ML20236E475

Special Rept Re Hydrogen Gas Accumulation in Charging (High Head Safety Injection) Pump Suction Piping.Caused by Diverse Set of Hydrogen Accumulation Situations Between Two Units Due to Difference in Piping Design.Design Change Initiated

ML20236E475
Person / Time
Site:	Beaver Valley
Issue date:	05/16/1989
From:	Noonan T DUQUESNE LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
ND3MNO:1885, NUDOCS 8905260375
Download: ML20236E475 (6)

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May 16, 1989 ND3MNO:1885 Beaver Valley Power Station, Unit No.s 1 and 2 Docket No. 50-334, 412, License No.s DPR-66, NPF-73 Soecial Report United States Nuclear Regulatory Commission Document Control Desk Washington, DC 20555 Gentlemen:

The attached report is being submitted to provide information regarding the Hydrogen Gas Accumulation in the Charging (High Head Safety Injection) Pump Suction Piping for Beaver Valley Power Station Units 1 and 2.

Very truly yours.

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T. P. Noonan General Manager Nuclear Operations Attachments

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May 16, 1989 ND3MNO:1885 Page two 4

cc: Mr. William T. Russell Regional Administrator United States Nuclear Regulatory Commission Region 1 475 Allendale Road King of Prussia, PA 19406 C. A. Roteck, Ohio Edison Mr. Teter Tam, BVPS Licensing Project Manager United States Nuclear Regulatory Commissicn Washington, DC 20555 J. Beall, Nuclear Regulatory Commission, BVPS Senior Resident Inspector CAPCO Nuclear Projects Coordinator Toledo Edison INPO Records Center Suite 1500 1100 Circle 75 Parkway Atlanta, GA 30339 G. E. Muckle, Factory Mutual Engineering, Pittsburgh Mr. J. N. Steinmetz, Operating Plant Projects Manager Mid Atlantic Area Westinghouse Electric Corporation Energy Systems Service Division Box 355 Pittsburgh, PA 15230 American Nuclear Insurers c/o Dottie Sherman, ANI Library The Exchange Suite 245 270 Farmington Avenue Farmington, CT 06032 Mr. Richard Janati Department of Environmental Resources P. O. Box 2063 16th Floor, Fulton Building Harrisburg, PA 17120 Director, Safety Evaluation & Control Virginia Electric & Power Co. 1 P. O. Box 26666 One James River Plaza Richmond, VA 23261

May 16, 1989 ND3MNO:1885 Page three BACKGROUND Unit 1 had experienced hydrogen accumulation in sections of Charging (HHSI) Pump piping which was attributed to degassing of Reactor Coolant System water. An investigation was performed and as a result periodic venting was initiated. In addition, procedural I requirements to vent charging pumps when returning to service following maintenance were already in practice. Past operating experience indicated no operational difficulties related to hydrogen accumulation. Unit 2 began venting shiftly following discovery of gas accumulation in March 1988. Based on engineering analysis of the quantities of gas found and the venting schedule being performed, system OPERABILITY was maintained as an investigation was initiated.

Following the discovery of hydrogen accumulation at Unit 2 and the issuance of 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, further investigation was also initiated at Unit 1. The investigations, found a diverse set of

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hydrogen accumulation situations between the two units, due to a difference in piping design. Additionally, NRC Information Notice 88-23, provided supplementary information on this area.

In March 1988, Unit 2 experienced gas accumulation in the suction piping of a charging pump during testing associated with a design change. Gas was detected in the suction piping of the "A" Charging Pump (the third Charging Pump not required operable per Technical Specifications). Samples collected from the suction piping vent were  ;

determined to be primarily hydrogen gas. Following this occurrence, l a periodic venting schedule was initiated to preclude the excessive )

accumulation of hydrogen and ensure pump operability. l At Unit 1, the gas accumulation was first noted when starting the "A" Charging Pump (CH-P-1A), due to the differences in recirculation  !

flows for this pump as compared to the other pumps. The "A" Pump recirculation flow is higher than the other pumps causing an increased pressure drop across the recirculation piping orifice, contributing to the off-gassing which is assumed to occur. The condition manifested itself whenever the "A" Pump was started with the "B" or "C" Pump already running. Immediate indications were fluctuating pump discharge pressure, charging header flow, and seal injection flow to the Reactor Coolant Pumps, followed by a recovery

.% to normal parameters within three (3) to five (5) seconds. Due to the rapid recovery it was not readily apparent what was causing this condition. Subsequent evaluations at Unit 1 noted that during a pressure increase to the Volume Control Tank (VCT) from hydrogen gas addition, there was a concurrent decrease in VCT level. As a result, the presence of a gas void somewhere else in the system was recognized. The most likely places being local high points in the system, such as the suction header piping to the Charging Pur.ps.

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DIFFERENCE IN DESIGN At Unit 2, the design utilizes one (8 inch) suction. header for normal charging flow and for both phases of Safety Injection. The-suction header is located below the pumps with an inverted-u design-suction and discharge piping delivering flow to and from each individual pump. The idle pumps can then potentially collect' gas individually as hydrogen is capable of accumulating in the suction piping, pump casing, and discharge piping. Presently a venting schedule has been implemented to preclude excessive gas accumulation I from occurring.

The Unit 1 design utilizes a main (8' inch) suction header during normal charging operations and to deliver flow from the Refueling Water ' Storage Tank (RWST) during the Injection. Phase of Safety Injection and from the "B" Train Low Head Safety Injection.(LESI)

Pump during the Recirculation Phase of Safety Injection. The suction header is located above the pumps with no inverted-u' piping:-  !

therefore, gas accumulation occurs in the main suction header end'not in the suction piping associated with each individual pump. A second (6 inch) header delivers flow from the "A" Train LHSI Pumps during the Recirculation Phase of Safety Injection also located in a suction header above the pumps. No gas has been detected in the discharge piping at Unit 1.

INVESTIGATION Investigations at both Units included venting at various locations during various system configurations to determine where and when hydrogen was accumulating and to determine desired operating configurations. In June 1988, numerous Ultrasonic Inspections (UT) were initiated to locate and quantify the hydrogen voids which had been detected. Specific locations and . quantities of voids were determined. The largest voids found were 11.0 cubic feet _at Unit 2 and 19.7 cubic feet at Unit 1. Based on the data taken and subsequent engineering review / evaluations, it was determined that the maximum voids which could exist are approximately 11 0 cubic feet at Unit 2 (same as actual worst case found) and 25.1 cubic feet at Unit

1. Venting schedules and desired operating configurations were recommended for both units as a prudent measure to prevent excessive hydrogen accumulation.

. May 16, 1989 ND3MNO:1885 Page five APPARENT CAUSE The apparent source of h'ydrogen gas is the Volume control Tank (VCT), in which an overpressure of hydrogen is maintained to enable control of the oxygen content of the Reactor Coolant System (RCS).

During normal plant operations, one (1) of the three (3) Charging Pumps is continuously operated to provide charging and seal injection water to the RCS and Reactor Coolant Pumps respectively. Part of the Charging Pump discharge flow is directed through an orifice into miniflow recirculation piping, which traverses back to the Charging Pump suction header. The miniflow path ensures that the Charging Pump will not operate in a " dead head" mode. It is the miniflow orifices which are suspected of being the primary point of introduction of gas bubbles into the Charging Pumps piping. This is due to the stripping of gas out of solution as the fluid undergoes the .large pressure drop (approximately 2500 psid) across the orifice. It is believed that once stripped from solution the gas bubbles remain out of solution and travel back tc the suction piping, via the recirculation lines, where they collect and form a large void. There are other possible locations, such as piping tees and elbows, where stripping may occur; however, no locations have yet  :

been verified.

SAFETY ANALYSIS No safety implications have resulted from this condition. To date, no Safety Injections, at Units 1 or 2, have occurred in which j the Charging Pumps have failed to perform their intended safety function as required by Technical Specifications 3.5.2 (Unit 1 and 2 Tech. Specs.). Based on an engineering analysis, a venting Echedule I has been implemented as a prudent temporary measure at both Units 1 along with a desired configuration list to paintain acceptable void i volumes in the Charging (HHSI) Pump piping. A design change to provide better accessibility for venting has been initiated for both Units. In addition, in the unlikely event that any or all of the  !

Operating, Standby, or Reserve High Head Safety injection (HHSI)

Pumps fail to perform their intended safety function when needed, Emergency Operating Procedures FR-C.1 " Response to Inadequate Core Cooling Condition" and FR-C.2 " Response to Degraded Core Cooling Condition", provide actions for operators to ensure a safe shutdown of the plant with alternate means of core cooling.

It is recognized that operating with hydrogen voids in the Charging (HHSI) Pump piping is not desirable; however, due to past operating experience and an engineering evaluation there is no l evidence that the gas voids would have prohibited a pump from performing its intended safety function if requirad. There_are, based on operating experience, data r and a engineering analysis, the pumps have been determined to be operable at both Units 1 and 2. In addition, prudent temporary measures have been taken.

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CORRECTIVE ACTIONS i

The following actions have been or will be performed to ensure l operability of the Unit 1 and 2 Charging (HHSI) Pumps: l l

1. As previously stated, venting schedules have been implemented at both Units 1 and 2, along with desired ,

developed i configuration lists, which were to maintain continued acceptable void volumes in the Charging System.

2. A design change has been initiated to provide better 1 accessibility for venting at both Units and to direct the  !

hydrogen to the gaseous waste system at' Unit 1.

3. Westinghouse has been requested to .onduct an investigation ,

of this phenomena. This investigation includes the j fabrication of a clear plastic model of the Unit 2 piping, i which will be used to simulate actual flow conditions at Unit 2 Fabrication of the model has been completed and testing has commenced. It ic believed this model will aid in determining the locations of gas stripping and long term i corrective actions for both Units 1 and 2. i

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