05000296/LER-2011-002, For Browns Ferry, Unit 3, Regarding Reactor Scram Due to Scram Discharge Volume High Water Level

For Browns Ferry, Unit 3, Regarding Reactor Scram Due to Scram Discharge Volume High Water Level

ML11203A517
Person / Time
Site:	Browns Ferry
Issue date:	07/21/2011
From:	Polson K Tennessee Valley Authority
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
LER-11-002-00
Download: ML11203A517 (8)

LER-2011-002, For Browns Ferry, Unit 3, Regarding Reactor Scram Due to Scram Discharge Volume High Water Level

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(iv)(B), 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)(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)(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 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
2962011002R00 - NRC Website

text

Tennessee Valley Authority, Post Office Box 2000, Decatur, Alabama 35609-2000 July 21, 2011 10 CFR 50.73 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Browns Ferry Nuclear Plant, Unit 3 Facility Operating License No. DPR-68 NRC Docket No. 50-296

Subject:

Licensee Event Report 50-296/2011-002-00 On April 27, 2011, severe weather in the Tennessee Valley Service Area caused grid instability and the loss of all 500-kV offsite power sources which resulted in a scram of all three Browns Ferry Nuclear Plant (BFN) units. This resulted in an extended forced outage for all three BFN units until the 500-kV lines could be restored. On May 22, 2011, with Unit 3 in Cold Shutdown during surveillance testing, Unit 3 received a valid Reactor Protection System (RPS) actuation signal from both channels of the RPS due to Scram Discharge Volume high water level.

The Tennessee Valley Authority (TVA) is submitting this report in accordance with 10 CFR 50.73(a)(2)(iv)(A), as any event or condition that resulted in manual or automatic actuation of any of the systems listed in 10 CFR 50.73(a)(2)(iv)(B).

U.S. Nuclear Regulatory Commission Page 2 July 21, 2011 There are no new regulatory commitments contained in this letter. Should you have any questions concerning this submittal, please contact J. E. Emens, Jr., Nuclear Site Licensing Manager, at (256) 729-2636.

Respectfully, K. J. Poison Vice President

Enclosure:

Licensee Event Report 296/2011-002 Reactor Scram Due to Scram Discharge Volume High Water Level cc (w/ Enclosure):

NRC Regional Administrator - Region II NRC Senior Resident Inspector - Browns Ferry Nuclear Plant

Enclosure Browns Ferry Nuclear Plant Unit 3 Licensee Event Report 29612011-002-00 Reactor Scram Due to Scram Discharge Volume High Water Level See Attached

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 3150-0104 EXPIRES 10/13/2013 (10-2010)

, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

3. PAGE Browns Ferry Nuclear Plant (BFN) Unit 3 05000296 1 OF 5

4. TITLE Reactor Scram Due to Scram Discharge Volume High Water Level

5. EVENT DATE

6. LER NUMBER

7. REPORT DATE

8. OTHER FACILITIES INVOLVED YA YERSEQUENTIALý REV MOT A

ER FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR SUMEN REN MONTH DAY YEAR N/A 05000 FACILITY NAME DOCKET NUMBER 05 22 2011 2011 -

002 00 07 21 2011 N/A 05000

9. OPERATING MODE

11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)

El 20.2201(b)

El 20.2203(a)(3)(i)

El 50.73(a)(2)(i)(C)

[] 50.73(a)(2)(vii) l[ 20.2201(d)

E] 20.2203(a)(3)(ii)

El 50.73(a)(2)(ii)(A)

El 50.73(a)(2)(viii)(A)

E] 20.2203(a)(1)

[I 20.2203(a)(4)

El 50.73(a)(2)(ii)(B)

El 50.73(a)(2)(viii)(B)

E] 20.2203(a)(2)(i) 0l 50.36(c)(1)(i)(A)

E] 50.73(a)(2)(iii)

El 50.73(a)(2)(ix)(A)

10. POWER LEVEL [I 20.2203(a)(2)(ii)

El 50.36(c)(1)(ii)(A) 0 50.73(a)(2)(iv)(A)

El 50.73(a)(2)(x)

[I 20.2203(a)(2)(iii)

El 50.36(c)(2)

[I 50.73(a)(2)(v)(A)

El 73.71(a)(4)

[I 20.2203(a)(2)(iv)

E] 50.46(a)(3)(ii)

[I 50.73(a)(2)(v)(B)

El 73.71(a)(5) 000 El 20.2203(a)(2)(v)

El 50.73(a)(2)(i)(A)

[I 50.73(a)(2)(v)(C)

El OTHER El 20.2203(a)(2)(vi)

[E 50.73(a)(2)(i)(B)

El 50.73(a)(2)(v)(D)

Specify in Abstract below

12. LICENSEE CONTACT FOR THIS LER FACILITY NAME TELEPHONE NUMBER (Include Area Code)

James W. Davenport, Licensing Engineer 256-729-2690MANU-REPORTABLE MANU-REPORTABLE

CAUSE

SYSTEM COMPONENT FACTURER TO EPIX

CAUSE

SYSTEM COMPONENT FACTURER TO EPIX

14. SUPPLEMENTAL REPORT EXPECTED

15. EXPECTED MONTH DAY YEAR SUBMISSION LI YES (If yes, complete 15. EXPECTED SUBMISSION DATE)

[

NO DATE N/A N/A N/A ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)

On May 22, 2011, at 17:37 hours Central Daylight Time (CDT), with Browns Ferry Nuclear Plant (BFN) Unit 3 in Cold Shutdown and surveillance testing in progress, Unit 3 received a valid Reactor Protection System (RPS) actuation signal from both channels of the RPS due to Scram Discharge Volume (SDV) high water level. The scram occurred as Maintenance personnel were performing Intermediate Range Monitor (IRM) correlation for range 6 to 7. Maintenance personnel were measuring voltage during the reconnection of a high voltage cable to IRM G channel. A spike occurred on IRMs C and D channels indicating an invalid (safety function had already been completed) full reactor scram. After diagnosing the cause of the IRM scram, Operations personnel reset the scram and immediately received a valid RPS scram signal due to Scram Discharge Volume (SDV) high water level.

The cause of the event was that Operations personnel did not place the SDV high water level switch in bypass as required by procedure before resetting the first RPS scram. Thus, as the initial scram was being reset, the SDV filled with water causing the second scram.

NRC FORM 366 (10-2010)

I

I. PLANT CONDITION(S)

On April 27, 2011, severe weather in the Tennessee Valley Service Area caused grid instability and the loss of all 500-kV offsite power sources that resulted in a scram of all three Browns Ferry Nuclear Plant (BFN) units. This resulted in an extended forced outage for all three BFN units until the 500-kV lines could be restored. At the time of the event being reported [May 22, 2011, at 17:37 hours Central Daylight Time (CDT)], BFN Unit 3 was in Mode 4 (Cold Shutdown) with power supplied from qualified 161-kV offsite power sources.

II. DESCRIPTION OF EVENT

A. Event:

On May 22, 2011, Unit 3 was in Mode 4 (Cold Shutdown) in an extended forced outage due to the loss of all 500kV offsite power sources. Surveillance testing was being performed in support of returning the unit to power operations. At 17:35 hours CDT, Maintenance personnel were performing Intermediate Range Monitor (IRM) correlation for range 6 to 7. The IRM measures neutron flux, and correlation of the two different amplifier circuits within the IRM ensures a smooth transition when switching ranges during reactor power increases. Maintenance personnel were measuring voltage during the reconnection of a high voltage cable to IRM G channel. A spike occurred on IRMs C and D channels indicating an invalid (safety function had already been completed) full reactor scram. At 17:37 hours CDT, after diagnosing the cause of the IRM scram, Operations personnel reset the scram and immediately received a valid Reactor Protection System (RPS) [JC] scram signal due to Scram Discharge Volume (SDV) high water level. The scram occurred because Operations personnel did not place the SDV high water level switch in bypass as required by Abnormal Operating Instruction (AOI) 3-AOl-100-1, Reactor Scram, before resetting the first RPS scram.

As previously stated, the unit was in Cold Shutdown and all control rods were already fully inserted prior to the scram. The reactor water level remained within the prescribed band of 70 to 90 inches, with the highest level of 85 inches recorded. There was no impact to plant operations as a result of this scram.

The scram was not part of a preplanned sequence; therefore, the Tennessee Valley Authority (TVA) is submitting this report in accordance with 10 CFR 50.73(a)(2)(iv)(A),

as any event or condition that resulted in manual or automatic actuation of any of the systems listed in 10 CFR 50.73(a)(2)(iv)(B).

B. Inoperable Structures, Components, or Systems that Contributed to the Event:

None

C. Dates and Approximate Times of Major Occurrences

April 27, 2011, at 16:36 hours CDT Loss of all 500-kV offsite power sources resulting in a scram of all three BFN units and an extended forced outage until the 500-kV lines could be restored.

I NRC FORM 366 (10-2010)

May 22, 2011, at 17:35 hours CDT May 22, 2011, at 17:37 hours CDT May 22, 2011, at 17:37 hours CDT While performing IRM correlation for range 6 to 7 by Maintenance personnel, the RPS initiated an invalid reactor scram.

Operations personnel entered 3-AOl-100-1, and attempted to reset the RPS scram signal and received a valid scram actuation by both RPS channels due to SDV high water level.

Operations personnel re-entered 3-AOl-1 00-1 and reset the scram signal in accordance with the AOI.

D. Other Systems or Secondary Functions Affected

None

E. Method of Discovery

The event was immediately self revealing to Operations personnel.

F. Operator Actions

Operations personnel re-entered 3-AOl-1 00-1 and reset the scram signal in accordance with the AOI.

G. Safety System Responses:

The safety systems (RPS and SDV) responded as designed.

I1l. CAUSE OF THE EVENT A. Immediate Cause:

The immediate cause of the event was RPS actuation due to SDV high water level.

B. Root /Apparent Cause:

The cause of this event was that Operations personnel did not place the SDV high water level switch in bypass as required by 3-AOl-100-1 before resetting the first RPS scram.

IV. ANALYSIS OF THE EVENT

Maintenance personnel were measuring voltage during the reconnection of a high voltage cable to IRM G channel. A spike occurred on IRMs C and D channels indicating an invalid (safety function had already been completed) full reactor scram. After diagnosing the cause of the IRM scram, Operations personnel reset the scram and immediately received a valid RPS scram signal due to SDV high water level.

The RPS initiates a reactor scram when one or more monitored parameters exceed their specified limits. This preserves the integrity of both the fuel cladding and Reactor Coolant System and minimizes the energy that must be absorbed following a loss of coolant accident. The operability of the RPS is dependent on the operability of the individual NRC FORM 366 (10-2010)

instrumentation channel functions specified in the Technical Specifications. SDV is one of the RPS channel functions. The SDV receives the water displaced by the motion of the Control Rod Drive pistons during a reactor scram. Should this volume fill to a point where there is insufficient volume to accept the displaced water, control rod insertion would be hindered. Therefore, a reactor scram is initiated while the remaining free volume is still sufficient to accommodate the water from a full core scram. The SDV function of RPS operated as designed. Operations personnel re-entered 3-AOl-1 00-1 and reset the scram signal, within seconds, in accordance with the AOI. The Unit 3 Reactor water level remained within the prescribed band of 70 to 90 inches, with the highest level of 85 inches recorded.

V. ASSESSMENT OF SAFETY CONSEQUENCES

The RPS and SDV both operated in accordance with the plant design. At the time of this event, BFN Unit 3 was in Mode 4 (Cold Shutdown) with all control rods fully inserted. The reactor scram from high SDV water level is part of the BFN design, and the occurrence of this event from at-power conditions has been analyzed.

Based on the above discussion, there was no adverse safety impact as a result of this event. Thus, there was no effect on the health and safety of the public.

VI. CORRECTIVE ACTIONS

Corrective actions are being managed within TVA's Corrective Action Program.

A.

Immediate Corrective Actions

" Operations personnel re-entered 3-AOl-100-1, and correctly reset the scram signal in accordance with the AOI.

The oncoming Operations crew reviewed 3-AOI-100-1 for resetting of scrams in outage conditions.

B.

Corrective Actions to Prevent Recurrence:

The specific corrective action for this event is the following.

Operations personnel involved were disciplined in accordance with appropriate TVA administrative procedures.

VII. ADDITIONAL INFORMATION

A.

Failed Components:

None B.

Previous LERS or Similar Events:

A search of BFN LERs from January 1, 2006 to the present identified two similar events.

LER 50-260/2005-003-00, Reactor Protection System Actuation from Scram Discharge Volume High Level While Shutdown. The cause of this LER was inadequate communication between Operations personnel and Maintenance personnel with regard NRC FORM 366 (10-2010)

to test equipment status. The corrective actions included that the essential nature of clear, unambiguous communication will be reinforced to site personnel involved in testing activities.

Also, LER 50-260/2009-006-01, Automatic Reactor Protection System Scram While Shutdown. The cause of this LER was that Control Room Operators were unaware of SDV system configuration and work in progress. The corrective actions for this event included performance of a training needs analysis of the event for possible inclusion into Licensed Operator Requalification training.

C.

Additional Information

The corrective action document for this report is PER 373365 which was closed to PER 335574 written to address a generic degradation of BFN Operator performance standards.

D.

Safety System Functional Failure Consideration:

This event is not a safety system functional failure in accordance with NEI 99-02.

E.

Scram With Complications Consideration:

This event was not a complicated scram in accordance with NEI 99-02.

VIII. COMMITMENTS

None NRC FORM 366 (10-2010)