Abstract
Radiological protection issues
A summary of the recent record linkage study into cancer in the offspring of workers was presented by Dr Colin Muirhead (NRPB). The aim of the study was to test the Gardner Hypothesis. Data from the NRRW were compared with records of cancer in children, and the statistical analysis was based on sets of cases and controls, with at least one parent identified from the NRRW records as having being monitored for external radiations. The records for fathers and mothers were analysed separately. The study showed that there was evidence of a raised risk for radiation workers, but that there was no association with the dose received. The study concluded that the data did not support the Gardner Hypothesis; this was in agreement with a number of foreign studies. He summed up saying that any observed excesses in the number of cancers cannot be explained by the radiation exposure of the parents; it was more likely that there were other explanations, such as chance or some form of infective or other agent.
Professor Charles Curtis (RWMAC) gave a presentation entitled `Waste Disposal - where do we go from here?', prepared jointly with Sir Gordon Beveridge to look at the long-term plan for dealing with radioactive waste in the UK. He described the current waste disposal arrangements and the volumes of waste that are currently in storage, awaiting disposal and the anticipated future requirement. For instance, the current volume of Intermediate Level Waste in storage is approximately 70000 m3, with a further 250000 - 300000 m3 already committed for the future, mainly from decommissioning work. Professor Curtis added that when NIREX was not given permission to build the test laboratory for the deep disposal facility near Sellafield, the nuclear industry was back to square one, having spent 15 years and £450 million! He went on to describe RWMACs recommendations on the way ahead, including the requirement for Governmental commitment to the preferred long-term solution, i.e. deep disposal of intermediate level waste, and the duty on the nuclear industry to be open and clear when describing and implementing the planned policy to ensure public acceptance of the chosen national policy. The policy should be based on proven science and technology and be explained and justified to ensure acceptance of the proposals, backed up by amendment to legislation to allow a more coherent approach to the planning process.
A regulator's view on the evolution of environmental regulations was given by Mr Martin Murray (Environment Agency (EA)). The development of the EA and its role as regulator was outlined, from the Radioactive Substances Act 1960 through to future legislation that will affect the environment, such as the Basic Safety Standards Directive. Martin ran through the various guises of the EA, from the 1960s, through HMIP to its current form as an agency in 1995, including some of the changes in regulatory duties of inspectors over time, even their title in the legislation as `Authorised Persons'. He also mentioned the requirement placed upon inspectors to justify granting an authorisation under RSA93, placed upon them after Justice Potts' inquiry, weighing advantages against detriment on a case-by-case basis. He concluded that he felt that the legislation had been developed by evolution, not revolution, and was robust.
Mr David Owen (BNFL, Safety, Health and Environment Directorate) gave an overview of the evolution of regulations and standards from a nuclear industry viewpoint. He reviewed the process from ICRP60, though the Basic Safety Standard to national legislation, e.g. IRR and RSA, but also included other regulations such as REPPIR (Radiation Emergency Planning and Provision of Information Regulations). He discussed the likely effect of the new regulations and concluded that the definitions of right and wrong were not as clear as they used to be and that other viewpoints should be taken into consideration. That radiation protection was no longer the sole domain of experts, and that the impact was often felt far wider than at first, seems obvious. He added that he believed that the experts must respond to this and try to build a concensus, possibly with the guidance of SRP.
Developments in dose and cost optimisation
The first session examined the ALARP justification for use of man or machine for Vessel Entries at Torness Power Station. Mr John Creasey (Torness Power Station) detailed the different types of vessel entries undertaken at Torness and explained the factors to be considered when assessing the requirement for either manned or machine entry. Examples of the machines currently used at Torness and the advantages and disadvantages of the two types of vessel entry were listed. Manned entries have the ability to carry out repairs or modifications but obviously increase the radiation exposure to personnel working in a hazardous environment, and the whole process is very time consuming. External inspections using machine entries reduce radiation exposure and have the capability to carry out sub-dome inspections. However, the equipment required for such operations has a limited repair capability and limited coverage with high maintenance and repair costs. The last manned entry at Torness is planned for later this year, but it was emphasised that, although all future vessel entries will be carried out remotely, British Energy should still maintain the capability for manned access.
The experience gained and lessons learned during the 1997 reprocessing shutdown at Sellafield were outlined by Mr Paul Vallance (British Nuclear Fuels plc). The 34 week shutdown was planned to allow plant maintenance and improvements to be undertaken including replacement of the south dissolver cell and the evaporator plant. Both of these were major projects, requiring detailed planning and consideration of the conventional health and safety requirements as well as radiological safety. Some of the techniques employed at the site to reduce doses and minimise waste production were illustrated during the presentation. The biggest success of the operation proved to be the workforce, who were consulted at every stage, providing valuable input into problem-solving and suggesting efficient and effective methods for carrying out a task.
New applications for existing technology that have been investigated at Heysham Nuclear Power Plant were outlined by Mr Alan Marsh (Nuclear Electric plc). Significant reductions have been made in the collective doses to workers at Heysham over the past few years, from 332 manSv in 1994 to 78 manSv in 1997, but further reductions were required. This was achieved through the innovative use of monitoring instrumentation currently available. A gamma tracer originally designed as an environmental monitor was adapted for monitoring in areas where previously there had been no access. Previously unknown doserates could now be measured under the pile cap during refuelling, the variation in these doserates could be monitored and they could determine whether access was possible in fault conditions. This instrument was also used when commissioning the new oxygen injection system to establish a dose profile and to determine doserate trends over time.
An overview of the dose control problems associated with the operation of cyclotrons was given by Mr Bill Hockey (Nycomed Amersham plc). The general operation of a cyclotron was discussed, with an explanation of the potential sources of radiation exposure such as the activated target and components and radiation damaged seals, supports and electrical components. Improvements in equipment reliability and beam quality have contributed to dose reduction, together with the use of equipment manufactured from low activation materials and the holding of several equipment spares, allowing unserviceable items to decay in the cyclotron before being removed for repair. Various dose-saving techniques have been introduced such as using mock-ups to rehearse procedures and carrying out tasks, where possible, with respirator rather than airhood to reduce exposure time. Dose reduction has been achieved through a combination of management commitment, planning and improved technology.
Health physics at the Joint European Torus (JET) was discussed by Mr Alan Haigh (JET). The main sources of radiation hazard at JET during operation arise from neutron production and, following the introduction of tritium into the reactor, from bremsstrahlung radiation. A thick outer wall provides shielding, and access to the area is prohibited during operation. Entry to the reactor after operation requires consideration of both the radiation hazards and the hazard from beryllium, which was introduced in 1989 as a very fine evaporated layer on the reactor wall. Polyurethane air suits are worn for reactor entries and engineering controls are employed for any breach of the vacuum boundary that is required. For example, to remove a flange from the reactor, the area is isolated using a polyurethane membrane to provide containment at source with respiratory protection provided as a form of secondary containment. A specially developed technique is employed for the direct transfer of contaminated items out of the facility using a freight container docking system that is designed to allow items to be transferred directly from the contaminated area to the freight container without coming into contact with the outside atmosphere.
Mr Peter Higginson (Nuclear Electric plc) gave an overview of the improvements that have been made in radiological practices at Hinkley Point Power Station. A radiological practices group was set up following the site split to provide a focus for improving the practices and procedures currently employed at the site. The group had contributors from various departments and were given the remit to reduce doses, reduce contamination levels and minimise waste production. Several plans of action were identified, and through a continual process of communication with the workforce these objectives were achieved. Nuclear Electric are keen to employ successful radiological practices from other sites and have found this beneficial in making improvements in all the areas detailed.
Training and exchange of information
Dr Keith Bowker (University of Oxford) gave an introductory overview of the IRR 85, RSA 93 and Transport regulations which had the most impact on the small user, in particular the requirements of Regulation 12 of the IRRs and the importance of RPS training to support this. He identified the practical problems faced by the University of Oxford in implementing these regulations, particularly the high turnover of staff, which created problems in scheduling training, and the fact that academics were not typically pro-safety and therefore ensuring attendance for statutory training was difficult. He took the view that the provision of such detailed training for the low hazard sources used by the University did not make economic sense in cost-benefit terms and posed the question that perhaps there was over-regulation or over-inspection. He believed similar problems arose in schools and the building industry, where again there was a lack of safety-culture. He closed with a plea for clearer statutory guidance for small users and more pragmatic regulations, in particular the removal of the requirement to undertake risk assessments.
Mr Monty Guest (SETS Ltd, University of Suffolk) described how, while there had been a revolution in the provision of training, in only a few areas had any attempt been made to recognise the ability of groups to absorb training. Furthermore there was a requirement to not just teach concepts but encourage workers to absorb them, i.e. `to love' ALARA. Often missing from training programmes was any attempt to consider whether the material being taught was actually interesting to the audience. He then went on to describe the various strategies for learning and training, stressing the importance of practical training. Because of some technical problems, a survey of training undertaken by SETS was not available, nor was other data on research into interactive training.
Ms Kathleen Stevenson (AWE Aldermaston) gave an interesting presentation on the systems AWE had in place for ensuring that work was undertaken on the site by contractors. The site standards, safety management systems and training requirements for the AWE site were all well documented, thus ensuring that operators had clear guidance on what was required. For low r/a risk work, contractors often chose to work within the AWE safety system. For high r/a risk work, with the facility manager remaining responsible for safety, a more complex system was required. Prior to the start of work, procedures were agreed, competencies assessed (e.g. RPA, RPS and HP staff), and communication routes and audit procedures were set out. The RPA will be interviewed and RPSs assessed. AWE would expect contractor RPSs to fulfil the same requirements as their own, i.e. to have received formal training and to maintain a workbook closing with an interview (by the RPA and the facility manager) and an assessment. Once work has started, AWE may undertake audits of emergency response procedures, documentation, sub-contractors and training.
Instruments and monitoring
Ms Griffiths gave a lively presentation on the implications of the Basic Safety Standards with particular reference to doses arising from iodine therapy. The Royal Hallamshire Hospital had undertaken a range of surveys on the potential doses to comforters and carers of patients who had received iodine therapy (typically in the range 200-800 MBq of 131I). The BSS indicated that such persons should not receive doses in excess of 1 (or 5) mSv. In practice, restricting exposure often presented real practical problems, for example patients with infant children. Significant variations in doses were observed, due not only to the size of therapy but also to social factors such as sleeping arrangements with partners. Mean doses were estimated to be 1.3 mSv though doses could be much higher, in some cases exceeding 4 mSv.
Mr Mike Bone (Nuclear Electric) gave an overview of the dose control policy at Sizewell B, describing how 85% of the total dose received arose from just 10% of the work, reflecting the high dose characteristics of work during refuelling outages. Use of the Siemens EPD had allowed closer monitoring of a wide range of dose statistics (job, individual, project etc) and had raised the profile of previously low visibility tasks. In particular, tasks such as scaffolding construction, being less well planned than major projects, resulted in repeat visits to controlled areas and hence higher doses. EPDs had also been used to show the dose reduction benefits of planned crud bursts and enabled `traffic flow' into and out of controlled areas to be monitored. In conclusion, use of the EPD had encouraged individuals to take responsibility for their own radiation protection, an increased awareness of plant radiological conditions and a greater visibility of where dose was arising from.
Mr Peter Burgess (NRPB) set out the pros and cons of modern intelligent instruments. Starting with instruments as a whole, the advantages were interchangeable detectors, storage of data, self-checking, versatile alarms and low battery warnings. The latest LCD displays were more robust than moving coil types, provided autoranging and were not affected by viewing angle. Surface-mounted components were smaller, better and tougher than older electronics and batteries had also improved. However, new systems had shown sensitivity to RF interference (particularly silicon diodes), more options to choose from could mean more to go wrong, instruments could be appearing to do something which in fact they were not and displays had become more crowded. In summary, Mr Burgess believed that the advantages outweighed the disadvantages but purchasers needed to consider the working environment, the individuals who would be using the equipment, provision of training and whether all the facilities available were actually required.
Mr Mike Davies (AEA Technology) set out the problems with standard environmental monitoring techniques, in particular the manpower costs. Modern equipment offered the advantages of recording all data, no operator bias or transcription error, auditability and multiple sensor measurements. AEA Technology's aim was to develop an automated monitoring and mapping system that was initially a single manned unit but which could be expanded to vehicle arrays. It was essential that the system could be validated using other on-site measurements, for example using in situ high resolution detectors in conjunction with laboratory analysis. Mr Davies went on to describe a case study involving an area contaminated with radium, showing the effect of natural boundaries and topography. He considered that such systems offered improvement by orders of magnitude in surveying such sites.
Natural sources
Mr Tony Powell (DRPS) presented a summary of the MOD experience of monitoring for radon in underground facilities. The presentation described the types of facilities where the monitoring had been carried out, either general storage facilities or tailored areas within old stone quarries. The facilities usually drew their air from the old mine workings, which had significant concentrations of radon. The ventilation systems were modified to bring fresh air down from the surface to reduce the amount of radon in the air in the occupied areas. The results from the example used showed that significant reductions in the radon levels were achieved. In the example described an unusual feature was that radon-loaded air was being `pumped' up to the surface by the lifts connecting the facility to the surface. This had the effect of increasing the radon levels at the top of the lift shaft, which was where the personal radon dosemeters were being stored. This resulted in an increase in the recorded doses on the control dosemeters placed here. This was reduced and more accurate dose results obtained by moving the storage location to a remote position.
One source of natural radiation occurs on oil and gas platforms in the form of low specific activity (LSA) scale. Mr Ron Wheelton (NRPB Scotland) explained the origin of LSA scale, which is naturally occurring radioactive material that is concentrated in manifolds and separators on the platform. The presentation concentrated on some of the problems associated with LSA scale and its removal. Pipework that is internally contaminated by LSA scale can produce measurable doserates, and if not controlled it may contaminate other areas of the plant. Classified workers are employed to replace pipes containing LSA scale, but are generally unskilled or semi-skilled. Work is carried out in limited space within a hostile environment and respiratory protection must be worn because there is no airborne monitoring on the platform.
Dr Mike Howes (RHP) gave an overview of the complexity of the mine workings in South Crofty, Cornwall, in particular that 95% of the radon present leaked in from older, disused mine workings. The mine had now closed, but while operating, miners received around 15-20 mSv per year, with 0.5% of the workers receiving 5-10% of the dose. Comparison with other mine workings indicated that South Crofty already had higher ventilation rates than, for example, uranium mine workings though doses in these mines were much lower, averaging 4.2 mSv/year. Isolation of the working areas in the mine from the older, higher radon areas had not proved entirely effective and radon breakthroughs contributed significantly to overall radon doses. Instead efforts had concentrated on reducing the high volume radon `lakes' and use of filtration to reduce levels of radon daughters.
Sarah Lee, Giles Cowling, Tony Powell and Mike Gooding