ML20044A799
| ML20044A799 | |
| Person / Time | |
|---|---|
| Site: | Byron, Braidwood  |
| Issue date: | 06/29/1990 |
| From: | Hunsader S COMMONWEALTH EDISON CO. |
| To: | Murley T NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM), Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 9007030183 | |
| Download: ML20044A799 (9) | |
Text
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Commonwealth Edison 1400 Opus Placo Downers Grove, Illinois 60515 June 29, 1990 Dr. Thomas Murley, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C.
20555 Attn: Document Control Desk
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Subject:
Byron Station Units 1 and 2 Braidwood Station Units 1 and 2 Containment Hydrogen Monttoring System NRC Docket Nos.50-15M 155_apd_50-1561151
References:
(a) July 25, 1989, L.N. 01shan letter to 1.J. Kovach.
(b) August 21, 1989 R.A. Chrzanowski letter to T.E. Murley.
(c) May 17, 1990 P.C. Shemanski letter to T.J. Kovach.
Dear Dr. Murley:
Reference (a) identified a difference between the Byron /Braidwood design of the containment hydrogen monitoring system, and the description given in the original Byron /Braidwood Safety Evaluation Report and the Updated Final Safety Evaluation Report.
The system design utilizes two containment isolation valves in series on each line with one valve powered from an ESF division 11 power supply and the other valve powered from an ESF division 12 power supply. The Safety Evaluation Report and the UFSAR describe the design of'the system of satisfy the single failure criterion.
The difference exists if the postulated accident assumes the failure of one electrical ESF division that would prevent the re-opening of one of the two isolation valves in each line and thus result in the loss of the hydrogen monitoring system.
Reference (b) provided the Commonwealth Edison response to the NRC Staff concern.
Subsequently, Reference (c) provided the status of the NRC Staff review and a request for additional information which stated the following:
1.
"The proposed UFSAR change does not provide adequate justification for using the hydrogen recombiners (and attached analyzers) as back-up system to satisfy the post-accident monitoring criteria for containment hydrogen concentration.
Describe the degree to which the alternative system would be able to perform the intended function of the normal hydrogen monitoring system (per Reg. Guide 1.97) in the event that the normal system was lost due to a single electrical 9007030183 900629 DR ADOCK 0500 4
e i
Dr. T.E. Murley June 29, 1990 L
- 1. (continued) failure.
Indicate the actions necessary to put the proposed back-up system into operation.
Provide information detailing the reliability and effectiveness of the analyzers attached to the hydrogen l_
recombiners, if needed to function, and how they are affected by the operability status of emergency power sources.
Provide the basis and i
rationale for use of the alternative hydrogen monitoring system."
2.
" Provide the rationale for not proposing an alternative electrical 1
configuration for the normal hydrogen monitoring system valves, which would ensure containment integrity and indication of hydrogen concentration in the event of a single electrical failure."
Reference (b) had provided a detailed technical discussion of the i
existing Hydrogen Monitoring System and concluded that the design is consistent with the intent of the applicable regulatory requirements.
The l
t 3
n basis for this conclusion was that no single failure would prevent containment isolation given that the probability of losing an entire electrical ESF division is very low because of the reliability and diversity of power supplies available to the isolation valves. Howestt,_Ed.is.on_ts_propnsing ita i
alternative _dtsign that enuttes_hattttoatainment isolation and hydro. gen moBitQting_s3 stem ooerability. In the_ event an_ electritaL125Ldc ESF division 1s lost following a loss-of-coolant _Lttidaat.
Enclosure I provides a detailed description of this change, j
Please address any further questions regarding this matter to this office.
l Very truly yours, l
[.
ewk S.C. Hunsader Nuclear Licensing Administrator
.ZNLD55/1mW: 1-2 cc:
Byron Resident Inspector Braidwood Resident Inspector l
T. Boyce, Project Manager - NRR S. Sands, Project Manager - NRR H. Shafer - Region III Office of Nuclear facility Safety - IONS l
ENCLOSURLI Connonwealth_EdisQtLCQeD&ny ByronIBraidwood_Sittton_ _Untts 1 & 2 Re sponse_toJteove si_for_Additj onaLinformation_by_the Nuclett_Resulatory_Coenh110tLINRCLResttning_the Deslen of ContalnmentJiydtogetLMonttor. ins _Systes A.
Descriotion of Existina Desian The current destgr, of the Hydrogen Monitoring System consists of two mechanically independent, physically separated and redundant trains.
Separate containment piping penetrations are utilized by each train of the system.
The containment piping penetration for the suction of each hydrogen monitor is provided with two isolation valves in series (i.e.
Valves IPS228A/228B and IPS229B/229B). One of the two isolation valves on each line is powered from electrical ESF Division 11 (i.e, valves IPS229A and IPS229B).
B.
HRC_Co.onto The NRC Staff has questioned whether this design meets the single failure criterion.
Specifically, the NRC Staff is concerned that failure of one electrical ESF division when the valves are closed would prevent remote re-opening of one of the two isolation valves in each line and thus result in the unavailability of the hydrogen monitoring system.
In reference (c) the NRC Staff requested that Commonwealth Edison (Edison) propose a design change to the system that would ensure both " containment integrity and indication of hydrogen concentration in the event of a single electrical failure."
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Econcied Modification Edison has re-evaluated the existing Hydrogen Monitoring System design and proposes to implement a modification to resolve the NRC Staff concern.
The existing design will be revised by replacing the operator for one of the two containment isolation valves in each line with an operator that l
fails open upon a loss of power.
The affected valves will be the 1
Division 12 (22) valve in the Division 11 (21) hydrogen monitoring line (Valve 1/2 PS229A) and the Division 11 (21) valve in the Division 12 (22) i hydrogen monitoring line (Valve 1/2 PS2288).. (Attachment A is a marked-up copy of P&lD M-68 Sheet 7 that identifies the valves affected by these proposed changes for Byron Unit 1, as an example.) A similar change is proposed for Byron Unit 2 and Braidwood Units 1 and 2.
This new design provides for two hydrogen sample lines each dependent on a single ESF division's power to perform its sampling function.
At the same time, the containment isolation function can be achieved for both lines with only one operable ESF division. Attachment B provides advanced marked-up copies of the revisions to the UFSAR pages which would i
result from this modification.
The proposed modification will ensure availability of the Hydrogen Honitoring System in the event of a loss of one electrical 125 Vdc ESF r
division.
Two separate Class IE power supplies will still be utilized to power redundant containment isolation valves in series.
D.
Implementation Edison has scheduled the implementation of the above modifications at the next convenient refueling outages. All modifications are scheduled to be i
completed not later than the end of the following refueling outages:
Sept. 1991 BIR04 Byron Unit 1 Byron Unit 2 Jan, 1992 B2R03 Braidwood Unit 1 Sept,1992 AIR 03 Braidwood Unit 2 Sept, 1991 A2R02 i
In the interim, continued plant operation is justified based on the technical discussion presented in Reference (b).
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R/B-UFSAR TABLE 6.2-58 (Cont'd)
HMC VALVE IACA-LEAR DISTANCE 70 GDC PENETRA-LINE ISOLATION TI05 (IWSIDE TEST OUTERNDST REQUIRE-TION SIZE ESSEN-REFERENCE VALVE OR OUTSIDE (YES ISOLATION VALVE SYSTEN_NAME PrENT_ NET _PUMBER_ FLUID (in.)
TIAL*_
_PRAWII8G_
_.NUNDEF_ COWT&IlWEFIl OR_D01 YALVE_litL TytT_.,
Off-Gas 56 13 Air & H2 3
YF.S N-47-2 10G079 Inside YES N/A
- But. Fly So 13 Air & H2 3
YES M-47-2 10G080 Inside YES N/A -
But. Fly i
56 23 Air & H2 3
YES N-47-2 10G081 Inside YES N/A But. Fly-56 69 Air &H2 3
YES N-47-2 10G057A Inside YES N/A Dut. FIy 56 13 Air & H2 3
YES N-47-2 10G082 Outside YES MIN.
But. Fly 56 69 Air & H2 3
YES N-47-2 10G083 Outside YES MIN.
But. Fly 56 13 Air & H2 3
YES N-47-2 10G084 Outside YES MIN.
Bot. Fly 56 23 Air & H2 3
YES N-47-2 10G085 Outside YES MIN.
But. Fly i
Process Radiation 56 52 Air 1
M-78-10 IFR001A Outside YES 1.4 Globe i
56 52 Air 1
N-78-10 1PR0018 Outside YES 3.5 Globe 56 52 Air 1
N-78-10 1PR066 Outside YES 4.3 Globe i
56 52 Air 1
N-78-10 1P9932 Inside YES N/A Check i
56 AL Air 2
N-78-6 IFW933A Outside YES MIN.
Globe
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56 AL Air 2
N-78-6 1PR0339 Outside YES MIN.
Globe i
56 AL Air 2
.M-78-6 IP9992E Outside YES MIN.
Globe i
56 AL Air 2
N-78-6 IFR992G Inside YES N/A Check 56 AL Air 2
M-78-6 1PR933C Outside YES MIN.
Globe 56 AL Air 2
M-78-6 179033D Outside YES MIN.
Globe 56 AL Air 2
N-70-6 1PR902F Outside YES MI N.-
Globe
-I 56 AL Air 2
N-78-6 1PR992N Inside YES 5/A Check Mydrogen Monitor 56 45 N2 + Air 1/2
.N-68-7 IPS229A Outside YES WIS.
Globe
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M 45 M3 + Air 1/2 N-69-7 IPS229A Outside TEEE MIS.
Globe 5612(sv)45(su) n2
- Air 1/2 N-68-7 1PS23ea Outside YES NIs.
Globe 5612(sY)45(su)
M2
- Air 3/4 N-68-7 1PS231A Inside YES 3/A Check
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56 36 M, + Air 1/2 N-68-7 1PS2200 Outside YSS WIN.
Globe 56 36 M2 + Air 1/2 N-60-7 1FS2298 Outside YES NIN.
Globe i
5631(BY)16(SH)
N2 + Air 1/2 N-64-7 1P32309 Outside YES WIN.
Globe 5631(BY)36(su)
M2
- Air 3/4 N-68-7 SFS2313 Inside-YES W/A Check
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6.2-199 REVISION 1 - DECEMBER 1989 k.
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TABLE 6.2-58 (Cont *d)
SECO8pD-l PRIsuurY AmY 1501.ATirm l
GDC VALVE POST-P088ER C145URE ISOLA-WODE OF WODE OF WALVE We0UISE-OpER-30EWEL SNUTDOWN ACCIDENT FAILUIrE TIfE*
- TIOEI ACTUA-ACTUA-P00sER CoWrtcu.
SYSTEIUIME:
PENI_ PET AID 9L IDSITl95 M ITIOR P9E17I0E8 E951T195 _iseCL SIGIES
_IJ0W__
_JJost_ SOUFCE _ RATION t
off-Cas 56 98 0 Closed
_ Closed Closed As Is 60 T
A aff IE 1
56 98D Closed Closed
. Closed As Is 60
.T A
get
~IE I
56 sep Closed Closed' Closed As Is 60 T
A set IE g
56 sto closed Closed Closed As Is 60 T
A get it 3
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56 see Closed Closed closed As Is 60 T
A apt gg 3
l 56 peo Closed Closed Closed As Is 60 T
A SWE 1E 1
i 56 14 0 Closed Closed Closed As Is 60 T
A set IE 3
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56 IED Closed Closed Closed As Is 60 T
A see IE 1
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Process mediation 56 A0/S Open Closed Closed Closed 4.5 T
A apt IE e
56 A0/S Open Closed Closed Closed 4.5 T
A apt It g
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56 AO/S Open Closed Closed Closed 5.0 T
j 56 W/A W/A
. W/A N/A N/A N/A W/A N/A N/A N/A 6
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56 It closed Closed.
Cloeod N/A N/A W/A W/A N/A -
W/A i
56 88 Closed Closed Clooed W/A N/A N/A N/A N/A II/A 56 st Closed Closed Closed W/A W/A N/A W/A N/A N/A 7
56 W/A W/A N/A N/A N/A W/A N/A W/A N/A N/A 7
56 se Closed-Closed Closed W/A N/A N/A IB/A N/A N/A l
56 38 Cleoed Closed Closed W/A W/A W/A N/A.
W/A N/A 56 st closed closed Closed N/A N/A N/A N/A N/A RfA 7
56 W/A N/A W/A N/A N/A N/A N/A
~B/A N/A W/A 7
l f
i' Wydrogen peonitor 56 S
Open Closed Closed As to 5
T A
Ist 1E JS S
Open Clo3ed Cloged Wousen 15 7
A me IE f
6 56 S
Closed Claie8 Close5 Closes 15 T
A me IE 1
56 W/A W/A N/A W/A N/A W/A W/A-W/A W/A IB/A i
56 5
Open Closed Cleoed
- emmeon, 15 T
A me II l
56 S
Open Closee
. Closes As Is 15 7
A gas
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Closed Closed Closed closed 15 T
A set 1E 56 W/A N/A N/A N/A N/A W/A N/A N/A N/A N/A 6.2-200 i
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B/B-VTSAR' s
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as ANSI B31.1.
The piping from the containment to the first l
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isolation valve will be designed to the requirements of SRP 3.6.2.
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OperationoftnehydrogenmonitorsisiNdependentofthehydrogen N-recombinet since both systems used separate piping and contain-.
l ment penetrations and are not dependent.upon the other to operate in any way.
The hydrogen monitoring system consists of two inde-pendent, physically separated and redundant subsystems and, thus, meets the single failure criteria.
Separate piping penetrations of the containment are utilised by each train of this system.
Each train's hydrogen monitor discharge containment isolation valve _ RS q0A/s) W ne of two series inlet containment isola-The i
ilon-valvesd28t*
'are powered from s g(... ate if sources.T f.F is powered hg isolation valve g
econd inlet conteinment from the alternate power train..q PSs296/219 A Byron /Braidwood stations meet the requirements for continuous.
indication in the main control room with IEEE 323-1974 qualified
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indicators.
The-monitors may be control. led from the control. room.
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'l' EAMPLE CONDITIONING The Model 225CM monitoring system is designed to monitor contain-ment gas for percentage by volume of hydrogen (dry analysis).
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The operating range is -5 to +50 psig, 40'r to 445'F and relative humidity from 10 to 100%.
A sample of the containment atmosphere will be taken at or near one of the containment penetrations and cc another approximately 180 degrees away on the other side of the
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containment.
The samples taken are representative of the contain-
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ment atmosphere due to the mixing system effects, which is dis-cussed in Subsection 6.2.5.2.3.
Radioactive sample gas is drawn from the containment vessel by means of a sample pump into the 1
analysis unit precooler where it is lowered from temperatures as high as 445'T to ambient temperature of the analyzing unit.
A solid state self-regulating thermoolectric cooler further reduces the gas temperature to below analysis unit ambients after which 0.4 scfh of saeple gas is directed to the sample measuring cell maintained-at 170'r.
After the gas passes through the cell, it is returned to the i
containment via a pressure regulating nwtwork which maintains pressure above containment assuring return of the sample gas.
Any condensation formed in either of the coolers is gravity
. drained to a water trap which is automatically purged back to the containment with the aid of the pressure regulating network.
CALIpRATION Instrument calibration is performed by actuating the appropriate solenoid valve directing zero or span gas with a known J
concentration through a flow controller and into the cell, y % W % + n ~ ~ designed to fail open
~n Isolation valves PS228B and PS229A are on loss of power.
Thus failure of one of the 1E electric power f~
sources will disable only one train of the nydrogen monitoring
~ ~.~ ws I% system.
E.30-7 REVISION 1 - DECEMBER 1989
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. UNITED STATES I,.
NUCLEAR REGULATORY COMMISSION g %,,
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WASHINGTON. D. C. 20666
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1 fiay 17, 1990
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l Docket Nos. STN 50-454, STN 50-455 i
STN $0-456, STN 50-457
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Mr. Thomas J. Kovach j
Nuclear Licensing Panage' Comonwealth Edison Com'jany-Suite 300 OPUS West !!!
'1400 OPU$ Place Downers Grove, 1111nvis 60515
Dear Mr. Kovach:
SUBJECT:
BYRON STATION, UNITS 1 AND 2 AND BRAIDWOOD STATION, i
UNITS 1 AND 2 - REQUEST FOR ADDITIONAL INFORMATION, CONTA1NMENT HYDROGEN MONITORING SYSTEM DESIGN l
(TACN05.74547,74548,74549AND74550)
The enclosed Plant Systems Branch request for additional information concerns Comonwealth Edison's submittal dated August 21, 1989, regarding the discrepancy between the existing Byron and Braidwood designs for the containment hydrogen mor.itoring system, and the designs approved in each plant's original Safety Evaluation Report as described in the Updated Final Safety Analysis Report. We find additional information from Ceco is necessary i
for us to continue our review.
You are requested to provide the additional
~
information (see enclosure) within 45 days of receipt of this letter.
t The reporting and/or recordkeeping requirements contained in this letter
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affect fewer. then. ten respondents; therefore, OMB clearance is not required i
under P.L.96-511.
Sincerely,
(*V PaulC.Shemanski,ProjectManager Project Directorate 111-2 Division of Reactor Projects - III, IV, Y and Special Projects Office of Nuclear Reactor Regulation
Enclosure:
As stated cc w/ enclosure:
See next page l
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496[fZg77V i
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Mr. Thomas J. Kovach Byron /Braidwood Power Station Commonwealth Edison Company Unit Nos. I and 2 cc:
Mr. Gabe ioth U. S. Nuclear Regulatory Commission Westinghouse Electric Corporation Byron / Resident lespectors Office Energy Systems Business Unit 4448 North German Church Road Post Office Box 355, Bay 236 West Byron, Illinois 61010 Pittsburgh, Pennsylvania 15230 Ms. Lorraine Creek Joseph Gallo Esq.
Rt. 1, Box 182 i
Hopkins and Sutter Manteno. Illinois 60950 888 16th Street, N.W.
Su ite 700 Mrs. Phillip B. Johnson Wai.nington, D.C. 20006 1907 Stratford Lane Rockford, Illinois 61107 Regional Administrator U. S. NRC, Region 111 Douglass Cassel, Esq.
i 799 Roosevelt Road Bldg. #4 109 N. Derarborn Street GlenEllyn, Illinois 60137 Suite 1300 Chicago, Illinois 60602 Ms. Bridget Little Rorem Appleseed Coordinator David C. Thomas, Esq.
117 North Linden Street 77 S. Wacker Drive Essex, Illinois 60935 Chicago, Illinois 60601 Mr. Edward R. Crass Michael Miller, Esq.
Nuclear Safeguards and Licensing Sidley and Austin Division One First National Plaza t
Sargent & Lundy Engineers Chicago, Illinois 60690 55 East Monroe Street Chicago, Illinois 60603 George L. Edgar Newman & Holtzinger, P.C.
U. S. Nuclear Regulatory Commission 1615 L Street, N.W.
Resident inspectors Office Washington, D.C.
20036 RR#1, Box 79 Braceville, Illinois 60407 Commonwealth Edison Company I
Byron Statio, Manager Mr. Thomas W. Ortciger, Director 4450 North German Church Poad Illinois Emergency Services Byron, Illinois 61010 and Disaster Agency 110 East Adams Street Springfield, Illinois 62706 Illinois Department of Nuclear Safety Office of Nuclear Facility Safety 1035 Outer Park Drive l
Springfield, Illinois 62704
I Enclosure REQUEST FOR ADDITIONAL INFORMATION PLANT SYSTEMS BRANCH PROPOSED REVISION TO THE UFSAR INCORPORATING THE EXISTING DESIGN FOR THE HYDROGEN MONITORING SYSTEM 4
BYRON STATION, UNIT NOS. I AND F BRAIDWOOD STATION, UNIT NOS. 1 AND 2 The proposed UFSAR change does not provide adequate justification for 1.
using the hydrogen recombiners (and attached analyzers) as a back-up system to satisfy the post-accident monitoring criteria for containment
)
Describe the degree to which the alternative hydrogen concentration.
system would be able to perfom the intended function of the normal i
hydrogen monitoring system (per Reg. Guide 1.97) in the event that the norm 61 system was lost due to a single electrical failure.
Indicate the actions necessary to put the proposed back-up system into operation.
l Provide information detailing the reliability and effectiveness of the analyzers attached to the hydrogen recombiners, if needed to function, i
and.how they are affected by the operability status of emergency power
/
Provide the basis and rationale for use of the alternative sources.
i hydrogen monitoring system.
Provide the rationale for not proposing an alternative electrical j
2.
configuration for the normal hydrogen monitoring system valves, which would ensure containment integrity and indication of hydrogen q
i concentration in the event of a single electrical failure.
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Ch cato. was 60600 0767 August 21, 1989 Dr. Tnomas E. Murley, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commtssion Washington, DC 20555
Subject:
Byron Station Units 1 and 2 Braldwood Station Units I and 2 Containment Hydrogen Monitoring System NRC Docket Not. 50-454/455 and 50-456/457
Reference:
(a) July 25, 1989, letter from LN Olshan to TJ Kovach
Dear Dr. Murley:
The referenced letter identified a difference between the Byron and Braldwood design of the containment hydrogen monttoring system and the original Safety Evaluation Report and the Updated Final Safety Evaluation Report.
The system design utilizes two containment isolation valves in series on each line with one valve powered from an ESF division 11 power. supply and l
the other valve powered from an ESF division 12 power supply.
The Safety Evaluation Report and the UFSAR describe the design of the system to satisfy the single failure criterion.
The difference exists if the postulated l
l accident assumes the failure of one electrical ESF division that would prevent the re-opening of one of the two isolation valves in each line and thus result t
in the loss of the hydrogen monitoring system.
Commonwealth Edison has carefully reviewed the hydrogen monitoring system and believes that the existing design is acceptable and meets the intent of the appItcable regulations. Attachment A to this letter contains the detailed justification of the existing design.
Please address any further questions on this matter to this office.
Very truly yours.
N R. A.
hrzanowski Nuclear Licensing Administrator 0258T:52 l-cc: Byron Resident Inspector Braidwood Resident Inspector t.
N. Olshan - NRR S. P. Sands - NRR Office of Nu~ clear Facility Safety - IDNS m os2AoGG8 9(v
5 ATTacHNENT A Reteente to Nuclear Reaulatory Cemmittien Letter dated July 25. 1989 Detion of Conta(nment Hydronen Monitorina tvitem Juttification of Existine Dation The practice of using two separate Class IE power supplies to power redundant containment isolation valves in series, is commonly _used throughout the plant.
! t meets the requirements of the applicable General Design Criterta (56) and the NRC guidance in Standard Review Plan Section 6.2.4.
The UFSAR criteria applicable to contairment isolation valves (reference UFSAR Section 6.2.4.1.2.d) is that "in lines where two automatic valves are provided, each valve operator is actuated by an independent signal, and each operator is also supplied from a sephrate emergency power supply".
The intent of this design criteria is to ensure that no single failure will prevent containment isolation.
Therefore the diversity of the isolation valve power supplies in a particular line normally takes precedence over the electrical independence of the redundant system lines.
The original design of the post accident monitoring system in 1981 utilized diverse isolation valve power supplies, and this configuration has been retained through construction and plant operation.
The FSAR and UFSAR do not accurately reflect the syster configuration shown on the design drawings.
However, it is CECO's position that the system as installed is acceptable.
This position is supported by the reliability and diversity of power sources available to each of the subject isolation valves.
The probability of a single failure resulting in loss of an entire electrical ESF division is very low based on the existing design features of the Class IE de Power System and as evidenced by its operating history.
Figure 1 is a simplified single line diagram of the ESF Division 11 auxillary power system design and power supply conf 1guration relied upon to remotely operate the subject isolation valves.
(A similar power system configuration exists for electrical ESF Division 12, 21. and 22).
The following can be seen from this diagram:
The primary source of Class IE de power to the Division 11 isolation valves is the 125Vdc battery charger 111.
The battery charger can be powered from either of three highly reliable safety related sources:
the Unit 1 Station Aux 111ary Transformer (SAT),
the Diesel Generator a
the Unit 2 SAT via the 4.16KV switchgear bus cross-tie breakers.
The second source of Class IE de poter to the Division 11 isolation valves is the 125Vdc Battery 111 located in a separate room from the batter charger.
/scl:0258T:2
i ATTACHMENT A (continued)
Retnonte ta j
Nuclear Raoulatory Committien Letter dated July 25. 1989 Dation of Containment Hvdronen Monitorina Svttem
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The tie breakers between the Unit I and Unit 2 125Vdc buses provide a third source of power to the subject isolation valves from the Unit 2 ESF Division 21 power system (consisting of a separate battery, i
battery charger, diesel generator and SAT that are interconnected-in a similar manner as that shown on Figure I for electrical ESF l
Division 11).
These tie breakers can be manually closed in the miscellaneous electrical equipment room utilizing the existing i
l procedural and administrative controls.
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It is evident from the above that a significant number of independent and
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diverse power supplies are available to support operation of the subject isolation valves.
The only single failure that could result in loss of koth hydrogen monitoring subsystems would be a failure of the 125Vdc ESF Ns/ distribution panel 111 and/or its main breaker feeding the isolation Ives.
Upon a containment isolation signal, the valves in question are
'equired to close.
Hydrogen monitoring is required to begin thirty minutes after SI initiation and continues isolation.
Since these valves are " fall as is", the above thirty minutes duration is the window during which the postulated failure must occur which we believe is highly unlikely.
This belief is supported by industry data on breakers and t
125Vdc buses (relative to probability of failure upon demand) and by past operating performance at the Commonwealth Edison Company Stations.
3 The existing design is considered to be acceptable for the following reasons:
t 4
In the event of a Loss of Coolant Accident (LOCA), containment isolation is required to be accomplished imediately.
The current Byron /Braidwood design accomplishes this function.
The hydrogen monttoring function is not required untti 30.
minutes after the accident.
In the event of the highly unlikely failure described above (occurring within 30 minutes after the LOCA), time is available to utilize alternative design features.
For example, the hydrogen recombiner could be started to accomplish the dual functions of a) reducing and hydrogen inventory present in the containmant atmosphere, and b) providing indication of hydrogen ;oncentration through the hydrogen monitoring instrumentation which is integral with the recombiners.
The hydrogen contertration as a function of time after an accident is shown in Se: tion 6.2.5 of the UFSAR.
As can be seen, the concentration tullds slowly with time.
This allows times for manual actions, prior to the' hydrogen concentration reaching the level where an explosion would occur.
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1 ATTACHMENT a (continued)
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Retoonte to N_uelear Raoulaterv Committien Letter dated July 25. 1989 4
Dation of Containment Hvdrogen Monitorina System In summary, we believe that the existing design is acceptable and meets the-intent of the applicable regulations.
In this case, in view of the conflicting requirements for system operability and containment isolation,.
it was judged that containment isolation was the more important of the two requirements.
The subject isolation valve power supplies have been.
selected so as to favor completion of the containment isolation function while at the'same time provide sufficient independence and reliability to a
ensure availability of the hydrogen monitoring system following a LOCA.
1 Even.in the event of the postulated single failure, alternative ESF equipment is available to perform the function of the hydrogen monitoring system, and because of the long time over which the hydrogen concentration builds up, sufficient time is available to restore the system to operable status via manual operator actions.
Commonwealth Edison Company concurs that the existing design of the hydrogen monitoring system has not been described in sufficient detall and/or accurately in all of the pertinent UFSAR sections.
It appears that because of this lack of specificity and detail in the UFSAR, the NRC misinterpreted the existing design as presently described and accepted in j
-the original Byron Safety Evaluation Report (SER), issued in February 1982.
He, therefore, propose to revise the affected UFSAR pages as 1
indicated on Attachment B to agree with the actual plant configuration.
Commonwealth Edison Company believes that the existing design of the hydrogen monitoring system is acceptable and consistent with the appIlcable regulatory requirements.
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ATTACHMENT B
?
CON 40NWEALTH EDISON COMPANY l
BYRON /BRAIDWOOD STATIONS - UNITS 1 L 2 UFSAR CHANGES BASED ON EXISTING i
DESIGN OF, HYDROGEN MONilQRING SYSTEM (Pages 6.2-68 and E.30-7) l i
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i 6.
Indication of hydrogen concentration is available
.. in the main control room when the monitors are operating.
e.
The hydrogen monitors are located in the auxiliary building elevation 401 feet.
Samples are piped from containment penetrations to the neonitors.
The accuracy of the monitors is 32.5% of full scale (dry basis).
Operation of the hydrogen monitors is independent of the hydro-gen recombiner and its associated hydrogen analyser since both j
systems use separate piping and. containment penetrations and I
are not dependent upon the other to operate in any way.
The hydrogen monitoring system consists of two independent,
+
physically separated and redundant subsystems h l
ti: rin ic ':11rr: ::it ri:.
Separate piring penetrations of
~
the containment are utilised by each train of this system. t dr, W l
Each train is powered from A separate IE pover,&
source seng; g tat w '
j i
canumw nelemss 4 teres. One.
- t w %e en e m.s m e r eser L
mg The portions of the hydrogen monitoring piping system which encf su, form the containment atmosphere isolation barrier are desig-Wssw d j
nated Seismic Category I, Quality Group B.
The remainder of p m.' /
the system outside the containment is Seismic Category I, dAe eg.: ;
Quality Group B up to the hydrogen monitoring instrumentation, asl3,y Piping internal to the instrumentation is classified as ANSI p.,
331.1.
The iping from the containment to the first isolation valve is des gned to the requirements of SRP 3.6.2. -
sq h '
A sample of the containment atmosphere is taken at or near one of the containment penetrations and another approximately 180 3egrees away on the other side of the containment.
The samples taken are representative of the containment atmosphere due to l
the mixing system effects.
The mechanical piping penetrations used for the hydrogen moni-toring system at Byron are IPC-12 and 1PC-31 for Unit 1 (IPC-45 L
l and 1PC-36 for Braidwood) and 2PC-12 and 2PC-31 for Unit 2 e
(2PC-45 and 2PC-36 for Braidwood),
penetrations 1PC-12 and 2PC-12 (IPC-45 and 2pC-45 for Braidwood) are for the Train A monitors and 1PC-31 and 2PC-31 (IPC-36 and 2PC-36 for Braid-wood) are for the Train B monitors.
Additional information concerning the mechanical penetration's elevations and asinuths are listed in Table 3.8-1..
6.2.5.2.3 Mydronan Mixina syntam namian The function of the mizing subsystem is to ensure that local concentrations with greater than 4% hydrog.en cannot occur within the primary containment following a LOCA.
The mixing is achieved by natural convection processes, containment fan cooler operation, and the containment spray system.
6.2-68
gr7MNNarWT 6 3/3-UFSAR j
as ANSI B3),1.
The piping from the containment to the first isolation valve will be designed to the requirements of SRP 3.6.2.
Operation of the hydrogen monitors is independent of the hydrogen recombiner since both systems used separate piping and contain-ment penetrations and are not dependent upon the other to operate in any.way.
The hydrogen monitoring system consists of two inde-pendent, physically separated and redundant subsystems.:nd, th.;,
.t. ;ingi; f:il;;; ::it::ir.
Separate piping penetrations of the containment are utilized by each train of this system iwlsw mxs.n is newered f rom a, separate IE power source e=cerP Ar"f4 W EAa
.Each trai cm f 4 rie.ne, r u n e, 7.:,a sn y A f e s in' H e ik (,j g,;q_, 4,ej_ sn yp 1
y Byron /Braidwood stations meet the requirements for continuous
.i p,n indication in the main control room with IEEE 323-1974 qualified Asm #1 indicators.
The monitors may be controlled f rom the control room, gym,'e I H
j SAMPLE CONDITIONING The Model 225CM monitoring system is designed to monitor contain-ment gas for percentage by volume of hydrogen (dry analysis).
The operating range is -5 to +50 psig, 40'T to 445'T and relative humidity from 10 to 100%.
A sample of the containment atmosphere will be taken at or near one of the containment penetrations and l
another approximately 180 degrees away on the other side of the containment.
The samples taken are representative of the contain-i ment atmosphere due to the mixing system effects, which'is dis-cussed in Subsection 6.2.5.2.3.
Radioactive sample gas is drawn from the containment vessel by means of a sample pump into the analysis unit precooler where it is lowered from temperatures as i
high as 445'F to ambient temperature of the analyzing unit.- A 4
l
. solid state self-regulating thermoelectric cooler further reduces the gas temperature to below analysis unit ambient; after which 0.4 scfh of sample gas is directed to the sample measuring cell i
maintained at 170'F.
l After the gas passes through the cell, it is returned to the l
containment via a pressure regulating network which maintains pressure above containment assuring return of the sample gas.
Any condensation formed in either of the coolers is gravity drained to a-water trap which is automatically purged back to the containment with the aid of the pressure regulating network.
r CALIBRATION Instrument calibration is performed by actuating the appropriate solenoid valve directing zero or span gas with a known concentration through a flow controller and into the cell.
CAS MEASUREMENTS - GTNERAL DISCUSSION Analysis is accomplished by using the well established principle of thermal conductivity measurement of gases.
This technique utilizes two pairs of self-heating filaments fixed in the center of separate cavities inside the analyzing cell housing.
One of E.30-7
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COMMONtEALTH EDISON COMPANY BYRON /8RAIDWOOD STATIONS UNITS I &2 PROCESS SAWLING POST ACCIDENT Hz MONITORING SYSTEM i
5 B-OPEN S 8-OPEN
@8-OPEN 8-OPEN
$ A-CLOSE
$ A-CLOSE
[$)A-CLOSE A-CLOSE 1PS228A IPS229A IPS2288 iPS2298
)
ESF DIV.ll ESF DIV.12 ESF O!V.ll ESF O!V.12 i
D.C.
I lA WW k
SAT t
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4.lSKY BUS 14l
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BUS TIE l
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MM 480V SWGR BUS 131X 1) t I
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BATT 125V MM un l
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I25VOC ESF BUS III p-SUSTIE
' TO UNIT 2-125VOC ESF O!$T PNL Ii1 1 P) 1
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l l Il vai,vE VALVE 1P522:A IPS22ss j-ESF DIVISION 11 SINGLE LINE DIAGRAM I
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FIGURE I
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l NUCLEAR RE ULATORY Colml8SION Ji 3 I 162 i
July 25, 1989 j
- 4.
- g fM ket Nos. 50-454, 50-455, 50-456, and 50-457 Mr. Thomas J. Kovach Nuclear Licensing Mar.tvar Comonwealth Edison Cospany Post Office Box 767 Chicago, IL 60690 J
Dear Mr. Kovach
SUBJECT:
DESteN 0F CONTAll0GT HYDR 0 GEN MONITORING SYSTEM J
AhpendiaE
)ge E.30-7 of the Byron /Braidwood Updated Final Safety Analysis Report (U discusses the design of the containment lqydrogen monitoring i
system. It states that ' separate piping penetrations of the containment are utilized by each train of this system. Each train is powered from a separate
- 1E power source."
j JFebruary1982,we'acceptedthisdesignonpages6-17,6-tIdated I
InouroriginalSafetyEvaluationReport(SER)NUREG-0876 t
and 7-26. On page 6 22, we stated that the itydrogen monitoring system meets the single failure j
criterion.
i i
Newever, on July 20, 1989,l plant configuration in one area does not agree with the Senior Resident Inspector at Byron Station l
notified us that the actua l
your UFSAR or our SER. Each of the two containment piping penetrations for the suction of.the hydrogen monitors has two isolation valves in series. One valve on each line is powered from DC Bus E11 and the other valve on each line is i
powered from DC Bus Ett. Thus, a single failure, the loss of either Sus E11 or Bus Elt, could result in the loss of both containment piping penetrations and a loss of the hydrogen monitoring system.
-Please provide a response to this letter within 30 days of receist. Your l
response should propose a design change to the system, with a setodule for
-t implementingthechange,orajustificationfortheexistingconfiguration.
Sincerely, k N, 1
Leonard M. 01shan, Project Manager
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Project Directorate !!!-t Division of Reactor Projects III,
.l IV, V, and Special Projects t
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