ML18114A727

Discusses Status of Util Study of Plant Feedwater Sys Water Hammer Potential

ML18114A727
Person / Time
Site:	Surry
Issue date:	12/02/1977
From:	Stallings C VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	Reid R Office of Nuclear Reactor Regulation
Shared Package
ML18114A726	List: ML18114A725 ML18114A727
References
393-090277, 393-90277, NUDOCS 7906250347
Download: ML18114A727 (5)

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e ATTACffifENT.

SERIAL NO. 393/0902 77 3 pages RESPONSE TO NRC REQUEST FOR INFORHATION FEEDWATER SYST2-1 \{ATER H.,~*l)IBR

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..L *~ Compnrisan of Feedwate~Svste~ Design at Surry Power Station, ~ 1 CREARE Recommendations The steam generators presently installed at Surry Power Station utilize top discharge feed water spargers CJ-tubes) to reduce the likelihood of feed-ring drainage. these modifications were completed during scheduled outages from late 1975 to early 1976.

Surry Power Station also utilizes inverted loop seals to provide the "short pipe 11 effect and to minimize slug propagation. These loops are installed in accordance with the Westinghouse re.commended piping layouts indicated in Figure 7 of the CREA.RE study.

The auxiliary feedwater system is automatically initiated by: a low level indication for the steam generators; a loss of off-site power; an opening of the main feed pump breakers; or through a delay, by any safety injection signal.

Operating procedures are in effect at Surry Power Station which control operator action in the event of low steam generator water level ..

Abnormal Procedure AP-21 details the steps to be taken by an operator in the event of co~plete loss of flow to a steam genera,tor to ensure prompt restoration of feedwater.

Operating Procedure OP-31.2 details the steps to be followed for auxiliary feedwater initiation. This procedure limits the auxiliary feedwater flow to less than 200 gpm under conditions of start-up, steam generator isolation, or hot standby. This would also.apply following cl unit trip on low steam generator level.

• The 11 subj ective" ranking of recommendations developed by CRE.J\RE in Table 19 of the report is based on an evaluation of the *effect: on water-.

hammer probability resulting in piping system overstress. The combinations are ranked from best (1) to worst (13). The feedwater system features employed at Surry Power Station .(J-tubes, flow-on-soon, short: pipe, and flow restriction) optimize the present state-of-the-art recommendations**

established in the report.

The* replacement steam generators to be installed at* Surry Power Station during 1978-1979 will incorporate two additional design features for water-hammer prevention. The proposed steam generator modifications will include the use of a replacement feedwater nozzle which incorporates a full penetration weld between the nozzle and feed ring rather than the present thermal sleeve. In addition, the proposed new feed rings will be offset.approximately 2 1/2 in. in elevation above the center line of* the feed nozzle. This offset will also minimize the possibility of draining the feed piping.

II. Review of Steam Generator Water-Hammer Demonstration Test Conducted at North Anna Power Station - Unit 1 On Harch 17, 1977, tests were performed at North Anna Power Station -

Unit 1 to demonstrate that the possibility of water harruner in the feedwater system follmving feed-ring recovery has been eliminated by J 7 tube and loop seal installation.* The tests were performed during the Hot Functional Testing period. ;7,

e e In summary, the test consisted of operating the steam generators at normal level while dumping steam to the main condenser. One steam generator was then isolated on the secondary side and the blowdown valve opened to drain the steam generator to a level of .three to five percent of narrow ra~ge (below the bottom of the feed ring). Following a 30-uinute period to allow any feed ring drainage to occur, auxiliary f eeclwater was initiated at a flow* rate of 2'2.0 r;pu. At the tirne of auxiliary feedwater initiation, vibration record~rs attached to the piping systeu1 were started to record any abnormal pressure pulses occuring in the system. The complete test was then repeated with raaximum auxiliary feedwater flow to the stea.'!l generator.

These tests were perforn:ed at two different operatini conditions. Phase 1 was cmnp],.eted with the .RCS average telilperature at 445 +5°F and_ a stean pressure of 380 psig. The second phase of the test ,*ms performed at RCS average te1~1perature at 547 +SF and a steau pressure of 1,005 psig.

During this phase, a drain t:Lne of two hours was used instead of JO r.1inutes to provide a better indication of the effects of sparger draining.

The tests perfonued at North Anna Power Station indicated no signs of water hammer occurr:i.ng following feed-ring recovery. Temperature measure-:

uents made throughout the tests of the loop seals indicite that rio pipe drainage occurred. The conclusion of the tests indicates that the J-tube and loop seal arrangements will effectively preclude operational water-

. haLlll1er events.

III. Comparison of the ?eedwater Piping Systei-us at Surry and i\orth.Anna Power Stations Surry and North Anna Power Stations are very sirnilar in overall design:

both plants employ subat~ospheric contairments of the s&ue basic dimensions and utilize three loop ~Jestinghouse NSSS system with .::Iodel 51 ser{es steam generators.

The present steam generators at both plants use cloverlea:f shaped feed rings equipped with J-tubes. The feed rings are attached to the inlet nozzle through a thermal sleeve. The radial pipe run from the con-tairuuent penetrations to the steam generators is similar for both stat ions t,ith the e..'Cception of the loop seals at the f eedwater inlet.

The loop seals at Surry are inverted upward; whereas the seals installed at iforth Anna are opposite. Both arrangements. are acceptable piping configurations to Westinghouse specifications, and both iuntion to limit the length of straight pipe at the steam. generator.

Essentially, the feedwater systems for Surry and North Anna Power Stations are so similar that the test data from North Anna can be reasonably applied to Surry Power Station.

{V. Conclusions As stated in Part I of this response, the feedwater systems for Surry Power Station incorporate all four of the recommendations addressed in the CREARE report.

In addition, test data from North Anna Power Station - Unit l, a unit very similar to Surry, indicate no water-hammer occurrence under varying flow and pressure conditions with an uncovered feed ring.

Operating experience at Surry Power Station, since the J-tube and loop seal modifications were installed, indicates that no appreciable water hammer or damage has occurred.

In conclusion, since the current state-of-the-art features are installed at Surry Power Station and in view of the above testing and operating experience, no further design or procedural changes are considered necessary. Consequently, there will be no impact on the design basis and supporting safety analysis for the station.