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Radiological protection

T/AST/038 - Issue 2

Issue date:

10/06/2009

Review date:

10/06/2011

Open Government Status:

Fully Open

Approved By:

A N Hall

1  Purpose and scope

1.1  A demonstration of the means of achieving effective radiological protection and control is an essential part of the licensee's nuclear safety submissions to NII.  The provision of adequate protection for persons against ionising radiations is required during normal operations and also under fault and accident conditions.  Fundamental Principle FP.8 of HSE’s Safety Assessment Principles for Nuclear Facilities (SAPs) [1] states the general requirement for people to be protected against radiation risks.  This is supported by FP.5 (see T/AST/004) that provides for the limitation of risks and specifically requires that no individual should bear an unacceptable risk of harm.  FP.3 requires protection to be optimised to give the highest level of safety that is reasonably practicable.  In addition to principles aimed, through engineering, management and operational provisions, at ensuring that the radiation safety objectives in these Fundamental Principles have been met, the SAPs include a specific section on the principles of radiation protection (RP1 – RP6).  This Technical Assessment Guide (TAG) gives guidance on these principles; notably, it does not give guidance on radiological analysis and the interpretation of numerical dose targets or emergency response arrangements.

1.2  The Radiation Protection section of the SAPs, paragraphs 476 - 495, contains specific guidance on measures to achieve the objectives of the principles. This TAG does not reproduce those paragraphs, rather it summarises them and provides supplementary guidance.  It should be noted that licensees of nuclear installations are required to comply with the Ionising Radiation Regulations 1999 (IRR99), which has an associated Approved Code of Practice and guidance [2,3] which lay down the statutory requirements for the protection of persons against ionising radiation.  This TAG contains guidance to advise and inform ONR assessors in the exercise of their professional judgement in reaching regulatory decisions in relation to the assessment of licensee’s safety submissions where additional safety provisions are expected because of the level of hazard present at nuclear installations.

1.3  Other guidance which is relevant to this TAG is given in T/AST/043 (Radiological Analysis – Normal Operation) which provides guidance on Targets 1 – 3 and also guidance given in T/AST/045 (Radiological Analysis – Fault Conditions) which provides guidance on Targets 4 – 9.

2  The site licence and other relevant legislation

2.1  Site licence conditions

Of the 36 conditions attached the standard site licence, seven are of particular relevance to the SAPs covered in this guide.
These are:

1. LC 9 (Instructions to persons on the site),
2. LC 14 (Safety documentation)
3. LC 18 (Radiological protection),
4. LC 23 (Operating Rules),
5. LC 26 (Control and supervision of operations),
6. LC 28 (Examination, inspection, maintenance and testing) and
7. LC 29 (Duty to carry out tests, inspections and examinations).

2.2  Ionising Radiation Regulations 1999 and Approved Code of Practice (ACoP)

1. The Ionising Radiations Regulations 1999 [2] and the supporting ACoP and guidance [3] lay down the statutory requirements for the protection of persons against ionising radiation.  A facility must be designed operated and decommissioned in compliance with these legal provisions.  Aspects of particular relevance to the SAPs are highlighted in the following paragraphs.
2. Reg 7 – Prior risk assessment – before work is undertaken every radiation employer must carry out a risk assessment to identify the hazards and evaluate the risks to the workforce and to others.  It should be noted that regulation 3 of the Management of Health and Safety at Work Regulations 1999 (MHSWR) requires the risk assessment to be reviewed and kept up to date. 
3. Reg. 8 - Restriction of exposure – this requires every radiation employer, in relation to any work with ionising radiation that he undertakes, to take all necessary steps to restrict so far as is reasonably practicable the extent to which his employees and other persons are exposed to ionising radiation.  The means of achieving this is the primary objective of the safety submission on radiological protection and all SAPs are relevant in judging the extent to which exposures are restricted.
4. Reg. 9 - Personal protective equipment - this requires that any such equipment provided by the employer for the restriction of exposure to be suitable, adequate and properly used.  SAPs RP.1 and RP.2 and associated guidance include the need for protecting persons entering and working in contaminated areas.
5. Reg. 10 – Maintenance and examination of engineering controls etc –  this requires the radiation employer to maintain, examine and test engineering controls and safety features.  The claims on the reliability of engineering controls and safety features e.g. interlocks should be presented in the safety case and are important in assessing the adequacy of the radiological protection aspects in RP.1 and RP.2.
6. Reg. 16 - Designation of controlled and supervised areas – this requires an employer to designate an area as a controlled area or supervised area depending on certain considerations such as the need to follow special procedures or likely dose to be received.  SAP RP.3 expects, where appropriate, areas to be further divided into zones depending on levels of radiation, contamination and airborne activity in the zones.  The special procedures required depend on the radiation, contamination and airborne levels in the zone.
7. Reg. 19 - Monitoring of designated areas – this requires an employer to ensure that the levels of ionising radiation are adequately monitored for each controlled and supervised area and that working conditions in those areas are kept under review.  Paragraphs 481 and 482 of the SAPs highlight the need to have monitors available for making estimates of doses and to detect breakdowns in systems and controls.  Such arrangements provide the operator with information to control exposure on an ongoing basis to ensure that exposure to ionising radiation is restricted as required by IRR Reg. 8.

3  Relationship to SAPs, WENRA reference levels and IAEA safety standards

Relevant SAPs

3.1  The SAPs covered by this TAG are RP.1 to RP.6 and the supporting paragraphs 476 - 495.

3.2  RP.1 specifies the need to provide adequate protection against radiation and contamination in those areas of a facility to which access needs to be gained during normal operations.  RP.2 specifies a similar need for accident conditions.  Adherence to these principles is fundamental to restricting radiation exposure 

3.3  RP.3 specifies the need for designated areas and controls to restrict exposures and the spread of contamination.  The control measures should be commensurate with the radiation risk in the area. 

3.4  RP.4 specifies measures for the protection of people entering and working in contaminated areas. 

3.5  RP.5 specifies the need for provisions for the decontamination of people, articles and areas.  It expressly covers articles to be removed from contaminated locations, local and central decontamination facilities.  Decommissioning also involves decontamination; see SAPs DC.1 to DC.8 and T/AST/026 for specific requirements and guidance on design for decommissioning and safety during decommissioning.

3.6  RP.6 specifies the need for shielding to be effective under all conditions. 

WENRA reference levels

This guidance is consistent with the current WENRA reference levels [4].  In particular,  Appendix E (Issue: Design Basis Envelope for Existing Reactors) states that:

“ The design basis shall have as an objective the prevention or, if this fails, the mitigation of consequences resulting from anticipated operational occurrences and design basis accident conditions. Design provisions shall be made to ensure that potential radiation doses to the public and the site personnel do not exceed prescribed limits and are as low as reasonably achievable. ”

In this TAG, guidance is given on the design provisions to ensure that radiation doses to persons on and off the site are restricted within the limits prescribed in IRR99 and to be ALARP.

IAEA safety standards

3.8  IAEA safety standards [5,6,7,8] and supporting documents are relevant to the numerical targets 1 – 9, IRR99 and are consistent with the guidance in this TAG.  Notably, the general nuclear safety objective in IAEA’s safety requirements on the design of nuclear power plant is supported by two key objectives relating to the prescribed limits and restriction of exposure, namely:

“To ensure that in all operational states radiation exposure within the installation or due to any planned release of radioactive material from the installation is kept below prescribed limits and as low as reasonably achievable, and to ensure mitigation of the radiological consequences of any accidents“ and,

“To take all reasonably practicable measures to prevent accidents in nuclear installations and to mitigate their consequences should they occur; to ensure with a high level of confidence that, for all possible accidents taken into account in the design of the installation, including those of very low probability, any radiological consequences would be minor and below prescribed limits; and to ensure that the likelihood of accidents with serious radiological consequences is extremely low“

4  Advice to assessors

4.1  A primary element of the safety case for a facility should be a strategy for restricting radiation exposure to show how restriction has been achieved. The strategy should cover all sources of radiation arising from the plant and should incorporate all reasonably practicable measures for reducing exposures.  SAP paragraph 479 states that minimisation of sources is a key consideration in design in terms of both volume and activity throughout the lifetime of the facility, and in relation to both generation of radioactive material and build-up of such material.  For example, consideration should be given to choice of materials to minimise the formation of activated corrosion products and incorporation of techniques such as flushing, washing and decontamination to remove radioactivity from circuit components and also to the minimisation of surfaces where radioactive material can accumulate.  Remotely operated devices should also be carefully considered to reduce the need for persons to work in high dose rate areas or to handle radioactive material directly.  Paragraph 479 also outlines the considerations for the optimisation of protection, noting that collective dose as well as individual doses should be ALARP.  Optimisation should relate to all significant tasks or operations. The balance between occupational exposure and public exposure should be considered, taking account of normal operation radiation risks and accident radiation risks.  Optimisation should be pursued at all stages of design and modification.

4.2  For RP.1 and RP.2, there is a need for a thorough assessment of the radiation hazards and risks, including the magnitude and location of all actual and potential radiation sources.  The safety case should provide evidence of a systematic process of radiation hazard and risk identification.  For RP.1, the safety case should demonstrate how the protection is adequate for the radiation hazards and risks during normal operation.  For RP.2, the protection should be shown to be adequate for radiation hazards and risks that might arise during accident conditions (also see T/AST/041 on criticality safety).

4.3  The SAPs also highlight guidance from the ACoP for IRR99 regarding a hierarchy of control measures for restricting exposure of people to radiation.  It is essential for radiation sources to be controlled so far as reasonably practicable before placing controls on individuals.  Thus, priority should be given to engineered means, including passive design features and engineered safety systems, before resorting to systems of work, other administrative measures or personal protective equipment.  Engineered features generally provide for high reliability whereas administrative controls such as access and occupancy are susceptible to defeat and inappropriate behaviour.  The provision and use of personal protective equipment is the last consideration in the hierarchy; it should be provided to further restrict exposure where reasonably practicable.  Safety should be ensured for people to enter any part of a facility to which access needs to be gained during normal operation or for the purpose of accident prevention or mitigation.  Assessors should seek evidence from the safety case that a design and operation philosophy based on these points has been developed and applied.

4.4  SAPs paragraph 481, relating to RP.1 and RP.2, refers to the requirement for the measurement of radiation doses to individuals.  The safety case should include the following points:

1. Classified persons in designated areas (see 4.6 below) should be provided with and should wear dosemeters issued by an Approved Dosimetry Service (ADS) in the facility.  There should also be provision for the monitoring of internal doses where assessment indicates the possibility of inhalation or ingestion of radioactive material.
2. Where a direct reading of the dose incurred can reasonably be used to help restrict exposure, people should be issued with and should wear, for example, electronic personal dosemeters (EPDs)
3. The estimation of individual dose through the use of installed monitoring instruments and by the use of hand held instruments together with estimates or predictions of the occupancy-times of individuals.
4. In areas where there is the potential for significant intakes of airborne radioactive material, people working in the area should normally wear personal air samplers (PASs).
5. The system of work should specify the areas that can be entered and for what purpose.  It should specify the level to which the radiation dose will be controlled. The measures for ensuring that exposure is reduced so far as is reasonably practicable should also be specified. The system of work and monitoring devices should be designed to enable corrective actions to be taken if appropriate.

4.5  Paragraphs 482-484 of the SAPs give further guidance on instrumentation and alarms for airborne and direct radiation monitoring, including the need for remote indication for accident situations.  The need for criticality incident detection is also addressed. Assessors should refer to these paragraphs for guidance on points to be covered in safety cases.

4.6  RP.3 indicates the need for controls in various areas of the facility commensurate with the radiation hazards in those areas.  The area design requirements and access controls should always aim to keep exposures ALARP.  The zone category should be an indication of the required degree of engineered and managerial controls and should increase e.g. C1, C2, C3 etc and R1, R2, R3 etc for increasing levels of contamination and radiation respectively.  The safety case should make clear the zone categorisation, or area classification system, and corresponding protection arrangements.

4.7  Control of entry to the lowest category zone may be sufficient through the installation of physical barriers and warning signs whereas the controls in the highest zone may require segregation through shielding and mechanical interlocks (see paragraph 490 of SAPs for more detail).  Access to the facility control room and other low-radiation areas with high occupancy should not require access through zones that would require substantial precautions.  Higher category zones should be nested within the less highly categorised zones; for example, a higher contamination zone should be surrounded by or at least accessed by a lower contamination zone   and the ventilation arrangements should ensure airflow is from lower to higher category zones (see T/AST/022).  The design layout should facilitate the radiation protection controls and restrict radiation exposure as far as is reasonably practicable.  For example, components containing little or no radioactivity should, where feasible be located outside areas where the radiation levels are high; components used in high radiation levels should be designed to be easily removable if maintenance is required and provision should be made, where necessary, to sample radioactive liquids in such a way as to minimise exposure and spread of contamination.

4.8  Paragraph 487 of SAPs relates to facility areas where the dose rates are sufficiently high that exposure for a matter of minutes could give rise to a significant dose.  A significant dose should be taken as 1/10 of any relevant dose limit. For such areas there must be effective control of entry to prevent unauthorised access.  Controls should include effective devices such as mechanical interlocks, alarms and/or locked doors.  Permits to work should also be considered. In assessing the arrangements, assessors need to ensure that the licensee has identified and minimised the risks of defeating the controls.  Paragraph 487 also highlights the need to have an unobstructed escape route for any worker who is required to enter such an area.  If it is not reasonably practicable to provide such measures then an equivalent standard of protection should be shown to apply.  In any such case where brief entry is envisaged as part of normal operation or remedial action, the safety case should be robust and show that statutory dose limits will be complied with and the exposure will be ALARP.

4.9  RP.4 relates to measures for the protection of people entering and working in contaminated areas.  Paragraph 488 of SAPs indicates that this includes monitoring for, and control of, the spread of airborne activity and contamination within and beyond each area; and there should be appropriate monitoring and precautions against associated radiation.  The provisions for protecting persons entering and working in an area should, so far as reasonably practicable, be engineered provisions, such as:

1. The ventilation of contaminated areas and areas with airborne activity (with due precautions to protect persons from concentrations of contamination in filters).
2. The use of shielding and also distance e.g. by use of long tools.
3. Clearly marked evacuation routes.
4. The use of containment.
5. Provision and use of change rooms and washing facilities to control entry to, and egress from, contamination areas.  

The above list is not exhaustive.  Engineered provisions are preferred to the use of protective equipment (see paragraph 4.3 above).  Nevertheless, personal protective equipment (PPE) will likely be essential in those situations where full protection is not provided by engineered means.  In such cases the appropriate PPE, including respiratory protective equipment (RPE), must be worn.  In selecting PPE the nature of the exposure, the performance of the PPE, and dose constraints should be considered.  Examples of PPE include disposable coveralls, gloves, overshoes and shielded aprons.  Examples of RPE include respirators (e.g. filtering face-piece, half mask, full face, powered) and breathing equipment such as ventilated pressurised suits.   In general, explicit consideration should be given during the design of a facility to the ease of worker access and minimisation of the time required for tasks in areas with substantial radiation and/or contamination risks.  The safety case should show how these principles are realised.

4.10  For monitoring and controlling airborne activity levels, contamination levels and direct radiation within and beyond each area, the provisions should include:

1)  Monitoring

1. Baseline survey e.g. a radon survey of the facility before the introduction and use of radioactive materials, including the site surroundings where appropriate.
2. The use of appropriate, well-maintained and calibrated instruments in each area and at the exit of the area.
3. A schedule of radiation surveys.
4. Records of the monitoring results and checking for trends.

2)  Controlling

1. Review of monitoring results to establish if action is needed e.g. removal of contamination from surface.
2. Use of change-rooms and sub change rooms.  Further information is given in the Industry Code of Practice [9].
3. Use of shielded enclosures and shielded packages.
4. The use of suitable surface finishes to facilitate decontamination.
5. The avoidance of inaccessible corners or crevices where contamination can accumulate.
6. The use of 'tacky mats' to limit the spread of contamination.
7. The use of hold-down coatings.

The above lists for monitoring and controlling the spread of airborne activity are not exhaustive, and safety cases should show how these and other provisions restrict exposures so far as is reasonably practicable.

4.11 RP.5 relates to decontamination. It should be recognised at the facility design stage that decontamination of people, articles and areas may be required.  Local decontamination plant should be included unless a centralised decontamination plant serving more than one facility is shown to be more appropriate.  The design provisions should be suitable to deal with contamination arising in both normal operation and accidents, and during decommissioning.  Features as in 4.10 above may also facilitate decontamination.

4.12  SAPs paragraph 492 relates to the manipulation of items having high surface radiation dose rates, including highly contaminated items, used fuel elements, irradiated items and radioactive sources.  There should be provision so that operators do not handle any radioactive sources with bare hands.  Any safety case proposing to allow sources to be handled by the operator protected by gloves should receive specific assessment attention.  The use of manipulators through a shielded wall is a common means of reducing the radiation dose to the operator.  Other means of dose reduction include self-propelled remotely operated or robotic devices, and taking advantage of pond water for shielding of operators.  For items likely to become highly contaminated, manipulation must be carried out in enclosures that are purpose built to minimise the spread of radioactive contamination.  Shielded enclosures and manipulation systems should be designed and operated to facilitate decontamination and decommissioning at end of life.

4.13  RP.6 on shielding emphasises the importance of the effectiveness of shielding under all conditions.  SAPs paragraphs 493 - 495 indicate some of the issues to be considered when assessing the adequacy of shielding. Shielding may be an effective passive safety measure if it is correctly installed and permanently fixed.  For complex shielding designs and long required lifetimes careful consideration is required of its engineering. Where liquids are used as the shielding medium, SAPs paragraph 495 highlights the need for special attention to the possibility of leakage or loss of fluid.  Consideration should be given to the provision of shielding to protect the public as well as on-site personnel following an accident.  Where radioactive material is to be transported or moved on-site, appropriate shielding and packaging should be used. (Transport off-site is subject to separate regulation).  Further guidance is given in T/AST/022.

4.14  Radiation protection should be covered in local rules and supervision of work, training, and arrangements for emergency response.  Staff health surveillance should include radiological considerations, including provision for monitoring for intakes of radioactivity.  Contractors should be covered, either with their own arrangements in liaison with the licensee or within the licensee’s arrangements.  It is important that the employers concerned cooperate to the extent necessary to ensure that each is enabled to comply with the statutory requirements (see Reg 15 IRR99).  Individual responsibilities in the direct management line and in specialist support functions at all levels, including those of the individual workers, should be clear and understood.  For example, individuals should be made aware of their responsibilities for keeping their radiation doses ALARP by following training and procedures.

4.15  In carrying out an assessment, NII assessors need to judge the extent to which a safety submission shows that the design of the plant and the proposed operations meets the expectations in the SAPs and the requirements in the IRRs, using the guidance above and in SAPs paragraphs and IRR Guidance. 

• For the assessment of existing plant there may be differences from what is reasonably practicable in plants currently being designed and built.  This difference needs to be borne in mind by assessors, for example when considering the practicalities of the restriction of access to areas with significant radiation intensity, or in decommissioning or other once-off activities. (see T/AST/005 on ALARP).

• There will also be a different emphasis on certain SAPs when assessing safety submissions for different types of plant e.g. reactor plants and chemical plants.  Chemical plants by their nature are likely to have several areas where there are significant sources of radioactivity with the potential for leaks and the resultant spread of radioactive contamination.  SAPs RP.4, RP.5 are particularly relevant to such cases.

• There is a range of national and international guidance on radiation protection.  Notably, NII assessment should take account of the guidance issued by the IAEA (i.e. Safety Standards and Guides, [5,6,7,8]), the International Commission on Radiation Protection (ICRP) and the UK’s Radiation Protection Division of the Health Protection Agency (HPA).

5  References

1. Safety Assessment Principles for Nuclear Facilities, 2006 Edition Version 1, HSE, 2006.
2. Ionising Radiation Regulations 1999, The Stationery Office, 1999.
3. Work with Ionising Radiation, Approved Code of Practice, L121, HSE Books 2000.
4. Western European Nuclear Regulators’ Association. WENRA Reactor Safety Reference Levels. January 2007.
5. SS115: International Basics Safety Standards for Protection against Ionising Radiation and for the Safety of Radiation Sources, IAEA, 2005. (Note: this reference is being revised as document DS379 and is due to go to member states for comment in 2009).
6. NS-G-1.13: Radiation Protection Aspects of Design for Nuclear Power Plants, IAEA, 2005.
7. NS-G-2.7: Radiation Protection and Radioactive Waste Management in the Operation of Nuclear Power Plants, IAEA, 2002.
8. IAEA Safety Guides on radiation protection in the series RS-G-1.x, particularly RS-G-1.1, 1.2, 1.3, 1.4, 1.7, 1.8.
9. Changeroom Design, Operation and Maintenance – An Industry Code of Practice, 2006.

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