Stephen Fennell, Radiological Protection Institute of Ireland, Chaiperson, ERPAN

Introduction

The concept of a dose constraint was established by ICRP in Publication 60 [1] and included in the 1996 European Basic Safety Standards Directive [2] (1996 BSS) which defined it as “a restriction on the prospective doses to individuals which may result from a defined source, for use at the planning stage in radiation protection whenever optimization is involved”. The Directive also stated that “it should be used, where appropriate, within the context of optimization of radiological protection”. As all member states of the European Union were required to implement this Directive in national legislation, the use of dose constraints should now be well established throughout Europe.

In 2010 the European Radiation Protection Authorities Network (ERPAN) undertook a survey to review how the concept of dose constraints had been implemented across Europe. In particular, the survey focused on its use in the context of the optimisation of occupational exposure in the non-nuclear sector. A total of 13 countries participated in the survey, eleven of which are member states of the European Union. The complete results of this survey have been included in the report “Dose constraints - Dose constraints in optimisation of Occupational Radiation Protection and implementation of the Dose constraint concept into Radiation Protection regulations and its use in operators' practices” published by the Nuclear Energy Agency (NEA) in September 2011 [3]. An overview of some of the results of the survey will be present in this article.

Survey results

Of the thirteen countries that responded to the questionnaire, nine stated that there is an explicit reference to the term “dose constraint” in their national legislation, with another two reporting that the reference to this concept in their regulations is implicit (table 1). When asked whether dose constraints are routinely used as an optimisation tool for occupational exposure in non-nuclear applications only eight of the 13 countries stated that it was.

Table 1. Summary of the application of dose constraints across Europe.

Setting dose constraints

While the 1996 BSS did not suggest who is responsible for setting numerical values for occupational dose constraints, it is interesting to note that in the non-nuclear sector there are different approaches as to whether the regulator or facility/employer sets them, or whether it is a joint decision making process. For the majority of countries that use dose constraints, the Regulatory Authority has a role in setting their value, albeit at different levels (Table 2). In the current draft new European BSS, it is proposed that the dose constraint used for occupational exposure will be set by the undertaking under the general supervision of the competent authorities [2].

Table 2. Responsibility for setting numerical values for occupational dose constraints

The use of dose constraints

Dose constraints by definition should be used at the planning stage in radiation protection. They can be used at the design and planning stage of a new facility where the size and nature of the specific sources are taken into account. In these cases these are sometimes referred to as source-related or design dose constraints and are used to determine levels of shielding material required in order that calculated doses to workers should not exceed the annual dose constraint value. They can also be used when planning a specific task, rather than a facility, to take account of the actual working procedures that will be used - in such instances they are often referred to as task-related or operational dose constraints. Table 3 summaries the typical uses of dose constraints for the countries surveyed.

Table 3. The use of dose constraints in occupational exposure

A potential difference between the intention of the 1996 BSS and how dose constraints are used in practice was noted in the survey by the fact that some regulatory authorities use dose constraints, or similar concepts, as a tool that enables retrospective evaluation of working practices when workers receive doses greater the expected values. While this can often result in beneficial changes to working practices, which is to be encouraged, the use of the term dose constraint for this purpose may be seen to be inconsistent with the intention of the 1996 BSS which explicitly stated that they should be used for prospective (rather than retrospective purposes). 

Further information on results of this survey, and the use of occupational dose constraints in the nuclear sector in other regions, is available in the NEA report [3].

Summary

The results of the ERPAN survey show that the majority of European countries have adopted the concept of dose constraints or similar instruments as an optimisation tool for occupational exposure in the non-nuclear energy sector in their national legislation. In analysing the results of the survey, it can be seen that there is an inconsistency in the use of terminology – while the majority countries use the term dose constraint, others use source related dose values, dose objective or other terms. Similarly, there can be observed inconsistencies in approaches as to how they are applied.

The revision of the 1996 BSS presents an opportunity to harmonise the application of dose constraints across Europe. To assist with this task, the European Commission’s Article 31 Group of Experts has recently established a Working Party on Dose Constraints in order to clarify the concept of the dose constraint and to clarify its applications in different areas in order to achieve this harmonisation. The working party intends to produce guidelines on the use of dose constraints covering occupational, public and medical exposure, in the context of the nuclear industry, non-nuclear industries, medical installations, NORM industries and other natural radiation sources.

References

[1]   1990 Recommendations of the International Commission on Radiological Protection.  ICRP Publication 60. Ann ICRP 21 (1-3).

[2]   Proposal for a Council Directive laying down basic safety standards for protection against the dangers arising from exposure to ionising radiation.

http://ec.europa.eu/energy/nuclear/radiation_protection/doc/com_2011_0593.pdf, accessed on 16th February 2012.

[3]   Nuclear Energy Agency (NEA) (2011), “Dose constraints - Dose constraints in optimisation of Occupational Radiation Protection and implementation of the Dose constraint concept into Radiation Protection regulations and its use in operators' practices”, NEA/CRPPH/R(2011)1, OECD, Paris 2011.

www.oecd.org/officialdocuments/publicdisplaydocumentpdf/?cote=NEA/CRPPH/R(2011)1&docLanguage=En, accessed on 16^th February 2012.