05000335/LER-2012-008, Regarding Control Room AC Single Failure Vulnerability

Regarding Control Room AC Single Failure Vulnerability

ML12310A064
Person / Time
Site:	Saint Lucie
Issue date:	10/22/2012
From:	Jensen J Florida Power & Light Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
L-2012-376 LER 12-008-00
Download: ML12310A064 (5)

LER-2012-008, Regarding Control Room AC Single Failure Vulnerability

Event date:
Report date:
Reporting criterion:	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 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
3352012008R00 - NRC Website

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October 22, 2012 L-2012-376 10 CFR 50.73 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C. 20555 Re:

St. Lucie Units 1 and 2 Docket Nos. 50-335 and 50-389 Reportable Event: 2012-008 Date of Event: August 23, 2012 Control Room AC Single Failure Vulnerability The attached Licensee Event Report 2012-008 is being submitted pursuant to the requirements of 10 CFR 50.73 to provide notification of the subject event.

Respectfully, 16oseph Jensen Site Vice President St. Lucie Plant JJ/KWF Attachment Florida Power & Light Company 6501 S. Ocean Drive, Jensen Beach, FL 34957

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/201, 10O-2010)

Estimated burden per response to comply with this mandatory collection request: 50 hours5.787037e-4 days <br />0.0139 hours <br />8.267196e-5 weeks <br />1.9025e-5 months <br />. Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments regarding burden estimate to the Records and FOIA/Privacy Service Branch (T-5 LICENSEE EVENT REPORT (LER)

F52), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to infocollects@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

3. PAGE St. Lucie Unit 1 05000335 1 OF 4

4.

TITLE Control Room AC Single Failure Vulnerability

5. EVENT DATE

6. LER NUMBER

7. REPORT DATE

8. OTHER FACILITIES INVOLVED Y

SEQUENTIAL REV DOCKET NUMBER MONTH DAY YEAR YEAR NUMBER NO.

MONTH DAY YEAR St.

Lucie Unit 2

05000389 IFACILITY NAME DOCKET NUMBER 08 23 2012 2012 -

008 00 10 22 20121 na na

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) rl 50.73(a)(2)(i)(C)

El 50.73(a)(2)(vii) 1[1 20.2201 (d)

El 20.2203(a)(3)(ii)

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

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

El 20.2203(a)(1)

[I 20.2203(a)(4) 0 50.73(a)(2)(ii)(B)

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

El 20.2203(a)(2)(i)

El 50.36(c)(1)(i)(A)

El 50.73(a)(2)(iii)

[3 50.73(a)(2)(ix)(A)

10. POWER LEVEL El 20.2203(a)(2)(ii)

El 50.36(c)(1)(ii)(A)

El 50.73(a)(2)(iv)(A)

[I 50.73(a)(2)(x)

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

El 50.36(c)(2)

El 50.73(a)(2)(v)(A)

El 73.71 (a)(4)

El 20.2203(a)(2)(iv)

El 50.46(a)(3)(ii)

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

El 73.71(a)(5) 100%

El 20.2203(a)(2)(v)

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

El 50.73(a)(2)(v)(C)

El OTHER El 20.2203(a)(2)(vi) 0 50.73(a)(2)(i)(B)

[E 50.73(a)(2)(v)(D)

Specify in Abstract below or in failure criteria.

For either St. Lucie Unit, single failure would not be met when the swing CRACS unit, HVA-ACC-3C, was in operation.

In addition, Unit 2 failed to meet single failure because the standby (e.g., not operating) HVA/ACC-3A or 3B unit on Unit 2 would not have restarted on a LOOP because the latching relay logic was not made up.

This condition is also reportable under 10 CFR 50.73(a) (2) (i) (B) as operation prohibited by the plant's Technical Specifications, as both St. Lucie Units have operated in the past three years crediting the swing CRACS unit, HVA-ACC-3C, for longer than the allowed outage time for an inoperable CRACS unit.

Each of the St. Lucie CRACS systems is similar, and is provided with three 50 percent capacity units and is sized for control room personnel habitability and equipment cooling purposes.

On St. Lucie Unit 1, two units are normally in operation.

On St.

Lucie Unit 2, one unit is normally in operation with the other unit(s) in standby available for manual alignment should a failure occur.

Upon a LOOP, the air conditioner units are automatically loaded on the emergency diesel generator sets.

Failure of all CRACS units to start post-LOOP would result in the slow heat up of the control room envelope (CRE).

Eventually, personnel habitability issues would drive the operators to manually start the available CRACS units before the temperature excursion could adversely affect equipment within the control room.

The St. Lucie Unit 1 control room emergency air cleanup system (CREACS) and St. Lucie Unit 2 control room emergency cleanup system (CRECS)

[EIIS:VI:FLT] are designed to provide air cleaning for the CRE atmosphere so that airborne radiological doses, experienced by control room personnel following a design basis accident (DBA) do not exceed limits imposed by Generic Design Criterion (GDC) 19.

Upon receipt of a containment isolation signal (CIS) or a high radiation signal from either of the outside air intakes, both of the CREACS/CRECS fans are automatically started, the outside air intakes are isolated, the kitchen and toilet exhaust ducts are isolated and the system recirculates the control room air through the HEPA filters and charcoal adsorbers for removal of radioactive particles and iodine (St.

Lucie Unit 1 has only one HEPA filter and charcoal adsorber shared between the CREACS fans, St. Lucie Unit 2 has independent HEPA filter and charcoal adsorber trains for each CRECS fan).

Although the CREACS/CRECS fans provide the radiological cleanup, the CRACS fans provide the required mixing of the CRE.

The CREACS/CRECS fans draw air from the CRACS return duct, filter the air and discharge the filtered air back into the CRACS return duct.

Without the CRACS fans operating the CREACS/CRECS fans will essentially recirculate the air inside the CRACS duct and filtration of the CRE will not occur.

Although the operators have detailed procedural requirements for operation of CREACS/CRECS post-accident, there was no specific procedural guidance to ensure that CRACS units are in operation for dose mitigation purposes.

An extent of condition and cause assessment was completed for all safety-related swing components and only the CRACS units were subject to this legacy design issue.

Analysis of Safety Significance This condition has no effect on core damage or large early release probabilities because no fission product barriers or mitigation equipment necessary to preserve these barriers are affected.

Thus, this condition had no adverse effect to the

health and safety of the public at large.

Failure of CRACS post-LOOP is a GDC-19 control room habitability issue.

The current design of the CRACS circuit for HVA/ACC-3C will not meet the requirements for a LOOP coincident with the DBA and a single failure when utilizing the HVA/ACC-3C unit.

Thus, the HVA/ACC-3C unit cannot be utilized for this purpose.

Additionally, St. Lucie Unit 2 normally operates with only one CRACS fan in service with one additional fan in standby.

In this alignment, only the running CRACS fan will restart following LOOP, and prior to implementation of the design modification to remove this vulnerability, this operational alignment would not meet the requirements for a LOOP coincident with the DBA and a single failure.

Although manual action can be taken to start the CRACS units to provide cooling of the CRE, there is not sufficient time for manual action during a DBA to ensure that the CRACS fan(s) are operating to provide mixing of the CRE air to support the CREACS/CRECS filtration function assumed for the GDC 19 control room dose analysis of record.

However, it is reasonable to assume that the operators would initiate the CRACS fans based on personnel comfort as the control room heats up without any air conditioning.

Based on this assumption, and the inherent conservatisms within the control room GDC 19 analysis of record, any postulated dose to the operators would not exceed the GDC 19 requirements of 5 rem TEDE by any appreciable amount.

Corrective Actions

The corrective actions listed have been entered into the site CAP.

Any changes to the actions below will be processed in accordance with the CAP.

1. The control circuitry for the St. Lucie Unit 1 swing CRACS unit, HVA/ACC-3C, was modified to ensure that the swing CRACS unit will start post-LOOP if it was operating prior to the event.

2.

The control circuitry for the St. Lucie Unit 2 swing CRACS unit, HVA/ACC-3C, will be modified in a similar manner as that completed on Unit 1 during the SL2-20 refueling outage.

Additionally, the Unit 2 HVA/ACC-3A and 3B CRACS units will have automatic start capability to ensure that they will start post-LOOP or post-ESFAS if aligned in the AUTO position or if operating prior to the event.

3.

St. Lucie Unit 1 procedures were changed to require two CRACS units to be in operation at all times.

4.

St. Lucie Unit 2 procedures will be changed during the SL2-20 refueling outage to allow one CRACS unit to be operating with a second unit aligned for automatic start.

Similar Events

None Failed Components None