05000323/LER-2013-002, Both Source Range Nuclear Instruments Inoperable While in Mode 6

Both Source Range Nuclear Instruments Inoperable While in Mode 6

ML13130A060
Person / Time
Site:	Diablo Canyon
Issue date:	05/09/2013
From:	Allen B Pacific Gas & Electric Co
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
DCL-13-050 LER 13-002-00
Download: ML13130A060 (6)

LER-2013-002, Both Source Range Nuclear Instruments Inoperable While in Mode 6

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 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)(8) 10 CFR 50.73(a)(2)(viii)(8) 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)(8) 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)(8)
3232013002R00 - NRC Website

text

Pacific Gas and Electric Company May 9, 201 3 PG&E Letter DCL-13-050 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC. 20555-0001 Docket No. 50-323, OL-DPR-82 Diablo Canyon Unit 2 Barry S. Allen Site Vice President 10 CFR 50.73 Diablo Canyon Power Plant Mail Code 104/6 P. O. Box 56 Avila Beach, CA 93424 805.545.4888 Internal: 691.4888 Fax: 805.545.6445 Licensee Event Report 2-2013-002-00, "Two Source Range Nuclear Instruments Inoperable While in Mode 6" Dear Commissioners and Staff; Pacific Gas and Electric Company (PG&E) submits the enclosed Licensee Event Report (LER) regarding the Diablo Canyon Power Plant (DCPP) Unit 2 loss of two source range nuclear instruments while in Mode 6. DCPP determined that the loss of the audible function provided by* the two source range instruments constituted a loss of a safety function required to maintain the reactor in a safe shutdown condition. Accordingly, PG&E is submitting this LER in accordance with 10 CFR 50.73(a)(2)(v)(A). PG&E will provide the cause of the event and associated corrective actions in a supplemental LER after completing a failure analysis.

PG&E makes no new or revised regulatory commitments (as defined by NEI 99-04).

in this report. All the corrective actions identified in this letter will be implemented in accordance with the DCPP Corrective Action Program.

This event did not adversely affect the health and safety of the public.

Sincerely, JiCJv-;5 ~ --

Barry S.~lIen.

dho6/50547324 Enclosure cc/enc:

Thomas R. Hipschman, NRC Senior Resident Inspector Arthur T. Howell, III, NRC Region IV James T. Polickoski, NRR Project Manager INPO Diablo Distribution A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway. Comanche Peak. Diablo Canyon. Palo Verde. San Onofre. South Texas Project. Wolf Creek

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2013 (10-2010)

, the NRC may digits/characters for each block) not conduct or sponsor, and a person is not required to respond to, the information collection.

3. PAGE Diablo Canyon Power Plant, Unit 2 05000-323 1 OF 5

4. TITLE Both Source Range Nuclear Instruments Inoperable While in Mode 6

5. EVENT DATE

6. LER NUMBER

7. REPORT DATE

8. OTHER FACILITIES INVOLVED YEAR I SEQUENTIAL I REV FACILITY NAME DOCKET NUMBER MONTH DAY YEAR NUMBER NO.

MONTH DAY YEAR FACILITY NAME DOCKET NUMBER 03 12 2013 2013

• 002

• 00 05 09 2013

9. OPERATING MODE

11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply) o 20.2201 (b) o 20.2203(a)(3)(i) o 50.73(a)(2)(i)(C) o 50.73(a)(2)(vii) 6 o 20.2201(d) o 20.2203(a)(3)(ii) o 50.73(a)(2)(ii)(A) o 50.73(a)(2)(viii)(A) o 20.2203(a)(1) o 20.2203(a)(4) o 50.73(a)(2)(ii)(8) o 50.73(a)(2)(viii)(8) o 20.2203(a)(2)~i) o 50.36(c)(1)(i)(A) o 50.73(a)(2)(iii) o 50.73(a)(2)(ix)(A)

10. POWER LEVEL o 20.2203(a)(2)(ii) o 50.36(c)(1)(ii)(A) o 50.73(a)(2)(iv)(A) o 50.73(a)(2)(x) o 20.2203(a)(2)(iii)

B 50.36(c)(2)

[(] 50.73(a)(2)(v)(A) o 73.71(a)(4) 000 o 20.2203(a)(2)(iv) 50.46(a)(3)(ii) o 50.73(a)(2)(v)(8) o 73.71(a)(5) o 20.2203(a)(2)(v) o 50.73(a)(2)(i)(A) o 50.73(a)(2)(v)(C) o OTHER o 20.2203(a)(2)(vi) o 50.73(a)(2)(i)(8) o 50.73(a)(2)(v)(D)

Specify in Abstract below or in YEAR

6. LER NUMBER I

SEQUENTIAL I NUMBER 2013

• 002 REV NO.

00 3

3. PAGE OF 5

When this event occurred, N-51 was out of service for maintenance. The maintenance was complete and N-51 indication was normal, but the instrument was not yet declared operable. Additionally, N-31 was already inoperable. A leaking reactor cavity seal [SEAL] had introduced moisture, which caused unreliable instrument indication. However, at the time of the N-32 cps increase, N-31 indication was normal. Therefore, when operators declared N-32 inoperable while N-31 was already inoperable, the control room audible count rate indication was no longer reliable. DCPP determined this condition constituted a loss of a safety function required to maintain the reactor in a safe shutdown condition. On March 12, 20l3, at 21:58 PDT, DCPP made an 8-hour nonemergency report (see NRC Event 48819) in accordance with 10 CFR 50.72(b)(3)(v)(A).

C. Status ofInoperable Structure, Systems, or Components That Contributed to the Event At the time of the event, Train A SR instrument N-31 was inoperable as a result of a leaking cavity seal that allowed moisture to cause unreliable indication. Cable testing confirmed insulation [INS] degradation and increased noise sensitivity. PAMS Channel A instrument N-51 was also inoperable for scheduled maintenance.

The maintenance was complete and N-51 indication was normal, but the instrument was not yet declared operable.

D. Other Systems or Secondary Functions Affected

No other system or secondary function was affected.

E. Method of Discovery

The High Flux at Shutdown alarm, along with an increase in the audible count rate, sounded in the control room making operators immediately aware of the condition.

F. Operator Actions

Upon receiving the High Flux at Shutdown alarm, operators appropriately responded by entering alarm response Procedure AR PK03-07, "Hi Flux at Shutdn Alarm." This procedure directed operators to enter operating Procedure OP AP-33, "Uncontrolled Boron Dilution At Shutdown." Operators observed elevated N-32 counts, but no other signs of a reactivity addition event. Therefore, operators declared N-32 inoperable and appropriately exited AP-33. Operators entered TS 3.3.1, action statements L.1 and L.2, and TS 3.9.3, action statements A.l, A.2, B.1, and B.2.

G. Safety System Responses This event did not initiate or require safety system responses.

III. Cause of the Problem YEAR

6. LER NUMBER I

SEQUENTIAL 1 NUMBER 2013

• 002 REV NO.

00 4

3. PAGE OF DCPP will provide the cause in a supplemental report, following completion of a vendor failure analysis and a causal determination.

IV. Assessment of Safety Consequences

The SR instruments provide protection from a rapid reactivity addition event at low power. At the time of the event, Unit 2 was shut down with all control rods fully inserted and all reactor trip breakers [BKR] open. These conditions ensure that a rapid reactivity addition event would not occur. A boron dilution event is a slow-moving reactivity addition. Other control room indications provided operators with SR indication. N-52 was operable.

N-51 and N-31 were both inoperable, but indicating correctly. Audible control room indication provided by N-31 was also functioning, but deemed unreliable. Additionally, operators subsequently set PPC alarms to provide an audible alert to any increase in SR power level. Given these conditions, the likelihood of an uncontrolled reactivity addition from a boron dilution accident had a low probability and therefore, the increase in risk is negligible.

V. Corrective Actions

A. Immediate Corrective Actions 5

DCPP established clearances to control sources of positive reactivity addition. Additionally, control room operators set PPC alarms to provide an audible alert to any increase in SR power level. These control room alarms served to replace the control room audible indication normally provided by the SR instruments.

B. Other Corrective Actions DCPP will provide corrective actions in a supplemental report.

VI. Additional Information

A. Failed Components At the time of the event, Train A SR instrument N-31 was inoperable as a result of a leaking cavity seal that allowed moisture to cause unreliable indication. Cable testing confirmed insulation degradation and increased noise sensitivity due to the moisture.

Preliminary results indicate that Train B SR instrument N-32 signal cable developed an internal fault. This fault caused unreliable indication that would vary when the N-32 signal cable was moved. This cable was previously tested on February 14, 2013, and showed no signs of an internal fault.

B. Previous Similar Events

No previous similar events were identified. YEAR

6. LER NUMBER I

SEQUENTIAL I NUMBER 2013

• 002 REV NO.

00 5

3. PAGE OF 5