05000410/LER-2002-004, Reactor Trip Due to Main Steam Isolation Valve Failure
| ML030230404 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 01/07/2003 |
| From: | Hopkins L Constellation Energy Group |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NMP2L 2080 LER 02-004-00 | |
| Download: ML030230404 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(1) 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(viii)(B) |
| 4102002004R00 - NRC Website | |
text
P.O. Box 63 Lycoming, New York 13093 Constellation Energy Group Nine Mile Point Nuclear Station January 7, 2003 NMP2L 2080 United States Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555
Subject:
Nine Mile Point Unit 2 Docket No. 50-410, NPF-69 Licensee Event Report 02-004, "Reactor Trip Due to Main Steam Isolation Valve Failure" Gentlemen:
In accordance with, 10 CFR 50.73(a)(2)(iv)(A), we are submitting Licensee Event Report 02-004, "Reactor Trip Due to Main Steam Isolation Valve Failure."
Very truly yours, JC-j4 Q, L2 Lawrence A. Hopkins Plant General Manager LAH/KLE/mlg Attachment cc:
Mr. H. J. Miller, NRC Regional Administrator, Region I Mr. G. K. Hunegs, NRC Senior Resident Inspector
NRQ ORW-*66 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 3150.0104 EXPIRES 7-31-2004 (1-2001)
, the NRC may not conduct or sponsor.
and a person is not required to respond to, the In ation collection.
FACILITY NAME (1)
DOCKET NUMBER (2)
PAGE (3)
Nine Mile Point, Unit 2 05000410 1 OF 4
TITLE (4) eactor Trip Due to Main Steam Isolation Valve Failure EVENT DATE (5)
LER NUMBER (6)
REPORT DATE (7)
OTHER FACILITIES INVOLVED ()
MO DAY YEAR YEAR SEQUENTIAL REV MO DAY YEAR ACILITY NAME DOCKET NUMBER NUMBER NO 05000 11 11 2002 2002 -
004 -
00 1
07 2003 ACILITY NAME DOCKETNUMBER 05000 OPERATING I
THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 ClR g: (Check all that apply) (11)
MODE (9) 120 2201 (b) 20.2203(a)(3)(ii) 50 73(a)(2)(il)(B) 50.73(a)(2)(a)(A)
POWER LEVEL (10) 100
_ 20.2201 (d) 20.2203(a)(4) 50.73(a)(2)(ui) 50.73(a)(2)(x) 20.2203(a)(1)
_ 50 36(c)(1)(i)(A)
X 50.73(a)(2)(iv)(A) 73 71 (a)(4) 20.2203(a)(2)(i) 50 36(c)(1)(i)(A) 50.73(a)(2)(v)(A) 73.71 (a)(5) 20.2203(a)(2)(1) 50.36(c)(2) 50.73(a)(2)(v)(B)
X OTHER 20.220(a)(2)Qfii) 150.46(a)(3)Qi)i07()()v()
Part 21 20.2203(a)(2)(iv) 50.73(a)(2)(i (A) 50 73(a)(2)(v)(D) 20.2203(a)(2)(v) 50.73(a)(2)(i)(B) 50 73(a)(2)(vii) 20.2203(a)(2)(vi) 50.73(a)(2)(1)(C) 50.73(a)(2)(viii)(A) a 20 2203(a)(3)(i 507(a)(2)(ii)(A) 50.73(a)(2)(viii)(B)
LICENSEE CONTACT FOR THIS LER (12)
NAMETELEPHONE NUMBER Qnclude Area Code)
D. P. Bosnic, General Supervisor Work Management 1
315-349 7952 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)
CAUSE
SYSTEM COMPONENT MANU-REPOT
CAUSE
SYSTEM COMPONENT MANU-REPORTABLE FACTURER TO EPI l FACTURER TO EPX B
SB ISV R340 Y
I SUPPLEMENTAL REPORT EXPECTED (14)
=EXPECTED NTH DAY YEAR SUBMISSION l
ES (Ifyescomplete EXPECTED SUBMISSION DATE)
X NO ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines) (1 6)
On November 11, 2002, at approximately 0515 hours0.00596 days <br />0.143 hours <br />8.515212e-4 weeks <br />1.959575e-4 months <br />, with Nine Mile Point Unit 2 (NMP2) at 100 percent power, an outboard main steam isolation valve (MSIV) disc separated from its stem allowing the disc/piston assembly to drop into the valve seat. This led to the rapid loss of flow in the *B' Main Steam Line resulting in a steam pressure transient.
As result of increasing reactor pressure, the reactor scrammed due to a aReactor Pressure High" trip signal.
After the reactor scram, all MSIVs received closure signals and closed. The cause of the closure signals to the MSIVs was a "Main Steam Line High Flow' MSIV auto-isolation signal. The high main steam line flow was caused by the increased reactor pressure and flow being restricted to three of the four main steam lines.
The reactor scram and MSIV closure are reportable in accordance with 10 CFR 50.73(a)(2)(iv)(A). This report also constitutes a Part 21 Notification.
The cause was a deficient MSIV design that did not ensure the proper stem-to-disc thread loading.
Contributors to the failure were marginal thread dimensions and inadequate torque specifications during assembly. Five of eight MSIVs had been modified incorporating an improved design. The failed MSIV had not been modified.
The corrective action was the incorporation of a modified stem-to-disc connection on the three remaining unmodified valves.
NRC FORM 366 (1-2001)
NRC FORN.M,66A U.S. NUCLEAR REGULATORY COMMISSION Of20t1e LICENSEE EVENT REPORT (LER)
FACILITY NAME (1)
DOCKET (2)
LER NUMBER (6)
PAGE (3)
NUNUEE (N E
Nine Mile Point, Unit 2 05000410 YEAR I
SEQUENTIAL REVISION 2
OF 4
2002 004 00
NARRATIVE
(If more space is required, use addtonal copies of NRC Fomn 366A) (17)
I. Description of Event
On November 11, 2002, at approximately 0515 hours0.00596 days <br />0.143 hours <br />8.515212e-4 weeks <br />1.959575e-4 months <br />, with Nine Mile Point Unit 2 (NMP2) at 100 percent power, an outboard main steam isolation valve (MSIV) disc separated from its stem allowing the disc/piston assembly to drop into the valve seat. This caused the AB" Main Steam Line (MSL) flow to go to zero. The instantaneous loss of "B" MSL flow resulted in a momentary reduction of pressure downstream of the four main steam lines. The turbine controls, sensing this reduction of pressure downstream of the MSIVs initiated the closing of all turbine control valves in an attempt to maintain upstream pressure.
As the turbine control valves started closing, pressure in the reactor increased and steam flow in the remaining steam lines also increased. Main steam line equalizing header pressure rose and continued to rise due to increasing reactor pressure and increasing steam flow through the remaining three main steam lines.
The turbine control valves then began to open as a result of the overpressure condition in the equalizing header. Turbine Bypass Valve 'A' fully opened and Turbine Bypass Valve 'B' started to open. The reactor scrammed at this time due to a "Reactor Pressure High' trip signal. Approximately one second after the reactor scram, all MSIVs received a "Main Steam Line High Flow" auto-isolation signal and started to close.
The high main steam line flow was caused by the increased reactor pressure and flow restricted to only three of the four main steam lines.
With the MSIVs closed, safety relief valves (SRV) 2MSS*PSV128 and 2MSS*PSVI33 opened automatically in the relief mode. Pressure control was then established using manual operation of SRV's. Reactor water level initially dropped below the level 3 setpoint of 159.3 inches and was returned to approximately 195 inches using reactor feedwater pump 2FWS-P1 B. Upon manually opening an SRV to maintain pressure, a swell in reactor water level caused a level 8 signal that tripped the operating feedwater pump. The operating crew started the Reactor Core Isolation Cooling System, in accordance with procedures, as a means to maintain reactor level and to assist with pressure control.
As designed, both recirculation pumps automatically downshifted to slow speed when reactor water level dropped below the level 3 setpoint of 159.3 inches following the scram. Both reactor recirculation pumps continued to operate at slow speed after the event.
No structures, systems, or components were inoperable at the start of the event that would have exacerbated the event. Operators and required equipment responded as expected.
(if more space is required, use add anal copies of (If more space Is required, use addItional copies of NRC Form 366A) (17)
IV. Corrective Actions
A disc/stem modification was performed on the three previously unmodified MSIVs, 2MSS*AOV7B, 2MSS*AQV6A, and 2MSS*AOV7A. The modification consisted of a new valve disc design that incorporates a new stem/disc assembly and provides an improved method of attachment between the pilot disc and stem.
V. Additional Information
- 1. Failed Components:
MSIV Make/Model: Rockwell 26" Wye-Pattem Globe Valve, model 1612JMMNTY
- 2.
Previous similar events
NMP2 has not experienced any previous similar reactor trips or reportable events due to MSIV stem-to-disc connection failures.
- 3.
Identification of components referred to in this Licensee Event Report Components IEEE 805 System ID IEEE 803A Function Main Steam System Feedwater System Turbine Bypass System Turbine Control System Reactor Recirculation System Reactor Core Isolation Cooling Reactor Pump Valve Vessel SB SJ JIl JJ AD BN AC BN, SJ, AD SB, JA, JJ AD N/A N/A N/A N/A N/A N/A N/A P