ML20084H493

Forwards Final Rept on Missing Steamline Plug Parts When C Steamline Plug Blew Out,Struck Vessel Wall & Hit Vent Line on Steamline Plug a 3 Inches Above Plug.Plug Sank to Near Ctr of Reactor on Top of Blade Guide Handles

ML20084H493
Person / Time
Site:	Browns Ferry
Issue date:	06/10/1974
From:	Gilleland J TENNESSEE VALLEY AUTHORITY
To:	Giambusso A US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20084H487	List: ML20084H489 ML20084H493
References
NUDOCS 8305040346
Download: ML20084H493 (6)

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s i 4 TENNESSEE VALLEY AUTHO AITY r~*" 'J 9 CHATTANOCGA, TENNESSEE  : ' .\

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. 4:j ~ l July 10, 1974 c._ y y ANND.TDEMW OF P'.2 0 5:1.5 iN 9/rWir1*^4kiHip hV'. l~ /

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. . . ug Mr. A. Gismbusso Siy ll?lpl [lb

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Deputy Director for Reactor Projects Directorate of Licensing

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U.S. Atonic Energy Commission ,"./ ' . 'l g,g/

Washington, DC 20545 s 4i.

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Dear Mr. Gianbusso:

In the Matter of the ) Docket Nos. 50-260 Tennessee Valley Authority )

Your letter dated June 21, 1974, requested a final report on the missing steamline plug parts from unit 2 of the Browns Ferry Nuclear Plant. Five copies of that report, which contains the information presented in our June 10, 1974, report as well as that requested duria;; o J-ec 13. 1074. . ~ ;.loi,. erc cacicacd.

Very truly yours, Y tt J. E. Gilleland Assistant to the Manager of Pouer Enclosure (5)

CC: Mr. R. R. Barris Mr. K. L. Sessions General Elcetric Company General Electric Company 832 Georgia Avenue 9040 Executive Park Drive Chattanooga, Tennessee 37402 Knoxville, Tennessee 37919 Mr. R. B. Beers TVA Projects General Electric Company Atomic Power Equipment Department j San Jose, California 95125

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TEHNESSEE VALLE'i AUTHORITY 1;RWIPJ FERRY IlUCIErdt PIAllT LRi1T P opt 3GTION WITH UURECOVERED STi%MLIUM PARTS Description of the Event During surveillance testing of the RCIC system, auxiliary boiler steam (150 psig) was inadvertently introduced into the main steamline. The MSIV's were closed and the GE-supplied steauline plugs (ref 733E860) were installed in the RPV steamlines. The inflatable seal on the plus was pressurized to 40 psig with instrument air. The "C" steamline plug blew cut and struck the vessel wall a glancing blow, at the same time hitting the vent line on steamline plug "A" 3- inches above the plug. The plug then fell, back into the vessel and sank, coming to rest near the center of the reacter cn top of the blade guide handles. The vessel was at normal operating level, which is 15 feet above the top guide. None of the handles on the blade guides on the tcp culde ma dwa >'-

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The guard flange (158B775A-P6) was stripped off of the steamline plug as it left nozzle "C". The 3/4-inch .f nylon rope (which was secured around the refueling bellcwr lifting clip and the handle in the plug vent line) was sheared 18 inches from the vent line handle. The steamline plug rotated 180 degrees before striking steamline plug "A". The guard flange struck the vessel vall at 350 degrees azimuth belcw nozzle "A". Steamline plug "C" vent line was turned down as it hit steamline plug "A" knocking off four 1/4-inch SS bolts, five 1/4-inch SS washers, and two pieces of safety wire. From steanline plug "C" eleven 1/4-inch SS bolts, one 1/4-inch bolt head, twelve 1/4-inch washers, six pieces of SS safety wire, one 3/16-inch allen head SS scre.7, and one 3/16-inch SS flat washer was knocked off and scattered over a wide area in the vessel and outside the vessel flange.

- A careful search of the reactor and currounding area result'ed in the recovery of all parts except one 1/4-inch SS bolt 1 inch long, three 1/4-inch SS washers, one 3/16-inch SS allen- head screw, and one SS piece of safety wire. A j

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s Description of the Event (continued)

The search was conducted by a written procedure on around-the-clock bauis for 6 day:

with an average of six persons Inrticipating continually expending approximately 864 man-heurs. The centrol red blade guides and fuel cupport cactings were removed, the manway in the chroud support was grund out to permit access below the core plate, and the vessel was searchcd theroughly short of removing the control rods. Thirty-ceven missing parts were located, as indicated below.

3 wachers and 1 bolt .on and around top guide 4 bolts, 4 washers, and 2 cafety wirec in main steam header "A" 1 bolt, 1 wacher, and 1 cafety wire on core plate 1 bolt, 2 washers, and 1 safety wire in the jet pump area 2 bolts and 1 safety wire at fuel support casting location 46-23 2 bolts and 1 cafety wire at fuel cupport cast $ng Jocation 50 43 1 boli, and i war.her ui, fuel :.,uovurL tuollun localica M-27 1 washer at fuel cupport casting location 54-39 1 washer under the core plate arcund the stub tubes 1 bolt and 1 wacher on thu feedwater cpargers and core spray headers 2 bolts,1 safety wire, and 1 Wacher in reactor well on bulkhead plate outside the RPV At this point, it was concluded the.t the missing parts had most likely been ejected from the reactor pressure vessel and had been cwept up and discarded by the floor cueepers before it was realized that come of the parts might be outside the vessel.

The only location within the reactor pressure vessel where parta might be was in the control rod guide tubes under the velocity limiters. This possibility was considered and is evaluated in Safety Evaluation, item B.

Follcwin6 a meeting with repierentatives of AEC, at the requent of AEC, TVA again drained the reactor preccure vessel; removed' all control rod blade guides, fuel support castings, and contrcl red bladec,and incpected the area of the control rod

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Description of the Event (continued)

+ o guide tubes under the control rod velocity liniters. The effort to remove control rods and castings and expose guide tubes required 3 days and expended approximately 600 ran-heurs. One additional washer was found in the ruide tube at location 50-27 All control rod blade guides were reinstalled, and the vessel was filled and nade ready to receive the operational sources.

I Safety Evaluatien A. The reactor pressure vessel cladding was visually examined (10X) where the steamline plug and the guard pInte made contact. There was no evidence of indentations or upset retal. Based on this information, the structural ,

l integrity of the reactor pressure vessel is not considered to be affected l l

by this incident. l l

B. If a part found its way into a guide tube, the part could nigrate into the control rod drive and be captured t;y the ciriva niter. Inis wculd noi, a Geev the drive's scram capabilities. Although it is extremely unlikely, it eculd lodge between the control rod guide tube base and the index tube of the drive.

This could result in preventing blade uithdrawal but not inserticn.

Although the above-mentioned situation could create an operational problem, it poses no safety problem.

C. The obvious concern associated with the lost parts is that associated with the potential for fuel bundle flow blockage and subsequent fuel da-age. A detailed study of flow blockage in a ElR has been made in a GE Topical Report (1). As stated in that report, based on analyses of high power density fuel operating at 18.5 IM/ft. :

(a) It could take r. ore than a 90-percent inlet area blockage to cause a MCIIFR less than 1.0; therefore, no fuel rod. darage would occur unless more than a 90-percent blockage occurs.

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Safety Eva3uation (centinued)

(b) If the blockage were more than 90 percent, clad me.lt and fuel crumbling would occur. This would lead to high radiation sensed by the main steamline radiation monitors which would ceram 'and isolate the reactor.

Offsite doses recain less than 10CRP20 limits.

i Based cn the information concerning the sice of the lost parts, the fellowing conclusions are drawn:

1. If the parts fcund their way into the lower plenum, the fluid velocities would be hich enough te sweep them up tcwurd the fuel bundles cn'y if the parts rsintained a horicental position. In the vertical position, the velocities are not hich enough to lift the parts. Also, if the parts were lying en the bettcm head where the fluid velocities are 1cw, it is censidered unlikely that they could Cet swept up off of the vessel surface.

IncreIore, e'ren Incugn it is pessloie lor tne washer: to get, lifted up toward the fuel, its occurrence is censidered unlikely.

2. Because the fuel bundle orifice diameters are considerably larger thmn the lost parts (center bundles 2.211 inches, peripheral bundles 1.l+c9 and 1.244 l

inches,-low enriched bundles 1.800 inches), it is not possible for the inlet arifices to beccme blocked.

3 If the parts were swept up toward the orifice recien, they would most likely pass through the crifice and become trapped against the lower tie plate. The cross-sectional area of the individual parts is so strall that the flow area reduction would be minimal.

h. If the parts becone frag .ented into small pieces, these pieces cculd l beccme lodced in the fuel bundle spacers, which would probably cause local boiling transiticn and over-beating with subsequent cladding darnge i

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Safety Evaluaticn (continued) due to fretting. However, this should only be limited to a small number of rods in the core becat.se of the limited amount of material.

D. It $ s virtually impossible fcr a part to have found its way into the recirculation punp sucticn piping because the pumps were not operating at the tire of the incident, and their duction is approxi.ately 30 inches above the botton of the annulus. Hcwever, the effect of foreica parts on a recirculatien pump has been considered ana has been judged to cause no significant adverse effect if one should get into a purp. The parts are s::all and would most likely pass throurJ1 the large openings in the recirculation pu*.:p inpeller with no effect whatsoever.

If a part did get caught in an area of close clearance, it cculd becone distorted or mar a pump ccepcnent slightly. Any of these effects wou]d be f l

e all sna inconsaquential in such a large punp. General Electric has experienced several 1/2-inch diareter,10- to 20-inch-long, stainless-steel i

rods passing thrcuch a recirculation purp at a foreign facility with no pump i l

dancCe.

l Therefore, it can be ccncluded that the lost parts will not pose a safety problen.

This has been considered by both the Plant Operations Review Cc=ittee and the Huclear Safety Review Board, and they conclude that the plant can be operated safely.

1. Consequences of a Postulated Flow BlockaCe Incident in a Eoiling Water Reactor -

HEDO-10174.

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