The decommissioning of a radiotracer laboratory, where a wide range of radionuclides with half-lives ranging from minutes to thousands of years in the form of unsealed source is used, can be undertaken by the laboratory workers, after a proper training. Often the laboratory manager has no previous decommissioning experience and a decommissioning strategy and cost projection with allocated resources is not considered up to the decision to decommission the laboratory is made. An immediate priority is to understand the new intended use of the site (unrestricted use or reuse involving radioactive materials, …). Characterization of a radiotracer laboratory is much easier when comprehensive records for the lifetime of the facility and plant workforce still exist, and often the existing laboratory assay and monitoring equipment are enough for sample

measurement and area monitoring. The decommissioning plan is typically a relatively short document, tailored specifically to the simplicity of the project, and should make reference to standardized laboratory procedures and safety rules, adapted to decommissioning activities. Furthermore, a comprehensive risk assessment is required and emergency arrangements should be identified. Some of the lessons learned from decommissioning of radiotracer laboratories are:

  • Late discovery of contamination in fridges and freezers immediately before their disposal as refuse: this could be due to an incorrect assumption during characterization that isotopes had always been stored in packages and there would be no migration of radioactivity. Stored isotopes such as tritium can be highly mobile and migrate during storage.
  • Recovery of equipment previously disposed of, such as liquid scintillation counters, because the in-built sealed source standard was not removed before the equipment was disposed of as refuse.
  • Contamination has been spread outside the laboratory owing to poor working practices. This occurred because the characterization survey was inadequate to establish the true boundary of the area requiring decommissioning or the staff was not adequately trained.
  • During refurbishment of an administrative office, contamination was found on the walls and was traced back to historical usage of an adjacent area as a tritium and carbon-14 (highly mobile) radiotracer laboratory.
  • The use of complex chemicals to remove contamination resulted in the production of a secondary waste that did not meet the waste acceptance criteria of the intended disposal route.

The decommissioning of nuclear multi-facility site could imply further complexities. The site may consist of a single multi-storey building with adjacent outbuildings or may extend over a large area of land with numerous buildings. They are likely to be contaminated with a wide range of radioactive materials, which may have a variety of chemical forms that can influence their solubility and ability to become airborne. Often the remediation of soil contamination is required. In this case, it is often more practical to adopt a strategy of dividing the overall task into a number of smaller decommissioning projects, each to be staged as a distinct phase of the overall decommissioning plan. At complex facilities, radioisotopes may be handled, typically using fume hoods, hot cells or glove boxes. The spread of airborne contamination in the ventilation ducts associated with hot cells and glove boxes is also a potential challenge during decommissioning. Often decommissioning of hot cells requires employment of an experienced decommissioning project consultant and his team of workers although the existing workforce may contribute to laboratory measurements, collation of records, contributing to the characterisation and further management of wastes for disposal. Fume hoods, glove boxes and hot cells have connections to an active ventilation system and may also have a connection to an active drainage system. It is essential when planning for decommissioning that these aspects are fully investigated and characterized. When decommissioning one or more of a series of

laboratories within a building, it is essential at an early stage to check the inter-relationship of services which may be common with other laboratories that are to remain in operation. For decommissioning purposes, it is important to record not only the type of contamination (beta, gamma and/or alpha) but also whether the facility was used for mechanical, e.g. cutting, or chemical activities. If chemical activities are carried out inside a hot cell or a glove box, the residual material and equipment may be more difficult to decontaminate, especially if a build-up of radioactive substances occurs over many years of operation. For example, when cutting of a glove box into manageable sizes is required before decontamination, the presence of chemicals might add to the possibility of fire or explosion or release of toxic fumes, so a comprehensive risk assessment is essential.
Lessons learned when decommissioning complex facilities include:

  • Changes in area designation or access routes must be timely communicated to all those who might be affected, especially to avoid inadvertent entry into a controlled area or the risk of spread of contamination.
  • As part of emergency arrangements, when only one or more laboratories within a larger facility are subjected to decommissioning, precise information on any changes in evacuation routes must be carefully communicated to all those who require entry to the building during the period that the new arrangements are in force.
  • Where common ventilation must remain in operation in the laboratories not subject to decommissioning, shutting off the ventilation system to facilitate decommissioning in other areas should be carefully planned to avoid accidental inhalation by workers whose system has been inadvertently interrupted.
  • Where common waste discharge pipes must remain in use at the time of decommissioning, the integrity of the pipes should be surveyed and financial provision made for future decommissioning of old clay pipes found to be leaking with resultant ground contamination.
  • Where ventilation discharge points are at roof level, this area should be fully characterised to assess any contamination from the ventilation exhaust point so that it can be properly dealt with.
  • Where piped gases are available throughout a building where one or more laboratories are to be decommissioned, and dismantling requires use of cutting equipment, the actual location of the gas pipes should be thoroughly surveyed rather than relying on engineering drawings. Gas lines not recorded in the original drawings could lead to a serious explosion once cutting is underway.
  • A ventilation system may contain asbestos products, so this should be assessed at the characterisation stage and, if so, specialist contractors are required to cut the ventilation system.
  • Failure to check the integrity of the drainage system before commencing decontamination of pipes can result in release of fixed contamination.