|The document was considered by the UK Shielding Forum (TSF) with the aim of giving the UK shielding practitioners a view on its scope and clarity. TSF consists of a number of organisations involved in the design of radiation shielding (e.g. British Nuclear Group, British Energy, NNC, Serco, Rolls Royce, Bae Systems, Nuclear Technologies, Health and Safety Executive). As a consequence its members have an intimate knowledge of the range of issues which must be considered during the optimisation of engineered radiation protection at design.
TSF welcomed the document as clarifying many issues and was generally very supportive of the principals it described.
Shielding Forum Perspective
The major comment arising from TSF is with regard to the scope of the document. The document does not appear to explicitly address the role of radiological protection in the design of facilities. It is our experience that optimisation must start at the conceptual stage of a facility and that making appropriate decisions at this stage can often have the greatest effect on the overall radiological protection performance. Of particular concern was the limited discussion in the foundation document of a hierarchy of protection measures, which if appropriately applied during design can minimise the need for supplementary operational radiological protection. Even if elimination cannot be achieved then reduction (e.g. minimisation by design ) should be pursued in preference to operational control. Without following a structured hierarchy it is unlikely that a final design will be properly optimised.
Other design concerns are listed below:
• There was no discussion of the need to take a long-term view with regard to 'cradle to grave considerations' i.e. that the optimisation during design must consider all phases of operation of a facility, including its decommissioning.
• There was no discussion of the decision processes surrounding the building of new facilities e.g. all the competing factors that effect its location, timing, and design philosophy.
• There was no discussion of the treatment of uncertainty in the optimisation process. This is of particular importance in design as, very often, important design decisions need to take account of significant uncertainty.
• The role of stakeholder involvement: it is very important to involve the relevant stakeholders early in the design process. Decisions made in the early stages are often the most significant and must be properly informed. During the various stages of design, the relevant stakeholders may change as different issues are considered.
• It was thought that the examples in the annexes did not really fulfil the promise in the abstract. It would have been very useful to illustrate the design aspects by detailed case studies.
More General Comments
The sub-group also thought that the broadening of the risk optimisation process should be taken further than is being suggested. It was thought that it is important to stress that radiation risks cannot be optimised separately to more conventional ones. For example the construction of a shield wall to reduce operator exposures may incur large conventional risks, e.g. associated with structural integrity or working at height, and this needs to be considered in the overall risk optimisation process. Similarly it was viewed that the trade off between 'normal' exposures and accident / potential ones was not stressed sufficiently.
The sub-group was fully supportive of the move towards optimisation of individual protection and the subsequent reduced usefulness of collective dose as an optimisation agent. However the sub-group felt that in certain well-defined operational situations collective dose (or group dose) is still a very useful optimisation tool. In particular, it was viewed that in some situations collective considerations are equally as important as individual ones and so optimisation should also be the subject of a collective dose constraint. It is not being suggested that ICRP should provide such constraints, as these would be dependent on group size for example, but that their definition (based on previous experience of similar operations) and use should be encouraged. Low collective occupational exposure indicates strong management attention to radiological protection. As an example, the occupational collective radiation exposure is one of the WANO key performance indicators. Such constraints would discourage 'dose sharing' as a means of achieving individual exposure requirements.
The role of agreed good practice in optimisation was not mentioned in the document. The sub-group's view is that the optimisation process can be made much more efficient if it starts from a position of agreed good practice. In this way optimisation is a learning process, building on what has been optimised in the past.
Although it was mentioned that the optimisation process may result in doses close to or well below the dose constraints, it was thought useful to discuss how the proximity to the constraints effect the degree of effort that should be employed to seek out improvements. For example it is expected that more effort should be expended in seeking improvements when exposures are close to the constraints. This concept is effectively already adopted in the UK by the use of Basic Safety Limits (BSLs) and Basic Safety Objectives (BSOs) by the nuclear safety regulator.