IA-98-351, Forwards Rept Re MSLB with Superheat Release.Rept Outlines NRR Actions & Conclusions to Date & May Be Useful in Auditing 10CFR50.49 Activities.Issue Has Received Significant NRC & Industry Attention
| ML20154D380 | |
| Person / Time | |
|---|---|
| Issue date: | 07/15/1985 |
| From: | Thompson H Office of Nuclear Reactor Regulation |
| To: | Jordan E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE) |
| Shared Package | |
| ML20154D284 | List: |
| References | |
| FOIA-98-351 IEIN-84-090, IEIN-84-90, NUDOCS 9810070206 | |
| Download: ML20154D380 (10) | |
Text
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July 15, 1985
. 1 i
Distribution Central file ORB #1 RDG Memo file CParrish Dwigginton SYarga WMiners HThompson BLaGrange Glainas JKnight RBernero WHooston LRubenstein MEMORANDUM FOR: Edward L. Jordan, Director Division of Emergency Preparedness &
Engineering Respanse Office of Inspection & Enforcement FROM: Hugh L. Thompson, Jr. , Director Division of Licensing Office of Nuclear Reactor Regulation
SUBJECT:
IE INFORMATION NOTICE 84-90, MAIN STEAM LINE BREAK EFFECT ON ENVIRONMENTAL QUALIFICATION OF EQUIPMENT
, IE Information Notice 84-90, Main Steam Line Break Effect on Environmental Qualification of Equipment, was initiated by NRR and issued by IE on December 7, 1984 with mutual concurrence.
l This issue has received significant attention both on the part of NRC and the industry.
The enclosed report outlines NRR actions and conclusions to date, and may be useful tc you in your activities in auditing compliance with 10 CFR 50.49.
Please note that, with regard to Westinghouse plants that are not included in the owners group, NRR will target this item for review in its forthcoming audits of environmental qualification at NTOL plants. If questions arise, they may be held open pending completion of the Westinghouse Owners Group programs or resolution may be required, depending on the significance of the item identified. IE is requested to make similar provisions in its forthcoming audits of environmental qualification at operating reactors.
Fra:n }.ri.. , ., L3/Qp Hugh L. Thompson, Jr. , Director Division of Licensing Office of Nuclear Reactor Regulation Main Steam Line Break with Superheat Releases cc w/ enclosure:
V. Stello "
R. Bernero i g.
J. Knight L. Rubenstein
. .(f V. Noonan W. Butler
- 0. Parr *See previous white for concurrences R. LaGrange ORB #1:DL* BC-ORB #1:DL* D:DSl* AD:DE* OELD *
- 8. Grimes DWigginton/ps SVarga RBernero JKnight WShields J. Partlow 5/2/85 5/2/85 5/6/85 5/10/85 5/13/85 U. Potapovs I CONTACT- AD:SA
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Dave Wi ginton DCrutchfield Glainas gHTrl on EJordan (X27354 5/20/85 f/ 2y85 7/g785 7/2/85 9810070206 980930 \
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y Distribution Central file ORBal RDG Memo file CParrish DWigginton 5'irga WMiners HThompson BlaGrange Glainas vAnight RBernero WHouston LRubenstein MEMORANDUM FOR: Edward L. Jordan, Director Division of Emergency Preparedness A .
Engineering Response Office of Inspection & Enforcement /
j FROM: Hugh L. Thompson, Jr. , Director /
Division of Licensing '
Office of Nuclear Reactor Regulati,on l
SUBJECT:
IE INFORMATION NOTICE 84-90, MAlf STEAM LINE BREAK l EFFECT ON ENVIRONMENTAL QUALIFJCATION OF EQUIPMENT IE Infonnation Notice 84-90, Main Steam Line Br k Effect on Environmental fiRR and issued by IE on Qualification December of Equipment, 7, 1984 was initiated with mutual concurrence. by/
/
This issue has received significant attent,fon both on the part of NRC and the industry. /
l j
The enclosed report outlines NRR actiof and conclusions to date, and may be l useful to you in your activities in 96diting compliance with 10 CFR 50.49 '
and in routine regional review of litensee actions regarding information Notices.
Hugh L. Thompson, Jr., Director Division of Licensing Office of Nuclear Reactor Regulation l
Enclosure:
l Main Steam Line Break with Superheat Releases cc w/ enclosure:
V. Stello R. Bernero J. Knight L. Rubenstein V. Noonan W. Butler
- 0. Parr /
R. LaGrange CONTACT *
/
Dave Wigginton (X27354)
- See previous white for concurrences ORB #1:DL* BC-0RB#1:DL* D:051* AD:DE* OELD* AD:SA ,
DWigginton/ps SVarga RBernero JKnight WShields DCrutchfield 05/ /85 05/ 2/85 05/6 /85 05/10 / 05/13/85 5/20/85 AD: ::DL D:DL D/4E ER ,
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Gla 3s HThompson 100 n
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Distribution Central file OR8sl RDG Memo file CParrish Dwigginton SVarga WMiners HThompson BlaGrange Glainas JKnight R8ernero WHouston LRubenstein MEMORANDUM FOR: Edward L. Joraan, Director Division of Emergency Preparedness &
Engineering Response Office of Inspection & Enforcement FROM: Hugh L. Thompson, Jr. , Director Division of Licensing Of fice of Nuclear Reactor Regula don
SUBJECT:
IE INFORMATION NOTICE 84-90, IN STEAM LINE BREAK ;
EFFECT ON ENVIRONMENTAL QUAL ICATION OF EQUIPMENT IE Information Notice 84-90, Main Steam line eak Effect on Environmental Qualification of Equipment, was initiated by 4RR and issued by I.C. on December 7, 1984 with mutual concurrence.
This issue has received significant atte ion both on the part of NRC and the industry.
The enclosed report outlines hRR acti s conclusions to date, and may be useful to you in your activities in diting compliance with 10 CFR 50.49 and in routine regional review of 1 ensee actions regarding Information ,
Notices. j Hugh L. Thompson, Jr. , Director Division of Licensing Office of Nuclear Reactor Regulation Main Steam Line Break with Superheat Releases cc w/ enclosure:
V. Stello R. Bernero J. Knight L. Rubenstein V. Noonan W. Butler
- 0. Parr R. LaGrange CONTACT:
Dave Wigginton (X27354)
- See previous hite for concurrences ORB #1:DL* BC-ORB #1:DL* 0:051* AD:DE* OELD*
DWigginton s SVarga RBernero JKnight WShields .
05/ 2 /85 05/ 2/85 05/6 /85 u'tc eld AD:0R:DL D:DL 05/10 /85 05/13/85 M'5L}>/85 Glainas HThompson 05/ /85 05/ /85
Distribution Central file ORBel RDG / Memo file CParrish DKigginton SVarga WMiners HThomps.n BlaGrange Glainas JVright RBerner WHouston LRubenstein MEMORANDUM FOR: Edward L. Jordan, Director Division of Emergency Pre aredness &
fngineering Response Office of Inspectiun A .nforcement FROM: Hugh L. Thompson, J , Director Division of Licens' q Office of Nuclear ,eactor Regulation
SUBJECT:
IE INFORMATION OTICE 84-90, MAIN STEAM LINE BREAK EFFFCT ON ENV ONMENTAL QUALIFICATION OF EQUIPMENT IE Information Notice 84-90, Ma i Steam Line Break Effect on Environmental Qualification of Equipment, wa initiated by NRR and issued by I.E. on December 7. 1984 with mutual ncurrence.
This issue has received sig ficant attention both on the part of NRC and the industry.
The enclosed report outl es NRR actions conclusions to date, and may be useful to you in your a tvities in auditing compliance with 10 CFR 50.49 and in routine regional review of licensee actions regarding information Notices.
Hugh L. Thompson, Jr. , Director Division of Licensing Office of Nuclear Reactor Regulation
Enclosure:
- 1) Main Steam Lin Break with Superheat Rel ases cc w/ enclosure-V. Stello R. Bernero J. Knight L. Rubenste V. Noonan W. Butler
- 0. Parr R. LaGra ge j CONTACT i f .iA- ,(M 4 Dave ginton (X27 4 r " ' y ( tt"bu l
ORBf1:0 'R #1:0L i0 -
A: ha OELO j 0Wiggin ps R ernero JKnight WShields 05/ 7 /85 /85 ,[05/,/85
) 05//c/85 05// ;/85 !
AD:0R:DL D:0L Glainas llThompson )
05/ /85 05/ /85 i i
~ ____. ._ _ __ __ _ _ . _ _ _ ____ _ __ __ _ .
3 ENCLOSURE MAIN STEAM LINE BREAK WITF SUpERHEAT RELEASE
- 1. Introduction The environmental qualification programs for safety-related electrical equipment must consider the time dependent temperature and pressure at the location of the equipment for the most severe design basis accident. A methodology for computing mass and energy ~ releases for postulated MSLB accidents for Westinghouse (W) reactors is described in Topical Reports WCAP-8821, and WCAp-8822.
In the course of our review of WCAP-8822, it was noted that the steam generator blowdown model did not account for the heat transfer from escaping steam. the uncovered portion of the steam generator tube bundle to the It was determined that certain break sizes would produce superheated blowdown calculated. The superheating and greater energy releases than had been previously of the steam occurs when the break area is sufficiently large that feedwater flow to the steam generator cannot keep up with the steam loss through the break and the water level in the generator falls, thus uncovering the steam generator tube bundle. The steam produced in the generator and is released is through thus superheated the break. byThethe uncovered portion of the tube bundle primary concern is the qualification of safety-related electrical equipment to the proper temperature environment.
In order to assure that all utilities were aware of the issue of superheat and its potential affect on equipment qualification, on December 7,1984, the NRC issued "lE Information Notice 84-90: Main Steam Line Breat Effect on Environmental Qualification of Equipment". In this notice, the NRC stated that the staff considers steam superheating during steam generator tube bundle uncovery as a result of postulated main steam line breaks and subsequent release to compartments, if omitted from plant analysis, to represent a potential deficiency in the equipment qualification required by 10 CFR 50.49.
In the notice it was suggested that licensees review their main steam line break analysis with regard to this issue.
The MSLB superheat issue appears to affect only W PWR plants, since i
- 1) B&W plants operate with steam generator superWeat, which is accounted for in the mass and energy reletse calculations, and 2) CE mass and energy release codes currently model superheat if tube bundle uncovery is predicted to occur.
The following sections summarize staff review of the superheat affect on the environment due to postulated pipe breaks:
- 1) inside large dry and subatmospheric containment,
- 2) inside ice condenser containments and i
3)outsidecontainment 1or use in determining environmental qualification of safety-related electrical equipment important to safety, i
i
io l .
1 II. Large Dry and Subatmospheric Containments On January 25, 1985 W met with the staff to present the results of their sensitivi'y studies oT the effects of superheat on temperature profiles inside large dry and subatmospheric containments. Using conservative parameters for a four-1 cop system with Model 51 steam generators (which bound the superheat effect for W reactors). W concludes that the effect of superheat on temperatureT inside large dry and subatmospheric containments is neglig'ble.
Pending confinnation of the information provided at the January meeting. (to be submitted by W~'in a supplement to the WCAP) the staff believes that the current mass and' energy release calculations for large dry and subatmospheric containments (without superheat models) are adequate, and revised qualification temperatures for equipment inside large dry and subatmospheric containments will not be required. '
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!!I. Ice Condenser Containment i Using the mass and energy release data based on the methodology of WCAP-8822, the approved 1.0 TIC-3 containment code predicts compartment temperatures higher than equipment qualification temperature. W has revised the LOTIC-3 code by I adopting a new wall heat transfer model ancfby accounting for the energy removal capability of the ice condenser drains. These chang s reduce the peak lower compartment temperatures to below equipment qualification temperatures.
The revised 1.0 TIC-3 (Topical Report WCAP-8354, Supplement 3) is currently under staff review with the Catawba and Watts Bar plants being used as the surrogate plants for supporting analyses, and a number of concerns have been identified which require analysis. They primarily involve uncertainties in (1)thecorrelationsusedtopredictthesizeofthedropletsproducedbythe '
drain flow, (2) the simplifying assumptions used in determining the effect major equipment located in the drain flow path would have on the droplet field, (3) the ice bed heat sink representation and corresponding ice-melt rates, and (4) the assumption that the lower compartment is well mixed.
W has comitted to conduct a program of tests and analyses to '
specifically address each of the preceding concerns. This program was initiated in mid-1984 and is scheduled to be completed in October 1985.
The results of our review of Catawba and Watts Bar will be applied to other plants with ice condenser containments.
The staff has concluded that interim operation of the ice condenser plants is acceptable pending completion of this work.
IV. Superheat Effects on Temperatures Outside Containments On. June 6, 1984 W notified plant owners that the temperature profiles resulting from a full spectrum of breaks in the main and branch steam lines outside containment may need to be revised because of the superheat resulting from uncovering of steam generator tubes.
A number of olants joined together into a Westinghouse Owners Group (WOG) to address this issue. A series of meetings have been held and letters exchanged
between the staff and WOG discussing the WOG program for resolution. The latest meeting was held on January 30, 1985.
described the program which vould provide fonnal documentation for mass andA energy releases to each of the participating utilities. This program is to be completed by August 1985.
The NRC has projected that it would take 2-3 months following the WOG program for each licensee to obtain revised compartment analyses using the mass and energy release data. These analyses by the licensees, which should be complete about December 1985, would redefine the temperature profiles in compartments outside containment and would establish whether or not the existing equipment qualification for the area was appropriate. At that time plants with equipment qualification problems as a result of new temperature profiles would be expected to correct them in accordance with the provisions of 10 CFR 50.49.
WOG has developed several generic arguments related to MSLB accideat in justifying continued operation of plants pending resolution as to whether or not any equipment qualification problems are identified. The generic argument relies upon the results of W scoping studies which indicate safety equipment operation occurs before superheated steam release begins. The WOG also presented additional arguments for consideration including the mechanistic I treatment of high energy line breaks and their probability of occurrence, the thennal lag of equipment exposed to superheated steam, the unlikely single failure of a main steam isolation valve (MSIV), and the small probability that
- a break will occur between the containment wall and MSIV.
The WOG Program and the justification for continued operation pending identification of equipment qualification concerns, if any, has been reviewed and found acceptable by the staff for those licensees referencing the program.
In regard to this issue, the staff has recently clarified its position on a MSI.B for the break exclusion region concurrent with a single active failure.
For those plants with pipes containing break exclusion regions (see definition in Section 3.6.2 of the Standard Review Plan, SRP) licensees should consider the one square foot break defined in SRP 3.6.1 and need not postulate a single active failure concurrent with such a break in detenntning the resulting environmental conditions.
V. Conclusion The following staff conclusion have been reached regarding the superheat issue:
1.) For MSLB inside large dry and subatmospheric containments, pending documentation of results presented by 'W, current temperature profiles are acceptable. No further j istification for continued operation because of this issue is required.
2.) For ice condenser containments, the resolution of current staff review of Catawba and Watts Bar (scheduled to be completed in October 1985) will be applied to the other ice condenser containment plants. Operation of ice condenser plants may continue pending completion of staff review.
. 3.) For superheat effects outside conta-inments, the WOG program, schedules for resolution of this issue, and justification for continued operation are acceptable.
To provide some further insight into the relative risk perspective of this issue, the staff notes that although the main steam line break (MSLB) accident is an important design basis accident in determining several design features !
of the plant, the accident sequences associated with MSLB generally are not regarded as :najor contributors to public risk; by itself, a MSLB will not uncover the reactor core. As long as either main or auxiliary feedwater is available, core cooling is achievable. For the particular concern here, i.e.,
superheated conditions causing equipment failure, the equipment which fails must in turn cause failure of auxiliary feedwater and main feedwater to all steam generators in order for a core melt to be of concern. The events thus form a sequence of probabilities which, when properly considered with other decay heat removal strategies, further support the staff findings that the actions underway to evaluate temperature profiles both inside and outside of containments continue as athis pending result of superheat are adequate and plant operation may evaluation.
If temperature profiles either inside or outside containments as a result of the superheat are affected, resolution of qualification of safety-related electrical equipment will be governed by the provisions of 10 CFR 50.49.
Finally, as noted previously, not all W reactors plants are members of the WOG (which was fonned to address the superTeat issue for MSLB outside containment). It is assumed that for those utilities not participating in WOG, they have addressed the concerns identified in IE Infonnation Notice 84-90 on this issue, and that subsequent regulatory audits of equipment qualification or review of utility actions regarding Infonnation Notices will confinn this assumption. This item will be targeted for review in the Office of HRR's forthcoming audits of environmental qualification for non-WOG operating license applicants. If questions arise, they may be held open pending completion of the WOG programs described abcve or a separate resolution may be required, depending on the potential significance of the problem. A similar approach will be used by the Office of Inspection and Enforcement for operating plants.
REFERENCES Letter W.J. Johnson _(W) to W.G. Smith (D.C. Cook) on " Environmental Qualification of Equipment for High Energy Line Breaks Outside of Containment" dated June 6, 1984.
Letter G.T. Goering to H.R. Denton on " Westinghouse Regulatory Response Group Actions In Regard to the High Energy Line Break Outside Containment Effect on Environmental Qualification of Equipment" dated July 26, 1984.
Letter G.T. Goering to li.R. Denton on " Westinghouse Owners Group Program to Address Postulated Mass / Energy Releases Associated With Superheated Steam Outside Containment" dated August 20, 1984.
Meeting Sumary dated September 6,1984 on meeting held on August 2, 1984 with WOG.
Memo V. Noonan to R.W. Houston on "High Energy Line Break Effects on Environmental Qualification of Equipment - Staff Program" dated October 11, 1984 Memo R.W. Houston to G. Lainas on " Adequacy of Westinghouse Nnera Group Program to Address MSLB Superheat Concern Inside Containment" dated October 11, 1984 Letter G.T. Goering to H.R. Denton on "Westinghoure Ownars Group Update on Program to Address Postulated Mass - Energy Lleases Associated With Superheated Steam Outside Containment" dated October 24, 1984 Memo R.W. Houston to G. Lainas on " Resolution of MSLB Superheat Concerns" dated December 6, 1984.
- IE Infonnation Notice No. 84-90: Main Steam Line Break Effect on Environmental Qualification of Equipment, dated December 7,1984.
Memo R.M. Bernero to Eisenhut, Spies, and Vollmer on " Restatement of DSI Position Regarding an MSLB In Superpipe" dated December 11, 1984
7- ..
Memo R.H. Vollmer to R. Bernero on " Restatement of DSI Position Regarding A MSLB in Superpipe" dated January 7,1985. !
Memo 0.G. Eisenhut to R. Bernero on " Restatement of DSI Position Regarding An MSLB in Superpipe" dated January 30, 1985.
Meeting Sunr.ary dated February 7,1985 Regarding the WOG Meeting on January 30, 1985.
Letter J.0. Cermak to D.L. Wigginton on " Westinghouse Owners Group High Energy Line Break /Superheated Blowdowrs Outside Containment i
Subgroup Followup to January 30, 1985 Feeting," dated February 25, !
1985.
Letter J.0. Cermak to D.L. Wigginton on ' Westinghouse Owners Group High Energy Line Break /Superheated Blowdowns Outside Containment i
Subgroup Additional Participant," dated March 21, 1985. !
Memo L.S. Rubenstein to G. Lainas on "MSLB With Release of Superheated Steam," dated April 11, 1985.
Memo R.W. Houston to G. Lainas on " Comments on Status Paper RE:
MSLB and Superheated Environments" dated April 12, 1985.
Memo H.R. Denton to V. Stello on " Position on a MSLB in Superpipe Concurrent with a Single Active Failure" dated April 29, 1985 i
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