ML19289F357

LER 79-034/01T-2 on 790103:HPI Pump 1-1 Stopped,Due to Low Recirculation Flow Indication.Caused by Inability of Heat Trace to Maintain HPI Pump Recirculation Line Temp Above Freezing.Thermostat Setting Increased

ML19289F357
Person / Time
Site:	Davis Besse
Issue date:	03/23/1979
From:	David Brown TOLEDO EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19289F353	List: ML19289F352 ML19289F357
References
LER-79-034-01T, LER-79-34-1T, NUDOCS 7906070272
Download: ML19289F357 (5)

Text

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EVENT DESCRIPTION AND PROBABLE CONSEQUENCES h o 2 l At 1400 hours0.0162 days <br />0.389 hours <br />0.00231 weeks <br />5.327e-4 months <br /> on 1/3/79, High Pressure Injection (HPI) Pump 1-1 was started per "Emer-j O 3 l gency Core Cooling System Subsystem Monthly Test", ST 5051.01. At 1406 hours0.0163 days <br />0.391 hours <br />0.00232 weeks <br />5.34983e-4 months <br />, HPI l o 4 i Pump 1-1 was stopped due to a low recirculation flow indication. This placed the unitj O 5 l in violation of T.S. 3.5.2 which requires that two independent Emergency Core Cooling l 0 6 i System subsystems be operable. There was no dange to the public or station personnel.l I

60 7 A safety evaluation determined the HPT m nn n ct voitld have oerformed their intended safet?

I 20 8 I function for any actual Reactor Coolant System leak that the HPI oumos are reauired. I D CODE SLBCO E COMPONENT CODE SUBC DE SU E O 9 8

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43 44 Bl0l1',0lh 47 CAUSE DESCRIPTION AND CORRECTIVE ACTIONS h i O l This incident was caused by the inability of the heat trace to maintain the HPI pump l i i l recirculation line temperature above freezing. The thermostat settine for the HPI I i 2 l pump recirculation line heat trace was increased and a temporary heated enclosure was l i a built around it. At 1105 hours0.0128 days <br />0.307 hours <br />0.00183 weeks <br />4.204525e-4 months <br /> on 1/5/79, ST 5051.01 was successfully completed and i i 4 l the unit was no longer in violation of Technical Specification 3.5.2. l 8 9 80 ST S  % POWER oTHER STATUS Dis O RY DISCOVERY DESCRIPTION 1 5 [ E,jh l 0 l 8 l 6 lhl NA l l B lhl Surveillance Test ST 5051.01 l ACTIVITY CONTENT RELEASED OF RELE ASE AMOUNT OF ACTIVITY LOCATION OF RELE ASE 1 6 8 9 lZlh 10

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LOSS OF OR D AV AGE TO F ACILITY TYPE DESCHiPTION 1 9 (_Z_jhl NA 8 9 10 80 DESCR1PTION e 2 o p;5UjEL 81 .., 79060702rt i 68 69 i i i i i i i i ii l 8 3 to 80 5 VR 79-048 NAME OF PREPARER David H. Brown PHONE:

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TOLEDO EDISON COMPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE SUPPLEMENTAL INFORMATION FOR LER NP-32-79-03 DATE OF EVENT: January 3, 1979 FACILITY: Davis-Besse Unit 1 IDENTIFICATION OF OCCURRENCE:

Inoperability of High Pressure Injection Pumps 1-1 >

and 1-2 due to minimum recirculation line freezing The unit was in Mode 1, with Power (MWT) = 2384, Conditions Prior to Occurrence:

and Load (Gross MWE) = 763.

Description of Occurrence:

At 1400 hours0.0162 days <br />0.389 hours <br />0.00231 weeks <br />5.327e-4 months <br /> on January 3,1979, High Pressure Injection (HPI) Pump 1-1 was started per " Emergency Core Cooling System Subsystem Monthly Tes ST 5051.01. At 1406 hours0.0163 days <br />0.391 hours <br />0.00232 weeks <br />5.34983e-4 months <br />, HPI Pump 1-1 was stopped due to a low flow indication on the HPI pump to the Borated Water Storage Tank (BUST) minimum recirculation line (3" HCC-91) . Further investigation discovered that this line Maintenance had frozen outside somewhere personnel were between the BWST Pipe Tunnel and the top of the BWST.

hmuediately notified.

Maintenance personnel increased the thermostat setting for the HPI pump minimum re-circulation line heat trace and built a temporary heated enclosure around the exposed line. The recirculation line was thawed and ST 5051.01 was successfully completed for HPI Pump 1-1 at 1105 hours0.0128 days <br />0.307 hours <br />0.00183 weeks <br />4.204525e-4 months <br /> on January 5,1979.

At the time of the incident, an analysis of the frozen recirculation line by the station indicated that the minimum flow rate required for pump cooling would flow through the injection line if the HPI pumps were started during a loss of coolant As a result, both HPI Pump 1-1 and HPI Pump 1-2 were considered operable, accident.

and the unit was not in violation of any Technical Specifications.

On March 12, 1979, in a discussion between station personnel and TECo Power Engineer-they had donc an analysis of a ing personnel, Power Engineering personnel stated that (see Licensee Event Report NP-32-77-16 dated September previous HPI initiation event the minimum required HPI flow may not have existed if 24, 1977) which indicates that As a result of this initial analysis, both HPI the recirculation line was plugged.

2l pumps must now be considered to have been inoperable between 1406 hours0.0163 days <br />0.391 hours <br />0.00232 weeks <br />5.34983e-4 months <br /> on January 3 1979 and 1105 hours0.0128 days <br />0.307 hours <br />0.00183 weeks <br />4.204525e-4 months <br /> on January 5,1979.

In April 1979, a detailed safety evaluation was performed which determined the HPI pumps would have performed their intended saf ety function and thewould not have HPI pumps been are re-2 damaged for any actual Reactor Coolant System (RCS) leak that quired. See the attached safety evaluation for details.

in violation of Technical Specifi-The inoperability of the HPI pumps two placed the unitEmergency Core Cooling System sub-independent cation 3.5.2 which requires that I pump, systems shall be operable with each subsystem comprised of one operable HP, one operable Low Pressure Injection Pump, one operable Decay Heat Cooler, and one operable flowpath capable of taking suction from the BWST.

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TOLEDO EDISON COMPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE SUPPLEMENTAL INFORMATION FOR LER NP-32-79-03 PAGE 2 Designation of Apparent Cause of Occurrence: This incident was caused by the inabi-lity of the heat trace on the HPI pump to BWST minimum recirculation line, 3" HCC-91, to maintain a pipe temperature above freezing. As a result, this line froze during sub-zero weather and rendered the HPI pumps inoperable.

Analysis of Occurrence: There was no danger to the health and safety of the public or to station personnel. No event requiring the actuation of the HPI pumps occurred.

The HPI pumps would have performed their intended safety function and would not have 2 been damaged for any actual RCS leak for which the HPI pumps are required. See the attached safety evaluation for details.

Corrective Action: Maintenance personnel increased the thermostat setting for the HPI pump to BWST minimum recirculation line heat trace and built a temporary heated enclosure around it. The recirculation line was thawed and ST 5051.01 was success-fully completed for HPI Pump 1-1 at 1105 hours0.0128 days <br />0.307 hours <br />0.00183 weeks <br />4.204525e-4 months <br /> on January 5,1979.

Facility Change Request 79-168 has been written to request a design change for the recirculation line heat trace to prevent recurrence.

Failure Data: There have not been any previous reportable occurrences with the HPI pumps recirculation line.

LER #79-014 '

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ATTACHMENT 1 TO LICENSEE EVENT REPORT NP-32-79-03 SAFETY EVALUATION FOR AN INOPERABLE HPI RECIRCULATION LINE 1.0 Reactor Coolant System pressure at time of HPI start The HPI pumps are automatically started at a RCS hot leg pressure setpoint of 1650 + 25 psig. Maximum instrument string inaccuracy including setpoint drift is 50.75 psig. Therefore, the HPI pumps may be started at a hot ]jgt pressure range from 1575 to 1725 psig.

Since the HPI pumps discharge into the cold legs of the RCS, the core pressure drop and the static pressure due to the dif ference in elevation of hot legs and cold legs must be considered. The core pressure drop with all four Reactor Coolant Pumps running (worst case) is approximately 100 psig and the static pressure due to difference in elevation amounts to approximately 20 psig.

Accounting for the above correction, the cold leg pressure range within which SFAS will actuate the HPI pumps is 1695 to ' *45 psig.  ;

2.0 Reactor Coolant System depressurization rate after HPI start To aid in this analysis, data from the September 24, 1977 depressurization transient was analyzed. This data reprasents a very small break in the RCS piping caused by the pressurizer electromatic relief valve being stuck open, and is a conservative representation of a small RCS-break leading to HPI initi-2 ation with a very low depressurization rate. The rate of depressurization was approximately 3.4 psi per second.

3.0 Time until minimum flow into Reactor Coolant System is obtained The HPI pumps require a minimum flowrate of 34 gpm to prevent the pwmps from heating up. By evaluating the pump head curves and suction pressure, it was determined the HPI pumps would attain the 35 gpm injection rate at an RCS cold Jygt pressure of 1680 psig. Since the HPI pumps would be started within the range of 1695 to 1845 psig cold ljgt pressure, and the rate of depressuriza-tion is at least 3.4 psi per second,1680 psig will be reached anywhere from 4.4 to 48.5 seconds after the pumps are started.

4.0 Time until pump damage would occur Based on the information from the HPI pump manufacturer (B&W Canada, now Hayward Tyler), if the minimum flow of 35 gpm was not obtained, boiling will eventually occur in the HPI pumps which could cause damage to them. The vendor has stated that with zero pump flow the pump seal temperature will raise 170F per minute, and the pump would be damaged at a seal temperature of 230 F. Assuming that the pump started at an ambient temperature of 1220F (500C), it would take approxi-mately six minutes to damage the pump.

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ATTACH'4E!iT 1 TO LICE';SEE EVENT REPORT !!P-32-79-03 PAGE 2 OF 2 5.0 Summary For any actual RCS leak for which the HPI pumps are required, it would have 2 taken ati most 48.5 seconds af ter the pump was started to establish the mini-mum required injection. HPI pump damage would not occur until approximately six minutes without flow. The re fore , the HPI pumps would perform their intended safety function and would not be damaged if they were actuated with the recirculation line frozen.

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