ML20093B621
| ML20093B621 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 10/08/1984 |
| From: | Tucker H DUKE POWER CO. |
| To: | Adensam E, Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8410100154 | |
| Download: ML20093B621 (14) | |
Text
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Dmm Powen GOMPANY P.O. DOX 'M3180 CHARLOTTE, N.C. 28242 HALB. TUCKER TE R.EPIEONE
-som emmesammt (704) 373~6531 October 8,1984 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D. C. 20555 Attention: lis. E. G. Adensam, Chief Licensing Branch No. 4 Re: Catawba Nuclear Station Docket Nos. 50-413 and 50-414
Dear Mr. Denton:
On September 28, 1984, representatives from Duke Power Company, Westinghouse Electric Corporation and the NRC Staff met at the NRC's office in Bethesda, Maryland to discuss Proposed License Condition 14b which concerns the main steam line break (MSLB) in the Doghouse. The purpose of this letter is to provide a summary of the justification for interim operation of Catawba Unit 1 pending the Staff's review of MSLB's outside containment.
An analysis of a MSLB in the Doghouse was submitted to NRC/ Region II on September 4,1984 and was discussed at the September 28, 1984 meeting. That analysis was based on conservative " worst case" conditions. Analysis of the effects of different break sizes had been performed which demonstrated that all safety functions required to mitigate the MSLB were completed prior to the atmospheric temperature exceeding the qualification temperature of the equipment in the Doghouse.
A more realistic analysis has been now performed which demonstrates substantial additional time margins between completion of the equipment safety function and the time at which the Doghouse atmospheric temperature exceeds the qualifi-cation temperature. This revised analysis is discussed in Attachment 1. A discussion of the sensitivity of the analysis to break size and power level is included in. Attachment 3 presents a discussion related to the specific doghouse equipment needed to mitigate an MSLB in either of the Catawba Doghouses.
As requested by the Staff during the September 28, 1984 meeting, a review of the effect of a MSLB in the Doghouse on control and power circuits has been performed and is included in Attachment 4.
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~Page Two October 8,.1984 As further justification, Westinghouse has performed a preliminary fracture mechanics evaluation to determine a maximum crack opening area for a MSLB.
This evaluation concluded that tube bundle uncovery would not occur and therefore the original equipment qualification temperature envelopes would not be exceeded. This evaluation is described in Attachment 5.
Based on the justifications noted above and a more realistic analysis which demonstrates substantial additional time margins, it is concluded that plant safety would not be adversely affected in the event of a MSLB in the Doghouse and that qualification of the required Doghouse equipment has been demonstrateo.
Very truly yours,
b Hal B. Tucker RW0: sib Attachment cc: Mr. James P. O'Reilly, Regional Administrator U. S. Nuclear Regulatory Commission Region II
-101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 NRC Resident Inspector Catawba Nuclear Sttation Mr. Robert Guild, Esq.
Attorney-at-Law P. O. Box 12097-Charleston, South Carolina 29412 Palmetto Alliance 21351 Devine Street Columbia, South Carolina 29205 Mr. Jesse L. Riley Carolina Environmental Study Group 854 Henley Place Charlotte, North Carolina 28207 s
--____,__--..-----___-a-
ATTACHMENT 1 Catawba Nuclear Station EVALUATION OF MSLB IN D0GHOUSE UTILIZING BEST ESTIMATE ANALYSIS The Doghouse MSLB, as discussed in the September 28, 1984 meeting with the NRC staff, was based on conservative " worst case" conditions. Analysis of the effects of different break sizes had been performed which demonstrated that all safety functions required to mitigate the MSLB were completed prior to the atmospheric temperature exceeding the qualification temperature of the equipment in the Doghouse.
However, questions were raised by NRC staff concerning the time margin between completion of the equipment safety function and the time at which the Doghouse atmospheric temperature exceeds the qualification temperature. The following infor-mation is provided to show that when utilizing a more realistic analysis and taking into account equipment temperature / time lag, substantial additional time margin car, be demonstrated.
In order to provide an indication of the conservatism of the original analysis results, Westinghouse performed a better estimate analysis (with some conservatisms maintained) on the limiting break size and power level determined from a spectrum of break size and power level combinations.
The assumptions which were modified in order to provide a comparison to the original report are indicated below:
a.
Nominal initial conditions without error allowances b.
1% additional control rod reactivity is inserted beyond that assumed in the original analysis. (Previously it was assumed the most reactive Rod Cluster Control Assembly remains in its fully withdrawn position.)
c.
100% ANS decay heat rather than 120% ANS decay heat.
d.
Nominal safety actuation setpoints for Low Steamline Pressure and Low Pressurizer Pressure signals, e.
Feedwater isolation is assumed to occur eleven seconds after reactor trip signal and coincident with Low-Low T function.
3yg f.
Auxiliary feedwater flowrates are defined as a function of steam generator pressures for the Catawba plant. The previous analysis used flowrates which were lower than the actual Catawba values to provide conservatism.
A failure of the turbine driven AFW pump is still assumed in order to conservatively limit mass addition to the steam generators.
g.
Best estimate safety injection flowrates.
h.
A more realistic initial atmospheric temperature in the Doghouse was used, 1200F rather than 1350F.
1.
Better estimates for steel surface areas in the heat transfer model were used, as the original values were approximately three times too low and thus conservative.
In this revised analysis, the time at which the atmospheric temperature in the Doghouse exceeds 340 F was generated for a 0.5 ft2 break at 70% power, (which was determined to 0
be the worst break) and is presented in Table I. Also in Table I, for comparison
. Attachment 1 (Cont'd)
Sheet 2 of -
purposes is.the corresponding information from the conservative analysis discussed at the September 28, 1984 meeting.
The time versus temperature analysis was conducted for breaks in compartments 1 and 3 of the doghouse (See Figure 1). Compartments 1 and 3 were chosen because they contain the safety related equipment required to mitigate the MSLB.
Mainsteam isolation' has been determined, by analysis, to be the limiting safety function, i.e., the last function to be completed in this accident scenario. Main-steam line isolation is completed at 360 seconds (6.0 min) and the Doghouse atmos-
- pheric temperature exceeds 3400F in compartment 3 (MSIV's location) at 445 seconds (7.4 min.) for a MSLB in compartment 3. Therefore, the revised analysis time margin of 85' seconds (1.4 min.) as compared to 16 seconds (.3 min.) yields a of the previous, conservative analysis.
~ In addition to the margin available in the revised analysis, temperature / time lag for the equipment has also been evaluated. A temperature / time lag calculation for a Valcor solenoid valve has been conducted. The Valcor solenoid valve was chosen for the heat transfer calculation due to its small mass and relatively large surface area. These physical parameters make it most sensitive to temperature rise as compared to the other safety equipment located in the Doghouse such as the MSIV solenoids. Both convection and radiative components of heat transfer were included in the. analysis. _ Calculation results show that the solenoid coil (critical component) temperature lags behind the atmospheric temperature by approximately 4.3 minutes. Conservatively applying the 4.3 minutes temperature / time lag to the MSIV solenoid and, combining the time margin provided by the best estimate analysis above, the MSIV's will have completed their safety function 5.7 minutes prior to its critical components experiencing a temperature in excess of its qualification tem-perature.
Based on the above margin along with consideration of a spectrum of breaks, a deter-mination that~the Doghouse equipment is not required to reposition later in the event, and that failure of the Doghouse equipment after its safety function is not detri-mental to plant safety, it is concluded that qualification of the required Doghouse equipment has been further demonstrated.
' (Cont'd)
Shest 3 of 4 TABLE-I REVISED ANALYSIS TIME AT WHICH ATMOSPHERIC TEMPERATURE EXCEEDS 3400F Break in Compartment 1 Break in Compartment 3 Compartment 1
. Compartment 3-Compartment 1 Compartment 3 Time Time Time Time 430'sec.. 450 sec..
Temperature 445 sec. (7.4 min.)
(7.2 min.)
(7.5. min.)
does not exceed
~
0 340 F (Tpeak=275Y 0 m 725 sec.)
PREVIOUS CONSERVATIVE ANALYSIS U
TIME AT WHICH ATMOSPHERIC TEMPERATURE EXCEEDS 340 F Break;in Compartment 1 Break in Compartment 3
-Compartment l' Compartment 3 Compartment 1 Compartment 3 Time Time Time Time 335'sec.. 360 sec.
Temperature does 355 sec. (5.9 min.)
(5.6 min.)
(6.0 min.)
not exceed 3400F (Tpeak = 255PF 0 s 490 sec.)
~ Attachment 1 (Cont'd)
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WORST CASE RESULTS FOR MSLB D0GHOUSE ANALYSIS
+
The Westinghouse portion of the MSLB Doghouse analysis _ determined results for a
-spectrum of over 60 break size and power level combinations with assumptions which were, in all cases, conservative for the_ Catawba plant. Westinghouse and Duke
' jointly determined from these results that the worst case for the safety actuation study is the 0.5 ft2 break at a-70% power level. It is possible that a small variation in power level (e.g.,13%) could produce slightly smaller actuation
- margins. However, the magnitude of the margins demonstrated herein utilizing the best' estimate analysis (e.g., 85 seconds between the time when all valves have aligned to their proper position and the time at which equipment qualification temperatures are exceeded) more than compensate for any decrease in margin due to power level variation. In addition, thermal lag in the equipment provides still more margin as discussed in Attachment 1.
1.
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Discussion of Class lE
- Doghouse-Equipment Required for Steamline Break Outside Containment I.
Criteria Used to Identify Required Equipment
- 1. : Steam Generator (SG) overfill should be prevented.
.2.
Adequate auxiliary feedwater must be supplied automatically to at least one steam generator to allow adequate operator action time to isolate faulted SG.and realign to intact SG.
3.
SG pressure boundary must be maintained to prevent loss of feedwater and to prevent overcooling.
II.
IE Equipment Locations
. See Section IV for a list of all. Class lE valves and instrumentation located
-in the Doghouses. Auxiliary Feedwater Pump Turbine Steam Supply Isolation Valves are located in the interior doghouse only. All other valve types are located in both interior and exterior doghouse.
III. lE Doghouse Equipment Required 1.
Valves required to prevent SG overfill SG overfill is prevented by tripping the main feedwater pumps and closing the pump discharge isolation valves (located in the Turbine Building) on a high steam generator level signal. In addition, feedwater control valves also located in the Turbine Building close on both a feedwater isolation signal and high steam generator level signal. Valves located in the doghouses are not required to prevent overfill but serve as a backup. These valves are the main feedwater ; solation, tempering isolation, and feedwater supply to the upper nozzle.
2.
Valves required to prevent loss of feedwater from the SG CF87AB~
[A Feedwater purge isolation AB CF90AB_
B81478 ~
BB10B BB1488 SG Blowdown isolation 8
BB57B BB1508 BB618.
' Loss of feedwater is prevented through the tempering line and the feedwater supply-line to the upper nczzle by two check. valves in series in each flow path.- Loss of feedwater' is prevented through the main feedwater line by
. (Cont'd)
Sheet 2 of 5 one check valve and by closure of the feedwater control valve (located in the Turbine Building) on a feedwater isolation signal. The only flow path from the main feedwater line that requires closure of lE valves in the Doghouse is the reverse purge line. Reverse purge isolation valves are fail closed air operated valves with redundant de-energize to close solenoids. Since the reverse purge lines are used only at low power, the valves will be normally closed. Non-safety grade motor operated valves located in the Turbine Building can also be used to isolate flow.
'SG blowdown is isolated in each Doghouse by two valves in parallel lines outside containment and by one valve in the connon line inside containment.
In addition, blowdown is isolated in the Turbine Building by closing the non-safety blowdown control valves. All blowdown isolation valves close on automatic auxiliary feedwater pump start on a low-low steam generator level signal.
SG blowdown and reverse purge valves will close automatically before equipment qualification is exceeded.
3.
Valves required to isolate to control cooldown SM1AB ~
Main Steam Isolation Valve (MSIV)
SM3AB SMSAB SM7AB.
SM9AB '
Main Steam Isolation Bypass SM10AB SMll AB SM12AB.
SVlAB ~
Steam Generator PORV SV7AB SVl3AB SVl9AB.
The MSIV's, MSIV bypass valves and the SG PORV's are required to isolate the SG pressure boundary to control cooldown. Each valve is air operated fail closed, supplied with redundant normally energized solenoids that deenergize to close the valves. These valves receive a main steam isolation signal to close and will be closed before equipment qualification is exceeded. The SG PORV block valve is supplied with lE power; however, since the SG PORV is qualified, the block valve is not required to close. Main Steam Low Point Drain Isolation is not required because lines are orificed to limit flow.
1 (Cont'd)
Sheet 3 of 5
.4.
Valves required to supply auxiliary feedwater flow and isolate the faulted SG.
CA38A' Auxiliary Feedwater Isolation CA428 CA46B CA50A CAS4B CA58A CA62A CA66B.
SA2AB.
Auxiliary Feedwater Pump SA5AB Turbine Steam Supply The motor driven (MD) and turbine driven (TD) auxiliary feedwater pumps are located in the feedwater pump room so they are not affected by the steamline break. The TD. pump is.not required for any steamline break. Assuming a single failure of one: MD pump, adequate time is available for the operator to realign the other MD pump to supply flow to intact, steam generators.
Die motor operated auxiliary feedwater isolation valves are normally open and are required to remain open to supply flow to the steam generators.
The adverse environment will not cause the valves to spuriously close. Flow to the faulted SG can be isolated by closing the control valves located in the feedwater pump room, by closing manual isolation valves or by tripping the pumps that are not required.
5.
Instrumentation The only post-accident monitoring instruments located in the Doghouse are the auxiliary feedwater flow transmitters, which are not required to mitigate
. the consequences of a Doghouse MSLB. Although these may fail under this environment, post-accident monitoring of the auxiliary feedwater function can be accomplished by the steam generator level transmitters which will not be affected by a steamline break in the Doghouse.
-Water level instrumentation in the Doghouses is not required to function in the event of a Doghouse MSLB.
t Attachment'3(Cont'd)
Sheet 4 of 5 IV. Class 1E Equipment Located in the Doghouses Type Operator Valve No.
Description SM1AB
' Nain Steam Isolation Air Operated Valve (A0V)
SM3AB SMSAB SM7AB
-SM9AB.
Main Steam Isolation Bypass A0V SM10AB SMll AB SM12AB SVlAB Steam Generator PORV's A0V SV7AB-SV13AB SVl9AB CF33AB "
Feedwater Isolation Electro-Hydraulic Operated CF42AB CF51AB CF60AB CF87AB Feedwater Purge A0V CF88AB CF89AB CF90AB CA149AB Feedwater Supply to Upper Nozzle A0V CA150AB CA151AB CA152AB CA185AB Tempering Isolation A0V CA186AB CA187AB.
CA188AB CA38A Auxiliary Feedwater Isolation Motor Operated Valve (MOV)
CA428 CA468 CA50A CAS4B CA58A CA62A CA66B
.. -. - - = -. -. -. - - -
6, (Cont'd)
Sheet 5 of 5 Valve No.
Description Type Operator SV250 Steam Generator PORV Isolation M0V
. SV26A
- SV27A SV2BB SM74B
' Main Steam Low Point' Drain Isolation MOV SM75B SM768
'SH77A~
.BB108 Steam Generator Blowdown Isolation MOV BB21B B8578 BB61B-
- bbl 47B Steam Generator Blowdown Isolation M0V BB148B Bypass-BB149B BB150B SA2AB Auxiliary Feedwater Pump A0V SA5AB Turbine Steam Supply Isolation Instrument No.
Description
- CAFE 5090 Auxiliary Feedwater Flow CAFE 5100 CAFE 5110 CAFE 5120 CFLS6000 Doghouse Water Level Transmitters
~
CFLS6030 CFLS6060 CFLS6090 L_
~
L Catawba Nuclear Station Review of Control and Power Circuits 'for Degradation A review has been completed to evaluate the effects of a MSLB in the Doghouse on safety-related control systens exposed to the harsh environment. The following is a _ summary of the findings:
.l.
No safety-related cables are routed through a Doghouse which terminate at equipment located outside the Doghou:e.
2.- Equipment located in the Doghouse that is required to mitigate the effects of the MSLB was reviewed. This equipment was previously confinned to be qualified to perform its safety function before qualification temperatures are exceeded. Further review was done to determine if component failures in the harsh environment could cause any valves to reposition that are required to stay in the safe position; No failures were identified that could cause any repositioning.
3.
All safety-related control circuits in the Doghouses were reviewed to determine if any component failures could affect other safety-related circuits. All safety-related control components in the Doghouses are protected by separate fuses that are coordinated with upstream feeder breakers to avoid affecting any other related circuits.
Additionally, no failure mechanism which would degrade, safety power was
~ identified.
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i Catawba Nuclear Station
- Preliminary Fracture Mechanics Evaluation Currently,-:the environmental'ana' lysis.for the MSLB in the Catawba Doghouses is performed by postulating.non-mechanistic, breaks in.which catastrophic pipe failure
-is' assumed. -More realistic estimates of crack opening area and the resulting thermal
~
'and mechanical loads can be obtained through application of fracture mechanics techniques. A~ scoping study has been carried _out by Westinghouse for in-containment MSLB's7and preliminary results obtained indicate that a non-mechanistic pipe break Jwill not occur in the main steam line.
The purpose of this scoping study was to show that a circumferential flaw larger than any that would be present-in the main steam lines will remain stable when subjected to the worst combination of plant loadings. The flaw stability criteria for the analysis examined both.the global and local stability. The global analysis was carried out.using the plastic instability method, based on traditional plastic limit load. concepts but accounting fo'r strain hardening and taking into account the presence of a-flaw. The local stability analysis was carried out for a postulated inch longithrough-wall circumferential flaw. The objective of the local analysis
'was to show that unstable crack _ extension will not result for the postulated flaw.
The crack. opening area resulting from. faulted load was calculated for the 10-inch flaw using simplified analysis; techniques.
The following results were obtained from the above evaluation:
a.
Limiti moment' calculations indicated that the critical-flaw size (beyond which the flaw is unstable) would be greater than the pipe diameter,
- b.. Aipostulated 10-inch long through-wall circumferential flaw will remain stable
.when subjected to maximum faulted load of less than 20 ksi.
i c.. : Available _ fatigue crack growth results for the main steam line of typical
_PWR ~ plants indicate no significant crack growth due to design transients.
a 2
2
' d.
The crack ~ opening area.is estimated to be about 0.2 in (0.001 ft ). If a 2
safety, factor:of 10 is used, the area would be about 2 square inches l(0.01 ft ).
' From these results it is judged that it could be demonstrated by fracture mechanics analysis-that catastrophic pipe breaks in the main steam line would not occur.
2 Westinghouse systems evaluations have shown that for crack areas less than 0.1 ft,
tube bundle uncovery will _ not occur. Therefore, no superheated steam would be generated and original _ equipment qualification temperature envelopes would not be exceeded..
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