05000301/LER-2011-004, Regarding Automatic Reactor Trip During Startup Physics Testing Due to Source Range Detector Failure
| ML112082516 | |
| Person / Time | |
|---|---|
| Site: | Point Beach  |
| Issue date: | 07/25/2011 |
| From: | Meyer L Point Beach |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NRC 2011-0069 LER 11-004-00 | |
| Download: ML112082516 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation 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)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(iii) 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 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3012011004R00 - NRC Website | |
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July 25, 201 1 BEACH NRC 201 1-0069 10 CFR 50.73 U. S. Nuclear Regulatory Commission AlTN: Document Control Desk Washington, DC 20555 Point Beach Nuclear Plant, Unit 2 Docket 50-301 Renewed License No. DPR-27 Licensee Event Re~ort 301/2011-004-00 Automatic Reactor Trio Durina BOL Phvsics Testinq Due to Source Range Detector Failure Enclosed is Licensee Event Report (LER) 3011201 1-004-00 for Point Beach Nuclear Plant (PBNP), Unit 2. This LER documents an automatic reactor trip from 0% power while performing beginning-of-life (BOL) physics testing. Pursuant to 10 CFR 50.73(a)(2)(iv)(A), the event is reportable as, "... an event or condition that resulted in manual or automatic actuation of the Reactor Protection System including reactor scram or reactor trip."
This submittal contains no new or revised regulatory commitments.
If you have questions or require additional information, please contact Mr. James Costedio at 9201755-7427.
Very truly yours, NextFra Energy Point Beach, LLC Larry Meyer Site Vice President Enclosure cc:
Administrator, Region Ill, USNRC Project Manager, Point Beach Nuclear Plant, USNRC Resident Inspector, Point Beach Nuclear Plant, USNRC PSCW NextEra Energy Point Beach, LLC, 6610 Nuclear Road, Two Rivers, WI 54241
LICENSEE EVENT REPORT (LER)
EI] 20.2203(a)(3)(i)
EI] 50.73(a)(2)(i)(C)
EI] 50.73(a)(2)(vii)
EI] 20.2203(a)(3)(ii)
EI] 50.73(a)(2)(ii)(A)
I7 20.2203(a)(4) 50.73(a)(2)(ii)(B)
EI] 50.36(c)(l )(i)(A)
- 50.73(a)(2)(iii) 50.36(c)(I)(ii)(A) 50.73(a)(2)(iv)(A)
EI] 50.73(a)(2)(v)(A)
- 20.2203(a)(2)(iv)
EI] 50.46(a)(3)(ii)
EI] 50.73(a)(2)(v)(B)
EI] 20.2203(a)(2)(v)
EI] 50.73(a)(2)(i)(A)
EI] 50.73(a)(2)(v)(C) 20.2203(a)(2)(vi)
EI] 50.73(a)(2)(i)(B)
EI] 50.73(a)(2)(v)(D) s testing with the reactor subcritical in dynamic rod worth testing of Shutdown Bank A control rods. As power lowered during testing, the two source range nuclear instruments automatically energized, however, one of the two instruments subsequently failed high, thus establishing the required logic to initiate the automatic reactor trip.
All plant systems functioned as required following the trip. All control rods fully inserted into the core. No emergency core cooling system or auxiliary feedwater systems actuated; the emergency diesel generators did not start; and power continued to be supplied from off-site sources. The reactor coolant system had forced circulation with the atmospheric steam dump valves being used for decay heat removal from the steam generators.
The event was caused by the failure of a high voltage power supply in the source range nuclear detector.
The failed power supply unit was replaced. Additional actions tracked in the corrective action program include establishment of a life cycle management program and periodic replacement of NIS high voltage power supplies in accordance with a preventive maintenance schedule.
NCR FORM 366 (10-2010)
Description of the Event On 0611 311 1 at 1924 CDT, during beginning-of-life (BOL) physics testing with the reactor subcritical in MODE 2, an automatic reactor trip occurred while operators were inserting a shutdown bank during dynamic rod worth testing of Shutdown Bank A control rods. At approximately 191 5 CDT, while inserting the Shutdown Bank A control rods from 228 steps to 2 steps, the Group 2 portion of the Shutdown Bank A step counter [STC] stopped at 152 steps, while the Group I portion of the step counter continued to insert.
Based upon the potential misalignment of the control rods, rod motion was stopped to evaluate the step counter condition. As a result of the previous rod insertion, there was a negative startup rate and reactor power was decreasing through the intermediate range.
The evaluation resulted in the decision to manually trip the Unit 2 reactor and to suspend BOL physics testing in order to determine the cause of the apparent step counter discrepancy. Approximately 30 seconds after the decision was made to manually trip the reactor and during preparations to manually open the reactor trip breakers, an automatic reactor trip occurred as a result of the power level dropping below the P-6 interlock. At the P-6 interlock, both source range nuclear instruments automatically energize, and the source range high flux reactor trip (greater than 1.5 x 10-E5 cps on one of two instruments) is unblocked. The determination that the reactor was subcritical at the time of the automatic trip was based upon the addition of -250pcm from a stable critical reactor condition and indication of a stable -113 dpm intermediate range startup rate with no additional reactivity changes.
Both source range nuclear instruments [DET] energized; however, one of the instruments immediately pegged high on counts and voltage. When this occurred, the source range high flux reactor trip logic (one-out-of-two) [JD] was satisfied, and a reactor protection signal actuated that resulted in the automatic reactor trip. Actions were taken by Operations in accordance with emergency operating procedures to stabilize the reactor in MODE 3 and a post-trip event investigation was initiated.
A four-hour ENS notification (EN 46957) was submitted to the NRC on 0611 311 1 at 2229 CDT as reportable in accordance in accordance with 10 CFR 50.72(b)(2)(IV)(B), "any event or condition that results in actuation of the reactor protection System when the reactor is critical..." A subsequent review of plant conditions just prior to the time of the trip indicated that the reactor was subcritical. Accordingly, a revised notification was made on 06/14/1 I at 2055 CDT to reflect an eight-hour notification via 10 CFR 50.72(b)(3)(IV)(A),"any event or condition that results in a valid actuation of the reactor protection system..." rather than the four-hour notification submitted on 0611 311 1.
This event was not a safety system functional failure. The failure of the 2N31 source range detector high voltage power supply resulted in the automatic trip of the Unit 2 reactor on the required one-out-of-two
Cause of the Event
The cause of the event was the failure of the nuclear source range detector high voltage power supply.
Analysis of the Event
Plant systems functioned as required following the automatic reactor trip. Control rods fully inserted into the core. Neither the emergency core cooling system nor the auxiliary feedwater system actuated; the emergency diesel generators did not start; and power continued to be supplied from off-site sources. The reactor coolant system had forced circulation following the trip and the atmospheric steam dump valves were used for decay heat removal from the steam generators.
Analysis of Safety Significance The source range neutron flux trip protects against reactivity excursions during reactor startup from subcritical conditions proceeding into the power range. The reactor is tripped when one-out-of-two source range channels are above the trip setpoint. This trip, which provides protection during reactor startup, can be manually blocked when one-out-of two intermediate range channels are above the P-6 permissive setpoint.
There are also two intermediate range channels that provide protection to the reactor. When both of these intermediate range channels are below the P-6 permissive setpoint, the reactor trip is automatically reinstated. The intermediate range trip is automatically blocked when two-out-of four high power range signals are above the P-I 0 permissive setpoint of approximately 10% power. The source range trip setpoint is between the P-6 permissive setpoint (P-6 allows the manual de-energization of the source range high voltage power supply) and the maximum source range power level detection limit.
When the source range detector failed, the one-out-of two logic to trip was established, resulting in the automatic reactor trip. Since the reactor was subcritical, the reactivity transient was small and the potential for core damage was minimal. Thus, the safety significance of the event was low. There was no impact on the health and safety of the public or plant personnel as a result of this event. There was no radiological release nor any release to the environment. Accordingly, the nuclear safety significance of this event was
Corrective Actions
The high voltage power supply for the source range detector was replaced. The root cause evaluation for this event determined a life cycle management plan had not been established for the periodic replacement of nuclear instrumentation high voltage power supplies. The preventive maintenance program has been revised to perform periodic replacement of the power supplies. Completion of the corrective actions to develop the life cycle management program and replace the high and low voltage power supplies is being tracked in the site corrective action program.
Similar Events
There were no similar reportable events.
Component Failure Data
Descri~tion Model Number High Voltage Power Supply UPMD-X54W-MI