ZHU Guixia()， BAO Xudong()， KANG Chengjie()， LIU Wei( )， QIN Feng( )， LU Bing( )

1 Research Institute of Nuclear Power Operation， Wuhan 430223， China2 CNNP Nuclear Power Operations Management Corporation， Ltd.， Jiaxing 314300， China

Abstract： Performance monitoring is the important part of the equipment reliability process description (AP913)， and the system performance is the main content of monitoring. The purpose of system performance monitoring is to identify early performance degradation of system and equipment in time， evaluate the overall health of system， and carry out corrective actions in a timely manner. Performance monitoring also has the corresponding experience feedback. The paper introduces the process of system monitoring program development. In the end， the paper takes an example of the turbine control fluid system (GFR) in a domestic nuclear power plant. The example shows the process is good for the analysis.

Key words： system performance monitoring plan; system function analysis; system performance monitoring; Turbine control fluid system

Introduction

AP913[1]is a standard process for reliability management of nuclear power plant equipment issued by Institute of Nuclear Power Operations (INPO). According to the concept of reliability-centered maintenance (RCM) maintenance， it includes scoping and identification of critical components， performance monitoring， corrective action， preventive maintenance (PM) implement action， continuing equipment reliability improvement， and life-cycle management. And it organically combines the six plates and forms a continuous improvement loop maintenance system of its own. System performance is the main content of the performance monitoring， and it plays an important role on the equipment reliability management. System monitoring program is the performance monitoring action program for system function and its key or important equipment. It defines needed parameters， sources， frequency acceptance bands and required actions. The development of system performance monitoring program includes system function analysis and system performance monitoring. System function analysis is that identify the needed important function for monitoring system according to the criteria of system function influence and screen out items causing the failure of the system important function. System performance monitoring is to develop the specific content from the point of system monitoring.

At present， the development of system monitoring program is not popular in the domestic. And it does not form a universal development process. Electric Power Research Institute (EPRI) issued a report in 1997 that is “Guideline for System Monitoring by System Engineers (TR-107668[2])”， and update it in 2010. This report is very important to develop system monitoring plan. EPRI issued a report in 1998 that is “System Monitoring by System Engineers， 37 System Monitoring Plans (TR-107434)”. This report provides utility system engineers with 37 monitoring plans to assist them in developing effective plans for their systems.

The system monitoring program development can produce a combination of cost savings， improved generation， and improved plant management. They are as follows.

(1) Identification of holes in current utility monitoring programs.

(2) Improvement in the ability to anticipate and resolve problems at an early stage.

(3) Documentation of the system monitoring basis.

(4) Elimination of monitoring unnecessary data by limiting the monitoring process to information needed， not information available.

(5) The completeness of information improves the ability of the system engineer to recognize and assess separate but compounding conditions on the system.

System monitoring is the important module of equipment reliability database for nuclear power plant. Its data is the foundation data of equipment reliability management. The work of system monitoring program development is very important and urgent. In this paper， the development of system performance monitoring program includes system function analysis and system performance monitoring. In order to facilitate understanding， we take an example of the turbine control fluid system (GFR) in a domestic nuclear power plant. There is a process， analysis and summary of the development of the system monitoring program in the example.

1 System Monitoring Program Development Process

According to the document TR-107434 issued by EPRI in 1998[3]， the development of system performance monitoring program includes system function analysis module and system performance monitoring module. System function analysis module analyzes system design function and its failure effect， and identifies the important of all functions to determine which resources are worth spending to develop and implement. At the same time，this module screens out the faults of important system functions. System monitoring development module is to develop the system monitoring scheme. Finally the system performance monitoring program is formed[4-5].

1.1 System function analysis

System design manual of nuclear power plant contains a detailed description of functions for each system. System function analysis is based on system design manual data， operating experience,etc. It can list system design functions and their corresponding faults or effects. System function analysis identifies the needed important function for monitoring system according to the criteria of system function influence. So it screens out items causing the failure of the system important function. The flow chart of system function analysis is shown in Fig. 1.

Fig.1 System function analysis process

1.1.1Definitionofsystemscope

Defining the scope of the system is very important to the system function analysis and PM program assigned. Because it cloud repeat or ignore the important function for crossing the system definition. Firstly， P & I diagram of the system is the basic paper. Secondly， it needs to check the system manual diagram and other files. Finally， the scope divides with a dotted line and makes the logo. The criterion of defining the scope is that implements a specific function and support the function of auxiliary function. It can analyze together with the main system if a subsystem can be individually as an analysis unit.

1.1.2Analysisofsystemdesignfunctionanditsfailureorfailureeffect

In the defined scope of the system， establish the all design function according system design manual， Final Safety Analysis Report (FSAR)， operating procedures and so on. Using the method of failure modes and effects analysis (FMEA) is to analyze system design function failure and failure effect， and obtain the priority of system important function or items for monitoring， it also proves that the monitoring is correct.

1.1.3Identificationofsystemdesignfunction

The next step is to evaluate if the function is important enough to expend the resources required to develop and perform system monitoring. Functions such as the following that can affect the utility criteria for critically should be included in the system monitoring program[4].

(1) Reactor shutdown;

(2) Entry into a short-term limiting condition of operation；

(3) Significant powerderate；

(4) Transient；

(5) Actuate emergency safeguard feature；

(6) Failure to control a critical safety function；

(7) Degraded capability to reach and/or maintain reactor safe shutdown；

(8) Half scram；

(9) Limiting conditions for operation of(LCO) the Technical Specifications；

(10) Loss of safety system redundancy；

(11) Operator workarounds(OWA)；

(12) Environmental impact；

(13) Radiological or personnel safety impact；

(14) Pressure from regulations increased significantly；

(15) Refuel outage extension；

(16) Startup delays.

1.1.4Screeningoutitemscausingfailureofsystemimportantfunction

The criterion of screening out items is that it will be a direct impact to system function if items fail. Some items will not have a direct impact. For example， local instrument， the valve that only has isolate maintenance function， RTF equipmentetc.

1.1.5Mergesystemdesignfunction(importantfunction)

It needs to merge system design function if it has all or part of the same. Besides， it also can base the experience of analysis people. The important function is the function that needs to develop items monitoring.

1.2 System performance monitoring

System monitoring development is to develop the specific content of system performance monitoring according to the guide for system monitoring program of the nuclear power plant. The object of the development of system monitoring program is identified the system important function and items. The complete process of developing every system monitoring program is as follows: recognize system important function and failure effect， make sure items degradation mechanism and indicators， identify data sources， determine the frequency of data collection and monitoring， clear trending and analysis method， build acceptance bands and required actions，etc. The flow chart is shown in Fig. 2.

1.2.1Definitionofdegradedmechanismsandindicators

Defining degradation mechanisms and indicators for critical system functions are methods that use the FMEA to analyze items according to the types and structures of the items. This step requires a thorough knowledge of system functions; the equipment that supports those functions; and the associated physical， electrical， and mechanical properties that can degrade. It is also important for the development people to understand both the short-term and long-term aging and operational wear processes for equipment. The step is the primary key to understand “what” and “how” to effectively monitor for early identification of system degradation.

Fig.2 System performance monitoring

1.2.2Identificationofdatarequirements

Developers need to identify the data that effectively reflect the degradation mechanism, rather than current monitoring data， and don’t have to consider whether data can obtain. The data includes type， collect /monitor frequency and accuracy. There has enough data to determine whether system degradation or potential downgrade. The purpose of this step is to identify required for supervision of the system direct parameters.

1.2.3Reviewofdatadifference

The developer lists the differences by comparing the identified data requirements in the previous step with the monitoring data in the power plant. Can the new monitoring data obtain by a feasible method or technology? The developer should investigate and evaluate before the application of new method or technology.

1.2.4Determinationoftrendingmethod

This step needs to take advantage of the developer’s knowledge and experience， and consider the aging condition of equipment， some parameters’ characteristics. The following questions can assist in determining trending method.

(1) Do the system monitoring data in source have carried out analysis?

(2) Are the data in a format requiring calculations or computer algorithms to indicate system performance?

(3) Does the variable parameter change with other parameters?

(4) Does analysis of system performance require the correlation of parameters acquired from various data sources?

(5) Is the cumulative effect of individual component degradation required to be analyzed to determine the aggregate reduction in system performance?

1.2.5Establishmentofacceptancebands

Establishing proper acceptance bands determines the effectives of monitoring. Acceptance bands are most effective when they allow sufficient time to carry out the associated action plans that are put into place when action levels are exceeded. If the acceptance bands have been established in an existing procedure or by another department， the system engineer must carefully review these bands or levels to determine if an appropriate margin exists. Information to assist in adjusting or developing new acceptance bands can be obtained from reviewing the design basis for the system， past site-specific experience， or industry experiences with the system.

1.2.6Establishmentofactionplans

Action plans are predefined decisions or actions that the system engineer will implement when an assigned action band trend level or limit has been reached. Defining action plans for specific monitoring parameters should be general enough to allow for engineering judgment， but specific enough to cause consistent actions to occur. Action plans can include items such as management notification， corrective action item initiation， increased monitoring， additional parameter monitoring， operational limits， operator actions， troubleshooting， testing， or maintenance.

1.2.7Establishmentofpointlocation

Measuring point position is corresponded to the data source. In general， if the data source is the power station computer system， the measuring point position is the specific sensor code of the corresponding system.

1.2.8Determinationofcalculationmethod

Calculation method is the mathematical expressions between direct supervision parameters and the degradation indicators.

2 Example Applications-GFR

In order to facilitate understanding， this paper takes an example of the turbine control fluid system(GFR) in a domestic nuclear power plant. There is a process， analysis and summary of the development of the system monitoring program in section 2.

2.1 Main composition and description of GFR system

The turbine control fluid system will supply power fluid to the shop valve， the governor valve and the emergency trip valves. The turbine control fluid system will also marshal the drain returns from the operating and trip gears.

The turbine control fluid system comprises dedicated reservoir， pumps， cooler and fluid conditioning all mounted on a common fabricated steel bedplate. The control fluid is a fire resistant fluid of the high resistivity phosphate ester type.

2.2 GFR system function analysis

2.2.1Definitionofthesystemscope

(1)Mechanicalscope

The mechanical scope all begins with GFR equipment including fluid tank， main pumps， fluid conditioning pump， cooling circuit pump， control fluid cooler， control fluid accumulators (the accumulators of valves analyze with valves monitoring)， kinds of vales and so on.

(2)Electricalscope

The electrical scope all begins with GFR monitors of main pumps， fluid conditioning pump and cooling circuit pump， electric heaters.

(3)Instrumentcontrolscope

The instrument control scope is all the local indicating instrument， analogue and digital measuring instruments of DCS.

2.2.2GFRsystemdesignfunctionandimportantfunction

(1)GFRsystemdesignfunction

According to the system design manual of GFR， FSAR， operating procedures and so on， the GFR system design function is as follows.

Function 1: provide qualified fluid supply pressure to meet the turbine hydraulic equipment requirements (design value 12 MPa).

Function 2: provide qualified fluid supply flow rate to meet the turbine hydraulic equipment requirements (design value 6 m3/h).

Function 3: provide qualified fluid supply temperature to meet the turbine hydraulic equipment requirements (design value 50 ℃).

Function 4: keep adjusting fluid tank at the appropriate level.

Function 5: maintain physical and chemical characteristics of fluid.

Function 6: marshal the drain returns from the operating and trip gears.

(2)GFRsystemimportantfunctionformonitoring

According to listing system design function， its corresponding function failure and failure effect， the developer identifies the needed important function for monitoring system， and screen out items causing the failure of the system important function. It needs to merge system design function if it has all or part of the same. Besides， it also can base the experience of analysis people. The important function is the function that needs to develop items monitoring. The GFR system important function of monitoring is as follows.

Important function 1: provide qualified fluid supply pressure and flow rate to meet the turbine hydraulic equipment requirements (design value 12 MPa， 6 m3).

Important function 2: provide qualified fluid supply temperature to meet the turbine hydraulic equipment requirements (design value 50℃).

Important function 3: keep adjusting fluid tank at the appropriate level.

Important function 4: maintain physical and chemical characteristics of fluid.

Due to space restrictions， Table 1 provides the analysis of important function 1.

Table 1 Analysis of GFR system important function 1

2.3 GFR system performance monitoring

According to the step and attentions of section 2，Table 2 provides the system performance monitoring of No.1 main pump (Code GFR 011PO) from important function 1.

Table 2 System performance monitoring of No.1 main pump (Code GFR 011PO)

(Table 2 continued)

Note: 1D-One day;1M-one month;1Y-a year;1C-a cycle;NA-not applicable

3 Conclusions

System monitoring program is the foundation work of equipment reliability database for nuclear power plant. Nuclear power plant can use the data of system monitoring module to evaluate the healthy state of system， analyze degradation model and mechanisms of equipment and so on. It also lays the foundation to carry out the equipment reliability management.

This paper introduces in detail system monitoring program development process in the nuclear power plant. In order to facilitate understanding， this paper takes an example of the turbine control fluid system(GFR) in a domestic nuclear power plant. There is a process， analysis and summary of the development of the system monitoring program in the example. The content of this paper has great reference significance for the present domestic nuclear power plant development system monitoring plan.