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The IAEA has regularly issued revisions to the transport regulations in order to keep them up to date. The main publication on which other
IAEA transport regulations are based is Safety Series No. ST-l, Regulations for the Safe Transport of Radioactive Material.
The objective of the regulations is to protect people and the environment from the effects of radiation during the transport of radioactive
material.
Protection is achieved by:
- Containment of radioactive contents
- Control of external radiation levels
- Prevention of criticality
- Prevention of damage caused by heat
The fundamental principle applied to the transport of radioactive material is that the protection comes from the design of the package, regardless
of how the material is transported.
Transport of uranium oxide from mines and uranium hexafluoride
Uranium oxide concentrate, sometimes called yellowcake, is transported from the mines to conversion plants in 200-litre drums packed into normal
shipping containers. No radiation protection is required beyond having the steel drums clean and within the steel container.
From the conversion plant, the uranium is in the form of uranium hexafluoride, which again is barely radioactive but has significant chemical
toxicity. It is in special containers, which also function for storage.
Transport of uranium fuel assemblies
Uranium fuel assemblies are manufactured at fuel fabrication plants. The fuel assemblies are made up of ceramic pellets formed from pressed uranium
oxide that has been sintered at a high temperature (over 1400°C). The pellets are aligned within long, hollow, metal rods, which in turn are arranged
in the fuel assemblies, ready for introduction into the reactor. Different types of reactors require different types of fuel assembly, so when the
fuel assemblies are transported from the fuel fabrication facility (where they are manufactured) to the nuclear power reactor, the contents of the
shipment will vary with the type of reactor receiving it.
In Western Europe, Asia and the US, the most common means of transporting uranium fuel assemblies is by truck. A typical truckload supplying a
light water reactor contains 6 tonnes of fuel. In the countries of the former Soviet Union, rail transport is most often used. Intercontinental
transports are mostly by sea, though occasionally transport is by air.
The annual operation of a 1000 MWe light water reactor requires an average fuel load of 27 tonnes of uranium dioxide, containing 24 tonnes of
enriched uranium. The assemblies containing this are normally supplied in one consignment occupying 4 to 5 trucks.
The fuel assemblies are transported in packages specially constructed to protect the precision-made fuel assemblies from damage during transport.
Uranium fuel assemblies have a low radioactivity level and radiation shielding is not necessary.
Fuel assemblies contain fissile material and in some circumstances fissile material can spontaneously become critical, i.e. start a self-
sustaining, nuclear chain reaction, releasing energy. Criticality is prevented by the design of the package, the arrangement of the fuel assemblies
within the package, limitations on the amount of material contained within the package, and on the number of packages carried in one shipment.
Transport of LLW and ILW
Low-level and intermediate-level wastes (LLW and ILW) are generated throughout the nuclear fuel cycle. The transport of these wastes is commonplace
and they are safely transported to waste treatment facilities and storage sites.
Low-level radioactive wastes are a variety of materials that emit low levels of radiation, slightly above normal background levels. They often
consist of solid materials, such as clothing, tools, or contaminated soil. Low-level waste is transported from its origin to waste treatment sites, or
to an intermediate or final storage facility.
A variety of radionuclides give low-level waste its radioactive character. However, the radiation levels from these materials are very low and the
packaging used for the transport of low-level waste does not require special shielding.
Low-level wastes are moved by road, rail, and internationally, by sea. However, most low-level waste is only transported within the country where
it is produced.
Low-level wastes are transported in drums, often after being compacted in order to reduce the total volume of waste. The drums commonly used
contain up to 200 litres of material. Typically, 36 standard, 200 litre drums go into a 6-metre transport container.
The composition of intermediate-level wastes is broad, but they require shielding. Much ILW comes from nuclear power plants and reprocessing
facilities.
Intermediate-level wastes are taken from their source to an interim storage site, a final storage site (as in Sweden), or a waste treatment
facility. They are transported by road, rail and sea.
The radioactivity level of intermediate-level waste is higher than low-level waste. The classification of radioactive wastes is decided for
disposal purposes, not on transport grounds. The transport aspects of intermediate-level waste take into account any specific properties of the
material, and provide shielding.
Classification of radioactive wastes
There are several systems of nomenclature in use, but the following is generally accepted:
- Exempt waste - excluded from regulatory control because radiological hazards are negligible.
- Low-level waste (LLW) - contains enough radioactive material to require action for the protection of people, but not so much that it requires
shielding in handling or storage.
- Intermediate-level waste (ILW) - requires shielding. If it has more than 4000 Bq/g of long-lived (over 30 year half-life) alpha emitters it is
categorised as "long-lived" and requires more sophisticated handling and disposal.
- High-level waste (HLW) - sufficiently radioactive to require both shielding and cooling,
generates >2 kW/m 3 of heat and has a high level of long-lived alpha-emitting isotopes.
Transport of used fuel
When used fuel is unloaded from a nuclear power reactor, it contains: 96% uranium, 1% plutonium and 3% of fission products (from the nuclear
reaction) and transuranics).
Used fuel looks the same as fresh fuel but when the fuel assembly is removed from a reactor it will be emitting high levels of both radiation and
heat. It is stored in water pools adjacent to the reactor to allow the initial heat and radiation levels to decrease. Typically, used fuel is stored
for at least five months before it can be transported, although it may be stored there long-term.
From the reactor site, used fuel is transported by road, rail or sea to either an interim storage site or a reprocessing plant where it will be
reprocessed.
Used fuel assemblies are shipped in Type B casks. These casks are shielded with steel, or a combination of steel and lead, and can weigh up to 110
tonnes each when empty. A typical transport cask holds up to 6 tonnes of used fuel.
Since 1971 there have been some 7000 shipments of used fuel (over 80 000 tonnes) over many million kilometres with no property damage or personal
injury, no breach of containment, and very low dose rate to the personnel involved (e.g. 0.33 mSv/yr per operator at La Hague). This includes 40,000
tonnes of used fuel shipped to Areva's La Hague reprocessing plant, at least 30,000 tonnes of mostly UK used fuel shipped to UK's Sellafield
reprocessing plant, 7140 t used fuel in 160 shipments from Japan to Europe by sea (see below) and 4500 tonnes of used fuel shipped around the Swedish
coast.
In the USA alone, one percent of the 300 million packages of hazardous material shipped each year contain radioactive materials. Of this, about
250,000 contain radioactive wastes from US nuclear power plants, and 25 to 100 packages contain used fuel. Most of these are in robust 125-tonne Type
B casks carried by rail, each containing 20 tonnes of used fuel.
Transport of plutonium
Plutonium is separated during the reprocessing of used fuel. It is normally then made into mixed oxide (MOX) fuel.
Plutonium is transported, following reprocessing, as an oxide as this is its most stable form. Plutonium oxide is a solid, and normally transported
as a powder in sealed packages. It is insoluble in water and only harmful to humans if it enters the lungs.
Plutonium oxide is transported in several different types of packages and each can contain several kilograms of material. Criticality is prevented
by the design of the package, limitations on the amount of material contained within the package, and on the number of packages carried on a transport
vessel.
Plutonium is subjected to physical protection controls and special physical protection measures apply to plutonium transports.
A typical transport consists of one truck carrying one protected shipping container. The container holds a number of packages with a total weight
varying from 80 to 200 kg of plutonium oxide.
A sea shipment may consist of several containers, each of them holding between 80 to 200 kg of plutonium in sealed packages.
Transport of vitrified waste
The highly radioactive wastes (especially fission products) created in the nuclear reactor are segregated and recovered during the reprocessing
operation. These wastes are incorporated in a glass matrix by a process known as 'vitrification', which stabilises the radioactive material.
The molten glass is then poured into a stainless steel canister where it cools and solidifies. A lid is welded into place to seal the canister. The
canisters are then placed inside a Type B cask, similar to those used for the transport of used fuel.
The quantity per shipment depends upon the capacity of the transport cask. Typically a vitrified waste transport cask contains up to 28 canisters
of glass. The main characteristics of the canister are as follows:
- height (with lid) = 1.34 m
- outside diameter = 0.43 m
- weight (empty) = 90 kg
So far, France is the only country that has carried out transports of vitrified waste. Since 1995, there have been five transports (two to Germany
by rail, six to Japan by sea). This figure should increase in the years to come.
In the UK, storage is on the same site as reprocessing and vitrification.
Sea shipments of wastes
Some 300 sea voyages have been made carrying used nuclear fuel or separated high-level waste over a distance of more than 8 million kilometres. The
major company involved has transported over 4000 casks, each of about 100 tonnes, carrying 8000 tonnes of used fuel or separated high-level wastes. A
quarter of these have been through the Panama Canal.
In Sweden alone, more than 80 large transport casks are shipped annually from nuclear power stations (all on the coast) to a central interim waste
storage facility called CLAB. Each 80 tonne cask has steel walls 30 cm thick and holds 17 BWR or 7 PWR fuel assemblies. The used fuel is shipped to
CLAB after it has been stored for about a year at the reactor, during which time heat and radioactivity diminish considerably. A purpose-built 2000
tonne ship is used for moving the used fuel. Some 4500 tonnes of used fuel had been shipped around the coast to CLAB by the end of 2007.
Shipments of used fuel from Japan to Europe for reprocessing use 94-tonne Type B casks, each holding a number of fuel assemblies (e.g. 12 PWR
assemblies, total 6 tonnes, with each cask 6.1 metres long, 2.5 metres diameter, and with 25 cm thick forged steel walls). More than 160 of these
shipments took place from1969 to the 1990s, involving more than 4000 casks, and moving several thousand tonnes of highly radioactive used fuel - 4200t
to UK and 2940t to France.
Return shipments from Europe to Japan since 1995 are of vitrified high-level wastes in stainless steel canisters. Up to 28 canisters (total 14
tonnes) are packed in each 98-tonne steel transport cask. Each is 6.6 metres long and 2.4 metres diameter, with a 25 cm thick wall. Over 1995-2007
twelve shipments were made from France of vitrified HLW comprising 1310 canisters containing almost 700 tonnes of glass. In 2008 return shipments
from the UK are due to commence, and there will be about 11 shipments to 2016.
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