05000263/LER-2008-001, Re Non-Conservative High Energy Line Break Analysis Discovered During Extended Power Uprate Review

Re Non-Conservative High Energy Line Break Analysis Discovered During Extended Power Uprate Review

ML080910155
Person / Time
Site:	Monticello
Issue date:	03/31/2008
From:	O'Connor T Nuclear Management Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
L-MT-08-019 LER 08-001-00
Download: ML080910155 (5)

LER-2008-001, Re Non-Conservative High Energy Line Break Analysis Discovered During Extended Power Uprate Review

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 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)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(x)
2632008001R00 - NRC Website

text

Monticello Nuclear Generating Plant Committed to Nuclear Excellence Operated by Nuclear Management Company, LLC March 31, 2008 L-MT-08-0 1 9 10 CFR Part 50.73 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555 Monticello Nuclear Generating Plant Docket No. 50-263 License No. DPR-22 LER 2008-001, "Non-Conservative High Energv Line Break Analvsis Discovered Durinq Extended Power Uprate Review" A Licensee Event Report (LER) for this occurrence is attached.

This letter contains no new commitments and no revisions to existing commitments.

&&/J*

Gfl 7 0,ALP'/

Timot J. 0 Connor Site vice President, Monticello Nuclear Generating Plant Nuclear Management Company, LLC Enclosure cc:

Administrator, Region Ill, USNRC Project Manager, Monticello, USNRC Resident Inspector, Monticello, USNRC 2807 West County Road 75 Monticello, Minnesota 55362-9637 Telephone: 763-295-51 51 Fax: 763-295-1454

NRC FORM 366 U.S. NUCLEAR REGULATORY (9-2007)

COMM~SS~ON LICENSEE EVENT RE PORT (LE R)

(See reverse for required number of digitslcharacters for each block)

FACILITY NAME (1)

Monticello Nuclear Generating Plant APPROVED BY OMB NO. 3150-0104 EXPIRES 8-31 -201 0

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

DOCKET NUMBER (2) 05000263 TITLE (4)

Non-Conservative High Energy Line Break Analysis Discovered during Extended Power Uprate Review PAGE (3) 1 of4 EVENT DATE (5)

M O 01 LER NUMBER (6)

LICENSEE CONTACT FOR THlS LER (12)

DAY 31 YEAR NAME Ron Baumer YEAR 2008 OPERATING MODE (9)

LEVEL (1 0)

REPORT DATE (7)

THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR 5: (Check all that apply) (11)

TELEPHONE NUMBER (Include Area Code) 763-295-1 357 100 2008 - 001 - 00 SEQUENTIAL NUMBER MO 03 OTHER FACILITIES INVOLVED (8) 20.2201 (b) 20.2201 (dl 20.2203(a)(I) 20.2203(a)(2)(i) 20.2203(a)(2)(ii) 20.2203(a)(2)(iii) 20.2203(a)(2)(iv) 20.2203(a)(2)(v) 20.2203(a)(2)(vi) 20.2203(a)(3)(i)

REV NO FACILITY NAME FACILITY NAME COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THlS REPORT (13)

DAY 31 DOCKET NUMBER 05000 DOCKET NUMBER 05000 20.2203(a)(3)(ii) 20.2203(a)(4) 50.36(c)(l)(i)(A) 50.36(c)(l)(ii)(A) 50.36(~)(2) 50.46(a)(3)(ii) 50.73(a)(2)(i)(A) 50.73(a)(2)(i)(B) 50.73(a)(2)(i)(C) 50.73(a)(2)(ii)(A)

YEAR 2008 X

TO EPIX

CAUSE

'OMPoNENT SYSTEM 50.73(a)(2)(ii)(B) 50.73(a)(2)(iii) 50.73(a)(2)(iv)(A) 50.73(a)(2)(v)(A) 50.73(a)(2)(v)(B) 50.73(a)(2)(v)(C) 50.73(a)(Z)(v)(D) 50.73(a)(2)(vii) 50.73(a)(2)(viii)(A) 50.73(a)(2)(viii)(B)

KXRER

CAUSE

YEAR 50,73(a)(2)(ix)(A) 50.73(a)(2)(x) 73.71 (a)(4) 73.71 (a)(5)

OTHER Specify in Abstract below or in NRC Form 366A ABSTRACT On January 31, 2008 during a review of the High Energy Line Break (HELB) calculations for the plant's Extended Power Uprate (EPU) project, it was determined that the existing HELB calculations failed to consider the actuation of the fire sprinklers in the condenser bay and the resultant flooding impact on the lower Division 1 4kV equipment. The station had previously installed a flood barrier near the 4kV Switchgear room door therefore present operability was not impacted. The station determined that prior to the installation of the barrier, there was a potential for the loss of the lower Division 1 4kV equipment. This LER addresses the past operability impact. The cause of the event was a failure to consider the impact of the fire sprinklers. Corrective actions taken or planned are: the flood barrier will remain in place and a revision of the affected HELB calculations will be performed.

SYSTEM MONTH EXPECTED SUBMISSION DATE (1 5)

SUPPLEMENTAL REPORT EXPECTED (14)

DAY COMPONENT NO YES (If yes, complete EXPECTED SUBMISSION DATE).

X FACTURER REPORTABLE EP'X (9-2007)

U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)

FACILITY NAME (1)

DOCKET (2)

LER NUMBER (6)

PAGE (3)

SEQUENTIAL REVISION Monticello Nuclear Generating Plant 05000263 YEAR NUMBER NUMBER 2of4 2008 - 001 -

00 I

TEXT (If more space is required, use additional copies of NRC Form 366A) (1 7 )

1

Event Description

On January 31, 2008, Monticello Nuclear Generating Plant (MNGP) personnel discovered during a review of the Extended Power Uprate (EPU) High Energy Line Break (HELB) calculations that the station had not considered the impact of the actuation of fire sprinklers [SPRNK] in the existing HELB calculations. Since the station had a flood barrier installed outside the lower Division 1 4kV [EC] switchgear room, current operability of the plant was not affected. However, for the plant conditions which existed prior to installation of the HELB barrier outside the 4KV switchgear room, the issue is reportable under 50.73(a)(2)(ii)(B) "Any event or condition that resulted in the nuclear power plant being in an unanalyzed condition that significantly degrades plant safety."

The station conducted a review of information related to NRC requirements and guidance as well as correspondence applicable to High Energy Line Breaks (HELB). Based on this review, it was determined that without the HELB barrier in place to protect the Division I 4KV room, the plant would be in an unanalyzed condition for the following HELB events in the condenser room: a feedwater [SJ] pump [PMP] discharge line break, a condensate [SD] (feedwater suction line) break, or a Main Steam [SB] line break in the condenser room. Without the barrier in place the additional volume of water from the fire suppression system causes the flood level within the Division I 4KV room to reach a level which renders the equipment within that room inoperable.

Event Analvsis The station determined there was no current operability concern and therefore the event was not reportable under 10 CFR 50.72. However, due to past operability concerns (the condition existed from November 29, 2001 to present), the event is reportable under 50.73(a)(2)(ii) (B)

"Any event or condition that resulted in the nuclear power plant being in an unanalyzed condition that significantly degrades plant safety, and a Licensee Event report is required for this event.

I The event is not considered a safety system functional failure.

Safety Significance

The Probabilistic Risk Assessment (PRA) group performed an evaluation of the risk of core damage attributable to floodwater resulting from actuation of the condenser bay sprinkler system upon a HELB event that exceeds temperatures at which the sprinkler heads activate.

This assessment is intended to address past risk associated with the postulated HELB events, I NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)

I TEXT (If more space is required, use additional copies of NRC Form 366A) (1 7)

FACILITY NAME (1)

Monticello Nuclear Generating Plant therefore the flood barrier erected outside of the lower 4KV switchgear room is assumed not to exist.

It was determined that a HELB frequency of 2.60 E-02Iyr (one HELB event every 39 years) would be required to result in a CDF increase of 1.00 E-O61yr for the scenario of interest. Since an annual increase in core damage probability of 1.00 E-06 is considered to be very small as reflected in guidance provided by RG 1.174, the frequency of the HELB break(s) of concern must therefore be greater than 2.60 E-021yr to be considered more than a very small risk impact. Since the Monticello plant and the commercial nuclear industry as a whole do not observe HELB events in general at or near this frequency, a reasonable conclusion can be drawn, that the additional CDF risk attributable to the vulnerability of division I 4KV switchgear to HELB events described 1 above, is very small.

DOCKET (2) 05000263 Combined flow resulting from the HELB and fire sprinkler activation was determined to be bounded by a large fire protection system break modeled in the PRA. Review of quantification results related to the postulated HELB scenario show that the flooding, unless detected and suppressed early, generally fails the lower 4KV equipment as well as offsite power, leaving

1. I2 EDG [DG] as the only remaining major power source to supply division II equipment.

Failure of #I2 EDG due to any of a wide array of causes will result in a station blackout (SBO),

and limited capability to provide long term core cooling to prevent melting of the core. Even with a SBO, however, adequate core cooling can be accomplished through the use of HPCl [BJ] and/or RClC [BN] for short term (several hours) high pressure injection followed by either manual operation of RClC or depressurization with low pressure injection of fire water (recovered from the sprinkler activation diversion). Both long term RClC operation and fire water injection are dependent on long term decay heat removal capability for success.

In conclusion, the risk of core damage attributable to floodwater resulting from actuation of the condenser bay sprinkler system upon a HELB event that exceeds temperatures at which the sprinkler heads would actuate is considered to be very small.

Cause

PAGE (3) 3of4 LER NUMBER (6)

MNGP calculations of record for HELB did not model the actuation of the fire water sprinklers in the condenser room when the condenser room exceeded 165 deg F during a postulated HELB. The sprinkler actuation adds to the liquid water volume emptied into the condenser room following a HELB. This extra liquid volume in the condenser room is enough to have exceeded the maximum allowable postulated water level of 3.75" in the lower 4 kV switchgear YEAR room.

I 2008 - 001 -

00 SEQUENTIAL NUMBER REVISION NUMBER

IRC FORM 366A 1-2007)

U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)

Zorrective Action FACILITY NAME (1)

Aonticello Nuclear Generating Plant

- he applicable HELB calculations will be revised to reflect the new data.

ailed Component Identification

'EXT (If more space is required, use additional copies of NRC Form 366A) (17)

DOCKET (2) 05000263

>revious Similar Events JlNGP LER 263-2000-004: An analysis of a high energy line break (HELB) on the 91 1ft

levation of the Turbine Building indicated flooding of the Division I 4kV switchgear room and

~ossible loss of the Division I 4kV switchgear. The analysis indicated that the peak flood level In the 91 Ift elevation of the Turbine Building Division I 4kV switchgear room would cause a oss of Division I 4kV power. With an assumed loss of offsite power, Division II Emergency liesel Generator was considered the worst case single active failure. Therefore, this event

odd potentially result in loss of the station AC power from both divisions of the 4kV listribution system. Modifications were installed to prevent water from entering the Division I 4kV switchgear room. PAGE (3) 4of4 LER NUMBER (6)

YEAR 2008 - 001 00 SEQUENTIAL NUMBER REVISION NUMBER