10.1. This section deals with design for the protection of site personnel from radiation that arises from accident conditions. In the design process, a proper assessment should be made of the magnitudes and locations and the possible transport mechanisms and exposure pathways for the radiation sources that will be present in and after accident conditions. All potential accident scenarios including severe accidents should be considered in this assessment (see Annex III).
10.2. The design should be such that the operator can ensure the safety of all persons on the site in the event of an accident or radiological emergency, in compliance with international requirements for emergency preparedness [20].
10.3. An analysis should be made of the areas of the nuclear power plant in which it is necessary to maintain habitability for the purpose of taking both accident management measures and emergency preparedness measures. Areas to which access is expected to be required in emergencies include the control
room, rooms where emergency systems are located (or spaces adjacent to such rooms), on-site sampling facilities (for the containment, the stack, etc.), the emergency control centre, the laboratories and the technical support rooms.
For this purpose, plant operating instructions for actions for accident management, maintenance and emergency preparedness should be developed.
Design modifications should be based on the findings of the habitability assess-ments, as discussed in Refs [21–23].
10.4. The anticipated hazardous conditions in which emergency workers may be required to perform response functions on or off the site should be identified. Arrangements should be made for taking all practicable measures to provide protection for emergency workers for the range of anticipated hazardous conditions in which they may have to perform response functions on or off the site. These arrangements should include: arrangements to assess continually and to record the doses received by emergency workers;
procedures to ensure that doses received and contamination are controlled in accordance with established guidance and in compliance with international standards [20]; and arrangements for the provision of appropriate specialized protective equipment, procedures and training for emergency response in the anticipated hazardous conditions.
10.5. Provisions should be made for shielding the radiation sources, in addition to those provisions required during operation, to ensure that personnel can have access to and can occupy the plant control room or the supplementary control points (e.g. the location of the remote shutdown panel) so as to operate and maintain essential equipment14 without exceeding established dose limits as specified in paras V.27–V.32 of the BSS [2] and paras 4.57–4.65 of Ref. [20].15 This includes access to equipment in cases where maintenance or repair may be necessary after an accident. In general, provision should be made to render direct intervention by operators superfluous by installing automatic or remote controlled equipment (e.g. remote controlled valves).
14 Essential equipment here means equipment that must continue to be operable to prevent the escalation of an accident or further radioactive releases (e.g. pumps in water cooled reactors or gas circulators in GCRs, which are required to maintain core cooling), and equipment that is required for monitoring the state of the plant after an accident.
15 In the event of an emergency, radiation dose limits for normal operation may be exceeded. Use should then be made of dose levels given in para. 6.13 of Ref. [7] and other conditions as established in Section 6 of Ref. [7] for interventions in emergencies.
10.6. Consideration should be given in anticipation to movements of the source material (e.g. the transfer of the core to the base of the reactor building), a decrease in the effectiveness of the shielding (e.g. due to concrete erosion), losses of shielding efficiency and scattered radiation including sky shine radiation, all of which may have a major impact on radiation levels after an accident.
10.7. Provision should also be made to minimize the airborne radioactive contamination in areas to which access will be required for ensuring the safety of the plant or the site personnel, such as the reactor building, the fuel storage area, the plant control room and supplementary control points. Such provision may be achieved by closing off the air intake and the exhaust. In this case heat removal would have to be provided by cooling the air in a recirculation system.
An appropriate fraction of the circulation air should be filtered if the inward leakage of contaminated air may be expected to be too high to permit occupancy of the room without the use of respiratory protection. The spread of airborne contamination throughout the plant can be limited by means of secondary containment or by ducting to the atmosphere, through filters if necessary. Requirements for control room habitability in particular should be addressed, in terms of the oxygen supply and habitability under conditions of releases of gaseous chemicals.
10.8. Consideration should be given to the requirements and the means for sampling of gases and liquids after an accident (e.g. remote sampling), and provisions for shielding should be made as necessary to enable such samples to be taken and tested without undue radiation exposures of site personnel.
10.9. Provision should be made for alerting and assembling site personnel and for — at least provisionally — sheltering site personnel not involved in accident control or firefighting. Communication should be possible between the control room, supplementary control points and assembly points for personnel.
10.10. The ready identification of rooms, clearly marked signs and the removal of any obstacles to the free movement of site personnel in passageways should be ensured for the protection of personnel, mainly by decreasing the duration of exposures during safety related actions under accident conditions. These factors should be taken into consideration and dealt with appropriately at the design stage.
10.11. In addition, areas should be identified within the plant in which radiation exposures are expected to remain low in accidents. These areas may be used in evacuating site personnel and monitoring them for contamination [23]. Recording devices for individual monitoring should also be stored here.