Is ICRP guidance on the use of reference levels consistent?

Abstract

In ICRP 103, which has replaced ICRP 60, it is stated that no fundamental changes havebeen introduced compared with ICRP 60. This is true except that the application ofreference levels in emergency and existing exposure situations seems to be appliedinconsistently, and also in the related publications ICRP 109 and ICRP 111.ICRP 103 emphasises that focus should be on the residual doses after the implementationof protection strategies in emergency and existing exposure situations. If possible, theresult of an optimised protection strategy should bring the residual dose below thereference level. Thus the reference level represents the maximum acceptable residualdose after an optimised protection strategy has been implemented. It is not an‘off-the-shelf item’ that can be set free of the prevailing situation. It should bedetermined as part of the process of optimising the protection strategy. If not,protection would be sub-optimised. However, in ICRP 103 some inconsistentconcepts have been introduced, e.g. in paragraph 279 which states: ‘All exposuresabove or below the reference level should be subject to optimisation of protection,and particular attention should be given to exposures above the reference level’.If, in fact, all exposures above and below reference levels are subject to the process ofoptimisation, reference levels appear superfluous. It could be considered that ifoptimisation of protection below a fixed reference level is necessary, then the reference levelhas been set too high at the outset.Up until the last phase of the preparation of ICRP 103 the concept of a dose constraint wasrecommended to constrain the optimisation of protection in all types of exposuresituations. In the final phase, the term ‘dose constraint’ was changed to ‘reference level’ foremergency and existing exposure situations. However, it seems as if in ICRP 103 it was notfully recognised that dose constraints and reference levels are conceptually different.The use of reference levels in radiological protection is reviewed. It is concluded thatthe recommendations in ICRP 103 and related ICRP publications seem to beinconsistent regarding the use of reference levels in existing and emergency exposuresituations.