PHYS 1110

Lecture 23

Professor Stephen Thornton

November 27, 2012

Reading QuizWhat size reactor is considered a small nuclear reactor?

A) any sizeB) any reactor below 2000 MWeC) any reactor below 1000 MWeD) any reactor below 1000 MWtE) any reactor below 100 MWe

Reading QuizWhat size reactor is considered a small nuclear reactor?

A) any sizeB) any reactor below 2000 MWeC) any reactor below 1000 MWeD) any reactor below 1000 MWtE) 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.

QuizWhich of the following statements is most true about Osmotic energy?

A) a membrane is requiredB) fresh and salt water are neededC) the energy is renewableD) none of the previous answers (A-C) are true.E) all of the previous answers (A-C) are true.

QuizWhich of the following statements is most true about Osmotic energy?

A) a membrane is requiredB) fresh and salt water are neededC) the energy is renewableD) 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 MWeOperating 434 372,760Under Construction` 64 64,174Planned 160 177,915Proposed 323 366,415

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

2E mc=

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), and , that can still be found naturally on Earth. Natural uranium contains 99.7% and 0.7% . It is 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.

235U 238U

238U 235U 235U

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 ( ) and plutonium-239 ( ). 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.

235U

235U

239 Pu

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 include1) 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 fuelModeratorControl rodsReflector – not shownCoolantRadiation 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 known1934 Induced radioactivity known1938 Germans, Austrians split atoms with neutrons1942 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 Idaho1954 First reactor to enter power grid in USSR1956 First commercial reactor, Calder Hall, England1957 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 contained2011 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 2000Increasing 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

System NeutronSpectrum

Coolant Temp 0C FuelCycle

Size (MWe)

VHTR(Very high temperaturegas reactor)

thermal helium 900 to1000

open 250-300

SFR (Sodium-cooled fastreactor)

fast sodium 550 closed 30-150,300-1500,1000-2000

SCWR (Supercritical water- cooled reactor)

thermal/fast

water 510-625 open/closed

300-7001000-1500

GFR (Gas-cooled fastreactor)

fast helium 850 closed 1200

LFR (Lead-cooled fastreactor)

fast lead 480-800 closed 20-180,300-1200,600-1000

MSR (Molten salt reactor)

epithermal fluoridesalts

700-800 closed 1000

Generation IV Proposed Reactor Systems

QuizWhich of the following countries (or unions, areas) has the most nuclear reactors under construction?

A) ChinaB) European UnionC) United StatesD) South AmericaE) India and Pakistan

QuizWhich of the following countries (or unions, areas) has the most nuclear reactors under construction?

A) ChinaB) European UnionC) United StatesD) South AmericaE) India and Pakistan

QuizHow many nuclear reactors are currently operating throughout the world?

A) less than 100B) 100 to 200C) 200 to 300D) 300 to 400E) over 400

QuizHow many nuclear reactors are currently operating throughout the world?

A) less than 100B) 100 to 200C) 200 to 300D) 300 to 400E) over 400

QuizWhat is an example of a supercritical reaction?

A) a reaction that produces B) a fusion bombC) a fission bombD) a reaction caused by a slow neutronE) a reaction caused by a fast neutron

239 Pu

QuizWhat is an example of a supercritical reaction?

A) a reaction the produces B) a fusion bombC) a fission bombD) a reaction caused by a slow neutronE) a reaction caused by a fast neutron

239 Pu

QuizWhich of the following is not a cause of the nuclear renaissance of the 2000s?

A) economics B) security of fuel supplyC) low cost of natural gasD) increasing energy demandE) climate change

QuizWhich of the following is not a cause of the nuclear renaissance of the 2000s?

A) economics B) security of fuel supplyC) low cost of natural gasD) increasing energy demandE) 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.

238 239 239 23992 92 93 94n U U Np Pub b- -+ ® ® + ® +

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.

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 non-OECD 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 Iran bombed a nuclear complex in Iraq1981 Israel destroyed a nuclear research facility in Iraq1984-87 Iraq bombed a nuclear plant in Iran six times1991 USA bombed three nuclear reactors and an enrichment facility in Iraq2007 Iraq launched Scud missiles at an Israeli nuclear

power plant2008 Israel bombed a Syrian nuclear reactor under

construction.2013-14 Israel/United States will bomb Iran nuclear facilities

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.