For the record13 October 2005
Radwaste management requires continued access to comprehensive and reliable information over decades and perhaps centuries. The UKAEA has chosen to use ‘permanent paper’ in preference to electronic systems. By Michelle Wise, David Gray and Ian Upshall
To help ensure safety, radwaste managers must have access to detailed information on their wastes far into the future. It is therefore necessary for waste package custodians to establish and implement a system for managing information records at an early stage.
The UKAEA, with the assistance of the radioactive waste agency Nirex, has carried out a study of the nature and of the specific and generic information to be recorded, and reached a decision on the best medium to ensure the information remains accessible for an extended period of time. The project involved radioactive waste package records for the Windscale Advanced Gas-Cooled Reactor (WAGR).
WAGR was the forerunner of a family fourteen commercial advanced gas-cooled reactors (AGR’s) on seven sites across the UK. It provided a test facility for fuels destined for the commercial plant; and operational experience of power production.
The reactor was shutdown in 1981 after satisfactory completion of all the research and development objectives and initial decommissioning began in 1983 when the fuel and some associated materials were removed.
It was decided at the time to decommission WAGR to Stage 3 – returning the site to a condition of unrestricted use. It is now the UK’s lead demonstration project to show that nuclear power reactor can be decommissioned safely, cost effectively and using existing technology.
Planning the decommissioning of WAGR started before the 1981 shutdown and has resulted to date in the accumulation of over 20 years of documents relating to both the decommissioning methodology and the nature of decommissioning wastes. The project began under operational staff but today is managed by a UKAEA supervisory team which has executive and supervisory responsibilities to ensure that contractors appointed to carry out the decommissioning operate in a safe and controlled manner.
The decommissioning work itself has progressed steadily, WGR changing from a fully fuelled reactor to a structure where basically only concrete shielding and the steelwork associated with the lower half of the pressure vessel remains.
Much of the decommissioning work was done in stages. The development design work associated with the concrete boxes used for storing the radioactive waste preceded the construction of a waste handling facility in the 1980s, the removal of the top dome of the reactor in 1991, the erection of a remote handling machine in the 1993-94 and the removal of the heat exchangers in 1995. Work began on removal of the reactor internals in 1999 under a contract with BNFL (later British Nuclear Group)
Intermediate- and low-level radioactive waste (ILW and LLW) from the decommissioning of WAGR is grouted into purpose-made steel reinforced concrete boxes, approved by Nirex, at the waste handling facility. The ILW, which includes most of the graphite core, loop tubes and neutron shield, is transferred to the WAGR ILW store on site, while the LLW is despatched to the nearby Drigg disposition site. In all, the project is expected to generate some 400t of LLW, contained in 119 boxes and 800 tonnes of ILW in 144 boxes.
The UKAEA has recognised that, because of the uncertainties concerning the timescale for the availability of a national repository, there will be a requirement to manage the ILW waste at Windscale and other UKAEA sites for possibly 50 years, or potentially 100 years, prior to their transfer. The long-term storage of these packages will also require the long-term management of the information intended to demonstrate that they are compatible with the present criteria for disposal at a national repository.
FOR THE RECORD
The principle behind recording data on waste packages is:
Information shall be recorded for each waste package to enable conformance with the necessary performance and acceptance criteria to be demonstrated for future phases of waste management.
Nirex requires that waste producers establish a data recording system for acquiring, recording and subsequently managing information for each waste package such that the package may be assessed against requirements for safe and cost-effective handling, transport, storage and potential disposal. What needs to be recorded, therefore, is information that can be used to establish, infer or predict package properties and performance under all relevant circumstances. Ultimately, this information may be used to demonstrate conformance with future transport, handling, storage and possible disposal (or long-term storage) acceptance criteria.
The range of information that will need to be recorded for each individual waste package will be unique and whilst a ‘standard’ approach will be used as far as possible, the development of a tailored system may be required for each waste type or packaging campaign.
Information will be created over the entire lifetime of the waste package, from process conception, through process development, waste package production, storage, transport and ultimately to disposal. It may be considered appropriate to split the information sources into four distinct groups:
- Generic information related to a number of packages.
- Batch specific data.
- Package specific data.
- Administrative information.
During the development of a process for packaging the waste, consideration would have to be given to the relevant properties of the final waste package and its evolution over time. Information created during this development programme will contribute to the knowledge on the final waste package. The following information should be recorded:
- Waste conditioning, packaging materials and processes.
- Encapsulation materials used in the creation of a waste package.
- A record of the proposed waste package properties and performance over time.
- The relationship between these and the nature and quantity of waste.
Information recorded on the findings of the development programme will form an important component of the package record. This information is likely to be retained as ‘traceable information’ which will be referenced from the package record or from other related documents such as the Waste Product Specification.
The Waste Product Specification will define the characteristics of the intended waste package and is the result of research and development programmes. It provides a means for specifying the waste package production envelope.
Batch specific information
Some information will be common to a number of packages. For example, relevant information will be created during the manufacture of the containers (where a batch of containers is supplied for a packaging campaign) or as a result of the purchase of bulk supply materials (such as the encapsulant). Information of this type may be duplicated in numerous of sets of package records, alternatively, it may be referenced as traceable information preserved elsewhere. The means of preserving such information will depend on its nature and the media used but it will be at the discretion of the waste producer. Nirex will offer support and advice on the optimum management arrangements for preserving such information sources.
In many applications a small number of failures may be acceptable but the preservation of radioactive waste data does not fall into this category
Package specific information
Package specific information is that which is unique to a single entity. Examples of this information include the package identity, data demonstrating conformance with prescribed limits (conformance data) and a description of the nature of the waste. Information may be derived from measurements or calculations conducted at any stage of the package manufacturing process or subsequent interim storage.
As suggested above, decades may elapse between the package manufacture and its ultimate disposal. Consequently, packages will be monitored during interim storage in order to demonstrate that they continue to comply with handling, transport, storage and disposal requirements. An historical record of the storage location, environmental conditions, duration and any significant events will complement the package specific information. A combination of package specific and storage information will enable a detailed history of the package to be built up thus providing valuable information on the expected long-term evolution of the package.
In addition to the information described above, there will be a requirement to derive data to demonstrate compliance with administrative and regulatory requirements related to the transport and disposal of the waste. Such administrative information will accompany the package throughout. In general, the information would not be required until the time of consignment of the waste for long-term storage or disposal.
Some waste will contain accountable quantities of safeguarded nuclear materials. Where this is the case, information on the precise quantities and locations, will have to be maintained and routinely declared to the safeguards authorities.
Information currently resides on a range of media including paper, microform, computer diskette, magnetic tape, CD-ROM and, to a lesser degree DVD-ROM. The majority of the information collated to date is stored under secure conditions, but there are currently very few site-based records storage facilities designed and constructed with the specific intention of preserving waste package records media for the long-term. The records management systems generally in place have been implemented to meet the immediate operational or regulatory needs of the nuclear facility licences – which extend to between 30 and 50 years. The issues affecting continued long-term accessibility to the information have not been explicitly addressed although, using the WAGR project as a typical case, progress is now being made.
Nirex undertook a study of the characteristics associated with the range of records media in use today and their suitability for storing information and ensuring continued accessibility over the long-term. The records media considered were initially categorised as ‘hard-copy’ and ‘electronic’. Hard-copy records were defined as those on which data can be recorded without the need for subsequent processing or conversion. Electronic records were defined as those created and presented electronically (for example, a spreadsheet) or those that undergo some form of secondary digital processing (for example, an electronically scanned hard-copy record).
Most papers display qualities compatible with long-term preservation and their longevity is further enhanced if they are stored in a controlled environment. There are a number of standards that provide recommended conditions for optimum preservation and these can be readily achieved given modest resources. Other measures are recommended to increase longevity including restricted access to originals, the use of lint-free gloves when handling paper records and the elimination of all metals and plastics such as staples, paper clips and PVC covers, all of which have been shown to have a detrimental effect. However, with the ever increasing pressure to implement ‘environmentally-friendly’ processes, the use of recycled paper is now commonplace. These papers should only be used with extreme caution, particularly where their constituents are poorly defined and long-term performance is unpredictable.
Microfilms have been a popular medium for many years where large volumes of data, drawings and diagrams require preservation. However, it is noticeable that with the increased use of electronic data storage systems the popularity of microfilm has declined. Continuing improvements to film construction, the introduction of laser printing techniques, combined with its long-term stability and competitive cost, suggest that this medium has the potential to feature in future waste-related information systems.
Analogue data stored on magnetic disk or tape was the principal storage medium until the mid-1980s. Much important historical information, potentially of interest to future waste custodians, resides on these media and whilst our understanding of the long-term characteristics of them is less well advanced than that of paper, there is a fairly substantial knowledge base. The subsequent development of optical media saw a move away from the relatively error-prone and delicate magnetic media to optical disks. On first inspection their apparent robustness and durable nature suggests an ideal storage medium that will complement any long-term information system architecture.
Digital information storage is dominated today by CD-ROM. They are undoubtedly hard wearing, require little maintenance, have a large storage capacity and are readily available at low cost. However, there is relatively little experience in their use and consequently, there is only limited knowledge, based on accelerated ageing, of their suitability for information preservation over the long-term. The low production and purchase costs of CD-ROM disks can be achieved by employing low-cost materials and mass production. In many applications a small number of failures may be acceptable but the preservation of radioactive waste data does not fall into this category. Care must be taken if CD-ROMS are used and high quality media combined with regular checks is highly recommended.
The past twenty years have seen a significant increase in the use of electronic systems for creating and storing data. The convenience, storage capacity and low cost of the media, makes an electronic-based system a very attractive option to a paper or microform-based system. Most organisations use computer systems for the creation of key records and it is understandable that there will be a strong incentive to assume that the advantages offered by electronic media in the short-term can provide a basis of an argument for their use over the long-term. Continued and long-term access to information is placing new and unfamiliar demands on the media and it would be unwise to make critical decisions without first fully understanding the real threats.
Development of a robust information management system requires firstly, the identification of the threats to data accessibility and, secondly, the measures necessary to eliminate or mitigate the risk of these threats. Measures employed could be ‘preventative’, such as the installation of a fire detection and suppression system, or ‘anticipatory’. An anticipatory measure pre-empts the effects of an unplanned event and ensures that a full recovery is possible, for example, copying records and transferring them to a remote storage facility.
One of the greatest and most tangible threats to the loss of information results from organisational change. The UK nuclear industry has undergone significant organisational change in the past and is likely to undergo further changes in the near future. The risk associated with changes to organisational structures lies in three areas: firstly, information is ‘lost’ or misplaced during the transfer of responsibilities; secondly, it is successfully transferred but its significance not recognised; and, thirdly, the recipient organisation operates a different management system with which the recorded information is incompatible.
Another threat, generally associated with electronic media, is loss of data accessibility as a result of technological advance. ‘Low-technology’ solutions (for example paper or microform-based records) are less likely to be affected than ‘high-technology’ solutions (for example, digitally based records). The latter rely heavily on a number of interacting technologies (both hardware and software) so whilst the ‘electronic’ solution has many short-term advantages; it also has great potential for long-term accessibility problems if migration onto replacement media is not carried out.
In terms of life expectancy only microfilm at 100-200 years comes close to the requirements for storing the information. Other electronic media are either liable to corrupt after 5-10 years or suffer obsolescense. Recent history is littered with examples of the failures of electronic storage. Some years ago a new ‘Doomsday’ book was recorded using the latest technology at the time and now 20 years later some of the data cannot be accessed. Meanwhile, the original version written over 900 years ago remains entirely accessible. Similarly, twenty per cent of the data collected during the 1976 Viking Mars mission can no longer be read. The list goes on.
The valuable work done by Nirex investigating suitable media mentioned above, together with the considerable anecdotal evidence, influenced the decision on the choice of media to be used for storing all the necessary information on ILW arising from the WAGR decommissioning project. Paper was chosen because of its proven performance over the other possible forms of media, more specifically ‘permanent’ paper which is acid-free and, unlike recycled paper, has a high lignin acid content; it will not deteriorate or discolour. As a result its life expectancy is a least several hundred years.
For extra assurance, to mitigate against the risk of loss due to events such as fire or aircraft impact, two further sets were produced for archiving at different locations.
In all some 423 documents were photocopied onto 11,718 of permanent paper, packed in copper-impregnated bags, and stored in 16 special long-life archive boxes. The specialist photocopying was carried out by Furness Engineering and Technology of Ulverston, West Cumbria.
The system will be used as a basis for the development of corporate guidelines on the management information in support of other UKAEA waste packaging projects.
Michelle Wise, David Gray, UKAEA WAGR Windscale, Seascale, Cumbria CA20 1P, UK. Ian Upshall, UK Nirex, Curie Avenue, Harwell, Didcot, Oxfordshire, OX11 0RH, UK.
|In many applications...|
|In many applications a small number of failures may be acceptable but the preservation of radioactive waste data does not fall into this category|