NRC-89-0186, LER 89-016-01:on 890711,Div 1 of RHR Svc Water Sys Declared Inoperable Due to Low Nitrogen Pressure for Cooling Tower Fan Brake.Caused by Leak in One Hose.Leaking Hose Replaced & Nitrogen Pressure restored.W/891006 Ltr

LER 89-016-01:on 890711,Div 1 of RHR Svc Water Sys Declared Inoperable Due to Low Nitrogen Pressure for Cooling Tower Fan Brake.Caused by Leak in One Hose.Leaking Hose Replaced & Nitrogen Pressure restored.W/891006 Ltr

ML19325C197
Person / Time
Site:	Fermi
Issue date:	10/06/1989
From:	Anthony P, Orser W DETROIT EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
CON-NRC-89-0186, CON-NRC-89-186 LER-89-016, LER-89-16, NUDOCS 8910120179
Download: ML19325C197 (6)

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NRC-89-0186  ;

U.. S. Nuclear Regulatory-Commission

-Attention - Document-Control Desk Washington. D.C. 20555 t

Reference:

Fermi 2  ;

NRC Docket No. 50-341 .

Facility Operating-License No. NPF-43 Transmittal of-Licensee Event Report ,

89-016-00 dated August 10, 1989 NRC-89-0136

Subject:

Licensee Event Report (LER) No. 89-016-01 Please find enclosed LER No. 89-016-01, dated October.6 1989, for a reportable event that occurredLon July 11 1989.. This report was revised to reflect the results of an evaluation of the necessity of the Residual Heat Removal Service Water Cooling Tower fan brakes in.various scenarios. A copy of this LER is also being sent to the Regional Administrator. USNRC Region III.

If you have any questions. please contact Patricia Anthony.at (313) 586-1617.

Sincerely, g/'

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Enclosure:

NRC Forms 366 366A cc: A. B. Davis J. R. Eckert R. C. Knop W. G. Rogers J. F. Stang Wayne County Emergency Management Division .

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On July 11 1989 Division I of the Residual Heat Removal Service. Water System (RHRSW) was declared inoperable due to low nitrogen pressure for one of the mechanical draft cooling 11 tower fan-brakes. The nitrogen supplies the motive force for the brakes. The brakes were installed to protect the fans from overspeeding in the event of a design basis tornado. 11 During the investigation and repair of the condition, it was L noted that control power to the brakes was being maintained in i

the AC supply position rather than the DC supply position as shown on the drawing.

Lack of nitrogen pressure would have prevented the brake from l fulfilling its design function in the event a tornado had occurred. A review of the original analysis and a more I realistic evaluation of the need for the mechanical fan brakes l

'has been conducted. The conclusions from this evaluation have Il reaffirmed the necessity of these brakes to protect the fan i from overspeed in the event of a design basis tornado. l The nitrogen supply was restored and a leaky hose replaced.

The system operating procedure was revised and the power supply properly aligned. As an enhancement, the design of the brake l system is being upgraded to QA1 status. This modification will 11 be completed during the First Refueling Outage s which is I currently underway. I

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Initial Plant-' Conditions:

OperationallCondition: . 1-~(Power Operation)  ;

.. ' Reactor' Power: 100.Lpercent W . Reactor Pressure: 998 psig ,

, Reactor. Temperature: 519 degrees Fahrenheit c l b . Description of Occurrence:-

On July 1 1 .--. 1 9 8 9 ' a t 1545 hours0.0179 days <br />0.429 hours <br />0.00255 weeks <br />5.878725e-4 months <br />, the Residual Heat Removal Service Water' System [(RHRSW)(BI)] Mechanical ~ Draft Cooling Tower [(MDCT)(CWT)) Fan C. which provides cooling for the-

.RHRSW. was declared. inoperable due..to the lack of nitrogen l1 for one of the fan brakes. The b rakes pro' vide protection-for -

th'e safety-related' fans against.a postulated tornado.: one of the design' basis.natura1' phenomena. Nitrogen pressure supplies

the-motive power for application'of the brakes.and, therefore.

is required for brake operation. A separate set of nitrogen bottles supply each fan independently. The plant entered the

~72 hour--Limiting Condition for Operation (LCO) 3.7.1.1.a.3.

A11eaking hose-in'the nitrogen system was replaced and nitrogen pressure was: restored. The LCO was exited at 0512 hours0.00593 days <br />0.142 hours <br />8.465608e-4 weeks <br />1.94816e-4 months <br /> on July '

12, 1989.

~During the investigation of the problem, it_was noted that the-_ power supply _for the brakes was aligned to the AC supply, per procedure, rather than the DC supply. The design-provides '

for control power from.a 125 volt DC power supply through an

, AC/DC inverter and selector switch. The selector switch can I connect to a balance of_ plant DC source or a class 1E 120 voit AC. source which is powered by the Emergency Diesel Generators.

If during a tornado the brakes were powered from the AC supply, the. brakes-would be de-energized f or a short period of time if offsite power was lost while the Emergency Diesel Generators l1 i are loading. In the unlikely event all offsite power is lost '

and the tornado passes over the tower, the brakes would be '

unavailable during the' period of time the Emergency Diesel Generators are loading. This could have allowed the fans ,

to overspeed and be damaged. Therefore, aligning the brakes to the DC power supply, which is contained in a structure which has a low probability of being damaged. was determined to be '

desirable. The system operating procedure involved has been ,

l revised and the power supply aligned to DC power. 11

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Additionally, the review identified some design anomalies.

Prior to licensing of the plant. the AC circuit was found to  :;

-have an electronic interference problem which could potentially cause the brakes to be applied unnecessarily. The control circuit was modified to add auxiliary control relays. These new auxiliary relays were not QA1. Since the.reirys were not seismically qualified, they could be postulated to fail during a safe shutdown earthquake; leading to inadvertent application of the MDCT' fan brakes temporarily. However, even under worst postulated meteorological. conditions, there is ample time to release the brakes and restore the MDCT safety function following a seismic event. As an added precaution, operating procedures and operator training to accomplish this have been provided.

1 Additional anomolies include u,s e of unqualified valves, which' l1 will be dedicated by similarity analysis, the use of 130V DC l BOP power suoply and use of an unqualified DC inverter. From tornado design aspects, prcbability analysis shows that the design with these unqualified components is adequate and will perform its intended protection against a tornado event. Any failure of the power supply or inverter during an earthquake has no. impact on the seismic qualification of the MDCT design.

Therefore the present design is adequate for tornado protection and ample time exists for corrective action, should brakes be 11 applied following an e'arthquake. l Cause of Event:

The loss of nitrogen pressure was due to a leak in one of the -

hoses. There was a lack of awareness on the part of Detroit Edison of the necessity for maintaining the fan brakes in an operable status. Since this was not an identified limitation to operability, corrective actions were not always completed in a timely manner.

The line up of the power supply to the AC supply rather than the DC supply was specified in the system operating procedure. SOP 23.208 in revision 6 which was approved on January 14 1985.

Analysis of Event:

At Fermi 2 the RHR reservoirs provide the ultimate heat sink l function. The system includes two cooling fans for I each reservoir cooling tower. Both cooling tower fans are 11 required to be operable, per Technical Specification 3.7.1.5 l for each reservoir to be operable. The MDCT fans are required I under certain conditions to provide for heat rejection cooling uxCrorus a ***"""* *"

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mi ru mm ea. n . ens a ,eww ww n. numm 1 for the Residual Heat Removal complex water. Per Section 9.2.5.2.2 of the Fermi 2 Updated Final Safety Analysis Report, the fans are provided with a brake system to prevent '

overspeeding from the design. basis tornado. With the brake 'l I system inoperable, a design basis tornado could have damaged 11 j the fans such that they may not have been able to perform l their function. j A review of the original analysis and a more realistic l evaluation of the need for the mechanical fan brakes has been I conducted. This evaluation assessed the tornado wind and i pressure loads, air flow through the fans under the postulated l l loads, the aerodynamic response of the fans. and potential fan 11 f failure modes. The conclusions from this evaluation indicate i J that significant overspeeding of the cooling tower fans is a l potential concern under the high winds associated with a l tornado. Therefore, the origina1' decision to install protective I brakea was valid. I Per the Technical Specification definition, a component is I operable when it is capable of performing its specified I function and when all necessary attendant auxiliary equipment I that is required for the component to perform its function is I also capable of performing its support function. The RHR l cooling tower fan brakes are necessary to maintain 11 functionality of the fans during a design basis tornado. l The fans are capable of performing their function during all I other circumstances, including the Design Easis Accident. I without the brakes. Therefore, except during a design basis I tornado, the brakes are not necessary support equipment for 1 -

the fans. I Following a design-basis tornado, the ultimate heat sink is capable of-performing its safety function without the fans being operable for at least four hours. The operators could take several possible courses in order to provide alternate cooling. An example of one of these options would be to restore power and use the circulating water system and the main condenser to provide blowdown. In-any case, the fans would be able to perform their design function with the brakes inoperable under all conditions except for a design i basis tornado scenario. 11 The existing design for the MDCT fan brakes, when they are properly aligned to the BOP DC battery power source and when the nitrogen bottles are sufficiently charged, provides adequate tornado protection.

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s Corrective' Actions:

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The nitrogen-hose that'.was. leaking was replaced and Eitrogen  ;

pressure restored in order-to return the system to sperable l

status. A revision'was made to SOP 23.208 in order to specify that.the:. power supply should be lined-up from the-DC supply.

A-review of the operability of the system was-performed. ll i It determined that the system is_. operable. As an added -l precaution, the abnormal operating procedure for earthquakes was.. revised to instruct'the operators to check <

MDCT Ian' operation'following an earthquake. The revision

.provides direction on how to manually release the brake, if 1

'necessary.  ;

-As_ discussed previously, an engineering review has confirmed 11 a- the necessity of the fan brakes to protect the fans from l' ,

'overspeed during a design basis tornado. As an enhancement. l the' current-design of the. brake system is being upgraded to l ,

QA11 status. -Engineering. Design Package 10518 will be l be: completed before restart from the First Refueling l- ',

10utage, which is currently underway. l A Design Basis Task Force effort was started in September of' 11 1989 to review . selected, systems and raise the consciousness l of plant ~ personnel to the licensing basis of the plant. 7 Additionally, the current corrective action program captures

. identified problems and tracks them until all necessary l

. actions.are completed. l1 Previous Similar Events:

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