Information Notice 2006-08, Secondary Piping Rupture At Mihama Power Station in Japan
| ML052910008 | |
| Person / Time | |
|---|---|
| Issue date: | 03/16/2006 |
| Revision: | 0 |
| From: | Grimes C I NRC/NRR/ADRA/DPR |
| To: | |
| Hodge, CV, NRR/DIPM/IROB, 415-1861 | |
| References | |
| IN-06-008 IN-02-008 | |
| Download: ML052910008 (5) | |
UNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF NUCLEAR REACTOR REGULATIONWASHINGTON, March 16, 2006NRC INFORMATION NOTICE 2006-08:SECONDARY PIPING RUPTURE AT THEMIHAMA POWER STATION IN JAPAN
ADDRESSEES
All holders of operating licenses, except those who have permanently ceased operations andhave certified that fuel has been permanently removed from the reactor vessel.
PURPOSE
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) involvingforeign operating experience to alert addressees of the root causes and lessons learned from a secondary piping rupture at the Mihama Power Station, Unit 3 (Mihama 3) in Japa It isexpected that recipients will review the information for applicability to their facilities and consideractions, as appropriate, to avoid similar problem However, suggestions contained in this information notice are not NRC requirements; therefore, no specific action or written responseis required.
DESCRIPTION OF CIRCUMSTANCES
The Mihama 3, is an 826 Megawatts electric, 3-loop Westinghouse type pressurized-waterreactor (PWR) owned by Kansai Electric Power Company, Inc., and licensed by the Japanese governmen This unit has been in service since 197 On August 9, 2004, a fire alarm annunciated in the central control room at Mihama Uponinvestigation, operators discovered the area covered by the alarm was filled with steam. Suspecting that steam or high temperature water was leaking from the secondary piping, the operators began an emergency load reductio While they were doing this, the reactor tripped automatically based on the steam flow from the 3A steam generator exceeding the feedwaterflow to that steam generator.The rupture occurred in a 55.9 centimeter (cm) (22 inch) outside diameter pipe in the 'A' loopcondensate system between the fourth feedwater heater and the deaerator, downstream of anorifice for measuring single-phase water flo At the time of the secondary piping rupture, 105 workers were preparing for the periodic inspections to commenc The accident resulted in five deaths and six injuries. A review of plant parameters did not uncover any precursor indicators before the accident norwere there any special operations that could have caused the pipe ruptur An investigationconcluded that water quality had been maintained since the commissioning of the plant. The rupture opening measured 51.5 cm (20.3 inches) in the axial direction and 93.0 cm(36.6 inches) in the circumferential direction of the carbon steel pip The nominal wall thickness of the pipe at the time of initial plant service was 10 millimeters (mm) (0.39 inches).
The thinnest section of the pipe wall was 0.4 mm (0.02 inches). The same section of piping in the 'B' loop was 1.8 mm (0.07 inches) at its thinnest plac The pipe was designed for a maximum service temperature of 195 Centigrade (C) (383 Fahrenheit (F)) and a maximumservice pressure of 1.27 megapascal (MPa) (184 pounds per square inch (psi)). At the time of the pipe rupture, the flow rate through the pipe was 1700 cubic meters per hour (7485 gallons per minute) with a temperature of 140 C (284 F) and a pressure 0.93 MPa (135 psi). A microscopic inspection of the inside surface of the ruptured pipe revealed a fish scale-likepattern over almost the entire inner surface of the pipe downstream of the orifice, except at thebottom of the pip The thickness along the bottom of the pipe was found to be the nominal wall thicknes The inside surface of the bottom of the pipe was covered with a thick surface fil These conditions are characteristic of flow-accelerated corrosion (FAC).
BACKGROUND
The condensate system and main feedwater system, as well as other power conversionsystems, are important to safe plant operatio Failures in these systems may challenge plantsafety systems required for safe shutdown and accident mitigatio All U.S. licensees havecommitted to adhere to criteria, codes and standards for high-energy piping systems describedin licensing document Part of this commitment is keeping pipes within the allowable thickness value The NRC has issued numerous generic communications, including IN 2001-09, "MainFeedwater System Degradation in Safety-Related [American Society of Mechanical Engineers]
ASME Code Class 2 Piping Inside the Containment of a Pressurized-Water Reactor," on various pipe wall thinning issues and events.
DISCUSSION
In May 1990, the operators of PWRs in Japan established "Guidelines for Secondary PipingWall Thickness Control at Nuclear Facilities (PWR)," (abbreviated PWR ManagementGuidelines, hereafter) which were implemented at Mihama These guidelines are based on the known wall thinning rate of secondary system piping at various plants and describe themethods for managing pipe wall thinnin The guidelines cover carbon steel piping in the secondary system, where flow makes the walls susceptible to wall thinnin Approximately 25 percent of the piping within the scope of the guide is inspected within a 10-year perio Thefrequency of inspection is determined by the calculated residual life before the minimum pipe wall thickness is reache Repeated inspections ensure that either the calculated residual life isgreater than 2 years or that the pipe is replaced with a pipe made of corrosion-resistant materia An investigation of the accident by the Nuclear and Industrial Safety Agency (NISA) found noreviews of the PWR Management Guidelines after 1990 to reflect new dat In addition, NISA concluded that the direct cause of the pipe failure was wall thinning but that the omission of thispipe from the initial inspection plan, ineffective management, ineffective quality management systems, and insufficient penetration of safety culture were contributing factor As a result, theplant owner and the owner's contractors developed preventive measures to address quality assurance and maintenance management, inspection plans, and assessment of managementprogram After reviewing the owner's preventive measures, NISA concluded that the actions described were appropriate.The Japanese regulatory authority has asked the Japanese Society of Mechanical Engineers todevelop new guidelines to replace the existing industrial guidelines on FA In its investigation report, NISA noted the importance of periodically examining program management and reviewing industry operating experienc NISA also emphasized that the success of these programs depends on owner corporate commitment to foster a strong safety culture.FAC is managed differently in Japan than in the Most U.S. licensees manage FAC byimplementing the Electric Power Research Institute (EPRI) guidelines described in NSAC-202L,
"Recommendations for an Effective Flow Accelerated Corrosion Program." Nevertheless, successful implementation of the EPRI guidelines relies on several of the factors addressed by the NISA investigation repor For example, a successful FAC program depends upon periodic review and re-evaluation of the program in the light of new information and operating experience, application of sound engineering judgement, evaluation of the effect of design changes with respect to FAC, a strong safety culture, and management suppor This and previous INs point to the continuing need for attention to the potential effects of FAC on pipingsystem integrity and to the elements of an effective degradation management program.REFERENCES
"Interim Summary on Secondary Piping Rupture Accident at Mihama Power Station, Unit 3 ofthe Kansai Electric Power Co., Inc.", (translated by Japan Nuclear Energy Safety Organization (JNES)), September 27, 2004, The Nuclear and Industrial Safety Agency."Secondary Piping Rupture Accident at Mihama Power Station, Unit 3 of the Kansai ElectricPower Co., Inc. (Final Report)", Revision 1 (translated by Japan Nuclear Energy Safety Organization (JNES)), May 14, 2005, The Nuclear and Industrial Safety Agency.
CONTACT
This information notice does not require any specific action or written respons Please directany questions about this matter to the technical contact listed below./RA/Christopher I. Grimes, Director Division of Policy and Rulemaking Office of Nuclear Reactor Regulation
Technical Contact:
Carolyn Lauron, NRR301-415-2736 E-mail: cll@nrc.govNote: NRC generic communications may be found on the NRC public Web site,http://www.nrc.gov, under Electronic Reading Room/Document Collection assurance and maintenance management, inspection plans, and assessment of management program Afterreviewing the owner's preventive measures, NISA concluded that the actions described were appropriate.The Japanese regulatory authority has asked the Japanese Society of Mechanical Engineers to develop newguidelines to replace the existing industrial guidelines on FA In its investigation report, NISA noted theimportance of periodically examining program management and reviewing industry operating experienc NISAalso emphasized that the success of these programs depends on owner corporate commitment to foster a strongsafety culture.FAC is managed differently in Japan than in the Most U.S. licensees manage FAC by implementing theElectric Power Research Institute (EPRI) guidelines described in NSAC-202L, "Recommendations for an EffectiveFlow Accelerated Corrosion Program." Nevertheless, successful implementation of the EPRI guidelines relies onseveral of the factors addressed by the NISA investigation repor For example, a successful FAC program dependsupon periodic review and re-evaluation of the program in the light of new information and operating experience,application of sound engineering judgement, evaluation of the effect of design changes with respect to FAC, astrong safety culture, and management suppor This and previous INs point to the continuing need for attention tothe potential effects of FAC on piping system integrity and to the elements of an effective degradation managementprogram.REFERENCES"Interim Summary on Secondary Piping Rupture Accident at Mihama Power Station, Unit 3 of the Kansai ElectricPower Co., Inc.", (translated by Japan Nuclear Energy Safety Organization (JNES)), September 27, 2004, TheNuclear and Industrial Safety Agency."Secondary Piping Rupture Accident at Mihama Power Station, Unit 3 of the Kansai Electric Power Co., Inc. (FinalReport)", Revision 1 (translated by Japan Nuclear Energy Safety Organization (JNES)), May 14, 2005, The Nuclearand Industrial Safety Agency.
CONTACT
This information notice does not require any specific action or written respons Please direct any questions aboutthis matter to the technical contact listed below./RA/Christopher I. Grimes, DirectorDivision of Policy and RulemakingOffice of Nuclear Reactor Regulation
Technical Contact:
Carolyn Lauron, NRR301-415-2736E-mail: cll@nrc.govNote: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, underElectronic Reading Room/Document Collections.DISTRIBUTION:IN FileThe Japanese have confirmed the accuracy of the notice.ADAMS ACCESSION NUMBER: ML052910008 (TAC #MC8529) OFFICEOES:IROB:DIPMTECH EDITOREMCB:DEC:EMCB:DETL:OES:IROB:DIPMNAMECVHodgePKleeneCLLauronWHBatemanICJungDATE 12/15/2005 10/21/2005 01/03/200501/ 03/200501/ 09/2005OFFICENRRLA:PGCG:DPRPGCG:DPRBC:PGCB:DPRD:PGCB:DPRNAMEMCCullingfordCHawesDBeaulieuCJacksonCIGrimes DATE 01/ 04/200503/07/0603/07/200603/14/200603/16/2006OFFICIAL RECORD COPY