Development of Instruments

Transcription

1 The 5th International Symposium on Material Test Reactors (ISMTR-5) October, 2012, Holiday Inn Executive Center, Columbia, USA Development of Instruments for Improved Safety Measure for LWRs T. Takeuchi 1, A. Shibata 1, H. Nagata 1, K. Miura 2, T. Sano 3, N. Kimura 1, N. Ohtsuka 1, TSaito T. 1, J. Nakamura 1 and K. Tsuchiya 1 1: Japan Atomic Energy Agency, 4002 Narita, Oarai, Higashiibaraki, Ibaraki , Japan 2: Sukegawa Electric Co., Ltd, Namekawa-honcho, Hitachi, Ibaraki, , Japan 3: Research Reactor Institute, Kyoto University, 2, Asashiro-Nishi, Kumatori-cho, Sennan-gun, Osaka Japan 0

2 Introduction The Fukushima Dai-ichi Nuclear Power Station (Fukushima NPS) accident has the following aspects: it was triggered by a natural disaster; it led to a severe accident with ihdamage to nuclear fuel, reactor pressure vessels (RPVs) and primary containment vessels; and accidents involving multiple reactors arose at the same time. IAEA reported the 28 lessons learned in the June Mission Report. As countermeasures against severe accident in the 28 lessons learned, IAEA pointed out the enhancement of measures to prevent hydrogen explosions and enhancement of instrumentation for reactors and Primary Containment Vessels (PCVs). The Japanese government referred to a lesson of necessity of instrumentation systems working under accident conditions and Nuclear and Industrial Safety Agency suggested preventing hydrogen explosion, securing the reliability of instrumentation systems under accidents, and strengthening supervision function of plant status, etc. so as not to seriously progress nuclear accidents. Therefore, developments of new instrumentations t ti which h work well even during station ti black out are demanded. 1

3 Accident Earthquake Tsunami (reactor progress scrum) supply) Measurement target Progress of Accident and Demand of Instrumentations Accident at TEPCO's Fukushima Nuclear Power Stations (loss of power Fuel dry out hether to watch demand RPV:Water level,pressure Temp. PCV:D/W press., Temp. S/Cwater level, press, Temp. Core damage RPV:Water level l PCV:Radiation, H RPV damage PCV damag SFPsteam Hydrogen explosion Recovery of power supply Additional watch PCV:D/W water level (severe condition) H, Temp.,Irradiation R/B:H, Radiation SFP:water level, Temp., sampling Un-measurable due to loss of power supply, loss of records Influence to instrumentation RPV: Reactor Pressure Vessel PCV: Primary Containment Vessel D/W:Dry well S/C:pressure suppression chamber R/B:Reactor building SFP:Spent fuel pool Loss of reliability of instrumentation t ti due to severe condition over design demand Impossible to access to measurement panel Ref: h ti /i f / t/ t [June Mission Report] Report of Japanese Government to the IAEA Ministerial Conference on Nuclear Safety (June 2011) Lesson14 The necessity of instrumentation system working under accident conditions [NISA] `Technical information on the Accident at TEPCO s Fukushima Nuclear Power Stations (March 2012) Measure 24 Prevent of Hydrogen explosion Measure 27 Secure the reliability of instrumentation system under accident Measure 28 Strengthen supervision function of plant status 2

4 Irradiation Techniques in JMTR Maximum linear po ower density (W/cm m) IASCC test of LWR core internals Life time extension of LWR shroud Power ramping test of LWR fuels Burn up extension <Project> Well Fail -High burn-up -High burn-up (Ramping test) -High performance -Reference data 3cycle 4cycle Segment average burn up (GWd/t) 5cycle Temp. control Saturation temp. Automatic constant temp. High temp. Environmental control Water chemistry, load Special instrumentation Displacement, crack propagation Re- instrumentation (temp., pressure) Power ramping Fuel power control by 3 He gas Neutron control Spectrum adjustment Pulse irradiation Re-irradiation Assembling in hot cell High accuracy temp. control Research of radiation damage dness Thermal ageing irradiation embitterment High temp. irradiation Development of HTTR hard ITER operation, He production rate/dpa simulation Development of fusion reactor In these irradiation techniques, many instrumentations under neutron irradiation conditions have been developed in JMTR. Time 3

5 Approach for Strengthen Foundations of LWRs Development of instrumentations for hydrogen concentration, water level, temperature, and dose rate based on the fundamental irradiation technologies accumulated at JMTR Reactor building Primary containment vessel Pressure vessel Environments during severe accidents RPV: high pressure, temperature, humidity, radiation PCV: high pressure, temperature, humidity, radiation Reactor building: high radiation Measure 24 Prevention of hydrogen explosion Application of the technologies on gas sensor at JMTR hydrogen concentration sensor with solid electrolysis Measure 27 Securement of instrumentation reliability during accidents Application of the technologies on temperature measurement at JMTR multi-paired thermocouple, water level gauge Measure 28 Enhancement of reactor status monitoring Application of the technologies on radiation measurement at tjmtr self-powered neutron detector, gamma-ray detector 4

6 Development of Hydrogen Gas Sensor Prevention of gas explosion by monitoring hydrogen concentration Fukushima accident Buildings were e damaged by hydrogen explosion. Investigation of Gas analyzer for hydrogen content in reactor Items Sensor Type Thermal Controlled potential ti Semi- Solid conductivity electrolysis conductor electrolysis Temperature <65 C <50 C <50 C 600 C Humidity <90%RH <80%RH <80%RH ~100%RH Irradiation experience none none none g-ray, Neutron Sensitivity of H 2 100% <0.1% <1% ~20% Et External power necessary necessary necessary necessary Response Accuracy 5

7 Principle and structure Hydrogen Concentration Sensor with Solid Electrolysis Measurement techniques of hydrogen isotopes in sweep gas at fusion reactor blankets had been developed at JMTR Proton conductor Difference in concentration of hydrogen Evolution of electric current due to movement of hydrogen ions heater electrode Reference material H 2 concentration highh low H 2 H + H 2 Thermocouple MI cable E Performance 1.0 Temperature at sensor:700 C romotive ce (V) Electr forc 0.9 1, ,000 (hydrogen concentration:ppm) Time (min) Response to change of hydrogen concentration: less than 1 min γ-ray resistance: Gy High-temperature(700 ) and high-radiation(γ dose: ~10 7 Gy) resistance Operation using common batteries(~12 V) 6

8 Development of Thermocouple for Multipoint Measurement Increase of measurement points and its operation under unusual environments Structure Thermocouple with sheath (K-type, N-type) Measurement point Dummy rod Protection tube [mm] Performance Upper Middle Lower Irradiation test specimen Dis stance from middle point (mm) Core Temperature ( ) Thin radius Accuracy of measurement point with ±1mm Performance for 17,000 h under neutron irradiation High-temperature(700 ) and high-radiation(γ dose: ~10 7 Gy) resistance Operation using common batteries(~12 V) 7

9 Development of Water Level Gauge in LWR Constant water-level monitoring and its operation under unusual environments RPV Steam generator Steam/water separator a Steam Differential pressure Type water level l gauge (Current method) steam Recovered water tank steam Fuel Control rod Stand. water column Measurement water column water Differential pressure gauge (Signal line) (Environment at accident) High temp. High dose 8

10 Water Level Indicator with Built-in Heater and Thermo-couple It achieves continuous monitoring of water level in reactor vessel and monitoring under special conditions. Structure MIcable 200 (100m m) 4 Measurement point 4.8 [Unit : mm] 1 sensor unit 4.8 Sheath (SUS316) K-type Thermoco ouple l Chrome Measurem ment point Alumel Heater (mm) from wate er surface Distance Result Water temperature :90 C :27 C Water surface Measurement point Tempereature ( C) Measureable at high accuracy in boiled water. Confirmed by the indicator with 100m MI cable Measurable in high temperature (700 ) and high dose condition(about 10 7 Gy ) Durable for long term measurement and accuracy was improved by using plural Water level indicator. 9

11 Development of γ-ray Detector Constant radiation monitoring and its operation under unusual environments Fukushima accident Delay of recovery efforts due to failure of radiation measurement Research of γ-ray detectors Gamma Ionization chamber thermometer type detector SPGD* Environme ent Under water Temperature <200 C <200 C 600 C Irradiation experience Measurement range (Gy/h) <10 6 >10 3 >10 2 External power supply Unnecessary Necessary Unnecessary Response bad good good Accuracy bad good good * : Self-power Gamma Detector 10

12 Results of Development of γ-ray Detector Constant radiation monitoring and its operation under unusual environments Principle and Structure Measurement of current due to Compton electrons induced by γ-ray irradiation Small cross-section of neutron capture Large atomic number φ3 3.5 Selection of Pb (Cross-section of (n, γ): 0.15 b) Collector Emitter Core wire(ni) 135 Insulator(Al 2 O 3 ) MI cable utput (A) SPGD o Performance temperature:14 : SPGD A : SPGD B Co 60 distance source SPGD γ-ray intensity (Gy/h) Linearity between γ-ray intensity and SPGD output Neutron attributable fraction less than 10% High-temperature(700 ) and high-radiation(γ dose: ~10 7 Gy) resistance Improvement of measurement accuracy 11

13 Further Enhancement of Monitoring Function PCV After hydrogen explosion during the Fukushima accident, the accurate situations inside the reactor buildings could not be assessed due to the highradiation environments. This is because the accident responses were one step behind. spent fuel pool RCP suppression pool RPV Monitoring under high temperature and high radiation Operation with common batteries even during severe accident :stationary camera :movable camera Therefore, developments of radiation-proof and highresolution monitoring cameras and placement of them at many position are planned. In addition, monitoring systems s Prevention of severe accident Visualization of information in reactors (reactor power, γ-ray intensity, and so on) Real-time monitoring Spent fuel pool (Fukushima Dai-ichi Unit 1) Before accident (from TEPCO HP) During severe accident High resolution under even unusual environments Inside of the PCV (Fukushima Dai-ichi i Unit 2) conduit thermo couple grating which work without any large electric source are desirable. (from TEPCO s document on 28th March 2012) 12

14 Monitoring System Using Cherenkov Light Enhancement of monitoring function by visualization of reactor core information using Cherenkov light Structure of System γ-ray intensity Wave length Image analysis Performance CCD camera (Acquisition of core image) Image analysis (Visualization) Pico-ammeter Spectroscope MI cable Optical fiber Controller Water surface Core analysis (Neutronic Characteristics) γ-ray detector (SPGD) Core CCD camera Image analysis Visualization of Cherenkov light by analysis of image from CCD camera Determination of fading rate of camera by wave length and luminance of Cherenkov light Visualization and quantification of reactor information (reactor power, γ-ray intensity, it fuel burnup) Radiation-proof and high-resolution monitoring cameras prepared for severe accident 13

15 Outline of Measuring System and Image Analysis System Calculation code γ-ray intensity Wave length Image analysis Neutronic Evaluation Gamma ray measurement Measurement of wave length and illuminance Image analysis 1SRAC code (Burn up evaluation of fuel) 2MVP code (Spatial distribution of Neutron flux) 3ORIGEN code (Gamma ray evaluation) KUR 1 Self-powered Gamma Detector (SPGD) (γ-ray calibration test) Co-60 gamma source Distance SPGD tensity Int 1 Spectroscope (Measurement of wave length and illuminance) Visible region Cherenkov light 1CCD camera (Acquisition of reactor image) 2Image analysis (Visualization) KUR Analysis of neutron flux distribution by MVP code SPGD calibration test by Co-60 gamma source 2In-pile γ-ray measurement (At KUR) Wave length Wave length of Cherenkov light 2 Evaluation of transparency (Performance of camera, effect on wave length measurement) Establishment of reactor core analysis Establishment of Image analysis of Cherenkov light Quantification of in-core information (Reactor power, γ-ray intensity, and burn-up of fuels) 14

16 Conclusions We are developing the instrumentation monitoring reactor situations for improved safety measure for LWRs based on the lessons from the Fukushima accident. Self-powered and low-voltage working type instrumentations were adopted considering station black out. The preliminary verification tests were successfully performed and their results suggested the possibility of the practical applications well. in future The in-pile testing at the JMTR to evaluate the performance of these objects. 15