ML19326C855

Interim Deficiency Rept Re Design of Horizontal Reinforcing Steel of Spent Fuel Pool Walls.Permanent Strut Will Be Installed in Tilt Pit

ML19326C855
Person / Time
Site:	Arkansas Nuclear
Issue date:	02/07/1975
From:	Phillips J ARKANSAS POWER & LIGHT CO.
To:
References
NUDOCS 8004280782
Download: ML19326C855 (5)

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ARK ANS AS POWER & LIGHT COMPANY 97H & LOUISIANA STAEETS . LITTt.E ACCK. /. AK ANSAS 72203 (5018372-4311

• February 7, 1975 7 8 Mr. Donald K. Knuth,, Director Io *

<7 Office of Inspection and Enforcement 2 G United States Nuclear Regulatory Commission /7 Washington, D.C. 20555 <

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Subject:

Arkansas Power 6 Light Company G &

' Arkansas Nuclear One-Unit 2 & 1 Docket No. 50-368 Significant Deficiency Report Spent Fuel Pool Walls

Dear Mr. Knuth:

On January 9, 1975 we reported a deficiency regarding spent fuel pool walls as required by 10 CFR 50.55(e) . Attached is an interim report providing information available at this time. We expect to have  !

sufficient information to submi+ 4 final report by April 1, 1975.

Yours truly, .

THIS DOCUMENT CONTAINS /. '

-r POOR QUALITY PAGES J. D. Phillips Senior Vice President .

JDP/ NAM /vm Attachment cc: Mr. Morris Howard, Director Office of Inspection and Enforcement Region IV U. S. Nuclear Regulatory Commission White Settlement, Texas 76108 THIS DOCUMENT CONTAINS POOR QUAllTY PAGES 8004280 p m

TA X P AYINf4 INV er CTMQ nwM c m n a c o m m e= a m e.m a. -aa..<. . - - - - -

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. c STATE OF ARKAtlSAS -) -

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COUNTY OF PULASKI )

9 J. D. Phillips, being duly sworn, states that he is' a Senior Vice President of Arkansas Power 4 Light Company; that he is authorized on the part of said Company to sign and file with the Nuclear Regulatory Commission this Supplementary Information; that_ he has read all of the 4

statements made and matters set forth therein. are true and correct to

,, the best of his- knowledge, information 2nd belief.

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./ J. D. ' Philli fs f

J SUBSCRIBED AND SNORN TO before me, a Notary Public in and -for the

County and' State above named this: 7b day of d h m , 197S.

, d du b.b o Notary Public Fly Commission Expires:

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INTERIM REPORT SPENT FUEL PCOL MALLS This report covers the design deficiency reported for the Arkansas -

Nuclear One - Unit 2 Spent Fuel Pool Walls.

1) Description of Deficiency The horizontal reinforcing steel on the inside face of the spent'fuci pool and the tilt pit is not properly detailed to develop the bars at points of high stress. This occurs at the junction of East West walls with North South walls.

The horizontal reinforcing steel in these walls is bent to form a 90 degree bend on the inside face of the pool rather ~

than extending through the wall where they should have~ been 1apped with the horizonta1 steel on the outer-face. -

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.. 2) Analysis of the Safety Imolications For purposes of this analysis we have conservatively assumed cat,astrophic failure of the tilt pit wall. Two cases were considered:

1) with the fuel transfer tube isolation valve closed, as would be the case during normal plant operations and 2) with the fuel transfer tube isolation valve open, as would be the case during preparation for start or ending ri-fueling operations.

i In case (1), water lost from the spent fuel pool would be contained in the tilt pit. In case (2), the water would' be contained in the tilt pit and the refueling canal. Case (2) obviously results in the greater loss 'of water from the spent fuel pool. Our analysis, however, has shown that, even in case (2), the fuel in the storage rack would not be un-covered.

Normally the water in the spent fuel pool is maintained at a level 26 ft. above the top of the active fuel in the spent fuel racks. As explained in FSAR Section 9.1.2 the water 1cvel in the pool minimizes doses at the operating floor

'during_ refueling operation.

For case (1) pool water 1cvel would drop less than 7 feet.

Radiation levels at the pool surface would not increase significantly. Indications availabic to the control room operator to alert him of-this condition are discussed in FSAR Section 9.1.2.5. . Methods of adding water to.the pool are discussed in FSAR Section 9.1.3.2. Makeup to the pool could be initiated and cooling re-established.

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For case (2) we conservatively assumed that, just prior to .

-the postulated failure, the refueling canal was completely -

dry. This situation could occur if, after completing operations, the refueling canal was completely drained with "

the fuel transfer tube' isolation valve open. For this case we found that the spent fuel pool water level could drop as much as 23 feet. Radiation levels above the pool would be high preventing local access to the refueling floor. Make-up to the pool could be accomplished remotely via the LPSI pumps and the refueling canal or via the fuel pool purifi-cation system. It is also likely that boiling would occur in the pool before the pool level was raised sufficiently to re-establish normal cool-ing.

From our analyses of the effects of a postulated failure of the wall between the spent fuel pool and the fuel tilt pit, we have concluded the following:

(1) Plant personnel in the vicinity of'the spent fuel pool at the time of this failure could receive doses in excess of the limits prescribed in 10CFR20.

The expected level will be made a part of the final report.

(2) No hatard to the health and safety of the genera.

public would exist and site boundary doses would not exceed tha limits prescribed in 10CFR100.

(3) _ No damage.would occur to spent fuel elements stored in the pool at the time of this accident. .

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3) Corrective Action Taken .

When the deficiency became known, a check of the calcula-tions was made to see how the wall h'ad been designed. A finite element- analysis was used to determine the stress under the final loading which took into account the thermal effects as well as the hydrostatic loading. The wall sep-arating the tilt pit and spent fuci pool was analy:ed by calculations which assumed the wall to be fixed on both sides and the bottom with a long slot (27') near one side accounting for the, spent fuel pool bulk head gate. The upper portion, due to the effect of the gate, was analyzed as a plate fixed on two sides.

To determine the extent of the problem the wall was re-

!analy:cd using different boundary conditions. Based on the manner in which the horizontal steel is anchored the edge conditions were. chan'ged from fixed to pinned and the 4e b -

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. wall.re-analyzed using a finite element-program. High -

loca'l shears resulted around the bottom of the slot for th'e_ bulk head gate and at the junction with the West wall -

• of the spent fuel pool. -

To bring the shear _ stress within an acceptable levelThea permanent strut will be installed in the tilt pit.

. strut will be made from stainless steel and will not inter-fere with the normal operation of the fuel handling and tilting equipment.

Additional analyses are being made to determine the amountIn of prestress force to be used in installing the struts.

addition, _ analyses are being run .to determine the effect on the other corners of the pool which have similar defects.

- Our preliminary figures indicate that these corners can act as pinned joints, however, the shear stresser.. are being verified by computt analysis.

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