Seismic-Initiated events risk mitigation

Transcription

1 Seismic-Initiated events risk mitigation in LEad-cooled Reactors The damaging effects of earthquakes on Nuclear Power Plants Dr. Antonio Moreno 1 Training course on seismic protection of lead-cooled reactors Verona, May 25 th 2012

2 TABLE OF CONTENTS Kashiwasaki-Kariva Fukushima-Daini Fukushima-Daiichi 5 6 Assessment of seismic margins Concluding remarks 2

3 2007 Niigata Chuetsu-Oki Kashiwasaki Kariwa 2011 Tohoku-taiheiyou-Oki Fukushima Daiichi 3

4 4

5 Eartquakes in Japan Kashiwasaki-Kariva 7 Units 5

6 Eartquakes in Japan NCO earthquake intensity 6

7 KK observed/ design 7

8 KK Site tour Components clasification 8

9 KK Site Three fundamental safety functions guaranted Shutdown Cooling Contaiment isolation 9

10 EPRI walkdown 10

11 KK Site tour Condition of class A/As SSCs. OK 11

12 KK Site tour Condition of class A/As SSCs. OK 12

13 KK Site tour Unit 3:_ House transformer fire 13

14 KK Site tour/epri Ground settlement caused displacement of bellows 14

15 EPRI Walkdown 15

16 EPRI Walkdown/KK tour Tank wall and anchorage damage 16

17 EPRI Walkdown 17

18 EPRI Walkdown 18

19 EPRI Walkdown 19

20 EPRI Walkdown 20

21 EPRI Walkdown/KK site tour Settlement generates road damages 21

22 EPRI Walkdown Crane damage 22

23 EPRI Walkdown 23

24 EPRI Walkdown 24

25 : EPRI Walkdown Conclusions and lessons learned. EPRI peer review Kashiwasaki-Kariwa KK safety-related structures, systems and components performed very well in response to the NCO earthquake. No significant damage was detected Supports and anchorage were very rugged with considerable seismic margin in their design Seismic system interactions( non-safety equipment) were minimed based on anchorage and maintenance practices Japanese seismic design criteris include conservatisms in both dynamic analysis as well as the static analysis of SSC s designs Soil failures affected many areas outside of the safety related structures 25

26 : EPRI Walkdown Instances of damages where identified: Some damage was found on the class B/C SSCs. House transformer fire Outside tank failures (buckling, attached pipes failures and tank wall ruptures Underground fire suppresion piping failures Yard structure fondation failures and subsidence (liquefaccion induced) Stack and transmission tower damage Pump house foundation and structure failures Water treatment component anchorage failures Falling control room ceiling items ( light fixtures and ceiling diffusers) 26

27 KK Post earthquake actions (TEPCO) 27

28 KK Post earthquake actions (TEPCO) Observed data as well as geological survey will define new design basis seismic acceleration Ss 28

29 Eartquakes in Japan: Design basis after KK earthquake Ss Fukushima : 489 Gal, Daiichi, 434 Gal, Daini Upgrading to 600 Gal ( 2008) Ss Kashiwasaki Kariwa 1000 Gal ( 2008) Upgrading to 2280 Gal Chubu s Hamaoka 800 gal ( 2007). Upgrading to 1000 Gal Diablo Canyon 735 Gal San Onofre 657 Gal Nort Anna 176 gal ( Shut down with 255 Gal) WNA nuclear power plants and earthquakes

30 KK Post earthquake actions (TEPCO) Strengthening Emergency Preparedness 30

31 Fukushima-Daini EPRI Walkdown 4 Units 31 Registered 254 Gal Design 434 Gal

32 Fukushima-Daini EPRI Walkdown 32

33 Fukushima-Daini EPRI Walkdown The seismic team inspected a cross-section of 27 types of SSC s important for safety in NPP s. Safety related SSCs did not appear to have evidence of seismic damage Non-safety related SSCs performed well to the seismic loading and very few instances of seismic damage to non safety items where observed Safety-related buildings,foundations and equipment were in excellent conditions,with no signs of damage 33

34 Fukushima-Daiichi INPO Report, 6 Units 34

35 Fukushima-Daiichi INPO Report Registered 550 Gal Design 489 Gal 35

36 Fukushima-Daini EPRI Walkdown 36

37 Fukushima-Daiichi INPO Report TSUNAMI: 14 m for both plants Local ground level: Daiichi 10 m above sea level Daini 13 m above sea level 37

38 NPPs structures Thick reinforced walls 38

39 Methodology for assessment of NPP seismic margin EPRI-NP-6041 PREPARATORY WORK: Sample of distribution systems and structures SCREENING CRITERIA: EPRI-NP 6041 Table 2,3 and 2,4 SAMPLE SELECTION The SSEL list ( Safe Shutdown Equipment list) 39

40 EPRI-NP-6041 STRUCTURES Containment ASME Sec III Concrete structures: ACI, Steel frame structures: AISC, ductility Masonry walls (blocks) (Stability) Ceilings in control room 40

41 EPRI-NP-6041 SUBSYSTEMS. Generic evaluation Electrical raceways & Conduits: Electrical equipment: Nº 1 : MCC,L&M Voltage switchgears Nº 2 batteries and racks Nº 3 battery charger and invertors Nº 4 transformers Nº 5 Control and Instrumentation Panels Nº 6 Instrument racks Nº 7 Distribution panels Nº 8 Local Instrument /temperature sensors Nº 9 Engine generator Nº 10 Motor generator 41

42 EPRI-NP-6041 PIPING Mechanical components: HVAC Nº 11 Horizontal pump Nº 12 Vertical Pumps Nº13 Air operatedpneumatic9 valves Nº 14 motor Operated valves Nº 15 solenoid Operated Valves Nº 19 Frame or Skirt supported Vertical tanks/ Heat exchangers Nº 20 Horizontal Saddle or cradle Supported tank/ Heat exchanger Nº 23 NSSS Components / Primary cooling Fans,chillers Air Compressor Nº 16 Air compressor Nº 17 Fan and air Handler Nº 18 Chiller Unit 42

43 SUMMARY OF CIVIL STRUCTURES SCREENING CRITERIA FOR SEISMIC MARGIN EVALUATION 43

44 SUMMARY OF CIVIL STRUCTURES SCREENING CRITERIA FOR SEISMIC MARGIN EVALUATION a. Major penetrations should be evaluated. b. Major and minor penetrations should be evaluated. The concrete containment structure only needs to be evaluated for a 5-percent damped peak spectral acceleration exceeding 2.0g. c. No evaluation required if base mat is integral part of pressure boundary or steel pressure boundary is keyed to base mat to prevent slipping. d. Mark I tori require evaluation for earthquakes exceeding the design basis. e. Evaluation not required for Category I structures if design was for a SSE of 0.1 g or greater. f. Evaluation not required for Category I structures if design was by dynamic analysis for a SSE of 0,1 g or greater, and if the structure complies with ACI or ACI or later editions ductility detailing requirements. g. Evaluation not required for Category I structures if design was by dynamic analysis for a SSE of 0.1 g or greater, and if the diaphragm complies with ACI or ACI or later editions ductility detailing requirements, provided the diaphragm seismic loads were explicitly calculated. h. Evaluation not required if structures were designed using dynamic analysis and meet the requirements of AISC, 7th Edition, 1970 or later. i. Inspect for adequacy of bracing or safety wiring. j. Investigation can be limited to potential for electrical malfunction (relay or contactor chatter) and loss of equipment anchorage in immediate vicinity of impact. k. Evaluation not required provided the structure is capable of meeting the 1985 UBC Zone 4 requirements. l. Refer to Appendix C and Section 7 for screening criteria. 44

45 SUMMARY OF EQUIPMENT AND SUBSYSTEMS SCREENING CRITERIA FOR S.M. EVALUATION 45

46 SUMMARY OF EQUIPMENT AND SUBSYSTEMS SCREENING CRITERIA FOR SEISMIC MARGIN EVALUATION Equipment Type <0.8g g >1.2g Transformers (u)(v) (u)(v) yes Battery chargers (w) (w) yes Inverters (w) (w) yes Instrumentation and control (s)(t) (s)(t) yes panels and racks Temperature sensors No (x) yes Pressure and level sensors No' (x) yes NOTES: a.bwr piping with suspected intergranular stress corrosion cracking may require evaluation. b.evaluation not required if supports are designed for combined loading determined by dynamic SSE and pipe break analysis. c.regardless of footnote (b), evaluation is recommended for PWR pressurizer supports and BWR reactor vessel and recirculation pump supports. d.evaluation not required if CRD housing has lateral seismic support. e.walkdown of representative piping and ducting systems should be conducted following Section 5 guidance. f.evaluation recommended for MOVs in piping lines of 2 inches diameter or less. g.walkdown to assure that valves do not ímpact adjacent structures or equipment. h.margin evaluation only needs to consider anchorage and supports. i.for vessels designed by dynamic analysis or equivalent static analysis enveloping vessel inertial and piping loading, only the anchorage and supports require evaluation. For vessels not meeting these criteria, all potential failure modes require evaluation. j.evaluation of piping connections is required. Other failure modes do not require evaluation. 'Note that pressure and level sensor will not fail at spectral accelerations below 0.8g; however, systems engineers should be aware that these sensors may record a change in state due to the earthquake motion 46

47 SUMMARY OF EQUIPMENT AND SUBSYSTEMS SCREENING CRITERIA FOR S.M. EVALUATION k. Batteries mounted in braced racks designed for seismic loads or qualified by dynamic testing do not require evaluation. Rigid spacers batteries and end restraints are required. Batteries should be tightly supported by side rails. l. Margin review should be conducted for anchorage and attachment of peripheral equipment. Can be done by visual inspection for a peak spectral acceleration of 0.8g or less. m. Margin evaluation required for vertical pumps with unsupported lengths of casing below the flange exceeding 20 feet or pumps with shafts unsupported at their lower end. n. All units supported on vibration isolators require evaluation of anchorage. o. Evaluation should focus on anchorage and supports. p. Evaluation required only for potentially large relative displacements between structures or equipment and structures. q. See Appendix A, "Cable Trays and Cabling" for guidance. r. No evaluation required if supports generally meet the National Electrical Code. s. Walkdown should be conducted to verify that the instruments are properly attached to the cabinets. t. Relays, contactors, switches, and breakers must be evaluated for chatter and trip if functionality during strong shaking is required. u. Anchorage evaluation required. v. Liquid-filled transformers require evaluation of overpressure safety switches. The transformer coils should be restrained within the cabinet for dry transformers. w. Solid state units require anchorage checks. Others require evaluation. x. Insufficient data are available for screening guidelines. Emphasis should be on attachments. y. Units mounted on structures at elevations exceeding 40 feet aboye grade should be reviewed if realistic (median centered) SME 5% damped horizontal floor spectra exceed 2g. z. Insufficient data to enable recommendations to be made. 47

48 48 Category 4 (GIP1, SMA 1): Motor Control Centers

49 Earthquake experience Anchorage 49

50 50 Category 4 (GIP2, SMA 1): Low Voltage Switchgear

51 Number of Low Voltage Switchgear Ceramic base and fiberglass supports 51

52 52 Category 2 (GIP HP 5, VP6, SMA HP 11,VP 12): Pumps

53 53 Category 2 (GIP HP 5, VP6, SMA HP 11,VP 12): Pumps

54 Number of Horizontal Pumps Ground settelement 54

55 Number of Vertical Pumps Ground settelment 55

56 Category 9 (GIP FOV 7, MOV8, SMA FOV 13,14, MOV15):Valves 56 Fluid operated valve

57 57 Category 9 (GIP FOV 7, MOV8, SMA FOV 13,14, MOV15):Valves

58 Category 9 (GIP FOV 7, MOV8, SMA FOV 13,14, MOV15):Valves Motor operated valve 58

59 Number of Motor-Operated Valves Interaction 59

60 CONCLUDING REMARKS NPPs perform properly their safety functions in case of earthquakes above design NPP structures are not damaged in case of earthquakes above design Seismic risk is continuously upgrading and translated to design SSCs of the NPPs have a significant seismic margin 60