ML19319E483

RO 50-313/77-19:on 770906,during Review of Emergency Ventilation Sys for North & South Electrical Equipment Rooms, & North & South Battery & Charger Rooms,No Qualified or Emergency Sys Found to Exist.Caused by Design Error

ML19319E483
Person / Time
Site:	Arkansas Nuclear
Issue date:	09/20/1977
From:	Cook R ARKANSAS POWER & LIGHT CO.
To:
Shared Package
ML19319E479	List: ML19319E478 ML19319E483
References
NUDOCS 8004110638
Download: ML19319E483 (5)

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Reportable Occurrence Report No.

50-313/77-19 2.

Report Date: September 20, 1977 3.

Occurrence Date: September 6, 1977 4.

Facility:

Arkansas Nuclear One Russellville, Arkansas 72801

~ ~ ~ ~ ~57 Identification of Occurrence On September 6,1977, after reviewing the adequacy _ of the HVAC equip-Iment provided to the South Electrical Equipment Room (Room 104), North Electrical Equipment Room (Room 149), South Battery and ' Charger Rooms (Rooms 109 and 110), and North Battery and Charger Rooms (Room 95),

it was concluded that sufficient qualified cooling was not available to maintain these rooms and the associated enclosed equipment (i.e.,

480V Motor Control Centers, Inverters, Battery Chargers, Instrument AC Panels, etc.) below the rated continuous operating temperatures (104F for MCC!s and Panels,122F for Chargers and Inverters) following a IDCA and concurrent loss of offsite power.

6.

Conditions Prior to Occurrence?

Steady-State Power Reactor Power 2568 MW' Net Output 778 MWe Percent of Full Power 100%

7.. Description of Occurrence:

The two Electrical Equipment Rooms (Rooms 104 and 149) contain the Instrument AC Panels YO1 and YO2, and MCC's controlling MOV's and drive motors (smaller than 75 hp) for safety-related equipment. The North room is provided with refrigeration cooling during normal opera-tion; however, this non-Q cooling must be assumed to be unavailable under DBA conditions, leaving this room with no cocling or ventilation.

The South Electrical Equipment Room is provided with a ventilarion system consisting of a supply and exhaust fan pulling in outside air.

Due to the non-Q nature of this ventilation system, it must be assumed that this cooling is unavailable under DBA conditions, leaving this room with no ventilation or cooling.-

The' Battery and. Charger Rooms have ventilation systems (approximately 1260 cfa) which cannot' be assured to operate during a DBA as a result of the equipment being non-Q. However, vital power is provided to these exhaust systems.

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8.' Designdien of apperent Causa of Occurrenca:

Design:

Description of Cause to Be provided by November 1,1977.

9.

Analysis of Occurrence:

Table A, attached, shows that information utili:ed to determine the maximum temperatures which may be expected in the affected rooms following LOCA and loss of offsite power. This data assumes that emergency ventilation (exhaust) is provided to the Battery and Charger Rooms, and circulating fans are provided in the Electrical Equipment Rooms.

It should be noted that Table A indicates that there is no emergency cooling in the Electrical Equip-ment Rooms. He heat load summary presented in Table A is based on that equipment which is expected to be operating during the DBA; i.e.,

circulating fans to be installed as an interim measure to prevent stratification of air in the Electrical Equipment was, as well as the ventilation system (existing) in the Battery and Charger.

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The heat input to all rooms provided by the electrical equipment contained therein is based upon the post-LOCA continuously operating loads connected to the electrical equipment. Additional heat is provided during the postulated accident which takes into account that heat from the Reactor Building which is transmitted through the walls. As can be seen, the maximum room temperatures which may be experienced are approximately 13%

higher than the continuous duty rating of the equipment for the worst case (i.e., 118F in the South Electrical Equipment Room after approximately 170 hours0.00197 days <br />0.0472 hours <br />2.810847e-4 weeks <br />6.4685e-5 months <br /> following LOCA). However, these maximum temperatures are not considered credible in that the diversity of AP6L's transmission system makes it highly improbable that a loss of offsite power will last longer than 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />. here-fore, the corrective action will be based upon the 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> figures rather than the absolute maximums.

We have investigated the equipment located in these rooms as to which compon-H ents would be most adversely affected by elevated temperatures. Our suppliers have indicated that the electrolytic capacitors are the weakest link in the charger design; the power semiconductors in the inverter design; and rubber bumpers in the FCC starter design. Because cf the numerous ;ub-suppliers involved, the DC control center manufacturer and the distribution panel manu-facturer have been unable to respond in the short time frame they were allotted.

Since the deterioration rate of e'.ectrical equipment is a complex function of temr,erature,' electrical loading, and time, the suppliers who have responded are opr61stic that their hardware will perform satisfactorily, but are unwilling to predict for how long. H ey have indicated that in the past similar equipment has been subjected to specific elevated temperature testing and has functioned satisfactorily; however, they are unwilling to extrapolate the results of these tests to the ccnditions postulated at ANO-Unit 1.

10.

Corrective Action:

Temporary emergency cooling provisions for the two Electrical Equipment Roor.ts (Rooms 104 and 149) will include the addition of O

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circulating fans ('as mentioned in' the Analysis of Occurrence section fq' of this report) which will be connected to an emergency power source.

s To assure the adequacy of this addition, the temperature of these rooms shall be monitored once per shift in order to maintain maximum ambient temperatures of 95F in the North Electrical Equipment Room and 104F in the South Electrical Equipment Room, which is consistent with the conditions assumed in the heat load calculations of Table A.

If the temperatures should exceed these limits during normal operation (which would imply that the cooling and ventilation equipnent is opera-ting improperly), measures will be taken to restore this limit by repairing the equipment and returning it to operable status. During the postulated DBA, the equipment will be checked as soon as possible (within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />) to assure 7 t'is operating. The room temperatures will be checked after two (2) days and, if the temperatures are greater than 107F, efforts to return the cooling and ventilation equipment (which is implied to be out of service if the 107F temperature limit is exceeded) to operable status.

The temporary emergency cooling provisions for the Battery and Charger Rooms (Rooms 95,109 and 110) will initially be limited to temperature monitoring in these rooms to assure a maximum ambient temperature in these rooms of 104F during normal operations. The room temperatures will be ' monitored at least twice per shift to ensure the conditions assumed in the analysis are met.

In approximately two (2) month:,, an additional interim measure will be implemented.

This additional 'easure involves providing a packaged cooling unit to these rooms ar.. powering it from vital busses. These measures will ensure that the design conditions of the equipment will not be exceeded during nomal operation.

Following the postulated DBA, these cooling and ventilation units will be checked as soon as possible (within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />) to ensure they are operating. These rooms will also be monitored 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> following IDCA to assure all HVAC equipment is operating properly and the temperatures in the rooms are within cal-culated limits.

Permanent' Installation The permanent measures which will be taken involves providing cooling to all rooms affected by means of a chilled water system (s). This sd ution provides the most advantageous mes.ns of maintaining acceptable temperature levels in the electrical equipment and battery rooms as the the chilled water system (s) will maintain nearly constant room tempera-R tures even under the most adverse outside air temperature extremes.

Two independent chilled water systems will be installed - one to l

cool " red" channel equipment and the other to cool " green" channel equipment. Each system shall be comprised of a condensing unit (cooled by service water) and a unit cooler in each area requiring cooling.

Because of the stringent "Q" documentation requirements, the permanent equipment has a one year delivery time and thus necessi-tates the previously described temporary installation.

11. Failure Data:

None

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