05000237/LER-2009-004, Shutdown Cooling System Isolation During Cooldown Due to Temperature Instrumentation Failure
| ML100141416 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 12/22/2009 |
| From: | Hanley T Exelon Generation Co, Exelon Nuclear |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| SVPLTR #09-0065 LER 09-004-00 | |
| Download: ML100141416 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 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), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2372009004R00 - NRC Website | |
text
F Exelon'.
Exelon Generation Company, LLC Dresden Nuclear Power Station 6500 North Dresden Road Morris, IL 60450-9765 www.exeloncorp.com Nuclear 10 CFR 50.73 SVPLTR # 09-0065 December 22, 2009 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Dresden Nuclear Power Station, Unit 2 Renewed Facility Operating License No. DPR-19 NRC Docket No. 50-237
Subject:
Licensee Event Report 237/2009-004-00, "Unit 2 Shutdown Cooling System Isolation during Cooldown due to Temperature Instrumentation Failure" Enclosed is Licensee Event Report 237/2009-004-00, "Unit 2 Shutdown Cooling.System Isolation during Cooldown due to Temperature Instrumentation Failure," for Dresden Nuclear Power Station, Unit 2. This event is being reported In accordance with 10 CFR 50.73(a)(2)(v)(B) "Any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to remove residual heat."
There are no regulatory commitments contained in this submittal.
Should you have any questions concerning this letter, please contact Ms. Marri Marchionda at (815) 416-2800.
Respectfully, Site Vice PresidentV Dresden Nuclear Power Station Enclosure cc:
Regional Administrator - NRC Region III NRC Senior Resident Inspector - Dresden Nuclear Power Station
(\\fr~F\\
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2010 eg-2007)
, the NRC may digits/characters for each block) not conduct or sponsor, and a person is not required to respond to, the Infnrmatlnn cnli*clnn.
- 3. PAGE Dresden Nuclear Power Station, Unit 2 05000237 1 OF 4
- 4. TITLE Unit 2 Shutdown Cooling System Isolation during Cooldown due to Temperature Instrumentation Failure
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED [FACILITY NAME DOCKET NUMBER YEAR YEAR SEQUENTIAL REV MONTH DAY YEAR N/A N/A NUMBER NO, FACILITY NAME DOCKET NUMBER 11 02 2009 2009
- - 004 -
00 12 22 2009 N/A N/A D. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
El 20.2201(b)
[I 20.2203(a)(3)(I) 0l 50.73(a)(2)(i)(C)
[I 50.73(a)(2)(vil) 3 El 20.2201(d)
El 20.2203(a)(3)(ii) 0l 50.73(a)(2)(ii)(A)
El 50,73(a)(2)(viii)(A)
El 20.2203(a)(1)
[l 20.2203(a)(4)
Ql 50.73(a)(2)(iI)(B) 0l 50.73(a)(2)(vIii)(B)
[] 20.2203(a)(2)(i)
[I 50.36(c)(1)(i)(A)
[E 50.73(a)(2)(iii)
El 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL El 20.2203(a)(2)(ii)
El 50.36(c)(1)(ii)(A)
[E 50.73(a)(2)(iv)(A)
[j 50.73(a)(2)(x)
El 20.2203(a)(2)(iti)
El 50.36(c)(2) 50.73(a)(2)(v)(A)
El 73.71(a)(4) 000 20.2203(a)(2)(iv)
El 50.46(a)(3)(l1)
[ 50.73(a)(2)(v)(B)
Q 73.71(a)(5) 0l 20.2203(a)(2)(v)
El 50.73(a)(2)(I)(A)
El 50.73(a)(2)(v)(C) 0l OTHER [I 20.2203(a)(2)(vi) 0l 50.73(a)(2)(i)(B)
[I 50.73(a)(2)(v)(D)
Specify in Abstract below or In NRC Form 3W0A
- 12. LICENSEE CONTACT FOR THIS LER F
d NILI-To NAME Dresden Nuclear Power Station - Bob Rybak (1.L 5tr)Q rt NUM416 R2 (In810 grea (815) 416-2810
[]YES (It yes, complete 15. EXPECTED SUBMISSION DATE)
ABSTRACT (Limit to 1400 spaces, I e., approximately 15 single-spaced typewritten lines)
On November 2, 2009, during shutdown for the Dresden Unit 2 Fall 2009 refueling outage, the Shutdown Cooling (SDC) System high temperature Isolation logic actuated causing the SDC isolation valves to shut, resulting in a loss of cooling to the Reactor Vessel. Troubleshooting determined that Temperature Element 2-0261-88, a thermocouple (TC), failed. The Resistance Temperature Detector (RTD), 2-0261 -8F, housed in the same assembly, had previously failed and was out of service since December 2008. The presence of an open signal from both instruments in the same recirculation loop caused the isolation logic to activate, as designed.
The apparent cause was failure at the soldered TC junction and the RTD element-to-lead solder joint attributed to corrosion and oxidation at the solder connection. A replacement switch was installed during the refueling outage.
The safety significance of this event is minimal as cooling flow was restored to the vessel in approximately 40 minutes. Plant response and operator actions were consistent with plant procedures. The protection of public health and safety and personnel safety were not compromised at anytime during this event.
NRC FORM 3B0 ie-2co7 PRINTED ON RECYCLED PAP NRC FORM 366 (9-2007)
PRINTED ON RECYCLED PAP
PLANT AND SYSTEM IDENTIFICATION
Dresden Nuclear Power Station (DNPS) Unit 2 is a General Electdc Company Boiling Water Reactor with a licensed maximum power level of 2957 megawatts thermal. The Energy Industry Identification System codes used in the text are identified as [XX].
A.
Plant Conditions Prior to Event:
Unit: 02 Event Date: 11-02-2009 Event Time: 0712 hours0.00824 days <br />0.198 hours <br />0.00118 weeks <br />2.70916e-4 months <br /> Reactor Mode: 3 Mode Name: Hot Shutdown Power Level: 0 Percent B.
Description of Event
On November 2, 2009, at 0712, shutdown cooling (SDC)[BO] function was lost on DNPS Unit 2 during cooldown for its Fall 2009 refueling outage (D2R21). The SDC system high temperature isolation logic actuated causing the SDC isolation valves to shut, resulting in a loss of cooling to the Reactor Vessel.
Reactor Recirculation (RR) system [AD] temperature was approximately 224 degrees F based on alternate indications. SDC was restarted at 0748 with Recirculation loop temperature at 260 degrees F. At approximately 0835, the reactor entered Mode 4 (i.e., Reactor Coolant temperature less than or equal to 212 degrees F and Mode Switch in Shutdown).
Troubleshooting determined that Temperature Element 2-0261-8B, a thermocouple (TC), had failed. The Resistance Temperature Detector (RTD), 2-0261-8F, housed in the same assembly, had previously failed and was out of service since December 2008. The presence of an open signal from both instruments in the same recirculation loop caused the isolation logic to activate, as designed.
The combined RTD/TC assembly is installed In the 2B RR System Pump suction line. Specifically, the RTD/TC probe is encased in a thermo-well located in the side of the RR suction piping in the first elbow off the reactor nozzle. The instrument is a model SRT-3375 RTD/TC assembly manufactured by Temp-Pro Inc. In this event, RTD 2-0621-8F had previously failed high meaning Isolation logic already had one open contact in the logic. When TC 2-0261-81 failed, the isolation logic experienced two open contacts, one in each logic string, which generated an isolation signal as designed.
The isolation of the SDC system event is reportable in accordance with 10 CFR 50.73(a)(2)(v)(B) "Any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to remove residual heat."
C.
Cause of Event
The apparent cause was the failure at the soldered TC (2-0261-86) junction and the RTD (2-0621-8F) element-to-lead solder joint attributed to corrosion and oxidation at the solder connection. Contributing causes included moisture intrusion aided by the hygroscopic (moisture absorbing) nature of the Aluminum Oxide (A120 3) filler material and chlorine contamination, potentially due to residual flux material, in combination with high temperatures creating a corrosive environment.
NRC FORM 380A (9-2007)
PrnNTEO ON RECYCLED PAPER
These RTD/TC assemblies have a history of failure at DNPS with at least 27 individual TE failures since 1987. This RTD/TC assembly is a commercial grade instrument with a poor performance history. The equipment is located in the suction recirculation line but has no radiation design specification. Additionally, a review of the bill of materials indicates that the epoxy used to seal the assembly has a maximum service temperature rating of 446 degrees F. Since the assembly is located inside the insulation surrounding the recirculation system piping while online, it would be exposed to temperatures at the upper range of this service temperature or greater.
The extent of condition pertains to both Unit 2 and Unit 3 Recirculation Suction line temperature elements.
Since the RTD/TC assembly is a unique part, custom made for DNPS, the extent of condition extending to other plants is unlikely. A replacement RR 2B temp instrument was installed during D2R21. Similar to the current Unit 2 configuration, logic to enhance reliability will be installed on Unit 3, which will require 2 instruments to fail In order to cause an inadvertent isolation on Unit 3.
D.
Safety Analysis
The safety significance of this event is minimal. The SDC was restored in 36 minutes, with reactor coolant temperatures rising approximately 36 degrees reaching 260 degrees F when SDC was restored. No other systems were affected and the system responded in a manner consistent with the plant design. The protection of public health and safety and personnel safety were not compromised at anytime during this event. Operator actions were appropriate and consistent with normal and emergency operating procedures.
E.
Corrective Actions
DNPS determined that the design of the existing temperature element assemblies would not ensure reliable performance, given the operational conditions (i.e., high temperature and radiation). Therefore, as the corrective action for this event, DNPS is in the process of identifying and procuring replacement temperature measurement assemblies suitable for installation in DNPS Units 2 and 3 RR suction lines.
NRC FORM 308A (9.2007)
PRINTED ON RECYCLED PAPER
F.
Previous Occurrences
A review of DNPS Licensee Event Reports (LERs) was performed and the following events were identified.
Licensee Event Report 237/2000-005-01, "Recirculation Loop Temperature Failure Causes Shutdown Cooling Inoperability" G.
Component Failure Data
Manufacturer Temp-Pro Inc Component Thermocouple Model SRT-3375 RTD/TC NRC FORM 306A (9.2007)
PRINTED ON RECYCLED PAPERPRINTED ON RECYCLED PAPER