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Insp Rept 50-454/88-19 on 880919-28.Violations Noted: Inadequate Procedures for Installation & Use of Tygon Tubing for RCS Level Indication.Major Areas Inspected:Loss of Train of RHR When Water Level in RCS Lowered on 880919
	ML20207N880
Person / Time
Site:	Byron
Issue date:	10/12/1988
From:	Hinds J; NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
To:	;
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ML20207N875	List: ML20207N873; ML20207N880;
References
	50-454-88-19, NUDOCS 8810190437
	Download: ML20207N880 (9)
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U. S. fiUCLEAR REGULATORY C0fYtISS10fi

REGION III

Report No. 50-454/88019(DRP)

Docket No. 50-454 License No. NPF-37

Licensee: Commonwealth Edison Company

Post Office Box 767

Chicago, IL 60690

Facility Name: Byron Station, Unit 1

Inspection At: Byron Station, Byron IL

Inspection Conducted: September 19 - 28, 1988

Inspectors: P. G. Brochman

N. V. Gilles

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Approved By: J. 1. Hinds , Jr. , i 10 12 86

V ctor Projects Section 1A Date

Inspection Suro,ary

inspection from September 19 - 28, 1988 (Report No. 50-454/88019(DRP))

Areas Inspected: Special, reactive safety inspection by the resident

inspectors to review the events surrounding the loss of one train of the

residual heat removal (RHR) system while the water level in the reactor

coolant system was being lowered on September 19, 1988.

Results: Two examples of one apparent violation were identified (procedures

inadequately directed installation and use of tygon tubing for reactor

coolant system level indication - paragraph 7). This apparent violation is

of safety significance due to the potential for the loss of both trains of

RHR when reactor vessel level is at the mid-plane of the hot leg nozzles and

both trains of RHR are in operation. However, this event did not affect the

public's health and safety due to the prompt actions by the control room

operator to prevent the loss of the RHR system.

S810190437 891012

PDR ADOCK 05000454

O PDC

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DETAILS

1. Persons Contacted

Conmonwealth Edison Company

R. Pleniewicz, Station Manager

T. Joyce, Production Superintendent

R. Waid, Services Superintendent

D. Winchester, Quality Assurance SJperintendent

T. Tulon, Assistant Superiatendent, Operating

G. Schwartz, Assistant Superintendent, Maintenance

L. Sues, Assistant Superintendent Technical Services

0. St. Clair, Assistant Superintendent, Work Planning

J. Schrock, Operating Fngineer, Unit 1

D. Brindle Operating Engineer. Unit 2

M. Snow, Regulatory Assurance Supervisor

W. Pirnat, Regulatory Assurance Staff

E. Zittle, Regulatory Assuranca Staff

B. Jacobs, Acting Unit 1 Operating Engineer

L. Bunner, Lead Operations Instructor

D Bump, Quality Assurance Inspector

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A. Chernick, Training Supervisor

D. Berg, Nuclear Safety

R. Polek, Regulatory Assurance

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The inspector also contacted and interviewed other licensee and

contractor personnel during the course of this inspection.

Denotes those present during the exit interview on September 28,

1988.

2. Purpose (93702)

This inspection was conducted to review the circumstances surrounding

the inoperability of the 1A train of the residual heat removal (RHR)

system after air was ingested into the RHR system us a vortex formed

while operators were lowering the water level in the refueling cavity

to support maintenance activities on September 19, 1988.

3. Description of the Event

Tne licensee entered the second refueling outage for Unit 1 on

September 3, 1988. On the morning of September 19, 1988, with the

reactor vessel (RV) head removed, repairs had been made to the refueling

cavity boot seal. The 1A RHR train was operating in the shutdown cooling

mode at a flowrate of aporoximately 3200 gpm. Operators had just

! completed filling the refueling cavity to the 402 foot elevation to

check the boot seal repairs when they noticed that a vessel stud hole

plug had come free and was floating on the surface of the water. At

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4:38 a.m., operators started the IB RHR pump in order to lower reactor

coolant system (RCS)/ refueling cavity water level to below the RV flange

so that maintenance personnel could replace the stud hole plug.

At 4:48 a.m., operators shut down the IB RHR pump with RCS level at

398 feet 8 inches, according to the temporary tygon hose level

instrumentation (the RV flange is at the 400 foot elevation). Between

approximately 6:00 a.m. and 7:00 a.m., a shif t change was occurring for

the operating shift. Atapproximately7:30a.m.,anequipmentattendant

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(EA) assigned the duty of "tube watch' relieved the EA from the previous

shift and told the control room that the tygon hose was reading approxi-

mately 401 feet. The control room attributed the difference from the

earlier indication to the fact that the tygon hose had been acting

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erratically on previous shifts. At 9:57 a.m., with level approximately

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3 inches above the RV flange according to visual observation, the Unit 1

Reactor Operator (RO) started the IB RHR pump to lower RCS level further

to allow reinstallation of the stud hole plug. At this time the EA and

a mechanical maintenance foreman were at the refueling cavity and in

comunication with the control room. At 10:05 a.m. , the RO shut wwn

the IB RHR pump when told that level had dropped below the RV flange.

The EA had checked the tygon hose and told the RO that level had dropped

approximately 1 foot. At approximately 10:45 a.m., the Unit 1 R0 was

relieved by an extra RO on shift due to increased activity because of the

outage.

At about the same time, the mechanical maintenance foreman sent a man

into the refueling cavity to check the water level and subsequently

informed the control room that there was still water standing above the

RV flange / stud holes. The foreman then asked to have level in the

refueling cavity lowsred further to ellow dewatering of the stud hole and

replacement of the plug. At 10:52 a.m., the Unit 1 R0 started the IB RHR

pump again to lower refueling cavity level. At 10:59 a.m., just as the

maintenance foreman told the R0 that level had dropped far enough, the RO

noticed the 1A RHR pump ameter oscillating (30 - 50 amps) and letdown

flow fluctuating. The RO isolated letdown flow and shut down the IB RHR

pump, to stop the draining. At 11:00 a.m., the R0 shut down the 1A RHR

pump, with amps now fluctuating between 20 and 60 amps. The R0 then

entered Byron Abnormal Operating Procedure B0A Refuel-4, "Loss of RH

During Refueling," and action statement a. of Technical Specification 3.9.8.2 for the loss of one RHR pump in Mode 6 with watcr level less than

23 feet above the RV flange. At 11:02 a.m., the RO segan a gravity fill

of the RV/ refueling cavity from the refueling water storage tank (RWST)

using the 1B RHR train. The 18 RHR pump was then started several minutes

later, after the R0 was certain that there was sufficient level in the RV

to prevent cavitation of the pump. By this time operators had checked

the containment radiation monitors and noted no changes in radiation

level. At 11:09 a.m., the R0 shut down the IB RHR pump with the refueling

cavity level approximately 6 inches above the RV flange. The R0 realigned

the IB RHR train for shutdcwn cooling and started the IB RHR pump at

11:14 a.m. Procedure B0A Refuel-4 was exited. Operations department

management directed operators to fill and vent the 1A RHR train. An

air and air / water mixture was vented from a 3/4-inch sample line for

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approximately 20 to 40 seconds, with its valyc 1/4 turn open. At

1:39 p.m., operators began a gravity fill of the refueling cavity from

the RWST using the 1A RHR train and shortly thereafter started the 1A

RHR pump. An EA at the pump indicated that everything looked and sounded

normal. Control room indications appeared nonnal. Based on these

observations, the licensee declared the 1A RHR pump operable at 1:46 p.m.

, and exited the Limiting Condition for Operation Action Requirement. At

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3:33 p.m., the 1A RHR pump was shut down with the refueling cavity filled

j to 24 feet 6 inches above the RV flange.

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4. Chrono' of Events

All of the 6 ;nts described below occurred on September 19, 1988, and

utilize the 24-hour clock. The times are approximate.

1 0430 Gravity fill of refueling cavity to 402 foot level to check the

effectiveness of the RV boot seal repairs.

0435 Boot repairs appeared satisfactory; however, an RV stud hole

plug came free,

j 0438 Started IB RHR pump to lower refueling cavity level to below RV

i flange to replace the stud hole plug.

, 0448 Shut down IB RHR pump. RV level at 398 feet 8 inches per tygon

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hose indication (corrected).

{ 0730 Equipment Attendant (EA) checked level in the tygon hose, which

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read approxiretely 401 feet. The control room attributed the

i difference between this reading and the reading at 0448 to the

j fact that the tygon hose indication had been acting erratically,

i 0957 Started IB RHR pump to lower RCS level further to allow

maintenance to reinstall the stud hole plug. Level now

! approximately 3 inches above RV flange by visual observation.

1005 Shut down IB RHR pump. Level lowered approximately 1 foot per

! tygon level indication.

i 1045 Unit 1 R0 relieved by extra RO.

i 1052 Started IB RHR pump again. Maintenance requested slightly

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lower level. Maintenance Foreman monitoring level at RV

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cavity, and individual at flange.

1059 Isolated letdown and shut down IB RHR pump due to fluctuating

indicaticns of letdown flow and amps on 1A RHR purp (IA RHR

{ aligned for shutdown cooling at approximately 3200 gpm).

i 1100 Shut down 1A RHR pump. Amps still fluctuating fro'A 20 to 60

amps. Entered Byron Abnormal Operating Procedure B0A Refuel-4,

"Loss of RH During Refueling." Entered action statement a, of

l Technical Specification 3.9.8.2 on loss of one FAR pump during

l refueling with water level less than 23 feet above RV flange,

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1102 Aligned 18 RHR train to gravity fill refueling cavity from the

RWST.

) 1108 Started the IB RHR pump. No change in containment low or high

i range area radiation monitors.

1109 Shut down IB RHR pump. RCS level approximately 6 inches above RV

{' flange.

1114 Started IB RHR pump to provide for shutdown cooling. Exited BOA

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1153 Checked a 3/4" sample line at 1A RHR pump discharge. Vented air

and air / water mixture for 20 to 40 seconds with valve 1/4 turn

open.

1339 Started gravity fill of refueling cavity from RWST using 1A RHR

train.

1342 Started 1A RHR pump. Pump observed locally. Control room

indicators checked and no problems indicated.

1346 Exited Limiting Condition for Operation Action Requirement on 1A

RHR pump.

1533 Filled refueling cavity to 24 feet 6 inches above reactoi flange.

Shutdown 1A RHR pump and aligned 1A RHR train for shutdown

cooling.

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5. Evaluation of the Event

Based on the inspectors' analyses of the event, it appears that water

level in the refueling cavity remained above the flange while the actual

level inside the RV dropped to approximately one inch below the center-

line of the hot leg norzles. This phenomenon was caused by the hydraulic

resistance of the small flow holes on the edge of the top hat, which

restricted the rate at whici; water could drain from the refueling cavity

into the RV while, simultaneous!y, the RHR pump was rapidly removing

water from inside the RV, as the control rod guide stub tubes provided

sufficient venting to allow for easy drainage. The uncoupling of water

levels inside and outside of the RV was compounded by tne operators

believing that water level indication inside the RV could be obsarved

visually with the upper internals installed. As a result, RCS level was

unintentionally lowered to approximately one inch below the centerline

ef the RV hot leg nozzles. This allowed a vortex to develop in the

suction line of the 1A RHR pump and air was entrained into the system,

thereby making it inoperable.

The procedure being ustJ to drain the re',eling cavity was BOP RH-9,

Revision 51A, "Pump Down of the Refueling Cavity to the RWST."

Prerequisite C.14 states, "ENSURE that the tygon hose connection, for

RCS level indication, is in place ... prior to lowering the water

level below the Reactor Vessel Flange (EL = 400'0")."

Subsequent to the event, the tygon hose was walked down by one of the

licensee's engineers. The engine removed several loon seals from the

hose and restructured the tygon hose to establish vertical installation

in all places. He also corrected a 2 foot level discrepancy with the

elevation markings for the tygon hose, which had existed since its

installation.

Based on interviews and discussions with licensee personnel and a review

of records, the inspectors have developed the following obs#:rvations

regarding this event:

There appeared to be o widely held, incorrect perception by the

licensed operators that water level inside the RV could be visually

cbserved with the upper internals installed, ho training was

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provided to the R0s or SR0s to either reinforce nor discredit this

idea. Licensed operator training discusses all of the approved

methods of RCS level indication however, no mention of visual level

indication is made.

The EAs had not received training which would allow them to relate

an elevation number to a physical point in the plant, e.g., the RV

flange is at the 400 foot elevation. Consequently, when the EA

reported that level was 398 feet 8 inches and then went up to the

refueling deck and observed level above the RV flange, he did not

recognize the disparity between these two observations and, conse-

quently, did not identify this fact to the control room.

Licensee management believes that the control room operators followed l

procedure BOP RH-9 and that direct visual observation is an l

acceptable method for determining refueling cavity water level. l

Management believes that the BOP does not require that the tygon i

hose be used and implies that visual observation is acceptable when i

draining the refueling cavity to the RV flange. Management stated j

that this had been done before, with no problems having occurred.

The inspectors have reviewed the BOP in detail and agree that there

is no explicit statement to utilize the tygon hose during evolutions

which lower water level below the RV flange. In fact, there is no

explicit statement in the BOP to utilize any means of level

indication while lowering RCS level.

I However, the inspectors note that prerequisite C.14 requires the

i operators to ENSURE (emphasis original) that the tygon hose

l connection is in place, prior to lowering water level below the RV

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flange. Consequently, the inspectors believe that it is the clear

I intent of this prerequisite to require that the tygon hose be

l utilized to detennine water level for any draining evolution which

will lower water level below the RV flange, as the licensee planned

to do. The inspectors agree that visual observation can be useful,

but believe that it should be used in addition to, rather than

in place of the tygon hose.

The licensee did not intend to lower water level to mid-loop, only

several inches below the RV flange. The licensee does not normally

use BOP RH-9 to drain down to mid-loop operation (below the RV

flange). However, the 80P does not have any restriction concerning

lowering RCS water level below the RV flange, other than not to go

below mid-plane of the hot legs. The inspectors believe that

several of the conservatisms utilized in BOP RC-4a, "Draining the

RCS" could be effectively utilized in B0P RH-9, such as reducing the

flow rate of the pump supplying shutdown cooling from 3000 gpm to

1000 gpm, draining via the letdown system (120 gpm) verses via RH8735

(RHR to Safety Injection pump isolation valve) to the RWST (750 -

1000 gpm), suspending draining operations if level indication is

unreliable, and resolving discrepancies in level indication before

resuming draining activities.

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The acceptar.ce by control room personnel that the tygon hose was

inaccurate (be it level error or slow response) while continuing

to perform draining operations, even if using another "acceptable"

method of level indication, does not appear to the inspectors to

be the most conservative method of operation.

The response of the control room operators, once they had received

i indication of problems with the 1A RHR train, was prompt and

l effective and prevented the potential for bo h trains to become

air-bound and inoperable.

The licensee has provided substantial training to the operators

on the hazards of mid-loop operation. The licensee believes that

because the operators continuously monitor the performance of the

RHR pumps while draining the RCS they would not allow the level

to drop to the point where both trai'is would become air-bound

without the RO initiating action to stop the evolution. The

licensee noted that even though the RO believed that RCS level

was in the vicinity of the flanca, the RO followed the conflicting

indications of RHR pump performance he was receiving and then

stopped the 1B RHR pump to secure the draining and initiated

corrective actions to recover level to a known elevation.

The licensee believes that the safety significance of this event is

mitigated by the ability of the RWST to gravity fill the refueling cavity

at 1500 gpm per train. In addition, the high and intermediate head

emergency core cooling system pumps could have been returned to service

and then utilized to inject water into the RV had both RHR pumps becoce

inoperable.

Technical Specification 3.9.8.2 requires that two RHR loops shall be

operable and at least one loop shall be in operation with the unit in

Mode 6 and water level less than 23 feet above the RV flange. With less

than two loops operable, action a requires that corrective actions be

initiated immediately to re'. urn the affected loop to an operable status

or that wate level be established at greater than 23 feet above the RV

flange. The inspectors have reviewed the licensee's actions and believe

that they comply with Technical Specification 3.9.8.2.

6. Corrective Actions Initiatcd by the Licensee

Subsequent to the event the following corrective actions were implemented

by the licensee:

a. The licensee issued a Daily Order prohibiting draining of the

refueling cavity below the 'too hat" of the RV upper internals.

On September 22, 1988, after further evaluation of the event, the

licensee issued a second Daily Order prohibiting draining of the

refueling cavity below the tops of the control rod guide tube

assemblies whe.1 the upper internals are installed. This is to

prevent the condition where flow into the RV plenum area is only

via the 32 small head bypass flow holes.

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b. The licensee conducted training sessions for all operating shifts

j to discuss this event and the lessons learned,

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c. The licensee has revised B0P RH-9 which now requires that two

methods of level indication must be utilized and functional prior

to any draining operations more than 2 inches below the top of

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the control rod drive shaft support housings. The procedure also

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contains a caution that visual indication of RV level at or below

the "top hat" area of the upper internals is not reliable or

] acceptable for one of the two methods for level indication while

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draining the RV. In addition, the procedure also requires that

draining below the 403 foot elevation (top of the control rod drive

shaf t support housing) be done at a slow draining rate, such as the ;

i minimum indicated flow rate on the RHR pump, and in any case, less

than 1000 gpm. Draining below the RV flange (400 feet) is required

to be done using letdown, which allows a maximum flow rate of 120 ,

gpm RHR to letdown, compared to a 500-1000 gpm flow rate when RHR #

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l d. New instructions for the tygon hose level indicator installation

are being developed which will utilize aa installation checklist.

! An SRO walkdown of the tygon hose after installation will be

required prior to its use.

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i e. The licensee has developed an operator aid which relates gallons of

water removed per foot of level change for both the reactor vessel

j and the refueling cavity.

I f. The Westinghouse Owners Group is evaluating a Technical Specifica-

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tion change which would utilize an RHR flow vs. time vs. level

j concept for requirements on RHR in Mode 6.

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j The licensee has deferred development of further long tem corrective

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actions until after the NRC issues the generic letter on mid-loop

operations, to ensure that no conflicts exist. This generic letter

1 provides significant new requirements for licensees on mid-loop

l operations.

7. Conclusion

10 CFR 50, Appendix B, Criterion V, as iniplemented by Commonwealth Edison

Company's Quality Assurance Manual, Quality Requirement 5.0, requires

that activities affecting quality shall be prescribed by documented

procedures of a type appropriate to the circumstances. Byron Operating

Procedure B0P RH-9, Revision 51A, "Pump Down of the Resctor Cavity to the

RWST " paragraph C.14, requires that the operator "ENSURE that the tygon

hose connection, for RCS level indication, is in place or LI-RYO46

Reactor Vessel level Instrumentation operable prior to lowering the water

level below the Reactor Vessel Flange (EL-400'0")." However, nowhere in

the procedure does it specifically require that the tygon hose, or any

other means of RCS level indication, be utilized during the drain down

process. The failure of B0P RH-9 to specify the use of an appropriat2

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means of RCS level indication while draining the refueling cavity to a

level below the RV flange is an apparent violation of 10 CFR 50, Appendix

B, Criterion V (454/S8019-01a(ORP)).

Additionally, BOP RC-4a, "Reactor Coolant System Orain," which contains

instructions for installation of the tygon hose level indication system,

provides no guidance for ensuring that the tygon hose was properly

installed to accurately reflect r<CS level. For example, the procedure

did not require verification that the tygon hose was installed vertically,

that there were no loop seals, or that the elevation narkings were

accurate. The failure of B0P RC-4a to provide adequate guidance for

installing the tygon hose is an example of an apparent violation of 10

CFR 50, Appendix B, Criterion V (454/88019-Olb(ORP)).

The failure of BOP RH 9 to require the use of the tygon hose for RCS

level indication during draining of the refueling cavity led the control

room operators to utilize a method of level indication which was

ineffective when level was below the control rod driv: shaft support

housings. The consequence of this action was to unintentionally drain

the RCS to an estimated 1 inch below the center line of the reactor

vessel hot leg nozzles, thereby allowing a vortex to develop and air to

be entrained into the 1A RHR system, rendering one train of RHR

inoperable.

During his follow-up of this event, the inspector identified a concern i

relating to the human factors design of the RHR flow indicators in

the main control room. The flow meter scale is non-linear and very -

compressed at the lower end, with only 1 graduation between 0 and 1000 !

gpm. Consequently, the licensee is requested to evaluate the l

desirability of rescaling the RHR flow meter or other options such as :

providing a second, lower-range meter, to improve the ability of the R0s l

to accurately monitor low RHR flow rates. This concern will be tracked !

as an open iten (454/88019-02(DRP)). I

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8. Open Items

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Open items are matters which have been discussed with the licensee, which

will be reviewed further by the inspector, and which involve some action !

on the part of the NRC or licensee or both. An open item disclosed

during the inspection is discussed in paragraph 7.

9. Exitinterview(30703) i

The inspectors met with the licensee representatives denoted in paragraph

1 at the conclusion of the inspection on September 28, 1988. The

inspectors sumarized the purpose and scope of the inspection and the !

findings. The inspectors also discussed the likely informational content

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of the inspection report, with regard to documents or processes reviewed

by the inspectors during the inspection. The licensee did not identify ;

any such docunents or processes as proprietary. l

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