ML18025A492

Letter Attaching an Interim Report on Potential Deficiency Which Was Discussed with Mr. Heishman on March 6, 1975

ML18025A492
Person / Time
Site:	Susquehanna
Issue date:	04/04/1975
From:	Curtis N Pennsylvania Power & Light Co
To:	O'Reilly J NRC/IE, NRC Region 1
References
Download: ML18025A492 (6)

Text

~ y PP:..IL TWO NORTH NINTH STRSPT, Al lEN TOWN, PA. 18101

~PHONE) (215) 821-5151 April 4, 1975 Qc~ulat'og Mr . James P. O'Reilly Director, Office of Xnspection and Enforcement U. S. nuclear Regulatory Commission 631 Park Avenue King of Prussia, PA 1/406 SUSQUEHANNA STEAM ELECTRIC STATIOH IIG'ERXiI RT'iMT Oil POTENTIAL DEFICIENCY "R 1OO450 FXLE 840-4 PLA-60

Dear Mr. O'Reilly:

In accordance T~ith 10CFR50.55(e), attached. are tvo copies of an interim report on a potential deficiency TThich TTas discussed with your Mr. Heishman on t~farch 6> 1975.

Very truly yours, N. Curtis Vice President-Engineering Sworn to and subsciibed before this ~2$ oi Notary Public

,'/ ', Ec Construction me 1975 My Commission Expires: P4~,li~<Q)P .

c-Mr. Donald F. Knuth Director Office of Xnspection and Enforcement U. S. huclear Regulatory Commission Washington, DC 20555

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PSNNSYlVANIA POWER 8, l IGHT COMPANY

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~~ DATE PomtTIAL'DEFICX...:Cr ID itTX"IED': !!arch. 6, 1975 FACILITY: Susquehanna Steam Electric Station, Units 1 and 2 TOPIC OF Xi~is Ibf H" PORT:

Additional loads have been identifi d which should, be considered in the design of the suppression pool structures and equipment. The magnitude of these 'loads and their applicability to the SSES design bases have not been determined.

SCOP"" OF IliTEHD< H" PORT:

As required by 1OC."-H50.$ $ (e) this interim report is submitted to describe a potential deficiency which may have acverse a< ectst. on tne Susquehanna Steam Electric Station Units 1 and. 2 (SSES). This repo also advises the Commission'f the phenomena involved, provides a preliminary indication of implications, and describes corrective action underway.

XDEbTIFXCATION OF PO'x~itTXAL DEFICIT 'FACY:

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

1) Svppression Pool Swell

2) Containment Vent Pipe Horizontal Loads from steam condensation

3) bhin Steam Safety/Relief Valve discharge pipe air clearing These phenomena were p eviously e'the considered not limiting or were considered not relevant to tne SSES .'K XX pressu e suppression containment. Two recent letters from General. Electric Company (NSSS vendor) to Bechtel Power Corporation (Architect Engineer) identify informati6n that has been developed from the Park XXX Pressure Suppression Test Faci3,ity (PS":) and "hich -may be applicable to the SSES Containment. The phenomena and their implications are described below.

DESCRIPTIO~ii OF FrZ)40'..- iA:

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

IX@A When the LOCA occu s thc air in the dry"ell 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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~,0 the wate in the suppression pool to rise as a ligament wnen the bubble causes is formed'nd then expands. As thc buoble expands and bubble r'ses in the pool, the ligament of water decreases until a poin at which tne breaks through the remaining layer forming a Cwo phase "froth" of air and water. - Str'uctures and equipment that are above the suppression pool will be subjected to an impingement anQ/or drag load. from this pool swell action. The type and'magnitude of load is a function of the height above Che initial water surface. These loads are not applied directly to the fission product oarrier.

A conservative extrapolation of the data available from G"'s Hark XXi verification test program in the PSTF has 'been prepared for prclimina>y determination of structural loads. From this peliminary conservative evaluation, there are indi-cations that some moQification and/or relocation 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 pool swell.

Following the pool swell transient, Chere is a period. of quasi steady state steam flow through the vent pipes Co the suppression pool. information from testing performed at a foreign pressure suppression containment indicates that there loads which occur on the vertical vent pipes. Nhen applying a load which are'ateral 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 discharge 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 non-condensables and forces Che water from thc pipe. The atmosphere follows the water in the form of a high pressure buoble. 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 buoble to overexpand and the bubble pressure becomes negative, This negative pressure slows down and finally reverses Che motion of the water, lead'ng 'o the compression of the bubble, and the sequence repeats itself until the buoble reaches the surface of the pool. Tne bubble oscillation causes pressure throughout the suppression pool resulting in oscillatory loads on pool boundaries and submerged components.

For preliminary evaluation, clearing loads vere established using the technique presented in IKBO-10859. it is felt Chat 'the loads used were very conservative.

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

M~en 'loads specifically a~U.cable to SSES due to these phenomena are defined. a review of adequacy of the SSES design features will be made.

STATUS OF TiE PROD..CT 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 diaphragn slab and are also in place. The Unit 1 suppression pool rebar 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 KG)ERdAY An intensive effort by PPM, 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 these issues and a schedule nave nearly been completed.

klork is proceeding on the development of mathematical models to determine 'd+amic load factors and to generate load data. inis 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 va. ious 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 iTRC in the near future.

PPM will keep the'ommission informed of developments as a result of. the work underwayo Concrete pours and other critical activities involving the Containment will be suspended unt'1 necessary modifications in this area have been identified. Prior to resuming construe ion of any affected portion of the Contain.",.,nt, the proposed.

modifications will be reviewed with the HRC.

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