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«Safety of Conversion Facilities and Uranium Enrichment Facilities Specific Safety Guide No. SSG-5 IAEA SAFETY RELATED PUBLICATIONS IAEA SAFETY ...»

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(e) Specification of the structures, systems and components important to safety that may be credited to reduce the likelihood and to mitigate the consequences of accidents. The structures, systems and components important to safety that are credited in the safety assessment should be qualified to perform their functions in accident conditions.

(f) Characterization of the source term (material, mass, release rate, temperature, etc.).

(g) Identification and analysis of intra-facility transport pathways for material that is released.

(h) Identification and analysis of pathways by which material that is released could be dispersed in the environment.

(i) Quantification of the consequences for the individuals identified in the safety assessment.

4.102. Analysis of the actual conditions at the site and the conditions expected in the future involves a review of the meteorological, geological and hydrological conditions at the site that may influence facility operations or may play a part in transporting material or transferring energy that is released from the facility (see Section 5 of Ref. [1]).

4.103. Environmental transport of material should be calculated with qualified codes or using data derived from qualified codes, with account taken of the meteorological and hydrological conditions at the site that would result in the highest exposure of the public.

4.104. The identification of workers and members of the public (the critical group of maximally exposed off-site individuals) who may potentially be affected by an accident involves a review of descriptions of the facility and of demographic information.

MANAGEMENT OF RADIOACTIVE WASTE

4.105. Conversion facilities and enrichment facilities should be designed to minimize the generation of waste both in operation and in decommissioning. For economic and environmental reasons, the recovery of uranium and the reuse of chemicals are common practices in conversion facilities and enrichment facilities. These practices minimize the generation of waste in both solid and liquid forms [8, 9].

4.106. In the design phase, including in the design for uranium recovery, a review of various techniques should be undertaken to identify the most appropriate technique to minimize waste generation. Safety related factors should also be taken into account in selecting the most appropriate technique.

4.107. In the case of conversion facilities and enrichment facilities, the nuclear material to be recovered is uranium both from scraps and as secondary outputs from ventilation filters or from cleaning of the facility. The process of recovering uranium from scraps may include dissolution and solvent extraction, which generate liquid effluents. An appropriate balance should thus be achieved between the loss of uranium through unrecovered waste and the generation of liquid effluents in the recovery process.

MANAGEMENT OF GASEOUS AND LIQUID RELEASES

4.108. Liquid effluents to be discharged to the environment should be suitably treated to reduce the discharges of radioactive material and hazardous chemicals.

4.109. Monitoring equipment should be installed as necessary, such as differential pressure gauges for detecting filter failures and devices for measuring activity or gas concentration and for measuring the discharge flow measuring devices by continuous sampling.

OTHER DESIGN CONSIDERATIONS

4.110. In the design of the facility and equipment, including the selection of materials, the need to limit the accumulation of uranium and the ease of cleaning and/or surface decontamination should be taken into account at an early stage.

4.111. For specific process areas, consideration should be given to the means by which the facility can be shut down safely in an emergency.

4.112. Minimization of the storage of hazardous materials on the site should be considered in the design.

Design of the storage area for UF6 cylinders

4.113. Provision should be made for avoiding any deep corrosion of cylinders that would result in a loss of confinement of depleted UF6.

4.114. The design of new storage areas should allow easy access to conduct periodic inspections of cylinders and should minimize occupancy (limitation of occupational exposure).

4.115. Flammable material should not be stored close to the storage area for UF6 cylinders.

4.116. A large aircraft crash on the storage area for UF6 cylinders is generally not considered as a design basis accident. In accordance with specific site considerations, engineered provisions such as drainage or rafts may minimize the potential of a significant pool fire.

5. CONSTRUCTION

5.1. For conversion facilities and enrichment facilities, the criteria used for the construction of the building and the fabrication of the process equipment and components used in the facility and for their installation, should be the same as or more stringent than those used for the non-nuclear chemical industry, and should be specified as part of the design (e.g. seismic design).

5.2. The extent of regulatory involvement in construction should be commensurate with the hazards posed by the facility over its lifetime. In addition to the process by which the operating organization maintains control over construction, frequent visits to the construction site should be used to provide feedback of information to the construction contractor to avoid future operational problems.





5.3. Enrichment facilities are complex mechanical facilities and, as such, modularized components should be used in their construction. This enables equipment to be tested and proven at manufacturers’ shops before its installation at the enrichment facility. This will also aid commissioning, maintenance and decommissioning of the facility. Components and cables in an enrichment facility should be clearly labelled, owing to the complexity of the control systems.

5.4. The construction and commissioning phases may overlap. Construction work in an environment in which nuclear material is present owing to commissioning can be significantly more difficult and time consuming than when no radioactive material is present.

–  –  –

6.1. For a conversion facility or an enrichment facility, the commissioning

should be divided into two main phases:

(1) Inactive or ‘cold’ commissioning (i.e. commissioning prior to the introduction of uranium into the facility).

In this phase, the facility’s systems are systematically tested, from both individual items of equipment and the systems in their entirety. As much verification and testing as possible should be carried out because of the relative ease of taking corrective actions in this phase. However, given the low radiation levels in a conversion facility or an enrichment facility, it would also be acceptable to carry out some of these activities in the subsequent phase.

The operating organization should also take the opportunity to finalize the set of operational documents.

(2) Active or ‘hot’ commissioning (i.e. commissioning with the use of uranium).

In this phase, the safety systems and measures for confinement and for radiation and chemical protection should be tested. Testing in this phase should consist of: (i) checks for airborne radioactive material and checks of levels of exposure at the workplace; (ii) smear checks on surfaces; (iii) checks for gaseous discharges and releases of liquids; and (iv) checks for the unexpected accumulation of material.

Testing in this second step should be carried out with the use of natural or depleted uranium to prevent risks of criticality, to minimize occupational exposure and to reduce the possible need for decontamination.

6.2. To minimize the contamination of equipment during commissioning, process testing with uranium should be used where necessary to evaluate the performance of instruments for the detection of radiation or processes for the removal of uranium.

6.3. The verification process, defined in para. 8.4 of Ref. [1], should be completed prior to the operation stage. The operating organization should use the commissioning stage to become familiar with the facility. The facility management should use the commissioning stage to develop a strong safety culture and good behavioural attitudes throughout the entire organization.

6.4. During commissioning and later during operation of the facility, the estimated doses to workers that were calculated should be compared with the actual doses or dose rates. If, in operation, the actual doses are higher than the calculated doses, corrective actions should be taken, including making any necessary changes to the licensing documentation (i.e. the safety case) or adding or changing safety features or work practices.

–  –  –

CHARACTERISTICS OF CONVERSION FACILITIES

AND ENRICHMENT FACILITIES

7.1. The distinctive features of a conversion facility or an enrichment facility that should be taken into account in meeting the safety requirements established

in Ref. [1] are:

— The relatively low radiotoxicity of the radioactive material but with the potential for chemical and toxicological impacts on workers, the public and the environment, mainly due to: (1) large amounts of UF6 at pressures above atmospheric pressure; (2) reaction products (UO2F2, HF) associated with liquid UF6 operations; and (3) storage and handling of large amounts of solid uranium compounds.

— The potential for fire and explosions resulting in a release of radioactive material (e.g. an H2 explosion in a reduction furnace in a conversion facility or a lubrication oil fire in a gaseous diffusion facility).

— The potential for criticality accidents that may result from enriched uranium operations.

— Significant chemical hazards, e.g. in conversion facilities, large amounts of anhydrous liquid HF and ammonia may be present; in diffusion enrichment facilities, a potential for a release of ClF3 may exist.

7.2. In this section, specific recommendations on good practices and additional considerations in meeting the safety requirements for a conversion facility or an enrichment facility are presented.

QUALIFICATION AND TRAINING OF PERSONNEL

7.3. The safety requirements relating to the qualification and training of facility personnel are established in paras 9.8–9.13 and III.18–III.21 of Appendix III of Ref. [1]. Recommendations are provided in paras 4.6–4.25 of Ref. [4]. The training on prevention and mitigation of fires and explosions that could result in a release of radioactive material (para. III.20 of Appendix III of Ref. [1]) should cover: (1) an H2 explosion in a reduction furnace in a conversion facility; and (2) a lubrication oil fire in a gaseous diffusion enrichment facility. In addition, personnel should be provided periodically with basic training in radiation safety.

GENERAL RECOMMENDATIONS FOR FACILITY OPERATION

7.4. To ensure that the conversion facility or enrichment facility operates well within the operational limits and conditions under normal circumstances, a set of lower level sublimits and conditions, the operating envelope, should be defined.

Such sublimits and conditions should be clear, published and well understood by the personnel operating the facility.

7.5. Operating documents should be prepared that list all the limits and conditions under which the facility is operated. Annexes III and IV give examples of parameters that can be used for defining the operational limits and conditions in the various processing areas of the facility.

7.6. Generic limits should also be set for the facility. Examples of such limits

are:

— The maximum enrichment of uranium allowed at the facility;

— The feed specification limits;

— The maximum allowed inventories for processes and for the facility.



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