Development of modern safe systems of work at the Imperial College Reactor Centre and their application to neutron detector testing and nuclear training courses

Full text: The 'CONSORT'-design reactor is owned by, and licensed to, Imperial College of Science, Technology and Medicine, and has been in continuous safe operation since 1965. Today, it is the only civil research reactor left in the UK. CONSORT is designated a 'low power research reactor' and is rated at 100 kW. This paper concentrates on the issues that have been addressed in ensuring that worker doses are maintained As Low As Reasonably Practicable or ALARP, and describes how robust systems have been implemented to ensure that all assessments are in line with this principle. Two case studies are described in detail showing the experience gained in the past few years at the Reactor Centre; these will provide useful information that managers of similar facilities may wish to consider in formulating their own arrangements. Imperial College operates the smallest of the UK nuclear licensed sites. Although the operation of the reactor is different to, and involves risks of much lower magnitude than, nuclear power plants and fuel cycle facilities, our activities are governed by the same 36 standard licence conditions of the Nuclear Installations Act 1965. In addition the site requires assessment of 'reasonably foreseeable' emergencies under the REPPIR (Radiation Emergency Preparedness and Public Information) regulations [1] and control of work with ionising radiation under IRR (Ionising Radiation Regulations) [2] and RSA (Radioactive Substances Act) [3]. These regulations and nuclear site licence conditions lead to more clearly defined sets of procedures and assessments of competency, than may be required in other parts of the college or other similar academic institutions. This paper will discuss the way these regulations are addressed through the two case studies. The approach adopted at the Reactor Centre to producing Safe Systems of Work is based initially on risk assessment of the planned task, taking into account both radiological, nuclear and conventional safety hazards. For straight forward not especially hazardous tasks the risk assessment is sufficient to control the operation and provides all the information and instructions for the work to be carried out safely. Operations with a radiological risk, particularly those involving non classified workers in controlled areas have additional written controls in the form of a Written System of Work which goes into details of radiological hazards and safeguards and may involve hold points. The most hazardous tasks (both radiological and conventional) are controlled through the use of Permits to Work. In all cases, operations which involve the use of contractors, require careful assessment of the Contracting Organisation and their plans for the work (method statements etc.) to ensure that the contractors are suitably trained and experienced to do the work. These procedures have allowed the development of the facility requiring man access into a Controlled Area with an open beam tube where doses are maintained ALARP. The CONSORT reactor provides a facility for the calibration and periodic testing of neutron flux detectors (primarily fission chambers and ion chambers). The first case study outlines the detector testing programme which requires the use of a broad range of well thermalised neutron fluxes over eleven orders of magnitude. The facility in which these tests are carried out consists of a beam tube penetrating the graphite thermal column located immediately outside of the tank housing the reactor core. During testing, the detectors are manually loaded into and unloaded from the beam tube with the reactor operating at low power (up to 2kW). This process has been developed, assessed and controlled using the procedures described, in order to ensure that the doses are minimised and acceptable in line with the ALARP principle. On line testing of the detectors is carried out by the manufacturer's employees on site, and involves the control and supervision of these workers working within Controlled Areas. The second case study that will be developed in this paper relates to the use of this integrated approach to safety management in the teaching environment. One of the practical activities that has historically generated enthusiasm amongst students and visitors to the CONSORT facility is the experience of viewing the Cerenkov radiation emitted from the critical core. This particular activity had been discontinued for some years on ALARP grounds, however, there had been no formal risk assessment carried out to indicate that the dose uptake was unacceptably high. As a result of a complete and quantitative reassessment of the operation it has been successfully proven that the direct viewing experiment can be carried out successfully in line with the ALARP principle and that the conventional hazards that may be encountered in the reactor top area actually outweigh the limited dose uptake received. (author)