ML20009G788
| ML20009G788 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 07/14/1981 |
| From: | Ippolito T Office of Nuclear Reactor Regulation |
| To: | Parris H TENNESSEE VALLEY AUTHORITY |
| References | |
| TASK-2.K.3.46, TASK-TM NUDOCS 8108040664 | |
| Download: ML20009G788 (9) | |
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Docket Hos. 50-259, 50-260 JUL f 4 !981 and 50-296 fir. Ilugh G. Parris Manager of Power Tennessee Valley Authority 500A Chestnut Street, Tower II Chattanooga, Tennessee 37401 s
Dear Mr. Parris:
SUBJECT:
T!11 ACTION PLAN ITD1 II.K.3.46, "MICHELSON C01;CERNS" RE: BROW!S FERRY PLANTS UNITS 1, 2 AND 3 Enclosed for your infonration is our evaluation of the BUR Owners Group response to Wil Action Plan Iten II.K.3.46 "lifchelson Concerns." We find the response to be acceptable.
Since your letter dated June 23, 1980 endorsed the Owners Group response, we consider Item II.K.3.46 to be co*1plete for your facility.
Sincerely, jp&
Mt 1
Thomas A. Ippolito, Chief '
Operating Reactors Branch #2 Division of Licensing
Enclosure:
Di tribution S
As Stated kDocket File
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Mr. Hugh G. Parris cc:
H. S. Sanger, Jr., Esquire General Counsel Tennessee Valley Authority 400 Commerce Avenue E 118 33 C Knoxville, Tennessee 37902 Mr. Ron Rogers Tennessee Valley Authority 400 Chestnut Street', Tower II Chattanooga, Tennessee 37401 Mr. H. N. Culver 249A HBD 400 Commerce Avenue Tennessee Valley Authority Knoxville, Tennessee 37902 Robert F. Sullivan U. S. Nuclear Regulatory Commission P. O. Box 1863 Decatur, Alabama 35602 Athens Public Library South and Forrest Athens, Alabama 35611 Mr, John F. Cox l
Tennes~see Valley Authority W9-D 207C 400 Commerce Avenue
(
Knoxville, Tennessee 37902 i
Mr. Herbert Abercrombie Tennessee Valley Authority P. O. Box 2000 Decatur, Alabama 35602 i
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ENC'LOSdRE EVAi.UAT'IONOF'BWROI!NERSGROUP GENERIC RESPONSE TO NUREG-0660 ITEM II.K.3.46
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STATEMENT OF REQUIREMENTS ~ ~ ~
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"A number of concerns related to decay heat removal following a very small break LOCA and other related items were questioned by Mr. C. Michelson of the Tenness'ee Valley Authority.
These concerns were identified for PWRs.
GE was requested to evalu, ate these concerns as they apply to BWRs and to assess the importance of natural circulation during a.small-break LOCA in BWRs.
GE has not yet responded-to the Michelson concerns; A brief description of natural cir:u-lation was addressed in NEDO-24708. The submittal was incomplete, however, inthat natural circulation for purposes of depressurizirg the reactor vessel
- was not addressed.
GE should provide a responsi to'the Michelson concerns as they relate to BWR plants."
SUMMARY
AND EVALUATION OF RESPONSE The concarns related to decay heat removal which were raised by Mr. Michelson were responded to in a letter to D. F. Ross (NRC) from R. H.Buhholz (GE),
MFN-041-80, " Response to Questions Po~ sed by Mr. C. Michelson "
February 21,
' 1980.
An additional question was issued in June, 1980'and the BWR Owners Group responded in a letteer to Darrell G. Eisenhut (NRC) from David B. Waters (BWR Owners Group), BWR03-8117, "BWR Emergency Procedure Guidelines Revision 1, and Responses to Related Questions," January 31, 1981.
A sdmary of our evaluation of the questions is given below':
Question 1: Press.urizer level is an incorrect measure of primary coolant inventory.
Response: BWRs do not have pressurizers.
BWRs measure primary coolant inventory.
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, directly using differential pressure ~s'ensors attached to the reactor vessel.
This concern does not apply to BWRs.
~Que's'tionL 2 :' The isolation of smal5 breaks (e.g., letdown line; PORV) is not a'ddressed
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or analyzed.
Resoonse:
Automatic isolation only occurs for breaks outside the containment.
Such breaks are addressed in NED0-2470B.
If the high pressure systems are available, no operator actions are required.
If all high pressure systems fail, the operator must depressurize to allow low pressure syst' ems to maintain vessel level....
Analyses show that the operator has sufficient information and time to perform these manual at.tions.
The requi'ed manual actions have been included in the guidelines for small break. acciden"s.
Ques [ ion 3: Pressure boundary damage due to loadings from (a) bubble collapse in subcooled liquid and (b) injection of ECC water in steam filled pipes.
Response: Because the BWR geometry and injection locations are not the same as for a PWR, this concern is not applicable to a BWR.
ECC injection in the BWR at high pressure is either directly into the reactor vessel (BWR/5-5 HPCS, HPCI on some BWR/4) or into the feedwater lines (FWCI, HPCI on most BWR/3-4).
The.feedwater l'ines are normally filled with relatively cool liquid (420 F or less).
ECC injection in the BWR at low pressure is eitfier direct 3y into the reactor vessel (LPCS, BWR/5-6 LPCI) or into the recirculation pura discharge line (BWR/3, 4 LPCI) near the automatically closed recirculation pump discharge valve.
The concern on collapse of bubbles in subcooled liquid was for steam bubbling upward through the. pressurizer surge line and pressurizer. There is no comparable BWR geometry.
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, Question 4:
In determining need for. steam generators to remove decay hea't, consider that break flow enthalpy is not core exit enthalpy.
Response: Since BWRs do not use s. team generators to remove decay heat, this concern'does not apply to BWRs.
' Question 5-Are sources ~ of auxiliary feedwater ade'quate in the event of a
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delay.in cooldown subsequent to a small LOCA?
Response: Since BWRs do not need feedwater to remove heat from the ' reactor -
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following a LOCA, this concern is not applicable to BWRs. The ECCS sub-systems which are available are adequate.
For breaks which are too small to remove all of the decay heat, the reactor coolant system pressure will increase to the relief valve setpoint. The high pressure systems are capable of pumping against the relief valve opening pressure.
Question 6:
Is the recirculation mode of operation of the HPCI pumps at high pressure an established design requirement?
Response: All recirculation modes of the high pressure systems in BWRs are established design requirements.
- Question 7:
Do the HPCI pumps and RHR pumps run simu.ltaneously? Do they share comon piping / suction? If so, is the system properly designed to accomodate this mode of operation?
Response: On some BWRs the RCIC/HPCI and RCIC/HPCS systems share a comon suction line from the condensate storage tank.
Also, many of the BWR LFCI pumps and LPCS pumps share comon suction.
It is an established design require.
ment to size the suction piping, including shared piping, such that adequate NPSH is available to RCIC, HPCI, HPCS, RHR/LPCI and CS pumps for a'.1 simultaneous - ~
operating modes.
Fre-operational and/or startup tests are conducted that demonstrate that this requirement is met.
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Question 8: Mechanical effects of slug flow on steam generator tubes needs to be addressed.
Response: Since BWRs do not have steam generators, this concern does not apply to BWRs.
Ouestion 9 :
Is there minimum flow protection for the HPCI pumps during the recirculation mode of operation?
Resoonse:
BWR/1 and BWR/2 units do not have special purpose HPCS or HPCI systems.
For BWR/3-6, the RCIC, HPCI, HPCS, RHR and CS/LPCS pumps all contain valves, piping and automatic logic that bypasses flow to the suppression pool as required to provide minimum flow protection.
Question 10: The effect of the accumulators dumping during small h-aak LOCAs is not taken into account.
Resoonse:
S'ince BWRs do not use accumulators to mitigate LOCAs, this concern does not apply.
Question 11:
What is the impact of continued running of the RC pumps during a small LOCA?
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Response: Analyses in NED0-24708 show that continued running of the recirculat' ion pumps results in little change in the time available for operator actions and does not significantly change the overall system response.
Question 12: During a smaTT break LOCA in which offsite power is lost, the possibility and impact of pump seal damage and leakage has no't been evaluated or analyzed.
Response: The RCIC, HPCI, HPCS, RHR, CS/LPCS pumps are provided with mechanical seals which are cooled by the pump primary process water.
No external cooling from auxiliary support systems is required for ECC pump seals. Should seal failure occur,
it can be detected by room sump high level a'larms. The RCIC, FPCI, HpCS, LPCS,
and RHR individual pumps are arranged, and motor operated valves provided, so that a pump with a failed seal can be shutdown and isolated without affecting
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other redundant equipment. The recirculation pump seals are cooled by service-water and control rod drive flow. On most BWRs, at least orie'of these sourchs ~
of cooling water is powered by emergency power; either source is capable of
, preventing damage to the pump seals.
While pump seal damage would be' expected if both sources of coolin; water are lo:t, laakage past the failed seals is~
calculated by GE to be.less than 50 GPM, a value within the normal makeup capability.
Que'stion 13: When transitioning from solid natur.al circulation to reflux boiling and back again, the vessel level will be unknown to the operators and emergency. procedures and operator training may be inadequate. This needs to be addressed and evaluated.
Response: There is no similar transition in the BWR case.
In addition, since the BWR has water level measurement within the vessel and the indication of the water level is incorporated into the operator guidelines, this concern does mot apply to BWRS.
Question 14: The effect of non-condensible gas accumulation in the steam generators and its possible disruption of decay heat removal by natur.a1 circulation needs to be addressed.
Response
Eor a BWR, vapor is present in the cop during both normal operation and natural circulation conditions.
Non-Condensibles may change the composition of the vapor but would have an insignificant effect on the natural or forced circulation itself, since the non-condensibles would rise with the steam to the top of the vessel. The natural circulation process would be expected to
v, continue since the upper sessel head ' area is well above the circulation paths through the jet pumps.
Question 15: Delayed cooldown following a small break LOCA could raise the containment pressure and activate the containment spray system.
Impact and
- onsequences need addressing.
Response
A Mark I and II Containments:
Except for a few early plants, most plants with Mark I and Mark II containments do not have an automatically ini-tiated drywell or wetwell spray-Only one of the newer plants has an automatic wetwell spray.
All essential equipment in the drywell has been qualified for the steem and temperature environmen' that would exist following a LOCA. There is no equipment in the wetwell'that is 2csersely a'fected by wetwell sprays.
r B.
Mark III Containments:
There is no drywell spray in a Mark III Containment. There is an automatic spray systes ;n the wetwell. All essential components have been qualified for this condition.
Question 16 : An operator ma. be inclined and perhaps even trained to isolate, l
where possible, a pipe break LOCA without realizing that it might be an unsafe
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action leading to high pressure and short-term core bakeout.
Before such isolation should be permitted it is first necessary to show by an appropriate analysis uncovered core without that the high pressure ECCS is adequate to reflood the assistance from the low pressure ECCS which can no longer deliver flow beca6se 6f the repressurization.
l Resoonse:
In order for the reactor vessel to repressurize following isolation of a recirculation line break, the isolation would, have to occur before initiation l
j of ADS due to a high drywell pressure in concurrer' with low water level 1 condition.
Isolation of a recirculation
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line break prior to obtaining a high drywell pressure signal might occur for 2
very small breaks (areas 0.0lft ) which may require several hundred seconds following the break to reach the high drywell pressure setpoint.
In this case, it has been shown (NED0-24708) that the high pressure systems are sufficient to maintain the water level above the top of the core; If isolation of the break -
were to occur prior to reaching level I but after the high drywell pressure setpoint, the vessel would pressurize to the SRV setpoint following isolation f the o
If no'hich pressure systems were available, the loss of mass through the SRVs would result in ADS acut& tion; this would allow the low pressure systems to begin injecting.
No adverse consequences result from isolation of a break in the recirculation line.
In summary, *'e have reviewed the responses given to the 16 concerns ex' pressed I
by Mr. Michelson and we find the responses acceptable.
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