ML20064N511
| ML20064N511 | |
| Person / Time | |
|---|---|
| Site: | LaSalle  |
| Issue date: | 08/30/1982 |
| From: | Schroeder C COMMONWEALTH EDISON CO. |
| To: | Schwencer A Office of Nuclear Reactor Regulation |
| References | |
| 4901N, NUDOCS 8209080396 | |
| Download: ML20064N511 (20) | |
Text
,
g Commonwe:lth Edison N) one First National Plaza. Chicago, lltinois
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O-Address Reply to: Post Office Box 767 Chicago, Illinois 60690 4
Augus t 30, 1982 l
Mr.
A. Schwencer, Chie f Licensing Branch #2 i
Division o f Licensing U. S. Nuclear Regulatory Commission l
Washington, DC 20555 t
Subject:
LaSalle County Station Units 1 and 2 Concerns Regarding the Adequacy of the Design Margins of the Mark I and II Containment Systems NRC Dockets Nos. 50-373 and 50-374 References (a):
R. L.
Tedesco letter to L. O.
DelGeorge dated July 2, 1982.
(b):
C.
W. Schroeder letter to A. Schwencer dated July 9, 1982.
Dear Mr. Schwencer:
Reference (a) listed 22 concerns which Mr. John Humphrey had identified regarding Mark III Containments.
It also asked that the licensee provide a schedule for responding to those concerns which were identified as being potentially applicable to LaSalle County Station.
Re ference (b) s tated that Commonwealth Edison Company expected to respond to these concerns by September 1, 1982.
The purpose of this letter is to provide our response to these concerns.
Several design features distinguish LaSalle from the basis of the concerns.
First, LaSalle's peak containment pressure occurs early in a transient during steam blowdown to the suppression pool.
This feature minimizes the concerns of long term containment temperature and pressure.
Second, drywell and wetwell sprays do not i
af fect heat removal capability o f RHR because flows remain nearly constant regardless o f RHR mode.
Therefore, spray operation and mode cycling are not significant concerns.
Finally, the equipment qualification environment in the wetwell is close to drywell conditions minimizing those concerns regarding environment.
With this transmittal, Commonwealth Edison considers our commitment in Reference (b) to be complete.
8209080396 820830 Apol PDR ADOCK 05000373 lJ A
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A. Schwencer Augus t 30, 1982 Enclosed for your use are one (1) signed original and thirty-nine (39) copies of this letter and the attachment.
If there are any further questions in this matter, please contact this of fice.
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Very truly yours, i
e hdez.
C. W.
Schroeder Nuclear Licensing Administrator l
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NRC Resident Inspector - LSCS j
M.D.
Ly n c h, Proj. Manager
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3.
ECCS Relief Valve Discharge Lines Below tne Suppression Pool Level 3.1 Tne design of the STRIDE plant did not consider vent clearing, condensation oscillation and cnugging loads whicn mignt be produced by the actuation of these relief valves.
Response
Ef f ects of RHR heat excnanger relief valve discharge into the suppression pool were considered in the design of LaSalle.
- However, tne loads were predicted to be insignificant or bounded by other loads, a.
Vent Clearing Relief valve lines discnarge througn ramshead devices ten feet below normal water level.
Discnarge tnrougn these ramsneads is directed norizontally along the containment wall.
No piping or structures lie in the patn of the ramsnead discharge.
Furtnermore, no piping or supporting steel are within 7 vertical feet of these ramsheads except downcomers whicn are not in tne patn of discnarging fluid.
Hence, no significant external loads will result from clearing of these lines.
b.
Air Clearing Tne air discharge througn the RHR discharge line produces an air bubble whicn loads components in the suppression close to tne discharge exit.
The maximum loading is on the pool boundary and is only 55% of the design basis load.
Tne downcomers column and downcomer bracing was also examined and all of the loads were well below the design basis loads.
c.
Steam Condensation Steam condensation vibration pnenomena can occur if hign-pressure, nigh-temperature steam is continuously discharged into the pool at high-mass velocity tnrough ramshead discharge devices, wnen tne pool is at elevated temperatures.
Tnese steam quenching vibrations may result in loads on pool coundaries and submerged structures.
ASME rated capacity tnrough the RHR relief valve is about 50 pounds /sec wnich is less than 20% of tne capacity of eacn MSRV line.
Due to tne substantially lower steam flow in the RHR relief lines and administrative controls to prevent neat addition to tne suppression pool sucn as this postulated scenario during nign pool temperatures, loads resulting from sucn steam condensation phenomena are judged to be insignificant.
Tne mass flux of tne RHR discharge is approximately 150 lbm/sec-ft 2 and examining tne condensation map in tne DFFR, Revision 2, at tne low pool temperature during tnis discnarge, steam condensation is smootn and steady.
This is the zone in which the discharge normally operates.
3.2 The STRIDE design provided only nine inches of submergence above tne RHR relief valve discharge lines at low suppression pool levels.
Response
At low suppression pool levels approximately ten feet of submergence is provided for tne RHR relief valve discharge lines (DAR Figures 1.1-3 and 1.1-4).
This submergence will provide for ample mixing and complete condensation of effluent from the discharge lines.
3.3 Discharge from the RHR relief valves may produce bubble discharge or other submerged structure loads on equipment in the suppression pool.
Response
We predict RHR relief valve discharge response amplitude and frequency content to be bounded by loads already in the LaSalle design basis.
Several sets of test data for ramshead air discnarges (e.g. Quad Cities and Monticello tests), snow a linear dependency of bubble pressure (and therefore air bubble loads) with air volume or mass.
RHR relief valve discharge lines represent small air volumes (typically 20-25%) as compared to MSRV discharge line air volumes.
As a result the RHR bubble source strengths are expected to be 25% of the MSRV first actuation source strengths.
Tne RHR source strengths are lower due to the reduced bubble pressure.
Consequently, submerged structure loads and pool boundary loads resulting from tnese RHR relief valve discnarges are substantially less tnan for corresponding design basis loads.
It has been found that RHR air bubble load magnitudes on sucn structures as adjacent downcomers, support columns, bracing pipes and pool walls are f rom 15-55% depending on proximity of tne corresponding targets to the RHR discharge points of their corresponding design basis magnitudes f or these targets.
Hence, RHR air bubble loads are well within the previously considered design basis f rom tne point of view of amplitude.
Frequency (f) of air bubble oscillation as a f unction of air mass (m) can be expressed as:
f~ m-1/3 Since tne RHR relief line air masses are tne order of 25% of MSRV line air masses tne above expression would predict RHR air bubble frequencies of about 1.6 times corresponding MSRV air bubble frequencies.
Nominal MSRV air bubble frequencies are typically around 5-6 nertz.
Tneref ore, RHR air DuDble f requencies of near 8-9.6 nertz might be expected, wnich is witnin the 3.4 hertz to 9.9 hertz range considered in the design basis. ;
3.4 The RHR neat exchanger relief valve discharge lines are provided with vacuum breakers to prevent negative pressure in the lines wnen discharging steam is condensed in the pool.
If the valves experience repeated actuation, the vacuum breaker sizing may not be adequate to prevent drawing slugs of water back through tne discnarge piping.
These slugs of water may apply impact loads to the relief valve or be discharged back i7to the pool at tne next relief valve actuation and apply impact loads to submerged structures.
Response
Repeated actuation of RHR relief valves is highly unlikely.
The nature of tnis event is such that the valve would lift and remain open until the heat excnanger was isolated or reactor pressure was reduced.
The low probability notwithstanding tne vacuum breaker valves are sized such tnat tney will limit tne amount of water being drawn back into the relief line after the relief valve closed.
A maximum of approximately 2.0 feet of water is anticipated in tne discharge line after the valve closes.
The vertical height of the discharge line before tne vacuum breaker valve is 4'-8".
Tnis height is sufficient to account for tne reflood of water in tne discnarge line.
Tne additional 2.0 feet during a subsequent actuation will not result more significant loads than tnose mentioneo in the response to question 3.2.
3.5 N/A for Mark I and II Containments
Response
The LaSalle plant does not have an upper pool dump capability.
3.6 If tne RHR neat exchanger relief valves discnarge steam to the upper levels of tne suppression pool following a design basis accident, tney will significantly aggravate suppression pool temperature stratification.
Response
The discnarge lines are submerged 10 feet below the suppression pool surface.
Tne suppression pool is 26 feet deep and the discharge of any not effluent into the suppression pool at the low submergence will provide for ample mixing and not cause stratification within tne pool.
During a LOCA, the RHR neat exchanger is not utilized in tne steam condensing mode which negates any stratification in the pool.
The steam condensing mode is only used during a controlled and normal operating condition.
At this time, the RHR steam condensing mode is in use, the suppression pool is at its low normal operating temperature.
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3.7 The concerns related to the RHR heat exchanger relief valve disenarge lines should also be addressed for all other relief lines that exhaust into pool.
(p. 132 of 5/27/82 transcript)
Response
Other than main steam SRV and RHR heat exchanger relief valves, only tne RCIC turDine exhaust line may discharge steam into the suppression pool.
The exnaust line has a diameter of 10 inches and is submerged 10 feet below the suppression pool low water level.
Tnis discharge is a very low energy discharge and is estimated not to cause appreciable loads or stratification in the pool.
The maximum operating condition of the discnarge line is saturated steam at 10 psig (1160.7 Btu /lbm) at a rate of 7.8 lbm/sec.
Inis rate is approximately 3% of the capacity of eacn MSRV line.
The MSRV discharge loads bounds the RCIC turbine discnarge.
All of tne otner discharge lines other than the MSRV only discharge water well below tne water surface.
4.
Suppression Pool Temperature Stratification 4.1 The present containment response analyses for drywell break accidents assume that the ECCS systems transfer a significant quantity of water from the suppression pool to the lower regions of tne drywell througn tne break.
This results in a pool in the drywell which is essentially isolated from the suppression pool at a temperature of approximately 1350F.
The containment response analysis assumes that the drywell pool is thorougnly mixed with the suppression pool.
If the inventory in the drywell is assumed to be isolated and tne remainder of the heat is discharged to the suppression pool, an increase in bulk pool temperature of 100F may occur.
(1)*
Response
Tne downcomers are raised 6 inches above the drywell floor (FSAR Figure 3.8-3) 50 the amount of water that would be trapped on the drywell floor is equal to 2% of the minimum suppression pool volume.
If the temperature of the suppression pool was raised from its initial value of 1000F to its upper limit of approximately 2000F, an additional rise of 20F would be expected.
The case of a pipe break inside containment is not the worst case for containment temperature response and an increased final temperature for tnis case is not significant.
Osee footnotes on page 18 4.2 The existence of the drywell pool is predicated upon continuous operation of the ECCS.
Tne current emergency procedure guidelines require tne operators to throttle ECCS operation to maintain vessel level below level 8.
Consequently, the drywell pool may never be formed.
(2) i
Response
No credit is taken for formation of a pool of water on the drywell floor at LaSalle.
If a pool is formed, the effect is negligible.
4.3 All Mark III analyses presently assume a perfectly mixed uniform suppression pool.
Tnese analyses assume that the temperature of the suction to the RHR heat exchangers is the same as tne bulk pool temperature.
In actuality, the temperature in the lower part of tne pool where the suction is located will be as much as 7 1/20 cooler than tne bulk pool temperature.
Thus, the heat-transfer through the RHR heat exchanger will be less than expected.
Response
A lower heat exchanger inlet temperature will reduce the heat removal rate, nowever tne effects of this are negligible.
Stratification effects are discussed elsewnere in this response; high pool temperature is a concern related to steam condensation stability.
Unstable steam condensation can be observed at hign pool temperatures above 2000F and 2100F (depending on mass flux) during SRV discharges.
Tne postulated 7 1/20F difference between RHR suction and bulk pool temperature will abate the steam condensation concern it creates.
LaSalle DAR Cnapter 6 provides pool temperature response data.
In the worst case, isolation / scram - loss of 1 RHR loop, the peak pool temperature was conservatively predicted to be 1870F.
This peak temperature was predicted to occur late in tne event when the maximum bulk pool temperature limit is 2100F.
If the 1870F were translated up 70F to 1940F, safety limits are not exceeded.
4.4 Tne long term analysis of containment pressure / temperature response assumes that the wetwell air space is in thermal equilibrium with the suppression pool water at all times.
Tne calculated bulk pool temperature is used to determine the air space temperature.
If pool thermal stratification were considered, the surface temperature, wnicn is in direct contact with the air space, would be nigner.
Therefore, the air space temperature (and pressure) would be higher.
Response
Tne submergence of all tne discharge piping into tne suppression pool is of such depth to provide for ample mixing.
Tnis will provide for uniform suppression pool temperature.
In addition the maximum wetwell air space pressure is governed by short term effect of a DBA.
The effect of slightly higher long term pressure is insignificant. A
4.5.
A number of factors may aggravate suppression pool thermal stratification.
Tne chugging produced through the first row of norizontal vents will not produce any mixing from the suppression pool layers below tne vent row.
An upper pool dump may contribute to additional suppression pool temperature stratification.
Tne large volume of water f rom the upper pool f urther submerges RHR neat exchanger effluent discharge which will decrease mixing of the notter, upper regions of the pool.
Finally, operation of the containment spray eliminates the neat exchanger effluent discharge jet wnich contributes to mixing.
(3)
Response
Although LaSalle's RHR suction and discharge are in the bottom half of the pool, we expected adequate mixing because of their opposing locations.
During tne operation of the wetwell spray to cool the wetwell air space, full flow through the RHR heat exchanger is utilized.
Tne excess flow not required for spray operation is diverted into tne suppression pool providing an effluent discharge jet which contributes to mixing.
No otner LaSalle design features contribute to pool statification.
4.6 The initial suppression pool temperature is assumed to be 950F while the maximum expected service water temperature is 900F for all GGNS accident analyses as noted in FSAR table 6.2-50.
If the service water temperature is consistently higher than expected, as occurred at Kuosneng, the RHR system may be required to operate nearly continuously in order to maintain suppression pool temperature at or below tne maximum permissible value.
Response
We are confident tnat the occurrence of maximum service water temperature is a short term event and regular RHR pool cooling will not be required for station operation.
LaSalle service water comes from the cooling lake whicn is similar to otner Commonwealtn Edison cooling lakes.
Peak temperatures have been observed to be of short duration.
Nevertneless, tne RHR neat excnangers and pumps are designed for long term continuous operation should it be required to maintain low suppression pool temperatures.
4.7 All analyses completed for the Mark Ill are generic in nature and do not consider plant specific interactions of the RHR suppression pool suction and discharge.
Response
No adverse interactions of tne RHR suppression pool suction and discharge effect conclusions of the generic pool temperature analyses.
Tne suction and disenarge for both RHR trains are located approximately 1300 apart for RHR train A and 700 apart f or RHR train B at a radius of approximately 40 feet.
Discharge velocity is near 4 feet per second.
Tnis is a sufficient distance between the suction and discnarge and discnarge velocity to provide for ample mixing. J
4.8 Operation of the RHR system in the containment spray mode will decrease the heat transfer coefficient through the RHR heat excnangers due to decreased system flow.
The FSAR analysis assumes a constant neat transfer rate f rom the suppression pool even with operation of-the containment spray.
Response
Because of near constant flow rates tnrough the RHR heat exchanger regardless of mode, operation of RHR in the containment spray mode will not adversely affect the heat removal rate of RHR.
When the drywell spray is initiated, tne flew througn the RHR heat exchanger is approximately equal to its normal flow.
Tnis will not decrease the neat transfer coefficient drastically.
The slightly reduced flow will provide for additional cooling of tne spray water.
During the wetwell spray operation, full flow is utilized througn tne RHR heat exchanger.
Tne flow not required for the wetwell spray is diverted back into the suppression pool.
During this mode of operation the heat transfer coefficient is not reduced.
4.9 Ine effect on tne long term containment response and the operability of the spray system due to cycling the containment sprays on and off to maximum pool cooling needs to be addressed.
Also provide and justify the criteria used by the operator for switching from the containment spray mode to pool cooling mode, and back again.
Response
Tne two modes of RHR (pool cooling and wetwell spray) run concurrently by procedure at LaSalle.
This practice nas been observed to minimize stratification and mode switening effects.
4.10 Justify that the current arrangement of the discnarge and suction points of tne pool cooling system maximizes pool mixing.
Response
Maximization of system performance has never been a design criteria for LaSalle's RHR.
Design adequacy is met by maximizing distances between suctions and discharges and sufficient discharge velocity to allow thermal mixing.
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5.
Drywell to Containment Bypass Leakage S.1 Tne worst case of drywell to containment bypass leakage has been established as a small break accident.
An intermediate break accident will actually produce the most significant drywell to containment leakage prior to initiation of containment sprays.
Response
Although an intermediate break may produce a greater amount of leakage, tne effects of bypass leakage were found most severe for a small break.
FSAR Section 6.2.1.1.5 describes the effects of suppression pool bypass on containment pressure.
Tne most limiting conditions for bypass leakage are tnose primary break sizes which do not cause rapid reactor depressuriza(ion.
This corresponds to breaks of less tnan approximately 0.4 ft'.
FSAR Figure 6.2-14 show the allowable leakage capacity as a function of primary system break area.
5.2 Under Tecnnical Specification limits, bypass leakage corresponding to A/ 3SI = 0.1 ft2 constitutes acceptable operating conditions.
Smaller-tnan-IBA-sized breaks can maintain break flow into the drywell for long time periods, nowever, because of the RPV would be depressurized over a 6 hour6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> period.
Given, for example, an SBA with A/3fR = 0.1, project time period for containment pressure to reacn 15 psig is 2 nours.
In tne latter 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> of tne depressurization the containment would presumably experience ever-increasing overpressurization.
(4)
Response
Allowable steam Dypass leakage capacity for all break sizes is provided in FSAR Figure 6.2-14.
Using conservative assumptions, containment pressurization predictions are made in FSAR 6.2.1.1.5 snowing ample time for operator action to mitigate bypass leakage consequences.
5.3 Leakage from the drywell to containment will increase tne temperature and pressure in tne containment.
The operators will have to use the containments spray in order to maintain containment temperature and pressure control.
Given tne decreased effectiveness of the RHR system in accompisning tnis objective in the containment spray mode, the bypass leakage may increase the cyclical duty of tne containment sprays.
Response
Tne response to item 4.8 establisned that tnere is no decreased effectiveness of the RHR system during operation of the wetwell spray mode and the response to item 4.9 described concurrent operation of pool cooling and spray modes.
LaSalle's RHR will not experience any adverse cycling effects from bypass leakage. )
5.4 Direct leakage f rom tne drywell to the containment may dissipate nydrogen outside the region where the hydrogen recombiners take suction.
Tne anticipated leakage exceeds the capacity of the drywell purge compressors.
This could lead to pocketing of hydrogen wnicn exceeds the concentration limit of 4% by volume.
(5)
Response
LaSalle containment is inerted, therefore the described phenomenon is not an issue.
5.5 Equipment may be exposed to local conditions whicn exceed the environmental qualification envelope as a result of direct drywell to containment bypass leakage.
Response
Tnere is no equipment in the wetwell which could be affected by bypass leakage.
Also, the design conditions for tne drywell and wetwell for LaSalle are more comparable than those for a Mark III design.
5.8 Tne possibility of high temperatures in the drywell without reacning the 2 psig nign pressure scram level because of bypass leakage througn tne drywell wall snould be addressed.
Response
An alarm will alert tne reactor operator of a high drywell temperature.
If tne drywell air temperature exceeds 1350F the operator is instructed to reduce it to within the limit or proceed to a hot and then cold shutdown.
Bypass leakage as described above would delay the containment pressurizationongneorderofsecqndsbecauseofaslightlygreater volume (386,600 ft vs. 221,500 ft3) if the wetwell air space is 1
included.
Tne delay notwitnstanding, operator guidance is provided to limit containment temperature.
No adverse nign temperature effects due to bypass leakage are predicted.
6.
RHR Permissive on Containment Spray 6.1 We understand tnat GE has recommended f or Mark III containments that tne comoustible gas control systems be activated if the reactor vessel water level drops to witnin one foot of the top of tne active fuel.
Indicate what your facility is doing in regard to this recommendation.
Response
Tnis is not applicable to tne LaSalle plant.
The LaSalle containment is inerted.
Tnis recommendation was not made to LaSalle.
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6.2 General Electric nas recommended tnat an interlock be provided to require containment spray prior to starting the recombiners because of tne large quantities of neat input to the containment.
Incorrect implementation of this interlock could result in inability to operate the recombiners witnout containment spray.
(5)
Response
There is no interlock between the wetwell spray and the recombiner.
6.3 The recombiners may produce " hot space" near the recombiner exnausts which might exceed the environmental qualification envelope or tne containment design temperature.
(5)
Response
The LaSalle containment is inerted and it is not expected that the recombiner will De used.
However, if tne recombiner is operated its exnaust will be cooled to below 2500F prior to its release to the wetwell.
Tnere is no equipment present in tne wetwell which could be affected by the recombiner exhaust.
The wetwell air space is a large open area which provides for ample mixing.
l 6.4 For the containment air monitoring system furnisned by General Electric, the analyzers are not capable of measuring hydrogen concentration at volumetric steam condensation above 60%.
Effective measurement is precluded by condensation of steam in the equipment.
Response
Tne analyzers used f or tne air monitoring system are kept at a temperature of 3000F.
This precludes any condensation of steam in the equipment.
6.5 Discuss the possibility of local temperatures due to recombiner operation oeing higher than the temperature qualification profiles
'for equipment in tne region around and above the recombiners.
State what instructions, if any, are available to the operator to actuate containment sprays to keep this temperature below design values.
Response
Tne recombiners are not located in the containment.
They are located i
in tne reactor building and the heat produced by their operation is such that the temperature produced from the heat released is below the environmental temperature envelope.
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7.
Containment Pressure Response 7.1 The wetwell is assumed to be in thermal equilibrium with a perfectly mixed, uniform temperature suppression pool.
As noted under topic 4, the surface temperature of tne pool will be higher tnan the bulk pool temperature.
This may produce nigher tnan expected containment temperatures and pressures.
Response
The peak containment pressure and temperature occurs briefly within the first 20 seconds of a DBA.
During tnis time there is a large amount of mixing in the wetwell and the ability of tne pool to stratify is very small.
Tne peak containment pressure and temperature will not increase due to ample mixing and tne short duration wnen the peak conditions occur.
The minimal long term effects of slightly higher temperatures and pressures can be mitigated by wetwell spray.
7.2 Tne computer code used by General Electric to calculate environmental qualification parameters considers heat transfer from the suppression pool surface to the containment atmosphere.
Tnis is not in accordance with the existing licensing basis f or Mark III environment qualification.
Additionally, the bulk suppression pool temperature was used in the analysis instead of the suppression pool surface temperature.
(6)
Response
The environmental parameters for the wetwell are described in FSAR Appendix M, Section M.4.1.1.
The wetwell conditions are based on tne long-term bases, rather tnan in tne first few moments following a LOCA.
Only the suppression pool, uniformly mixed, was considered in the analyses and it was assumed that the wetwell air space would be equal to tne bulk suppression pool temperature.
The envelope was conservatively determined based on tne above and is snown in Table M.4-3.
The neat transfer from suppression pool to atmospnere is inconsequential because tnere is no equipment in the wetwell air space.
7.3 Tne analysis assumes tnat the wetwell air space is in thermal equiliorium witn tne suppression pool.
In the short term this is non-conservative for Mark III due to adiabatic compression effects and finite time required for heat and mass to be transferred Detween the pool and containment volumes.
(6)
Response
During pool swell, isentropic compression is assumed for the wetwell air space.
No neat or mass transfer is considered between tne suppression pool and the wetwell air space.
The pool swell analysis is performed to determine the maximum pool swell heignt to maximize the pool swell load and is not used to determine environmental parameters.
Since tne pool swell transient is of short duration, approximately two seconds, it is judged that the heat and mass transfer effects will be small and will not affect tne pool swell transient.
The determination of tne environmental parameters and reasons why this is inconsequential are given in tne response to question 7.2.
8.
Containment Air Mass Effects 8.1 This issue is based on consideration that some Tech Specs allow operation at parameters values that differ from the values used in assumptions for FSAR transient analyses.
Normally analyses are done assuming a nominal containment ual to ambient (0 pressureegF)anddonot 4
psig) a temperature near maximum operating (90 limit the drywell pressure equal to the containment pressure.
Tecn Specs limit operation under conditions such as a positive containment pressure (1.5 psig), temperatures less than maximum (60 or 700F) and drywell pressure can be negative with respect to the containment (-0.5 psid).
All of these differences would result in j
transient response different than the FSAR descriptions.
Response
Model conservatisms and a bounding design basis justify Tecn Specs that allow operation at conditions different from values used in the FSAR containment transient analyses.
Maximum drywell temperature (1350F) to maximize peak drywell temperature and expected containment pressure i
(0 psig) were used as initial conditions.
I Conservatisms in analytic models used in transient analyses understate design margin.
Although it is reasonable not to always use bounding values, the effect of bounding values would be minimized if a less conservative model were used tnat did not understate design margin.
Tne results of conservative calculations predict containment pressure and temperature below the design basis so that any small increase in the predictions would not change the conclusion of design adequacy.
8.2 The draft GGNS technical specifications permit operation of the plant witn containment pressure ranging between 0 and -2 psig.
Initiation of containment spray at a pressure of -2 psig may reduce the containment pressure by an additional 2 psig wnich could lead to buckling and failures in the containment liner plate.
Response
Tne LaSalle plant technical specificiations permit operation of the plant witn the containment pressure ranging between -0.5 and 2 psig.
Tne initiation of the containment spray at a pressure of -0.5 psig will i
reduce the containment pressure to approximately -3.7 psig (see response to FSAR Question 021.45 where the initial conditions of the drywell and wetwell were -0.75 psig).
Tne containment liner plate is designed to a pressure of -5 psig as snown in FSAR Table 3.8-11, Page 3.8-76.
The design will take into account the effect of the i
containment spray actuation.
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8.3 If tne containment is maintained at -2 psig, the top row of vents could-admit blowdown to tne suppression pool during an SBA without a LOCA signal being developed.
(7)
Response
Not applicable to Mark II plants.
8.4 Describe all of the possible methods both before and after an accident of creating a condition of low air mass inside the containment.
Discuss tne effects on the containment design external pressure of actuating the containment sprays.
Response
During normal operation, automatic controls provide an inerted atmospnere in both drywell and wetwell.
During accident conditions, calculations predict containment pressure response due to spray actuation (see response to 8.2).
Only one scenario provides possibility of creating conditions mentioned above-venting containment witnout allowing purging air in.
This is done only under iminent containment failure past the point of containment buckling concerns.
9.
Final Drywell Air Mass 9.1 Tne current FSAR analysis is based upon continuous injection of relatively cool ECCS water into the drywell through a broken pipe following a design basis accident.
Since the operator is directed to throttle ECCS operation to maintain the reactor vessel water level to about the level of tne steam lines, the break will be releasing saturated steam instead of releasing relatively cool ECCS water.
Tnerefore, tne drywell air which would have been purged and tnen drawn back into tne drywell, will remain in the wetwell and higher pressures than anticipated will result in both the wetwell and tne drywell.
Response
Tne maximum containment pressure is controlled by a recirculation line break, all drywell atmosphere is assumed blown down to the wetwell.
Tne pressure peaks in the snort term while mass is still flowing tnrough the downcomers.
The ef fect of slowly blowing down tne drywell atmosphere to the wetwell is clearly bounded by the recirc line break.
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9.2 The continuous steaming produced by tnrottling the ECCS flow will cause increased direct leakage from the drywell to the wetwell.
Tnis could result in increased wetwell pressures.
Response
In the event that tne wetwell pressure will increase due to direct leakage from tne drywell during ECCS throttling, the EPG's indicate at what conditions the wetwell spray should be initiated.
The RHR wetwell spray mode can mitigate the effects of prolonged leakage into the drywell having no effect or suppression pool cooling.
9.3 It appears tnat some confusion exists as to wnether SBA's and stuck open SRV accidents are treated as transients or design basis accidents.
Clarify how they are treated and indicate whether the initial conditions were' set at nominal or licensing values.
Response
Tne SBA is treated as a design basis accident (FSAR Section 6.2.1.1.3.1.4) and stuck open SRV accidents are treated as transients (FSAR Section 15.6.1).
Tne SBA and stuck open SRV accident utilize licensing initial conditions.
11.
Operational Control of Drywell to Containment Differential Pressures Mark III load definitions are based upon the levels in the suppression pool and the drywell weir annulus being tne same.
Tne GGNS technical specifications permit elevation differences between these pools.
This may effect load definition for vent clearing.
(8) 1
Response
Tecn Specs limit operation under conditions of wetwell pressure greater tnan drywell pressure over 0.5 psi.
The small increase in vent water level will not cause significant changes in predicted loads.
i
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14.
RHR Backflow Through Containment Spray A failure in tne cneck valve in the LPCI line to the reactor vessel could result in direct leakage from tne pressure vessel to the containment atmosphere.
This leakage might occur as the LPCI motor operated isolation valve is closing and the motor operated isolation valve in the containment spray line is opening.
This could produce unanticipated increases in tne containment spray.
Response
Tne failure of the check valve in the LPCI line will not result in direct leakage from the pressure vessel to the containment atmosphere through the containment spray header.
There are two motor operated isolation valves in series in the containment spray line.
An interlock is provided between these valves and the LPCI motor operated isolation valve.
The containment spray line isolation valves can not begin to open unless tne LPCI isolation valve is fully closed.
Tnis precludes any flow into tne spray line due to a check valve failure in the LPCI line.
15.
Secondary Containment Vacuum Breaker Plenum Response The STRIDE plants had vacuum breakers between the containment and the secondary containment.
With sufficiently high flows through tne vacuum breakers to containment, vacuum could be created in the secondary containment.
Response
Tnere are no vacuum breaker valves between containment and the secondary containment (reactor building).
16.
Effect of Suppression Pool Level on Temperature Measurement Some of tne suppression pool temperature sensors are located (by GE recommendation) 3" to 12" below the pool surface to provde early warning of nigh pool temperature.
However, if the suppression pool is drawn down below the level of tne temperature sensors, the operator could be misled by erroneous readings and required safety action could be delayed.
Response
When the suppression pool water level reaches 2.0 inches below the minimum water level, an alarm sounds.
At this time the operator must take action to shutdown the reactor or restore water level to the minimum of 2.0 incnes below tne minimum water level.
Tne pool temperature sensors are located approximately 1.0 feet below the minimum suppression pool level and, therefore, the sensors are submerged under all operating conditions.
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17.
Emergency-Procedure Guidelines The EPGs contain a curve which specifies limitations on suppression pool level and reactor pressure vessel pressure.
The curve presently does not adequately account for upper pool dump.
At present, the operator would be required to initiate automatic depressurization when the only action required is the opening of one additional SRV.
(9)
Response
1 LaSalle Power-Plant nas no upper pool that could be dumped into the suppression pool.
If, however, the suppression pool water level rises, at a given reactor pressure, above the suppression pool load limit for i
whatever reason, the operator is instructed, to restore and maintain the water level below the suppression pool load limit or, if that cannot be done, to maintain the reactor pressure below the limit.
18.
Effects of Insulation Debris (10) 18.1 Failure of reflective insulation in the drywell may lead to blockage of the. gratings above the weir annulus.
This may increase the pressure required in the drywell to clear the first row of j
drywell vents and perturb the existing load definition.
Response
The existing load definitions will not be changed due to the effect of insulation blockage of downcomers.
The downcomers are equipped with caps and it is not believed that blockage of the downcomers or the extensive gratings above the downcomer can occur.
The controlling parameter in containment pressurization during a blowdown is the loss coefficient of the downcomer vent deflection shield.
The area of the grate above the vents is greater than ten times the vent area.
Any plausible restriction due to insulation blockage'is clearly insignificant in the flow pressure drop from drywell to wetwell.
18.2 Insulation debris may be transported through the vents in the drywell wall into the suppression pool.
This debris could tnen cause blockage of tne suction strainers.
Response
LaSalle drywell piping insulation is stainless steel casing with thin rigid stainless steel spacers.
Its strength is expected not to allow creation of many small pieces which would be transported into the suppression pool.
Furtner strainer design allows system operation with 3
50% blockage.
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21.
Containment Makeup Air for-Backup Purge Regulation Guide 1.7 requires a backup purge H2 removal capability.
This backup purge for Mark III is via the drywell purge line which discharges to the shield annulus which in turn is exhausted througn the standby gas treatment system (SGTS).
The containment air is blown into the drywell via tne drywell purge compressor to provide a positive purge.
The compressors draw from the containment, however, witnout hydrogen lean air makeup to the containment, no reduction in containment hydrogen concentration occurs.
It is necessary to assure tnat tne shield annulus volume contains a nydrogen lean mixture of air to be admitted to the containment via containment vacuum breakers.
For Mark I and II facilities, discuss the possibility of purge exnaust being mixed with the intake air whicn replenishes the containment air' mass.
Response
Primary containment makeup is from the nitrogen inerting system or the secondary containment.
The primary containment purge exhaust is through the standby gas treatment system to the vent stack.
The purge exhaust, therefore, cannot be mixed witn the primary containment makeup.
22.
Miscellaneous Emergency Procedure Guideline Concerns The EPGs currently in existence have been prepared with the intent of coping witn degraded core accidents.
They may contain requirements conflicting with design basis accident conditions.
Someone needs to carefully review the EPG's to assure that they do not conflict with tne expected course of the design basis accident.
Response
The EPG is prepared to nandle all accident conditions and therefore are symptom oased.
Tne guidelines were reviewed by GE owners' representative and tne NRC.
I i
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v.
l TABLE OF FOOTNOTES APPLICABLE TO MARK I AND MARK II CONTAINMENTS Footnote Comment 1
Tnis concern is related to the trapping of water in the drywell.
t 2
Tnis issue applies only to those facilities for whicn EPG's are in effect.
[
3 For Mark I and II facilities, confine your response on tnis issue to those concerns which can lead to pool stratification (e.g., operation of the containment spray).
t 4
For Mark I and II facilities, refer to Appendix I to Section 6.2.1.lc of the Standard Review Plan (SRP).
5 This concern applies to those facilities at which
[
nydrogen recombiners can be used.
6 Tnis issue as phrased applies only to a Mark III facility.
However, the concern can be generalized and applied to the earlier containment types.
For Mark I and II facilities, indicate wnat metnodology was used to calculate the environmental qualification parameters including a discussion of heat transfer between the atmosphere in the wetwell and the suppression pool.
l i
7 Not applicable to Mark II facilities.
8 For Mark I and II f acilities, consider tne water i
in the downcomers.
9 This issue as phrased applies only to a Mark III facility.
However, tne concern can be generalized.
Accordingly, discuss what actions the reactor operator would take in the event that the limitations on the suppression pool level and tne pressure in the reactor vessel are violated.
I 10 This issue as phrased applies only to a Mark III facility.
However, the concern can be generalized.
Accordingly, discuss now the effects of insulation debris could perturb existing load definitions or could block suction strainers.
In responding to this issue, you may refer to existing generic studies; e.g.,
the study done for the Cooper facility.
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