Chapter 13 – Energy from Nuclear Power

APES

Chapter 13 Reading Quiz

1. Why was the Nuclear Regulatory Commission started?2. What is the difference between nuclear fission and nuclear

fusion?3. All current plants use the nuclear ________ of ____________.4. What is enrichment?5. Control rods absorb _____.6. What is half-life?7. The EPA recommends a 10,000 year minimum and the

National Research Council opted for _______ years to provide protection from long-lived isotopes.

8. What does NIMBY stand for and how does it apply to this chapter?

Tokaimura, Japan

Village near Tokyo Japan Atomic Energy Research Institute 9/30/99 – 3 workers mixed nitric acid and uranium

in buckets --- amounts were well above the approved levels Began a nuclear fission reaction Not large enough to explode but emitted large

amounts of gamma rays and neutrons Took 24 hours to shut down rxn

13.1 Nuclear Energy in Perspective

The Nuclear Age After WWII there was a push for nuclear power in

effort to show that the power of the atom could benefit humankind

US government began supporting research and companies began building nuclear power plants

NRC (Nuclear Regulatory Commission) and the Atomic Energy Commission was created to set safety standards for operation and maintenance of new plants

Figure 13-2 p. 351

13.2 How Nuclear Power Works

Objective: control nuclear rxns so that energy is released gradually as heat Heat will then be used to boil water to produce

steam…which drives a turbogenerator Usually a base load plant

Always operating unless being refueled Generates 1,400 MW

Mass to Energy

Usually energy comes from breaking chemical bonds. Oil, coal, gas

Break bonds between C-C and energy is released Nuclear energy involves changes on the atomic

level so there is greater energy release The mass of the products after fission or fusion is less than

the mass of the starting material this loss of mass is converted to energy Law of mass – energy equivalence

E=mc2; tells you how much energy a certain mass would have if it suddenly turned into energy

Mass to Energy

E=mc2

Energy = mass (speed of light)2

Speed of light is 3.00x108

Ex: In 1kg of water, the mass of hydrogen atoms is 111g or 0.111kg. How much energy would be released if the mass of energy is suddenly released?

Or if you had just 1kg of material….it would release 90,000,000,000,000,000 J of energy…that would run a 100 watt light bulb for 28,519,279 years!!!

13.2 How Nuclear Power Works

From Mass to Energy Fission and Fusion

Fission- a large atom of one element is split to produce two smaller atoms of different elements uranium-235

Fusion – two smaller atoms combine to form a larger atom of a different element Isotopes of hydrogen helium Can only occur at temperatures in excess of 40,000,000°C

Figure 13-5 p. 353

The Fuel for Nuclear Power Plants

All current plants use the fission of uranium -235 2 forms of uranium that occur naturally in the

earth U-235 and U-238 Isotopes – differ in numbers of neutrons

How many protons and neutrons are found in the isotopes? Why are they still uranium even though they have different

numbers?

The Fuel for Nuclear Power Plants

U-235 will readily undergo fission while U-238 will not To begin a reaction to produce energy, there has to be a

specific combination of U-235 and U-238 in a sample. The U-235 is unstable and so it begins to release neutrons

by means of radioactive decay (naturally) Neutrons moving at the right speed hits another U-235

which then becomes U-236 which is highly unstable and undergoes fission immediately Continues in a chain reaction,

Nuclear Fuel

How do we get uranium to use? Mine….

Uranium ore is mined and then purified into uranium dioxide (UO2) and then enriched. 99.3% of all uranium found in nature is U-238 0.7% is U-235

Enrichment involves separating U-235 from U-238, small differences in mass Very technical and prevents less developed countries

from advancing their own nuclear power

Enrichment

The combination of U-235 and U-238 is critical Too much enrichment or a higher percentage or

U-235 can cause the frequency of a chain reaction to occur Nuclear weapons and bombs use highly enriched U-

235 20% U-235 is “highly enriched”; 80-93% for nuclear

weapons programs

The Nuclear Reactor….Figure 13-8 p. 357

The Nuclear Reactor for power plants

Designed to sustain a continuous chain reaction but not allow it to amplify into a nuclear explosion Control- enriching only to 4% U-235 and 96% U-238

Will not support a chain reaction that will result in an explosion Japan accident the U-235 mixed with nitric acid was 18.8%

enriched In the process of fission, some of the faster neutrons are

absorbed by U-238 atoms, converting them into Pu-239 which then undergoes fission 1/3 of the energy of a nuclear reactor comes from Pu fission

The Nuclear Reactor for power plants

Moderator A chain rxn can be achieved if:

1. there is a suitable amount of U-235 2. arranged in a geometric pattern 3. surrounded by a material called a moderator

Substance, usually water (light water reactors; LWR in US) or can be graphite or deuterium oxide (D2O; heavy water)

Slows down the neutrons that produce fission so that they are traveling at the right speed to trigger another fission

The moderator gains some of the heat produced during the fission reactions

The Nuclear Reactor for power plants

Fuel Rods To achieve the geometric pattern, UO2 is made

into pellets and loaded into long metal tubes fuel rods or fuel elements Fuel rods are placed close together to form a reactor

core inside a strong vessel that holds water (moderator and heat exchange fluid or coolant) Over time, daughter products accumulate in the fuel rods

and most be removed and replaced

The Nuclear Reactor for power plants

Control Rods Chain rxn is also controlled by control rods Placed between fuel rods to absorb neutrons

Moveable IN = fewer neutrons = power or energy goes down Out = more neutrons = power goes up

Can be made out of anything that is a neutron poison or something that will take neutrons away (cadmium)

Figure 13-7 p. 356

LOCA

Loss-of-coolant accident If the reactor vessel should break, the sudden

loss of water could cause the core to overheat. The coolant water loss (moderator) would cause

fission to cease 7% of the reactor’s heat comes from radioactive

decay and overtime uncontrolled decay would cause a meltdown The materials in the core melting

Steam explosion….

Comparing Nuclear Power with Coal Power

13.3 The Hazards and Costs of Nuclear Power Facilities

Radioactive Emissions When an element undergoes fission, the split “halves” are

direct products Direct products are unstable isotopes called radioisotopes Radioisotopes spontaneously eject alpha, beta, gamma

particles and neutrons Alpha particles: contains 2 protons and 2 neutrons and a double

positive charge; written as 42He or α

Low penetration and can be shielded by paper or clothing Beta particles: Occurs when a neutron is split into a proton

(hydrogen) and an electron which is the beta particle; written as 0-1e or β

Moderate penetration and can be shielded by metal foil Gamma particles: high energy photon; no mass and no electrical

charge; written as γ Very high penetration; will penetrate body easily and can be

partially shielded by lead and concrete

Radioactivity

Measured in curies 1g of Ra-226 gives off 1

curie per second Radioactive wastes-

direct and indirect products of nuclear fission Figure 13-10

Biological Effects of Radiation

Exposure to low levels of radiation could elevate the risk of cancer and other disorders The ability to do damage is measured in sieverts (Sv)

High Dose (over 1 Sv) May cause enough damage to prevent cell division

Used in cancer treatment because it focuses the radiation to prevent the tumor from dividing.

If whole body is exposed: generalized blockage of cell division which could prevent the repair of blood, skin and other tissues – results in radiation sickness and death within a few days or months

Biological Effects of Radiation Low Dose

May damage DNA Increase mitosis

Malignant tumors Leukemia

DNA damage to egg or sperm can lead to birth defects Effects could go unseen for many years Also weakens the immune system, could cause mental

retardation and the development of cataracts

How much exposure will do harm? 100-500 millisieverts (mSv) increases the risk of developing

cancer

Sources of Radiation

Background radiation: “normal”

uranium and radon gas naturally found in Earth’s crust Cosmic rays Medical and dental x-rays

During normal operations of a nuclear power plant Radiation detectors will pick up more background radiation

from the ground or concrete than it will held with in 150 yards of a nuclear power plant Less than 1% public exposure

Radioactive Wastes

Radioactive decay: Unstable isotopes ejecting particles and radiation

eventually become stable and cease to be radioactive

Half-Life The amount of time it takes for half the material to

decay Always the same, no matter how big the starting

material is Range from a fraction of a second to many thousands

of years

Disposal of Radioactive Wastes

Short term containment: allows the radioactive decay of short-lived isotopes (half-life is in days) In 10 years 97% of the radioactivity will be gone

Long term containment: long lived isotopes (half-life is in years) EPA recommends a 10,000 year minimum and the National

Research Council opted for 100,000 years to provide protection from long-lived isotopes

Government standards require isolation for 20 half-lives So if Pu has half-life of 24,000 years….how many years will

it take for Pu to be declared “safe”

Tanks and Casks

Short term containment: 1st the waste is stored in a swimming pool like tank on site of the

nuclear power plant H2O dissipates waste heat and shields escape of radiation Accommodate 10-20 years of spent fuel Storage pools reached 50% by 2004 and will be 100% by 2015

Casks Air-cooled Interim storage until long-term storage becomes available

Military Radioactive Wastes

Worst failures in handling wastes Connection with manufacture of nuclear weapons Deliberate releases of uranium dust, Xe-133, I-

131 and tritium have occurred Handford, WA, Oak Ridge, TN, Fernald, OH and

Savannah River, SC DOE in charge of cleaning

Russian military

Chelyabinsk-65 Russian military weapons facility 20 years, nuclear waste was dumped into the

Techa River and then into Lake Karachay 1,000 cases of leukemia Standing on the shore of Lake Karachay for 1 hour will

cause radiation poisoning and death with in a week Legacy of the Cold War

High-Level Nuclear Waste Disposal

Geologic burial is the only option for long-term containment of nuclear wastes Basic problem: no rock formation can be

guaranteed to remain stable and dry for 10,000+ years

Yucca Mountain

Efforts to locate a long-term containment facility have been hampered by….. NIMBY

Many states have passed legislation prohibiting the disposal of nuclear wastes within their boundaries

Nuclear Waste Policy Act of 1982- federal government to begin receiving nuclear waste from commercial power plants in 1998 1987- Congress called a halt to the debate and

selected Yucca Mtn in Nevada to be the nation’s civilian nuclear waste disposal site

Yucca Mountain Nevadans passed a law in

1989 that prohibits anyone from storing high-level radioactive waste in the state Federal government has

the power to override July 2002 President Bush

signed a resolution that was passed by Congress voiding a veto by Nevada’s Governor Kenny Guinn that had attempted to block further development

Nuclear Power Plant Accidents

Three Mile Island March 28, 1979 Near Middleton, PA

Partial meltdown- result of human and equipment failures and flawed design

No injuries or death Reactor was badly damaged

Chernobyl April 26, 1986

Ukraine Engineers were conducting tests

Removed control rods, shut off flow of steam to generators and decreased flow of coolant water to reactor

Reactor began to heat up extra steam could not escape and had the effect of rapidly boosting the energy production of the rxn

Engineers put in carbon-tipped control rods which acted as moderators

Neutrons were still moving too fast; more fission rxns which eventually led to a split-second power surge 100x the maximum allowed level

Steam explosions blew the 2000 ton top off the reactor which led to a meltdown – graphite moderator burned for days

50 tons of dust and debris bearing 100-200 million curies of radioactivity 100x the radiation fallout from the bombs dropped on Hiroshima and

Nagasaki in 1945

Could an accident in US US uses LWR moderators not graphite

LWR are incapable of developing a power surge more than twice their normal power A surge generated in this situation would be within the

designed capacity of the reactor vessel There are also more backup systems that prevent

overheating

Reactors are housed within a thick walled containment building designed to withstand explosions like Chernobyl – which had no containment building

….but with all of these precautions there still could be a total loss of coolant accident

Nuclear Power and Safety As a result of Three Mile Island the NRC upgraded

safety standards

Terrorism and Nuclear Power Question: could a jetliner penetrate the thick walls

of the containment vessel…..NO But.. A jetliner could destroy the control building and

bring on a LOCA Spent fuel storage pools…..targeted protection not

as thick and there could be a loss of water which would expose people to radiation.

Economic Problems

Risk…starting, maintaining and safety Cost of electricity is rising Embrittlement- neutrons from fission

bombarded the reactor vessel and other hardware – metals become brittle and must be replaced to prevent a LOCA

Corrosion- from water

Resources

www.eoearth.org/article/Tokaimura_criticality http://www.worsleyschool.net/science/files/e

mc2/emc2.html http://www.fas.org/nuke/intro/nuke/uranium.ht

m <ahref="http://science.jrank.org/pages/

4754/Nuclear-Reactor-Control-rods.html">Nuclear Reactor - Control Rods</a>

www.ohiocitizen.org