Safety re-evaluation of research reactors. A new trend in license requirements

Full text: Introduction: NRG acquired more than 40 years of experience in the nuclear field. Amongst others this includes experience in the operation of a wide range of nuclear facilities, viz: Operation of the 45 MW High Flux Reactor of the European Commission for materials testing, (medical) isotope production and BNCT; Operation of a 30 kW Argonaut Low Flux Reactor for training and biological applications; Operation of Hot Cells for materials testing and isotope separation; Overall responsibility of a Molybdenum Production Facility; and Operation of a Decontamination and Waste Treatment facility for both internal and external services. Up to the mid 90's operations of most research reactors were covered by an open ended license without any requirements for a periodic safety review. The licensing policy for nuclear installations however has been changed over the last 10-15 years in the most western countries. In the majority of new nuclear act licenses has a requirement for a periodic safety review. In the framework of relicensing process for the LFR in 2000 and in the framework of the running relicensing process of the HFR a safety re-evaluation for both reactors has been performed on request of the Dutch Nuclear Regulatory Body. Stages of a safety re-evaluation. A safety re-evaluation should consists of an evaluation of the Technical, Organisational, Personnel, and Administrative (TOPA) provisions with respect to the nuclear safety and the health physics aspects of the operation and utilisation of the facility and consists normally of 4 stages. Stage 1: Compliance check. Although all licensing conditions shall be fulfilled at all times a systematic check on the fulfilment of the present licensing conditions is not always performed. At the other hand very often the present licensing basis is not always clear and sometimes hidden in the documentation. Besides the formal license also the Safety Analyses Report and safety analyses performed; Operational Limits and Conditions and additional requirements i.e. additional agreements with competent authorities, approvals for modifications belongs to the operational licensing basis and compliance should be proved. Stage 2: Reference licensing basis. The reference licensing basis shall present the safety requirements for all TOPA aspects of the safe operation and utilisation of a modern research reactor. Conform to IAEA's guidelines IAEA's Safety Series SS 35 should serve as main reference documents for the overall safety re-evaluation for research reactors up to several 10 MW For reactors with a higher power level additional guidelines could be found in IAEA's Safety Series SS 50. In addition to the references for nuclear safety (inter) national legislation and regulations should be considered i.e. environmental protection; occupational hazard and labour protection; radiation protection and conventional safety requirements. Stage 3: Comparison with the reference licensing basis. During this stage all safety related TOPA aspects of the installation, operation and utilisation should be compared with the reference basis. As a part of this stage also safety related operational experiences and the evaluation of ageing management of the facility should be evaluated during this stage. Especially attention should be paid to the maintenance and periodic inspection programme which should be able to detect and to mitigate ageing in an early stage. This stage should result in an overview of the shortcomings and weaknesses with proposed improvement measures. Stage 4: Improvement plan. The shortcomings and weaknesses being identified during the evaluation should be translated into proposals for the implementation of safety improvement measures. The identified shortcomings and weaknesses should be ranked. This ranking mechanism should be based on the gain in safety level, estimated implementation costs and estimated dose consequences (ALARA). The priority ranking has to be agreed with the regulatory body. Safety re-evaluation of the HFR In the framework of the relicensing process of the HFR also a safety re-evaluation, based on a detailed working plan which has been agreed with the regulatory body, has been carried out. The indicated TOPA improvement measures have been presented to the regulatory body. Since also an application for a new license is in progress, all safety analyses are being updated conform to state of the art regulations too. These new analyses could also result in a number of technical improvement measures. The proposed improvement measures of the safety re-evaluation will be combined with the improvement measures resulting from the safety analyses. Based on the improvement proposals a detailed implementation plan will be drawn up in the near future. (author)