05000259/LER-2007-009, Invalid High Level in Moisture Separator Results in Turbine Trip and Reactor Scram

Invalid High Level in Moisture Separator Results in Turbine Trip and Reactor Scram

ML073450844
Person / Time
Site:	Browns Ferry
Issue date:	12/11/2007
From:	O'Grady B Tennessee Valley Authority
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
LER 07-009-00
Download: ML073450844 (9)

LER-2007-009, Invalid High Level in Moisture Separator Results in Turbine Trip and Reactor Scram

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
2592007009R00 - NRC Website

text

December 11, 2007 U.S. Nuclear Regulatory Commission 10 CFR 50.73 ATTN: Document Control Desk Mail Stop: OWFN, P1-35 Washington, D. C. 20555-0001

Dear Sir:

TENNESSEE VALLEY AUTHORITY - BROWNS FERRY NUCLEAR PLANT (BFN)

- UNIT 1 - DOCKET 50-259 - FACILITY OPERATING LICENSE DPR LICENSEE EVENT REPORT (LER) 50-259/2007-009-00 The enclosed report provides details of an October 12, 2007, automatic reactor scram due to a turbine trip as a result of an invalid high level signal in the 1A1 moisture separator drain tank.

TVAs investigation into this event found that the turbine trip level switch instrument routing was the cause the event. The high level reference leg is routed to the moisture separator high point vent line and the low level reference leg is routed to the moisture separator drain piping.

Additionally, unique to Unit 1 only, the moisture separator high point vent line also has a 3 inch reducer in very close proximity to the turbine trip level switch high reference leg. Once the moisture separator is void of condensate, high velocity steam flow is established through the moisture separator, the presence of this reducer creates a venturi effect on the high level reference leg connection; thus, increasing the differential pressure between the moisture separator and the level control tank. This results in the high level reference leg having a lower pressure than the level reference leg, thus causing the turbine trip level switch floats to lift to above the trip setpoint.

U.S. Nuclear Regulatory Commission Page 2 December 11, 2007 This event is similar to the event that occurred on June 9, 2007, reported in LER 259/2007-005. The root cause investigation for LER 259/2007-005 concluded that the dump valve for the moisture separator was oversized for the

plant conditions

TVAs investigation into this event found that the dump valve for the moisture separator was oversized for the current plant conditions:

however, it heavily contributed to both events.

Additional analysis and plant testing at full reactor power found that with the dump valve flow restricted to 30 percent, a turbine trip would not occur. So, as an interim measure until corrective actions to address the root cause can be implemented, TVA has restricted the flow though the dump valve.

TVAs corrective actions for both of the events include rerouting the instrument reference legs so that flow through the moisture separator cannot create a venturi effect on the instrument reference leg.

TVA is reporting this in accordance with 10 CFR 50.73(a)(2)(iv)(A), as an event that resulted in a manual or automatic actuation of the systems listed in paragraph 10 CFR 50.73(a)(2)(iv)(B) (i.e., Reactor Protection System including reactor scram or trip, and general containment isolation signals affecting containment isolation valves in more than one system). There are no commitments contained in this letter.

Sincerely, Original signed by Brian O'Grady cc: See page 2

U.S. Nuclear Regulatory Commission Page 3 December 11, 2007 Enclosure cc (Enclosure):

Ms. Eva Brown, Project Manager U.S. Nuclear Regulatory Commission (MS 08G9)

One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852-2739 Branch Chief U.S. Nuclear Regulatory Commission Region II Sam Nunn Atlanta Federal Center 61 Forsyth Street, SW, Suite 23T85 Atlanta, Georgia 30303-8931 NRC Resident Inspector Browns Ferry Nuclear Plant 10833 Shaw Road Athens, Alabama 35611-6970

U.S. Nuclear Regulatory Commission Page 4 December 11, 2007 JEE:SWA:BAB Enclosure cc (Enclosure):

G.P. Arent, EQB 1B-WBN W. R. Campbell, Jr. LP 3R-C J. R. Douet, LP 3R-C S. M. Douglas, POB 2C-BFN R. F. Marks, Jr., PAB 1C-BFN D. C. Matherly, BFT 2A-BFN L. E. Nicholson, BR 4X-C B. A. Wetzel, BR 4X-C B. J. OGrady, NAB 2A-BFN S. A. Vance, WT 6A-K E. J. Vigluicci, ET 11A-K INPO:LEREvents@inpo.org NSRB Support, LP 5M-C EDMS WT CA-K, S:/Licensing/Lic/submit/lers/LER 259-2007-009 Reactor Scram.doc

NRC FORM 366 (6-2004)

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION (6-2004)

LICENSEE EVENT REPORT (LER)

(See reverse for required number of digits/characters for each block)

APPROVED BY OMB NO. 3150-0104 EXPIRES 06/30/2007

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

1. FACILITY NAME Browns Ferry Unit 1

2. DOCKET NUMBER 05000259

3. PAGE 1 of 5

4. TITLE: Invalid High Level In Moisture Separator Results in Turbine Trip and Reactor Scram

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 None DOCKET NUMBER N/A 10 12 2007 2007-009-00 12 11 2007 FACILITY NAME None DOCKET NUMBER N/A

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

9. OPERATING MODE 1

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)

X 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

10. POWER LEVEL 100 20.2203(a)(2)(vi) 50.73(a)(2)(i)(B) 50.73(a)(2)(v)(D) specify in Abstract below or in (If more space is required, use additional copies of (If more space is required, use additional copies of (If more space is required, use additional copies of NRC Form 366A) (17) Reactor scram from a turbine trip from 100% power is a transient for which BFN is analyzed.

Therefore, TVA concludes that the health and safety of the public was not affected by this event.

VI. CORRECTIVE ACTIONS

A.

Immediate Corrective Actions

Operations personnel placed the reactor in a stable condition in accordance with plant procedures.

B.

Corrective Actions to Prevent Recurrence (1)

To address the root cause and contributors to this event, TVA will relocate the reference legs, both the high and low reference points, for the high level turbine trip instruments. TVA will also eliminate the 3 inch reducer in the 6 inch vent line.

VII. ADDITIONAL INFORMATION

A.

Failed Components None.

B.

Previous LERs on Similar Events Unit 1 License Event Report 259/2007-005 provides details of an automatic scram from a moisture separator high level signal very similar to the one discussed in this report. The root cause of the report was the sizing of moisture separator dump valve. The valve is oversized for the application. TVAs corrective action to prevent recurrence of LER 259/2007-005 was to evaluate the valve size and either replace or modify the valve. Implementation of the corrective actions would not have prevented the turbine trip and reactor scram discussed in this report.

C.

Additional Information

Corrective action document for this report is PER 131878.

D.

Safety System Functional Failure Consideration:

This event is not considered a safety system functional failure according to NEI 99-02 E.

Scram With Complications Consideration:

This event did not result in a complicated scram according to NEI 99-02.

VIII.

COMMITMENTS

None.

(1) TVA does not consider these corrective actions as regulatory requirements. The completion of these actions will be tracked in TVA's Corrective Action Program.