ML20125A469

Summarizes Info Obtained to Date Re Fuel Rod Failures in Plant Fuel Assemblies

ML20125A469
Person / Time
Site:	Monticello
Issue date:	07/03/1975
From:	Siegel B Office of Nuclear Reactor Regulation
To:	Ross D, Rubenstein L Office of Nuclear Reactor Regulation
References
NUDOCS 9212080357
Download: ML20125A469 (3)

Text

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JUL' 3 1975 h '-

.i 53eo CElF&" n"u-D. - F. Ross, Chief, Coro Perfomance Dranch, TR j0/(

THRU: L. S. Rubenstein, Soction Leader, CPB, TR PUEL f AILUPES IN M0!!TICCLLO TUEL ASSD:PLICS

'l This ncno sun .ari::es the inferr.ation obtained to dato reCardin0 the fuel rod failures in Monticello fuel cosenblies. A conferenet en11 betroen the NPC cnd representatives of :Jorthern States Power (NSP) '

was hold on July 1, 1975 to discuno the fuel failures observed during a recent inspection of ton dochannoled fuel assa:blics from the in-itial core loadinc ot !!onticello (see attached ' list of participants).

! Three of these fuel ansemblics selected for inspection had visual' i

observationa of failure. There assemblies had been re-constituted crter the first cycle of cporation and subsequently renoved from the e renetor after the second cyclo (l' arch 1974). The renaininc seven assmblics selected hid the larr.ont leak indications based on sipping -

results. Visual observations durant: tho inspection were cade with an-l underwater TV cr. ora and according to USP the poor quality of the pic-ture and the pheten taken soverely restricted tho detail that could bo

-seen. In addition, the notes taken durinc, the exa .ination ucre con-taninated and could not be renoved fron tho inapoetion_ aren.

IISP is in the process of fabricatinc a borescopo mount so inproved visual o5acrvations can be r.ade within- the next few days (July -3 or 4th). Pased on our conversations with NSP the following preliminary -

infomation was obtained:

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Approximately 30 of the 40 corner rods had observable: failures.

The corner rod diagonally opposite the control rod blades l

(nearest the instrunent tubes) had the cost failures, l

l- The cornce rods ncarcat the blade tips had the second nost I

failures.

Few failures were obccrved on the ' corner rod adjacent to the control blade.

'i Cracks ranged in length from'approximately- 1 to 36 inches.

l . Claddinc cracks ranged in width from hairlino to'as cuch as 1/4 inch.

l-In'one corner rod a series of discontinuous cracks was observed extendirc almost the entire rod length.

4 9212080357 750703 PDR ADOCK 05000263 g PDR a- ~ , . -a___-. -- ., . . - - . - . - . - , - . - . . . . . .-

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jut. 3 1375 D. F. Roos j i Some indications of hydriding in the fom of hydride blisters were observed, however, no r.ajor blisters associated with tho l

cracks were soon.

Hairlinc cracks were observed in fuel pins adjacent to sono corner pins. ,

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!!ost of the failures appear to be in the low enrictnent pins.

Docause of the equi;rient, only peripheral pine of the fuel asamblics could be seen.

i' As previouelv nentioned these fuel assenblics were from the initial

' core loadinz; and 260 of the initini 404 fuc1 asamblice still re"nin

! in the core.

However, cil of these initini assemblics will be re-Delivery of the placed during the scheduled October 1 refueling.

l neu fuel assocblics will etart July 15th and be completed by I August 15th. The remaining fuel asocablico currently in the core are ccepriced of 20 nou inproved 7x7, which have been in two cycles, and 196 reload Cx0 fuel asac: blion,116 of which have been in opera-tion 1 cycle. Durinr, the lact reload (cnd of cycle 3), all the

' inproved 7x7 fuel cosentlios and 25% of the exS reload asacablies i

(30) wore nipped. Ho indication of failurcs for any of those fuel asscnblies was observed.

The plant is currently operatinf at about 835 of full power and tho i power operatins level is beins controlled by the activity level at the etcan jet air ejector. The plant has an augmented holdup systen that appreciably reduces the activity in the off-cas prior to stack releaso. The activity release at tho stack is approxir.ately 10,000 ci/ soc compared to the technical specification linit of 270,000 ci/ccc. Proconditioning procedurcs ne reccrm, ended by Cencral Electric

! (PCIGIR) have been in uco.

In stnrary, based on the prelininary infomation, it oppctre that failurcs are lirited to the initial ruol assemblies containinc,_ fuel rods fabricated during a timo period prior to initiation of inproved l

design and fabrication. procedurcs (vacuun out.-cassini; and gettering).

i l

' In particulce these failures appear to be prinarily associated with Iou enrichnent rods within the asscnblies. Drcsden 2 experienced a

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larco numbor of fuel failuroc on similar vintage fuel reds; however,

! the fuel was removed earlier in life and the failures seen were not I

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JUL  ; 137 5 l

D. F. Ross as extensive as those observed in !!onticello. Additional infomation i is nooded to explain why the failures are occurring, in the locations identified and the specific cause of failuro.

B. Siegel

iiccetor Fuels Section

+

Coro Perforr.ance cronch l Divicion of Technical Review Offico of Huelcar Reactor Roculetion i

! Enclosure!

/.a Stated

, cc: S. !!anauer l F. Schrocdcr i R. Fralcy, ACPC (21)

P. Flin-DL/i'.! ADa

, IE (3)

D. Duckley i V. Stello l L. Rubenstein i R. l'cycr l D. Houston

?!. Tokar DISTRIBUTION:-

! Central File

! NRR Reading File l CPB Reading File i

B. Siegel l

l l

o r ,,c e ,. TR: TR:CPB y _-.. _ . . . . ..._. .

.u,.., B. Sieg . L. Rubens tein /A

, , , , , 7/J/75 7/3/75 r.,.i Arc.318 (Rev. 9 3 3) AECM 0240 # u, s. oovsRhMENT PRINTING OFFICE 11874 828-104