05000263/LER-2011-004, Regarding Secondary Containment Inoperability Due to Ventilation Alignment Issue

Regarding Secondary Containment Inoperability Due to Ventilation Alignment Issue

ML112201462
Person / Time
Site:	Monticello
Issue date:	08/08/2011
From:	O'Connor T Northern States Power Co, Xcel Energy
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
L-MT-11-047 LER 11-004-00
Download: ML112201462 (4)

LER-2011-004, Regarding Secondary Containment Inoperability Due to Ventilation Alignment Issue

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
2632011004R00 - NRC Website

text

August 8,201 1 Monticello Nuclear Generating Plant 2807 W County Road 75 Monticello, MN 55362 L-MT-11-047 10 CFR 50.73 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Monticello Nuclear Generating Plant Docket No. 50-263 Renewed Facility Operating License No. DPR-22 LER 201 0-004, "Secondan/ Containment Inoperability Due to Ventilation Alignment Issue" The Licensee Event Report (LER) for this occurrence is attached.

Summan/ of Commitments o new commitments and no revisions to existing commitments.

onticello Nuclear Generating Plant '

ern States Power - Minnesota Enclosure cc:

Administrator, Region Ill, USNRC Project Manager, Monticello, USNRC Resident Inspector, Monticello, USNRC

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION (10-2010)

LICENSEE EVENT REPORT (LER)

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

APPROVED BY OMB NO. 3150-0104 EXPIRES 10/31/2013

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

3. PAGE Monticello Nuclear Generating Plant 05000 263 1

OF 3

4. TITLE Secondary Containment Inoperability Due to Ventilation Alignment Issue

5. EVENT DATE

6. LER NUMBER

7. REPORT DATE

8. OTHER FACILITIES INVOLVED FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR SEQUENTIAL NUMBER REV NO MONTH DAY YEAR 05000 FACILITY NAME DOCKET NUMBER 06 08 2011 2011 - 004 - 0 08 08 2011 05000

9. OPERATING MODE

11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply) 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) 1 20.2203(a)(2)(i) 50.36(c)(1)(i)(A) 50.73(a)(2)(iii) 50.73(a)(2)(ix)(A)

10. POWER LEVEL 20.2203(a)(2)(ii) 50.36(c)(1)(ii)(A) 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) 100 20.2203(a)(2)(vi) 50.73(a)(2)(i)(B) 50.73(a)(2)(v)(D)

OTHER Specify in Abstract below or in Frequency is not significantly impacted since CDF is not affected, and the duration of the low SCT vacuum was very small. Based on the above, the safety significance was minor.

CAUSE

Although V-AH-4A and B are equally sized air handling units, significant differences in flow rates existed between them due to a seized reheat coil bypass damper on V-AH-4A. This resulted in significant swings in the SCT differential pressure during fan swapping before system dampers were repositioned to compensate. Following the previous fan swap that removed V-AH-4B from service and placed V-AH-4A into service on June 5, 2011, the Reactor Building exhaust fan variable inlet vane settings had been throttled closed from 80% to 55% to lower Reactor Building differential pressure to compensate for the lower air throughput of V-AH-4A. It was not recognized that when V-AH-4B was returned to operation for post maintenance testing on June 8, 2011, that the incoming Reactor Building supply air flow would increase and the previously throttled variable inlet vane setting would prevent the Reactor Building exhaust fans from maintaining the Reactor Building greater than 0.25 inches WC vacuum. Although the seizing of the reheat coil bypass damper had been identified in January 2011, the effect was masked somewhat during fan swaps during cold weather because the reheat face dampers were free to modulate as heating needs required. During warm weather the reheat face dampers are closed and no longer modulate flow.

CORRECTIVE ACTIONS

1. The bound reheat coil bypass damper on V-AH-4A will be reworked.

2. A procedure change has been generated to add precautions to the operating procedure for transferring refuel floor fans.

PREVIOUS SIMILAR EVENTS

On February 11, 2011 secondary containment was declared inoperable due to ice buildup on a SCT isolation damper (LER 2011-003).