Development and Application of Maintenance Template in Pressurized Water Reactor Nuclear Power Plant

ZHANG Sheng(张 圣), CHEN Yu(陈 宇), CAO Zhi-peng(曹智鹏), MO Chun-ni(莫春铌)

Suzhou Nuclear Power Research Institute, Shenzhen 518028, China

Development and Application of Maintenance Template in Pressurized Water Reactor Nuclear Power Plant

ZHANG Sheng(张 圣)*, CHEN Yu(陈 宇), CAO Zhi-peng(曹智鹏), MO Chun-ni(莫春铌)

SuzhouNuclearPowerResearchInstitute,Shenzhen518028,China

Good practices of maintenance optimization in nuclear power field need to be effectively consolidated and inherited, and maintenance optimization can provide technology support to create a long-term reliable and economic operation for nuclear power plants (NPPs) especially for a large number of nuclear powers under construction. Based on the development and application of maintenance template in developed countries, and combining with reliability-centered maintenance (RCM) analysis results and maintenance experience data over the past ten years in domestic NPPs, the development process of maintenance template was presented for Chinese pressurized water reactor (PWR) NPP, and the application of maintenance template to maintenance program development and maintenance optimization combined with cases were demonstrated. A shortcut was provided for improving the efficiency of maintenance optimization in domestic PWR NPP, and help to realize a safe, reliable, and economic operation for domestic NPPs.

pressurizedwaterreactor(PWR)nuclearpowerplant;maintenancetemplate;maintenanceprogram;maintenanceoptimization

Introduction

Daya Bay nuclear power plants (NPP), Tianwan NPP, and Qinshan NPP have conducted reliability-centered maintenance (RCM) (streamlined RCM, SRCM) analysis for many years, especially the Daya Bay NPP with more than ten years experience in analysis and application of RCM, and have accumulated rich failure analyses and maintenance data. Moreover, many researches and applications were related to failure modes and maintenance templates, for example, preventive maintenance (PM) basis database developed by EPRI in 1997. Meanwhile, the role of maintenance templates under a multi-reactor operational mode is more significant[1]. Under the background of domestic NPPs implemented multi-reactor management mode, to develop and establish a national database of PM template for domestic NPPs can provide useful information and valuable data for scientific decision-making in production and maintenance, especially maintenance optimization and reliability management. We present the development process of maintenance template for domestic pressurized water reactor (PWR) NPP, and also demonstrate the application of maintenance template to maintenance program development and maintenance optimization combined with cases. This study can provide reference and technical guideline for domestic PWR NPP, help to develop and optimize preventive maintenance program, and perform cycle demonstration on projects.

1 Maintenance Template Definition

A maintenance template is a documented maintenance strategy for a particular equipment type based on maintenance experience and reliability analysis of a similar equipment type[2]. This maintenance template outlines the maintenance and monitoring tasks used to prevent a particular equipment type failure with similar structure and process, as well as covers monitoring methods (for example, test, experiment, and requalification) and the necessary maintenance measures (for example, parts replacement, and lubrication), and also includes the main failure modes, failure effects, and maintenance strategies to manage the failure modes.

2 Technical Route

Through investigation of the successful experience in development and applications of foreign maintenance template data (database), and combined with the results from failure analyses and maintenance data for over ten-year RCM (SRCM) implementation in domestic NPPs, as well as consideration of equipment criticality, service conditions, and reliability analyses(including qualitative and quantitative analyses), this paper will study and develop equipment failure modes and maintenance strategy template database for domestic PWR NPP. Choose a typical equipment type as an example to introduce the development and application process.

3 Maintenance Template Development

Based on foreign good practices and actual situation of domestic NPPs, maintenance template development generally includes equipment classification, collection and analysis of references, cycle and maintenance tasks selection, as well as information input to the platform for effective management and continuous optimization of the maintenance template. Development process of equipment maintenance template is shown in Fig.1.

3.1 Equipment information needed during the development process

The needed information is as follows:

(1) the subcomponent list of possible degradation or failure within the equipment boundary;

(2) the degradation process and main influence factors for each failure;

(3) the time characteristic of the degradation process;

(4) the most common failure locations and failure mechanisms;

(5) tasks used for detecting equipment condition, preventing or avoiding equipment degradation;

(6) including all of above preventive maintenance tasks package;

(7) technical efficiency (high, medium, low) of each task in solving the corresponding failure mechanism;

(8) the scope and contents of each PM;

(9) definitions of frequency and service condition affecting PM implementation;

(10) introduction of the typical working patterns and related resources when performing maintenance;

(11) description of all of the above factors how to support the maintenance tasks and their frequency selection;

(12) recommended PM tasks and task cycle depending on criticality, duty cycle, and service conditions-PM template;

Fig.1 The development process of equipment maintenance template

(13) the main goal for each PM task, and impact of its cycle change on the effectiveness of the task;

(14) a sheet embodies overlapping of various tasks in PM program, and covers all of tasks;

(15) useful industry reference information.

3.2 Development process

The main steps of equipment maintenance template are as follows.

(1) There are many kinds of equipment types in domestic PWR NPP, including pump, motor, transformer, turbine, valve, heat exchanger, instrument and control equipment,etc. Combining criticality (four levels), duty cycle (two levels) and service conditions (two levels), usually equipment can be divided into twelve equipment types[3]. Equipment classification is conductive to successful development and application of targeted equipment maintenance template, and convenient to develop equipment maintenance template applicable to different occasions[4].

(2) In the template classification stage, task analysis of reference documents is the main source of the template maintenance tasks. These reference documents include: equipment operation and maintenance manual (EOMM), failure modes and effects analysis (RCM analysis results), periodic test program, experience feedback from system and equipment, and any existing templates from Exelon/Constellation/Electricite De France (EDF).

(3) Identification of maintenance and monitoring tasks, and analysis of maintenance and monitoring tasks and corresponding failure modes.

(4) Selection of appropriate maintenance tasks and periods.

(5) Review and taking into effect.

(6) Input to maintenance template management platform.

3.3 Development principles of maintenance templates

A template is the technical document to ensure reliability level of equipment, thus template development should not include too much economic factors or human resources[5].

The template should outline practical experience about equipment maintenance from domestic PWR NPP and maintenance practice from interactions with foreign operators and organizations. Considerations for maintenance template development include: existing maintenance templates from Exelon/Constellation and EPRI, existing maintenance templates from EDF, experience feedback, and vendor recommendations.

Templates should include a series of means to ensure equipment in good running condition in support of long-term reliability of equipment. At the same time, necessary adjustment means (for example, alternative items) should be considered prior to template development[6].

Each template is suitable for a particular equipment type with similar process, for example, pneumatic valve template is applicable to Masoneillan and Fisher pneumatic valves because they have similar structure and design.

Each template should be correlated with the functional location code in the equipment database, because for equipment given a functional location code, its components also have the same function code[7]. So the template should include the entire equipment, namely the main components and other related components, taking pneumatic valve as an example, the template should cover all maintenance and monitoring methods performed on the pneumatic valve and its limit switch, regulator, and actuator.

For different equipment, or the same equipment with different maintenance tasks, their maintenance templates are different.For example, two plates from a control cabinet, if their maintenance tasks are different, they do not belong to the same template.

In order to better integrate the template and equipment classification during development and optimization of maintenance program, specific tasks should be avoided for a particular equipment type[8].

In support of better establishment and optimization of maintenance program, for some equipment with large numbers and different functional location can be seen as an equipment (for example, the feedwater pump), we can create a template covering all equipment.

The template should be followed by a form illustrating various equipment parameters, values, and other elements associated with the maintenance tasks[9]. For example, the template of lead-acid battery of generator unit in Daya Bay NPP must be accompanied by a form containing all parameters illustration associated with monitoring and maintenance tasks on the lead-acid battery of 900 MW generator unit.

Tasks description is not necessary to clearly define the equipment manufacturer or special technology or special tools used by the power plant, but it can give the corresponding reference instructions. For example, valve template should avoid such writing: “Carry out valve motor Quiklook test” and the correct writing should be “Carry out valve motor operational test (such as using Quiklook diagnostic tool)”[10].

Due to lack of understanding on a few types of new equipment, the scope covered is limited in the maintenance plan of system and equipment. Meanwhile, there is a lack of proven maintenance strategies and maintenance criteria. Therefore, the template of this type should be continuously optimized with further understanding and experience accumulation.

3.4 Template tasks

The tasks are as follows:

(1) diagnosis: refers to the tasks associated with equipment inspection and failure diagnosis, such as operator rounds, the person in charge of the system or equipment walkdowns, oil analysis, infrared thermometry, and vibration;

(2) general operating guideline (RGE) periodic test: involves the periodic test used for improving the maintainability and availability of the unit;

(3) diagnosis results based maintenance: the maintenance tasks listed are carried out only when required based on the monitoring and diagnosis analysis results;

(4) routine scheduled maintenance: is used for ensuring normal operation of the equipment, for example, lubrication of bearings;

(5) periodic maintenance: is mainly performed during the outage;

(6) monitoring tasks (SIR) associated with pressure equipment:cover all of the monitoring tasks required by the pressure equipment;

(7) regulatory tasks: refer to the other tasks required by other rules and regulations in addition to SIR and RGE;

(8) rPMQ tasks: contain the monitoring tasks required by maintaining equipment qualification.

3.5 Cycle selection

For each maintenance task, because of its applicable equipment type up to twelve levels, it is required to determine twelve execution cycles, and the execution cycles for adjacent levels may be the same[11]. Maintenance cycle can be determined based on criticality, duty cycle, and service conditions.

The main references of cycle selection include: EOMM, equipment operating experience feedback, recognition of equipment and professional skills, failure mode and effect analysis (RCM analysis results), and quantitative analysis.

4 Case Study

Taking the pneumatic components of a pneumatic valve as an example, this section gives a brief description of development process of PM template, which provides a good reference for maintenance strategy optimization of pneumatic valve in domestic NPPs. Above all, determining the analysis object is the pneumatic components used for the pneumatic valve (not pneumatic valve body).

Based on the results of failure modes and effects analysis(FMEA), as well as existing regulations requirements and maintenance programs and field application feedback, and with consideration of failure history of equipment and analysis of failure data, and reference to external feedback of similar equipment, finally maintenance cycle is determined according to equipment classification.

Since maintenance tasks address the management of failure modes, correlation data between FMEA results and maintenance tasks is acquired after maintenance tasks determination[12]. When specific maintenance task is searched, the corresponding failure mode, and failure information such as failure component and failure mechanism, are also provided; conversely, a list of maintenance tasks will be put forward to select proper task to manage such failure after identification of the failure mode. The corresponding relationship between the maintenance task and the failure mode is established after identification of maintenance task and cycle. Based on this established correlation, and equipment classification and selection criteria of maintenance cycle, the correlation between the maintenance cycle and the equipment type is built, then ultimate maintenance template of the equipment is generated. The maintenance tasks and maintenance cycles within maintenance template are determined on a basis of equipment classification and FMEA results. The maintenance template contains all possible failure modes, possible failure components, and failure mechanisms for a particular equipment type and appropriate maintenance strategies to manage the failure modes[13].

According to the working principle of pneumatic components of pneumatic valve and internal experience feedback, and combined with failure modes and reliability analysis of pneumatic components, maintenance template (taking the filter relief valve as an example) is developed as shown in Table 1.

Table 1 The maintenance template of filter relief valve

Componenttype:filterreliefvalveComponenttype1234567CHSCLSCHMCLMNHSNLSNHMCriticalityCrticalNon-criticalDutycycleHighLowHighLowHighlowHighServiceconditionsSevereMildSevereMildMaintenancetaskCycleVisualinspection1W1W1W1W1C1C1COperationalcheckNSMNSM1C1CNSMNSMNSMPeriodiccheck1C1C3Y3YNSMNSMNSMVulnerablepartsreplacement4Y4Y6Y6Y8Y8Y8Y

Note: NSM means non-scheduled maintenarce

5 Applications

Upon completion of all equipment classification grading and maintenance template development of their equipment types for a system or a functional equipment group, we can integrate them into relevant platform to generate or optimize equipment maintenance program. The primary means of maintenance program optimization is functional equipment group through optimizing maintenance cycle of the equipment from the same functional equipment group to achieve the same maintenance cycle in support of maintenance work optimization[14].

However, domestic RCM technology lacks appropriate reliability maintenance decision support tool resulting in inefficiency of analysis and restricting RCM promotion. Development of this template can greatly improve the efficiency of RCM analysis. With RCM analysis on a system or a piece of equipment , data associated with failure modes, failure effects, maintenance decisions, and other relevant information can directly reference corresponding data from the template, which greatly improves the efficiency of RCM analysis[15]. But it should be noted that template contents should be timely adjusted and upgraded based on feedback from field application. After the establishment of a sound maintenance template, it is usually to upgrade the template for each five years, and the maintenance program should be updated accordingly. Figure 2 shows the process of program development and optimization using maintenance template.

Fig.2 The process of program development and optimization using maintenance template

6 Conclusions

Based on foreign maintenance template database and its application investigation, and combined with the actual situation of domestic NPPs, this paper developed an equipment maintenance template for domestic NPPs, and carried out the development and application verification of typical equipment type template. This study will provide important technical support for equipment reliability management in maintenance decision-making, failure analysis,etc. Development of equipment maintenance templates for domestic NPPs can inherit the good practices of maintenance and failure management in NPPs, promote applications of maintenance optimization concepts and results, and improve operational level of the units in operation and under construction. The research results and subsequent development of template database will lay a good foundation for operation and maintenance management of domestic NPPs, and provide important support for domestic NPPs to realize standardized and efficient equipment reliability management, thus the application prospect is extremely broad.

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TL 364 Document code: A

1672-5220(2015)01-0162-04

Received date: 2014-08-08

*Correspondence should be addressed to ZHANG Sheng, E-mail: yysbtzhang@163.com