05000263/LER-2001-012
| Monticello Nuclear Generating Plant | |
| Event date: | 11-08-2001 |
|---|---|
| Report date: | 0-7-2002 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2632001002R00 - NRC Website | |
Description copies of NRC Form 366A) (17) outage, local leak rate testing indicated that limits for Containment Isolation Valve Leakage were main steam isolation valve leakage to "Less than maximum flow path leakage for all main steam isolation leakage associated with main steam isolation valve exceeded. See table below for more details.
states: "A combined maximum flow path leakage rate and valves, subject to Type B and C tests the maximum allowable leakage rate in percent by at Pa. "Pa" is the calculated peak containment pressure The leakage associated with three containment isolation Water Cleanup System) and CV-27903 (Recirculation See table below for more details.
is the total containment maximum pathway lowest leakage in each penetration failed to close.
or AO-2- of when weight leakage During the November 2001 refueling established in the Technical Specification exceeded.
Technical Specification 3.7.A.2.b.3 limits equal to 46 scf per hour combined valves when tested at 25 psig." The 86 C and Di caused this limit to be Technical Specification 3.7.A.2.b.2 less than or equal to 0.6La for all penetrations pressurized to Pa, 42 psig." "La" is of the containment air volume per day related to the design bases accident.
valves, MO-2397, MO-23982 (Reactor System)caused this limit to be exceeded.
The combined maximum flow path leakage that would exist if the valve with the Valves with Technical Specification Excessive Leakage Test Date Valve Name Valve Description "As Found" Leakage Rate4 1118/01 AO-2-86C Outboard Main Steam Isolation Valve on the "C" Main Steam Line 18" Venturi, Spring Actuated double disc gate Valve (Installed in 1994) 33 scfh @ 25 psig 11/8/01 AO-2-86D Outboard Main Steam Isolation Valve on the "D" Main Steam Line 18" Venturi, Spring Actuated double disc gate Valve (Installed in 1994) 27 scfh @ 25 psig 11/11/01 MO-2397 Reactor Water Cleanup Inlet Inboard Isolation Valve Motor Operated 4" 600# Double Disc Gate Valve (Installed in 2000).
95 SCfh @ 42 psig 11/11/01 MO-2398 Reactor Water Cleanup Inlet Outboard Isolation Valve Motor Operated 4" 600# Double Disc Gate Valve (Installed in 2000).
839 scfh @ 42 psig Code = ISV scf per hour 1 � EIIS System code = SB, EIIS Component 2 � EllS System code = CE 3 EIIS System code = AD 4 � Standard Cubic Feet Per Hour = scfh or a less was a Valve 11/10/01 CV-2790 RECIRC Sample Line Inboard Isolation Valve Air Operated 3/4" - Double Disc Gate Valve (Installed in 1991).
138 scfh @ 42 psig
Event Analysis
accordance with 10 CFR 50.73(a)(2)(i)(B): "Any operation Technical Specifications . . ..
occurred, since the combined minimum flow path minimum pathway leakage was less than 0.6La. If isolation had occurred, any releases would have been safety analysis. The health and safety of the public Valve on the "C" Main Steam Line Valve on the "D" Main Steam Line Valves are double disc gate valves with discs. The upstream disc is equipped with locking. The downstream disc therefore accomplishes Isolation Valves were disassembled. Packing leakage, only) and radial cracks in the disc seating excessive leakage in AO-2-86C and D.
found in AO-2-86B, Outboard Main Steam Isolation These radial cracks did not compromise the leak tightness Analysis This report or condition No safety leakage Safety condition than those not affected
Cause
The measured of Reportability is being submitted in prohibited by the plant's system functional failure rate was less than 0.6La.
Significance total containment requiring containment assumed in the plant by this event.
Outboard Main Steam Isolation Outboard Main Steam Isolation outboard Main Steam Isolation upstream and downstream hole to prevent pressure valve isolation function.
four outboard Main Steam surface scratches (A0-2-86C were the cause of the radial cracks were also the "B" Main Steam Line.
the valve.
independent seating surfaces Minor AO-2-86C, AO-2-86D, The small the All on of Valve body wear was also discovered on all four valves, although it did not affect the isolation function. The upper portion of the downstream body seat and the valve body guides were worn by the disc rotating during service. The cause of the radial cracks is due to a combination of residual stresses from manufacturing and mechanical stress associated with the disc rotating during service and interacting with the stationary seats.
Reference — CR 20017070 MO-2397 Reactor Water Cleanup System Inlet Inboard Isolation Valve MO-2398 Reactor Water Cleanup System Inlet Outboard Isolation Valve The seating surface of MO-2397 was found to be gouged. The seating surface of MO- 2398 was found to be severely scored. No source of the foreign material could be identified. These valves were replaced during the last refueling outage.
Reference — CR 20017090 and 20017091 CV-2790 RECIRC Sample Line Inboard Isolation Valve The valve actuator bench setting was found to be lower that the manufacturer's recommendation. The leakage was caused by a small amount of corrosion products on the seats and the air operator had a spring setting below specifications.
Reference — CR 20017092 Actions AO-2-86C, Outboard Main Steam Isolation Valve on the "C" Main Steam Line AO-2-86D, Outboard Main Steam Isolation Valve on the "D" Main Steam Line The downstream discs of all four outboard Main Steam Isolation Valves were replaced, the body seats were lapped and the valves were repacked. A galled stem on AO-2-86D was replaced.
All four valves were modified to prevent disc rotation.
The outboard Main Steam Isolation Valves were successfully retested.
MO-2397 Reactor Water Cleanup System Inlet Inboard Isolation Valve MO-2398 Reactor Water Cleanup System Inlet Outboard Isolation Valve The valve seats were repaired and were successfully retested. No source of the foreign material could be identified nor was any foreign material recovered..
CV-2790 RECIRC Sample Line Inboard Isolation Valve The valve seats were cleaned and the air operator adjusted. The valve was successfully retested.
Failed Component Identification AO-2-86C and D - Outboard Main Steam Isolation Valve on the "C" and "D" Main Steam Line Valve Manufacturer: Flowserve (formerly Anchor/Darling Valve Company) Size of Valve: 18" venturi Pressure Class: 900 psig Model Number: W9324183 (NX-56482) MO-2397 and MO-2398 Valve Manufacturer: Flowserve (formerly Anchor-Darling) Size of Valve: 4" double-disc gate valve Pressure Class: 900 psig Model Number: W9925312 (NX-9235-45), Serial Number E-758A-2-1 (MO-2397), E- 758A-2-2 (MO-2398) CV-2790 Valve Manufacturer: Flowserve (formerly Anchor/Darling Valve Company) Size of Valve: 3/4" - Double Disc Gate Valve Pressure Class: 1878 psig Model Number: Valve Serial Number EB069-1-1 (Tech Manual NX-17293) Similar Events In the Last Ten Years There have been past LERs on failed Main Steam Isolation Valves of the inboard Main Steam Isolation Valve design, but there have been no failures of Main Steam Isolation Valves of the outboard valve design. Testing verified that the inboard Main Steam Isolation Valves performed the function properly. The inboard Main Steam Isolation Valves were original plant equipment and have a different design than the outboard valve design.
No other similar failures have occurred.