ML20085G501
| ML20085G501 | |
| Person / Time | |
|---|---|
| Site: | 05000000, Browns Ferry |
| Issue date: | 10/15/1973 |
| From: | Gilleland J TENNESSEE VALLEY AUTHORITY |
| To: | Kruesi F US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20085G474 | List: |
| References | |
| 10CFR-050.55E, 10CFR-50.55E, NUDOCS 8308290110 | |
| Download: ML20085G501 (5) | |
Text
_ _ _ _ _ _ _ _ _ _ _ _
TENNESSEE VALLE v AUTHO AITY C T'. 77 A O
c"arr^mooo'JTENNESSEE
. '/ ~
l
\\
i 37401 0
.\\
,QR (
b.:. [ 9 October 15, 1973 numWchuxr.iy 055YiStYHS b-M
}2 ?)lL Y4+2#4 y NE,LE Mr. F. E. Kruesi, Director Directorate of Regulatory Operations U.S. Atomic Energy Commission Washington, DC 20545
Dear Mr. Krucsi:
On September 13, 1973, TVA made initial report to AEC-DRO Inspecto W. S. Little of deficiencies discovered in Browns Ferry Nuclear Plant units 1, 2, and 3 drywell cooling systems. This is intended to be the final report on those deficiencies.
While the initial nuclear heatup on unit 1 of the Browns Ferry plant was being conducted, the temperature readings in the 1
top of the drywell reached 170*F., exceeding the high temperature limits (135*F. average,150*F. local) for the drywell.
Therefore, the nuclear heatup was discontinued and the plant shut down in order to determine the cause of the abnormal temper-
)
atures and the corrective action to be taken. The difficulty arose from poor distribution of the cooling air for the drywell.
The portion of the drywell affected was the upper part between i
the bellows and a horizontal line approximately 10 feet below the bellows.
At the time the high temperature readings occurred in the top part of the drywell of unit 1, the cooling air supply system was composed of three approximately circular supply ring headers. The lowest supply ring header was located near the bottom of the spherical part of the drywell. The second (termed " middle") supply ring header was located just below the transition between the spherical portion and the larger cylindrical portion. The upper (and third) supply ring header was situated just below the transition between the larger and the smaller cylindrical portions. Air was supplied in series to j
the three supply ring headers starting with the lowest header, then flowing to the second header and finally to the header near the top
)
l of the drywell. The air from these three supply ring headers was distributed in such a way as to achieve what was initially predicted to be adequate air distribution in the entire drywell.
i 8308290110 731107 PDR ADOCK 05000259 S
PDR l
i l
O O
- Mr. F. E. Kruesi October 15, 1973 The cooling air return system for unit I was div'ided into two parts.
The part in the bulk of the spherical portion comprised two-thirds of the total flow and flowed directly from the spherical portion to the recirculating fans. The other part (approximately one-third of the total flow) passed in series through a two-ring header return system.
The upper ring return header was located near the upper ring supply header and the lower ring return header near the intermediate ring supply header. Air flowed in this.part of the return system initially to the upper header and subsequently to the lower ring return header before going to the recirculating fans.
The design of the cooling air systen for unite 2 and 3 is similar to that for unit 1.
Safety implications of high temperatures in the drywell are discussed in the Browns Ferry FSAR in the answer to Questions 12.2.16 of May 22,1971. The conclusion reached in that discussion is that the drywell with its essential equipment will be operable at temperatures greater that 320*F.
Therefore, unless the temperatures in the drywell exceed the drywell temperature limits (135*F. average, 150'F. local) by at 1 cast 170*F. there are no adverse safety implications. Consequently, temperatures considered to be "high" in the context of this report do not imply a safety problem.
The corrective action taken to prevent a recurrence of excessive temperature in the drywell was to redistribute the cooling air flow to achieve a more uniform temperature throughout the drywell.
This corrective action involved the following changes in the cooling air supply and return systems:
A.
Cooling Air Supply System 1.
The cooling air supply ring header in the upper part of the drywell was blanked off, and the excess portion removed.
2.
One riser was removed from the middle cooling air supply ring header of the drywell.
3.
Two risers were taken from the bottom cooling air supply ring header to the top of the drywell. Two air distribution grilles were installed on one of these risers, and one air distribution grille was installed on the other riser.
O O
Mr. F. E. Krucsi October 15, 1973 4.
Several grilles were plugged in the supplies and returns of the original drywell air cooling system.
B.
Cooling Air Return System 1.
Every other inlet to the upper return ring header was eliminated.
2.
Four inlets to the lower return rint-header were installed.
3.
The flow from the bulk of the spherical portion was increased somewhat and the flow in the upper part of the drywell reduced somewhat.
After the corrective measures were completed for unit 1, temperatures in the drywell with the reactor vessel at 550*F. were below the limits (135*F. average,150*F. local) except for the reading of one thermocouple.
The location of this thermocouple is above the bulkhead.
Its reading of 170*F. is nonrepresentative because it ic located in a dead air space behind insulated pipe unreached by cooling air, and because it receives heat by way of thermal radiation from the reactor vessel.
The corrective measures were or will be taken for the three units at the plant as follows:
1.
The corrective measures on unit 1 were completed on September 26, 1973.
2.
The performance of the unit 1 cooling air system for the drywell will be observed closely during the early operating period.
When definitive information for unit 1 has been obtained and analyzed, the design to be used for unit 2 and 3 will be prepared and incorporated into those units.
Very truly yours,
.f f l
. E. Gilleland Assistant to the Manager of Power CC:
Mr. Norman C. Moseley, Director Directorate of Regulatory Operations U.S. Atomic Energy Con: mission Region II - Suite 818 230 Peachtree Street, NW.
Atlanta, Georgia 30303 i
O O
FS&EB ACTION CONTROL FORM A.
Action Code CDR#190 Name of Licensee and Facility TVA (Browns Ferry 1,2, 6 3)
Docket No. or License No.
50-259,-260 & -296 Title CDR Evaluation and Followup Origin CDR Date Rec'd 10/31/73 B.
FS&EB Branch Coordinator:
Bryan Dreher Ellis Paulus X
Complet, ion Requested by C.
Action Requested of:
ADREMP M&PPOB EPB RPB ADC0 II OB CB TAB 00E Region Date Requested 11/6/71 Completion Requested by Reference Letter dated 10/15/73 from Gilleland to Kruest f
D.
Action Requested In accordance with PI 0600/6, " Construction Deficiency Reporting",
the TVA- (Browns Ferry) deficiency report regarding deficiencies in the drywell cooling nystems is being assigned to Region II for evaluation of the technical adequacy of the corrective action l
and the final resolution of the deficiency.
I i
E.
Date Action Coepleted Close-out (Date & Method)
Comments: If completion date is not consistent with your work schedule, please let us know.
I JohnG. Davis,DeutyDirector for Field Operations Directorate of Regulatory Operatior.s
. O O
FS&EB ACTION CONTROL FORM l
A.
Action Code CDR#192 Name of Licensee and Facility TVA (Browns Ferry 2 & 3)
Docket No. or License No.
50-260, 50-296 Title CDR Evaluation and Followup.
Origin CDR Date Rec'd 11/1/73 B.
FS&EB Branch Coordinator:
Bryan Dreher Ellis Paulus X
Completion Requested by C.
Action Requested of:
ADREMP M&PPOB EPB RPB ADC0 l
OB CB TAB 00E Region II Date Requested 11/6/73 Completion Requested by.
t Reference Letter dated 10/29/73 from Gilleland to Krussi i
i D.
Action Requested In accordance with PI 0600/6, " Construction Deficiency Reporting",
the TVA (Browns Fer.ry 2 & 3) deficiency report regarding inverted control rod tubes is being assigned to Region II for evaluation of the technical adequacy of the co'rrective action and the final resolution of the deficiency.
I E.
Date Action Completed Close-out (Date & Method)
Concents: If completion date is not consistent with your work schedule, please let us know.
/
Joi
. [ avis, epu Director or Field Operations Directorate of Regulatory Operations
TENNESSEE VALLEY UTF-lO AITY CHATTANOOGA, TENNESSEE 37401 4O October 29, 1973
@ %'yg a f 0 7,
PAATN E ASHIP Mr. F. E. Krucsi, Director Directorate of Regulatory Operations U.S. Atomic Energy Commission Washington, D.C.
20545
Dear Mr. Kruesi:
An initial report of a possible deficiency involving inverted control rod absorber tubes for Browns Ferry Nuclear Plant units 2 and 3 was made by L. D. Weber to AEC-DRO Inspector B. J. Cochran on August 21, 1973. The initial report was followed by an interim report, J. E. Gilleland to F. E. Kruesi, dated September 19, 1973, in compliance with paragraph 50.55(e) of 10 CFR 50.
Enclosed is a final report on this deficiency.
Very truly yours, y,/
J. E. Gilleland Assistant to the Manager of Power Enclosure CC (Enclosure):
Mr. Norman C. Moselev, Director Directorate of Regulatory Operations U.S. Atomic Energy Commission Region II - Suite 818 230 Peachtree Street, NW.
Atlanta, Georgia 30303
/
\\
m
( [l Rb Wl
[4yug(($
\\q Spf s,
a,are" a
O O
~ ~
BROWNS FERRY NUCLEAR PLANT UNITS 2 AND 3 INVERTED ABSORBER TUBES IN CONTR0u RODS FINAL REPORT
References:
1.
Letter from J. E. G111 eland to Norman C. Moseley, AEC, Director of Region II of the Directorate of Regulatory Operations, Final Report Concerning Inverted Control Rod Absorber Tubes for Browns Ferry Nuclear Plant Unit 1, dated August 13, 1973.
2.
Millstone Nuclear Power Station, Unit 1, Special Report -
Reactor Control Blade Evaluation, dated July 23, 1973.
~
The initial report of the inverted absorber tubes in some of the control rods of units 2 and 3 at the Browns Ferry Nuclear Plant was made on August 21, 1973, by L. D. Weber to B. J. Cochran, Principal AEC-DRO Region II Inspector for Browns Ferry Units 2 and 3, in compliance with paragraph 50.55(e) of 10CFR50.
An interim report was submitted on September 19, 1973.
Because 33 out of the 185 control rods in unit 1 of the Browns Ferry Plant contained inverted absorber tubes as reported in reference 1, the control rods of units 2 and 3 were suspected of having similar defects. Likewise, similar conditions were' reported for the control rods of unit 1 of.the lii11 stone Nuclear Plant in July 1973 as described in reference 2. ' This difficulty was caused b'y errors in the control' rod assembly operations.
All control rods for units 2 and 3 were x-ray inspected for proper tube' orientation at the General Electric-Wilmington, N.C. plant. All control rods found with-inverted tubes are being repaired by removing the tubes.and reassemblin'g rods -
properly. Correct re-assembly is. verified by x-ray inspection. This corrective 7
action is planned to be completed by' November 1,:1973.
1 4
e y-t
=
t P
r l
o o
In the x-ray inspection, radiographs were taken of each control blade sheath at the bottom end (velocity 1! miter end) of each control rod. The presence of the steel wool packing used in each absorber tube indicates that the tube is correctly installed.
If difficulties were experienced in positively determining the presence of steel wool and an identifying dimpic was not found 1-1/4 in from the top end, a radiograph of the top end was taken, and the control rod assembly was accepted if steel wool was not observed t.t the top and an identifying dimple was found approximately 1-1/4 in, from the top.
It was found that any control rod assembly having inverted absorber tubes probably had a large fraction of its tubes inverted.
In fact, the assemblies with inverted tubes had an average of slightly more than 56 tubes inverted. Each assembly contains 84 tubes, with 21 in each wing of the cruciform. The data obtained during the inspection are given in the table below:
Item Number Number of Control Rod Assemblies Inspected 378 Number of Absorber Tubes Inspected 31,752 Number of Absorber Tubes Found Inverted 7,480 Percent of Absorber Tubes Found Inverted 24 Number of Control Rod Assemblics Found to Contain One or More Inverted Absorber Tubes 132 i
Absorber. tube inversion could possibly result in about a 15-inch settling of the contained B C level at the top of an inverted rod as discussed in reference 2.
4 I
Reference 2 also' presents results of studies of reactivity changes resulting from possible B C settling in Millstone Point unit 1, and these results are 4
approximately applicable to the Browns Ferry cores. Substantial numbers of I
l l-1
.r v
,u--
y<
, -~--, - -
,9
,y
, ~,
f
,r
[*
V 3,
inverted tubes and consequent B C settling would have been detected during the 4
periodic tests which demonstrate compliance with the technical specification requirculent for 0.38 percent a k shutdown margin with the strongest control rod fully withdrawn from the core and the reactor would have been kept shut down.
/
e e
l i.
e k