05000321/LER-2003-001, Edwin I.Hatch Nuclear Plant - Unit 1 Regarding Broken Reactor Protection System Neutral Bolt Results in RPS Bus Trip
| ML032190365 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 08/04/2003 |
| From: | Sumner H Southern Nuclear Operating Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NL-03-1625 LER 03-001-00 | |
| Download: ML032190365 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3212003001R00 - NRC Website | |
text
a H. L Sumner, Jr.
Southern Nuclear Vice President Operating Company. Inc.
Hatch Project Post Office Box 1295 Birmingham, Alabama 35201 Tel 205.992.7279 August 4, 2003 SOUTHERN Energy to Serve Your World Docket Nos.:
50-321 NL-03-1625 50-366 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555-0001 Edwin I. Hatch Nuclear Plant Licensee Event Report Broken Reactor Protection System (RPS)
Neutral Bolt Results In RPS Bus Trip Ladies and Gentlemen:
In accordance with the requirements of 10 CFR 50.73(a)(2)(iv)(A), Southern Nuclear Operating Company is submitting the enclosed Licensee Event Report (LER) concerning a trip of a RPS bus due to a broken neutral bolt.
This letter contains no NRC commitments. If you have any questions, please advise.
Sincerely, H. L. Sumner, Jr.
HLS/IL/daj Enclosure: LER 50-321/2003-001 cc:
Southern Nuclear Operating Company Mr. J. D. Woodard, Executive Vice President Mr. G. R. Frederick, General Manager - Plant Hatch Document Services RTYPE: CHA02.004 U. S. Nuclear Regulatory Commission Mr. L. A. Reyes, Regional Administrator Mr. S. D. Bloom, NRR Project Manager - Hatch Mr. D. S. Simpkins, Senior Resident Inspector - Hatch
I
Abstract
On 06/09/2003 at 0445 EDT, Unit 1 was in the Run mode at a power level of 2763 CMWT (100 percent rated thermal power). At that time, the "A" Reactor Protection System (RPS, EIIS Code JE) bus (IC71) tripped while the RPS MG Set (IC71SOO1A) continued to run with the output breakers closed in. The design of the RPS is "fail-safe" in that loss of power or control signal causes systems powered by the RPS power supply to change states to their emergency configurations. Thus, the trip of the bus caused Group 2, Group 5, and inboard small-bore Group 1 Primary Containment Isolation System (PCIS, EIIS Code JM) valves to receive an automatic isolation signal. The Main Control Room Environmental Control System (MCRECS, EUS Code VI) entered the pressurization mode; both units' Standby Gas Treatment Systems (SGTS, EHS Code BH) initiated; the Primary Containment Hydrogen and Oxygen Analyzers (EIIS Code IK) isolated. Also, the Reactor Water Cleanup (RWCU, EIS Code CE) system, the Fission Product Monitoring (FPM, EIS Code U) system, and the operating Steam Packing Exhauster tripped.
Licensed personnel verified the proper plant response to the initiating signal per procedure 34AB-C71-002-IS, "Loss of RPS." By 0607 EDT, licensed personnel energized the RPS bus from its alternate supply and affected systems were subsequently returned to their normal lineups. The cause of the RPS bus trip was determined to be a broken neutral RPS cable bolt located in panel 1 C7 1-POO1. The broken bolt was removed and replaced with a new bolt.
IU.S. NUCLEAR REGULATORY COMMISSION (1t2001)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME (1)
DOCKET LER NUMBER (1D PAGE (3)
YEAR I SEQUENTIAL REISION YEAR NUMBER Edwin I. Hatch Nuclear Plant - Unit 1 05000-321 2003 001 00 2 OF4 TEX (if more space Is rquired, use additional copies of NRC Form 366A) (17)
PLANT AND SYSTEM IDENTIFICATION
General Electric - Boiling Water Reactor Energy Industry Identification System codes appear in the text as (EIIS Code XX).
DESCRIPTION OF EVENT
On 06/09/2003 at 0445 EST, Unit 1 was in the Run mode at a power level of 2763 CMWT (100 percent rated thermal power). At that time, the "A" Reactor Protection System (RPS) bus (IC71) tripped while the RPS MG Set (1C71SOO1A) continued to run with the output breakers closed in. As a result, Reactor Protection System (RPS) bus "lA" trip power was lost to the logic systems the RPS bus powered including the RPS trip logic, the Main Control Room Environmental Control System (MCRECS) initiation logic, Primary Containment Isolation System (PCIS) trip logic, and Steam Packing Exhauster trip logic. All affected systems responded per design on the loss of power, producing a half scram signal, PCIS valve isolations, MCRECS pressurization mode initiation, and other actuations.
As a result of the Reactor Protection System (RPS, EUS Code JC) bus "1A" lost power causing some Group 2, Group 5, and inboard small-bore Group 1 Primary Containment Isolation System (PCIS, EUS Code JM) valves to receive an automatic isolation signal. Those valves open at the time of the event closed per design. Also, the Main Control Room Environmental Control System (MCRECS, EUS Code VI) entered the pressurization mode; the Primary Containment Hydrogen and Oxygen Analyzers (EIIS Code IK) isolated; and the Reactor Water Cleanup (RWCU, EUS Code CE) system, the Fission Product Monitoring (FPM, EIIS Code IJ) system, and the operating steam packing exhauster tripped.
Loss of power to Standby Gas Treatment (SGT, EUS Code BH) system logic components resulted in isolation of the secondary containment and the initiation of the Unit 1 and Unit 2 SGT system trains.
By 0607 EDT, licensed personnel energized the RPS bus from its alternate supply and affected systems were subsequently returned to their normal lineups.
CAUSE OF EVENT
The cause of the "A" Reactor Protection System (RPS, EIIS Code JE) bus (1C71) trip was determined to be a broken bolt for the neutral RPS cable located in panel 1 C7 1-POO1. Preliminary analysis of the bolt failure indicated that it was the result of tensile overload. The tensile overload of this bolt was most likely the result of a combination of stresses induced on the bolt from torquing and cable strain from the electrical conductor secured by the bolt. Metallographic examination of the bolt showed no unexpected grain structure or material conditions.
NRC Penn =5A (1ZUU1)
iU.S. NUCLEAR REGULATORY COMMISSION (1.2001)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME (1)
DOCKET LER NUMBER (6)
PAGE (3)
YEAR I
SEQUENTIAL lREMISION
]
YEAR N UMBER Edwin I. Hatch Nuclear Plant - Unit 1 05000-321 2003 001 --
00 3 OF4 TEXT {If more space Is required, use additonal copies of NRC Forn 366A) 117)
REPORTABILITY ANALYSIS AND SAFETY ASSESSMENT This event is reportable per 10 CFR 50.73 (a)(2)(iv)(A) because unplanned actuations of engineered safety features (ESFs) occurred. Specifically, several ESFs actuated in response to a trip of RPS power supply bus "A."
The RPS power supply system is designed to supply stable 120-volt AC power to a variety of plant instrumentation systems including the Process Radiation Monitoring System, the Neutron Monitoring System, the Reactor Protection System, the Primary Containment Isolation System, and the Offgas Radiation Monitoring System. A high degree of power stability is achieved by using two motor-generator sets to condition the power supplied by the RPS power supply system. The electrical output of each motor-generator set energizes one of two RPS busses.
In this event, the "A" Reactor Protection System bus (IC71) tripped because of a broken bolt for the neutral RPS cable located in panel 1C71-POO1. Upon loss of power or control signal, systems powered by the RPS de-energize to their "safe" configuration (i.e., they initiate their emergency or accident functions). All systems affected by this event responded per design for a power interruption, and this was verified by licensed personnel immediately after the event occurred. No unexpected actuations occurred. Had a design basis accident occurred during this event, all affected plant systems would already have been in their emergency configurations and no further automatic actuations of these particular systems would have been required to mitigate the accident.
Based on this analysis, it is concluded that this event had no adverse impact on nuclear safety. This analysis is applicable to all power levels.
CORRECTIVE ACTIONS
The broken silicon bronze bolt for the neutral RPS cable located in panel IC7 1-POOl bolt was removed and replaced with a new stainless steel bolt per Maintenance Work Order (MWO) 10302706. A stainless steel bolt was used to ensure that the strain caused by the conductor securing this bolt would not cause another tensile overload. The risk associated with reducing the amount of strain exerted on this connection from the electrical conductor was determined to be unacceptable during plant operation so it was decided that this work would not be performed until the next refueling outage. An MWO (10302759) to reduce this strain during the next refueling was generated.
NRC Form 356A (1-101)U.S. NUCLEAR REGULATORY COMMISSIONU.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME (1)
DOCKET LER NUMBER (6)
PAGE (3)
YEAR I SEQUENTIAL IREMlONI Edwin I. Hatch Nuclear Plant - Unit 1 05000-321 2003 001 00 4 OF4 TEXT ff more apace Is rewired, use addio copies of NRC Fonm 366A! (17)
ADDITIONAL INFORMATION
There have not been any previous similar events reported in the last two years in which a trip of RPS bus resulted in unplanned safety system actuations.
Commitment Information: This report does not create any permanent licensing commitments.
Failed Component Information
Master Parts List: IC71-POOl Manufacturer: GE Manufacturer Code: G080 Model Number: 238X928RJG1 Type: RPS Power Cable EIIS System Code: JE EUS Component Code: CBL5 Root Cause Code: X Reportable to EPIX: Yes I
NRC Fonn 356A 11 4-21)