Part 21 Report - 1998-090
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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