Transport of radioactive materials

Published: December 6, 2009, 10:13 am

Topics:

Nuclear Energy (main) Transportation (main)

This EOE article is adapted from an information paper published by the World Nuclear Association (WNA). WNA information papers are frequently updated, so for greater detail or more up to date numbers, please see the latest version on WNA website (link at end of article).

Introduction

About 20 million consignments of radioactive material (which may be either a single package or a number of packages sent from one location to another at the same time) take place around the world each year. Radioactive material is not unique to the nuclear fuel cycle and only abut 5% of the consignments of such material are fuel cycle related. Radioactive materials are used extensively in medicine, agriculture (Transport of radioactive materials) , research, manufacturing, non-destructive testing and minerals exploration.

International regulations for the transport of radioactive material have been published by the International Atomic Energy Agency (IAEA) since 1961. These regulations have been widely adopted into national regulations, as well as into modal regulations, such as the International Maritime Organisation’s (IMO) Dangerous Goods Code. Regulatory control of shipments of radioactive material is independent of the material's intended application.

Nuclear fuel cycle facilities are located in various parts of the world and materials of many kinds need to be transported between them. Many of these materials are similar to materials used in other industrial activities. However, the nuclear industry's fuel and waste materials are radioactive, and it is these 'nuclear materials' about which there is most public concern.

Nuclear materials have been transported since before the advent of nuclear power over forty years ago. The procedures employed are designed to ensure the protection of the public and the environment. For the generation of a given quantity of electricity, the amount of nuclear fuel required is much smaller relative to all other fuel. Therefore, the conventional risks and environmental impacts associated with fuel transport are greatly reduced with nuclear power.

In the USA 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.

Materials Being Transported

Transport is an integral part of the nuclear fuel cycle. There are some 430 nuclear power reactors in operation in 32 countries but uranium mining is viable in only a few areas. Furthermore, in the course of over fifty years of operation by the nuclear industry, a number of specialized facilities have been developed in various locations around the world to provide fuel cycle services. It is clear that there is a need to transport nuclear fuel cycle materials to and from these facilities. Indeed, most of the material used in nuclear fuel is transported several times during its progress through the fuel cycle. Transport is frequently international, and often over large distances. Radioactive materials are generally transported by specialised transport companies.

The term 'transport' is used in this article only to refer to the movement of material between facilities, i.e., through areas outside such facilities. Most consignments of nuclear fuel material occur between different stages of the cycle, but occasionally a material may be transported between similar facilities. When the stages are directly linked (such as mining and milling), it is sometimes advantageous to construct facilities for the different stages on the same site, eliminating the need for transport.

With very few exceptions, nuclear fuel cycle materials are transported in solid form. The following table shows the principal nuclear material transport activities:

* Not yet taking place

Although some waste disposal facilities are located adjacent to the facilities that they serve, utilizing one disposal site to manage the wastes from several facilities usually reduces environmental impact. When this is the case, transport of the wastes from the facilities to the disposal site will be required.

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 categorized 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/m³ of heat and has a high level of long-lived alpha-emitting isotopes.

Packaging

The principal assurance of safety in the transport of nuclear materials is the design of the packaging, which must allow for any foreseeable accidents. The consignor bears primary responsibility for this. Many different nuclear materials are transported and the degree of potential hazard from these materials varies considerably. Different packaging standards have been developed according to the potential hazard posed by the material.

'Type A' packages are designed to withstand minor accidents and are used for medium-activity materials such as medical or industrial radioisotopes. Ordinary industrial containers are used for low-activity material such as U₃O₈.

Type B transport cask

Containers for high-level waste (HLW) and spent fuel are robust and very secure and are known as 'Type B' packages. They maintain shielding from gamma and neutron radiation, even under extreme conditions. There are over 150 kinds of Type B packages, and the larger ones cost some US$1.6 million each.

In France alone, there are some 750 shipments each year of Type B packages, among 15 million shipments classified as 'dangerous materials', 300 000 of these being radioactive materials of some kind.

Smaller amounts of high-activity materials (including plutonium) transported by aircraft will be in 'Type C' packages, which give even greater protection than Type B packages in accident scenarios.

Radiation Protection

When radioactive materials, including nuclear materials, are transported, it is important to ensure that radiation exposure of both those involved in the transport of such materials and the general public along transport routes is limited. Packaging for nuclear materials includes, where appropriate, shielding to reduce potential radiation exposures. In the case of some materials, such as fresh uranium fuel assemblies, the radiation levels are negligible and no shielding is required. Other materials, such as spent fuel and high-level waste, are highly radioactive, requiring the use of purpose-designed containers with integral shielding. To limit the risk in handling highly radioactive materials, dual-purpose containers (casks), appropriate for both storage and transport of spent nuclear fuel, are often used.

As with other hazardous materials being transported, packages of nuclear materials are labelled in accordance with the requirements of national and international regulations. These labels not only indicate that the material is radioactive, by including a radiation symbol, but also give an indication of the radiation field in the vicinity of the package.

Personnel directly involved in the transport of nuclear materials are trained to take appropriate precautions and on how to respond in case of an emergency.

Environmental Protection

Packages used for the transport of nuclear materials are designed to retain their integrity during the various conditions that may be encountered while they are being transported and to ensure that an accident will not have any major consequences. Conditions for which packages are tested to withstand include: fire, impact, wetting, pressure, heat, and cold. Packages of radioactive material are checked prior to shipping and, when it is found to be necessary, cleaned to remove contamination.

Although not required by transport regulations, the nuclear industry chooses to undertake some shipments of nuclear material using dedicated, purpose-built transport vehicles or vessels.

Regulation of Transport

Since 1961 the International Atomic Energy Agency (IAEA) has published advisory regulations for the safe transport of radioactive material. These regulations have come to be recognised throughout the world as the uniform basis for both national and international transport safety requirements in this area. Requirements based on the IAEA regulations have been adopted in about 60 countries, as well as by the International Civil Aviation Organisation (ICAO), the International Maritime Organisation (IMO), and regional transport organisations.

The IAEA has regularly issued revisions to the transport regulations in order to keep them up to date. The latest set of regulations is published as TS-R-l, Regulations for the Safe Transport of Radioactive Material, 2009 Edition.

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; and
• 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 mines to conversion plants in 200-liter 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. The material is transported in in special containers, which also function as storage vessels.

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 nuclear reactor.

Different types of reactors require different types of fuel assemblies, 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 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 material are normally supplied in one consignment, occupying 4 to 5 trucks.

The precision-made fuel assemblies are transported in packages specially constructed to protect them from damage during transport. Uranium fuel assemblies have a low radioactivity level and radiation shielding is not necessary.

Fuel assemblies contain fissile material and criticality is prevented by the design of the package (including the arrangement of the fuel assemblies within it, and limitations on the amount of material contained within the package), and the number of packages carried in one shipment.

Transport of low-level and intermediate-level wastes

Low-level and intermediate-level wastes (LLW and ILW) are generated throughout the nuclear fuel cycle and from the production of radioisotopes used in medicine, industry and other areas. The transport of these wastes is commonplace and they are safely transported to waste treatment facilities and storage sites.

Low-level radioactive wastes consist of 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 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. 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.

The composition of intermediate-level wastes is broad, but they do require shielding. Much ILW comes from nuclear power plants and reprocessing facilities.

Intermediate-level wastes are taken from their source to either 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 wastes take into account any specific properties of the material, and requires shielding.

Transport of spent fuel

When used fuel is unloaded from a nuclear power reactor, it contains: 96% uranium, 1% plutonium and 3% fission products (from the nuclear reaction) and transuranics.

Used fuel will emit high levels of both radiation and heat and so is stored in water pools adjacent to the reactor to allow the initial heat and radiation levels to diminish. Typically, spent fuel is stored on site for at least five months before it can be transported, although it may be stored there for the long-term.

From the reactor site, spent fuel is transported by road, rail or sea to either an interim storage site or a reprocessing plant.

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 spent fuel.

Since 1971, there have been some 7000 shipments of spent fuel (over 80,000 tonnes) over many million kilometers 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, France). 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.

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, more than 80 large transport casks are shipped annually 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. 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 used 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.

Within Europe, used fuel in casks has often been carried on normal ferries, e.g. across the English Channel.

Transport of plutonium

Plutonium is separated during the reprocessing of spent fuel. It is normally then made into mixed oxide (MOX) fuel.

Plutonium is transported, following reprocessing, as an oxide powder since this is its most stable form. 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 the number of packages carried on a transport vessel. Special physical protection measures apply to plutonium consignments.

A typical consignment 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 power reactor are segregated and recovered during the reprocessing operation. These wastes are incorporated in a glass matrix by a process known as 'vitrification', which stabilizes 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.

Return nuclear waste 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 94-tonne steel transport cask, the same as used for irradiated fuel. Over 1995-2007 twelve shipments were made from France of vitrified HLW comprising 1310 canisters containing almost 700 tonnes of glass. Return shipments from the UK are due to commence, and there will be about 11 shipments over eight years.

Purpose-built vessels

Sweden has a purpose-built 2000 tonne ship used for moving used fuel from reactors to the interim waste storage facility. Apart from this small ship, there are five purpose-built 5100 tonne ships, with elaborate safety provisions, which carry the casks. These have double hulls with impact-resistant structures between the hulls, together with duplication and separation of all essential systems to provide high reliability and also survivability in the event of an accident. Twin engines operate independently. Each ship can carry up to 17 used fuel flasks or 14 waste transport flasks.

The ships conform to all relevant international safety standards, notably one known as INF-3 (Irradiated Nuclear Fuel class 3) set by the International Maritime Organisation. This allows them to carry highly radioactive materials such as high-level wastes, used nuclear fuel, mixed-oxide (MOX) fuel, and plutonium. The ships belong to a British-based company Pacific Nuclear Transport Ltd (PNTL), which is now owned by International Nuclear Services Ltd (INS, 62.5%), Japanese utilities (25%) and Areva (12.5%). PNTL is currently renewing its fleet. INS is 51% owned by Sellafield Ltd and 49% by the UK's Nuclear Decommissioning Authority and is managed by Sellafield Ltd.

Accident scenarios

There has never been any accident in which a Type B transport cask containing radioactive materials has been breached or has leaked.

For the radioactive material in a large Type B package in sea transit to become exposed, the ship's hold (inside double hulls) would need to rupture, the 25 cm thick steel cask would need to rupture, and the stainless steel flask or the fuel rods would need to be broken open. Either borosilicate glass (for reprocessed wastes) or ceramic fuel material would then be exposed, but in either case these materials are very insoluble.

The transport ships are designed to withstand a side-on collision with a large oil tanker. If the ship did sink, the casks will remain sound for many years and would be relatively easy to recover since instrumentation including location beacons would activate and monitor the casks.

Further Reading

• WNA paper on Transport of radioactive materials
• BNFL, Cogema, JNFL, SKB and ANSTO publications and papers.

Citation

Hore-Lacy, I., & Association, W. (2009). Transport of radioactive materials. Retrieved from http://editors.eol.org/eoearth/wiki/Transport_of_radioactive_materials