ML19324C201
| ML19324C201 | |
| Person / Time | |
|---|---|
| Site: | McGuire  |
| Issue date: | 10/31/1989 |
| From: | Mconnell T, Sipe A DUKE POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| LER-88-019, LER-88-19, NUDOCS 8911150177 | |
| Download: ML19324C201 (12) | |
Text
'a-Duht hwr Corrupany (IM) 875 4000 ' Y McGuire Nuclear Station l'O Bat 488 t Cornelius. N C 2ko.tl.Mb8 DUKEPOWER i
l October 30, 1989 U.S. Nuclear Regulatory Comission Document Control Desk ;
. Washington, D.C. 20555
Subject:
McGuire Nuclear Station Units 1 and 2 Docket No. 50-369 :
Licensee Event Report 369/88-19-02 !
Gentlemen: l Pursuant to 10 CFR 50.73 Sections (a)(1) and (d), attached is Licensee Event !
Report 369/88-19-02 transmitting additional information as comitted in LER '
369/88-19 dated September 9, 1988. This report is being submitted in accordance ;
with 10 CFR 50.73(a)(2)(1)(B). This event is considered to be of no significance ;
with respect to the health and safety of the public.
r Very truly yours.
Q.z. m,9 C~af i T.L. McConnell .
DVE/ADJ/cb1 L !
. Attachment -
l xc: Mr. S.D. Ebneter American Nuclear Insurers Administratcr. Region II c/o Dottie Sherman, ANI Library i U.S. Nuclear Regulatory Comission The Exchange Suit 245 i 101 Marietta St., NW, Suite 2900 270 Farmington Avenue Atlanta, GA 30323 Farmington, CT 06032 i INPO Records Center Mr. Darl Hood ,
o Suite 1500 U.S. Nuclear Regulatory Comission 1100 circle 75 Parkway Office of Nuclear Reactor Regulation Atlanta, GA 30339 Washington, D.C. 20555 ,
M&M Nuclear Consultants Mr. P.K. Van Doorn '
1221 Avenue of the Americas NRC Resident Inspector ;
New York, NY 10020 McGuire Nuclear Station 1
$4 8911150177 891031 '
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'A.S. Daughtridge R.C. Futrell R.L. Gill-
{c R.M. Glover. (CNS) 11- T.D.' Curtis (ONS)
P.R. Herran S.S. Kilborn (W)-
'S.E. LeRoy
.R.E. Lopez-Ibanez-J.J. Maher.
R.O. Sharpe'(MNS)
G.B. Swindlehurst K.D. Thomas L.E.' Weaver R.L. Weber J.D. Wyliu (PSD)
J.W. Willis QA Tech. Services NRC Coordinator (EC 12/55)
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On 11/08/87, during a Unit 1 Containment Closcout Inspection, NRC noticed some Hydrogen Skimmer (VX) system dampers appeared to be closed. NRC questioned
- Operations about the positions of the dampers and Operations inspected and verified that each Unit 1 VX system dampers was in its pre-operational position. Because of '
NRC concerns, Operations agreed to perform a flow balance test on the Unit 2 VX system during the 1988 Reitteling Outage. On 07/19/88, Performance took "As Found" flow measurements on the Unit 2 VX system and found that some damper compartment flows did not meet flow requirements. Design was consit1ted to evaluate the test results, and requested flow measurements be taken again using a more accurate 1 measuring device. The required flow distributions for individual compartments were reanalyzed. The result of the re-analysis was a significant lowering of the flow j rates required to limit potential local hydrogen concentration to less than four l percent by volume. Design concluded that the VX system with its present flow balance condition is sufficient and the VX system is considered operable. This event is assigned a cause of Defective Procedure because the pre-operational flow balance test procedure demonstrated the VX system would meet the Tech Spec requirements; therefore, Design waived the fini.1 test and flow balance of the VX system. >
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INTRODUCTION:
On November 8,1987, during a Unit 1 Containment Closecut Inspection, NRC personnel noticed that some Hydrogen Skimmer (VX) system dampers appeared to be closed. NRC personnel questioned Operations personnel about the positions of the Unit 1 VX system dampers and Operations personr.el inspected and verified that each Unit i VX system damper, was in its pre-operational position as evidenced by paint shadows on the damper actuators. Since some of the Unit i VX system dampers appeared to be closed. NRC personnel were concerned about the positions of the Unit 2 VX system dampers, and consequently, Operations agreed to perform a flow
' balance test on the Unit 2 VX system during the 1988 Unit 2 Refueling Outage.
On July 19, 1988, Performance personnel took "As Found" flow measurements using "
a velometer on Unit 2 Train A and Train B of the VX system and found that some VX system damper compartment flows did not meet the flow requirements listed in the McGuire Final Safety Analysis Report. Design Engineering was consulted to assist in evaluating the test results. Design Engineering requested that flow l measurements be taken again using a more accurate measuring device, and the required flow distributions for individual compartments were reanalyzed in a manner consistent with Regulatory Guide 1.7, Revision 2, and 10CFR50.44. The net overall result of the re-analysis was a significant lowering of the flow rates required to limit the potential local hydrogen concentration to less than four percent by volume. Design Engineering concluded that the VX system with its present flow balance condition is sufficient and the VX system is considered operable. The NRC is evaluating the Unit 2 Operability Determination.
Unit 2 was in Mode S. Cold Shutdown, at the time of this event and had been operational in all modes prior to this event.
This event is assigned a cause of Defective Procedure because the pre-operational l flow balance test procedure for the Unit 2 VX system did not require that proper ;
flow rates be drawn from individual containment compartments with each VX system I fan operating independently. This event is also assigned a cause of Design Deficiency because Design Engineering was satisfied that the completed l l
pre-operational flow balance test- procedure demonstrated that the VX system would meet the Technical Specification requirements; therefore, they waived tho' final ,
test and flow balance of the VX system. This event is also assigned a o l contributing cause of Design Deficiency because the physical arrangement 'f the VX l
system does not allow for flow balancing on an individual fan basis.
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EVALUATION:. '
Background:
i The purpose of the VX system [ Ells:88) is to prevent the accumulation of hydrogen in confined compartments of containment. As described by the McGuire Final Safety :
Analysis Report (FSAR) in Section 6.6, " Hydrogen accumulation is prevented by '
continuously drawing air out of each of the confined areas at such a rate as to limit the potential local hydrogen concentration to less than four percent by ;
volume." The required purge flow rates for the confined compartments were i 1
originally calculated by Westinghouse in April 1972, consistent with AEC Safety I Guide 7, dated March 10, 1981, and are listed in the McGuire FSAR, Table 6.6.2-1 (the original analysis was based on a hydrogen concentration of 3.5 percent by volume).
Following the original analysis, the NRC issued 10CFR50.44 and published Revision 2 of Regulatory Guide 1.7, " Control of Combustible Gas Concentrations
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in Containment following a loss-of-Coolant Accident." Several of the assumptions in the original Westinghouse calculation for the VX system are no longer applicable under Regulatory Guide 1.7. However, Section 6.2.5 of the McGuire FSAR, which describes the design and functions of the Hydrogen '
Recombiners [ Ells:RC8) and the Hydrogen Purge system, have been consistent with Regulatory Guide 1.7, Rev. 2. A re-analysis was initiated by Design Engineering n a result of problems with McGuire Unit 2 in achieving flow distributions which were consistent with the original design analysis.
( Description of Event:
On November 8, 1987, during a Unit 1 Containment Closeout inspection, NRC NRC personnel noticed that some VX system dampers apoeared to be closed. ,
l Questioned Operations about the positions of the Unit 1 VX system dampers ,
l (Ells:0MP), and on November 9, 1987, Operations inspected and verified that eae l VX system damper was in its pre-operational position as evidenced by paint shac:as I
on the damper actuators. Prior to Unit 1 initial criticality, painting on eacn i l
damper body and actuator handle left a shadow mark on the damper position l indicator. Each damper was verified to be in the same painted mark Since some of the Unit i VX system dampers appeared *:
pre-operational position.
be closed, the NRC was concerned about the positions of the Unit 2 VX system +
l dampers,'and consequently, Operations agreed to perform a flow balance, test on Unit 2 VX system during the 1988 Unit 2 Refueling Outage.
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On July 19, 1988, Performance (PRF) took "As Found" flow measurements on the /'*
2 VX system in an attempt to verify distribution and balance the system as nee:e:
while running either VX system Fan (E!!S: FAN) 2A or 28. Flow measurements wera When -a performed using a hand held velometer across the intake of the dampers.
FSAR values for individual compartment flow could not be achieved, Design :
Engineering (0.E.) was consulted to assist in evaluating the test results.
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,en . .ar a mer.m i recommended the floiv balance test be repeated using a more accurate flow i
measurement device, a flow hood, because the hood is relatively unaffected by the i inlet velocity profile and does not depend on operator judgement for locating a representative flow area. D.E. also reevaluated the FSAR VX system flow values based on a hydrogen concentration of less than four percent which lowered the required VX system flow rates. After the flow balance test was repeated using the flow hood, some flow distributions increased significantly; however, results for J
medium range and higher flow rates did not vary as dramatically.
On July 21, 1988, flow measurement tests were terminated h^cause the planned i Unit 2 Operability Determination issued by D.E. did not ret on flow numbers but on the operability of the Hydrogen Mitigation system (E!!$p.6]. PRF evaluated the l l
data to determine optimum damper positions. PRF observed '.nat the "As Found" ;
damper positions were essentially the same as the pre-operational Two dampers,positions both serving as the i evidenced by paint shadows on the damper actuators. )
Reactor head area, were found closed and left in a throttled position. On July l 22, 1988, D.E. issued an Operability Determination which was based on the fact -
l that the maximum hydrogen concentration assumption used in the original design analysis of the VX system was more conservative than required, the hydrogen l generation source term had been decreased by 10CFR50.46 and subsequent Emergency Core Cooling system analyses. Also, the Operability Determination stated that tne !
Hydrogen Mitigation system was available and operable to provide added assurance that hydrogen would not build up to concentrations capable of being detonated.
NRC rejected the Operability Determination because the bases for the Technical Specification requirements for the Hydrogen Mitigation syst6m were not the same is for the VX system and NRC stated that the Hydrogen Mitigation system cannot te relied upon as a substitute for the VX system.
Between August 2,1988 and August 15, 1988, D.E. pursued reevaluating the reaui e:
VX system flow rates in a manner consistent with Regulatory Guide 1.7, Revision -
and 10CFR 50.44.
While some of the new assumptions have the effect of increasic; the required flow rates, the majority have the result of reducing the reautred flow rates. The overall effect of the reevaluation has been a significant lowering of the flow rates required to limit the potential local hydrogen concentration to less than 4 percent by volume. On August 16, 1988, PRF completed ~
flow measurements on Train B of the VX system. On August 19, 1988 0.E. issued a ;
Unit 2 Operability Determination based on the re-analysis and concluded that the l
present flow balance condition of the VX system is sufficient and the VX system is considered operable. The NRC is evaluating the Operability Determination.
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Conclusion:
This event is assigned a cause of Defective Procedure because pre-operational r :n !
balance testing of the Unit 2 VX system did not require that proper flow rates te drawn from individual containment compartments with each VX system fan operati n '
independently. PRF believed that the same flow resistance would be experience: .ns with either fan operating; therefore, the pre-operational flow balance testieg
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the Unit 2 VX system showed that each VX system fan experienced different flow !
resistance. The pre-operational test procedure was implemented and approved with only one train of the VX system being flow balanced.
This event is also assigned a cause of Design Deficiency because the final turnover package for the Unit 2 VX system documented that 0.E. personnel were satisfied that the completed pre operational flow balance test procedure demonstrated that the VX system would meet the Technical Specification :
requirements; therefore, D.E. waived the final test and flow balance of the VX system. This event is also assigned a contributing cause of Design Deficiency '
because the VX system has a single header that draws air from each of the containment compartments by use of redundant fans located on either end of the header. Either fan is capable of drawing the total design basis flows from areas l serviced; however, the equipment configuration of the system is such that balance of the individual compartment flow rates is difficult to achieve when operating -
each fan independently.
Two VX system dampers, both serving the Reactor (E!!S:RCT) head area, were found ,
closed. It could not be determined during this investigation how long these dampers had been closed. There are no periodic surveillances on these dampers which would verify their positions.
A review of the McGuire Licensee Event Reports revealed no other similar events; therefore, this event is not considered recurring.
This event is not reportable to the Nuclear Plant Reliability Data System (NPRDS). ;
CORRECTIVE ACTIONS:
Immediate: PRF took "As Found" flow measurements while operating first one fan, then the other to determine optimum damper positions.
Subsequent: 0.E. reevaluated flow rates using Regulatory Guide 1.7 and 10CFR50.44 and issued an Operability Determination for Unit 2. ;
Planned: 1) PRF will take "As Found" flow measurements on the Unit i VX system during the 1988 Unit 1 Refueling Outage.
- 2) Based on the results of the Unit i VX system "As Found" flow measurements, a revision may be submitted for this e v e r.t .
3')
0.E. personnel will evaluate modifying the Unit 1 and Unit 2 VX systems in order to achieve proper flow balancing of the system.
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- 4) After Planned Corrective Action No. 2 is completed and implemented, PRF will perform a flow balance of the Unit 1 and Unit 2 VX systems to determine optimum damper positions and appropriately mark these positions.
- 5) Operations will develop a VX system Valve Checklist to verify the optimum damper positions that were determined in Planned Correc,tive Action No. 3.
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- 6) A Special Task Force will be reviewing specific pre-operational test procedures for all systems that were not supplied by Westinghouse to determine if the Design Bases of.
the system was verified by the testing.
SAFETY ANALYSIS:
The re-analysis of the Hydrogen Skimer system flow requirements, performed by D.E, did not lead to an increase in fission product inventory, containment leak rate, or off site dose. The new flow rates are adequate to ensure that the system
- can limit potential local hydrogen concentration to less than 4 percent by volume as required by the design basis. In addition, the new flow rates resulting from VX system re-analysis have no discernible effects on the post-accident containment pressure response, Containment Hydrogen Recombiner operation, Containment Purge dose, or Control Room dose, because the VX system flows p ,
rate, fission product inventory, or ice condenser performance.
I Although Two dampers, both serving the Reactor head area, were found closed.
f it is recognized that the Hydrogen Mitigation system cannot be relied upon as a substitute for the VX system, the Hydrogen Mitigation system was operable and
' would have provided added assurance that in the unlikely event of a dr.stpn basis accident, the hydrogen would not build up to concentrations capable of being .
detonated. .
The single failure analyses for the Hydrogen Recombiner and Purge system, severe accident Hydrogen Mitigation system, and Containment Air Return sys. tem l as discussed in McGuire FS/,R Sections 6.2.5, 6.2.7, andThe 6.6 review have been concludedreviewed and assessed by 0.E. for any differences in consequences.that the re measured flow rates have no discernible effect on the performance of the VX system.
There were no personnel injuries, radiation overexposures, or releases of l
radioactive material as a result of this event.
1 This event is considered to be of no consequence with respect to the health and safety of the public.
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Introduction:
This section of the revised LER orovides the results of the Unit i Hydrogen Skimmer (VX) system "As Found" flow measurements and the additional corrective actions that will be implemented on the Unit 1 and Unit 2 VX systems.
On November 8, 1987, during a Unit 1 Containment Closecut inspection NRC NRC personnel noticed that some VX system dampers appeared to be closed.
personnel questioned Operations personnel about the positions of the Unit i VX system dampers, and Operations personnel inspected and verified that each Unit i VX system damper was in its pre-operational position as evidenced by paint
' shadows on the damper actuators. Because some of the Unit i VX system dampers appeared to be closed, NRC personnel were concerned about the positions of the Unit 2 VX system dampers and consequently, Performance (PRF) personnel agreed to do a flow balance test on the Unit 2 VX system during the 1988 Unit 2 Refueling Outage.
On July 19, 1988, PRF personnel took "As Found" flow measurements using a velometer on Unit 2 Train A and Train B of the VX system and found that some VX ;
system damper compartment flows did not meet the flow requirements listed in '
the McGuire Final Safety Analysis Report. Design Engineering personnel were consulted to assist in evaluating the test results. Design Engineering personnel requested that flow measurements be taken again using a more accurate measuring device, and the required flow distributions for individual compartments were reanalyzed in a manner consistent with Regulatory Guide 1.7, Revision 2, and 10CFR50.44. The not overall result of the re-analysis was a significant lowering of the flow rates required to limit the potential local Design Engineering hydrogen concentration to less than four percent by volume.
personnel concluded that the VX system with its present flow balance condition .
was sufficient and the VX system was considered operable:
Evaluation:
On October 19, 1988, PRF personnel took "As Found" flow measurements on the Unit i VX system using a flow hood. Initial readings in two compartments'(Reactor Head area and the Pressurizer) were found to be below the minimum flow requirements for limiting hydrogen concentration to less than 4.0 volume percent.
According to Design Engineering (DE) analyses, the circulation produced by thermal effects in the Reactor Head area, in conjunction with time dependent reduction in rhdiolytic hydrogen generation, would likely have prevented the compartment hydrogen concentration from reaching 4.0 volume percent.
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011 l 9 02g 0 ,8 o, ip m,.. n em .. . ea The Pressurizer compartment is a dead-ended region that does not directly benefit from circulatien produced by the containment air return fans. The calculated minimum skimmer system flow rate to limit compartment hydrogen concentration to below 4.0 volume percent is 121 cubic feet per minute (CFM). The measured flow rate with VX Fan 18 operating was 281 CFM, and the measured flow with VX Fan 1A operating was 85 CFM. :
Based on the flow measurement recorded for VX Fan 1A, the Pressurizer compartment Although 4.8 volume hydrogen concentration could have reached 4.8 volume percent.
percent exceeds the conservative design basis limit of 4.0 volume percent, it is very unlikely that hydrogen at 4.8 volume percent would ignite and burn even in dry air and in the presence of an ignition source. However, if burning were to occur, essential equipment located in the Pressurizer compartment has been analyzed and determined to be able to survive even the burning of hydrogenThe from the postulated 75% zircaloy-water reaction of a degraded core accident.
anticipated maximum concentration of 4.8 volume percent is clearly well below levels that could detonated, and is not considered a detriment to maintaining containment integrity and to conducting a stable post accident recovery.
Tne "As Found" condition for each of the Unit i VX system dampers was open or throttled. The dampers that serve the Steam Generators were 100% open, with the remaining compartment damper position: varied or throttled closed by as much as 95%.
Ouring the preparation of Nuclear Station Modifications (NSMs) MG-127.11 and MG-22211 by DE personnel on the Unit 1 and Unit 2 VX systems, respectively, wn' "
' cross connect the suction piping of the VX syctem to improve the f, low balance capability of the system, it was recognized that suction Such a situation dampers were could needed occur follow'to ;
prevent reverse flow through an idle fan.
a design basis accident if both trains receive an auto-start signal, isolation dampors open and fans start on both trains. If power is subsequently lost on c ~
l of the trains, the fan would stop but the motor operated damper would fail in t e open position. As a result, air would back flow through the idle fan and open damper. With the present piping. configuration, the open damper was initially no:
considered significant because of the high flow resistance of the piping.
Following flow balance testing of the Unit i VX system by PRF personnel during t-e current 1988 Refueling Outage, the decision was made by Station Management
~ personnel to perform additional flow balance testing with the idle fan isolation'"
damper in the open position. The test was conducted by measuring the ' flows in These compartments were four compartments farthest away from the operating fan.
selected on the assumption that they would see the greatest impact from the coen isolation damper. Total fan flow and reverse flow through the open isolation l
damper were also measured. The results on Unit 1 indicated that the failed oce-idle fan isolation damper did not reduce any of the flows in the me.sured compartments below the acceptance criteria.
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'Ise ,ggWg6 6 l ey McGuire Nuclear Station, Unit 1 , g ,9,,,,,3,6,9 8, 8 Q 0,1,9 _ 0,2 o;9 o, 1 0 ven . . - a . ara.- an...in Wnen the Unit 1 test data was compared to the previous Unit 2 results, it was not possible to conclude that the corresponding Unit 2 compartment flows would be acceptable with the idle fan suction damper open. At 1045 on October 26, 1988, Unit 2 entered the action statements of Technical Specification (TS) 3.0.3 because both trains of the VX system were declared inoperable. Subsequently, power was removed from the VX system Train B fan and isolation damper at 1110 on October 26, 1988 and Unit 2 exited the action statement of TS 3.0.3 becaun this action er.sured that the isolation damper for Train B of the VX system was closed and it rntored Train A to operable status. With one VX system hoperable Unit 2 was placed in a 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> action statement.
NSMs MG-12211 and MG-22211 which are to be implemented on the Unit 1 and Unit 2 VX systems, respectively, would overcome this single failure vulnerability by the use of passive check dampers.
The modification was ready for installation during the 1988 Refueling Outage on Unit 1 but the design calculations had not been completed for Unit 2. Therefore, a temporary modification was identified on October 26, 1988 which would overcome the identified single failure. This modification would provide an alternate -
source of power to close the idle fan suction damper by cross connecting the respective power supplies through normally deenergized cables and red-tagged open breakers. The temporary modification would only be installed on the Unit R VX system until NSM MG-22211 was implemented on Unit 2 during the 1989 Refueling Outage or during an outage of sufficient duration following completion of the design package. NRC concurred with the implementation of the temporary modification.
The temporary modification to provide backup power to each Unit 2 VX system
suction isolation damper was completed. Appropriate revisions were approved for l station emergency procedures and the training package was released for review by on-shift operators. With these maasures in place, the Unit 2 VX system was restored to a normal alignment and removed from the TS Action Item Log at 2355 on October 28, 1988.
l- Planned Corrective Actions:
1)
After NSMs MG-12211 and MG-22211 are implemented on the Unit 1 and Unit 2
\lX systems during the 1988 Unit 1 Refueling Outage and the 1989 Unit 2 l
Refueling Outage, respectively, PRF personnel will perform a flow balance I of the Unit 1 and Unit 2 VX systems to determine optimum damper positions and appropriately mark these positions.
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an A v.s. =uctsma uutony cou.ies o= r LICENSEE EVENT REPORT (LER) TEXT CCNTINUATION oeRowo o=s wo. mo-om ;
Exetett. 4/31/W FActLITV NAMS qu Docat ? NUMBER 138 4th NUMSG A 44.6 *AOS (3)
"^a ' I"ut.W 7Jo'.O McGuire Nuclear Station, Unit 1 0l2 1l 0 OF o l5 l 0 l o l o l 3 l 6[9 8 l 8 0l 1l9 1 l0 rent s . v. m==waac r asiawim
- 2) "As Found" flow measurements will be performed by PRF personnel on Steam Generator 2C compartment during the next Unit 2 outage of sufficient duration. .
- 3) After Planned Corrective Action No. 1 is implemented, Operations personnel will develop a method to verify and control the optimum damper positions that were determined by PRF personnel.
ADDITIONAL INFORMATION:
.This section of the revised LER provides the results of the Planned Corrective Actions addressed in Revision 1 of this LER.
NSMs.MG-12211 and MG-22211 have been implemented on the Unit I and Unit 2 VX systems. Performance personnel have performed flow balances which positioned the dampers for Unit I and Unit 2 VX system in their optimum positions. The handles have been removed from valves [EIIS:V) which could possibly interfere with personnel working in the area. White marki'ng paint was used to mark each valve in its as left position. All lock nuts were verified to be installed on the valves or were replaced as necessary. The loch nuts were tightened with a wrench. Baklite tags '
were hung from each valve informing personnel not to reposition the valves.
As Found flow measurements were performed by Performance personnel for the Steam Generator (S/0) [EIIS:SG] 2C compartment. The results are as follows: With the idle fan suction open, flow to S/G 2C compartment was 61 SCFM with a total system
. flow of 3338 SCFM. With the idle fan suction closed, flow to the S/G 2C compartment <
was 69 SCFM with a total system flow of 3300 SCFM. The acceptance criteria for S/G l 2C was 121 SCFM. The measured flows af ter positioning the dampers were 247.2 SCFH j i
with VX fan 2A in service and 216.6 SCFM with VX fan 2B in service. '
l Operations personnel have developed periodic test procedure PT/1,2/A/4450/26, Hydrogen Skimmer System Valve Alignment, to verify and control the damper positions l at their optimum positions. ,
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