s– Some Built around the World

• Gen III+– Current Advanced Designs in

the Approval Process– Pebble Bed Reactor

• Gen IV– Deploy in 2030– Economical– Safe– Minimize Waste– Reduce Proliferation

World Nuclear Power

• 443 Nuclear Reactors in 30 Countries in Operation, January 2006

• Provided ~16% World Production of Energy in 2003

• 24 Nuclear Power Plants under Construction

http://www.insc.anl.gov

Alternatives

• Renewable energy– Wind– Bioenergy– Solar– Hydro– Wave– Tidal– Geothermal

• Energy efficiency– Combined heat & power

(CHP)– Building insulation– Efficient lighting– Efficient appliances– Efficient vehicles

• Controlling demand– Behaviour change

• Carbon capture and storage– ‘burial’ of carbon from

fossil fuels

Nuclear (fission) and renewable energy R&D spending in industrialised countries (1975-1999)

0

1000

2000

3000

4000

5000

6000

7000

8000

1975 1980 1985 1990 1995 1999

year

mil

lio

n d

oll

ars

renewables

nuclear fission

Source: IEA (2001)

Alternatives

• Renewable energy– Wind– Bioenergy– Solar– Hydro– Wave– Tidal– Geothermal

• Energy efficiency– Combined heat &

power (CHP)– Building insulation– Efficient lighting– Efficient appliances– Efficient vehicles

• Controlling demand– Behaviour change

• Carbon capture and storage– ‘burial’ of carbon from

fossil fuels

Figure 2: Wind Power Capacity, Top 10 Countries, 2005 (MW)

200230200250360

10880

3902,070

2,050

120240500450450

201,430

2,4301,760

1,810

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000

20,000

Germany Spain US India Denmark Italy UK China J apan Netherlands

Added in 2005Added in 2004

Source: REN21 Renewables Global Status

Report 2006 Update, www.ren21.net



3. General features





What is the Public Hazard?

chemical?biological?physical?radiological?

psychological?

Chlorine for water treatmentNoneNuclear explosion impossibleSmall risk of delayed effects, very small risk of promptChernobyl, Fukushima, nuclear tests

What Is the Goal of Reactor Safety?

To prevent prompt effects with a high degree of assurance and minimize the risk of delayed effects

Typicallyfrequency of a large release < 10-6 per reactor-yearfrequency of a core melt (intact containment) < 10-5 per year

Careful, cautious, scrupulous!

Safety

• Public remains wary of nuclear power due to Chernobyl and three mile island accidents

• Nuclear plants vulnerable to terrorist attacks

• Safer, more efficient, and more secure plants planned for the future



3. The Chain Reaction in a Thermal Fission

4. The Finite Reactor

5. Reactor Operation



8. Nuclear Reactor Accidents Key elements: fuel, neutron moderator, control rod, neutron detector and radioactivity detectors, products

Three Mile Isle

March 28, 1979, 4:00 am

• Secondary cooling loop stops pumping. • Rising temperatures caused emergency

valve to open to release pressure, but indicator light malfunctioned

• Due to loss of steam, water level drops, water overheats and burns out pump

• Reactor core overheats and begins to melt (a “meltdown”)

March 28, 1979, 6:30 am

• Overheated water contains 350 times normal level of melted down radioactive matter

• A worker sees the open valve and closes it

• To prevent an explosion, he reopens it, releasing radioactive steam into the atmosphere

March 28, 1979, 8:00 am

• Nuclear Regulatory commission is notified

• White House is notified

• TMI is evacuated

• All small children and pregnant women within a five mile radius are evacuated

• A fifteen-year clean up project awaits

No Nukes Words: Pat DeCou, Music: Tex LaMountain, ©1977, ASCAP

Look across the sky from your home, Can you see the tower blinking while you sit a spell at home?

Can you see the branches growing? Can you feel the awesome power?

Can you sense its evil purpose and its doom?

It grows in ways we all can understand, And its limbs are spreading all across the land.

The leaves they look like dollars and the sap it ain’t so sweet.

It rests upon the profits hungry people cannot eat.

With promises of quiet, comfort, and peace, The hanging tree can lure to its side.

But the darkness of its shadow gives us warning of the greed

That tries to sell us more electric power than we need.

No nukes for me, ‘cause I want my air to be Free from radiation poison falling over me.

These reactors that they’re building are a giant hanging tree. Don’t you build a hanging tree over me.

People soon will stop this money tree, And we’ll stop its hangin’ people, you and me.

And as we struggle all together all the powers that be will go down with their own hanging tree.

And out of this struggle we can plant a seedling tree, A tree that lets the sunlight share its space.

A tree in tune with living, whose branches lift the soul, When you’re watching from a distance and you’re sitting all alone.

Uranium Mining

There are three main methods:

• Underground mining

• Open pit mining

• In Situ Leaching (ISL)

Underground MiningThe Case of the Olympic Dam Mine

• Olympic Dam mine is located in South Australia

• Most of the mine’s profit actually comes from the copper that they mine as well

• Tunnels are dug into the earth, where ore is extracted

• The ore is crushed into a powder, then soaked in a lake. The impurities precipitate and the rest is dried by heat.

Ya Got Trouble….

• Lake uses an intense amount of water

• Rabbit popluation has crashed as a result of drinking from the lake

The Western Mining Corporation (WMC) is owned by BP

In Situ Leaching ( 现场浸取）

• Wells are drilled into aquifers （蓄水层） , the water is removed, and a solvent, such as hydrogen peroxide （过氧化氢） , is pumped in

• The peroxide dissolves the uranium, and the solution is pumped back up

• An ion exchange system causes the uranium to precipitate （沉淀） in the form of UO42H2O (uranium peroxide)

In Situ Leaching

ISL has its woes

• Ground water supply has radioactive residues

• There are ISL mines in Texas, Wyoming, and Nebraska that share the same aquifers as residents



3. General Features




7. Uranium Mining


中核 www.cnnc.com.cn

中广核 http://www.cgnpc.com.cn/Areva http://www.areva.com/Westinghouse www.westinghouse.com

http://www.cnnc.com.cn/

http://www.cnnc.com.cn/

http://www.cgnpc.com.cn/

http://www.cgnpc.com.cn/

http://www.westinghouse.com/

Lindsey GarstJay NargundkarJonah Richmondhttp://www.astro.umd.edu/~hamilton/teaching/HONR268Afall05/presentations/Nuclear.pptHiroshi Sekimoto

http://www.astro.umd.edu/~hamilton/teaching/HONR268Afall05/presentations/Nuclear.ppt

http://www.astro.umd.edu/~hamilton/teaching/HONR268Afall05/presentations/Nuclear.ppt

chapter 4. nuclear power 1.introduction 2.characteristics of fission 3. general features 4....

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