Workshop on Research Reactor Ageing and Self-Assessment Methodologies

Transcription

1 Workshop on Research Reactor Ageing and Self-Assessment Methodologies Module 4 Ageing Management 4.6 Case Study

2 Originally presented December 2001 as: PREPARATION OF AN AGEING MANAGEMENT PROGRAM AND ACTION PLAN Adalberto José Soares IPEN-CNEN/SP Brazil

3 What follows is an example of an Ageing Management program, followed by an action plan, and its adjustment to the methodology established on IAEA TECDOC 792. Brazilian IEAR1 Research Reactor is used as the reference installation.

4 IEA-R1 Reactor construction started on September 1956 Achieved its first criticality on September 1957 Power : 2 MW - Thermal Flux :3.5E13 n/cm2.s Used for basic and applied research, neutron radiography, silicon doping, and experimental production of radioisotopes

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8 Core Support Structure

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10 1971: - First modification of reactor building ventilation system. 1974: - Duplication of the primary coolant system to redundancy; - Introduction of flywheels on the primary centrifugal pumps; - Installation of a N16 decay tank to reduce operational dose; - Upgrade of the electric system with the installation of two emergency diesel-generators. -Chemical cleaning of original heat exchanger 1976: - Replacement of the original nuclear instrumentation channels, control console, and control drive mechanism; - Modification of pneumatic irradiation system (replacement of aluminum by steel, and repositioning)

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13 1978: - Replacement of the ceramic tiles of the pool walls by a steel liner; 1987: - Separation of reactor building into radiological hot and cold areas; - Installation of access chambers; - Installation of a new cooling tower; 1991: - Construction of a radiation shielding for the purification system

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15 In 1995 following a decision to upgrade the reactor and to uprate its power from 2 to 5 MW, the first action was to make an preliminary ageing assessment, i.e. to make a detailed analysis if the systems and components of the reactor, to make one estimate of how long the reactor could operate, and if the installation would comply with safety requirements for the power uprate. Then, several activities started to be performed in parallel, with emphasis on Collection of Data (Historic Review), and a technical analysis of the main components, like reactor core structure, reactor pool, heat exchangers, pumps, cooling tower, etc..

16 PLANNED ACTIVITIES Evaluation of Physical Mechanisms of Ageing Search of Information Final Assessment Action Plan

17 Evaluation of Physical Mechanisms of Ageing Evaluation of neutron fluence effects : Thermal and fast neutron flux are below 2,5x1013 For fuel and reflector neutron fluence is a point of concern Outside fuel region, fluence < 2x1020 Far below 7x1021 and 3x1022 n/cm2 (fast and thermal)

18 Evaluation of Core Support Structure Stress Cycling (aluminum) : 4 L shaped frames, with dimensions 2,5 x 0,375 inches2 IEAR1 has 923 Kg STATIC LOAD : 1.91 N/mm2 (200) Core P = 0,016 N /mm2 Flow rate = 3000 GPM Area of Matrix Plate : 5640 cm2 PEAK DYNAMIC LOAD : 3,78 N/mm2 (260)

19 Additional Activities Regarding Evaluation of Physical Mechanisms of Ageing measurement of vibration levels on rotating equipment, check of electrical and electronic cables, visual inspection of reactor core components and structures

20 Inspection of Core Components

21 Inspection of Graphite Reflectors

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24 Control/Safety Elements

25 Control/Safety Elements

26 Additional Activities Regarding Evaluation of Physical Mechanisms of Ageing Concrete ageing: Inspections were performed to check if there were damages to the reactor building and pool concrete. No faults were detected. Secondary coolant system: The cooling towers and piping were checked and found many corroded areas on all piping of the system. Inspection of heat exchangers : Tubes considered compromised were plugged.

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32 Evaluation of Non-Physical Mechanisms of Ageing Review of safety analysis concept and viability to comply with requirements for power uprate,

33 Search of Information : Safety analysis report, Operational records and reports, Technical reports, Log books, Audit reports from the Safety Revision Committee, Abnormal event reports, Thousands of pictures

34 Once the technical information was available, a final assessment was made with the conclusion to continue operation and plan all necessary modifications to uprate the reactor power, considering the necessity to comply with all safety standards and guides.

35 IAEA Safety Series 35 had just been revised, incorporating the requirements mentioned on IAEA TECDOC 792, namely : (a) (b) (c) (d) (e) Surveillance and testing programmes to assess degradation of components and systems; A preventive maintenance programme; Periodic evaluation of operating experience; Optimization of operating conditions; Repairing, replacing or refurbishing of components. It oriented the activities planned for uprating the reactos power

36 Activities planned before applying for the license to operate the reactor at 5 MW. Seismic Qualification of Building, Structures and Components: A seismic evaluation of the reactor site, based on seismic risk, was done and showed that the seismic level is so small that no additional seismic qualification was required. Reactor Core: Graphite reflectors showing signs of corrosion were put on places with low neutron flux, and provision was made to acquire new Beryllium reflectors. Irradiation devices were modified to avoid excess of water passing through then, and assure the cooling of the fuel elements.

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38 Spent Fuel Racks: Two new Aluminum set of racks were installed to increase the spent fuel storage capacity, and provision was made to provide a liner to existing SS storage racks (to avoid galvanic corrosion) Primary Coolant System: Four isolation ball and gate type valves electrically actuated were installed at the inlet and outlet of the primary piping. They form the Reactor Pool Isolation Valve system (PRPIV) and isolate the reactor pool within one minute in case of a primary system piping break (LOCA). Pumps also had components replaced due ageing. Secondary Coolant System: Piping of secondary cooling system was completely replaced due to corrosion. The new piping were installed above the ground to facilitate inspection.

39 Drain System: Replacement of all piping and valves from the reactor building to the retaining tank, and internal impermeabilization of the walls of the tank to avoid infiltration. Fire Detection and Extinguishing Systems: A new detection and fire extinguisher system was installed covering all areas of risk, according to evaluation previously performed. Heating, Ventilation and Air Conditioning (HVAC) System: A new system was installed with the separation of reactor building into two distinct and isolated areas

40 Electrical System: New power control panels were provided to distribute power from the main switch gear and emergency generators directly to a set of consumers and motor control center. All wiring was checked, revised, and distributed into new cable trays. It was divided in Normal, Essential, and Vital Instrumentation and Control: Improvements in the reactor protection system and in safety related instrumentation. New panels were installed in the control room, and in the emergency room for the new safety related systems.

41 Vibration Monitoring System : An on-line vibration and temperature monitoring system was installed to monitor vibration levels on all main rotating equipment, like flywheels, driving motors and pumps on primary and secondary cooling systems, and diesel generators. Radiation Monitoring System: Old monitors were replaced and new gaseous effluent monitors were installed. Also new panels in the control room were installed.

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44 Emergency Core Cooling System (ECCS) : It was installed to ensure residual heat removal from the reactor core in case of a loss of coolant accident (LOCA). It is a fully passive system. It has two redundant 78 m3 water storage tanks, and two physically independent piping systems, one from each tank. Flow rate is 3 m3/hr, to spray water directly from reservoirs into uncovered reactor core during 26 hours after reactor shutdown.

45 Defense in Depth : Using the principle of defense in depth, the emergency core cooling system (ECCS) is one of two systems available to ensure residual heat removal from the reactor core in case of a loss of coolant accident. The second is the reactor pool isolation system (RPÌV) described above.

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47 Revision of Safety Documents : Review of all safety related documents, like the Safety Analysis Report, Emergency Plan, Radiation Protection Plan, and Security Plan. Provision for surveillance and testing: In collaboration with an IAEA Coordinated Research Program (CRP), provision was made to assess the degradation of materials used in the reactor pool. A material surveillance programme was established to irradiate coupons of materials used in the reactor pool. Several coupons were suspended in the reactor pool to be periodically removed and inspected.

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50 COMPLIANCE WITH IAEA TECDOC 792 Aspects considered : Culture, Organization < 1970 : No dedicated group in charge of maintenance on IEA-R1 reactor. The maintenance was carried out by specific groups inside IPEN functional structure, managed and allocated as necessary by the reactor Operation Division (only when the reactor presented some problem) : Groups of maintenance were created within the Operation Division (examples: electronics, water treatment, etc) for part time activities.

51 COMPLIANCE WITH IAEA TECDOC : Specialized staff dedicated to maintain the reactor and its facilities. A permanent program was established for maintenance of the reactor : Due to changes in the organization of the Institute and other factors, the maintenance staff was dismantled. Since then these activities returned to reactor Operation Division, which was only responsible for the execution of the routines established in the Maintenance Program. Again, there was no dedicated group to discuss results and to propose changes in the maintenance program.

52 COMPLIANCE WITH IAEA TECDOC : A plan for maintenance (and testing) was elaborated with the main objective to satisfy commissioning requirements established in the Safety Analysis Report. It was a list of activities, methodologies and periodicity of tests required to assure safe operation. Another plan, called Inspection plan was presented as the Ageing Management Program. It was volunteer, and did not follow methodology of IAEA TECDOC 792.

53 COMPLIANCE WITH IAEA TECDOC 792 Maintenance program for IEAR1 Research Reactor Check of Area Radiation Monitors 1, 2 e 5 (connected to RPS) Q Check of Area Radiation Monitors 3, 4, 6, 7, 8 e 9 Y Test of nuclear overpower interlock Q Calibration of thermocouples and temperature measurement channels Q Measurement of vibration spectra for primary cooling pumps M Test of primary cooling system isolation valves Y Calibration of conductivimeters Y Test of draining system Y Maintenance of electric generators M Test of fire extinguisher (hydrants) system Y Y Yearly Q Quarterly M Monthly W Weekly

54 COMPLIANCE WITH IAEA TECDOC 792 Maintenance program for IEAR1 Research Reactor Measurement of air flow rate on reactor pool room Y Total insertion time for control rods Q Partial test of emergency core cooling system W Visual inspection of control rods Y Calibration of start up nuclear channel S Primary cooling system isolation valves Y Full test of emergency core cooling system Y Replacement of organic cables and connectors of start up nuclear channel Y Measurement of vibration spectra for primary cooling pumps M

55 COMPLIANCE WITH IAEA TECDOC 792 Inspection Program TASK COMPONENTS TEST / INSPECTION FREQUENCY 1 ESNR ( Structure ) Visual 2 Emergency coolant system Visual Bimonthly / 3 Pool liner Visual Semesterly / 4 Primary system: piping, etc Visual Annually / 5 Retention tank Leak Test Monthly / 6 Fuel elements Visual Sipping Quarterly / Semesterly / 7 Core elements storage Visual Monitoring Three years / 8 Control Element Visual Sipping Quarterly / Semesterly / 9 Control and Safety rods Visual Fall Test Semesterly / Quarterly / 10 Control rods leader Visual Semesterly / 11 Reflectors Visual 3 years / 17 Rotative equipment Vibration Monitoring Since January/97 18 Grounding System Check/ Measuring 2 years / 19 Light protection system Check/ Measuring 2 years / 24 Power command panels Full Check Annual /

56 COMPLIANCE WITH IAEA TECDOC 792 It is important to notice that, even not complying with IAEA TECDOC 792, some major repairs had to be done as a result of the testing and inspection plan, like rotation of a heat exchanger (it was found that HX A was inverted, rotated 180o), refurbishment of cooling towers, replacement of body guard on reactor pool, refurbishment of electric panels, replacement of all bearings of pumps of primary and secondary cooling systems, and corrective maintenance on blowers on cooling towers.

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62 Blower of cooling tower B

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64 COMPLIANCE WITH IAEA TECDOC The organization of IEA-R1 was restructured again, with the aim to achieve a better organizational structure and to manage adequately the ageing program. A new division, named Division of Technical Support and Maintenance, was created, and designated the responsible for the compliance of the ageing program with IAEA TECDOC 792. Other tasks were assigned : general maintenance, core management, and continuing modernization of the installation.

65 COMPLIANCE WITH IAEA TECDOC 792 After a comprehensive study of IAEA TECDOC 792, the next step was to actually apply the IAEA recommended methodology : - Selection and categorization of systems/ components/equipment susceptible to ageing - Selection of Critical Items - Ageing surveillance activities: Test/Inspection Program, Maintenance Program, and Monitoring and Diagnosis. - Data collection and records keeping. - Proposed Systems to be Monitored and Diagnosed

66 COMPLIANCE WITH IAEA TECDOC 792 To categorize the systems, components and equipment, a preliminary list containing a detailed break down of all systems into their components was prepared based on information contained in the Operational Manual and SAR. This listing was analyzed by the senior operating staff and the engineering group involved in this project until a final version was defined. The result is presented on tables 4 and 5.

67 Operation days per month 12 days Operation hours per day 24 hours 960 MWh 2 MW Total Kwh per month Average power Core: Number of fuel elements Number of dummy elements Number of control rods Number of safety rods Core Reactivity excess Pool internal condition: During the last 5 years have you observed any defect(d), discolouring (C) or corrosion (R); or carried out any modification (F) or major maintenance (T) in the followings items? A. Fuel B. Core Structure C. Pool liner D. Reflector ,6 % k/k - D,C,R,F - D,T - - D,R Cooling Systems: Have you renewed (N); carried out major maintenance (T) on, or detected any corrosion (R), malfunction (M), or leakage (L) in the followings systems? - T,L A. Primary B. Pool - N,T C. Emergency D. Make-up - T,R,M,L E. Purification - N,T,R,M F. Secondary

68 SYSTEMS / COMPONENTS SAFETY RELATED Rep. ease MECHANISMS Primary Water Coolant System 001- Pool/structure Y-Y* A 1,5,10, Liner Y-Y* B 1,5,9, Hopper Y-M B 1,5,7,9,10,12 B 1,5,7,9,10, Header Y-Y*(1) 005- Diffuser Y-M B 1,5,7,9,10, Header Movement System Y-M B 1,4,5,7,9,10, Primary Circuit Pump - B 101A Y-M B 4,5,7,8,9,10, Primary Circuit Pump - B 101B Y-M B 4,5,7,8,9,10, Inertial Flywheel - Pump 101A Y-M C 4,5,7,8,9,10, Inertial Flywheel - Pump 101B Y-M C 4,5,7,8,9,10, Heat Exchanger TC - A ( BW) Y-M B 5,7,8,9,10, Heat Exchanger TC - B (CBA) Y-M B 5,7,8,9,10, Primary Piping Y-M B 5,7,8,9,10, Radioactive retention tank (N16) Y-M B 1,5,7,9,10,12 B 4,5,7,8,9,10, Isolation Valves Y-Y*(1) 016- Check Valve Y-M B 3,5,7,9,10, Flow Control Valve Y-M C 4,5,6,7,8,9,10, Flow Meter (orifice plate) Y-M C 5,7,9,10, Valves Y-M C 4,5,7,8,9,10, Matrix Plate Y-Y* B 1,5,8,9,10, Matrix Plugs Y-Y* C 1,5,8,9, Standard Fuel Element Y-Y* B 1,2,4,5,8,9, Control Fuel Element Y-Y* B 1,2,4,5,8,9, Fission Chamber Y-Y* C 1,2,4,5,8,9,10, Compensated Ion Chamber Y-Y* C 1,2,4,5,8,9,10, Non-Compensated Ion chamber Y-Y* C 1,2,4,5,8,9,10,12 Reactor Core

69 Conclusions The pool Structure, the building structure and the biological shielding are the most important items because they are not replaceable. The pool gate, the header movement system and the dry material storage, usually not considered an important item to be monitored, showed up as an important ageing related item. Fuel elements were also included as item to be studied even though they are generally considered consumables. This is because fuel elements are in the process of qualification and also due to the fact that some of them remain quite a long time in the core ( usually between 1 and 2 years).

70 Final Recommendations. The following recommendations for future activities on IEA-R1 reactor ageing management are proposed : Maintenance a) Verify if every selected item for ageing management is included in the new revised Maintenance Program. b) Analyze whether the maintenance is adequate for the selected item. c) Review Maintenance Program accordingly. d) Verify if organizational structure, human resources and equipment inside the Institute is adequate to perform the maintenance, particularly by centralizing the management. e) Enhance predictive maintenance capability. f) Organize the history and the records about past maintenance executed and the future record keeping structure should also be analyzed.

71 Final Recommendations. Testing and Inspection Program a) Verify if every selected items for ageing management are included in the present Testing and Inspection Program. b) Analyze whether the procedures are adequate to test and inspect all ageing mechanisms involved. c) Review the Testing and Inspection Program accordingly d) Verify if organizational structure, human resources and equipment inside the Institute is adequate to perform the program, particularly by centralizing the management of the program. e) Organize the Testing and Inspections Program record keeping system.

72 Final Recommendations. Documents and Records Organization a) Full implementation of the Quality Assurance Procedures b) Reorganize the older documents performing at least classification, identification and control. c) Centralize the management of the documentation. d) Complement or redraw the missing documents.

73 Final Recommendations. Proposed Systems to be Monitored and Diagnosed a)primary Pumps Vibration Monitoring and Diagnosis System. This system was chosen because they were considered important for safety and availability of the plant. Also, reviewing the primary pumps maintenance history, one can observe that these pumps present high frequency of corrective maintenance indicating that predictive and preventive maintenance as well as testing and inspection are not effective. b) IEA-R1 Data Acquisition System (SAD) To add capability to on-line monitoring and detection of early faulty sensors, equipment and systems, the most effective way is through a plant condition on-line monitoring system. Therefore, it is advised that this system be upgraded to include artificial intelligence capability.