05000244/LER-2013-003

LER-2013-003, Unanalyzed Condition for Potential Floodwater Intrusion into Vital Battery Rooms

R.E. Ginna Nuclear Power Plant
Event date:	09-20-2013
Report date:	09-12-2014
Reporting criterion:	10 CFR 50.73(a)(2)(vii)(D), Common Cause Inoperability 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition
2442013003R02 - NRC Website

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A. PRE-EVENT PLANT CONDITIONS:

The reactor was in Operational Mode 1 at 100% power, 2235 psig and 574 degrees F.

B. EVENT:

On September 20, 2013 at 1600, a flow test was performed on drain lines for cable vaults that share a wall with the Main Battery Room B. This test was performed when it was determined on September 17, 2013 during a review of pictures taken during an earlier visual inspection of the cable vault, that the drain grate appeared to be missing. There was concern that since it appeared to have a missing grate that there was a potential for blockage in the cable vault drain. In addition, during the extent of condition review, two smaller conduit penetrations were discovered that were not sealed.

TO THE EVENT:

None

D. DATES AND APPROXIMATE TIMES OF MAJOR OCCURRENCES:

1967 Original Construction 1972 Maximum flood elevation evaluated at less than 253.5ft 1983 Flooding analysis revised under the Systematic Evaluation Program, maximum flood elevation raised to 273.8ft for areas West and South of containment 05/29/2013 During a planned flooding walkdown, it was identified that there were apparently unqualified environmental penetrations. A followup inspection was initiated for further evaluation of the condition of the cable vault drainage.

09/17/2013 Determination of missing drain grating and potential drain obstruction, and compensatory actions consisting of monitoring the weather forecast and placement of plastic and sandbags on top of the manhole covers to prevent potential rainwater into the cable vault are initiated.

09/20/2013 Flow test failure, reinstated compensatory actions for plastic and sandbags.

10/04/2013 Penetrations from cable vault into B Battery Room sealed watertight.

07/08/2014 During the extent of condition review, unsealed penetration by two 4" conduit into B Battery room were found. Compensatory actions including Operations monitoring of the weather forecast with a conservative criteria to initiate further action including installation of sandbags if the weather forecast meets the criteria initiated.

07/14/2014 4" Conduit Penetrations Sealed

E. OTHER SYSTEMS OR SECONDARY FUNCTIONS AFFECTED:

None

F. METHOD OF DISCOVERY:

The cable vault drain lines failed to pass the expected flow during testing. This was performed as followup to the initial flooding walkdown that identified the unqualified penetrations. The additional unsealed penetrations were discovered during an extent of condition review.

G. MAJOR OPERATOR ACTION:

On-shift Operations Crew reinstated compensatory actions consisting of monitoring the weather forecast and placing plastic covering and sandbags over the manholes that would provide a leak path for rainwater into the cable vault.

H. SAFETY SYSTEM RESPONSES:

The failed flow test of a cable vault drain had no direct impact on safety systems.

II. CAUSE OF EVENT:

The primary cause of the condition was the apparent lack of rigor concerning verifying the assumptions of the flooding analysis during the 1983 Systematic Evaluation Program.

Original construction of the cable vault occurred during construction of Ginna. The drawing was last revised in 1967, and shows the Battery Room cable penetrations. The drawing also shows that the floor drains were to be installed in each room in the vault of manhole 1. The original flood analysis showed a maximum flood elevation of 253.5 ft, well below the 270 ft elevation of manhole 1. For this reason, flood protection measures were not required. In December of 1982, the NRC published NUREG-0821, Integrated Plant Safety Analysis for the Systematic Evaluation Program for R.E. Ginna Nuclear Power Plant. As discussed in section 4.5 of this report, the NRC concluded that Ginna was required, as a minimum, to provide Deer Creek flood protection to a level consistent with a standard projected flood plus one foot. After additional correspondence, in 1983 protection was provided through procedural actions and modifications to a level of 273.8 ft, corresponding to approximately 80% of the creek flow producing the Probable Maximum Flood. It does not appear that Ginna evaluated the potential for flooding through this manhole or underground sources.

The cause of the obstructed cable vault drain is the drain was clogged with legacy construction debris from original construction and the drain grate screens appear to have been never installed at the time of plant construction or possibly removed sometime later.

The condition was entered into the corrective action program as CR-2013-005643.

The two additional penetrations were entered into the corrective action program as CR-2014-004023.

III. ANALYSIS OF THE EVENT:

This event is reportable in accordance with 10 CFR 50.73, Licensee Events Report System under items (a)(2)(ii)(B), Unanalyzed Condition; (a)(2)(v)(D) Condition that could have Prevented the Fulfillment of a Safety Function; and (a)(2)(vii)(D), Common Cause Inoperability of Independent Trains.

This condition is reportable under 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition, because the Ginna flooding analysis does not consider floodwater entering the battery rooms. This is due to legacy issues where when the flood analysis was recalculated in 1983, the flood level was raised and it does not appear that Ginna evaluated the potential for flooding through this manhole or any other underground sources. The original design and licensing basis did not consider flooding from Deer Creek to be credible. Two levels of flooding re-analysis were required during the Systematic Evaluation Program. The first level was determined by the NRC to be the minimum acceptable level and was represented by a Standard Project Flood with one foot of additional margin. This flood level would not have challenged the battery room penetrations. Second, Ginna was required to perform a cost/benefit analysis to justify why protection to a higher level was not warranted. Ultimately, Ginna agreed to provide protection to a higher level of flood flow despite asserting that the design basis should remain the Standard Project Flood. It is this higher level flood determined through cost/benefit and probabilistic analyses that result in the unanalyzed condition.

This condition is reportable under 10 CFR 50.73(a)(2)(v)(D), Condition that could have Prevented the Fulfillment of a Safety Function, because had a design basis flood occurred prior to sealing the cable vault — battery room penetration, the Safety Function of the Station Batteries could have been lost. Loss of the DC system will lead to an eventual loss of all AC power to the site with no capability for using installed plant equipment for decay heat removal or inventory control.

This condition is reportable under 10 CFR 50.73(a)(2)(vii)(D), Common Cause Inoperability of Independent Trains, because had the design basis flood occurred prior to sealing the cable vault — battery room penetration, the flood waters entering into the B Battery Room could have entered into the A Battery room under the Fire Door that connects them. The sump pump in A Battery room may not have been able to accommodate the flood water causing the water level to rise in both rooms such that both trains of the vital batteries would become inoperable. The impact of the two additional penetrations was bounded by the potential consequence of the original unsealed penetrations from the cable vault.

This issue had no actual nuclear, radiological, industrial, or environmental impact. Since the flooding did not occur, the penetrations into the battery room did not leak and the operability of the batteries was not challenged. In addition, the penetrations into the battery room have been made watertight. Although the cable vault drains were subsequently determined to have little impact on the threat from postulated design basis flood conditions, the cable vault drain lines have been cleared of obstruction. Therefore, this event had no impact on the health and safety of the public.

IV. CORRECTIVE ACTIONS:

A. ACTION TAKEN TO RETURN AFFECTED SYSTEMS TO PRE-EVENT NORMAL

STATUS:

The cable vault drain line has been cleared of obstruction.

B. ACTION TAKEN OR PLANNED TO PREVENT RECURRENCE

The penetrations into the B battery room have been sealed watertight.

A Barrier Control Program has been developed and has been implemented.

The High Water (Flood) Plan Procedure has been updated incorporating a more comprehensive strategy.

A. FAILED COMPONENT

None

B. PREVIOUS LERS ON SIMILAR EVENTS

A review of recent Ginna events identified one similar event: