ML19186A196

Interim Report on Potential Deficiency, Er 100450, PLA-60

ML19186A196
Person / Time
Site:	Susquehanna
Issue date:	04/04/1975
From:	Curtis N Pennsylvania Power & Light Co
To:	O'Reilly J NRC/IE
References
Download: ML19186A196 (4)

Text

TWO NORTH NINTH STREET, ALLENTOWN, PA. )8101 PHONEs l215) 821-5151 April 4, l975 s

~fr. James P. O'Reilly /pe (

Director, Office of Inspection and Enforcement ~4~g U. S. Nuclear Regulatory Commission 631 Park Avenue King of Prussia, PA 19406 l ~ II SUSQUK10QiVA STEAM ELECTRIC STATION IViERDl REPORT ON HPiEhTIAL DEFICIENCY ER 100450 FILE 840-4 PLA-60

Dear Mr. O'Reilly:

In accordance Irith 10CFR50.55(e), attached are tIro copies of an interim report on a potential deficiency Irhich Lras discussed with your Mr. Heishman on March 6, l975.

Very truly yours, ss. W. Curtis Vice President-Engineering & Construction this ~6 of;/

S"orn to and subscribed before

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Notary Puolic jl vg Commission Expires: ~ r5< rP74 c-'~ih. Donald.F. Knuth ': .

Director Office of Inspection and Enforcement (0 cP U. S. Nuclear Regulatory'ommiss'on

• Washington, DC 20555 . - =-

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PENNSYLVANIA POWER 8 L I GH T COMPANY Rojgg+n+ ii88.4p

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DATE POTENTXAL DEFICIENCY.IDENTIFIED: hInrch 6, 1975 FACXLXTY: Su" quehanna Steam Electric Station, Units 1 and. 2

'OPXC OF XVa ZERXbf REPORT:

Additional loads have, been identified which should bemagnitude considered in the design of the suppression pool structures and equipment. The of these loads and their applicability to the SSES design bases have not been determined.

SCOPE OF INTERIM REPORT:

As required by 10CFR50.55(e) this interim report is submitted to describe a "

potential deficiency. which may have adverse affects on the Susquehanna Commission Steam Electric Station Units 1 and 2 (SSES). This report also advises the of the phenomena involved, provides a preliminary indication of implications, and describes corrective action underway.

IDENTXFICATXON OF POTENTXAL'DEFICIENCY:

The primary containment design bases and. load combinations described in the SSES PSAR Sections 5.2.2 and. C.2.6 do not explicitly include the following phenomena:

1) Suppression Pool Swell

2) Containment Vent Pipe Horizontal Loads from steam condensation

3) hiain Steam Safety/Relief Valve discharge pipe air clearing These phenomena were previously either considered not limiting or were considered.

not relevant to the SSES tlK XX pressure suppression containment. Two recent letters from General'Electric Company (NSSS vendor) to Bechtel Power Corporation (Architect Engineer) identify information that has been developed from the )lark IIX Pressure Suppression Test Facility (PSTF) and. which may be applicable to the SSES Containment. The phenomena and. their implications are described below.

DESCRIPTION OF Pier"NO.'~HA:

Two groups of phenomena have been identified. One group occurs as a result of the postulated. loss of coolant accident (XQCA) while tne other group occurs as a result of the actuation of main steam safety/relief valves. Xt should be realized. that the precise loads applicable to SSES have not been fixed at present; however, preliminary conservative estimates indicate that portions of the existing design may require modification.

LOCA M>en the LOCA occurs the air in the drywell is forced down the vent pipes into the suppression pool. The compressed air bubble formed at the end of each vent

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causes the water in the suppression pool to rise as a ligament when the bubble is formed and then expands. As thc bubble expands and rises in the pool, the ligament of water decreases until a point at which the bubble breaksStructures through the remaining layer forming a two phase "froth" of air and. water. and equipment that are above the suppression pool will be subjected to an impingement and/or drag load from this pool swell action. The type and magnitude of load. is a function of the height above the i'nitial water surface... These loads are not applied directly to the fission product barrier.

A conservative extrapolation of the data available from GE's Park XXI verification test program in the PSTF has been prepared .for preliminary determination of indi-structural loads. From this geliminary conservative evaluation, there are cations that some modification and/or relocati'on of equipment or structural members could. be required. Pipe seismic bracing, drywell to wetwell vacuum breakers, S/R Valve piping, suppression pool hydrogen recombiners and. the diaphragm slab are in the region affected.,by'ool swell.

Following the pool swell transien , there is a period of quasi steady sta e steam, flow through the vent pipes to the suppression pool. Information from testing performed at a foreign pressure suppression containment indicates that there are lateral loads which occur on the vertical vent pipes. Mhen applying a load which was determined from bounding the data available from the foreign tests, it was determined that additional bracing for the vents may oe required to accommodate the load.

S/R VALVE DISCHARGE The discha'rge piping of a safety/relief valve contains non-condensable containment atmosphere and. a column of water prior to actuation. Following safety relief valve actuation pressure builds up inside the piping as steam compresses the and forces the water from the pipe. The atmosphere follows the non-'ondensables water in the form of a high pressure bubble. Once in the pool, the bubble expands analogous to a spring and accelerates the surrounding water radially outward. The momentum of the water causes the bubble to overexpand and. the bubble pressure becomes negative. This negative pressure slows Gown and finally reverses the motion of the water, leading to the compression of the bubble, and, the sequence repeats itself until the bubble reaches the surface of the pool. The bubble oscillation causes pressure throughout the suppression pool resulting in oscillatory loads on pool boundaries and. submerged components.

For preliminary evaluation, clearing loads were established using the technique presented in N"-DO-10859. Tt is felt that the loads used were very conservative.

This preliminary investigation indicates that some modification to the safety relief valve discharge piping may be required.. This piping may be re-routed to minimize the magnitude of the pressure oscillations on the liner plate or it may be necessary to change the configuration of the end of the pipe to break up the high pressure air bubble.

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Page 3 When loads specifically anplicable to SSES due to these phenomena are defined a review of adequacy of the SSFS design features will be made.

STATUS OF THE PROJECT The construction of SSES is approximately 10$ complete. The suppression pool base slabs and. liner plates are complete and in place. The Unit 1 reactor support pedestal and its liner plate are complete up to the diaphragm'slab and 'are also in place. The Unit 1 suppression poo'ebar is complete and in place while the Unit 2 suppression pool rebar is being fabricated. Installation of structural steel and rebar for the Unit 1 diaphragm slab is nearly complete.

CORRECTIVE ACTION Ul'H)ERWAY An intensive effort by PP8cL, Bechtel and General Electric Co. to better identify the loads due to these phenomena is underway. The preliminary tasks of developing a plan for resolution of tnese issues and a schedule nave nearly ocen completed.

Work is proceeding on the development of mathematical models to determine dynamic load factors and to generate load. data. This will be augmented by a test program which is applicable to verification of the mathematical models deveLoped. The last task will be to determine the various loads for the SSES containment, to determine load combinations to be used, and to complete any required design changes.

A schedule for these activities will be submitted. to the liR~ C in the near future.

PP&L will keep the Commission informed of developments as a result of 'the work, underway.

Concrete pours and other critical activities involving the Containment wil be suspended. until necessary modifications in this area have been identified.. Prior to resuming construction of any affected portion of the Containment, thc proposed modifications will be reviewed with the HRC.