£ IN THE UNITED KINGDOM

FOR DISPOSAL AT THE DEEP REPOSITORY S.V. BARLOW

UK Nirex Ltd, Harwell, Didcot, United Kingdom

Abstract

UK Nirex Ltd is responsible for developing a deep repository for the safe disposal of intermediate and low level radioactive wastes (ILW and LLW), and is concentrating its investigations on Sellafield as a potential location. Nirex in co-operation with the producers of radioactive waste, has developed a range of standard containers suitable for the wide variety of wastes arising and predicted to arise in the future. The standard range includes unshielded containers, such as the 500 litre drum and 3m³ box as well as shielded containers such as the 4m box for ILW and the 4m box for LLW. The unshielded containers require to be packaged into reusable shielded containers for transport whereas the shielded containers form transport packages in their own right. Waste Package Specifications have been produced for each of the standard packages and these provide the essential link between waste package design and the design of the repository. Nirex will eventually be producing Conditions for Acceptance but these cannot be defined until the authorisation and other regulatory requirements are known. Until that time, the Waste Package Specifications provide a sound basis for the packaging of waste. Detailed information on stocks and predicted future aristngs of waste are published in the United Kingdom Radioactive Waste Inventory. The information provided in the Inventory is used by Nirex to determine the volume of waste which will require disposal at the repository. Disposal volumes ranging from 400,000m³ to 2,000,000m³ are currently being considered. Detailed data available in the Inventory are used to classify the waste for transport and to estimate the numbers and types of packages requiring transport and disposal.

1. INTRODUCTION

United Kingdom Nirex Limited (Nirex) has been established by the major organisations in the nuclear industry, with the agreement of Government, with the task of developing a deep repository for disposal of solid intermediate and low level radioactive wastes (ILW and LLW). Nirex is concentrating its investigations on a site adjacent to the Sellafield reprocessing plant operated by British Nuclear Fuels pic.

Nirex working in co-operation vvitli the producers of radioactive waste has developed a range of standard containers suitable for the wide variety of wastes arising in the UK, as well as those predicted to anse in the future. Each standard package meets an identified need and is defined by a Waste Package Specification.

The Waste Package Specifications provide the essential link between waste package design and repository design, and define dimensional, functional and performance criteria. They establish a minimum levé! of performance for all package designs and provide a firm basis for repository and transport system design. Conditions of Acceptance will be issued but cannot be provided until the conditions of the authorisation and other regulatory requirements are known.

This paper describes the range of standard waste packages adopted by Nirex and explains the role of the Waste Package Specifications. Waste volumes currently being considered by Nirex are given and estimates presented on the numbers and types of package requiring transport and disposal.

2. NIREX STANDARD WASTE CONTAINERS

Nirex has long recognised the desirability of standardising on a limited range of waste containers and, apart from some minor changes, ihe standard range has remained essentially unchanged since 1988. The need for standardisation has been confirmed by recent design studies which have had to consider methods for the emplacement of around 100 disposal packages per day. Standardisation is essential if the repository is to achieve the necessary throughput and is also desirable from safety, logistic and economic reasons. The range of standard containers which has been developed by Nirex and the waste producers is given below. Each standard container has been justified on the basis of an identified need for packaging a particular range of wastes.

Nirex Range of Standard Containers ILW

LLW

500 litre drum 3 cubic metre box 3 cubic metre drum 4 metre box 4 metre box 2 metre box

0.8m diam by 1.2m high 1.7? x 1.72m plan by 1.225m high 1.72m diam by 1.225m high 4.013 x 2.438m plan by 2.2m high 4.013 x 2.438m plan by 2.2m high 1.969 x 2.438m plan by 2.2m high

500 litre Drum for ILW

The principal container for ILW is the 500 litre drum. It will be used mainly for operational wastes, arising from day-to-day operations of nuclear facilities. At the

Sellafield Magnox Encapsulation Plant, 500 litre drums are currently being filled with waste and stored. Other plants are also neanng the stage where the packaging of waste can commence

It has not been possible to standardise on one single design of 500 litre drum because the processes for immobilising different wastes require variations to the drum, mainly in the lid area and in the internal drum furniture. A limited number of drum shapes have been adopted, but all have common lifting and handling arrangements.

The 500 litre drum is not designed to provide any radiation shielding, but is to be transported within one of a family of reusable shielded transport containers being developed for the purpose by Nirex [1]. The transport container, which will carry four drums located in a handling stilläge, will be designed to Type B requirements as required by IAEA Safety Series 6 [3]. The transport container family is currently assumed to consist of four thicknesses comprising 70mm, 145mm, 210mm and 285mm steel shielding.

Figure 1 shows the 500 litre drums in a transport container, and also serves to illustrate the terms waste container, wasteform, waste package, transport container and transport package which are used in this paper.

TRANSPORT PACKAGE!

WASTE PACKAGE

TRANSPORT

CONTAINER WASTE

CONTAINER

N>

S

WASIEFORM

Figure 1 - 500 litre Drums in a Re-usable Transport Container

3 cubic mclrc Box

While the 500 litre drum is the principal container for [LW, some items will be too large for it, for example redundant items of equipment or decommissioning waste.

For these wastes a standard box of nominal capacity 3m3 will be used. The box is cuboidal with rounded corners. The shape corresponds to the outline of a stilläge containing four 500 litre drums and hence the 3m3 box can be transported within the same reusable transport container.

The 3m3 box, in contrast to the 500 litre drum is not yet in use, but Nirex has produced a preliminary design in order to demonstrate the feasibility of the concept and has manufactured and successfully tested two prototypes [2]. The design is currently being revisited to take account of the latest information from repository design and site investigation.

The 3m3 box will be transported within the same family of Type B reusable shielded transport containers as will be used for the 500 litre drums.

3 cubic metre Dram

The 3m3 drum is a cylindrical version of the 3m3 box which is suited to in-drum mixing of waste. Although currently being developed for a particular application, it has potential uses throughout the industry and has therefore been adopted as a Nircx standard waste container. As with the 3m' box, one 3m3 drum can be transported within a reusable Nirex transport container and when compared against a payload of four 500 litre drums, it is some 30% more efficient.

4 metre Box for ILW

The three ILW containers described so far - the 500 litre drum, 3m3 box and 3m3

drum - all need to be transported within a reusable transport container which is being designed to Type B requirements. However, wiien filled with waste, the 4m ILW box complies with IAEA Safety Series 6 [3] as a transport package in its own right, and is designed to be disposed of without being opened.

The 4m box is designed as a non-fissile Industrial Package Type 2 (IP-2), according to the 1985 Edition of the IAEA Transport Regulations. It is Intended to be used for short-lived ILW complying with the requirements for low specific activity material (LSA II or LSA III) or for surface contaminated objects (SCO; complying with SCO I or SCO ÎI requirements.

The box incorporates its own shielding, with reinforced concrete waits up to 250mm thick. The box dimensions have been specified to fc;iow the principles established for Series 1 ISO freight containers [4]. The standard ISO width of 8 feet (2.438m) has been adopted and the length has been specified as a two-thirds module of the standard 20 foot (6m) ISO container. The box incorporates JSO-style corner fittings to permit lifting by twistlock frame and tie-down to a transport vehicle. The box is likely to

K) O ON

have a maximum weight of 65 tonnes when filled with grouted waste, although it is currently limited to 50 tonnes pending clarification of handling limitations at the repository [5]

Containment of radioactivity is provided by the monolithic nature of the wasteform and by the reinforced concrete walls. Qualitative methods are proposed for the demonstration of compliance with regulatory containment requirements when subject to normal conditions of transport tests [3]. The reinforced concrete has been designed in accordance with the requirements of paragraph 523 of Safety Series 6 [3], so the package can withstand the loads specified in ISO 1496/1 [6] with crack widths limited to 0.2mm. In practice the most onerous load case will be that of lifting from above.

This box is likely to be used mainly for reactor decommissioning and similar wastes.

Acceptable contents are currently judged to be activated materials such as steel, graphite, concrete and similar materials for which it can be claimed that the activity is uniformly distributed. It may be some time before there is need for this package but Nirex is currently developing the design in order to provide a basis for repository design.

4 metre Box for LLW

The 4m LLW box is designed as a non-fissile Industrial Package Type 2 (IP-2) for use with LSA-II, LSA III, SCO-I or SCO-II waste material. The design is based on ISO container principles and is in accordance with the requirements for an IP-2 freight container [para 523, ref 3]. Containment of the radioactive contents is provided by a sheet steel structure which is fabricated by continuous seal welds at sheet interfaces. The complete fabrication is intended to be bubble tested to check for leaks. The lid closure is affected by an elastomeric seal which is compressed by lid clamps; the seal can be pressure tested at manufacture.

Low level waste does not require shielding and, unlike ILW, grouting will not normally be required for transport or disposal in the deep repository. Since it does not incorpp'ate shielding or carry a grouted wasteform, the gross weight of the package is likely to be in the region of 20 - 26 tonnes. This means that the box will be suitable for transport by an ordinary Heavy Goods Vehicle of 38 tonnes gross vehicle weight. A version of the box weighing up to 65 tonnes is also being considered for the disposal of heavy wastes.

An important element of the design is commonality of dimensions and handling features with the 4m ILW box. This has major benefits since it permits the use of standard equipment for transport and handling operations Furthermore, since the boxes are based on the ISO container standards, advantage can be taken of proven technologies from the freight handling industry.

2 metre Box for LLW

This container is a half-length version of the 4m box for LLW, and similarly is a transport package in Us own right. It is envisaged that the 2m box will be used for

packaging of denser wastes which would exceed the weight limit if packaged into the 4m LLW box. It has been sized such that it can be filled with high density steel waste and still remain suitable for road transport; like the 4m LLW box its maximum weight will thus be 26 tonnes. It is also likely to be of particulsc benefit1 m decommissioning situations where a smaller be* u required at the 'working face'.

3. NON-STANDARD WASTE PACKAGES

All the waste containers described s.j far are Nirex standard designs that will be suitable for the vast majority of waste producers needs. Non-standard packages will however have to be used for some wastes. These may arise for instance where the design predates the establishment of Nirex standards, or where the waste is of a size and shape which would require expensive size reduction before it could be packaged into a standard container. An example of such a container h the WAGR box, a concrete IP-2 container designed for packaging waste from the decommissioning of the Windscale Advanced Gas-cooled Reactor [7].

Nirex will consider requests to use non-standard packages, but additional costs are likely to be incurred at the repository owing to the need to make special arrangements to handle and dispose of the packages. In every case, the level of safety provided by the non-standard package will have to be equivalent to that of a standard package.

4. SPECIFICATIONS

Following on from the need for standardisation of containers, there is a need for specifications to define these standard containers and set minimum standards of performance. The Nirex Waste Package Specifications provide the essential link between waste package design and repository design. For waste producers, the specifications are required in order that waste packaging plants can be built and waste containers designed. For Nirex, the specifications provide a key element of the basis of design for the repository and transport system and also for the various safety cases to be made to the regulatory authorities.

Two facts in particular have been important in the development of the Nirex Waste Package Specifications:

(i) Long before the repository is ready to receive any shipments of waste, many producers wish to package waste and store it on site.

(ii) In the process of designing any waste processing or handling facility -including the repository itself - an important early input is the waste container dimensions and characteristics. Once design work gets under way the scope for accommodating changes becomes limited, and such changes are costly.

For these reasons the designers of waste containers, waste packaging facilities, transport containers and repository facilities have needed, as early as possible, the

detailed dimensional, functional and performance criteria for waste packages together with any related requirements and supporting information The Nirex Waste Package Specifications fulfil this role, providing the link between waste package design and repository design.

Specifications have been produced for each of the standard packages. They incorporate the various requirements for disposal and transport and are compatible with the requirements for waste packaging, storage and handling at the sites of origin.

They are based on design and safety case needs; supported by research and other technical studies on the performance of waste packages under repository (handling and disposal) and transport conditions.

Each specification defines dimensional, functional and performance criteria for the waste container and wasteform. These criteria include activity content, dose rate, surface contamination, heat output, dimensions, shape, handling features, venting and filtration, impact performance, integrity and stackabihty.

In formulating the specifications, the aim has been to minimise the risk that the requirements of the eventual Conditions for Acceptance will be more restrictive. This has been achieved by ensuring that the specifications allow for the inevitable uncertainties that exist at the present stage of repository development. This is necessary if future design options are not to be curtailed.

5. DEVELOPMENT OF ACCEPTANCE CRITERIA

Acceptance criteria will be identified by Nirex once all the constraints governing the disposal of waste at the repository have been identified. It is anticipated that the acceptance criteria will be made available to customers in the form of Conditions for Acceptance.

The Conditions for Acceptance will have to take account of any constraints imposed by the authorisation for disposal. The authorisation which will be issued under the Radioactive Substances Act 1993 [8] may result in limits being placed on:

total volumes of waste for disposal total radioactivity

activity of certain radionuclides mass of particular materials

In addition to the authorisation, the Conditions for Acceptance will have to encompass all the other constraints including conditions imposed by the Nuclear Site Licence, Transport and other Regulations as they exist at the time, operational and post-closure safety, and repository design and operational requirements. It is clear therefore, that the Conditions for Acceptance will not be available until much closer to the start of repository operations.

The Conditions for Acceptance will incorporate the standards and Waste Package Specifications. Inevitably there will be some changes in the latter as the development of the repository progresses and the regulatory requirements are updated. However, since the specifications have purposely been designed to be robust to uncertainties, it is expected that any changes will lead to a relaxation in requirements rather than a tightening.

6. NUMBER OF PACKAGES

As noted previously, intermediate level waste is already being packaged for disposal in the deep repository. As of January 1991 some 80,000m' of 1LW was in stock, and by lanuary 1994 some 2,000m3 had been immobilised and packaged for disposal in standard 500 litre drums. By the time the repository opens for business in the early years of the next century (around the year 2010), accumulated wastes will have increased to about 156.000m3 and further wastes will contine to arise throughout the lifetime of the repository.

Estimates of the volumes of waste which will arise over the next 15 years and during the nominal 50 year lifetime of the repository are central to all Nirex's work on transport and repository design. Information on existing stocks and predicted future arisings of radioactive waste are published in the United Kingdom Radioactive Waste Inventory [9]. This inventory, together with companion documents providing data on radionuclide content and the physical and chemical characteristics of waste [10, 11], are produced by Nirex in conjunction with the UK Department of (he Environment. The Inventory is regularly updated and is published every 2 or 3 years.

The Inventory contains detailed information on accumulated stocks and predicted arisings on a waste stream basis. The 1991 Radioactive Waste Inventory details nearly 1000 separate ILW and LLW waste streams. The projections of future arisings of radioactive wastes are made by the producers of the waste on the basis of their programmes and policies, and their best estimates of the nature and magnitude of future operations and activities. The Inventory includes estimates of the quantities of future arisings up to the year 2030. This is the furthest dale into the future to which waste producers could reasonably be expected to make predictions. However, estimates of decommissioning wastes predicted to anse from reactors and other facilities operating before 2030 are included.

The volumes of waste recorded m the 1991 Radioactive Waste Inventory are shown in Table 1.

The Radioactive Waste Inventory is not in itself sufficient for Nirex to determine the required capacity for the deep repository. This will ultimately be determined by customer demand and so Nirex has to plan its future strategy in a flexible mar.-.er so that it can accommodate changes in waste arisings. In order to provide a basis for planning, design and safety case preparation, Nirex is considering a range of waste

too oo

Table 1 : Waste Volumes Recorded in the UK Radioactive Waste Inventor}

Waste

Table 2 : Scenarios for Repository Capacity

Table 2 : Scenarios for Repository Capacity