A mature and capable industry30 May 2000
Delegates to Transport in the Nuclear Industry heard that the issue of contaminated spent fuel casks has been addressed, and turned their attention to new revisions of transport regulations.
The UK Institution of Nuclear Engineers (INucE) organised its first conference and technical exhibition on Transport for the Nuclear Industry in 1988. Subsequent meetings have been held about every third year with 30-35 papers (including poster papers) being presented. They take place between the much larger conferences organised by the United States on Packaging and Transport of Radioactive Materials (PATRAM) where typically over 250 papers are offered. The most recent INucE gathering took place at the Savoy Hotel, Blackpool, UK on 2-4 November 1999. It attracted 124 participants from 12 countries, including contributions from France, Germany, South Africa, the UK, the International Atomic Energy Agency (IAEA) and the World Nuclear Transport Institute (WNTI). Unusually, no papers were presented from Japan or the US.
There is an underlying feeling of maturity and capability in the industry and the trend is to replace historic flask designs. However this was tempered by some concern regarding the problems of surface contamination of large spent fuel transport flasks, a topic which has been running particularly strongly in Germany since May 1998.
In a keynote opening paper Clive Young of the UK Department of the Environment, Transport and the Regions, described the future system of review and revision of the IAEA Regulations for the Safe Transport of Radioactive Material. First formulated in 1961, the Regulations were comprehensively reviewed in 1964, 1967, 1973, 1985 and 1996 and have become the standard for national and international regulations.
Normally it takes 5-6 years to bring a revision into force after it has been published. In the mid-1990s the revision process was examined and this led to a major change in the way regulations are produced. They were reclassified as Safety Standards and four senior advisory committees were set up. At about the same time the UN Committee of Experts on the Transport of Dangerous Goods began to modify the structure and format of its recommendations and present them as a set of ‘model’ regulations. The worthy aim was to establish common regulations for all classes of dangerous goods. The UN Model Regulations were published in 1999.
The IAEA is not a free agent in making changes to international regulations as it has to obtain consensus from Member States and may need to negotiate compromises. During the discussion of this paper the apparent complexity of the overall process of revision was remarked.
An anomalous position regarding the International Nuclear Event Scale (INES) was also pointed out. Although it was introduced in 1989 it has not been formally extended to embrace transport incidents and, possibly more important, is not part of the transport regulations.
In the other keynote paper the IAEA’s Ron Pope described the range of the Agency’s activities towards introducing the 1996 revision of the Regulations (published as Safety Standard ST-1). He analysed the status of the related advisory and emergency response planning documents and showed how the IAEA had co-ordinated with other international bodies to prepare to introduce the ST-1 regulations on 1 January 2001. A new revision cycle, due to begin in January 2000, would publish a new edition of the Transport Regulations late in 2003.
The continuing focus on the safety of radioactive material transport has led the IAEA to set up a series of co-ordinated research projects. It has also convened a series of training meetings in various parts of the world and set up a number of databases recording items such as shipments, radiation exposures and incidents. The IAEA has also initiated a Transport Safety Appraisal System (TransSaS) to assist Member States in implementing the regulations. So far only one TransSaS mission has taken place, to Slovenia.
A class of ‘low specific activity’ material was included in the original 1961 Transport Regulations. In the 1985 revision, categories of low specific activity materials and surface-contaminated objects were introduced, but inherent problems of definition and implementation rapidly emerged. Some material was in both categories. The best technical solution was considered to be using a dose-based approach to revise this part of the Regulations, but the details of the modification were not sufficiently advanced by the time of the 1996 revision.
Consultant Iain Gray described the progress of the IAEA’s research project on this subject, initiated in 1997 and being carried out in Brazil, Canada, France, Germany, the UK and the US. The project will probably allow this area of research to be cleared up but it does require experimental work to study the behaviour of different types of waste. However any change must have an IAEA Member State or a recognised international organisation as its sponsor.
The impact of adopting the European Union Directive 96/35/EC on the appointment and training of safety advisers for the transport of dangerous goods was described by Tony Slatter of the UK Department of the Environment, Transport and the Regions. The UK objected on the grounds that it would increase industry costs without adding to safety but nevertheless is implementing the Directive with as ‘light a touch as possible’.
There were three papers on the headline subject of contamination of large spent fuel transport flasks.
Richard James of British Energy presented a distillation of much experimental work carried out by the Central Electricity Generating Board and Nuclear Electric, the predecessors of British Energy, and extensive operational experience. This work has enabled the multitude of factors involved in the difficult task of estimating the amount of non-fixed contamination on a flask or wagon to be identified. They range from the swabbing process (where many variables are involved) to the paint system and the instrumentation. As a result it has been possible to define the best current practice for minimising and measuring contamination. Bearing in mind the complexity of the contamination test procedure as described by Richard James, the methods must be standardised and details made available.
There were two very topical reports from Yves Brachet (Transnucléaire) and David Krembel (representing the French regulatory authorities) on the spent fuel flask contamination problem which disrupted European irradiated fuel transport in 1998 and 1999. The French Nuclear Installations Safety Directorate (DSIN) took over regulatory authority for radioactive materials transport in June 1997. The matter of flask contamination was raised by DSIN and domestic and international spent fuel transport by French railways was halted: similar action followed in Belgium, Germany, Switzerland and the Netherlands.
In May 1998 the French newspaper Libération brought up the subject while the PATRAM ‘98 conference was taking place in Paris. A brouhaha rapidly developed, following a report from DSIN commissioned by the French prime minister. A committee was set up, comprising regulators from France, Germany, Switzerland and later the UK, to establish the causes and make recommendations. The Common Report of the Competent Authorities of France, Germany, Switzerland and the United Kingdom was published on 24 October 1998 (see Int. J. Radioact. Mater. Trans. 10, (2), pp73-84, 1999).
DSIN implemented an inspection programme which revealed that many flasks and wagons arriving at Cogema’s Valognes (Manche) rail terminal, prior to transfer by road to La Hague, had surface contamination in excess of the routine limit of 4Bq/cm2. The data related to shipments from other countries as well as France and covered a period going back to the early 1990s. The report concluded that:
•There were no radiological safety implications because of the large safety margins in the limits and further conservatism in the contamination testing method.
•The contamination measurement procedures were deficient and results were not co-ordinated between organisations.
•State controls were inadequate.
It recommended that an international database be set up and a report published annually.
Undoubtedly there had not been a clear enough definition of what was meant by compliance when faced with flasks or wagons showing a non-fixed contamination level above 4Bq/cm2. The advisory material for the IAEA Regulations, Safety Series No 37 (SS37) recognises that this value could be exceeded but adds that this is unlikely to present a significant hazard because of the in-built safety margins. Non-compliant surface contamination results had been occurring and were being recorded for up to 10 years. SS37 requires contamination levels to be as low as reasonably acheivable (ALARA), and this also was not well defined. The text of the regulations should be examined.
Probably if the INES had been applied to transport incidents the problems would have surfaced much earlier, but the situation on INES is changing. France brought in a system with effect from 1 October 1999, there has been a UK study for the European Commission and the IAEA has recently convened a meeting on the subject.
The contamination affair has been a shock to the industry but great efforts have been made to rectify the situation with special emphasis on revised technical features. These included improved cleanliness, achieving level zero contamination, more contamination check points and checking by an independent organisation.
Transport was authorised to restart in France in July 1998 and spent fuel shipments have restarted in all the countries involved, though in Germany there have been special political factors within the governing coalition which delayed a resumption until the spring of this year.
Among other papers, three were from the Bundesanstalt für Materialforschung und Prüfung (BAM), the German authority for assessing and design-testing transport flasks. The first paper described experimental and analytical methods used to demonstrate flask behaviour under test conditions and experience in defending the methods in German legal proceedings. The second described an improved method employing dynamic fracture mechanics to assess the safety of a ductile cast iron flask.
A third paper, presented by Professor Droste of BAM, described a spectacular test where an LPG tank explosion was initiated by engulfing it in a fire adjacent to a CASTOR flask (see photographs). The flask had been designed for the transport and storage of THTR/AVR pebble bed reactor spent fuel but for this test it was not fitted with impact limiters. Obviously this was a highly improbable scenario but the impact was similar to that sustained during a regulatory test. Post-test investigation showed no loss of leaktightness or shielding integrity. A video of the event provided a dramatic record rivalling some of the footage from Sandia Laboratories.
Ian Curl of AEA Technology described the improvements in shielding and criticality assessment made possible by the considerable developments in readily available computing power over the last decade.
The paper, which he was presenting on behalf of the authors, detailed the application of Monte Carlo methods, such as the MONK and McBEND codes developed by AEA Technology and BNFL, to actual flask assessments. The codes enable accurate modelling of the physical geometry, more precise representation of nuclear data and improved neutron tracking.
Jean-Luc Mondanel of Transnucléaire presented a broad view of trends in packaging. For several decades the front-end nuclear industry used packages developed in the US. But the situation has been changing: regulations have slowly evolved and traditional partners such as shipping lines, port authorities and airlines have tended to see increasing risks and constraints. Designs have had to evolve to take account of this.
Since transport costs less than 1% of the total value of the material transported, new does not necessarily imply increased cost. Indeed it can unlock the opportunity to specify new and cheaper operations, lower maintenance requirements, save weight and reduce the number of shipments.
An example of a new secondary package for the transport of enriched UF6, using fibre-reinforced composites adapted from the defence and offshore oil industries, was presented by Howard Whittaker of BNFL. Similarly, V Roubertie of Cogema presented a poster paper on the new overpack designed by Transnucléaire for use with 30B containers carrying enriched UF6. The new overpack is intended to overcome constraints with existing packages.
During the poster session J P Denizou and Mme Robin (Framatome) presented the details of a replacement for the RCC fresh fuel transport containers which were designed over 30 years ago. A replacement design called FCC, initiated in 1997, takes new requirements into account including:
•Impact on a 1.2m bar.
•Maintaining sub-criticality during all normal and accident conditions of transport complying with the regulatory tests.
ISO freight containers are now being used more frequently. In recent years technical papers have described tests on 20ft containers. Jürgen Migenda of STM Baden described a drop test on a prototype 40ft (12.19m) ISO box container which was part of its qualification as a Type IP2/IP3 package. This paper led to a long discussion generated by the fact that IP packages have to withstand ‘normal’ conditions of transport, and centred around the need for clarification regarding the tests for normal conditions of transport including the acceptance criterion for ‘leaktight’. Some difficulty was caused by the fact that although ST-1 had been issued, the advisory material to the 1996 revision of the Regulations (ST-2) had not yet been formally published.
MOX fuel use has increased significantly in the last ten years, since its performance has improved. Yves Brachet (Transnucléaire) described French experience in the development of plutonium oxide and MOX fuel transports and packaging. About 200 transports are now performed each year, so it has become well established on an industrial basis. The designs must satisfy stringent security standards, due to the high plutonium inventory, as well as maintaining sub-criticality and providing adequate shielding and heat dissipation.
As an interim measure, existing flasks were converted to provide transport capacity. In 1996 BNFL decided to initiate a new design of MOX transport package fully compliant with all the foreseen technical requirements. Peter Purcell (BNFL) described the technical challenge posed by the Euromox package design which is scheduled to enter service in 2003.
OPERATION AND EMERGENCY PLANS
Iain Gray presented a paper on behalf of Kasturi Jutle which gave an interesting overview of transport in South Africa. Because South Africa is a significant force in the world supply of minerals, large amounts of contaminated materials and equipment are generated, particularly from the gold mines where uranium is a by-product. The mining industry produces about 150,000t of scrap steel annually, of which about 10% is estimated to be contaminated. Consequently large numbers of potentially contaminated equipment items are sent for repair off-site.
Roger Norman of BNFL Magnox described the procedures and controls covering the design, hardware provision, safety assessment, quality assurance, operations and maintenance of the Magnox Mk M2 flask design which has been in use since the early 1990s.
Underlining the point that there is a continuing need to comply with radiation protection requirements, Roger Gelder of the UK National Radiological Protection Board summarised assessments made for the UK regulator of the radiological impact of transport operations. Probably the most interesting conclusions are that:
•Most current exposures are ALARA.
•Variations in natural background radiation exceed the values of public exposure to man-made radiation by a large factor.
The inference is that resources should be concentrated on reducing the exposure of the small number of workers who are subject to higher radiation doses.
Ian Hudson (BNFL) summarised experience in the sea transport of research reactor fuel from Japan to the US via the UK on behalf of the Japanese Atomic Energy Research Institute. In the last 20 years the BNFL marine transport fleet has performed more than 330 voyages and transported 8000t of fuel.
Vallette Fontaine described the steps taken by Transnucléaire to develop and implement its own emergency response plan. It includes the means for recovering a large flask after a transport accident. One situation considered was that of a train carrying a heavy flask derailed in a 100m ravine without road access.
There have been four emergency plans in the UK: NIREP, covering transport other than flasks; IFTFEP, for irradiated fuel transport flasks; a Scottish equivalent to IFTFEP; and the National Arrangements Involving Radiation (NAIR). Nigel Board (BNFL Magnox) explained that a replacement plan, RADSAFE, had been implemented on 1 August 1999 to clarify the confusing situation. The previous complexity was not justified because the three earlier plans had only been invoked three times in the previous five years. For the moment NAIR has been left as a ‘backstop’ plan which can be invoked by the police where no other emergency plan exists.
Lorne Green of the World Nuclear Transport Institute, which was inaugurated in April 1988, described the Institute’s aims. It had set about providing the nuclear transport industry with a focus for dealing with intergovernmental organisations such as the IAEA and the International Maritime Organization. He said that it is not sufficient for the industry to operate safely and economically. Because this is the age of the sound bite and the simplistic catchphrase, the future of nuclear power also depends on public confidence, and the industry must be proactive.
Colin Dixon (AEA Technology) described the major operations involved in October and November 1995 when four large decommissioned heat exchangers from the Windscale AGR were individually conveyed 16km, mainly on public roads, to the Drigg low level waste repository for eventual burial. Each heat exchanger, which was 20.6m long with a pressure vessel weighing 188t, was carried on a self-propelled modular vehicle. The packagings were classified for transport as ‘surface-contaminated objects, Category SCO-1’.
There was a report on the position of UK NIREX, whose proposal to build an underground Rock Characterisation Facility was rejected by the UK government in 1997. The work of NIREX has been realigned to maintain its core scientific and technical programmes. A continuing aim is to develop a non-site specific generic transport safety assessment to determine the consequences of transport operations. Thus the paper from Steve Barlow of NIREX appeared to be describing a holding position until the government decides the strategy on radioactive waste disposal.