- Nuclear power is the only energy-producing technology which takes full
responsibility for all its wastes and fully costs this into the product.
- The amount of those wastes is very small relative to the wastes produced by
fossil fuel electricity generation.
- Two different strategies are utilised for managing high-level wastes.
- The radioactivity of all nuclear wastes diminishes with time.
- Safe methods for the final disposal of high-level waste are technically proven and there is international consensus that this be geological disposal.
All parts of the nuclear fuel cycle, from uranium mining and the preparation of fuel, through to the management of used fuel and decommissioning of a nuclear plant produce some radioactive waste. The cost of managing and disposing of this is internalised.
Uranium mining generates fine sandy tailings, which contain virtually all the naturally occurring radioactive elements found in the uranium ore. These are emplaced in engineered tailings dams and finally covered with a layer of clay and rock to inhibit leakage of radon gas from them and to ensure their long-term stability. In the short term, the tailings material is often covered with water. After a few months, the tailings material contains about 75 percent of the radioactivity of the original ore.
At each stage of the fuel cycle there are proven technologies to safely dispose of the radioactive wastes but in some cases they have not have been implemented due to public acceptance problems or because they are not presently required.
The radioactivity of all nuclear waste decays with time.
All radionuclides contained in nuclear waste have a half-life - a term which refers to the time it takes for any given radionuclide to lose half of its radioactivity. Thus radioactive waste eventually decays into non-radioactive elements. The more radioactive a particular isotope, the faster it decays.
The basic objective in the management and disposal of radioactive (or other) waste is the protection of people and the environment.
This means achieving sufficient isolation or dilution of the waste so that any return of radionuclides to the biosphere is at a rate or concentration which is innocuous. Some wastes therefore need deep and secure burial.
In the European Community 160 000 tonnes of radioactive waste of all kinds is produced each year, compared with 20 million tonnes of toxic chemical waste (most of which remains hazardous indefinitely).
TYPES OF RADIOACTIVE WASTE:
Low-level Waste is generated from hospitals and industry, as well as the nuclear fuel cycle. It comprises paper, rags, tools, clothing, filters etc which contain small amounts of mostly short-lived radioactivity. It does not require shielding during handling and transport and is suitable for shallow land burial. To reduce its volume, it is often compacted or incinerated before disposal.
Intermediate-level Waste contains higher amounts of radioactivity and some requires shielding. It typically comprises resins, chemical sludges and metal fuel cladding, as well as contaminated materials from reactor decommissioning. It may be solidified in concrete or bitumen for disposal.
Generally short-lived waste (mainly from reactors) is buried in a shallow repository, but long-lived waste (from fuel reprocessing) will be disposed of deep underground.
High-level Waste arises from the use of uranium fuel in a nuclear reactor. It contains the fission products and transuranic elements generated in the reactor core. It is highly radioactive and hot. It can be considered the "ash" from "burning" uranium. The high-level waste accounts for over 95 percent of the total radioactivity produced in the process of nuclear electricity generation.
CONVERSION, ENRICHMENT AND FUEL FABRICATION:
The uranium oxide concentrate from mining is not significantly radioactive, - barely more so than the granite of Australia's Parliament House. It is refined, then converted to uranium hexafluoride gas so that it can undergo enrichment of the U-235 content from 0.7 percent to about 3.5 percent. It is then turned into a hard ceramic oxide (UO2) for assembly as reactor fuel elements.
The main by-product of enrichment is depleted uranium, principally the U-238 isotope, which is stored, either as UF6 or as U3O8. Some is used in applications where its extremely high density makes it valuable, eg the keels of yachts. It is also used (with recycled plutonium) for making mixed oxide fuel (see below) and to dilute highly-enriched uranium from weapons stockpiles now being redirected to become reactor fuel.
MANAGEMENT of HIGH-LEVEL WASTES from SPENT FUEL:
Spent fuel gives rise to high-level waste which may be either:
- the spent fuel itself in fuel rods, or
- the principal waste arising from reprocessing this (see next section).
Either way, the amount is modest - about 25 tones of spent fuel or three cubic metres per year of vitrified waste for a typical large nuclear reactor. In either case it can be effectively and economically isolated.
To ensure that no significant environmental releases occur over periods of tens of thousands of years, a 'multiple barrier' disposal concept is used to immobilise the radioactive elements in high-level and some intermediate-level wastes and isolate them from the biosphere.
The main barriers are:
- Immobilise waste in an insoluble matrix such as borosilicate glass or
synthetic rock (fuel pellets are already a very stable ceramic: UO2);
- Seal inside a corrosion-resistant container, such as stainless steel;
- Locate deep underground in a stable rock structure; &
- Surround containers with an impermeable backfill such as bentonite clay if
the respository is wet.
The high-level waste from reprocessing UK, French, Japanese and German spent fuel consists of the highly-radioactive fission products and some transuranic elements with long-lived radioactivity. It generates a considerable amount of heat and requires cooling. This is vitrified into borosilicate (Pyrex) glass, encapsulated into heavy stainless steel cylinders about 1.3 m high and stored for eventual disposal deep underground.
On the other hand, if spent reactor fuel is not reprocessed, all the highly radioactive isotopes remain in it, and so the whole fuel assemblies are treated as high-level waste. After 40-50 years the heat and radioactivity have dropped to one thousandth the level at removal, providing a technical incentive to delay disposal until this low level of about 0.1 percent of original radioactivity is reached.
After storage for about 40 years they are ready for encapsulation and permanent disposal underground. This direct disposal option is the US and Swedish policy, though in the latter case it will be recoverable if future generations come to see it as a resource.
Increasingly, reactors are starting off with fuel enriched to over 4 percent U-235 and burning it longer, to end up with less than 0.5 percent U-235 in the spent fuel.
Source: www.uic.com.au
Waste Management in the Nuclear Fuel Cycle – part one.
Nuclear Issues Briefing Paper 9
August 2000
· Nuclear power is the only energy-producing technology which takes full responsibility for all its wastes and fully costs this into the product.
· The amount of those wastes is very small relative to the wastes produced by fossil fuel electricity generation.
· Two different strategies are utilised for managing high-level wastes.
· The radioactivity of all nuclear wastes diminishes with time.
· Safe methods for the final disposal of high-level waste are technically proven and there is international consensus that this be geological disposal.
All parts of the nuclear fuel cycle, from uranium mining and the preparation of fuel, through to the management of used fuel and decommissioning of a nuclear plant produce some radioactive waste. The cost of managing and disposing of this is internalised.
Uranium mining generates fine sandy tailings, which contain virtually all the naturally occurring radioactive elements found in the uranium ore. These are emplaced in engineered tailings dams and finally covered with a layer of clay and rock to inhibit leakage of radon gas from them and to ensure their long-term stability. In the short term, the tailings material is often covered with water. After a few months, the tailings material contains about 75 percent of the radioactivity of the original ore.
At each stage of the fuel cycle there are proven technologies to safely dispose of the radioactive wastes but in some cases they have not have been implemented due to public acceptance problems or because they are not presently required.
The radioactivity of all nuclear waste decays with time. All radionuclides contained in nuclear waste have a half-life - a term which refers to the time it takes for any given radionuclide to lose half of its radioactivity. Thus radioactive waste eventually decays into non-radioactive elements. The more radioactive a particular isotope, the faster it decays.
The basic objective in the management and disposal of radioactive (or other) waste is the protection of people and the environment. This means achieving sufficient isolation or dilution of the waste so that any return of radionuclides to the biosphere is at a rate or concentration which is innocuous. Some wastes therefore need deep and secure burial.
In the European Community 160 000 tonnes of radioactive waste of all kinds is produced each year, compared with 20 million tonnes of toxic chemical waste (most of which remains hazardous indefinitely).
TYPES OF RADIOACTIVE WASTE
Low-level Waste is generated from hospitals and industry, as well as the nuclear fuel cycle. It comprises paper, rags, tools, clothing, filters etc which contain small amounts of mostly short-lived radioactivity. It does not require shielding during handling and transport and is suitable for shallow land burial. To reduce its volume, it is often compacted or incinerated before disposal.
Intermediate-level Waste contains higher amounts of radioactivity and some requires shielding. It typically comprises resins, chemical sludges and metal fuel cladding, as well as contaminated materials from reactor decommissioning. It may be solidified in concrete or bitumen for disposal. Generally short-lived waste (mainly from reactors) is buried in a shallow repository, but long-lived waste (from fuel reprocessing) will be disposed of deep underground.
High-level Waste arises from the use of uranium fuel in a nuclear reactor. It contains the fission products and transuranic elements generated in the reactor core. It is highly radioactive and hot. It can be considered the "ash" from "burning" uranium. The high-level waste accounts for over 95 percent of the total radioactivity produced in the process of nuclear electricity generation.
CONVERSION, ENRICHMENT AND FUEL FABRICATION
The uranium oxide concentrate from mining is not significantly radioactive, - barely more so than the granite of Australia's Parliament House. It is refined, then converted to uranium hexafluoride gas so that it can undergo enrichment of the U-235 content from 0.7 percent to about 3.5 percent. It is then turned into a hard ceramic oxide (UO2) for assembly as reactor fuel elements.
The main by-product of enrichment is depleted uranium, principally the U-238 isotope, which is stored, either as UF6 or as U3O8. Some is used in applications where its extremely high density makes it valuable, eg the keels of yachts. It is also used (with recycled plutonium) for making mixed oxide fuel (see below) and to dilute highly-enriched uranium from weapons stockpiles now being redirected to become reactor fuel.
MANAGEMENT of HIGH-LEVEL WASTES from SPENT FUEL
Spent fuel gives rise to high-level waste which may be either:
· the spent fuel itself in fuel rods, or
· the principal waste arising from reprocessing this (see next section).
Either way, the amount is modest - about 25 tones of spent fuel or three cubic metres per year of vitrified waste for a typical large nuclear reactor. In either case it can be effectively and economically isolated.
To ensure that no significant environmental releases occur over periods of tens of thousands of years, a 'multiple barrier' disposal concept is used to immobilise the radioactive elements in high-level and some intermediate-level wastes and isolate them from the biosphere. The main barriers are:
· Immobilise waste in an insoluble matrix such as borosilicate glass or synthetic rock (fuel pellets are already a very stable ceramic: UO2);
· Seal inside a corrosion-resistant container, such as stainless steel;
· Locate deep underground in a stable rock structure; &
· Surround containers with an impermeable backfill such as bentonite clay if the respository is wet.
The high-level waste from reprocessing UK, French, Japanese and German spent fuel consists of the highly-radioactive fission products and some transuranic elements with long-lived radioactivity. It generates a considerable amount of heat and requires cooling. This is vitrified into borosilicate (Pyrex) glass, encapsulated into heavy stainless steel cylinders about 1.3 m high and stored for eventual disposal deep underground.
On the other hand, if spent reactor fuel is not reprocessed, all the highly radioactive isotopes remain in it, and so the whole fuel assemblies are treated as high-level waste. After 40-50 years the heat and radioactivity have dropped to one thousandth the level at removal, providing a technical incentive to delay disposal until this low level of about 0.1 percent of original radioactivity is reached.
After storage for about 40 years they are ready for encapsulation and permanent disposal underground. This direct disposal option is the US and Swedish policy, though in the latter case it will be recoverable if future generations come to see it as a resource.
Increasingly, reactors are starting off with fuel enriched to over 4 percent U-235 and burning it longer, to end up with less than 0.5 percent U-235 in the spent fuel.
Source: www.uic.com.au
© 2000 Mena Report (www.menareport.com)
