Transcript Physics 201 - University of Virginia

PHYS 1110
Lecture 23
Professor Stephen Thornton
November 27, 2012
Reading Quiz
What size reactor is considered a small
nuclear reactor?
A)
B)
C)
D)
E)
any size
any reactor below 2000 MWe
any reactor below 1000 MWe
any reactor below 1000 MWt
any reactor below 100 MWe
Reading Quiz
What size reactor is considered a small
nuclear reactor?
A)
B)
C)
D)
E)
any size
any reactor below 2000 MWe
any reactor below 1000 MWe
any reactor below 1000 MWt
any reactor below 100 Mwe
actually below 300 MWe
Remaining schedule:
Today: HW 6 on Ch. 9 due
Tuesday, Dec. 4: HW 7 on Ch. 10 due
Quiz on Chs. 9 and 10
Thursday, Dec. 6: HW 8 on Ch. 11 due
Osmotic Energy
When rivers empty into oceans, the fresh water reduces the salinity
of the seawater as the rivers flow into the ocean. If a membrane is
placed between the fresh and sea water, the process of osmosis takes
effect. The membrane only allows small molecules like water
through the membrane leaving the larger salt molecules behind.
The water strives for equality for the salt concentration so the fresh
water flows through the membrane to the ocean water side to lower
the salt concentration of the ocean water. The osmotic process,
however, creates a higher pressure in the salt solution side as shown
in the figure. The pressure is then used to drive a turbine and
produce electricity. The whole thing sounds incredibly simple. The
energy is renewable and it is always available. The biggest
disadvantage is the cost of the membranes, but significant
breakthroughs in membrane research have occurred. It has been
estimated that 2.6 TW of electrical power may be derived from the
osmotic process.
The process just shown will eventually stop when the
pressure builds up. We need a cyclic process that will work
continuously. See below. Fresh water, say from a river, comes in at
the top left, and salt water, from the ocean, comes in at the bottom
right. Fresh water passes through the semi-permeable membrane
through the osmotic process. In the upper right the higher pressure
salt water drives the turbine, and the brackish water is expelled.
If we continuously
flow through both
fresh and salt water
that has a salinity
difference of 3%,
the theoretical
potential energy
corresponds to a
waterfall of 250 m
height.
The Norwegian University of Science and
Technology and the Norwegian utility company
Statkraft have taken the lead. After a decade of
collaborative research and development, including a
high-performance membrane, Statkraft opened the
first prototype osmotic power plant in the world on
the Oslo fjord in 2009. Although small, it only
produces 2-3 kW, but they have shown that it works.
Their system has 10 liters of water flowing through
a membrane each second. Stadkraft believes that
Norway has a salinity gradient between its rivers
and seawater that may allow electrical generation of
up to 12 TWh per year.
The commercialization of osmotic energy is still
somewhat uncertain, and its role in producing competitive electricity
is clearly far into the future. We read projections like 2012, 2015,
and 2020, but these dates come and go. The Norwegian pilot plant
shows the concept is feasible. The problem is still high capital costs.
The next step is a demonstration plant which would scale up the
current technology, verify the expected cost of electricity produced,
and optimize the operation and maintenance. The improvement in
the membranes has been significant, and there are now international
conferences on just osmotic membrane development. Early
membranes were cellulosic, and more recent ones are thin film.
More research and development is needed to improve the cost,
maintenance, cleaning, and lifetime of membranes. Nevertheless,
we may be only a breakthrough away in membrane development
from osmotic energy being truly useful and price competitive.
Quiz
Which of the following statements is
most true about Osmotic energy?
A)
B)
C)
D)
a membrane is required
fresh and salt water are needed
the energy is renewable
none of the previous answers (A-C)
are true.
E) all of the previous answers (A-C) are
true.
Quiz
Which of the following statements is
most true about Osmotic energy?
A)
B)
C)
D)
a membrane is required
fresh and salt water are needed
the energy is renewable
none of the previous answers (A-C)
are true.
E) all of the previous answers (A-C) are
true.
Nuclear energy – Chapter 10
The share of global electricity produced annually
by nuclear power and the total energy production.
There has been a renewed interest in developing nuclear
power in both developed and developing countries partly because of
volatile fossil fuel prices. In the United States where construction
had ceased for decades, construction has started again and new
reactor designs have been certified. European countries have
continued their political debate, but nuclear power is now a key
element in the European Union’s climate change policy. Finland
decided to build a new fifth nuclear reactor in 2002, the first such
decision to do so in Western Europe in over a decade. Other
European countries had overturned previous decisions not to build
nuclear reactors, and debates are ongoing in Europe. We point out
that the 2011 Fukushima Daiichi disaster have changed some of
these plans.
China has 25 nuclear reactors under construction and plans to build
more, but they are unlikely to exceed the number of reactors in the
US. The licenses of almost half the reactors in the US have been
extended to 60 years and new reactors are both planned and under
construction.
Table 10-1 World Nuclear Power Reactors
Reactors
Number
Operating
434
Under Construction` 64
Planned
160
Proposed
323
MWe
372,760
64,174
177,915
366,415
Source: http://www.world-nuclear.org/info/reactors.html
During the period 1996-2009, 43 reactors were retired and 49
started operations. The WNA estimates that at least 60 reactors
operating now will close by 2030. The 2011 WNA Market Report
suggests 156 reactors will close by 2030, and 298 new reactors will
come on line for a net gain of 143 reactors or a total of 587 reactors
in 2030.
How Nuclear Energy Works
E = mc
2
The mass of a bound nucleus is less than the sum of its
constituent nucleons. This mass difference, sometimes
called mass defect, is a measure of the nuclear binding
energy, which in turn is related to the strong nuclear force
that holds the nucleons together. This mass defect is the
energy released when the nucleus is formed.
Iron nuclei are most tightly bound. Energy is
liberated when heavy nuclei like uranium break apart
into lighter nuclei.
Fission
and
Fusion
Nature prefers equal numbers of neutrons
and protons, called nucleons. Why do
heavy nuclei have more neutrons?
A few of these heavy, unstable nuclei have such long decay
times that some of them are still stable from early in the
universe when they were first formed. That is the case for
two isotopes of uranium (element number 92), 235 U and 238 U,
that can still be found naturally on Earth. Natural uranium
contains 99.7% 238 U and 0.7% 235 U. It is 235 U that is most
useful in nuclear reactors, so natural uranium must be found
in deposits, mined, isolated, and then separated so that the
percentage of it is enhanced.
Nuclear fission usually produces two
fragments of unequal sizes and
additional neutrons. Material that is
able to undergo fission is called fissile.
The most common fissile material is
uranium-235 ( 235 U ) and plutonium239 (239 Pu ). The latter is manmade
and does not occur in nature on Earth.
These two nuclei are known to fission
as the result of absorbing what is
called thermal neutrons. These are
neutrons that have the kinetic energy
associated with the temperature of
their environment.
235 U
Each of the fissions shown in the previous slide
produces two or three additional neutrons. If each
of these neutrons in turn is absorbed by another
nucleus, a so-called self-sustaining chain reaction
may occur. If one neutron, on the average,
produces fission, the chain reaction becomes
critical. A sufficiently large amount of fissile
material, called critical mass, must be present for
this to occur. If less than one neutron interacts, the
process is called subcritical. If slightly more than
one neutron interacts, the process is called
supercritical, an example of which is the atomic
bomb.
There are several components required to construct a device
capable of producing energy using a controlled nuclear fission
reaction. These include
1) Fissionable fuel like 235U. Long fuel rods.
2) A moderator to slow down neutrons to make them thermal
(water and graphite).
3) Control rods to control the criticality (high neutron absorbing
material like cadmium, boron, or hafnium).
4) A reflector system to surround the moderator and fuel to prevent
neutrons from escaping from the area.
5) A coolant circulating through the core used to remove heat.
Crucial as the energy transfer system to produce heat and
electricity. Water is used in light water reactors as both a
moderator and coolant.
6) A reactor vessel, radiation shield, and containment vessel.
Note:
Fissile fuel
Moderator
Control rods
Reflector – not
shown
Coolant
Radiation shield
A simple schematic of a Boiling Water Reactor
(BWR). Note that the water surrounding the nuclear
core boils to steam and this same steam is used to turn
the turbine.
Schematic of a Pressurized Water Reactor (PWR).
Note that there are two regions of water; one source
does not leave the containment structure. About 2/3
US reactors are PWR.
Two containment structures at Diablo Canyon
nuclear power plant in California.
The various power ratings of a nuclear power reactor depend on where
the power is determined. The Net MWe is what enters the electrical grid.
History
1930s neutrons and protons known
1934 Induced radioactivity known
1938 Germans, Austrians split atoms with neutrons
1942 Enrico Fermi built reactor at Chicago. Start of
Manhattan project.
1945 Terrible, terrible atomic bombs on Japan.
1953 Ike promised “Atoms for Peace”
1951 First reactor to generate electricity in Idaho
1954 First reactor to enter power grid in USSR
1956 First commercial reactor, Calder Hall, England
1957 Shippingport reactor, PA.
Top: Installed global nuclear capacity and, since
1991, the actual realized capacity. Bottom: Active
number of reactors and those under construction.
1979 Three Mile Island accident – water pump failure followed
by human error.
1986 Chernobyl accident – sudden power surge not contained
2011 Fukushima problem – earthquake followed by tsunami
As a result of the Three Mile Island and Chernobyl accidents,
health and safety concerns have played a huge role in stopping
current and new construction projects in several countries.
However, a study by the Brookings Institution suggests that a
soft demand for electricity and cost overruns played a larger role.
The average time for plant construction had reached seven years
by the 1980s.
Nuclear renaissance around 2000
Increasing Energy Demand Population growth, industrial
development, and third-world country economic development creates a
growing demand for electricity. Need fresh water and electric vehicles.
Security of Supply Worldwide political insecurities make countries
concerned about the delivery of fossil fuels, especially gas and oil.
Abundance of uranium.
Climate Change Global warming and climate change may make
nuclear power more attractive than fossil fuels.
Economics Nuclear power is cost competitive. As carbon emission
reduction requirements are added, the economic benefits of nuclear
power are increased.
Insurance Against Future Price Exposure The uncertain price of
fossil fuels, especially oil, has been a huge global problem. The
primary cost of nuclear power is due to capital costs.
Location of March 2011 earthquake with
respect to Onagawa and Fukushima.
Public attitudes toward nuclear power in the
United States from 1983-2008. Source: Nuclear
Energy Institute. September 2012 survey shows
Americans still favor nuclear power, 65% - 29%.
Divide up into groups and discuss the
following, then make reports.
• Mining
• Conversion
& Enrichment
• Fuel
• Reprocessing
• Waste
Schematic of CANDU power reactor.
The first new power reactor beginning construction in the
United States since 1977 is near Waynesboro, Georgia at Plant
Vogtle. The two AP1000 units are being constructed by Southern
Nuclear and are expected to be completed in 2016 and 2017. The
Watts Bar 2 nuclear reactor in Tennessee was about 80% complete
when construction was stopped on it in 1988. Construction
resumed in 2007, and it is expected to be the first new nuclear
reactor to be completed in more than a decade in the US. But it has
gone over budget and behind schedule. It is now hoped that it will
be finished by the end of 2015.
As of October 2012 there were 64 nuclear reactors under
construction in 13 countries, most of them in Asia, 26 in China, 10
in Russia, 7 in India. There are currently 434 operable nuclear
reactors, capable of producing 373 GWe. The 64 under
construction will add another 64 GWe, and many of the new ones
will be Gen III.
Gen IV Reactors
• Nuclear waste that is radioactive for a few
hundred, rather than thousands, of years.
• More energy yield (by 100-300) than existing
nuclear fuel.
• Ability to consume current nuclear waste to
produce electricity.
• Enhanced operational safety.
• Reduced capital costs.
Look over goals: 2 sustainability, 2 economic, 3
safety and reliability, 1 proliferation resistance
Generation IV Proposed Reactor Systems
Temp 0C Fuel
Cycle
900 to
open
1000
Size (MWe)
sodium
550
closed
thermal/
fast
water
510-625
open/
closed
30-150,
300-1500,
1000-2000
300-700
1000-1500
fast
helium
850
closed
1200
LFR (Lead-cooled fast fast
reactor)
lead
480-800
closed
MSR (Molten salt
reactor)
fluoride
salts
700-800
closed
20-180,
300-1200,
600-1000
1000
System
Neutron
Spectrum
thermal
Coolant
SFR (Sodium-cooled
fast
reactor)
SCWR (Supercritical
watercooled reactor)
fast
GFR (Gas-cooled fast
reactor)
VHTR
(Very high temperature
gas reactor)
epithermal
helium
250-300
Quiz
Which of the following countries (or
unions, areas) has the most nuclear
reactors under construction?
A)
B)
C)
D)
E)
China
European Union
United States
South America
India and Pakistan
Quiz
Which of the following countries (or
unions, areas) has the most nuclear
reactors under construction?
A)
B)
C)
D)
E)
China
European Union
United States
South America
India and Pakistan
Quiz
How many nuclear reactors are currently
operating throughout the world?
A)
B)
C)
D)
E)
less than 100
100 to 200
200 to 300
300 to 400
over 400
Quiz
How many nuclear reactors are currently
operating throughout the world?
A)
B)
C)
D)
E)
less than 100
100 to 200
200 to 300
300 to 400
over 400
Quiz
What is an example of a supercritical
reaction?
A)
B)
C)
D)
E)
a reaction that produces 239 Pu
a fusion bomb
a fission bomb
a reaction caused by a slow neutron
a reaction caused by a fast neutron
Quiz
What is an example of a supercritical
reaction?
A)
B)
C)
D)
E)
a reaction the produces 239 Pu
a fusion bomb
a fission bomb
a reaction caused by a slow neutron
a reaction caused by a fast neutron
Quiz
Which of the following is not a cause of
the nuclear renaissance of the 2000s?
A)
B)
C)
D)
E)
economics
security of fuel supply
low cost of natural gas
increasing energy demand
climate change
Quiz
Which of the following is not a cause of
the nuclear renaissance of the 2000s?
A)
B)
C)
D)
E)
economics
security of fuel supply
low cost of natural gas
increasing energy demand
climate change
Small nuclear reactors
•
cheaper to construct and run than larger reactors.
•
Placed in remote areas not having sufficient electrical grids. 100,000 people.
•
used in places like third-world or remote island countries.
•
can be used for specialized purposes like desalination or hydrogen production.
•
do not have to be custom designed.
•
can be factory built and delivered as needed.
•
have short construction times and can even be “shelf” ready.
•
can be returned to specialized facilities for decommissioning.
•
do not necessarily need to be cooled by water and, therefore, placed near large
bodies of water. They can be cooled by air, gas, low-melting point metals.
Left: schematic of Babcock & Wilcox mPower reactor.
Right: underground containment structure for two
mPower reactors.
The TerraPower Travelling Wave Reactor (TWR) The concept
is that the reactor can breed its own fuel inside the reactor from natural or
depleted 238U. It only needs a small amount of enriched 235U to begin the
process. Thereafter neutrons produced by fission are in turn absorbed by 238U
and in turn decay, eventually producing the fissile material 239Pu.
n+
238
92
U®
239
92
U®
239
93
Np + b - ®
239
94
Pu + b -
The TWR nuclear core does not move. We show a schematic of the
“breed and burn” concept below. The reaction started on the far left
with enriched 235U and the breeding and fission areas are moving slowly
to the right, thus the traveling wave.
Fast breeder reactors and fusion reactors.
A fast breeder reactor (FBR) is a nuclear reactor that utilizes
fast neutrons to produce more fissile material than it consumes.
Remember nuclear fission normally produces fast neutrons that
have to be slowed down or thermalized by a moderator.
Reactions like the previous produce 239Pu from fast neutrons
interacting with the highly abundant uranium isotope 238U.
The extra 239Pu produced could be used to start another nuclear
reactor. There was considerable interest in fast breeder
reactors about 50 years ago, because of the fuel economy, and
there was concern about lack of uranium reserves. There
currently seems to be enough uranium reserves to last for
decades, and there does not seem to be difficulty in finding
new reserves when needed. Uranium enrichment using
centrifuges and eventually lasers is much more economical
than the older gaseous diffusion process.
Deaths from energy related accidents per
unit of electricity generated.
The primary concern about nuclear reactors is if a large
amount of radioactive fission products were dispersed over a wide
area, where the radiation material could contaminate the soil and
vegetation and be ingested by humans and animals. It is impossible,
however, for a commercial nuclear reactor to detonate like a nuclear
bomb, because the fuel is not highly enriched enough and it cannot
be forced to a high enough density.
Except for the Chernobyl disaster, no nuclear workers or members of
the public have ever died due to radiation received due to a
commercial nuclear reactor event. There have been at least ten
accidents in military and experimental reactors. Only one resulted in
significant radiation release. There is also a significant difference in
safety between well-developed countries in the OECD and nonOECD countries. Hydropower has caused many more
fatalities/TWy, followed by coal and then natural gas. Nuclear is a
factor of more than 200 safer than hydropower.
Attacks on Nuclear Facilities
Year
Event______________________________
1980
1981
1984-87
1991
Iran bombed a nuclear complex in Iraq
Israel destroyed a nuclear research facility in Iraq
Iraq bombed a nuclear plant in Iran six times
USA bombed three nuclear reactors and an
enrichment facility in Iraq
Iraq launched Scud missiles at an Israeli nuclear
power plant
Israel bombed a Syrian nuclear reactor under
construction.
Israel/United States will bomb Iran nuclear
facilities
2007
2008
2013-14
There are a number of ways in which a nuclear
reactor can fail. The primary concern is a loss of
coolant, which may cause the fuel to melt or cause the
containment vessel to overheat and melt. This event
is called a nuclear meltdown. The Generation IV
reactors presently being considered and designed
hope to completely alleviate this concern.