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Safety of Nuclear Fuel Reprocessing Facilities
Safety of Nuclear Fuel Reprocessing Facilities
1Nuclear fuel reprocessing facilities are referred to in this Safety Guide as ‘reprocessing facilities’.
2Shearing involves cutting spent fuel into short lengths to allow its dissolution inside its metallic cladding.
3Decladding involves removing the metallic cladding of spent fuel prior to its dissolution.
4Accident conditions include design basis accidents and design extension conditions . Design extension conditions are postulated accident conditions that are not considered for design basis accidents, but that are considered in the design process for the facility in accordance with best estimate methodology, and for which releases of radioactive material are kept within acceptable limits; see Safety of Nuclear Power Plants: Design, IAEA Safety Standards Series No. SSR-2/1 (Rev. 1) .
5A safe shutdown state implies there is no movement of radioactive material or liquids, with ventilation and (essential) cooling only.
6The fail-safe state of a valve, controller or other device is a valve position, for example, that can be shown, by analysis, to be the least likely to cause a deterioration in the safety of the system or facility. Fail-safe devices are designed to fail to this position usually in response to a loss (failure) of motive power or control input, e.g. a spring that moves the valve to a preset position in the event of a power failure. The device might still fail in any position owing to other causes, e.g. mechanical failure, and these events should be analysed in the safety assessment.
7A contactor is a liquid–liquid extraction device.
8“In the context of fuel cycle facilities, a design basis accident is an accident against which a facility is designed according to established design criteria such that the consequences are kept within defined limits. These accidents are events against which design measures are taken when designing the facility. The design measures are intended to prevent an accident or to mitigate its consequences if it does occur.” (para. III–10 of NS-R-5 (Rev.1) ).
9The critical value of a parameter is its value for keff = 1.
10The immediate activation of the alarm system is to minimize doses to workers in case of repeat or multiple criticality events.
111 Redundant sub-systems may be provided to ensure continuous availability during, for example, maintenance or filter changes.
12A firewall is an engineered feature specifically designed to prevent, limit or delay the spread of fire.
13A bulge is typically a shielded, stainless steel, windowless, glovebox type enclosure with mechanically sealed openings to allow for the remote removal of items into a shielded transport flask via a shielded docking port.
14A cell sump is a designed ‘low point’ in a (normally stainless steel lined) cell base to collect any liquid arising from leakage or overflow.
15Highly active liquid waste is also referred to as high level liquid waste
16An air lift or jet lift with disentrainment capabilities is a system or device for separating liquid from a motive air or steam with minimum carry-over (entrainment) of activity into the ventilation system.
17Such flasks are sometimes referred to as mobile equipment replacement casks.
18The phenomenon of such deposition is called ‘plate-out’ in some States.
19A sniffer is an air sampling point or device.
20In some States, fires involving nuclear materials (e.g. an actinide loaded solvent fire) and general (internal, conventional) fires (e.g. a control room fire caused by an electrical fault) are considered separately and explicitly in the safety assessment for additional clarity and to help to ensure all potential radiological and non-radiological hazards from both categories of fire are addressed adequately.
21A room or suite of rooms within a firewall, possibly with separate fire detection and firefighting provisions, inventory controls and evacuation procedures.
22Some regulatory bodies have specific requirements for the design for ‘nuclear loads’ or ‘nuclear lifts’, e.g. requiring the use of multiroped cranes, or the maximum load to be a smaller fraction of the test load than for non-nuclear lifts.
23Typical support systems in a reprocessing facility, including utilities, are: off-site and on-site electrical power systems, compressed air systems (instrument air and pneumatic power), systems for the supply of steam or cooling water, ventilation systems, emergency electrical power systems, uninterruptable power supply systems (instrument power), battery backup systems, reagent and chemical supply systems, inert gas supply systems and all other services and supplies the loss of which may have consequences for safety.
24Contributions to reliability include the use of diverse and redundant electric power sources, switching and connections, the design of power supplies to withstand external risks, and the use of uninterruptible power sources when necessary.
25Examples of supply systems include air reservoirs, uninterruptible power supplies and diverse cooling.
26Further guidance on hazardous chemicals is given in Refs [25, 26].
27Most equipment in reprocessing plants operates at or close to atmospheric pressure; exceptions are evaporators operating at reduced pressures for safety reasons, possibly some equipment designed to resist potential violent or run-away reactions and service supplies (air, steam, etc.).
28Emergency control panels: where justified by the safety assessment, control or monitoring functions required during or after a design basis accident may not need to be located in a designated supplementary control room.
29At-line instruments are devices that remove a small sample or flow (proportional sampling) from a process flow or vessel for measurement rather than measuring in the bulk material directly.
30In this context ‘representative and fresh’ means that, where the main process or flow is not being measured directly, it has to be demonstrated (to the same reliability as specified for the system, structure or component by the safety assessment) that the sample is fully representative of the main flow in composition at the time of sampling and measurement (with allowable deviation as specified in the safety assessment) and is delivered to the point of measurement reliably.
31Posting ports are an engineered provision for the transfer of items into, out of and between gloveboxes.
32Optimization of protection (and safety) is the process of determining what level of protection and safety makes exposures, and the probability and magnitude of potential exposures, “as low as reasonably achievable, economic and social factors being taken into account” (ALARA), as required by the International Commission on Radiological Protection System of Radiological Protection (Ref. ). See also Fundamental Safety Principles, IAEA Safety Standards Series No. SF-1 , Principles 5 and 6.
33Skyshine is radiation reflected from the sky; the other forms of shine are defined in the IAEA Safety Glossary .
34Bounding cases (also called limiting cases or enveloping cases) are used for the estimation of consequences, see paras 4.136 and 4.161 in this Safety Guide.
35Foreign material can cause breakdowns, blockages or flow restrictions, either in situ or by displacement to a more restricted location (e.g. a pump, valve or ejector nozzle). Foreign material may also cause or promote corrosion by forming electrochemical cells or crevices or impeding heat transfer.
36‘Senior management’ means the person or persons who are accountable for meeting the terms established in the licence, and/or who direct, control and assess an organization at the highest level. Several different terms are used, including, for example: board of directors, chief executive officer (CEO), director general, executive team, plant manager, top manager, chief regulator, site vice-president, managing director and laboratory director.
37In commissioning, grading should be applied in accordance with the potential hazard or risk associated with the item being commissioned (or temporarily modified) failing to deliver its safety function on demand at any time in its anticipated operational (qualified) life.
38Upstream sections are parts of the fuel cycle facility or site that provide feeds (reagent, utilities, etc.) to the section being commissioned.
39Downstream sections are parts of the fuel cycle facility or site that accept products or waste from the section being commissioned.
40Support sections are parts of the facility ancillary to the section being commissioned but which are necessary to allow or monitor its operation.
41In some States, the use of natural or depleted uranium may require regulatory approval.
42Tracers are small quantities of very low active (or inactive) materials that mimic the behaviour of the operational material and are used to determine process parameters.
43In some States, the format and content of a commissioning report may be defined by the regulatory body.
44Examples of access equipment are ladders, scaffolding, access platforms and powered access equipment (hydraulic platforms).
45Allowing waste (including industrial waste material that is suspected to contain radioactive material) to accumulate in work areas contributes to worker doses, both directly as sources and indirectly by impeding work progress. This can cause delays and complicate the identification of (new) sources of contamination, particularly airborne contamination. It can also lead to action levels for decontamination being raised (owing to an increase in background levels of radiation).
46Intrusive maintenance is maintenance involving a significant reduction in shielding, the breaking of static containment or a significant reduction of dynamic containment, or a combination of these.
47Where the level of risk is difficult to determine (e.g. for new tasks or initial breaking of containment following a fault), the precautions taken should initially be cautious, based on the assessed hazard and operational experience, until the risk assessment can be reviewed in the light of new data.
48An enclosure is a (usually temporary) combination of a static barrier (containment) supplemented by a dynamic barrier (ventilation) with appropriate entry facilities, completely enclosing (boxing in) a work area and sealed, as far as practical, to local surfaces (walls, floors, etc.) to limit and minimize the spread of contamination. Where possible, enclosures should be modular with a rigid or heavy duty plastic outer ‘skin’ (that is resistant to damage) and a lighter weight (thinner), easily de-contaminable, inner skin to allow for maximum recycling and reuse and to minimize waste volumes. In some States, the inner skin is called a ‘tent’ or ‘greenhouse’.
49The radioactive fingerprint is the mixture of radioactive nuclides and their ratios that characterize the waste. The radioactive fingerprint may be estimated from the material processed in the area and then confirmed during initial operation of the facility
50Even for small facilities, off-site resources may be called upon to provide public reassurance and for on-site response to localized events.
Tags applicable to this publication
- Publication type:Specific Safety Guide
- Publication number: SSG-42
- Publication year: 2017