United States Nuclear Regulatory Commission - Protecting People and the Environment


ACCESSION #: 9801130101



Duquesne Light Company   Beaver Valley Power Station

                         P.O. Box 4

                         Shippingport, PA 15077-0004



RONALD L.  LeGRAND                                         (412) 393-7622

Division Vice President -                              Fax (412) 393-4905

Nuclear Operations and Plant Manager

                                        January 7, 1998

                                        L-98-004



Beaver Valley Power Station, Unit No. 1

Docket No. 50-334 License No. DPR-66

LER 97-039-00



United States Nuclear Regulatory Commission

Document Control Desk

Washington, DC 20555



     In accordance with Appendix A, Beaver Valley Technical

Specifications, the following Licensee Event Report is submitted:



     LER 97-039-00, 10 CFR 50.73(a)(2)(ii) and 10 CFR 50.73(a)(2)(v),

     "Gas Accumulation in Charging/High Head Safety Injection Pump

     Piping."



                                        R.  L.  LeGrand



KAM/ds



Attachment





January 7, 1998

L-98-004

Page 2



cc:  Mr.  H.  J.  Miller, Regional Administrator

     United.  States Nuclear Regulatory Commission

     Region 1

     475 Allendale Road

     King of Prussia PA 19406



     Mr.  D.  S.  Brinkman

     BVPS Senior Project Manager

     United States Nuclear Regulatory Commission

     Washington, DC 20555



     Mr. David M. Kern

     BVPS Senior, Resident Inspector

     United States Nuclear Regulatory Commission



     Mr.  J.  A.  Hultz

     Ohio Edison Company

     76 S.  Main Street

     Akron, OH 44308



     Mr.  Steven Dumek

     Centerior Energy Corporation

     6670 Beta Drive

     Mayfield Valley, OH 44143



     INPO Records Center

     700 Galleria Parkway

     Atlanta, GA 30339-5957



     Mr.  Michael P.  Murphy

     Bureau of Radiation Protection

     Department of Environmental Protection

     RCSOB-13th Floor

     P.O.  Box 8469

     Harrisburg, PA 17105-8469



     Manager, Nuclear Licensing and

     Operations Support

     Virginia Electric & Power Company

     5000 Dominion Blvd.

     Innsbrook Tech. Center

     Glen Allen, VA 23060





*** END OF DOCUMENT ***



 

ACCESSION #:  9801130109

                       LICENSEE EVENT REPORT (LER)



FACILITY NAME:  Beaver Valley Power Station Unit 1        PAGE: 1 OF 5



DOCKET NUMBER:  05000334



TITLE:  Gas Accumulation in Charging/High Head Safety Injection

        Pump Piping



EVENT DATE:  12/08/97   LER #:  97-39-00    REPORT DATE:  01/97/98



OTHER FACILITIES INVOLVED:  Beaver Valley Power     DOCKET NO:  05000412

                            Station Unit 2



OPERATING MODE:  5   POWER LEVEL:  NA



THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR

SECTION:

50.73(a)(2)(ii), 50.73(a)(2)(v) & OTHER Part 21



LICENSEE CONTACT FOR THIS LER:

NAME:  R.D. Hart, Senior Licensing          TELEPHONE:  (412) 393-5284

       Supervisor, Safety and Licensing

       Department



COMPONENT FAILURE DESCRIPTION:

CAUSE:      SYSTEM:       COMPONENT:       MANUFACTURER:

REPORTABLE NPRDS:



SUPPLEMENTAL REPORT EXPECTED:  NO EXPECTED SUBMISSION DATE 02/28/98



ABSTRACT:



On December 8, 1997 it was determined that Unit 1 and Unit 2 may have

operated in a condition that is outside the design basis of the plant.  A

minimum of one charging/High Head Safety Injection (HHSI) pump may not

have been available to provide emergency core cooling as described in the

UFSAR due to intrusion of gas into the suction of the pumps, and

subsequent gas binding.  The determination is based on engineering

evaluation of the results of scoping experiments conducted to assess

fluid now patterns entering the Unit 1 and Unit 2 charging pumps.



The cause of the condition was attributed in part to the design of

charging/HHSI pump minimum flow recirculation line orifices.  These

orifices were found to strip non-condensable gas from the recirculation

flow.  In the event of a loss of coolant accident concurrent with a loss

of offsite power, this design defect could have resulted in a loss of

safety function necessary to mitigate accident consequences.



Flow orifices are being replaced at Unit 1, and at Unit 2, to reduce the

generation of gas bubbles.  In addition, increased monitoring and vent

system improvements are planned.



On December 8, 1997 at 0412 hours, a one hour non-emergency notification

of this condition at Unit 1 and Unit 2 was made pursuant to the

requirements of 10 CFR 50.72 (b)(1)(ii).  The determination that a

minimum of one HHSI/charging pump may not have been available to provide

emergency core cooling as described in the UFSAR, is considered a

condition outside the design bases of the plant and a condition that

alone could have prevented the fulfillment of the safety function of

structures or systems that are needed to mitigate the consequences of an

accident.  Therefore, this condition is reportable in accordance with 10

CFR 50.72(b)(1)(ii), 10 CFR 50.73(a)(2)(ii), and 10 CFR 50.73(a)(2)(v).



The design defect associated with the charging/HHSI pump minimum flow

recirculation line orifices could create a substantial safety hazard, and

is reportable pursuant to 10 CFR 21 requirements.  This report

constitutes a 10 CFR 21 notification.



The ability to provide emergency core cooling via the charging/HHSI pumps

could have been adversely affected and the safety system may not have

performed its' safety function.  However, there were no actual concurrent

failures of redundant charging/HHSI pumps at either unit.  Therefore,

there were no safety consequences to the health and safety of the public.



END OF ABSTRACT



TEXT                                                          PAGE 2 OF 5



PLANT AND SYSTEM IDENTIFICATION



Westinghouse - Pressurized Water Reactor

High Pressure Safety Injection System / Pump {BQ/P}*

High Pressure Safety Infection System / Orifice {BQ/OR}*

* Energy Industry Identification System (EIIS) codes and component

function identifier codes appear in the text as {SS/CCC}.



IDENTIFICATION OF OCCURRENCE



Discovery Date: December 8, 1997



CONDITION PRIOR TO OCCURRENCE



Unit 1: Mode 5, N/A Reactor Power (Plant Shutdown for Maintenance and

Refueling)

Unit 2: Mode 1, 100% Reactor Power



DESCRIPTION OF EVENT



On December 8, 1997 it was determined that Unit 1 and Unit 2 may have

operated in a condition that is outside the design basis of the plant.  A

minimum of one charging/High Head Safety Injection (HHSI) pump {BQ/P} may

not have been available to provide emergency core cooling as described in

the UFSAR due to intrusion of gas into the suction of the pumps, and

subsequent gas binding.  The determination is based on engineering

evaluation of the results of scoping experiments conducted to assess

fluid flow patterns entering the Unit 1 and Unit 2 charging/HHSI pumps.



There were no structures, components or systems that were inoperable at

the start of the event and that contributed to the event.  There were no

automatic or manually initiated safety system responses associated with

the event.  No operator errors, or procedural deficiencies contributed to

the event.



Westinghouse Electric Corporation provided the design specifications for

the HHSI system, supplied the Unit 1 and Unit 2 multistage, horizontal,

centrifugal charging/HHSI pumps, and flow restricting orifices {BQ/OR)s

in associated minimum flow recirculation lines (five of six total

orifices are affected).  Pacific Pumps Division, Dresser Industries, Inc.

manufactured the pumps and orifices.  The model number for the pumps is

2.5RL-IJ.  The orifice part number is B-19049.



CAUSE OF CONDITION



Two root causes have been identified.  The root causes involved design

inadequacies and inadequate corrective actions including inadequate

questioning attitudes toward past events.  The design inadequacies

included: 1) a system that generates gas, 2) a system configuration that

supports accumulation of gas, and 3) a system that cannot ensure positive

venting of existing gas voids.



Nuclear Regulatory Commission (NRC) Information Notice 88-23, "Potential

for Gas Binding of High-Pressure Safety Injection Pumps During A Loss of

Coolant Accident," dated May 12, 1988, alerted licensees to potential

problems resulting from hydrogen transport from the volume control tank

and accumulation in emergency core cooling system piping.  In June of

1988, numerous ultrasonic inspections were performed to locate and

quantify hydrogen voids in system piping at both Unit 1 and Unit 2.

Based on the data taken and subsequent engineering evaluation, a vent

frequency was established to limit void size.  Piping to support hydrogen

gas venting operations was installed at Unit 1 and Unit 2, in 1989 and

1990 respectively.



The inadequate corrective actions included weaknesses in the engineering

evaluations performed in response to NRC Information Notice 88-23.  In

appropriate void fractions were established based upon superficial

reviews of previous safety injection actuation signals.  Additionally,

the vents installed were deficient in that both units lacked the ability

to positively verify adequate venting and the Unit 2 configuration

presented minimal vent path differential pressure.  Subsequent inadequate

corrective actions and questioning attitudes were evidenced in response

to actual gas voiding events in which causal analysis did not question or

address gas void impact on high head safety injection system operation.



TEXT                                                          PAGE 3 OF 5



ANALYSIS



On September 12, 1997 an operational surveillance test showed that Unit 2

charging/HHSI pump 2CHS*P21C could not meet the required performance

criteria.  The pump was declared inoperable and a spare pump was

installed in its place.  Upon inspection the pump shaft was found to be

cracked.  The crack is thought to result from abnormal impact loading on

the pump.  The abnormal loading is attributed in part to ingestion of gas

voids during pump starts.



Following this event, a Multi-Disciplined Analysis Team (MDAT) was formed

to comprehensively investigate the gas generation phenomenon.  Past

operating experience at Unit 1 and Unit 2 was reviewed and scoping

experiments were conducted to assess fluid flow patterns entering the

Unit 1 and Unit 2 charging/HHSI pumps.  The MDAT 1) established a design

basis void fraction for both units based on scaled model analysis and

engineering evaluation, 2) established void generation rates for both

units based on an eleven stage orifice, and during steady-state and pump

swap operations, 3) established venting frequencies based on both fixed

time intervals and operational pump evolutions, and 4) implemented

ultrasonic tests to verify void size and to provide positive indication

of venting adequacy.  On December 8, 1997, it was determined, based on

engineering evaluation of the results of the scoping experiments, that

Unit 1 and Unit 2 may have operated in a condition that is outside the

design basis of the plant.



For certain design basis accidents and pump operating alignments, the

potential existed for accumulated gas to create a condition in which the

charging/HHSI pump flow may have been interrupted or lost due to

gas-binding.  Under these conditions, it cannot be conclusively stated

that flow would be re-established, or that damage to the charging/HHSI

pump would not occur such that long term operation could be assured.  The

results of the evaluation for Unit 1 and Unit 2 are discussed below.



The results of the evaluation for Unit 2 indicate that under certain

operating alignments, enough gas could accumulate in the suction piping

of an individual charging/HHSI pump to interrupt pump suction under all

flow conditions.  For Unit 1, evaluations of the conditions which could

have led to gas binding of the charging/HHSI pumps indicates that this

would only be expected to occur under large break loss of coolant

accident conditions with a single pump operating.  For more than one pump

operation and for other accidents which result in lower high head safety

injection flow (e.g., small break loss of coolant accident),

charging/HHSI pump flows are low enough at Unit 1 to preclude void

fractions at the pump suction which would cause gas binding.



Introduction of entrained gas into the suction of a centrifugal charging

pump can result in a reduction of pump developed head, and effectively

increase the required Net Positive Suction Head (NPSH) of the pump.  The

gas can also result in increased vibration levels and bearing loads.  If

very large voids are present in the suction piping, the gas voids can

result in loss of pump prime.



Each charging/HHSI pump was designed with a minimum flow recirculation

line to protect the pump.  The minimum flow recirculation lines include a

flow restricting orifice.  The MDAT investigation determined that the

orifice strips non-condensable gas from the recirculation flow (except

for the restricting orifice associated with the Unit 2 "B" pump which has

a different design).  Stripped gas is transported by the fluid and

accumulates at local high points in stagnant or low flow sections of the

charging/HHSI pump suction piping.



The flow restricting orifice associated with the Unit 2 "B" charging/HHSI

pump has fourteen stages.  Flow restricting orifices associated with the

other charging/HHSI pumps accomplish pressure reduction in eleven stages.

Experience and testing demonstrated that the eleven stage orifice is

subject to cavitation and gas generation.  The MDAT identified a

twenty-two stage orifice that significantly reduces cavitation and

virtually eliminates the evolution of gas at all anticipated operating

conditions.



Replacement of the flow restricting orifice provided in the minimum flow

recirculation line for each charging/HHSI pump is expected to reduce the

stripling of non-condensable gas from solution.  The replacement orifices

have more stages.  This decreases the pressure drop at each stage.

Ultrasonic tests performed to quantify hydrogen voids in charging/HHSI

pump suction piping have shown no gas accumulation following orifice

replacement.  This manual method of monitoring gas accumulation has beep

effective thus far in ensuring recently instituted vent limits will not

be exceeded.



TEXT                                                          PAGE 4 OF 5



CORRECTIVE ACTIONS



COMPLETED:



1.   Twenty-two (22) stage flow restricting orifices have been installed

     in all three Unit 1 charging/HHSI pump minimum flow recirculation

     lines.  Replacement orifices were installed and operationally

     accepted by December 12, 1997.



2.   Twenty-two (22) stage flow restricting orifices have been installed

     in the Unit 2 charging/HHSI pump minimum flow recirculation lines

     associated with the "A" and pumps.  Replacement orifices were

     installed and operationally accepted by January 3, 1998.



3.   An acceptable gas void fraction limit has been established for Unit

     1 and Unit 2 charging/HHSI pump suction piping.  This limit was

     established on December 19, 1997 for Unit 1, and on December 23,

     1997 for Unit 2.



4.   Gas accumulation rates and venting frequency have been evaluated to

     ensure the void fraction at the Unit 1 and Unit 2 charging/HHSI pump

     suction is maintained below levels established by corrective action

     3 above.  This action was completed on December 18, 1997 for Unit 1,

     and on December 22, 1997 for Unit 2.



5.   A manual method of providing positive monitoring for gas

     accumulation was developed to ensure the venting process is

     maintaining the void fraction at the Unit 1 and Unit 2 charging/HHSI

     pump suction at levels below that established by corrective action 3

     above.  This action was completed on December 19, 1997 for Unit 1,

     and on December 24, 1997 for Unit 2.



FUTURE:



6.   Based on the charging/HHSI pump suction void fraction limit and gas

     accumulation rate established by corrective action 3 above, if

     needed develop a vent system that will maintain gas accumulation

     below the limit with minimal operator action by June 30, 1998.



7.   Develop an effective strategic planning process that assures safety

     significant issues will be resolved in a timely manner by June 30,

     1998.



8.   Formalize the MDAT process that was initiated and piloted in

     response to this event, by June 30, 1998.



9.   The flow orifice associated with the "B" charging/HHSI pump at Unit

     2 will be replaced prior to the end of the next refueling outage.



REPORTABILITY



The UFSAR for Unit 1 and Unit 2 assumes that a minimum of one

charging/HHSI pump would be available to operate in the event of an

accident.  Generation and subsequent accumulation of gas bubbles in

stagnant charging/HHSI piping could result in both trains of pumps being

unable to operate.  For certain design basis accidents and pump operating

alignments, the potential existed for accumulated gas to create a

condition in which the charging/HHSI pump flow may have been lost due to

gas-binding.  Under these conditions, it cannot be conclusively stated

that flow would be re-established, or that damage to the charging/HHSI

pump would not occur such that long term operation could be assured.

Thus, the ability to provide emergency core cooling via the charging/HHSI

pumps could have been adversely affected and the safety system may not

have performed its' safety function for the postulated accident.



On December 8, 1997 at 0412 hours, a one hour non-emergency notification

of this condition at Unit 1 and Unit 2 was made pursuant to the

requirements, of 10 CFR 50.72 (b)(1)(ii).



The determination that a minimum of one HHSI/charging pump may not have

been available to provide emergency core cooling as described in the

UFSAR, is considered a condition outside the design bases of the plant

and a condition that alone could have prevented the fulfillment of the

safety function of structures or systems that are needed to mitigate the

consequences of an accident.  Therefore, this condition is reportable in

accordance with 10 CFR 50.72(b)(1)(ii), 10 CFR 50.73(a)(2)(ii), and 10

CFR 50.73(a)(2)(v).



TEXT                                                          PAGE 5 OF 5



The original design of the charging/HHSI pump minimum flow recirculation

line orifices did not minimize the generation of noncondensable gas

bubbles.  This design defect could have resulted in a loss of safety

function necessary to mitigate the consequences of an accident.

Therefore this condition could create a substantial safety hazard, and is

reportable pursuant to 10 CFR 21 requirements.  This report also

constitutes a 10 CFR 21 notification.



SAFETY IMPLICATIONS



For certain design basis accidents and pump Operating alignments, the

potential existed for accumulated gas to create a condition in which the

charging/HHSI pump flow may have been lost due to gas-binding.

Therefore, the ability to provide emergency core cooling via the

charging/HHSI pumps could have been adversely affected and the safety

system may not have performed its' safety function.  However, emergency

procedures are in place to respond to this condition.



Based on the operating alignments for the Unit 2 charging/HHSI pumps, a

conservative estimate indicates that approximate 2.7 percent of the total

operating time since 1992 the potential existed for gas accumulation to

occur at a level which would potentially cause gas binding of the pumps.

This time could be further reduced as the charging/HHSI pumps were most

vulnerable during the time interval until the initial vent following pump

swap when gas accumulation in the stagnant pump suction piping was most

significant.



Evaluation of the loss of Unit 1 charging/HHSI pump flow during a large

break loss of coolant accident with credit taken for the actual

performance of the low head safety injection pumps and the resulting

injection flows indicates that the peak clad temperature limits could be

met when other margins are considered.  These include such things as

margin in peaking factors, and steam generator tube plugging levels.



There were no actual concurrent failures of redundant charging/HHSI pumps

at either unit.  Therefore, there were no actual safety consequences to

the health and safety of the public.



PREVIOUS SIMILAR EVENTS



A review of Licensee Event Reports for Beaver Valley Unit 1 and Unit 2

did not identify any similar events within the past two years.



*** END OF DOCUMENT ***





 

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