3. FOREIGN MATERIAL MANAGEMENT THROUGHOUT NUCLEAR POWER
3.5. Operation phase
During the consequent operation of nuclear power plant to achieve its purpose of safe, reliable, economic and regular production of electricity, FMM that is governed by a mature FMMP is essential to operate and maintain the plant with no-adverse effects from foreign material by providing foreign material awareness and control during operational activities in two folds:
— Ensure that the FMs do not affect the fit, form and functions of SSCs such that meeting or exceeding the design and operational requirements, limits and margins for ensuring safety, reliability and quality are not compromised;
— Protect assets against FM that may impact their availability and operability with longevity for an effective plant performance and efficient electricity generation.
Upon the grant of authorisation to operate (i.e. operating license) by the regulatory body, the owner/operating organisation is fully responsible for safety of the nuclear power plant [43] and for safe, reliable and sound operational decision making and operational activities. Therefore, for safe operation and asset management, the organisation owns an established, mature and structured FMMP with processes and procedures for control and management of FM and its impacts, including the management of organisational interfaces.
There may be variations in the focus of FMM during the operation phase depending on the plant activity, as well as the corporate strategy, style and tradition of owner/operating organisation;
however, the key elements (defined in Section 2 and later described in Section 4) apply at all times. For example:
— For the FMM needs for daily or frequent operational activities, the owner/operating organisation may focus on exclusion (e.g. collective awareness and vigilance, detection, monitoring and observation);
— For routine maintenance tasks and periodic refuelling or maintenance tasks protection and exclusion, prevention and protection (and potentially search and detect aspects of mitigation) are the focus;
— For one-time, first of a kind and special cases, such as cases involving major facility modifications (e.g. major equipment replacement, plant refurbishment), FMMP could have wider focus that include all FMM aspects from anticipation to evaluation.
The FMMP during the operation stage also entails continuous learning and improvement, which will collect lessons learnt from the FMI events, near misses and close calls that point out areas for improvement in the programme and associated processes and procedures, as well as new knowledge on foreign material and associated impacts. It is useful for an owner/operating organisation to regularly consider lessons learned from its own experience, as well as those learned from the OPEX of other nuclear power plants (or even other industries), in order to avoid recurrence of problems and to improve the programme. Consequently, it is also important to maintain and update of OPEX database in a timely manner.
Many activities during the operation stage can expand the knowledge and awareness, can introduce FM into SSCs or may create opportunities, hazards and events for FMIs, for example, among others:
— Plant asset and performance optimisation and improvement measures, particularly those involving major equipment replacements and/or refurbishments;
— Preventive and corrective maintenance activities, particularly I&C, electrical, mechanical maintenance areas;
— Refuelling and maintenance outage activities;
— Plant design and physical modifications, including operating procedure modifications (see Section 3.5.2);
— Operator walkdowns;
— Surveillance testing;
— Chemistry and lube oil controls.
Although certain activities especially those involve working on or around open systems, such as maintenance create more opportunities for FMI events, an effective FMMP during operations requires application of the systematic management process to all activities at the plant/site, e.g. operation, engineering, work planning, oversight, surveillance, testing, chemistry control, radiological control.
Such systematic management process (and associated programme) provides a framework for coordinating all programmes and activities concerning the understanding, control, monitoring and mitigation of FM. More importantly, it ensures that the FM awareness is a normal part of daily behaviours and thoughts, i.e. not only during the times when the plant SSCs are open and susceptible to FMI.
Additionally, open and effective communication and coordination between organisations and between individuals is applied at all times of plant operations so that departments and people are collectively and continuously aware and vigilant of possible latent and/or cross effects of foreign material issues. In this manner, organisational understanding, awareness and vigilance is not specific to the special periodic activities as maintenance or refuelling outages, or
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time plant evolutions such as major SSC replacement and plant refurbishment, but rather it is common to all activities during the operation stage.
Here, two particular work evolutions that are shown by the OPEX to be very critical with respect to occurrences of FMI events and/or FMC capabilities, need to be highlighted: periodic maintenance/refuelling and design modifications. These two topics are, therefore, specifically discussed in the following Sections.
3.5.1. Maintenance and outage activities and foreign material management
Routine and special plant maintenance (both online or offline) and periodic outage4 periods of operation phase are particularly concern FMM and FMC since these are the periods when:
normally closed plant SSCs are open (and thus becoming FM paths and targets); there are substantial presence and movement of equipment, parts, tools (creating and bringing in FM) within and around activities; and the activities take place in large, multiple or adjacent areas and systems (establishing foreign material paths). Such periodic or urgent activities also may include both onsite and offsite fabrication, transportation, storage and disassembly/assembly activities of systems and components.
Operating experience shows that the maintenance and outage periods during plant operation phase are very critical with respect to occurrences of FMI events and makes the control and management of FM essential also (similar those in construction phase) due to:
— Wide variety and number of tasks together with changing environmental conditions generating and moving potential foreign materials at the work zones and around the site;
— Large number of personnel from different companies, qualifications, backgrounds, even sometimes different languages, conducting activities simultaneously, independently or intermittently.
Therefore, in most Member States, the FMMP is typically owned and maintained by the maintenance organisation of the owner/operator, as discussed in Section 5.6.2.
3.5.2. Design changes and foreign material management interfaces and roles during operation
Although nuclear power plants and their SSCs are designed for a target lifetime, many factors and drivers (e.g. obsolescence, component upgrades, long term operation measures, performance improvements) may make some earlier changes to the plant design and configuration desirable or, sometimes as in case of equipment obsolescence , inevitable.
The activities involved with such modifications directly or indirectly may challenge/modify the existing FMMP elements and involves special focus on the FMM.
Particularly major plant modification, such as refurbishment, major component/component replacement or main structure improvement/additions can involve FMM as extensively as in the initial design and construction stages that were described in Section 3.2 and Section 3.3, respectively. However, unlike in those initial design and construction, the owner/operating
4 In some Member State NPPs, there may be three levels of periodic outages: refuelling outages with minor maintenance
at the end of each fuel cycle; refuelling and maintenance outages at the end of every other cycle; and an outage that consists of refuelling, major plant system maintenance and renovation activities, typically every 10 years.
organisation is now primarily and solely responsible for the control of the facility. Therefore, it is the owner/operating organisation that initiates and implements the activities involved with the design change activities (although, as aforementioned) there will be cases with share of labour in the performance of these activities.
Maintaining the very high level of safety and performance expected of a plant requires that modifications arising during the operation, no matter they are major or minor, are made with a full understanding of design criteria and bases of the ‘as built’ plant, as well as the operational specifications for each system, equipment and component. It also requires an integrated assessment of their fit, form and function and their design interfaces and interactions with other SSCs. This full understanding includes the design basis and specifications of the systems and components that were considered, established and specified for FMM and FMC in the design.
When the owner/operating organisation carries out design modifications that includes change, replacement or refurbishment of SSCs, all activities are to be thoroughly assessed regarding the FMM requirements and expectations in design basis and O&M specifications. The results of these assessments need to be communicated with the responsible designers; since if the operating organisation may not be fully aware of changes to the installed design or in the materials or components selected or engineered FMC measures/means, some changes to the original design may have a detrimental effect on SSCs. Such communication with the responsible designers prevents those situations where some design and construction options that were chosen by the designer to prevent FM concern are not explicitly documented (or the records were not obtained or retained by the owner/operating organisation), and thus, the plant owner/operating organisation is not aware of those.
Failure to ensure adequate knowledge of FMM considerations in plant design will result in decisions on modifications, changes in operating procedures, and new or revised specifications for replacement and spare parts, etc., without a full understanding of the FM effects.
Consequently, changes in design may have impact on the safety and performance of the plant and its SSCs, including the adverse conditions from changes to the built-in FMM features in the original design. Some examples for lack of proper FMM considerations in design changes, from OPEX, include:
— Erroneous design change of SSC fit and form: A certain strainer in the feedwater line to prevent foreign material of certain sizes or larger from entering the system was a built-in feature in the design to protect the target, e.g. fuel assemblies. Thus, the size selection of the strainer was based on the result of an evaluation/analysis of the impact from foreign material, larger than a certain size, entering the system and target component, fuel.
Additionally, another design sizing analysis was performed to ensure that the strainer would not create flow restriction to affect the system hydraulic or thermal performance.
For the design change proposing to replace the strainers to increase thermal and hydraulic performance, the design organisation’s approval necessitated a complete assessment of all requirements for all other design functions, including the function for foreign material prevention and protection. Since the design records did not explicitly state such specific design criterion, requirement and assessment for foreign material impact, the operating organisation’s decision makers reached a wrong conclusion that there is no design restriction to increase the size of the strainer to make the hydraulic performance better.
This resulted in inappropriately changing the design (i.e. strainers) to improve thermal and hydraulic performance but created a potential foreign material induced fuel failures in the future.
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— Design change involving wrong choice of materials: The design information concerning the originally selected material, e.g. consumable specification, was unknown (or omitted in design documents), resulting in the replacement of a chemical additive with a new
‘alternative’ material that was not compatible. The new material, as a foreign material (in this example, a foreign liquid material in a liquid system), created an adverse impact for system chemistry posing a potential risk for the plant operator for the maintaining integrity of the system.
— Operating procedure change unknowingly modifying design intent: Design requirements and measures are translated into operational specifications and procedures to ensure the SSC configuration remains consistent with the design intent and evaluations. These also include, cleaning methods and requirements, system as-left configuration, etc. In several cases, such operating procedures (instructions of which were directly tied to design requirements and assumptions) were intentionally revised to have SSCs with ‘foreign material’, with assumptions of those being ‘minor instructional change’. These particularly included procedures for draining, venting, filling or flashing of systems and components. For example, draining emergency core cooling system (ECCS) piping to prevent water from flowing to the containment sump after a periodic test (although the design requires that piping to be normally filled with water) leaving air in the piping as a foreign material (i.e. air in liquid). In another case, while design is requiring complete draining of water from outdoor piping system, flashing procedure was omitted to note to ensure that the system is completely water-free without considering water becoming foreign material. Importance of such omission can be expanded to, for example, air and moisture left in systems that will be filled with sodium that may have severe consequences.
— Wrong assessment of ‘like for like’ basis in the replacement of parts: It was decided to use available spare parts in stock which fit and function would indicate ‘like for like’
replacement; although new parts were made of slightly different materials than those originally used. The original material had a design basis for its selection for minimisation of erosion/corrosion and associated foreign material generation, without a proper assessment of the potential material compatibility, the replacement resulted in generation of foreign material in the system and consequences due to its impact.
Therefore, the design change process needs to require continuity in the design for FMC, such as design organisation’s approval and clearance for installation and changes to FMM requirements and engineered controls, with appropriate evaluation and justification during the operation phase.