05000366/LER-1978-006-03, /03L-2 on 780724:during Heatup Plateau of Startup Testing,Average Drywell Temp Exceeded 135 F Limit.Reactor Heatup Then Terminated.Following 780727 Shutdown,Drywell Air Temp Stratification Found.Details Encl as Revision 2: Difference between revisions

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{{Adams
#REDIRECT [[05000366/LER-1978-006-03, /03L-1 on 780724:average Drywell Temp Exceeded Limit of 135F as Set Forth in Tech Specs 3.6.1.7.Caused by Stratification of Air Temp in Drywell]]
| number = ML19270F513
| issue date = 02/09/1979
| title = /03L-2 on 780724:during Heatup Plateau of Startup Testing,Average Drywell Temp Exceeded 135 F Limit.Reactor Heatup Then Terminated.Following 780727 Shutdown,Drywell Air Temp Stratification Found.Details Encl as Revision 2
| author name = Greene T
| author affiliation = GEORGIA POWER CO.
| addressee name =
| addressee affiliation = NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
| docket = 05000366
| license number =
| contact person =
| document report number = LER-78-006-03L, LER-78-6-3L, NUDOCS 7902150363
| package number = ML19270F512
| document type = LICENSEE EVENT REPORT (SEE ALSO AO RO), TEXT-SAFETY REPORT
| page count = 22
}}
{{LER
| Title = /03L-2 on 780724:during Heatup Plateau of Startup Testing,Average Drywell Temp Exceeded 135 F Limit.Reactor Heatup Then Terminated.Following 780727 Shutdown,Drywell Air Temp Stratification Found.Details Encl as Revision 2
| Plant =
| Reporting criterion =
| Power level =
| Mode =
| Docket = 05000366
| LER year = 1978
| LER number = 6
| LER revision = 3
| Event date =
| Report date =
| ENS =
| abstract =
}}
 
=text=
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S 60 01 DOCsc ET NUMUER ed 63 EVENT DATE le 7b HEPOH T DATE 6J EVENT DESCRIPTION Af40 PROOAULE CONSEQUENCES h O 2 Durina tho heatun tilateau of Unit 2 Startun Testing the average drywell tenperature l
o a i exceeded the limit of 135 F as set forth in Tech. Specs. Section 3.6.1.7.
UpOn l
o 4 l discovery of this condition, reactor heatup was terrainated in the ef fort to resolve l
o 5 l the problem.
l lO 161 I l
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7 8 9 80 SYSTEM C AUS E
 
==CAUSE==
C OY P.
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11 11l l and Georcia Power Comonnv perconnel revealed str,tifiention nf nie t r e,, o r, t o -n <- 4n I
i y
l tha drvvell.
Analvsis of the nroblems resulted in an ournee from 8-?O-78 to 0 1;-78 l 13 l a l ]
as detailed in the attachmont.
The attach'.cnt was in,dsortently loft off Revisin" Tl
]t l41 [ and is beine transnitted as Revision ?
7 8 9 80 FAC1LITY V E T54 DD OF STATUS
% POWE R OTHER ST ATUS CE OVEHY DISCOVERY DESCRIPTION La_l@ lo lo lo l@L N/A l
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. Creene, Supt, of Mr Fng. SNON E:
(017)
 
PLANT E.
I.
H ATCH UNIT II PRIMARY CONTAINMENT C00 LINO MODICICATION During the heatup plateau of the Unit II Startuo Program it was observed that the average drywell air tencerature was exceeding the 135 de g ree limit as specified in the Hatch Unit II Technical Specifications.
The Technical Specification violtion was first obse"ved by Jeff Chumley, Georgia Power Test Engineer, while he was performing startup test HNP-2-10244, "Drywell Temperatures," on July 20, 1978.
The arithmetic average at th is time was dete" mined to he 143 degrees F with the reactor at 160 psig and 370 degrees F.
To bring the drywell air te mp era tu re below the Technical Specification limit, all of the standby Drywell Cooling Fans were placed in service.
Within three hours the average drvwell temperature had been reduced to 132.5 degrees F, and in another 4 hours it had dropped to 124 degrees F.
The following morning, July 21, B ec h te l was notified of the problem we were experiencing.
Their mechanical design groun asked us to begin mon icoring d"vwell air temocratu"es on a regular basis while experimenting with various cooling and reutreulation fan alignnants.
Again, on July 23, the Technical Scoc i.'i en tion linit of 135 degrees F was exceeded when reactor p"essu e was increased to 524 psig.
In an effo"t to derrease the drvwall temocrature, two of the Reactor Building coolers were taken out of service to reduce the load on the Reac tor Building chillers.
This b"ought the te mo e"a tu re down to 131 degrees F.
As reactor prersiae war ine" eared to 500 osig at 480
.; rm.3 LL; d.c,
_ te at e w. ; r
*;d 3.
.e g ees F.
Standby Gas Treatment and the Dryuell Purge Fan were placed in service, as reac tor pressure was lowered, t r.
order to help reduce the drywell temperatures.
Bill Papproth of Bechtel arrived on site July 24 to analyse the Drywell Cooling System.
On July 26, management decided to bring the reactor to cold shutdown to allow Bechtel to enter the drywell for an inspection of the Drywell Cooling System.
Bech te l re o re sen ta t ive s and Georgia Power Company engineers and maintenance personnel entered the drywell of July 27 to begin their inspection.
They found the rupture discs missine, f"on the s a c r i f '. c i a l shield which allowed the a i r, designed to flow in the annulus between sacrificial chield and the reac tor insulation, to escace.
They also discovered that the annulus was less than one inch wide where design had specified 3 inches, thus cutting down on the area for air flow fron the Drvwell Cooling System.
See Figure 1 for schematic of the D.' y we ll Cooling Syste m.
 
=====
Bechtel direc ted that several runs of temporary ducting he installed to redistribute the cool air at the bottom of the drywell to the hotter upper regions and duct the hotter air from the top of the drywell to the larger capacity coolers at the bottom.
Following the installation o r the rupture discs and the tanoorary duct work per temporary DCR 78-212 the reactor was again haought critical on July 29.
The reac tor was brought to 165 psig on July 10 and eleven hours later the drvwell temperature exceeded 135 degrees F.
Reac tor shutdown began immediately to allow Bech te l to do further woak in the drywell.
From July 31 to August 3, under Bech te l 's d irec tion the following changes were made:
(1) Reversed the d i re c,ti on of air flow of 2T47-C002 A and B to force core air up through the annulus area per temporary DCR 78-223 (2) Installed two thermocouples in the aia gap between the sacrificial shield and reactor insulation, two thermocouples on reactoa
:- insulation and relocated te mp era tu re elements 2T47-N002, 2T47-N010 and 2T47-N001K per temporary DCR 78-232.
(3) In s t a ll e d te mp ora ry 24 inch du c two rk from fan 2T47-C001A to inlet of fans 2T47-B008 A&B and replaced existing suction ductwork for 2T47-C001 A with flexible du c twork per temporary DCR 78-?30.
(4) Scaled off CRD cavity a.ea by the instal't.'
c.) of a docr at the CRD cavity entrance to allow cavity area to b e p re r~
aized to help in the noving of air up through the a n nu lu s, area per temporary DCR S
(5) Installed wedges between the sacrificial shield and reactor insulation to increase the air gap of the annulus to increase air fl ow.
(6) Inspec ted reac tor insulation for oroper installation.
(7) Reduced chilled water flow to the lower drywell cooling units, 2T47-8008 A &B and 2T47-B009 A&B, to increase
' low to uppea cooling units, 2T47-B007 A&B.
(8) Carl Sox of Environmental Balance Corocration rebalanced drvwell cooling fans air flow per Bechtel's instructions.
Reac tor was. irought to 500 psig and 470 der-ces F on Augu st 4 to evaluate the Drywell Cooling System.
Drvwall average air te mp era ture again exceeded 135 degreen F approx'natelv
'?
hours after the reactor went critical.
Reactor was again brought to cold shu tdown, on Augu s t 5, for additional changes.
 
'The following changes were made under Bechtel's instructions on August 5 and 6:
(1) Blade pitch on fans 2T47-B007 A&B were inc rea sed, to increase air flow through t'h e s e units by approximately 50%, per TER 78-6.
(?) The supply duc ts to the CRD cavity f rom 2T47-B008 A&B and 2T47-B009 A& B were blanked off to direct more air up through the annulus and up to the hotter upper regions of the drywell per TER 78-6.
(3) A sheet metal ring wa s intalled around the reac tor skirt to isolate the annulus from CRD cavity area per TER 78-6.
(4) Existing te mp ora ry fl e xib le duc t wa s removed from 2T47-C001A and replaced with a temporary sheet metal suction bell.
2T47-C001B was also fitted wiqh suc tion bell per TER 78-6, (5) The 2T23 instrumentation in drywell was put back in service to provide add it iona l te mp era tu re readings.
On Augu s t 7, reactor was brought to 575 psig and 485 degrees F for evaluation of changes made in drvuell thus far.
Drywell temperature exceeded 135 degrees F about 30 hours after reaching 575 psig.
The reac tor pressure was then reduced to 400 psig on August 9 to maintain dryvell temperature at approximately 130 degrees F, while management was waiting word from URC for a Techincal Specification change which "ould allow use of a volumetricly weighted formula for computing average drywell air te=perature.
Due to a problem with tbc drywell tn toru: vacuum brefeers the cacto.
.s
'roup,
L, c. s i d snu do on ps-
.1.
o While the reac tor was down the following additional changes were made per TER 78-8:
(1) The bottom of the reac tor vessel insulation was flashed so that air could not flow between reacto" vessel and insulation which could cause higher heat transfer from the reactoa vessel to the drywell thus placing a greater load on the Drywell Cooling System.
(2) The reac tor st a b ili z er covers were removed in hopes of inc reasing air fl ow in the annulus area.
(3) The reac tor /dy rwe ll bellows wa s insulated to dec rea se the amount of heat flux from reacton vessel to drywell air.
(4 ) Temporary te mp era tu re elements were installed by request of Transco, R?V insulation supplier, to evaluate insulation and to estimate heat load.
9 I
 
(5)'The annulus between the sacrificial shield wall and the RPV insulation was checked for debris which might have blocked air fl ow.
S ev e ra l i t e ms, including a welder's b rush and miscellaneous trash, were found in the air space and removed.
(6) Aia fl ow read ings were taken to determine air flow being suopited to annulus and amount leaving a n nu lu s at the top of the sacrificial shield.
It was found that 13,500 c fm wa s being supplied to the annulus but only approximately 690 cfm exhausting at the top, which showed a substantial amount of air leakage from the annulus through the sacrificial shield penetrations.
Following the completion of the items above, the reac to r was broght critical on August 14, after being down for three days.
Also on August 14, Max Manary, Plant Manager, received wond from'the NRC that the volumetric weighting for drywell temperature averaging was a c c e p ta b.l e.
on Augu s t 16, 32 hours after going critical and at 1005 psig, the drywell temperature reached 134.7 degrees F and all the standby cooling fans had to be started to reduce drvwell te mpera te e.
Reactor pressure was reduced to 940 psig and drywell cooling r e tu rn e d to normal c on fi gu ra ti on.
At this lower p re ssu re the d rywe ll was maintained at 132 degrees F.
Plant management decided on August 19, to bring the reac tor to cold shu tdown to allow construction to enter the drywell and make permanent mod ifi ca tions to the "rywell Cooling S ystem.
The reactor was in cold shetdown on Augus t 20, and all startap test i
_or Hatch Un it II was discontinued until the c omp le ti on of the Drywell Cooling Modifinrtion Outage.
DRYMELL COOLING OUTAGy August 20 to September 15 To best describe the outage and what was done, a before and after look at the Drywell Cooling System design will be presented here, which will encompass all work done to the system per DCR 78-270.
ORIGIMAL DRYUELL COOLING DESIGN Fi gu re 1 shows the original Drywell Cooling System design s chem a t ic a ll y.
The original fan line up was to have the following fans running:
2T 47-2007 A, 2T47-9003A, 2T47-B009A, 2T47-C001A, 2T47-C002A and 2T4 7-C00 2B with the other four fans in standby.
With this line up, 4000 cfm was bein6 supplied to the CRD cavity area by 2T47-B00SA and 2T47-B009A, 4000 cfm was being exhaust the CRD cavity area by rec ircu la t i on fans 2T47-C002A and 2T47-C0023.
Fans 2T47-B008A and 2T47-B009A were also to supply a total of 8000 cfm to the annular space between the cacrificial shield and the reactor vessel insulation.
Th i s 8000 cfm was to travel up the annulus picking up
.amassme es. O C_
_-we I
 
heat lost from the RPV insulation, thus reducing sacrificial shield temperature, until it reached the top of the sacrificial shield where it would exit into the uoper drywell region at elevation 185'.
The remaining 38,000 era supplied by 2T4 7-B008 A an d 2T47-B009A was d irec ted at other loations o f drywell between the 130' and 158' elevations.
Air movement between elevations 158' and 185' was to be by natural circulation.
In the upoer elevation of the drywell, 2T47-B007 A supplied 5000 cfm through a ring header in the drywell dome and 1000 c fm into the d rywe ll below the bellows at elevation 200'.
Recirculation fan - C001A removed 5000 cfm from the drywell dome through a single inlet and 1000 cfm from below the bellows at elevation 200' and d is charged the total 6000 cfm down the drywell at elevation 182' just below the - B007A intake.
The four standby fans were only to come on i t' an operating fan failed or if the air area exceed 148 degrees F.
temperature in the CRD c a v i,t y Chilled water flows to the fans were as follows:
B007A -
53 gpa B008A - 213 gpa B009A - 211 gom Total - 479 gpm The chilled water is s up p li e d by the Rea c tor Building chillers which also supplies the Reactor Building and Radwaste Building area coolers.
The duc twor k in the drywell was fabricated from ASTM A 167, stainless steel sheet, Type 304, No. 2D finish.
.REVi3ED DRYWELL COOLING DESI.GN---
As a ro s -' t
* t"e ' n'rimen in and d a '-
a'r ly - :
*s' en
"'v 20, 19/b anc August 20, a final cesign was formulated by Becatel unac would optimise the Dr v we ll Cooling System with the least amount of down time for the reactor.
A reactor outage was necessary due to high te mp eaa tu re and radiation levels in the drvuell and the length of time needed to do the work.
Also the northeast drywell hatch plug had to be removed to allow the transfer of eculoment and materials in and out of the drywell.
A 28 day outage was aporoved by Georgia Power Company management to implement design change 78-270.
Fiqure 2 shows the resulting Drywell Cooling System design.
The present fan line un is : 2T47-B007A, 2Tu7-B007B, 2T47-8008 A,
2T47-B009A, 2Th7-C001A, 2T 4 7-C 0 01 B, 2T47-C002A, and 2T4 7-C00 2B running with 2T47-B0083 and 2T47-B009B in standbv.
The only logic change needed to accomplish this was to remove the interlock between 2T 47-B007 A and 2T47-B007B which p rev en ted both fans from running simultaneously.
All of the te mp ora ry duc twork, installed during the previous short outages, was removed from the drywell before the actual installation of the mod ifi ed ductwork began.
 
A ring header extending 90 de g ree s around the devuell. from east to south was tied into the existing d is cha rge duct of B007A as seen in Figure 3 This ring header delivers 6500 cfm to the upper drywell through two outlets as seen in Figure 4.
Fan 2T47-B007 A also delivers 1500 cfm to the ring header in the drywell done.
(The resister which previously d e live re d 1000 cfm, just below the bellows, wa s closed).
The rated ca p ac it y of "ans 2T47-3007 A&B is now 8000 cfm due to the change in pitch of the blades made August 5 and 6, per TER 78-6.
Fan 2T47-B007B wa s modified in a similar manner as 2T47-B007 A with the same air flows.
The most extensively changed po" tion of the D"ywell Cooling System was t! e upper recirculation fans 2T4 7-C 001 A an d B.
The existing 7.5 hp fans were removed and reBlaced with 30 hp 12,000 cfm capacity fans.
The two Joy Fans. pu rcha sed were r e c e iv e d with 480 volt motors and 4 blade rotors.
The motors were removed and sent to Reliance (the manufacturer) to be rewound f or 600 volt duty.
The 4 blade rotor was not sufficient to produce the desi"ed pe"formance cu"ve, so the twelve
~
blades were removed from the o"iginal 2T47-C001 A& B fans and installed on th'e new rotors.
'Jh e n the rewound motors were back on site, the fans were reassembled and mounted on test stands in the maintenance shop to be balanced under the direc tion of a Jov Manu f ac turins Company representative.
After the success ful completion of fan t alancing, the two new fans were installed where the original fans had been removed at elevation 185.
New cable and conduit was also recuired due to the larger motors.
The duc twork for 2Th7-C001 A&B was completelv redesigned.
The new design included two 2 4" discharge ducts, see Fi gu re 5 one each from the ran ou tle ts at elevation 185' down to elevation 128' sea F"-urn 6 (ty''ca' of bot' "ams'.
The Fuct'on d u c..t e r. was a eo moc..ted tr._ sactio.i j.-- selow the sulknead at elevation 203' r2ther than from the drywell done area.
The intent of
.these changea was to move as much of the hot air from the top of the drywell down to the lower levels where the higher capacity cooling units were.
Two additional 24" supcly ducts were addeo, one each from 2T47-B003A and 2T47-B009A, see Figure 7 an d 8, to supply 6000 cfn each to the middle elevations of the d rywe ll, see Figure 9.
The supply ducts to the CRD cavity were left blanked of f per TER 78-6.
The lower recirculation fans 2T47-C002 A&B were le f t with their flow direc ted into the CRD area per DCR 78-223.
Following the completion o f duc twork and fan installation, Carl Sox of Env i ron m en tal Balance Corporation rebalanced the Drywell Cooling System per the new PPD issued by B ech te l.
 
Other changes made included the ins t a ll a t ion o f re flec tor shields on RTD's that were in areas of high heat radiation so that a more S
accura te air te mp era ture could be recorded.
The RTD's which had the reflec tor shields 1nstalled where 2T 4 7-N 002, 2T4 7-N 0 0 3, 2T4 7-N 0 09, 2T47-N010, 2T47-N014 and 2 T 47-N015.
In addition to the shields, temperature elenents 2 T 4 7-N 0 0 2, 2T4 7-N010, 2T 4 7-N014 and 2T4 7-N015 were relocated approximately one foot farthen away from the vessel into the air stream.
From the data recorded by TER 78-8 concerning the annulus air gao air flow, it was found that most of the cooling air being supplied to the annulus was being lost around the pene tra tion s th-ough the in service inspec tion doors.
To alleviate this problem, neoprene gasket material and flashing was installed on the following doons: '2B11-N2A through 2B11-N2H, 2 B 11 -N 2J, 2B11-N2K, 2B11-NB A an d 2B11-NSB.
The CRD cavity door added by DCR 78-231 was fi t t e d with hinnes so that entrance into the area would be less difficult.
The stabilizer covers removed by TER 78-8 were reinstalled per original design.
The wedges b etween the sacrificial shield and reactor insulation were left in place to maintain the needed air g'ap.
The increased chilled water flow to 2T47-B007 A&B was left as balanced on August 3 The flashing around the reactor skirt and at the botton o f the reac tor insulation as we ll as the bellows insulation was left as installed per TER 78-6 and 8.
Two additional fans, designated as 2T47-C0u A&B, were to be added into the new 23" supply ducts f"on 2T47-B008 A and 2T47-B009A, however d e l i v e ry was such that installation du ring the 28 day ou tage wa s not poscible.
New cables were pulled out side the drywell in anticipation-of their arrival and need.
Bechtel has determined f"om data taken during o 1. a n t operation, since the ou tag e, that these fans will not bc 2 svined.
The ou tag e lasted 26 days, two da? s less than scheduled.
The
.gt w'a' v
y acor' Sly c.
,5 c ;
u-to tb,
serat' a
'34e Generation Departnent Outage Coordinators and. Maintenance Deoartment, Construction Department and their contractors, and the on s w e Bechtel representatives.
At p re sen t, the mod ified Drywell Cooling System is maintaining the average temperature between 128 degrees F and 130 degrees F at rated te mp era t u re and p re ss u re.
See Attachment I for c or. lusions d ra wn by B ech tel regarding existing system performance a.i d future changes required.
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Beci tel Power Corporation 15740 Shyfy Grove Road
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Gaithersburg, f.laryland 20700 W, j 301-D.sB 27Co October 6,1978
~
Mr. M. Manry
'?-
Ccorgia Power Company Production Department P.O. Box 442 Bax1cy, Georgia 31513
. sy,,.
 
==Dear Mr. Manry:==
~
~
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E. I. Hatch : uclear Plant Unit 2 Bechtel Job 6511-020
~ -
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Dryuell Coolin; Systen Modifications and Post-Xcdificctica Testing File:
A-29. 3/ S S -2102 -160/ S S -2115 -2/ B -GP -5899 As you are aware, subsequent to accenpliching the drywell cooling systen ductuork modifications, the air handlin:; equip = cat was balanced by Envircer.catal Salance Corporation. We have reviewed the data supplied
~
by Environ =catal 3 lance, and find the syste a balance reported, to be acceptchla.
Also, we have reviewed the dry rell temperature data acquired during the post-codificatica testing period and we draw the follcuing
~
conclusions; Addition:1 codification will be required, during the first A.
refueling cutage, fer the ductuerk above the reactor well bulkhecd, to enh:nce air distribution in the volume over the RPV head (see attached sketch) and, i
B.
In order to regain ccolcr redundancy, the RP7 insulation syste:n probicas cust be corrected, at 1 cast for the insulation above the top of the sacrificial shield s.all. (i.e. - above el. 183'0")
Refer to probicas report ettcched, fer more informat ion.
Enclosed is a su=ary report of the Dryucil Cooling System Prob 1c=s.
If 90 tn'ay, be of service in the future, picace advisc.
Very truly yours U bM~AAf l
T. J. Mcdonald MSD:WJP: din Project Engineer Enclosure cc:
V. C. Valekis, w/cncl.
W. A. Widner, w/ ene L.
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J. R. Jordan, w/cncl.
H. H. Gregory, III, w/cncl.
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CEO2CI.i P& #1 CO""A:!'
DRY'..?.LL COOLI::C SYST" pROBLE''S Back?round:
, I.}.,l -
On July 19 and 20,197S, Georgia Power Co pany informed Bechtel-Gaithersburg that they were experiencing difficulty with the drywell cooling systca, a systca.which Zechtcl-Gaithersburg had designed and provided.
Specifically, the system could not be operated in a fashica which would maintain an average contai=ent dryuell air tenperature of 1350F or less, as recuired by the plant technical specifications. On Sunday, July 23, 197S, a team of engineers was dispatched to the plant site to evaluate system per-formance.
Descrintien o f the S es ter -
~
The drywell cooling system for $'!P-2 is a chill water-to ai.r.. cooling system with a design of approximately 415 tons (~ 5 x 10 */F.r) of heat removal capacity. The systen (shown sche =ctically on Bechtel Drawin;
~'
11-26074) utilizes three (3) no=21 operating air-to-chill water coolers and three (3) nor=al operating air circulating fans.
As provided, the system represents a co=prc=ise with consideratiens
~
given to equipment space availability n'nd optinun system perfor=ance.
In order to provide proper air roverent and cooling, the system relics i
on the principle that hot, or heated air rises and cold, or cooler air descends. Design paraccters for the sacrificial shield inside diancter end the RPV insulatica outside dic.eter were specified to provide a 3 :.nch airjap for ventilatica cooling air flow frc= botte= to top.
Based on an 80 tU/lir. heat loss frca the insulation surface, and with 8000 Cfm cooling air at 75 F entering the base of the sacrificial shield, it van esti.ated t. hat the air exit temperature to the upper drywell area would have been approxi
:ely 1100F (plus or minus 100F).
Itcated air uithin the upper drywell was at icipated to cix with the exiting air frem the sacrificial shield annulus, and be cooled and exhausted by the air handling equipment provided. The vole-c above the reacter well floor, confined by the drywell head, was to be cooled by rupplying 75 F supply air to the region, and then exhausted to the annulus created by the con-centric configuration of the sacrificial shield and the cylindrical portion of the drywell.
9 E
''''.2.... :
: ~ ~ ~~- n -
 
y-s Drywell Cooling Systc= Proble=s Page Two
(.
a_......
The large volu=c vithin the spherical section of the drywell, as well as the CRD cavity uithin the RPV pedestal are served by two chill water cooling units which provide cooled air at a design tc=perature of 75 F to the base of the sacrificial shicid, the upper CRD cavity and the elevation 127' and 150' (MSL) vole =es.
Disetission of the Problers Encountered:
Upon arrival at the jobsite, and for a period of approximately 60 hours, an evaluation of syste= performance was conducted with the following findings:
Cooling Units 2T47-E007A and 2T47-E0073, located in the drywell n.
upper volene (elevation 185' 0") were operating si=ultaneously, with a heat removal duty of approximately 1.1 nillica ETU/HR (almost twice the design sp2cified capacity) per unit.
b.
Cooling Units 2T47-3003A and 2T47-3009A, located in the drywell spherical vole =c (elevatien 127') were operating at a he2t rc= oval duty of approxi=arely 660 thousand 3TU/ER lonly about 30 percent of the design specified capacity) per unit.
I.
Peak dryvell te=perarures were recorded as high as 250 F (near I
c.
the reacter well bellows, el. 200') and sinultaneously as low as 80 F (in the CED Cavity).
On July 26, 1978, the unit was placed in a shutdown and cooled down condition, uith the follouing course of action:
1.
Provide a supply air header for. cooling. unit 2T47-3007A, to be located atn-clevaticn 193', i==ediately below the reactor well bulkhead.
2.
Provide discharge duct for circulating fan 2T47-C0013, to allow fan discharge to cooler suctions for cooling units 2T47-3009A and/or 2T47-LC093. (1-24" Elephant Trunk) 3.
Elininate exhaust air ductin; for fan 2T47-CC013 above elevation 190', to allow evacuation of the volu=e i==ediately below the reactor well bulkhead.
4.
Pr' ovide 4000 c f= of supply air to drywell elevation 175', 'tc provide cooling air injection at the main stea= line chase vole =c.
(2-16" Elephant Trunks) x
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.c a3 Dryvell Cooling System Problems Page Three
[
During the period of plant downtine to effect the above codificaticas, an I
inspectica of the drywell revealed that two closure devices at the base of the sacrificial shield had been c=itted during plant construction.
The caission of the closure devices (Rupture Discs 2TL7-D001 A and 3) resulted in the annulus ecoling air bypassing the annulus and "short g
circuited" a cooling air flow of 8000 cf=, intended to be provided to the upper drywell voluna.
Additionally, the inspectica revealed that j
the specified cooling air gas of 3", between the RPV insulatica and the sacrificini shield had not been u.aintained, and the actual gap thickr.ess was found to be non-unifera and varying frca 0" in sc e locations to %"
in others.
(This is due to the sacrificial shield not being plumb and also due to insulation not being installed as shown on engineering dwgs.).
in an effort to assess the ramifications of the lack of cooling air for the sacrificial shield, Civil and Nuclear Engineers at Gaithersburg were con-suited.
It was de crnined that the concrete within the sacrificial shie'd vall does not contribute te the stability of the structure, but is pro-vided to shield che dryvell cc ponents frca the nucicar radiation emitted from the reactor core during picnt operation.
The temperature of the outer surface of the sacrificial shield will be monitored and the resulting data will be used to calculate concrete te=peratures within the shield.
Then the adecuacy of the concrete with respect to neutrca shielding can be evaluated.
1.
k It was also noted that the RPV flange be110ws was uninsulated and as s
~
such conservatively trcnsnits core than 100,0C0 STU/Hr.
to ambient.
GPC agreed to insulate this shicid.
During the evalttatica of the shield, it was also determined tFat nerercus holes had been provided in the RFV pedestal by the ccatainment These holes, or porta were provided to allcw access to the vessel skirt crector.
hold-down bolting during vessel seating and torquing.
These ports previde a path for air ficw to and frem the annulus and CRD Cavity.
A review of the drywell cooling systen design has revealed that these ports were not considered during the design phase, and nay have centributed to poor sys te_t performance had th7 previously centioned deficiencies not occurred.
In addition to the =cdifications above, Cecrgia Power Cenpany Constructica Management effected the installation of rupture discs. 2T47-DOOl A and B.
To11owing the above repairs and modifications,.the unit rest cd startup testing, and the Ecchtel engineering team proceeded to evaluate the,
effectiveness of the system modifications.
On July 30, 1973, with reactor ccolant temperature at 4cS F, the average drywell temperature was ec=puted to be 135.2 F, and plant management decided to terminate the test program for additional modificatien.
The following additional modifications were effected:
1.
Reverse the flow direction for fans 2T47-C002A and B, so that
~
cooled air may be exhausted fres elevation 118' 0" and pumped
:..-- ~~. ~ 5: -
 
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(>. k-o\\ lu Page Four to the CRD Cavity, to provide pressurizaticn of the RPV pedestal and, via the hand-holes, the sacrificial shield annulus.
n.
2.
Provide a closure for the louer CRD Cavity access, to allow pressur-ication of the ce=partment via fans 2T47-CC02 A and 3, i
as mentioned above.
i 3.
Provide discharge ducting and codify the suction duct network i
for fan 2T47-C001A, as previously described for fan 2T47-CC013.
i 4.
Evaluate volume flow rates for cooling systes units 2T47-CC01A, C0013, 3007A, 20033, and 30093.
j l
S.
With the advice of North Erothers, Inc. and Georgia Power Cc=pany i
Construction, open the RPV insulation-to-shield wall gap I
to the maxi =ca possibic vidth.
6.
Measure air gap flous.
Prior to resu=ing plant testing, the total volume flow rates for the various paths era cuantified as follows:
a.
Frcm 2T47-3003A/3 to clevation 179' (MSL),1600 cubic feet per minute.
(Through a 16" elephant trunk) b.
From 2T47-3003A/3 to the R?V insulation-to +ield wall air gap, 7,500 cubic feat per ninute.
c.
Frca 2T47-3009A/3 to elevatica 179' (MSL),1300 cubic f:ct per ninute (Throu;h a 16" elephant trunk) d.
From 2T47-3009A/B to the RFV.insulatien-to-shield wall air gap, 6,000 cubic feet per minute.
c.
Froa 2T47-C001A to Coolin; Unit 2T47-30033, 3,400 cubic fcer per minute.
(Thrcugh a 24" elephant trunk) f.
From 2T47-C0013 to Ccoling Unit 2T47-30093, 3,000 cubic feet per minute. (Through a 24" elephant trunk) g.
RPV insulation-to-shield wall gap discharge, 1,200 cubic feet per ninute.
Resuming' plant heatup cn August 3, 1973, we found dryvell average temperature.again cr.cceding 135 ?, and in an atte=pt to corrcet the -
apparent heating probica Bechtc1 suggested reducing air flow to the RPV insuistion-to-shield wall pap by closing first two volume dampers and
~
then isolating the air gap completely. The intent was to reduce air Icakage to annulus between RPV and insulation. The effcet was not noticcabic.
Stopping circulating fans 2T47-C002A and B proved to have no effect on reducing the average drywell te=perature; however, the reduction of CR3 Cavity pressurizing air also had no effect on CRD Cavity temperature.
~
On August 4, 1973, the plant was again shutdown for further ventilation modifi. cations.
me.S e
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~
b T T A C_ M NI\\G MT 1
p. 'l o{ ( O s
Drywell cooling System Problems Page Ftvc
~
i:.....-.... Through the period August 5 through August 7, 1973, the following modifications were e f fected:
1.
Supply air ducts to the CRD Cavity were closed with in-duct blanking gaskets.
2.
Construction debrid was removed frem the RPV insulatien-to-shield wall air gap, to the extent possible.
3.
Discharge ducting fre circulating fan 2T47-C001A was re-connected to the fan discharge flange.
4.
Suction ducting for fans 2T47-C001 A and B, including suction bells, were fabricEted and installed, to allow exhausting air frca the refueling bellous.
5.
RPV pedestal bolting rin; holes were covered to provide pressurication of the RPV insulation-to-shield wall air sap.
-~
6.
Insulatica was installed en the RPV refueling bellows.
7.
Obvious openings in the RPV insulation can were closed wi a sheet metal plates.
8.
Tc=perature cic enes 2T47-TI-N002, N014 and UO15 were relocated away frc= the shield wall.
9.
Temperature cle=2nts 2T47-TE-5014, 3015, N003 and n009 were shielded frc= the unpainted shield t'11.
10.
Ther=occuples were installed to monitor the following locations:
RPV insulation-to-shield wall air gap temperature at a.
cicvations 145 and 190 b.
Shield trail interior temperature at clevation 190 and 145 Insulation surface tc=perature at elevation 190 and 145, c.
interior and exterior d.
Inservice Incpection gap tc=perature at elevation 190 and 145 s.
c. 1 Shield wall exterior temperatures at elevations 160, 170, and 180, and f.
RPV refueling bellows surface temperature.
b....
 
o t t
. ~> t g
te Dryvell Cooling Systen Probicas Page Six Resening plant testing cperations on August 7, 197S, in lieu of utilizing an arithmetic averanc temperature, a chan;c to plant technical specifications
""~~~ ~~'-
allowed volumetric weighting of the dryuell air temperatures.
Although the peak tenperatures within the containment were greater than desired, the average drvrall temper 2ture uns calculated to be less than 135 ?
(i.e.,133 F) with a reactor coolant temperature of 545 F (rated).
On August 21, 1973, plant operations were curtailed to allow installation of pern:nent duct.rar% and modifications or nsulation and instrumentation. The follouing work was acec=pli. u:
1.
Sixteca (16) gau;c, 24 inch nc=inal dia=eter stainicss steel ductwork was installed to provide; Air distribution-to elevation 175'0" (MSL) frca cooling a.
units 2T47-B005 A (3) and 2T47-3009 A (3) and, b.
Heated air transport frca clevation 200'0" (MSL) to clevatica 120'0" (MSL) via circulating f ans 2T47-C001 A & 3.
2.
Twenty-two (22) irch nominal dia=cter ductwork was also added to cooling units 2T47-3007 A and 3 to provide coolcl air distributica at elevatica 190'0" (MSL).
3.
Circulating fans 2T47-C001 A and 3, cri;inally specified as Joy Manufacturin,Co. Medcl 23-17.5-1750, were replaced
^
vith Model 23-17.5-3500, accuired frca Philadelphia Electric Company's Linarick station. This "as accc=plished to provide an increase in enhaust air ficw rate, frea c,000 cfa to 12,000 ch.
4.
Fan blades in cooling units 2T47-3C07A And 3 were adjusted to provide a ncainal air volume flow late of 5,000 cf= per unit.
5.
In un effort to reduce the convecticn heat transfer uithin the inservice inspection volume bounded by the EFV insulation and the RTV shell, North Erethers, Inc. applied stainicss steel flashings at insulation penet:::icas fer no les NSA and 3, UllA and 3, N12A and B, and F.6A and 3.
6.
To reduce the chic 1d wall to RPV insulatica annulus coolin;
'nir bypass flo, inservice inspection door penetrations seal f1' ashing was installed at doors USA and 3 and 32A,B,C,D,E F',
C,ll,.1, and K.
7.
To enhance air ter.perature samplina, RTD's 2T47-TE-3002, N010, 5014, and NOIS were relccated and reficctive shicid cans were installed on RTD's 2T47-TE-3003, M009, and the a fo rc=ent ioned, to reduce and/or clininate radiant heat gain of the sensor probe.
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A T T AC_ M bA \\- N ~I p.l o
I
. Drywell Cooling System problems Page Seven Following the post-modification balancin; of the drywell cooling systca,
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~ the plant was returned to start-up testing operation.
As of this date, (October 2, 1973)., the unit has achieved 207 thermal power and average drywell tc peratures have t/pically not exceeded 1270F.
Peak contain-ment temperaturas below the reacter uell bulkhcad is as 167'F, in the vicinity of elevation 203'0" (MSL). The containment te=peratures arc distributed as falluss:
Elevation ("SL)
Avera?e Tencerature (OF) 190'0" 143 (average of 3 RTD's) 175'0" 126.5 (average of 2 RID's) 158'0"
:- 152.3 (average of 3 RTD's) 130'0" 126 (average of 8 RTD's)
Pre-modification contain=ent te=perateres were distributed as follows:
Elevatien (MSL)
Averare Tercerature (o~
190' 175.7 (average of a RTD's) 175' 152.5 (average of 2 RTD's) 158' 146.3 (average of 3 RTD's) 130' I
106.75 (average of 8 RTD's)
And, containment peak tempercture prior to the nodifications was recorded as high as 2550 s.
Due to the difficulties associated with accurately esti=ating the interior surface tcuperature of the shield uall and thus deterning sacrificial shield ccacrete te=peratures, Georgia Power Co:pany has agreed to install (ca both the cuter & inner surface of the sacrificial chicid) te porary ther:occuplas in the vicinity of the "16A and E dcors.
Data provided by thase ther=occuples will allow an accurate deternination of shield wall ccncrete tc peratures. Esti=ates to date indicate 4 concrete to ben 200 F, below c1cvation 175'0".
To regain redundancy in the upper drywell volume cooling units (2T47-E007 A and B) the cenvection currents within the inservice inspectica annulus rust be cli=inated/ reduced. As previously stated, thase
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convection currents result in failure of the RFV insulation to perform i
its intended function, thus causing excessive heat transfer to the upper drywell. Transco, Inc., the insulatica supplier, has stated that it is possibic to do at 1 cast two things, in the interest of reducit.g vessel heat loss. These are:
1.
Add a convection air break (i.e., baffic) at, or near the top of the sacrificial shield wall within the inservice e
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inspection annulus, or
: 2. Eli.inate the intervice inspection annulus above the sacrificial
* shield wall cud apply the vessel insulation directly to the R?V outside dicmeter.
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