Environmental Science Name: Blk:
CH 9 (9.8 – 9.10): STUDY GUIDE
Fill-in the spaces below (This is only for sections 9.8 – 9.10)
9.8 Nuclear Fission Reactors
• Control rods made of ______(boron, graphite) are lowered into the reactor to absorb ______and control the rate of ______.
• What occurs to the rate of fission, when they are withdrawn?
• A ______is a substance that absorbs energy, which slows neutrons, enabling them to split the nuclei of other atoms more effectively.
• ______and ______are the most commonly used.
• Coolant, usually water, manages ______.
• In the production of electricity, a nuclear reactor serves the same function as a
______: it produces heat, which converts ______
______, which turns a ______, generating electricity.
• The 3 most common types of reactors are:
• ______(60%)
• ______(20%)
• ______(10%)
• Gas-Cooled Reactors are not popular, and no new plants of this type are being constructed.
• Pressurized-Water Reactor: Why is the water kept under high pressure?
• ______reactors produce nuclear fuel as they produce electricity.
• Liquid ______efficiently moves heat away from the reactor core.
• Hence they are called Liquid Metal Fast Breeder Reactors.
• A fast moving neutron is absorbed by ______and produces ______
• P239 is fissionable fuel.
• Most breeder reactors are considered experimental.
• Because P239 can be used in nuclear weapons, breeder reactors are ______sensitive.
9.9 The Nuclear Fuel Cycle
· The Nuclear cycle follows the process of mining of uranium to the disposal of the waste from powerplants.
1. Mining and Milling
· The nuclear fuel cycle begins with the mining of low-grade uranium ore primarily from ______, ______, ______,
______, ______, and the
______.
· It is milled, and ______and ______with a solvent to concentrate the uranium.
· Milling produces yellow-cake, a material containing ______%_ uranium oxide.
2. Enrichment
· Naturally occurring uranium contains about ______% non-fissionable U238, and ______% fissionable U235.
· It must be enriched to ______% U235 to be concentrated enough for most nuclear reactors.
· Centrifuges separate the isotopes by their slight differences in mass.
3. Fuel Fabrication
· Material is fabricated into a ______and then into pellets.
· The pellets are sealed into ______(fuel rods) and lowered into the reactor.
4.______
· As fission occurs, U-235 concentration ______
· After about ______years of operation, fuel rods don’t have enough radioactive material remaining to sustain a chain reaction, thus spent fuel rods are replaced by new ones.
· Spent rods are still very radioactive, containing about ______% U-235 and ______% plutonium.
· Spent fuel rods are radioactive, and must be managed carefully to prevent health risks and environmental damage.
5. Reprocessing or storage
· Rods can be reprocessed.
· U-235 and plutonium are separated from the spent fuel and used to manufacture new fuel rods.
· Less ______of the world’s fuel rods are reprocessed.
· Rods can undergo long-term storage.
· At present, ______, ______, ______, ______, and ______operate reprocessing plants as an alternative to storing rods as waste.
Steps in the Nuclear Fuel Cycle. What are the steps of the Nuclear Fuel Cycle? (Refer to Figure 9.22)
· All of the processes involved in the nuclear fuel cycle have the potential to generate waste.
6. ______
· Each step in the nuclear fuel cycle involves the ______of radioactive materials.
· Each of these links in the fuel cycle presents ______
______or ______that could release radioactive material.
9.10 Issues Related to the Use of Nuclear Fuels
· Most of the concerns about the use of nuclear fuels relate to the danger associated with ______.
· The absorbed dose is______. It is measured in ______or ______.
· The damage caused by ______is 20 times greater than that caused by ______or ______.
· The dose equivalent is the absorbed dose times a quality factor.
The Biological Effects of Ionizing Radiation
· When alpha or beta particles or gamma radiation interact with atoms, ______are formed. Therefore, it is known as ______radiation.
· Ionizing radiation affects ______and can cause ______.
· ______that occur in some tissues of the body may manifest themselves as abnormal tissue growths known as ______.
· Large doses of radiation are clearly ______.
· Demonstrating known harmful biological effects from smaller doses is much more difficult.
· The more radiation a person receives, the more likely it is that there will be ______.
· ______, ______, and ______are the basic principles of radiation protection.
· ______, ______, and ______are common materials used for shielding from gamma radiation.
· Protective Equipment: Why is it important to wear protective gear when handling radioactive material?
· Radiation Effects
· Reactor Safety
o There are currently______operating nuclear power plants and about an additional 150 which have operated in the past.
o Three accidents generated concern about nuclear power plant safety. What were they?
· The Three Mile Island nuclear plant in ______experienced a partial core meltdown on ______.
o It began with pump and valve malfunction, but ______compounded the problem.
o The containment structure prevented the______
______from the core, but radioactive steam was vented into the atmosphere.
o The crippled reactor was defueled in ______at a cost of about $1 billion.
o Placed in monitored storage until its companion reactor reaches the end of its useful life.
· Chernobyl is a small city in Ukraine, north of Kiev.
o It is the site of the world’s ______which occurred ______.
o Experiments were being conducted on reactor.
o Operators violated ______important safety rules.
o They shut off ______, ______, and the ______.
o In ______seconds, the energy level of the reactor increased ______times.
o The cooling water converted to steam and blew the 1102-ton concrete roof from the reactor.
o The reactor core caught fire.
o It took 10 days to bring the burning reactor under control.
o There were ______deaths; ______people hospitalized (______with acute radiation sickness); ______people evacuated.
o ______evacuees received high doses of radiation.
o Children or fetuses exposed to fallout are showing increased frequency of thyroid cancer because of exposure to radioactive ______released from Chernobyl.
· The Fukushima nuclear power plant was damaged on ______following a magnitude 9 earthquake and tsunami.
o Heat exchangers were damaged, power to the site was cut off, and the diesel generators designed to provide power in an emergency were flooded and stopped operating.
o Explosions, fires, and leaks in the cooling system released radiation into the atmosphere and sea water.
Terrorism
· After Sept. 11, 2001, fear arose regarding nuclear plants as potential targets for terrorist attacks.
· Nuclear experts feel aircraft wouldn’t significantly damage the containment building or reactor, and normal emergency and containment functions would prevent the release of radioactive materials.
· Probably the greatest terrorism-related threat is from ______(RDDs), or dirty bombs. They cause panic, not numerous deaths.
Decommissioning Nuclear Power Plants
· The life expectancy of most electrical generating plants (fossil fuel or nuclear) is ______years.
· Unlike other plants, nuclear plants are ______, not demolished.
Decommissioning is a 2-step process. What are these 2 steps?
There are three options to this second stage of the decommissioning process: What are the three options?
· Today, about 100 commercial nuclear power plants and about 45 experimental reactors in the world have been shut down and are in various stages of being decommissioned.
· Recent experience indicates that the cost for decommissioning a large plant will be between ______million and ______million, about 5 percent of the cost of generating electricity. Although the mechanisms vary among countries, the money for decommissioning is generally collected over the useful life of the plant.
Summary
Resources are naturally occurring substances of use to humans.
Reserves are known deposits from which materials can be extracted profitably with existing technology under present economic conditions.
Coal is the world’s most abundant fossil fuel.
The supply of oil, like all fossil fuels, is limited.
Natural gas is another major source of fossil-fuel energy, but transport of natural gas to consumers is problematic.