05000410/LER-2002-002, Reactor Water Cleanup System Differential Flow Isolation Signal Inoperable
| ML022630493 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 09/12/2002 |
| From: | Hopkins L Constellation Nuclear |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NMP2l 2072 LER-02-002-00 | |
| Download: ML022630493 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 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)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(1) 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(B) |
| 4102002002R00 - NRC Website | |
text
P.O. Box 63 Lycoming, New York 13093 Constellation Nuclear Nine Mile Point Nuclear Station September 12, 2002 A Member of the NPL27 Constellation Energy Group NMP2L 2072 United States Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 RE:
Nine Mile Point Unit 2 Docket No. 50-410 NPF-69
Subject:
Licensee Event Report 02-002, "Reactor Water Cleanup System Differential Flow Isolation Signal In operable" Gentlemen:
In accordance with 10 CFR 50.73(a)(2)(v)(C) and 10 CFR 50.73(a)(2)(vii)(C) we are submitting Licensee Event Report 02-002, "Reactor Water Cleanup System Differential Flow Isolation Signal Inoperable." This LER is being submitted 2 days late and the resident inspector has been informed.
Very truly yours, Lawrence A. Hopkins Plant General Manager LAH/KE/jm Attachment cc:
Mr. H. J. Miller, NRC Regional Administrator, Region I Mr. G. K. Hunegs, NRC Senior Resident Inspector
'St17
I NRC tRM)66 U.S. NUCLEARREGULATORYCOMMISSION
'1-20
' I I
LICENSEE EVENT REPORT (LER)
APPROVED BY OMB NO. 3150-0104 EXPIRES 7-31-2004 the NRC may not conduct or sponsor, and a person is not required to respond to, the (See reverse for required number of dinits/characters for each block) -
FACILITY NAME (1)
DOCKET NUMBER (2)
PAGE (3)
Nine Mile Point, Unit 2 05000410 1 OF 4
TITLE (4)
Reactor Water Cleanup System Differential Flow Isolation Signal Inoperable EVENT DATE (5)
LER NUMBER (6)
REPORT DATE (7)
OTHER FACILITIES INVOLVED (8)
MO DAY YEAR YEAR SEQUENTIAL REV MO DAY YEAR FACILITY NAME DOCKET NUMBER NUMBER NO 05000 3
16 2002 2002 -
002 -
00 9
12 2002 FACILITY NAME DOCKET NUMBER m m ~~ m~ 1 05000 OPERATING 1
THIS REPORT IS SUBMITTED PURSUANTTO THE REQUIREMENTS OF 10 CFR §: (Check al that apply) (11)
MODE (9) 1 POWER 018 20.2201 (b) 20.2203(a)(3)(ii) 50.73(a)(2)(ii)(B) 50.73(a)(2)(Ix)(A)
LEVEL (10) 0 20.2201(d) 120 2203(a)(4) 50.73(a)(2)(iii) 50.73(a)(2)(x) 20.2203(a)(1) 50.36(c)(1)(i)(A)
__ 50.73(a)(2)(iv)(A) 73.71 (a)(4) 20.2203(a)(2)Q()
50.36(c)(1)(i)(A) 50.73(a)(2)(v)(A) 73.71 (a) (5) 120 2203(a)(2)(ii) _
50.36(c)(2) 50.73(a)(2)(v)(B)
OTHER
,20.2203(a)(2)(aii) 50.46(a)(3)(ii)
X 50.73(a)(2)(v)(C) 20 2203(a)(2)(iv) 50.73(a)(2)(i)(A) 50.73(a)(2)(v)(D) we 20.2203(a)(2)(v) 50.73(a)(2)(1)(B)
X 50.73(a)(2)(vii) 20 2203(a)(2)(vi) 50.73(a)(2)(i)(C)
_5073(a)(2)(vi)(A)l' 20.2203(a)(3)(i) 50.73(a)(2)(ii)(A) 50.73(a)(2)(viii)(B) ;
LICENSEE CONTACT FOR THIS LER (12)
NAME lTELEPHONE NUMBER (Include Area Code)
Stewart B. Minahan, Manager Unit 2 Operations J
315-349-7432 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)
CAUSE
SYSTEM COMPONENTl MANU-REPORTABLE
CAUSE
SYSTEM COMPONENT MANU-REPORTABLE FACTURER TO EPI FACTURER TO EPIX D
CE FT R369 Y
l;__
SUPPLEMENTAL REPORT EXPECTED (14)
EXPECTED MONTH DAY YEAR I
SUBMISSION DATE (15)
I
_I I
YES (If yes, complete EXPECTED SUBMISSION DATE).
X NO ABSTRACT (Limit to 1400 spaces, i e., approximately 15 single-spaced typewritten lines) (16)
On March 16, 2002 at approximately 0030, Reactor Water Cleanup System (RWCU) Division I and Division II differential flow instruments were declared inoperable. The plant was shutting down for Refueling Outage 8 with thermal power approximately 18 percent. Flow from the RWCU was being directed to the condenser to control reactor vessel water level. As operators increased flow to the condenser, the differential flow indication also increased, which was unexpected. The purpose of the differential flow instrumentation is to identify breaks in the RWCU and automatically isolate RWCU from the Reactor Coolant System when the differential flow value reaches a predetermined setpoint and remains there for a specified period of time. Operations investigated the unexpected response and concluded that there was no leak or break in the RWCU system and that the differential flow instrumentation was malfunctioning. Operations then declared the differential flow instrumentation inoperable and entered the Action Statements for Technical Specification (TS) 3.3.6.1. The actions were to isolate the penetration within one hour, or be in hot shutdown within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and cold shutdown within the following 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. Operations continued with the planned shutdown.
Although the differential flow instrumentation was inoperable, the Isolation valves would still close on reactor vessel low water level, and high ambient temperature in sections of the reactor building where the 'hot leg" portion of RWCU is located. Unit 2 reached cold shutdown at approximately 0840 on March 16, 2002 and exited the TS action statement. The event was initially evaluated by Operations as not reportable at the time the instrumentation was declared inoperable. Further evaluation by the Licensing and Engineering Departments concluded that the event was reportable.
The cause of the unexpected response of the RWCU differential flow instrumentation was incomplete filling and venting of the RWCU piping post maintenance. The cause of the incorrect reportability assessment was the incorrect understanding that the reactor vessel low level and high ambient temperature isolation signals were redundant to the differential flow isolation signal.
Corrective actions include a procedure change to address venting of RWCU differential flow instrumentation lines post maintenance and a procedure change to address the reportability of inoperable RWCU differential flow instrumentation.
NRC FORM 366 (1-2001)
P J
NRC FM S3oA U.S. NUCLEAR REGULATORY COMMISSION 1E 2001)
LICENSEE EVENT REPORT (LER)
FACILITY NAME (1)
DOCKET (2)
LER NUMBER (6)
PAGE (3)
Nine Mile Point, Unit 2 05000410 YEAR lEQUENTIAL REVISION 2
OF 4
_NUMB I
N E (2 NUMBER
NARRATIVE
(if more space is required, use additional copies of NRC Forn 366A) (17)
I. Description of Event
On March 16, 2002 at approximately 0030, Reactor Water Cleanup System (RWCU) Division I and Division II differential flow timers were declared inoperable because of unexpected response. The plant was shutting down for Refueling Outage 8 with thermal power approximately 18 percent. Flow from the RWCU was being directed to the condenser to control reactor vessel water level. As operators increased flow to the condenser, the differential flow indication also increased, which was unexpected. The purpose of the differential flow instrumentation is to identify breaks in the RWCU and automatically isolate RWCU from the Reactor Coolant System when the differential flow value reaches a predetermined setpoint and remains there for a specified period of time. Operations investigated the unexpected response and concluded that there was no leak or break in the RWCU system and that the differential flow instrumentation was malfunctioning. Operations then declared the differential flow instrumentation inoperable and entered the Action Statements for Technical Specification (TS) 3.3.6.1. The actions were to isolate the penetration within one hour, or be in hot shutdown within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and cold shutdown within the following 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. Operations continued with the plant shutdown. At 0156 the mode switch was placed in shutdown and the plant reached cold shutdown at approximately 0840 on March 16, 2002. The plant exited the TS action statement after reaching cold shutdown. Operations initially assessed the inoperability of the RWCU differential flow instrumentation as a condition that was not reportable.
Upon reviewing the Deviation I Event Report for the event, Licensing questioned the reportability determination.
Subsequent evaluations included a review of the Unit 2 Updated Final Safety Analysis Report (UFSAR), TS, and TS Bases. A consensus was reached that the differential flow isolation was redundant to the level 2 reactor water level isolation and area high temperature isolation of RWCU and therefore the inoperability of the differential flow instrumentation was not a loss of function. The decision was in part based on the UFSAR statement "diversity of trip initiation signals for a RWCU system line break is provided by instrumentation for reactor water level, differential flow, and ambient temperature in RWCU equipment areas." Further evaluation by Engineering and Licensing Departments concluded that although the differential flow isolation, low reactor water level isolation and high temperature isolation were diverse they were not redundant. Specifically, in the design of the RWCU system a "cold leg" break would be isolated by a differential flow signal and there was no analysis or calculation showing that either the high area temperature isolation or the low reactor vessel water level isolation are redundant to the differential flow isolation.
There is no supporting design analysis substantiating the redundancy, therefore the inoperability of the differential flow instrumentation was determined to be reportable per 10 CFR 50.73(a)(2)(v), "Any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to: (C) Control the release of radioactive material," and per 10 CFR 50.73(a)(2)(vii), "Any event where a single cause or condition caused at least one independent train or channel to become inoperable in multiple systems or two independent trains or channels to become inoperable in a single system designed to: (C) Control the release of radioactive material."
II. Cause of Event
The cause of the unexpected differential flow indication was inadequate restoration of RWCU after maintenance.
Previously, the RWCU system had been removed from service and portions drained to allow modification to the isolation valves for the filter/demineralizers. After returning RWCU to service, some of the air migrated to the differential flow sensing lines and became trapped there, resulting in the instrument response observed by operators.
The determination of the reportability of the event was a knowledge based activity. The cause of the incorrect reportability determination is an incomplete understanding of the relationship among the RWCU isolation signals of low reactor water level, high ambient area temperature and differential flow. Personnel involved in determining that the event was not reportable incorrectly understood that the other system isolation capabilities were redundant to the differential flow isolation.
(If more space is required, use additional copies of (If more space is required, use additional copies of NRC Form 366A) (17)
IV. Corrective Actions
- 1.
Flow transmitter sensing lines were vented and differential flow indication returned to expected behavior.
- 2.
Modified procedure N2-OP-37, REACTOR WATER CLEANUP SYSTEM, to vent instrumentation for all the flow transmitters during the restoration of the RWCU.
- 3. The generic issue of venting systems or instrumentation has been entered into the corrective action program as DER 2002-2323.
- 4. Procedure N2-OP-37, REACTOR WATER CLEANUP SYSTEM, will be modified to include reportability guidance for conditions in which both Division I and Division II of RWCU differential flow instrumentation are inoperable.
- 5. The specifics of this event and the lessons learned will be covered in Operations Training for Senior Reactor Operators.
V. Additional Information
A. Failed Components:
Component Manufacturer Model Number Flow transmitter 2WCS*FT69X Rosemount 1153DB4 Flow transmitter 2WCS*FT69Y Rosemount 11 53DB4
B. Previous similar events
LER 00-010 and LER 01-004 describe events involving flow instrumentation sensing lines. Although the category of equipment, flow instrumentation, is similar the causes are different and corrective actions would not have prevented the inoperability of the RWCU differential flow instrumentation.
C. Identification of components referred to in this Licensee Event Report Components IEEE 805 System ID IEEE 803A Function Reactor Recirculation System AD N/A Reactor Water Cleanup System CE N/A Condenser System SG N/A Containment Isolation System JM N/A Nuclear Leak Detection System IJ N/A Reactor Vessel AD RPV Condenser SG COND Valve CE, JM ISV Transmitter CE, IJ FT, TT Filter Demineralizer CE FDM Heat Exchanger CE HX