Target Audience: Facilities Handling Irradiated Nuclear Fuel- Mode: Sea

M12.2

TRANSPORT OF RADIOACTIVE MATERIAL

(Target audience: Facilities handling Irradiated Nuclear Fuel- Mode: Sea)

Introduction

Transport radioactive material is governed by national and international regulations. The International Atomic Energy Agency (IAEA) has published the Regulations for the Safe Transport of Radioactive Material [1]. All references to “Regulations” in this module pertain to the IAEA Regulations. The objective of the Regulations is to establish requirements that must be satisfied to ensure safety and to protect persons, property and the environment from the effects of radiation in the transport of radioactive material. This protection is achieved by requiring, among others:

a)containment of the radioactive contents; and

b)control of external radiation levels.

These requirements are satisfied first by specifying -

a)performance standards for package design based on the radioactive contents and

b)administrative controls and

c)approval by competent authorities.

Confidence in this regard is achieved through quality assurance and compliance assurance programmes.

Scope of this module

This module relates to the regulatory requirements for the safe transport of radioactive material from nuclear reactors to facilities handling irradiated nuclear fuel or spent fuel.

This module describes how the transport of spent fuel can be carried out in conformity with the applicable regulatory requirements.

Tasks before the consignor

The consignor should –

a)Familiarize himself with the regulations

b)Select the package in which the radioactive material has to be transported

c)Procure a package of currently approved design

d)Obtain the necessary approvals from the concerned competent authority/authorities

e)Prepare the package for transport (e.g. load the radioactive material in the package, fasten the closure, decontaminate the exterior of the package)

f)Mark and label the package

g)Conduct the tests before the shipment

h)Complete the transport documents including consignor’s declaration and information to the carrier.

i)Forward the package through a carrier

j)Implement radiation protection requirements and quality assurance

Familiarization with regulatory requirements

IAEA Regulations

The IAEA Regulations [1] form the basis of many national and international regulations for transport of radioactive material.

The Agency has published a Safety Guide advising the user about how the regulatory requirements can be satisfied [2]. In order to guide the consignor through the regulatory requirements, IAEA has published the Schedules for the Regulations as a Safety Guide [3]. The schedules provide specific guidance on the regulatory requirements for each type of consignment.

National Regulations

Transport of radioactive material is governed by national regulations of each State. Member States of IAEA adopt the IAEA Regulations within the frame work of the local laws and the international conventions to which the nation is a party. Accordingly, responsibilities are assigned in the National regulations to consignor, carrier and consignee. Consignors, carriers and the concerned public authorities ensure that the shipments are made in compliance with the applicable national regulations. There could be some differences between the national regulations and the international regulations for the safe transport of radioactive material because of the difference in the legal system among the states.

International Maritime Organization (IMO)

The International Maritime Organization (IMO) is a United Nations agency. The regulations, standards and recommendations (IMDG Code) that it has developed, are recognized, followed, and observed by ships of many nations. This code includes provisions for the transport of radioactive material by sea.

In addition, there is the MERCOSUR/MERCOSUL agreement that concerns road, rail, air and sea transport among certain South American countries.

Definitions of terms

Certain terms are assigned specific meanings in the Regulations. For example the terms contamination means the presence of a radioactive substance in excess of 0.4 Bq/cm2 for beta, gamma and low toxicity alpha emitters or 0.04 Bq/cm2 for other alpha emitters. The term conveyance includes road vehicles, rail cars, vessels or aircraft. A packaging together with the radioactive content is defined as package. Many definitions are provided in the Regulations. It is necessary to understand the meanings assigned to various terms in the Regulations.

A1 values and A2 values

Familiarity with A1 and A2 values defined in the Regulations would be useful. Radioactive material may be transported either in special form (essentially indispersible) and other form. The A1 value refers to the activity of special form radioactive material and the A2 value refers to the activity of other than special form radioactive material. The values of A1 and A2 have been determined for most common radionuclides and are listed in the Regulations.

If the radioactive material is amixture of radionuclides, then the effective A1 or A2 value is calculated thus:

A1 = 1 / [ Σ {f(i)/A1(i)}]

where f(i) of the radionuclide I in the mixture and A1(i) is the A1 value for the nuclide given in the Regulations.

A2 = 1 / [ Σ {f(i)/A2(i)}]

where f(i) of the radionuclide I in the mixture and A2(i) is the A2 value for the nuclide given in the Regulations.

Multiples and fractions of A1 and A2 (for example, 3000A1, 10-3 A1, 3000A2 and 10-4 A2) are used in specifying criteria throughout the Regulations.

Non-fissile and fissile-excepted material

The consignment of spent fuel to be transported may include fissile material. However, the consignor should first confirm that the radioactive material to be transported is considered fissile for the purposes of the Regulations.

Fissile material

The term, fissile material, means a material containing any of the fissile nuclides. The only fissile nuclides are uranium-233, uranium-235, plutonium-239 and plutonium-241. That is, no other nuclide is considered a fissile nuclide.

The following materials are excluded from the definition of fissile material:

(a) natural uranium or depleted uranium which is unirradiated, and

(b) natural uranium or depleted uranium which has been irradiated in thermal reactors only.

Any radioactive material that does not include any fissile nuclide is non-fissile. Natural uranium or depleted uranium which is unirradiated, and natural uranium or depleted uranium which has been irradiated in thermal reactors only are considered to be non-fissile material.

Fissile-excepted

Now there are radioactive materials which include fissile material, for example, irradiated nuclear fuel. However, the total quantity of fissile material or the concentration of fissile nuclides in the radioactive material or the physical properties of the radioactive material may not be conducive to the formation of a critical assembly. That is, criticality of safety is not an issue with that sample of radioactive material. Such materials are excepted from the regulatory requirements applicable to fissile materials. The radioactive materials which qualify for such exception are referred to as fissile-excepted. The material to be transported being radioactive would, however, need to satisfy the requirements applicable to its radioactive nature. The following consignments are fissile-excepted.

(1) A consignment of enriched uranium is fissile-excepted provided that all the following conditions are satisfied:

enrichment of uranium (235U by mass) ≤ 1%
the total plutonium mass and 233U mass ≤ 1% of the mass of 235U
the fissile nuclides should be distributed essentially homogeneously throughout the material
if 235U is present in metallic, oxide or carbide forms, it should not form a lattice arrangement.

(2) A consignment of liquid solutions of uranyl nitrate is fissile-excepted provided that all the following conditions are satisfied:

enrichment of uranium (235U by mass) ≤2%
the total plutonium and 233U mass ≤ 0.002% of the mass of uranium and
nitrogen to uranium atomic ratio (N/U) of ≥ 2.

(3) A consignment being carried in or on a vessel is fissile-excepted if

the smallest external dimension of each package is not less than 10 cm
no package in the consignment contains more than 15 g of fissile nuclide and
the mass of the fissile nuclides in the consignment meets the condition:

[{ mass of 235U (g) / 400 } + { mass of other fissile nuclides (g) / 250 }] < 1;

if the fissile nuclides are mixed with substances having an average hydrogen density less than or equal to water the mass of fissile nuclides per consignment should not exceed the limit.

Beryllium should not be present in quantities exceeding 1% of the applicable consignment mass limits except where the concentration of beryllium in the material does not exceed 1 gram beryllium in any 1000 grams.

Deuterium should also not be present in quantities exceeding 1% of the applicable consignment mass limits except where deuterium occurs up to natural concentration in hydrogen.

(4) A consignment being carried in or on vessel is fissile-excepted if

the smallest external dimension of each package is not less than 10 cm
no package in the consignment contains more than 15 g of fissile nuclide and
the mass of the fissile nuclides in the consignment meets the condition:

[{ mass of 235U (g) / 290 } + { mass of other fissile nuclides (g) / 180 }] < 1.;

if the fissile nuclides are mixed with substances having an average hydrogen density greater than water , the mass of fissile nuclides per consignment should not exceed the limit

Deuterium should also not be present in quantities exceeding 1% of the applicable consignment mass limits except where deuterium occurs up to natural concentration in hydrogen.

(5) A consignment being carried in or on a vessel is fissile-excepted if

the smallest external dimension of each package is not less than 10 cm
the fissile material is a homogeneous hydrogenous solution or mixture where the ratio of the mass of fissile nuclides to the mass of hydrogen is less than 5%;

(6) A consignment being carried in or on a vessel is fissile-excepted if

the smallest external dimension of each package is not less than 10 cm
there is more than 5 g of fissile nuclides in any 10 litre volume of material.

Deuterium should also not be present in quantities exceeding 1% of the applicable consignment mass limits except where deuterium occurs up to natural concentration in hydrogen.

(7) Up to a maximum of 1 kg of plutonium per consignment may be considered fissile-excepted provided that

plutonium contains ≤ 20% of fissile nuclides by mass and
the shipment is made under exclusive use.

If theradioactive material to be transported qualifies as fissile-excepted then the requirements specified for the transport of fissile materials do not apply to the transport of such material.

Selection of Package

Selection of the type of package for the transport of radioactive material is determined by the radionuclide and its activity to be transported.

The radioactive materials considered in this module need to be transported in a wide range of activities. They have to be transported in a Type B(U) / (M) packaging or in a Type C packaging. Type C packaging may be needed only if the activity exceeds 3000 A1 or 100 000 A2 for special form radioactive material and 3000 A2 for other form radioactive material.

The design of packages used for transport of spent fuel requires approval by the competent authority. Such approval could be either unilateral [The letter U in the designation Type B(U) represents Unilateral approval.], or multilateral [The letter M in the designation Type B(M) represents Multilateral approval.]. Certain design features of the packaging and the form of the radioactive material to be transported in the package determine the need for obtaining multilateral approval. Even if the package satisfies all the design requirements applicable to a Type B(U) package, multilateral approval is required to be obtained if the spent fuel to be transported is a fissile material.

Unilateral approval needs to be issued by the competent authority of the country of origin of the package design. Multilateral approval needs to be issued not only by the competent authority of the country of origin of the package design but also by those of the countries through or into which the package is to be transported. If a consignment is carried by air over a country multilateral approval is not required from that country in respect of that consignment, provided that there is no scheduled stop in that country.

Specific design requirements for packages containing fissile material

These design requirements address only the fissile nature of the radioactive material. They apply in addition to the design requirements relevant to the radioactive nature of the fissile material to be transported. That is, if the activity of the fissile material warrants a Type B(U)/(M) package to be used for the transport of the material then it should be ensured that the Type B(U)/(M) package satisfies, inaddition, the specific design requirements given below.

Subcriticality should be maintained during normal and accident conditions of transport.In particular, the following contingencies should be considered:

(i) water leaking into or out of packages;

(ii) the loss of efficiency of built-in neutron absorbers or moderators;

(iii) rearrangement of the contents either within the package or as a result of loss from the package;

(iv) reduction of spaces within or between packages;

(v) packages becoming immersed in water or buried in snow; and

(vi) temperature changes.

The smallest overall external dimension of the package should not be less than 10 cm.

The outside of the package should incorporate a feature such as a seal which is not readily breakable and which, while intact, will be evidence that the package has not been opened.

Contents specification for assessments of package designs containing fissile material

Packages containing fissile material should not contain:

(a) a mass of fissile material (or mass of each fissile nuclide for mixtures when appropriate) different from that authorized for the package design,

(b) any radionuclide or fissile material different from those authorized for the package design, or

(c) contents in a form or physical or chemical state, or in a spatial arrangement, different from those authorized for the package design, as specified in their certificates of approval where appropriate.

The criticality safety assessment for the purpose of safe transport of fissile materials comprises assessment of an individual package in isolation, assessment of package arrays under normal conditions of transport and assessment of package arrays under accident conditions of transport.The three assessments are described in this module. Where the chemical or physical form, isotopic composition, mass or concentration, moderation ratio or density, or geometric configuration is not known, the criticality safety assessment should be performed assuming that each parameter that is not known has the value which gives the maximum neutron multiplication consistent with the known conditions and parameters in these assessments.

For irradiated nuclear fuel, the criticality safety assessmentshould be based on an isotopic composition demonstrated to provide:

(a) the maximum neutron multiplication during the irradiation history, or

(b) a conservative estimate of the neutron multiplication for the package assessments.

After irradiation but prior to shipment, a measurement should be performed to confirm the conservatism of the isotopic composition.

Geometry and temperature requirements

The package, after being subjected to the Regulatory tests demonstrating the ability to withstand normal conditions of transport (water spray test, free drop test, stacking test and penetration test)should:

(a) preserve the minimum overall outside dimensions of the package to at least 10 cm, and

(b) prevent the entry of a 10 cm cube.

The package should be designed for an ambient temperature range of -40°C to +38°C unless the competent authority specifies otherwise in the certificate of approval for the package design.

Assessment of an individual package in isolation

The assessment should consider the package conditions that result in the maximum neutron multiplication consistent with

(a) routine conditions of transport (incident free);

(b) normal conditions of transport (following water spray, free drop, stacking and penetration tests);

(c) accident conditions of transport (following the tests specified in this module under assessment of package arrays under accident conditions of transport).

The package should be subcritical under the conditions of described below:

For a package in isolation, it should be assumed that water can leak into or out of all void spaces of the package, including those within the containment system. However, if the design incorporates special features to prevent such leakage of water into or out of certain void spaces, even as a result of error, absence of leakage may be assumed in respect of those void spaces. Special features should include the following:

(a) Multiple high standard water barriers, not less than two of which would remain watertight if the package were subject to the tests specified in this module (assessment of package arrays under accident conditions of transport), a high degree of quality control in the manufacture, maintenance and repair of packagings, and tests to demonstrate the closure of each package before each shipment; or

(b) For packages containing uranium hexafluoride only, with maximum uranium enrichment of 5 mass per cent uranium-235:

(i) packages where, following the tests specified in this module (assessment of package arrays under accident conditions of transport), there is no physical contact between the valve and any other component of the packaging other than at its original point of attachment and where, in addition, following the thermal test the valves remain leaktight; and

(ii) a high degree of quality control in the manufacture, maintenance and repair of packagings, coupled with tests to demonstrate closure of each package before each shipment.

It should be assumed that the confinement system should be closely reflected by at least 20 cm of water or such greater reflection as may additionally be provided by the surrounding material of the packaging. (Confinement system means the assembly of fissile material and packaging components specified by the designer and agreed to by the competent authority as intended to preserve criticality safety.).However, when it can be demonstrated that the confinement system remains within the packaging following the tests specified in this module (assessment of package arrays under accident conditions of transport), close reflection of the package by at least 20 cm of water may be assumed in the assessment for accident conditions of transport.

Assessment of package arrays under normal conditions of transport

A number “N” should be derived, such that five times “N” packages should be subcritical for the arrangement and package conditions that provide the maximum neutron multiplication consistent with the following: