ML20042D401

LER 89-010-01:on 890612,control Room Ventilation Sys Declared Inoperable Due to Compressor High Pressure Trips. Caused by Tripping of Refrigerant Pressure Switch on High Pressure.Switch Reset & Sys retested.W/900102 Ltr

ML20042D401
Person / Time
Site:	Davis Besse
Issue date:	01/02/1990
From:	Storz L, Stotz J TOLEDO EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-89-010, LER-89-10, NUDOCS 9001090094
Download: ML20042D401 (4)

Text

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January 2, 1990

! Log No.: BB89-01332 NP33-89-010, Rev. 1 Docket No. 50-346 License No. NPF-3 I United _ States Nuclear Regulatory Commission L Document Control Desk

!' ;Vashington, D. C. 20555 t

! Gentlemen:

LER 89-010, Revision 1 Davis-Besse Nuclear Power Station, Unit No. 1 Date of Occurrence - June 12, 1989 Enclosed please_ find revision 1 to Licensee Event Report 89-010. The revisions are indicated by a revision bar in the left hand margin. Please discard or mark superseded any prtvious copies of this LER.

Yours truly, Louis F. Storz Plant Manager' Davis-Besse Nuclear Power Station i

LFS/plf i Enclosure cc: Mr. A. Bert Davis Regional Administrator USNRC Region III Hr. Paul Byron DB-1 NRC Sr. Resident Inspector 9003090094 900102 i PDR ADOCK 05000346 s PDC

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, of the Contr01 Room Emergency Ventilation System (CREVS) Honthly Test, DD-SS-03041, the cooling system compressor would not start. The CREVS Train 1-1 was declared inoperable and '

the Station entered the seven-day action statement of Technical Specification 3.7.6.1. The cause was a refrigerant pressure switch located inside pan'el C6706 that had tripped on high pressure. The switch was reset and the system retested successfully and was declared operable at 1730 hours0.02 days <br />0.481 hours <br />0.00286 weeks <br />6.58265e-4 months <br /> on June 27, 1989. Further evaluation concluded that the pressure switch had tripped on June 12, 1989, when the system had been operated. Therefore, the system had  !

been in a degraded condition for a period of time longer than allowed by the action statement.

1 This is reportable under 10CFR50.73(a)(2)(1)(B) as a condition prohibited by the Technical Specifications.

It is also recognized that since CREVS Train 1-2 had been declared inoperable on June 8, 1989, to support maintenance on the backup air cooled condenser damper and not declared operable until 1455 hours0.0168 days <br />0.404 hours <br />0.00241 weeks <br />5.536275e-4 months <br /> on June 12, 1989, both CREVS (

trains were inoperable at the same time. This is also a condition prohibited by the Technical Specifications. ,

1 CREVS Operating Procedure, SP1104.69 (DB-0P-06505), was changed to add the local verification of the compressor operation. Setpoint Change Request (SCR) 89-0027 was implemented in October 1989 vhich raised the compressor " transfer" l setpoint to 175 psig. l 1

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l Description of Occurrences j On June 26, 1989, during the performance of DB-SS-03041, Control Room Emergency Ventilation System (CREVS) (VI) Monthly Test, the refrigerant j compressor would not start. The CREVS Train 1-1 vas declared inoperable, 1 and the Station entered the seven-day action statement of Technical Specification 3.7.6.1. The condition that prevented the compressor from starting was corrected and the system was declared operable at 1730 hours0.02 days <br />0.481 hours <br />0.00286 weeks <br />6.58265e-4 months <br /> on June 27, 1989.

During evaluation of the event, it was concluded that CREVS Train 1-1 had 3

been in this condition since shutdown from use at 0542 hours0.00627 days <br />0.151 hours <br />8.96164e-4 weeks <br />2.06231e-4 months <br /> on June 12, 1989.

This meant that the train cooling function had been in a degraded condition for a period of time longer than allowed by the action statement. This is reportable under 10CFR50.73(a)(2)(1)(B) as a condition prohibited by the l Technical Specifications. /

It vac also recognized that CREVS Train 1-2 had been declared inoperable on .

June 8, 1989, to allow maintenance on a backup nir cooled condenser damper, HV4907. It was not declared operable until 1455 hours0.0168 days <br />0.404 hours <br />0.00241 weeks <br />5.536275e-4 months <br /> on June 12, 1989.

Therefore, both trains were inoperable on June 12, 1989. This is also reportable as a condition prohibited by the Technical Specifications.  ;

Apparent Cause of Occurrence: -

CREVS vas inoperable because the refrigerant compressor required for cooling would not start. The compressor would not start because the refrigerant high pressure switch (PSHL) had tripped. It is concluded that this svitch tripped during the 11 minute system run on June 12, 1989, and was not reset. It is concluded that the switch tripped because a high pressure condition occurred when the cooling system inadvertently switched from the normal vater cooled mode of operation to the backup air cooled mode with manual valves isolated in the refrigerant lines. These valves are normally maintained closed. They must be manually opened by the operator when the air cooled mode is desired.

With the valves closed and the compressor running, pressure of the refrigerant would increase rapidly until it reaches the compressor trip setpoint of 220 ,

psig. Further investigation has concluded that the transfer from the water cooled to air cooled mode of operation is due to a refrigerant pressure spike that occurs when starting the compressor. The amplitude of this spike is dependent on the temperature of the stagnant leg of service water and its flovrate which is limited by the opening time of SV 2927. During CREVS startup on June 12, 1989, this spike was sufficient to actuate PS5900 (setpoint of 160 psig + 5 psig) which re-aligned the compressor to the air cooled condenser. Vite the air cooled condenser manual isolation valves closed, the refrigerant pressure quickly rose to the compressor trip setpoint of 220 psig.

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Indication of the selected cooling mode and the fact that the compressor is  !

off is only available locally. The operator's only indications in the control room are that the air recirculation fans are on or off. The high pressure switch is only visible by physically looking inside the local control panel, C6706.

1 Analysis of Occurrence, The operability of the CREVS is intended to ensure that 1) ambient air  !

temperature does not exceed the allovable temperature for continuous duty j rating for the equipment and instruments cooled by this system and 2) the .l control room vill remain habitable for Operations personnel during and i following all credible accident conditions. By design, CREVS must be manue.lly  !

initiated following an automatic isolation of the normal CRHVAC. The automatic isolation of normal CRHVAC is not affected by the cooling function problem. However, this problem would require operator action from outside of the Control Room to re-initiate cooling.

Although CREVS Train 1-2 was declared inoperable from June 8 to June 12 to support maintenance on a damper for the backup air cooled condensing mode of operation, the normal water cooled mode could have been used on June 12 had it  !

been needed.

C_orrective Actions:

The high pressure switch was reset and DB-SS-03041 successfully run. CREVS l'

Train 1-3 was declared operable at 1730 hours0.02 days <br />0.481 hours <br />0.00286 weeks <br />6.58265e-4 months <br /> on June 27, 1989.

1 l; Procedure SP1104.69 (DB-0P-06505) was changed by adding details to be checked ,

when shutting down the system. The procedure requires checking that not only the mode switch is on the water cooled side, but also that the compressor is operating in the water cooled condensing mode. The monthly surveillance test procedures, DB-SS-03041 and DB-SS-03042, already contained adequate direction.

Under Maintenance Vork Order (MVO) 1-89-1831-01, Setpoint Change' Request (SCR) l 89-0027) vas implemented for CREVS Train 2 on October 6, 1989. Under MVO l 1-89-1831-00, SCR C9-0027 was implemented for CREVS Train 1 on October 11,

! 1989. This SCR raised the compressor " transfer" setpoint to 175 psig.

Failure Data u

This is the first report of CREVS problems since LER 84-022, when the makeup flovrate was greater than allowed.

REPORT NO. NP33-89-010 PCAO NO. 89-0335 pf'ea= aa .u a oao ieenn4.sid

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