«Safety of Conversion Facilities and Uranium Enrichment Facilities Specific Safety Guide No. SSG-5 IAEA SAFETY RELATED PUBLICATIONS IAEA SAFETY ...»
7.7. Consideration should be given to ensuring that uranium is present only in areas designed for the storage or handling of uranium. Programmes should be put in place for routine monitoring for surface contamination and airborne radioactive material, and more generally for ensuring an adequate level of housekeeping.
7.8. Operating procedures to control process operations directly should be developed. The procedures should include directions for attaining a safe state of the facility for all anticipated operational occurrences and accident conditions.
Procedures of this type should include the actions required to ensure criticality safety, fire protection, emergency planning and environmental protection.
7.9. The operating procedures for the ventilation system should be specified for fire conditions, and periodic testing of the ventilation system should be carried out and fire drills should be performed.
MAINTENANCE, CALIBRATION AND PERIODIC TESTING AND
7.10. When carrying out maintenance in a conversion facility or an enrichment facility, particular consideration should be given to the potential for surface contamination or airborne radioactive material, and to specific chemical hazards such as hazards due to hydrogen fluoride, fluorine, hydrogen and nitric acid.
7.11. Maintenance should follow good practices with particular considerationgiven to:
— Work control, e.g. handover and handing back of documents, means of communication and visits to job sites, changes to the planned scope of work, suspension of work and ensuring safe access.
— Equipment isolation, e.g. disconnection of electrical cabling and heat and pressure piping and venting and purging of equipment.
— Testing and monitoring, e.g. checks before commencing work, monitoring during maintenance and checks for recommissioning.
— Safety precautions for work, e.g. specification of safety precautions, ensuring the availability of personal protective equipment and ensuring its use and emergency procedures.
— Reinstallation of equipment, e.g. reassembly, reconnection of pipes and cables, testing, cleaning the job site and monitoring after recommissioning.
7.12. Attention should also be paid to the handling of radioactive sources and X ray equipment used in a conversion facility or an enrichment facility for specific purposes, e.g. those used for the inspection of welds.
7.13. Additional precautions may also be necessary for the prevention of a criticality accident (see paras 7.20–7.23).
7.14. Compliance of the operational performance of the ventilation system with the fire protection requirements (see para 4.45) should be verified on a regular basis.
7.15. A programme of periodic inspections of the facility should be established, whose purpose is to verify that the facility is operating in accordance with the operational limits and conditions. Suitably qualified and experienced persons should carry out inspections.
Inspection of cylinders in storage
7.16. Paragraph III.22 of Appendix III of Ref.  establishes the requirements relating to the inspection of cylinders in storage. Information on maintenance and periodic testing of UF6 cylinders is provided in Sections 4 and 5 of Ref. .
CONTROL OF MODIFICATIONS
7.17. A standard process for any modification should be applied in a conversion facility or an enrichment facility. This process should use a modification control form or an equivalent management tool. The modification control form should contain a description of the modification and why it is being made. The main purpose of the modification control form is to ensure that a safety assessment is conducted for the modification. The modification control form should be used to identify all the aspects of safety that may be affected by the modification, and to demonstrate that adequate and sufficient safety provisions are in place to control the potential hazards.
7.18. Modification control forms should be scrutinized by and be subject to approval by qualified and experienced persons to verify that the arguments used to demonstrate safety are suitably robust. This should be considered particularly important if the modification could have an effect on criticality safety. The depth of the safety arguments and the degree of scrutiny to which they are subjected should be commensurate with the safety significance of the modification.
7.19. The modification control form should also specify which documentation will need to be updated as a result of the modification. Procedures for the control of documentation should be put in place to ensure that documents are changed within a reasonable time period following the modification.
7.20. The modification control form should specify the functional checks that are required before the modified system may be declared fully operational again.
7.21. The modifications made to a facility should be reviewed on a regular basis to ensure that the combined effects of a number of modifications with minor safety significance do not have hitherto unforeseen effects on the overall safety of the facility.
7.22. In a conversion facility or an enrichment facility, the main radiological hazard for both the workforce and members of the public is from the inhalation of airborne material containing uranium compounds. In conversion facilities, insoluble compounds of uranium such as the uranium oxides UO2 and U3O8 pose a particular hazard because of their long biological half-lives (and therefore effective half-lives)2. Thus, close attention should be paid to the confinement of uranium powders and the control of contamination in the workplace. In enrichment facilities most uranium compounds have a short biological half-life.
The chemical hazards for the uranium compounds found in enrichment facilities dominate the radiological hazards.
7.23. In conversion facilities and enrichment facilities, in normal operation, the main characteristic that needs to be taken into account in the development of measures for radiation protection is that the external and internal dose rates are relatively low. It is required to put in place emergency arrangements for criticality incidents, which are the only events in which a high external dose rate would be encountered.
7.24. Interventions for maintenance and/or modifications are major activities that require justification and optimization of protective actions, as specified in
Ref. . The procedures for intervention should include:
— Estimation of the external exposure prior to an intervention in areas such as those for the processing and handling of ashes containing thorium gamma emitters arising from the fluorine reactor in conversion facilities;
— Preparatory activities to minimize the doses due to occupational exposure,
• Identifying specifically the risks associated with the intervention;
• Specifying in the work permit the procedures for the intervention (such as for the individual and collective means of protection, e.g. use of masks, clothing and gloves, and time limitation);
The biological half-life is the time taken for the amount of a material in a specified tissue, organ or region of the body to halve as a result of biological processes. The effective half-life is the time taken for the activity of a radionuclide in a specified place to halve as a result of all relevant processes.
— Measurement of the occupational exposure during the intervention;
— Implementation of feedback of information for identifying possible improvements.
7.25. The risks of exposure of members of the public should be controlled by ensuring that, as far as reasonably practicable, radioactive material is removed from ventilation exhaust gases to prevent its being discharged to the atmosphere.
“The monitoring results from the radiation protection programme shall be compared with the operational limits and conditions and corrective actions shall be taken if necessary” (para. 9.43 of Ref. ). Furthermore, these monitoring results should be used to verify the dose calculations made in the initial environmental impact assessment.
Control of internal exposure
7.26. Internal exposure should be controlled by the following means:
(a) Performance targets should be set for all parameters relating to internal exposure, e.g. levels of contamination.
(b) Enclosures and ventilation systems should be routinely inspected, tested and maintained to ensure that they continue to fulfil their design requirements. Regular flow checks should be carried out at ventilation hoods and entrances to containment areas. Pressure drops across air filter banks should be checked and recorded regularly.
(c) A high standard of housekeeping should be maintained at the facility.
Cleaning techniques should be used that do not give rise to airborne radioactive material, e.g. the use of vacuum cleaners with HEPA filters.
(d) Regular contamination surveys of areas of the facility and equipment should be carried out to confirm the adequacy of cleaning programmes.
(e) Contamination zones should be delineated and clearly indicated.
(f) Continuous air monitoring should be carried out to alert facility operators if levels of airborne radioactive material exceed predetermined action levels.
(g) Mobile air samplers should be used at possible sources of contamination as necessary.
(h) An investigation should be carried out promptly in response to readings of high levels of airborne radioactive material.
(i) Personnel and equipment should be checked for contamination and should undergo decontamination if necessary, prior to their leaving contamination zones. Entry to and exit from the work area should be controlled to prevent the spread of contamination. In particular, changing rooms and decontamination facilities should be provided.
(j) Temporary means of ventilation and means of confinement should be used when intrusive work increases the risk of causing contamination by airborne radioactive material (e.g. activities for vessel connection and/or disconnection, periodic testing, inspection and maintenance).
(k) Personal protective equipment should be made available for dealing with releases of chemicals (e.g. acid gas) or radioactive material from the normal means of confinement in specific operational circumstances (e.g. during disassembly or the cleaning of process equipment).
(l) Personal protective equipment should be maintained in good condition, cleaned as necessary, and should be inspected.
(m) Any staff having wounds should protect them with an impervious covering for work in contamination zones.
7.27. In vivo monitoring and biological sampling should be made available as necessary for monitoring doses due to occupational exposure. Since most of the uranium present in conversion facilities and enrichment facilities is in soluble form, the frequency of sample collection and the sensitivity of analytical laboratory equipment should be appropriate to detect and estimate any uptake of uranium for routine or emergency purposes.
7.28. The extent of the monitoring should be commensurate with the levels of airborne radioactive material and the contamination levels of workplaces.
7.29. The method for assessing doses due to internal exposure may be based upon the collection of data from air sampling in the workplace, in combination with worker occupancy data. This method should be assessed, and should be reviewed as appropriate by the regulatory body.
7.30. On the completion of maintenance work, the area concerned should be decontaminated if necessary, and air sampling and smear checks should be carried out to confirm that the area can be returned to normal use.
7.31. In addition to industrial safety requirements for entry into confined spaces, if entry is necessary into vessels that have contained uranium, radiation dose rate surveys should be carried out inside the vessel to determine whether any restrictions on the allowed time period for working are required.