Verification of Safety for Reinstalled Class-1E Cable in Shin-Kori Unit 3

Transcription

1 ID Verification of Safety for Reinstalled Class-1E in Shin-Kori Unit 3 Sang-Hwa Lee, Hong-seok Jang, Young-sik Cho Korea Institute of Nuclear Safety 62, Gwahak-ro, Yuseong-gu, Daejeon , Korea Abstract In 2013, Korea Institute of Nuclear Safety (KINS) had found that Environmental Qualification (EQ) test data of Shin-Kori nuclear power plant unit 3under construction was counterfeited by certificate holder. We had immediately performed regulatory actions which included thorough inspections to find out at which units these falsely certified cables were installed and replacement of them once found. After the Korea Hydro & Nuclear (KHNP) had carried out replaced medium and low voltage power cables, control and instrument cables, we had verified integrity of cable performance through review EQ test report and preoperational inspection of reinstalled cables. In this results, we had not only reconfirmed the safety of the Advanced Reactor 1400 (APR 1400) but also special inspection results reporting to the Nuclear Safety and Security Commission (NSSC). Finally, Shin-Kori unit 3 had been approved operating license by the NSSC and preparing for commercial operation until July Keywords: Aging,, Environmental Qualification, Nuclear power plant 1 INTRODUCTION After the Fukushima Daiichi nuclear power plant accident, the Ombudsman System was adopted to prevent such an absurdness of nuclear safety by the NSSC in Korea because the public have been getting more anxiety about the safety of nuclear power plant. In this regard, the ombudsman received a report of falsified EQ data about safety class cables installed in Shin-Kori Unit 3. Therefore, the KINS staff had identified the counterfeit facts about EQ data on Loss of Coolant Accident (LOCA) and flame testing of installed cable which was not meet the regulatory standards. We recommended that the all of installed power, control, instrumentation cables should be replaced by new qualified cable. In order to replace the safety cables, the KHNP made purchasing contract with the cable manufacturer about Class-1E 5 kv power cable and 600 V power, 600 V control and instrument cables. EQ test was performed by cable manufacture and EQ report for verifying performance of cables that was reviewed by the Korea Electric Corporation Engineering Company (KEPCO E&C). And its result was submitted to the KINS, we performed to technical review according to technical standard requirements, IEEE Std. 323 and IEEE Std Also, the special inspect of supplied cables were confirmed with verifying fault of cable insulation, withstand voltage test and continuous shielding tape of cable test in order that verify by acceptance and performance test result of new installed cables. After reinstalled all of cables, the installation inspection and performance tests equivalent to preoperational inspection were carried out for verifying relevant safety system performance of nuclear power plant. These regulatory experience could be an exceptional circumstance in domestic as well as internationally. Besides the strengthen regulation on the EQ of nuclear power plant facility will be good practice in regulatory field. In this work, we had performed to verify the integrity of cable by reviewing the EQ report and inspecting performance of reinstalled Class 1E cables. On the basis of results, performance of cables had been evaluated in Shin-Kori unit 3 according to IEEE standards. 2 QUALIFICATION TEST OF CABLES The objective of EQ test is to provide reasonable assurance that the cable will operate or demand, under specified service conditions, meet system performance requirements. The specified service conditions include normal operating and DBE (Design Basis Event) conditions at end of its expected service life. EQ test have performed on a generic basis on a plant specific basis developed around predicted worst case accident condition [1]. EQ test are performed following as the test step: 1. Test specimen preparation 2. Baseline functional test 3. Thermal aging 4. Radiation aging 5. Post-Thermal & radiation aging functional test 6. DBE environment simulation 7. Post-DBE functional test manufacturer had carried out EQ test of Class 1E cables considering operating and accident condition of Shin-Kori unit 3. In order to verify conformity of test results, we performed to review each step in EQ test process and result according with

2 technical requirement and standards [2-4]. 2.1 Conformance of test specimens The test specimens shall be representative of a conductor, insulation, filler, jacket, binder type, shielding, and splice of installed cables. Therefore, the qualified specimen cables of the same basic design and materials were selected as shown Table 1 based on IEEE standard [3]. Table 1. Specimens of installed cable in Shin-Kori Unit3 description 5 kv Medium Voltage 600 V & Control 600 V Control & Instrument 2.2 Thermal aging 1/C 4/0 AWG compressed bare copper conductor 5 kv 90 Conductor stress control layer (0.3 mm) Ethylene propylene rubber insulation (2.79 mm) Semiconducting insulation shield (0.76 mm) Tinned copper (0.13 mm) 1/C 4 AWG Single Conductor 600 V 90 1/C 4 AWG 7 StrandX1.96mm Tinned Copper Irradiation Cross-Linked Flame Retardant Polyethylene (0.64 mm) CSPE Jacket (1.14 mm) 7/C 14 AWG and Control 600 V 90 7X1/C 14 AWG 7 Strand X0.61 mm Tinned Copper Irradiation Cross-Linked Flame Retardant Polyethylene (0.81 mm) Mylar Binder Tape (0.05 mm) CSPE Jacket (1.14 mm) 1/C 14 AWG Single Conductor 600 V 90 1/C 14 AWG 7 StrandX0.61 mm Tinned Copper Irradiation Cross-Linked Flame Retardant Polyethylene (0.64 mm) 2/C 16AWG Control and Instrumentation 600 V 90 Irradiation Cross-Linked Flame Retardant Polyethylene (1.32 mm) 18 AWG 16 Strand X0.03 mm Tinned Copper Drain Wire Copper/Polyester Shield Type Overall (0.05 mm) Nomex Binder Tape (0.05 mm) CSPE Jacket (1.14 mm) Thermal aging always exists to installed cables inside containment. Accelerated thermal aging is achieved by exposing the cables to temperatures significantly higher than the expected operation temperature. The parameters of Arrhenius relationship between temperature and rate of degradation is typically used for determination of the acceleration factor. Each of cable materials was evaluated to calculate activation energy by elongation at break. The activation energy value of cable materials were used for evaluation service life time of cable and determined thermal aging temperature and time through Arrhenius eq.(1) [5], [6]. = ( ) (1) Where Ø is the Activation energy(ev), K is the Boltzman s constant ( ev/ K), t is aging period at test temperature (hours), T Ser is the normal service temperature ( K), T Age is the thermal aging temperature ( K). Aging parameter of all specimens was considered to operating temperature for operating time 60 years. In the case of medium voltage power cable, the activation energy of cable insulation was estimated ev and aging parameters were calculated temperature 438 K(165 ) and aging time 620 hours at operating temperature 363 K(90 ) for operating years. The jacket activation energy was obtained ev and its aging parameters were calculated aging temperature 438 K(165 ), aging time 150 hours at operating temperature 343 K(70 ) for operating years. The specimens of 600 V control & instrument cable, activation energy of insulation was calculated ev and aged temperature 423 K(150 ) aging time for 1300 hours at operating temperature 363 K(90 ) for years. The jacket activation energy was estimated ev and calculated aged temperature 394 K(121 ), aging time for 660 hours considering at operating temperature 328 K(55 ) for years. In case of 600 V power cable, the activation energies of insulation and jacket were estimated and ev, aging time for 1300 and 1100 hours at aging temperature 423 K(150 ) and 409 K(121 ), operating temperature at 363 K(90 ) and 343 K(70 ) for and years. In this reviewed results, each activation energy values of cable insulation and jacket were used to determine appropriate thermal aging temperature and time based on the normal operating condition temperature and operating time 60 years according to IEEE standards [3],[4]. And cable manufacture properly performed to thermal aging of all cable specimens of Shin-Kori unit 3. The calculated aging temperature and time values of each cable are tabulated in Table 2. Table 2. Thermal aging parameters of cable 5 kv Medium 600 V 600V Voltage Control & Parameters Instrument Insulation Jacket Insulation Jacket Insulation Jacket t (hours) TSe r( K ) TAge( K ) Ø (ev) K Boltzman's constant ( ev/ K)

3 2.3 Radiation aging The radiation aging component of an accelerated aging test normally includes subjecting the test specimen to the total expected lifetime dose before DBE in a short time, which means a much higher dose rate than under normal operating conditions. The acceleration factor is defined by the ratio between the dose rate used in the artificial aging and the dose rate in operating conditions. In a radiation environment, insulation materials of cable are known to be sensitive to dose rate effects. The radiation dose was determined according to environment condition of installed cables, thus radiation aging values of cable have differential values [1]. The medium power voltage cable specimens were subjected to gamma radiation from a Cobalt-60 source in air at a rate less than less than Gy per hour for a total minimum dose of Gy air equivalent dose. For 600 V power, control and instrumentation cables, 10% over the standard Gy total integrated dosage was used ( Gy). This irradiation values were assumed for the normal service dosage and the accident dosage. Actual received dose values of each cable are showed in Table 3 [5], [6]. From reviewed EQ report, we confirmed to meet the requirement when NPP dose values compared to test dose values. In results of functional test, all of cables were satisfied with relevant criteria. ID 1 2 Table 3. specimens for radiation aging specimens Total Integrated Dose rate(gy) 5 kv Medium Voltage V Control & Instrument Insulation V Control V Control & Instrument 600 V Insulation V Following the insulation resistance measurement, the mandrels containing the specimens were immersed in room temperature water. While immersed, the specimens were subjected to for 5 minute withstand voltage test. The voltage is applied 80 V/mil AC and insulation resistance is measured. In standard requirement, criteria values of leakage current are defined as, IR criteria values are defined as control & instrument cable 2.5 MΩ, and low power cable above 1 MΩ In case of medium voltage power cable, Flame test shall be performed Vertical Tray Flame Test (VTFT) according to IEEE standard [3]. The completion of thermal and radiation aged and unaged specimens were installed cable tray and applied flame source temperature at 815 for 20 minutes. Acceptance criteria should not only be burned, but extinguished the fire. From reviewed test report, specimen suitability, test method, procedure and results were satisfied with requirement. 2.5 DBA environment simulation testing After completion of thermal aging and radiation exposure, the specimens were subjected DBE tests in accordance with requirement. The tests were conducted to determine the ability of the cables to function during postulated environmental conditions simulating normal and DBE/LOCA service conditions expected within the containment area of nuclear power generating station [4]. Specimen cables were subjected to exposure environment of steam and chemical-spray according to environmental condition of installed cable while electrically energized at rated voltage and current. manufacturer carried out DBE test considering cable operating condition as shown in Fig.1. The first ramp was performed using superheated steam. The duration was only 8 minutes. Superheated steam was used for the first 8 minutes of the second ramp. At the 8 minute point, the test requirements were 350 (177 ) and 120psig, which was saturated. Saturated steam was used from the 8 minute point until the end of the test [6]. 2.4 Post-thermal and radiation aging functional testing Generally, upon completion of the thermal and radiation aging of the test program, a visual examination, a 20 times mandrel bend, dielectric proof tests, and insulation resistance tests were performed on sample cables to evaluate specimen integrity. Finally, visual examination of the specimens is performed to determine the physical condition of the sample after the mandrel test. Functional test of EQ program is measured using megaohmmeter and applying 500Vdc for a minimum of one minute. (a) Temperature

4 3 INSPECTION AND PERFORMANCE TEST 3.1 Facility inspection After reviewed EQ report of reinstalled safety class cables, we performed follow-up inspect to verify suitability of replaced cable in Table 5 concerning redundancy, independence, separation distance, identification visible, support installation and ground condition in accordance with IEEE standard [7]. (b) Pressure Fig.1 Temperature and pressure profiles of LOCA test In this results, test conditions satisfied with operating hours, pressure and temperature of the final safety analysis report (FSAR) 3.11 section environment conditions of Shin-Kori 3 as shown in Fig. 2. Table 5. Replaced cable distance in Shin-Kori Unit 3 Type of 5 / 15 kv 600 V Control & Instrument Distance 10 km 117 km 305 km 155 km In inspection process, we detected several of major insulation and internal defects among supplied cables. Control cable (12 Core 16 AWG) was discovered the regularly interval damage of insulation in 3 core of 12 core shown in Fig. 3 (a). And Fig. 3 (b) shows the defect cable which was damaged in external jacket and insulation. We carried out visual inspection and immerged withstand voltage test of including this defect of cable reels through 10ft sampling method applying EPRI technical report [8]. Fig.2 Temperature and pressure profile during LOCA in containment building of Shin-Kori Unit 3 The specimens of cable were sprayed with chemical solution after reaching at 320 during approximately sixth hour and continuing through the end of the environmental exposure. Chemical spray solution consisted of 0.48 molar H 3BO 3 and Molar NaS 2O 3 buffered with NaOH to a PH of 10.5 at 25±5 in according to FSAR and IEEE standard [4], [6]. All cables successfully completed the LOCA simulation while electrically energized at rated voltage with a load current. Post LOCA functional tests successfully were completed by IR measurement and withstand voltage test. We confirmed integrity of accelerated aging cables and EQ report satisfied with standard requirement by reviewing EQ test results [5], [6]. (a) Damage of insulation (b) Damage of jacket and insulation Fig. 3 Control cable (12 Core 16 AWG) defect

5 Fig.4 shows the experimental set up was comprised of a DC overvoltage generator for withstand voltage test. The test criteria was adopted DC voltage source rated increasing to 7.5 kv dc during 60 sec and retaining 5 minutes without insulation breakdown according with NEMA Code [9]. From this test result, all specimen cables were satisfied with test criteria. Fig. 6 Signal measuring test setup Mandrel specimen Fig. 4 DC withstand voltage test setup In case of Fig. 5, I&C cable (2C 16AWG) was detected that omitted part of shielding type in cable. KHNP had performed to discard detected defect cable drum and requested a detect method test of defect cable to Korea Test Laboratory (KTL) for verify integrity of relevant I&C cable. Fig. 5 I&C cable (2 Core 16 AWG) defect Fig. 6 shows a brief layout of the signal detecting experiment method by KTL. In order to measure from cable signals, experiment was consisted using signal generator, sensor, and signal receiver. The source signal applied the signal generator was detected by sensor and then measured using signal receiver. In order to conduct this test, two kinds of specimens were used normal and omitted shield type cable for analysis differential signal wave magnitude. From the test result, signal wave magnitude of defect cable was measured high than normal cable and obtained a reference value. KHNP adopted signal measuring test method invented by KTL and performed test of sampling cable through EPRI technical report [8], thereby verifying the integrity of I&C cables. We finally verified integrity relevant to all defect cables through the KHNP performance and facility inspection result. 3.2 Performance inspection After completion of reinstall class-1e cables, we performed to recheck cable performance through operating condition of major facility and main control room (MCR) alarm relation with safety system. The inspected facilities in approximately 52 equipment were including Reactor Cooling System (RCS), main device, facility, and system. From the inspect result, all of major device and system were confirmed to meet criteria values in procedure and requirement as shown in Table 6. Table 6. Performance inspect results of main system Inspection item Reactor Coolant System Control rod and system Inspection content - Conformance with performance of RCS valve, pump - Pressurizer heater and MCR indicate position - Control and cable voltage - continuous - Signal indication of ex-core instrument system Inspection result The operation test results of RCS valve, pump, and pressurizer heater were confirmed to meet the procedure criteria values In 4 control cable, cable voltage was measured up to 127 Vdc. In 189 control cable, continuous characteristic was confirmed to maintain safety condition. Also Signal indication values were verified to meet the procedure criteria.

6 Shutdown Cooling System - Confirmation of start and stop of Motor operation valve (MOV) and pump at MCR control signal The test results of 2 motor and 24 MOV units were confirmed to meet the procedures and technical standards Contact Address: k720lsh@kins.re.kr 6 CONCLUSION The KHNP had replaced with medium and low voltage power cables, control and instrument cables in Shin-Kori unit 3 because EQ date of Class-1E cable was counterfeited by certificate holder. And we had confirmed to verify the integrity of cable and meet the technical requirements through reviewing EQ test report and preoperational inspection of reinstalled cables. From this reviewed results, we had not only reconfirmed the safety of the APR 1400 nuclear power plant equipment but also special inspection results reporting to the NSSC. Finally, Shin- Kori unit 3 had been approved operating license by the NSSC and preparing for commercial operation until July ACKNOWLEDOGEMENT This work was supported by the Nuclear Safety Research Program through the Korea Foundation of Nuclear Safety (KoFONS), granted financial resource from the Nuclear Safety and Security Commission (NSSC), Republic of Korea (No HD130). REFERENCES [1] S.H Lee, J.D Lee, M.Y Kim, H.S Jang, C.H Jeong, Evaluation of Accelerated Aging s Used in Nuclear Plant, International Conference on Condition Monitoring and Diagnosis (CMD), pp , 2012 [2] Qualification Tests of Electric s, Field Splices, a nd Connections for Light-Water-Cooled Nuclear Plants Reg. Guide [3] IEEE Standard for Type Test of Class IE Electric s, Field Splices, and Connections for Nuclear Generating Stations, IEEE [4] IEEE Standard for Qualifying Class IE Equipment for Nuclear Generating Stations, IEEE & 1983 [5] Environmental Qualification Document for MV s, E241D-ER-A01-02 [6] Environmental Qualification Document for LV s, E241D-ER-A01-01 [7] IEEE Standard Criteria for Independence of Class 1E Equipment and Circuit, IEEE Std [8] Guideline for Sampling in the Commercial-Grade Item Acceptance Process, EPRI TR R1 [9] Standard Test Methods for Extruded Dielectric, Control, Instrumentation, and Portable s for Test, ANSI/ICEA T /NEMA WC 53