05000390/LER-2006-007-02, Regarding High Range Radiation Monitors - Temperature Induced Current
| ML080570300 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 02/26/2008 |
| From: | Brandon M Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 06-007-02 | |
| Download: ML080570300 (10) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 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)(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)(v), Loss of Safety Function |
| 3902006007R02 - NRC Website | |
text
10 CFR 50.73 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555 Gentlemen:
In the Matter of
)
Docket No. 50-390 Tennessee Valley Authority
)
WATTS BAR NUCLEAR PLANT (WBN) UNIT 1 - LICENSEE EVENT REPORT 390/2006-007, REVISION 2 - HIGH RANGE RADIATION MONITORS - TEMPERATURE INDUCED CURRENTS On February 14, 2008, TVA submitted Revision 1 of LER 2006-007, which updated the corrective actions based on cable testing performed by TVA. Revision 0 of the LER was submitted on September 18, 2006, and was reported under 10 CFR 50.73(a)(2)(i)(B).
Subsequent to the release of Revision 1, it was noted that the LER number listed on NRC Form 366 was 2006-006 instead of 2006-007. Revision 2 corrects this error.
There are no regulatory commitments in this letter and if there should be questions concerning this matter, please call me at (423) 365-1824.
Sincerely, M. K. Brandon Manager, Site Licensing and Industry Affairs Enclosure cc: See Page 2 February 26, 2008 Original signed by
U.S. Nuclear Regulatory Commission Page 2 Enclosure cc (Enclosure):
NRC Resident Inspector Watts Bar Nuclear Plant 1260 Nuclear Plant Road Spring City, Tennessee 37381 ATTN: Margaret H. Chernoff, Senior Project Manager U.S. Nuclear Regulatory Commission MS 08G9a One White Flint North 11555 Rockville Pike Rockville, Maryland 20852-2738 U.S. Nuclear Regulatory Commission Region II Sam Nunn Atlanta Federal Center 61 Forsyth St., SW, Suite 23T85 Atlanta, Georgia 30303 Institute of Nuclear Power Operations 700 Galleria Parkway, NW Atlanta, Georgia 30339-5957 February 26, 2008
E-1 ENCLOSURE
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION (9-2007)
LICENSEE EVENT REPORT (LER)
(See reverse for required number of digits/characters for each block)
APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2010
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 1. FACILITY NAME Watts Bar Nuclear Plant
- 2. DOCKET NUMBER 05000 390
- 3. PAGE 1 OF 7
- 4. TITLE High Range Radiation Monitors - Temperature Induced Current
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTH DAY YEAR YEAR SEQUENTIAL NUMBER REV NO.
MONTH DAY YEAR FACILITY NAME N/A DOCKET NUMBER N/A 07 21 2006 2006 - 007 - 02 02 29 2008 FACILITY NAME N/A DOCKET NUMBER N/A
- 9. OPERATING MODE 1
- 10. POWER LEVEL 100%
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check all that apply) 20.2201(b) 20.2203(a)(3)(i) 50.73(a)(2)(i)(C) 50.73(a)(2)(vii) 20.2201(d) 20.2203(a)(3)(ii) 50.73(a)(2)(ii)(A) 50.73(a)(2)(viii)(A) 20.2203(a)(1) 20.2203(a)(4) 50.73(a)(2)(ii)(B) 50.73(a)(2)(viii)(B) 20.2203(a)(2)(i) 50.36(c)(1)(i)(A) 50.73(a)(2)(iii) 50.73(a)(2)(ix)(A) 20.2203(a)(2)(ii) 50.36(c)(1)(ii)(A) 50.73(a)(2)(iv)(A) 50.73(a)(2)(x) 20.2203(a)(2)(iii) 50.36(c)(2) 50.73(a)(2)(v)(A) 73.71(a)(4) 20.2203(a)(2)(iv) 50.46(a)(3)(ii) 50.73(a)(2)(v)(B) 73.71(a)(5) 20.2203(a)(2)(v) 50.73(a)(2)(i)(A) 50.73(a)(2)(v)(C)
OTHER 20.2203(a)(2)(vi) 50.73(a)(2)(i)(B) 50.73(a)(2)(v)(D)
Specify in Abstract below or in II.
Description of Event (continued):
E.
Method of Discovery
This condition was first identified some years ago and was subsequently evaluated as not affecting operability of the high range radiation monitors. However, upon reevaluation in response to questions from the resident inspectors, it was determined that this condition may cause the monitors to not meet reliability expectations due to the temperature induced currents.
F.
Operator Actions
The crew response was to enter the appropriate TS action which met Operations expectations.
There were no human performance issues.
G.
Safety System Responses There were no safety system responses as a result of this condition.
III.
CAUSE OF EVENT
NRC Information Notice 97-45, Supplement 1 identified a potential equipment qualification deficiency on the coaxial signal cables associated with containment high range radiation monitors from temperature induced currents (TIC). The potential exists for TIC on the signal cables associated with these monitors to cause erratic and inaccurate readings of post accident radiation levels inside of containment.
The TIC phenomenon correlates to the temperature change magnitude, rate of change and the type of cabling used. TVA evaluated the potential impact of TIC on instrumentation and the only devices impacted at WBN are the containment high range (2 located in upper containment, 2 located in lower containment) radiation monitors. At WBN, the monitors are manufactured by Sorrento and are identified as 1-RE-90-271, -
272, -273, and -274.
This phenomenon could cause these monitors to go into high alarm during the rapid temperature increases associated with Loss of Coolant Accidents (LOCAs) and Main Steam Line Breaks (MSLBs) inside containment. The monitors could also alarm as failed low due to negative TIC effects during rapid cooling for the same events. These monitors are used to estimate post accident fuel damage which factors into post accident emergency classifications and in certain Emergency Operating Procedures (EOPs).
As part of the effort to establish the WBN impact, new cables from the same production run as the cables installed at WBN were sent to the Electrical Insulation Research Center at the University of Connecticut for testing. Testing demonstrated that the WBN cables were impacted by TIC in magnitudes large enough to challenge the accuracy of monitor readings. Testing also demonstrated that repeated temperature transient cycling and aging of the cables at elevated temperatures both had an effect on the magnitude of TIC response. However, testing also demonstrated that the time constant for the WBN cables would allow the TIC effects to dissipate in approximately three minutes or less after temperature stabilization. This three minute period was substantiated using a computer program developed by the University of Connecticut.
III.
The tests described above are conservative with respect to the actual cabling installation since both the upper and lower compartment monitor coaxial cables are routed through the lower compartment in conduit. Other studies performed for cabling, in conduit exposed to high temperatures in the valve vaults, demonstrate that the conduit can reduce the thermal impact of transients by reducing short term temperature peaks and smoothing the thermal transient. However, based on the conservative test results, it has been assumed that the monitors would read high and would initially go into alarm during the rapid temperature rises inside of containment during LOCAs and MSLBs. It has also been assumed that the monitors will read low and go into low failure alarm during rapid temperature decreases inside of containment during LOCAs and MSLBs.
In order to validate the two assumptions discussed above, TVA initiated a series of tests to quantify the effects of temperature induced current (TIC) documented in EPRI Report TR-112852 and Southern California Edison (SCE) EQ report M85114 on a radiation monitor. The results of the tests were documented in a report titled High Range Radiation Monitor TIC Test Report. The report was approved on October 12, 2007, and a copy of the report has been provided to WBNs Resident Inspector. The methodology and results of the tests are summarized as follows:
Testing Methodology:
EPRI research quantified the TIC through a series of tests on typical cables using an electrometer.
EPRI tested the charge released between the center conductor and shield on an open circuit cable.
TVA duplicated the EPRI testing to verify TVAs ability to perform further testing.
This first set of tests was restricted to water and for this test, two types of cable were used; WTL-6 (RSS-6-160) and WTK-58 (RSS-6-154). The initial phase used water at the ice point and the cable was plunged into the water container. The water was drained and replaced with near boiling water and the cable again plunged. The same model electrometer used by EPRI was used in the TVA test.
Throughout the testing, the output of the electrometer was recorded using a computer based data acquisition system at a significantly higher data rate than what was used in the EPRI testing. In addition to recording the TIC, the water temperature was measured by a thermocouple and recorded by the data acquisition system.
Subsequently, three other test setups were then explored.
The first modified test recorded the current on a simulated radiation monitor detector loop.
The radiation monitors in question use only the center conductors out to and back from a radiation detector. The shield conductor is not used for measurement in the Sorrento radiation monitors. The detector was simulated with a capacitor and the charge from one center conductor to the other center conductor was measured and recorded by the electrometer and the data acquisition system.
The second modified test used a Sorrento radiation monitor and a detector. The radiation monitor output was recorded by the data acquisition system as the cable was initially placed in the ice water and subsequently in the near boiling water.
III.
The final test used a Sorrento radiation monitor and peanut oil to simulate the expected temperatures in containment. The initial oil temperature was 320°F. The cable was then transferred to 200°F oil to simulate containment spray cooling.
Test Results and Conclusions:
The results of TVAs testing documents that the TIC error produced on a radiation monitor during a worst case temperature increase compiled from a combination of all accidents, will last for less than one minute. The error for the cool-down phase that results from the activation of containment spray is even shorter. Therefore, TVA has implemented procedural guidance (administrative controls) to ensure the Operations staff understands the initial reaction of the monitors since the time duration of the TIC condition is limited. In this guidance, the duration of the TIC event is conservatively specified to last for two minutes.
IV.
ANALYSIS OF THE EVENT
The bulk of the cable runs for the upper containment monitors are in lower containment, so the effect on the four monitors will predominantly depend upon the rate of change of lower containment temperature. The four high range radiation monitors will initially experience inaccurate readings during post accident LOCA or MSLB conditions as a result of TIC. However, once the temperature has stabilized following an accident, the monitors will be functional for normal and post accident indication of radiation.
V.
ASSESSMENT OF SAFETY CONSEQUENCES
Since no automatic actuations result from these monitors which only provide alarms and indication to the operators indicating post accident conditions, there are no significant safety consequences associated with this event VI.
CORRECTIVE ACTIONS
A.
Immediate Corrective Actions
The information below has been provided to onshift personnel and to selected members of the Emergency Response Organization that are involved in making event classifications. For the purposes of REP classification the following considerations apply:
For a LOCA inside containment, other symptoms of Fuel Clad Barrier loss and potential containment barrier loss are listed in the Fission product barrier matrix (such as rapid unexplained pressure decrease following initial increase) and should be used to validate the indications from the high range radiation monitors.
VI.
For MSLB inside containment, the absence of other symptoms listed in the fission product barrier matrix for loss of fuel clad barrier or potential loss of containment barrier, as well as diverse diagnostic information provided in the plant Emergency Operating Procedures are intended to help in distinguishing between a primary system LOCA and a steam line break.
Information from these diverse sources should be used to validate the monitor readings.
B.
Corrective Actions to Prevent Recurrence
- 1.
As discussed in Section III, Cause of Event, of this LER, TVA has performed additional testing to quantify the effects of the TIC on the high range radiation monitors. The results of the testing are documented in a report titled High Range Radiation Monitor TIC Test Report, that was approved on October 12, 2007. The report concluded that, due to the limited duration of the TIC condition, administrative/procedural controls are adequate to address the condition.
- 2.
Consistent with the test results, TVA has revised Emergency Plan Implementing Procedure (EPIP) 1, Emergency Plan Classification Flowchart, to clarify the anticipated operation of the high range radiation monitors as a result of TIC.
Recently, WBN Unit 1 was shut down to begin the Cycle 8 refueling outage and when the unit entered Mode 4, LCO 3.3.3, Action G, was no longer applicable to the high range monitors. When the unit is returned to power operation following the completion of the outage, TVA will declare the high range monitors operable based on the above two corrective actions to prevent recurrence.
VII.
ADDITIONAL INFORMATION
A.
Failed Components There were no failed components due to this condition.
B.
Previous LERs on Similar Events A review performed of the previous WBN Licensee Event Reports (LERs) for any events associated with high range radiation monitor reliability did not reveal any previous issues.
C.
Additional Information
TVAs letter dated December 21, 2007, provided a report in accordance with Technical Specification 5.9.8, PAMS Report, for high range radiation monitor, 1-RE-90-272. This report documented that the monitor had been inoperable for more than 30 days. The report also contained a discussion regarding the analysis of the TIC issue associated with the high range radiation monitors and indicated that a revision to LER 2006-007 would be initiated to update the planned corrective actions.
Further the December 21st letter indicated that the operational status of the 1-RE-90-272 would be updated in the revision to the LER. Regarding this, the monitor was returned to service on January 4, 2008 after completion of repairs to the connector for the detector along with the replacement of the detector.
VII.
D.
Safety System Functional Failure This event did not involve a safety system functional failure as defined in NEI 99-02, Revision 4.
E.
Loss of Normal Heat Removal Consideration There was no loss of normal heat removal due to this condition.
VIII.
COMMITMENTS
None.
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