Regulation Experience and Analysis Result for LOOP of Nuclear Power Plant in KOREA

Regulation Experience and Analysis Result for LOOP of Nuclear Power Plant in KOREA

S. U. Moon

Korea institute of nuclear safety,

P.P. BOX 114, Yuseong, Daejeon, 305-600

K. J. Kim

Department of Electrical Engineering, ChungNam National University, Daejeon, 305-764

AbstractCaused Analysis for LOOP (Loss of Offsite Power) in NPP shall be review and inspection, before performing evaluation, for trip signal was caused T/G or reactor trip. LOOP event has affected for safety class in NPP. This paper was show that experience and result for LOOP, and presently compared and comment for proposal to reduce it.

Index Terms LOOP, reliability, deregulation and frequency

1. INTRODUCTION

   Treferred power supply (PPS), which power supply from the transmission system to the Class 1E distribution system that is preferred to furnish electric power under accident and post-accident conditions. LOOP means completely loss for offsite ac source of PPS and EDG shall be automatically started by under-voltage signal at Class 1E bus. [4]

   LOOP sorted 4 categories by 2009 from KR #1 to UJ #6 in Korea by NUREG/CR-6890 comments, and LOOP frequency related to situation of every country by electric-power restructured policy. [6]

   NRC should requires to FERC and NERC for reflect reliability concept at power system and for performance evaluation and corrective activity about interface facility, and LOOP evaluated that is influenced directly or indirectly to CDF (core damage frequency) by systems failure and LOOP event are steadily increased by interface equipment of NPP and Grid. [5][6][13][14]

   This paper compared and analyzed for cause and frequency of LOOP event by 2009 in Korea that noticed regulation position and experience.

2. REGULATION EXPERIENCE AND ANALYSIS RESULTS

   1. Nuclear position

      1. Korea

         2009, nuclear energy focus on stable electric power source at 35% in total power generation with table , and more is increasing construction sites by green growth policy and global warming effect. [3]

         Table Power generation condition for 5 years (GWh, %)

         Year	nuclear	Coal	LNG	oil	hydro	recycle	total
         2005	140,367 (41.42)	129,231 (38.13)	48,281 (14.25)	16,704 (4.93)	1,503 (0.44)	2,774 (0.82)	338,861 (100)
         2006	142,114 (40.05)	134,480 (37.89)	57,074 (16.08)	15,482 (4.36)	1,741 (0.49)	3,976 (1.12)	354,869 (100)
         2007	136,599 (36.49)	149,113 (39.83)	65,666 (17.54)	16,556 (4.42)	1,398 (0.37)	5,051 (1.35)	374,384 (100)
         2008	144,254 (36.77)	166,728 (42.50)	65,155 (16.61)	8,965 (2.29)	2,480 (0.63)	4,740 (1.21)	392,322 (100)
         2009	141.123 (34.79)	186,137 (45.88)	57,555 (14.19)	12,689 (3.17)	2,814 (0.69)	5,193 (1.28)	405,692 (100)

      2. America and Canada

      2005, nuclear energy has of base or preliminary power source by 20% in electric power, and construction of the latest new nuclear reactor is planned more than 20 reactors. And NRC assisted and FERC approved NERC NUC-001-1 at 2007, including probability reliability evaluation for electric power since North America blackout. 2005, Canada Nuclear Regulatory Commission (CNSC) approved regulation guideline S-98. [8] [9]

   2. Frequency Model [16]

   General frequency model use Poisson distribution and binomial distribution by trip events

   1. Poisson distribution

      1. The frequency event occurred in any specified short exposure time period is approximately proportional to reactor operation of time period

      2. Approximately simultaneous events do not occur.

      3. Occurrences of events in disjoint exposure time period are statistically independent.

      4. As a minimum, the total number of events and the corresponding time period are observed.

      5. The above assumptions, number of occurrences X in some Fixed time t is a Poisson distributed random variable with mean =t, Pr(X = x) = /!

   2. Binomial distribution

      1. On each demand, the outcome is a failure with some probability , and a success with probability 1- . This probability is the same for all demands.

      2. Occurrences of failures for different demands are statistically independent.

      3. As a minimum, the total number of failures and number of demands are observed.

      4. The above assumptions, the random number is failure X, in some fixed number of demands n, Pr(X = x) = ()(1 ), = 0, , where

   excluded in Table . LOOP events are total 13, power plant related (5:38%), weather related (4:31%) are mostly occupy on LOOP caused, and 2 of 6 LOOP happened during O/H by a human errors. Therefore, security minds usually consistently

   shall be emphasis on to workers. [15]

   !

   () = ! ( )!

   1. LOOP regulation experience and result

      1. America

         System accident of Grid and interface equipment faults had increased due to avoiding maintenance investment for power system since electric power market deregulation, 1996. According to Table and Table , classifies LOOP Event total 135 events by electric-power restructured, but the US reduces owing to force on corrective activity and reliability evaluation for PPS on utilities, interface facility, since 2003 North America blackout, and recently it is in declining tendency that LOOP event only happens one event for 104 reactors from 2007 to 2009 after NUREG 6890 report. [6][10] [11] [12]

         Table Power system restructure (before and after) frequency

         3.59E-02

         Items	Categor y	1986-1996			1997-2004
         		even t	Op/yea r	frequenc y	even t	Op/yea r	frequenc y
         Operation	Plant	11	877.2	3.31E-02	1	724.3	2.07E-03
         	SWYD	23	877.2	2.68E-02	7	724.3	1.04E-02
         	Grid	1	877.2	1.71E-03	13	724.3	1.86E-02
         	Weather	3	877.2	3.99E-03	3	724.3	4.83E-03
         	total	38	–	4.56E-02	24	–
         Stop/ maintenanc e	Plant	14	278.5	5.21E-02	5	104.7	5.25E-02
         	SWYD	31	278.5	1.13E-01	7	104.7	7.16E-02
         	Grid	1	278.5	5.39E-03	2	104.7	2.39E-02
         	Weather	9	278.5	3.41E-02	4	104.7	4.30E-02
         	total	55	–	2.05E-01	18	–	1.91E-01

         Table Event count LOOP cause

         Category	Externa l	Hard ware	Human error		Power syste m	Weathe r worst	tota l	Percen t
         			Ope r atio n	Sto p O/H
         Plant	–	1 1	8	12	–	3	34	23
         SWYD	–	4 2	3	21	1	8	75	51
         Grid	–	3	1	–	14	–	18	12
         Weathe r	6	–	–	–	–	15	21	14
         total	6	5 6	12	33	15	26	148	100
         Percent	4	3 8	8	22	10	18	100

      2. Korea

      Since KR #1 commerce at 1978, LOOP event analyzed for actuality occurrence signal, for 31 years operation, total 20 nuclear reactors to 2009 presently. Trip number for Initial operation periods was decreased by repair and design change of power system at prefer time under government control for PPS and interface facility, but difficulty is started after possession and administration control were divided since electric-power industry restructured. Here, Small LOOP

      Table LOOP Event in Korea (*source: Http://opis.kins.re.kr)

      No	Plant	Occ Time	Occurrence Causes	RTN Time
      1	W1	1985.04.19	#1, #2 T/L trip by CB trip delay	1985.04.25
      2	K4	1986.08.28	LA destroy, M.Tr 87 By BERA	1986.09.04
      3	K2	1987.04.21	T/L grounding and short	1987.04.22
      4	K1	1987.07.15	T/L short by storm and cascading	1987.07.15
      5	K4	1993.01.17	PCB trip at SWYD pro relay (HE)	1993.01.17
      6	U2	1997.01.01	T/L short and grounding by storm	1997.01.01
      7	U1	2001.01.30	M.Tr B HV overheating	2001.02.02
      8	Y5	2002.11.03	TBN H vibration and T/L grounding	2002.11.05
      9	Y6	2002.11.03	#1T/L trip On Pre-operation	2002.11.05
      10	W2	2004.06.19	ES close during O/H in SWYD (HE)	2004.06.23
      11	Y5	2006.11.29	M.Tr SPR mis-operation during O/H	2006.11.30
      12	K1	2008.08.08	T/L 2lines was lighting at same time	2008.08.11
      13	W2	2009.09.03	Gen 32r injection for O/H (HE)	2009.09.03

      LOOP trip signal show below Table , and LOOP Event classified by Plant, Weather, Grid, SWYD. Figshows analyzed that SKR 1, 2 LOOP calculation value (operation years (1978 ~ 1998) are 95.8 reactors/year, and LOOP event are 3 from PSAR (preliminary safety analysis report), presently total operation years are 320.63 reactors/year by 2009, LOOP event are 6 by 1998. [7] [17]

      Fig LOOP frequency compare by fault tree

      Table LOOP Electrical Trip Signal

      Items	Trip source
      switchyard	7(8)x51, 7(8)x00,x 7(8)x22
      GCB	phase discrepancy, over-current, reverse-power etc.
      Frequency	57.3(0.99s), 57.7(10s), 58.1(1m), 58.5(10m)
      Pro PNL	21, 50BF, 50/51, 59G, 60(voltage balance), 87, 96B, 96D, 96P

   2. Deregulation experience and analysis results

      Source dada obtained by http://opis.kins.re.kr. LOOP frequency has contracted at YK and UJ site for before and after electric-power restructured by below Tablet , and 61% was occupied at fall season (3/4 quarter), and Fig shows LOOP frequency that before and after deregulation.

      Table showed for events numbers by plant, weather, grid-SWYD orders. Table , , and show for trip events and frequency in NPPs, respectively.

      Table Power system restructure (before and after) frequency

      plant	1978.5-2001.4			2001.5-2009.12
      	count	Op-year	frequency	count	Op-year	frequency
      KR	4	70.26	5.69E-02	1	33.60	2.97E-02
      YK	0	39.20	–	3	47.98	6.25E-02
      WS	1	25.37	3.94E-02	2	33.60	5.95E-02
      UJ	2	27.36	7.30E-02	0	43.26	–
      Total	7	162.19	4.31E-02	6	158.44	1.39E-01

      before

      KR

      K after

      R

      UJ

      YK

      W

      Y

      K

      U

      J

      WS

      Fig LOOP frequency compare

      Table LOOP cause classification

      Category	KR	YK	WS	UJ	Total
      Plant	0	3	1	1	5
      Grid	1	0	1		2
      Weather	3	0	0	1	4
      SWYD	1	0	1		2
      total	5	3	3	2	13

      Table LOOP number of item by site divergence

      Plant	1978.5-2009.12			Plant	1978.5-2009.12
      	Quarter	Count	Quarter		Count
      KR	1	1	WS	1	0
      	2	1		2	2
      	3	3		3	1
      	4	0		4	0
      YK	1	0	UJ	1	2
      	2	0		2	0
      	3	0		3	0
      	4	3		4	0

      Table Trip Count and frequency by YK N/P, UJ N/P

      WK

      1978.5-2009.12

      UJ

      1978.5-2009.12

      coun t

      Op-ye ar

      %

      frequenc y

      coun t

      Op-ye ar

      %

      frequency

      #1

      G

      –

      22.81

      –

      –

      # 1

      G

      –

      20.78

      –

      –

      P

      –

      –

      –

      P

      1

      10 0

      4.81E-02

      S

      –

      –

      –

      S

      –

      –

      –

      W

      –

      –

      –

      W

      –

      –

      –

      #2

      G

      –

      21.94

      –

      –

      # 2

      G

      –

      19.75

      –

      –

      P

      –

      –

      –

      P

      –

      –

      –

      S

      –

      –

      –

      S

      –

      –

      –

      W

      –

      –

      –

      W

      1

      10 0

      5.06E-02

      #3

      G

      –

      14.45

      –

      –

      # 3

      G

      –

      10.83

      –

      –

      P

      –

      –

      –

      P

      –

      –

      –

      S

      –

      –

      –

      S

      –

      –

      –

      W

      –

      –

      –

      W

      –

      –

      –

      #4

      G

      –

      13.60

      –

      –

      # 4

      G

      –

      9.60

      –

      –

      P

      –

      –

      –

      P

      –

      –

      –

      S

      –

      –

      –

      S

      –

      –

      –

      W

      –

      –

      –

      W

      –

      –

      –

      #5

      G

      1

      7.37

      50

      1.36E-01

      # 5

      G

      –

      5.25

      –

      –

      P

      1

      50

      1.36E-0 1

      P

      –

      –

      –

      S

      –

      –

      –

      S

      –

      –

      –

      W

      –

      –

      –

      W

      –

      –

      –

      #6

      G

      1

      7.01

      10 0

      1.43E-01

      # 6

      G

      –

      4.41

      –

      –

      P

      –

      –

      –

      P

      –

      –

      –

      S

      –

      –

      –

      S

      –

      –

      –

      W

      –

      –

      –

      W

      – –

      TT L

      3

      87.18

      –

      3.44E-0 2

      TTL

      70.6 2

      -2.83E-0 2

      –

      2

      Table Trip Count and frequency by KR N/P, WS N/P

      KR		1978.5-2009.12				WS		1978.5-2009.12
      		count	Op-year	%	frequency			count	Op-year	%	frequency
      #1	G	–	31.41	–	–	#1	G	1	26.42	100	3.78E-02
      	P	–		–	–		P	–		–	–
      	S	–		–	–		S	–		–	–
      	W	2		100	6.37E-02		W	–		–	–
      #2	G	1	25.86	100	3.39E-02	#2	G	–	11.94	–	–
      	P	–		–	–		P	1		50	8.38E-02
      	S	–		–	–		S	1		50	8.38E-02
      	p>W	–		–	–		W	–		–	–
      #3	G	–	23.75	–	–	#3	G	–	10.90	–	–
      	P	–		–	–		P	–		–	–
      	S	–		–	–		S	–		–	–
      	W	–		–	–		W	–		–	–
      #4	G	–	22.84	–	–	#4	G	–	9.75	–	–
      	P	–		–	–		P	–		–	–
      	S	1		50	4.39E-02		S	–		–	–
      	W	1		50	4.39E-02		W	–		–	–
      TTL		5	103.86	–	4.81E-02	TTL		3	59.01	–	5.08E-02

   3. Future study directions

   Risk control includes electrical problem, as EDG failures, and recently offsite power problems is affected at safety class of plants by transient phenomenon, power quality as voltage sag and swell in grid or plant.

   Nuclear is a hazard and important energy, and as possibly probability concept will be apply all electrical system in plants, and do develop regulation guideline in detail aspect.

   Recently LOOP is repeated and increased from human error, and need that review to safety culture, policy decision

   and regulation direction establishment. These may be troubled to costs, additional responsive and times on utilities or regulators during short-terms, but judge that fairly strength at safety side, and risk or failure events can be decrease by ours actions. [1][2]

3. REFERENCES

1. KINS operational performance information system for NPP report, http://opis.kins.re.kr/1978-2009

2. KIEE, Reliability establish method of SWYD, p51-53, Moon Su-Cheol, Kim Kern-Joong, 2007.

3. KPX, electric power market statistics, p19, 2009.

4. IEEE 765-2002, IEEE Standard for Preferred Power Supply (PPS) for Nuclear Power Generating Stations.

5. INPO SOER 99-01 Loss of Grid Addendum.

6. NUREG/CR-6890, Vol.1, Reevaluation of Station Blackout Risk at Nuclear Power Plants.

7. SKR #1, #2 Preliminary Safety Analysis Report, KHNP, 2006.

8. NERC Standard NUC-001-1 Nuclear Plant Interface Coordination.

9. CNSC Standard S-98 Reliability Programs for Nuclear Power Plants.

10. http://www.nrc.gov/reading-rm/doc-collections/gen-comm/info-notices.

11. NRC Regulatory Issue Summary 2004-05 Grid Reliability and The Impact on Plant Risk and The Operability of Offsite Power.

12. NUREG-1784, Operating Experience Assessment-Effects of Grid Events on Nuclear Power Plant Performance.

13. SECY-05-0219, Grid Reliability and The Impact on Plant Risk and The Operability of Offsite Power.

14. NRC GL 06-02 Grid Reliability and the impact risk and the Operability of Offsite Power.

15. Http://opis.kins.re.kr

16. NUREG/CR-6823, Handbook of Parameter Estimation for Probabilitic Risk Assessment

17. MPAS software manual, KINS, 2006

Su-Cheol, Moon was born in Korea, on August, 1973. He received his B.S. degree from Jeju National University, Korea, in 1992, M.S. degree from ChungNam National University, Korea, in 2008. From 2000 to 2005, he worked as an inspector engineer at KESCO. He has been with KINS since 2005 and is now a senior research engineer. His interests include power system stability, voltage stability, and reliability of power plant. He is a Member of KIEE, IEEE and KNS and PE(Generation Transmission and Distribution)

Kern-Joong, Kim was born in Korea, on February, 1953. He received his B.S., M.S, and Ph.D degrees in Electrical Engineering from Seoul National University, Korea, in 1975, 1977 and 1985, respectively. He is currently a Professor of Electrical Engineering in ChungNam National University, Korea. His research interests include the power system economic dispatch analysis, optima power flows, network stability for reliability and quality. He is a Member of KIEE and IEEE.