05000445/LER-2012-001
| Document Numbersequential Revmonth Day Year Year Month Day Year Cpnpp Unit 2 05000 446Number No. | |
| Event date: | 03-01-2012 |
|---|---|
| Report date: | 04-30-2012 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition |
| 4452012001R00 - NRC Website | |
I. DESCRIPTION OF THE REPORTABLE EVENT
A. REPORTABLE EVENT CLASSIFICATION:
This event is reportable per 10CFR50.73(a)(2)(ii)(B) as any event or condition that resulted in an unanalyzed condition that significantly degraded plant safety.
B. PLANT CONDITION PRIOR TO EVENT:
On March 1, 2012, Units 1 and 2 were both in Mode 1 operating at 100% power prior to the battery door event.
C. STATUS OF STRUCTURES, SYSTEMS, OR COMPONENTS THAT WERE
INOPERABLE AT THE START OF THE EVENT AND THAT CONTRIBUTED TO THE
EVENT
There were no inoperable structures, systems, or components that contributed to these events.
D. NARRATIVE SUMMARY OF THE EVENT, INCLUDING DATES AND APPROXIMATE
TIMES:
On March 1, 2012, at 1353 hours0.0157 days <br />0.376 hours <br />0.00224 weeks <br />5.148165e-4 months <br />, an issue was identified by engineering (Utility, Non licensed) with the doors [EIIS: (DR)] for the safety related battery rooms and their normal position. Several doors to the battery rooms were found to be held open via electromagnetic door devices. These hold-open devices utilize an electromagnetic lock, which requires a continuous supply of low voltage direct current (DC) power to generate the magnetic forces restraining the doors in the open position. Inadvertent closure of the doors following a momentary loss of power could prevent their design function fulfillment. Door closure is required in response to a fire detection and protection system actuation to protect the battery rooms from fire damage. Conversely, the doors are maintained open for the dual purposes of 1) allowing airflow into the room to support the room exhaust heating, ventilating, and air conditioning (HVAC) within the room (and credited for the removal of hydrogen accumulation), and 2) reduce differential pressures across the rooms structural surfaces during tornado events. Further research determined the hold-open devices are powered from only non-vital AC power sources [ElIS: (JX)] (which is converted into DC power within the fire panel) and thought not to include battery backup protection.
Compensatory measures were implemented later that day (March 1, 2012) to secure the doors open to maintain the hydrogen purging function. A fire watch was implemented to comply with the fire protection function of the doors.
Comanche Peak Nuclear Power Plant Unit 1 05000 - 445 YEAR I SEQUENTIAL I� REV NUMBER� NO.
As an extent of condition on 3/12/12, the cable spread room (CSR) doors were also identified to utilize the same design and electrical supply configuration as the battery room doors. The CSR is located above the battery rooms in the Electric and Control (E&C) Building. Contingency actions were put in place to secure the CSR doors open and a fire impairment in the event of a tornado risk.
On 4/11/12, it was discovered that the battery room and CSR doors have small battery backup units [EIIS: (UJX)] which could sustain the doors with adequate power to maintain their position for 45 seconds, sufficient to allow AC power to be restored through the EDGs [EIIS: (EK) (DG)] during a tornado. However, the backup units were found to be in a state of degradation, challenging the ability of the backup batteries to maintain their power supply to the door hold-open devices during a tornado event. No recent preventive maintenance work orders exist for the inspection or replacement of these units.
With respect to hydrogen generation; components which are designated as non-safety non seismic category I, cannot be credited by design to maintain their function during a design basis accident (such as a Loss of Coolant Accident concurrent with a LOOP or a seismic event), and as such the battery room doors could not be ensured to maintain their position.
This would result in a 10 second loss of power to the hold-open devices assuming loss of the non-safety batteries and a diesel generator load, allowing the doors to close and challenge the hydrogen generation analysis of the room during hydrogen generating conditions.
E. THE METHOD OF DISCOVERY OF EACH COMPONENT OR SYSTEM FAILURE, OR
PROCEDURAL PERSONNEL ERROR
The battery room condition was identified by engineering on 3/1/2012 to determine if the Unit 1 and 2 fire doors for the Train A, B, and C battery rooms are equipped with electromagnetic hold-open mechanisms.
The CSR door condition was identified as an extent of condition of the battery room door closure mechanisms issue on 3/12/12 in that the cable spread room doors were also identified to utilize the same closure mechanism as the battery rooms.
II. COMPONENT OR SYSTEM FAILURES
A. CAUSE OF EACH COMPONENT OR SYSTEM FAILURE
Not applicable — No component failures were identified during this event.
B.FAILURE MODE, MECHANISM, AND EFFECTS OF EACH FAILED COMPONENT Not applicable — No component failures were identified during this event.
C. SYSTEMS OR SECONDARY FUNCTIONS THAT WERE AFFECTED BY FAILURE OF
COMPONENTS WITH MULTIPLE FUNCTIONS
Not applicable — No component failures were identified during this event.
D. FAILED COMPONENT INFORMATION
Not applicable — No component failures were identified during this evens.
III. ANALYSIS OF THE EVENT
A. SAFETY SYSTEM RESPONSES THAT OCCURRED
Not applicable — No safety systems responses occurred as a result of this event.
B. DURATION OF SAFETY SYSTEM TRAIN INOPERABILITY
Not applicable — No safety systems were rendered inoperable as a result of this event.
C. SAFETY CONSEQUENCES AND IMPLICATIONS OF THE EVENT
There were no inoperable structures, systems, or components at the time that contributed to this event. In the past three years, CPNPP has never experienced a LOOP that caused the battery doors or the CSR doors to close coincident with a tornado. Compensatory measures were taken to secure the battery room doors open to maintain the hydrogen purging and tornado venting functions including a roving fire watch to comply with the fire protection function of the battery room doors.
With respect to battery room hydrogen generation, computations performed show that in the most limiting safety related battery room (Unit 1, Train B) the Lower Flamability Limit (LFL) would not be reached until 113 hours0.00131 days <br />0.0314 hours <br />1.868386e-4 weeks <br />4.29965e-5 months <br /> at 120 degree F after closure of the doors. The adjacent non-safety rooms (Train C Battery Rooms) may reach the LFL limits earlier than the safety related counterparts on the order of 35 hours4.050926e-4 days <br />0.00972 hours <br />5.787037e-5 weeks <br />1.33175e-5 months <br /> into the closure of the doors. If left uncorrected, hydrogen ignition in the adjacent rooms may potentially compromise the function of the safety related counterparts.
Existing plant procedures require performance of local Shiftly Surveillances between the hours of 0630 — 0930 and 1830 — 2130. These Surveillances include Train A battery room and Train B battery room for each Unit. This Surveillance is applicable for any Mode of plant operation. Furthermore, normal Operator rounds which occur twice a Shift, two Shifts per day include a General Area Inspection of Trains A, B, and C battery room ventilation and equipment status. Specifically, any abnormal conditions or out-of-specification readings shall be immediately reported to the Field Support Supervisor, Radiation Waste Supervisor, or Unit Supervisor per procedure. Plant procedures also require checking battery room exhaust fans following severe weather damage from acts of nature. Additionally, guidelines require inspection of the battery room for proper room ventilation for a variety of events Comanche Peak Nuclear Power Plant Unit 1 05000 - 445 YEAR I SEQUENTIAL .I� REV NUMBER� NO.
including loss of AC power. Nuclear Equipment Operators are also trained on battery room ventilation and the flowpath from the battery room corridor, through the battery rooms to the exhaust fans.
Based on the above, there is a reasonable expectation that normal battery room ventilation, which includes flow through the doors, would be restored prior to conditions being reached that would cause the battery rooms to become inoperable based on hydrogen or temperature concerns.
Tornado venting capabilities are only required during the event of a tornado being present in the immediate vicinity of the plant. Actions were taken to provide for the temporary restraint of the CSR doors open during periods of elevated tornado risks to ensure tornado venting position is maintained and measures for the assurance of fire protection function.
With respect to battery room and CSR tornado venting, the E&C Building structure is sufficiently robust such that there is reasonable expectation that the equipment inside would fulfill the specified safety functions in the event of a tornado coincident with a LOOP.
Based on the above, it is concluded that the health and safety of the public were unaffected by these conditions and these events has been evaluated to not meet the definition of a safety system functional failure per 10CFR50.73(a)(2)(v).
IV. CAUSE OF THE EVENT
The electromagnetics were installed in August of 1983 to ensure the battery rooms were adequately protected from the propagation of fire in the adjacent rooms and still satisfying the HVAC requirements.
The condition leading to loss of power to the hold-open devices during loss of offsite power was identified in 1989 as non-compliant with the tornado venting analysis requirements. Corrective actions were implemented in the form of a new controller unit to the fire protection panels which utilize small battery backup unit which could sustain the doors with adequate power to maintain their position for 45 seconds, sufficient to allow AC power to be restored through the EDGs during a tornado.
However, the battery room door controller batteries were inspected on 4/11/2012, and found to be in a state of degradation, challenging the ability of the batteries to maintain their power supply to the door hold-open devices during a tornado event. Research into the preventative maintenance (PM) jobs performed on the batteries indicates that no PM exists for the inspection or replacement of the units. Without PMs, the batteries could not be ensured to perform their function under operating conditions, resulting in a challenge to the ability of the doors to maintain their venting position.
The cause analysis for the existing design without supporting PMs are:
- the failure of the responsible engineer for the device installation to involve the cognizant individuals in the design phase as well as failure to institute changes to the design documents utilized by later tornado venting engineers which may have identified the error in LOOP protection, and
- the failure of an interdisciplinary group involved in the original installation to identify the required LOOP protection for the system.
V. CORRECTIVE ACTIONS
On 3/1/2012 at 1913 hours0.0221 days <br />0.531 hours <br />0.00316 weeks <br />7.278965e-4 months <br />, the battery rooms were restrained and on 3/2/2012 at 1532, the fire impairments were implemented including a roving fire watch to ensure fire protection requirements are maintained.
After the cable spread room doors were also identified to utilize the same closure mechanism as the battery room doors on 3/12/12 at 1714 hours0.0198 days <br />0.476 hours <br />0.00283 weeks <br />6.52177e-4 months <br />, actions were implemented to provide contingencies to secure the CSR doors open and implement a fire impairment during periods of heightened tornado risk.
The cause was a design process legacy issue, and current design processes are significantly different from those in place during early operation of CPNPP. The specific conditions have been addressed in the corrective action program and, along with current programs and practices, are adequate to prevent future occurrences.
Existing batteries will be replaced as required and PMs will be created to inspect and replace controller panel batteries for fulfillment of tornado venting function.
VI. PREVIOUS SIMILAR EVENTS
There have been no previous similar reportable events at CPNPP in the last three years.