View source for AECM-82-321, Forwards Descriptions of Actions Planned for Resolving Concerns Raised by J Humphrey.Formal Program Results Will Be Provided by 820819,1001 & 1101

{{Adams
| number = ML20055A581
| issue date = 07/15/1982
| title = Forwards Descriptions of Actions Planned for Resolving Concerns Raised by J Humphrey.Formal Program Results Will Be Provided by 820819,1001 & 1101
| author name = Dale L
| author affiliation = MISSISSIPPI POWER &amp; LIGHT CO.
| addressee name = Denton H
| addressee affiliation = NRC OFFICE OF NUCLEAR REACTOR REGULATION (NRR)
| docket = 05000416, 05000417
| license number = 
| contact person = 
| document report number = AECM-82-321, NUDOCS 8207190205
| document type = CORRESPONDENCE-LETTERS, INCOMING CORRESPONDENCE, UTILITY TO NRC
| page count = 47
}}

=Text=
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B O X 164 0, J AC K S O N. MIS SIS SIP PI 3 9 2 05 NUCLEAR PROOUCTION DEPARTMENT July 15, 1982 U.S. Nuclear Regulatory Commission Office of Nuclear Reactor Regulation Washington, D.C.         20555 Attention:       Harold R. Denton, Director

==Dear Mr. Denton:==

Grand Gulf Nuclear Station Units 1 and 2 Docket Nos. 50-416 and 50-417 File: 0260/0272/L-860.0 Action Plans for Resolution of Humphrey's Concerns AECM-82/321 Mississippi Power and Light Company (MP&L) committed to provide the Nuclear Regulatory Commission (NRC) staff with descriptions of the actions planned to provide final resolution of the concerns raised by Mr. John Humphrey.
Attachment one to this letter provides summaries of the work which MP&L has undertaken to respond to Mr. Humphrey's concerns and to address formal questions which were transmitted from the NRC to MP&L by Mr. Al Schwencer's {{letter dated|date=July 7, 1982|text=letter dated July 7, 1982}}. Attachment 2 provides a cross reference showing the action plans in which each of Mr. Humphrey's concerns will be addressed and the action plans in which the NRCs questions will be answered.
MP&L's anticipated schedules for submitting to the NRC information which is developed during completion of the planned activities are included in Attachment 1. MP&L intends to group the results of this program into submittals on August 19, 1982, October 1, 1982, and November 1, 1982. The August 19, 1982 submittal will include preliminary results for analyses which will be submitted in October and November where appropriate, a summary of assumptions being used in all analyses, and comprehensive descriptions of analytical methodology. This submittal will also include justification for operating the Grand Gulf Nuclear Station at full power pending completion of the work which will continue after issuance of the full power license.
MP&L has reviewed a letter and miscellaneous attachments dated June 17, 1982 JE         which Mr. Humphrey sent to Mr. Al Schwencer at the NRC. This letter contained m o.       some additional clarifications of Mr. Humphrey's concerns based upon the S8 meeting involving the NRC, Mr. Humphrey, and MP&L on May 27, 1982.
Attachment 3 to this letter provides MP&L's responses to Mr_ Humphrey's hDD[
o        clarifications of his concerns. MP&L has provided a numbering system
$3:        compatable with the existing issue numbering scheme for the clarifications
@8         discussed in Attachment 3, however, we do not consider these items to be
 &c        additional concerns. Based upon these responses and the work described in 7         Attachment one which MP&L has undertaken to resolve Mr. Humphrey's. concerns,
 @@        MP&L does not believe that any additional effort is required to address these mo.o-     clarifications.
Member Middle South Utilities System     ,

1 MICOISSIPPI POWER O L12HT COMPANY i
AECM-82/321 July 15, 1982 MP&L remains committed to providing resolutions to Mr. Humphrey's concerns that are satisfactory to the NRC. As attachment one to this letter
;             demonstrates, MP&L has undertaken a substantial program to provide appropriate resolutions.      If you need any additional clarifications of MP&L's program, please contact me.
Yours very truly, L. F. Dale Manager of Nuclear Services RWE/JDR:tlj cc: Mr. N. L. Stampley, (w/a)
Mr. G. B. Taylor, (w/a)
Mr. R. B. McGehee, (w/a)
Mr. T. B. Conner, (w/a)
Mr. Richard C. DeYoung, Director Office of Inspection and Enforcement U.S. Nuclear Regulatory Commission Washington, D.C. 20555
 ;                   Mr. J. P. O'Reilly, Regional Administrator Office of Inspection and Enforcement U.S. Nuclear Regulatory Commission, Region II 101 Marietta St. , N.W. Suite 3100 Atlanta, Georgia 30309 i
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Attachment One f.ECM-82/321 Action Plan 1
: 1. Issues Addressed 1.1 Presence of local encroachments such as the TIP platform, the drywell personnel airlock and the equipment and ficor drain sumps may increase the pool swell velocity by as much as 20
                   -percent.
1.2 Local     encroachments in the pool may cause         the bubble breakthrough height to be higher than expected.
1.4 Piping impact loads may be revised as a result of the higher pool swell velocity.
II. Program For Resolution
,             1.         Provide details of the one-dimensional analysis which was completed and showed a 20% increase in pool velocity.
: 2.         The two-dimensional model will be refined by addition of a bubble pressure model and used to show that pool swell velocity decreases near local encroachments. The code is a version of SOLA.
l             3          The inherent conservatisms in the code and modeling assumptions will be listed.
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: 4.         The modified code will be benchmarked against existing
;                        clean pool PSTF data.
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: 5.         A recognized a'Jthority on hydrodynamic phenomena will be retained to provide guidance on conduct of the analyses.
: 6.         The effects of the presence of local encroachments on pool swell will be calculated with the two dimensional code. Three-dimensional effects (such as bubble break through in non-encroached pool regions) will be included based upon empirical data.
,       III. Schedule Items 1-6 will be completed for submittal on October 1,1982.
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_                                                           _                    .              ~-
i Action Plan 2 I. Issues Addressed                                                                                                       ,
1.3 Additional _ submerged structure                                  loads may be applied to
                          -submerged structures near local encroachments.
II. Program for Resolution
: 1.        The results obtained from the two-dimensional analyses completed as part of the activities for Action -Plan 1 will be used to define changes in fluid velocities in the suppression                                   pool   which   are  created    by        local encroachments.                                  Supporting arguments to verify that the results from two-dimensional cnalyses will be bounding j                              with respect to velocity changes in the suppression pool will be provided.
: 2.        The new pool velocity profiles will be used to calculate revised submerged structure loads using the existing or modified submerged structure load definition models.
: 3.        The newly defined submerged structure loads will be compared to the loads which were used as a design basis for equipment and structures in the Grand Gulf Nuclear Station suppression pool.
III. Schedule-Items 1-3 will be completed for submittal on November 1,1982.
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. Action Plan 3
: 1. Issues Addressed 1.5 Impact loads on the HCU floor may be imparted and- the HCU modules may fail which could prevent successful scram if the bubble breakthrough height is raised appreciably. by local' encroachments.
II. Program for Resolution
: 1.          The analytical   results obtained from the activities completed .under Action Plan 1 will be evaluated.. If the bubble breakthrough height is increased significantly, additional analyses of the structural capabilities of the HCU floor to _ withstand water slug impacts .will be completed.
III. Schedule Item l' will be completed for submittal on October 1,1982.
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Action Plan 4
: 1. Issues Addressed 1.6 Local encroachments or the steam tunnel may cause the pool swell froth to move horizontally and apply lateral loads to the gratings around the HCU floor.
II. Program for Resolution
: 1.        A bounding analysis for determining the horizontal liquid and air flows created by the presence of the steam tunnel and HCU floor will be performed. The forces imposed on the HCU floor supports and grating will be calculated from this information.
: 2.        It will be demonstrated that the affected structures can withstand the calculated loads.
III. Schedule Items 1 and 2 will be completed for submittal on October 1, 1982.
Action Plan 5 I. Issues Addressed 2.1 The annular regions between the safety relief valve lines and the drywell wall penetration sleeves may produce condensation
,                                    oscillation       (C.O.) frequencies -near                      the drywell        and containment wall structural resonance frequencies.
2.2 The potential condensation oscillation and chugging loads produced through the annular area between the SRVDL and sleeve may apply unaccounted for loads to the SRVDL. Since the SRVDL i                                    is unsupported from the quencher to the inside of the drywell
:                                   - wall, this may result in failure of the line.
I 2.3 The potential condensation oscillation and chugging loads produced through the annular area between the SRVDL and sleeve may apply unaccounted for- loads to the penetration sleeve.
,                                    The loads may also be at or near the natural frequency of the sleeve.
II. Program for Resolution
;                         1.         The most expeditious method for resolving these issues for Grand Gulf appears to be sealing the annular vent at the drywell wall. An evaluation of design . modifications to seal the vents is in progress.
i III. Schedule
!                         Item 1 will be completed for submittal on October 1,1982.
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Action Plan 6 I. Issues Addressed 3.1 The design of the STRIDE plant did not consider vent clearing, condensation oscillation and chugging loads which might be i             produced by the actuation of the RHR heat exchanger relief i              valves.
3.7 The concerns related to the RHR heat exchanger relief valve discharge lines should also be addressed for all other relief lines that exhaust into the pool.
II. Program for Resolution
:         1. The vent clearing loads associated with actuation of the RHR i              relief valves will be calculated. The water jet loads will also be calculated. The dynamic loads associated with relief
;-             valve operdion will be recalculated to evaluate relief valve discharge line design.
The following information will be submitted for all relief valves which discharge to the suppression pool.
 ;        2. Isometric drawings and P& ids showing line and vacuum breaker l               location will be provided. This information will include the
  ,            following: The geometry (diameter, routing, height above the l             suppression pool, etc.) of the pipe line from immediately downstream of the - relief valve up to the line exit.       The maximum and minimum expected submergence of the discharge line exit below the pool surface will be included. Also, any lines equipped with load mitigating devices (e.g., spargers, j              quenchers) will be noted.
: 3. The range of flow rates and character of fluid (i.e., air, water, steam) which is discharged through the line and the plant conditions (e.g., pool temperatures) when discharges occur will be defined.
: 4. The sizing and performance characteristics (including make, model, size, opening characteristics and flow characteristics) of any vacuum breakers provided for relief valve discharge lines will be noted.
l l         5. The potential for oscillatory operation of the relief valves in any given discharge line will be discussed.
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: 6. The potential for failure of any relief valve to reseat following initial or subsequent opening will be evaluated.
: 7. The location of all components and piping in the vicinity of the discharge line exit and the design bases will be provided.
III Schedule Item 1 will be completed for submittal on October 1 1982. Items 2-7 will be completed for submittal on August 19, 1982.
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2 Action Plan 7 I                                     1.                   Issues Addressed 3.2 The STRIDE design provided only nine inches of submergence i
above the RHR heat exchanger relief valve discharge lines at low suppression pool levels.
II.                 Program for Resolution
: 1.           The   Humboldt                   Bay    pressure                   suppression                        test   data demonstrated the relationship of discharge submergence on condensation effectiveness. An evaluation based on this data will be submitted which shows that the maximum i                                                                       discharge from the relief valves can be quenched under all possible submergence conditions.
III Schedule                                                                                                                                                  .
i Item 1 will be completed for submittal on October 1,1982.
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Action Plan 8
: 1. Issues Addressed 3.4 The RHR heat exchanger relief valve discharge lines are provided with vacuum breakers to prevent negative pressure in the lines when 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 the discharge piping. These slugs of water may apply impact loads to the relief valve or be discharged back into the pool at the next relief valve actuation and apply impact loads to submerged structures.
3.5 The RHR relief valves must be capable of correctly functioning following an upper pool dump which may. increase the suppression pool level as much as five feet creating higher i
back pressures on the relief valves.
II. Program for Resolution
: 1.              A failure mode analysis on the pressure controller to establish all possible failure modes will be performed.
: 2.              The vacuum breaker performance will           be quantified.
This will include a calculation showing the maximum elevation to which water can be drawn in the RHR relief valve discharge line.
: 3.              An analysis will be completed to establish the water jet and air bubble load which will be created by a first and second actuation of the relief valves.
: 4.              The relief valve performance will be reviewed to assure that a water column in the relief valve discharge line will not adversely effect the performance.
: 5.             All of the above analyses will be repeated for the higher suppression pool levels which would result from upper pool dump.
i             6.             Analyses demonstrating that the heat exchangers are capable of withstanding an overpressure transient will be completed.
III Schedule Item 1 will be completed for submittal on August 19, 1982. Items 2, 3 and 5 will be completed for submittal on October 1,1982.
Items 4 and 6 will be completed for submittal on September 1, 1982, i

T Action Plan 9 I. Issues Addressed                    ,
3.6 If the RHR heat exchanger relief valves discharge steam to the upper levels of the suppression pool following aidesign basis accident, they will significantly aggravate suppression;-pool temper-ature stratification.
                                                                   ?
II. Program for Resolution T.          The maximum quantity of energy which can be added to the suppression pool will tur quantified.        This will include an evaluation of all scenarios which could lead to discharge from these relief valves.      ,
: 2.         The discharge plume from the - relief valves will be investigated. This plume will establish the maximum area of the pool which can be affected.           .
III Schedule Items 1 and 2 will be completed for submittal on October 1,1982.
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Action Plan 10 I. Issues Addressed 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
:                         the drywell through the break. This results in a pool in the drywell which is essentially isolated from the suppression pool at a temperature of approximately 135 F. The containment response i
analysis assumes that the~drywell pool is thoroughly mixed with the suppression pool. If the inventory in the drywell is assumed l                         to be isolated and the remainder of the heat is discharged to the i                        suppression pool, an increase in bulk pool temperature of 10 F may occur.
;              II. Program for Resolution
: 1.           Details of the analysis which predicted a maximum temperature increase of 6 F will be provided. -
;              III Schedule
!                    Item 1 will be completed for submittal on August 19, 1982.
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Action Plan 11                                                j                                 ',            i' *
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Issues Addressed                                                                / '
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1 4.2 The existence of .the drywell                                   pool          is          predicated upon                                                        y continuous operation of the ECCS.                                       The, current emergencyj i                                                                         procedure guidelines require the operitorn, t,o throttle ECCSj operation             to       maintain         vessel                level' ! below level 8. j Consequently, the drywell pool may neve,ri be formed.                                                                                                  s 9.1 The current FSAR analysis is based upon. continuous injection of relatively cool ECCS water into $the drywell through a broken pipe following a design bas'& accicent. The EPG's direct the operator to throttle ECCS' operation to -maintain .                                                                                                              ,
reactor vessel level gt about level 8.                                              Thus , , instead of                                                                    '
releasing relatively cool ECCS water,t tha break will be-                                                                                                                           '
l                                                                         releasing            saturated steam _ which                           might             produce                              higher.                           ,
!                                                                         containment             pressurizations than                           currently; a.iticipated.                                                            "                            !
!                                                                         Therefore, the drywell air which would have been 'drwn back into                                                                                                                ,
the drywell will remain in the containment end higS                                                                                                                            '
will result in both the containment and the drywell.p                                                                g pressures                    ..
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;                                                                   1. Calculations will be submittdd to demonstrate thatifaiiur'e to                                                                                                     6 form the drywell pool will nat entail adverse conseiiuences.                                                                                                                    [
The calculations will . quantify the variation of stdpression
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pool level without formation of the drywelt pool and with                                                                                                   ;
upper pool dump.                             *          -
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l                                                                  2.      Interactions between ESF systein operation and suppressior.jpool level will be reviewed to a'isare that higher suppression . pool                                                                                                              4 level will not degrade'perfonnance.                                                                                                                                                     '
[                                                                  3. A realistic analysis of the effects of failure to recover /the                                                                                                                       ;
l                                                                         drywell air mass will be performed.                                          This analysf5 will .
!                                                                         include the effects of containment heat sinks and ~the:
!                                                                         mitigatingeffectsofcontainment/ spray.           '       '
l III. Schedule                                                                 I           ?
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                                                                                                                        ..                                                      .s                                             s Items 1-3 will be completed for submittal on October 1, 1982.
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Action Plan 12 I.              Issues Addressed 4.3 All Mark III analyses presently assume a perfectly mixed uniform suppression pool. These analyses assume that the i                                                   temperature of the suction to the RHR heat exchangers is the
:                                                   same as the bulk pool        temperature. In actuality,  the j
temperature in the lower part of the pool where the suction is i                                                  located will be as much as 71       cooler than the bulk pool temperature. Thus, the heat transfer through the RHR heat i                                                  exchanger will be less than expected.
;-                         II.            Program for Resolution i
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: 1.             A study will be completed to ident.ify and quantify the major conservatisms which have been used in the analyses
,                                                        of RHR suppression pool cooling performance.
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      .                                  2.              An assessment will be provided of the maximum difference which could exist between the bulk suppression pool I                                                        temperature and the RHR heat exchanger inlet temperature.
 !                 o-Based on existing test data this assessment should show that the difference will be below 71"F. An analysis will l         )                                            be performed to assess the effect of this temperature j                                                        difference on peak pool temperature.
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: 3.              Applicable heat exchanger test data and other test data i                                                        will be reviewed to provide assurance that the correct
:                                     .                  heat exchanger capacity has been used.
l       .                           / i l           _. _           III.rSchedule l                                         Items 1-3 will be completed for submittal on October 1,1982.
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Action Plan 13
: 1. Issues Addressed 4.4 The long term analysis of containment pressure / temperature response assumes that the wetwell airspace is in thermal equilibrium with the suppression pool water at all times. The calculated bulk pool temperature is used to determine the airspace temperature. If pool thermal stratification were considered, the surface temperature, which is in direct contact with the 31rspace, would be higher.      Therefore the airspace temperature (and pressure) would be higher.
7.1 The containment is assumed to be in thermal equilibrium with a perfectly mixed, uniform temperature suppression pool. As noted under topic 4, the surface temperature of the pool will be higher than the bulk pool temperature. This may produce higher than expected containment temperatures and pressures.
II. Program for Resolution
: 1. The maximum increase in bulk suppresion pool temperature which could occur as a result of temperature stratification will be determined from Action Plan 12. The maximum suppression pool surface temperature will be estimated based on the current understanding of thermal stratification as contained in GESSAR. The effects of this higher surface temperature on containment   airspace pressure and temperature will be calculated.
: 2. The conservatism inherent in assuming thermal equilibrium
;             between the containment atmosphere and suppression pool i             surface will be quantified.
l III. Schedule I
!       Items 1 and 2 will be completed for submittal on October 1, 1982.
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Action Plan 14
: 1. Issues Addressed 4.5 A number of factors may aggravate suppression pool thermal stratification. The chugging produced through the first row of horizontal vents will not produce any mixing from the suppression pool layers below the vent row.       An upper pool dump may contribute to additional suppression pool temperature stratification. The large volume of water from the upper pool further submerges RHR heat exchanger effluent discharge which will decrease mixing of the hotter, upper regions of the pool.
Finally, operation of the containment spray eliminates the heat exchanger effluent discharge jet which contributes to mixing.
II. Program for Resolution
: 1. Testing information will be submitted to demonstrate the effectiveness of chugging as a mixing mechanism in the suppression pool.
: 2. Analyses will be submitted or a          test program will be developed to demonstrate that the suppression pool does not experience significant stratification during containment spray or following upper pool dump.
III. Schedule Items 1 and 2 will be completed for submittal on August 19, 1982.
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Action Plan 15
: 1. Issues Addressed 4.6 The initial suppression pcol temperature is assumed to be 95 F while the maximum-expected service water temperature is 90 F 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 Kuosheng, the RHR system may be-required to operate nearly continuously in order to maintain suppression pool temperature at or below the maximum permissible value.
II. Program for Resolution
: 1. A discussion of peak service water temperature which is expected under nonaccident conditions will be provided . Also the expected peak suppression pool temperature under normal operating conditions will be discussed.
: 2. The conservatisms in the existing analyses defining peak service water temperature will be quantified to the -extent possible.
III. Schedule Items 1 and 2 will be completed for submittal on August 19, 1982.
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Action plan 16
: 1. Issues Addressed 4.7 All analyses completed for the Mark III are generic in nature and do not consider plant specific interactions of the RHR suppression pool suction and discharge.
4.10 Justify that the current arrangement of the discharge and suction points of the pool cooling system maximizes pool mixing.   (pp.150-155 of 5/27/82 transcript)
II. Program for Resolution 1.M An analysis will be provided or a test program will be developed to quantify the interaction effects.
III. Schedule Item 1 will be completed for submittal on August 19, 1982, 1982.
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Action Plan 17
: 1. Issues Addressed 4.8 Operation of the RHR system in the containment spray mode will decrease the heat transfer coefficient through the RHR heat exchangers due to decreased system flow. The FSAR analysis assumes a constant heat transfer rate from the suppression pool even with operation of the containment spray.
II. Program for Resolution
: 1.        Additional analyses will be completed which incorporate lower RHR heat exchanger heat transfer coefficients during the period when the RHR system is in the containment spray mode. The analyses will be performed both with and without the presence of the bypass leakage capability.
: 2.        The analyses performed in Item I will be repeated so that the effects of containment heat sinks can be included and quantified. The containment spray will be assumed to be operational only when it is necessary to assure pressure control.
III. Schedule Item 1 and 2 will be completed for submittal on November 1, 1982.

Acticn Plan 18
: 1. Issues Addressed 4.9 The effect on the long term containment response and the operability of the spray system due to cycling the containment sprays on and off to maximize pool cooling needs to be addressed. Also provide and justify the criteria used by the operator for switchino from the containment spray mode to pool cooling mode, and back again.
5.3 Leakage from the drywell to containment will increase the temperature and pressure in the containment. The operators will have to use the containments spray in order to maintain containment temperature and pressure control.           Given the decreased effectiveness of the RHR system in accomplishing this objective in the containment spray mode, the bypass leakage may increase the cyclical duty of the containment sprays.
II. Program for Response
: 1.         A criteria for transferring the RHR system from contdn-ment spray mode to suppression pool cooling mode will he developed.
: 2.         The emergency procedures will be revised to incorporate the criteria.
: 3.         Detailed information on the capability of the valves and valve operators to withstand cyclical duty will          be provided.
III. Schedule Items 1 and 2 will be completed for submittal on October 1, 1982.
Item 3 will be completed for submittal on November 1,1982.
Action Plan 19 I. Issues Addressed 5.1 The 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 I.
drywell to cantainment                     leakage       prior to           initiation of containment spilys.
l                               5.6 The test pressure of 3 psig specified for the periodic
;                                         operational drywell leakage rate tests does not reflect l                                         additional pressurization in the drywell which will result
!                                         from upper pool dump. This pressure also does not reflect additional drywell pressuraization resulting from throttling i                                         of the ECCS to maintain vessel level which is required by the current EPGS.
9.2 The continuous steaming produced by throttling the ECCS flow                                                  !
1                                       will cause increased direct leakage from the drywell to the
{                                         containment.      This could result in increased containment j                                         pressures.
II. Program for Resolution
,                               1.               A complete spectrum of analyses for varying break sizes.
will be completed neglecting depressurization of the l                                                drywell prior to initiation of containment sprays, but including the effects of containment heat sinks.
: 2.               Analyses which will be completed will 'show that the allowable leakage of A/fE equal to 0.9 is valid for Grand Gulf.
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: 3.               An evaluation of the need for redecing the allowable technical specification limiting conditions for drywell leakage will be provided.                       Any revised limit would be based upon a pressure of 6 psig in the drywell which would reflect the additional pressure produced ~ by upper j                                                pool dump.       In the evaluation, credit will be taken for
;                                                drywell and containment heat sinks.
III. Schedule-for Completing NRC Program Items 1 through 3 will be completed for submittal on November 1, 1982.
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Action Plan 20 I. Issues Addressed 5.4 Direct leakage from the drywell        to the containment may dissipate hydrogen outside the region where the hydrogen recombiners take suction. The anticipated leakage exceeds the capacity of the drywell purge compressors. This could lead to pocketing of hydrogen which exceeds the concentration limit of 4% by volume.
II. Program for Resolution
: 1.         The total allowable leakage will be assumed to be released from the electrical penetrations. The potential for pocketing of hydrogen which is contained in this leakage will be reviewed.
III. Schedule Item 1 will be completed for submittal on August 19, 1982.
Action Plan 21
: 1. Issues Addressed 5.5 Equipment may be exposed to local conditions which exceed the environmental qualification envelope as a result of direct drywell to containment bypass leakage.
II. Program for Resolution
: 1. A list of essential equipment located near the drywell wall will be provided.      The list will   include a qualitative assessment of the equipment's sensitivity to temperature and the distance of the equipment from the drywell wall.
III. Schedule Item 1 will be completed for submittal on August 19, 1982.
Action Plan 22
: 1. Issues Addressed 5.8 The possibility of high temperatures in the drywell without reaching the 2 psig high pressure scram level because of bypass leakage through the drywell wall should be addressed.
II. Program for Resolution
: 1.         A new analysis will be performed using the capability bypass leakage. This analysis will show that a temper-ature of 330 F is not reached in the drywell until after ten minutes. In this interval, the operator will have received sufficient information to manually scram the reactor.
: 2.         A detailed list of alarms and parameter displays will be developed which inform the operator of conditions in-the drywell . This will include drywell cooling performance, temperature, airflows, leak detection, etc.
III. Schedule Item I will be completed by for submittal on November 1,1982.
Item 2 will be completed for submittal on August 19, 1982.
Action Plan 23
: 1. Issues Addressed 6.3 The recombiners may produce " hot spots" near the recombiner -
exhausts which might exceed the environmental qualification envelope or the containment design temperature.
6.5 Discuss     the possibility of local       temperatures due to recombiner operation being higher        than the temperature qualification profiles for equipment in the 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.
II. Program for Resolution
: 1.        Arrangement drawings for the region above the recombiner exhausts will be submitted.          These drawings will conclusively demonstrate that no essential equipment can be effected by the recombiner thermal plume. MP&L ' will also submit a table showing all essential equipment on the operating floor and the distance from the equipment to the recombiners will also be submitted.
: 2.        A description of the criteria used for actuating the containment sprays on high temperature will be submitted.
This description will include details regarding location and response time for the temperature sensors which are used to actuate the containment sprays.
III. Schedule Items 1 and 2 will be completed fc submittal on August 19, 1982.
l Action Plan 24
: 1. Issues Addressed 7.2 The computer code used by General Electric to calculate environmental qualification parameters considers heat transfer from the suppression pool surface to the containment atmosphere.                This is not in accordance with the existing licensing basis for Mark III environmental qualification.
Additionally, the bulk suppression pool temperature was used in the analysis instead of the suppression pool surface temperature.
II. Program for Resolution
: 1.         MP&L will list and justify the assumptions used in calculating the environmental qualification parameters for the containment air space.
III. Schedule Item 1 will be completed for submittal on October 1, 1982.

                                                .~.- .                                        -                _           -
Action Plan 25 t
I.      Issues Addressed 8.1 This issue is - based on consideration that ' some technical specifications allow operation at parameter values that differ.
from the values used in assumptions for FSAR transient analyses. Normally analyses are done assuming a nominal containment pressure equal to ambient (0 psig) a temperature near maximum operating (90 F) and . do not limit the drywell pressure equal to the containment pressure. The technical specifications permit operation under conditions such as a positive containment pressure (1.5 psig), temperatures less than maximum (60 or 70 F) and drywell pressure can be negative with respect to the containment (-0.5psid).
                                                                                            ~
All of these differences would result in transient response different than the FSAR descriptions.
II. Program for Resolution
: 1.          A detailed summary of all conservatisms which currently exist in the containment response analyses which are part of the FSAR will be provided.                               Conservatisms in the suppression pool temperature analysis will be identified in Action Plan 12.
;                                                      2.          MP&L will complete an end point analysis to demonstrate that with all initial containment parameters at worst case values, the containment design pressure is still not significantly exceeded.
: 3.          Perform an analysis with worst case values taking credit for realistic temperature differences between containment and suppression pool and the containment heat sinks.
: 4.          A complete review of the technical specifications for containment             conditions          versus                 accident             analysis i                                                                  assumptions will be made. A comparison of technical specification values and values used as initial assump-tions in the accident analysis will be submitted.
III. Schedule Items 1-3 will be completed for submittal on November 1,.1982.
Item 4 will be completed for submittal on August 19, 1982.

Action Plan 26 I. Issues Addressed 8.2 The draft GGNS technical specifications permit operation of the plant with 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 which could lead to buckling and failures in the containment liner plate.
8.3 If the containment is maintained at -2 psig, the top row of vents could admit blowdown to the suppression pool during an SBA without a LOCA signal being developed.
II. Program for Resolution
: 1. The    technical specification limitation      for containment pressure will be revised to -0.1 psi to +1.0 psi.
III. Schedule Complete - This change has been incorporated in NUREG 0926 dated June, 1982.
Action Plan 27 I. Issues Addressed 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 the effects on the containment design external pressure of actuating the containment sprays.
II. Program for Resolution
: 1.              A complete list of scenarios which might result in reduced containment air mass will be developed.
: 2.              The list of scenarios developed in Item 1 will be reviewed and a worst case, bounding scenario will be selected.
: 3.              An analysis will be completed to establish the containment response under the bounding scenario.
III. Schedule Items 1 through 3 will be completed for submittal on October 1, 1982.
i I
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Action Plan 28 I.            Issues Addressed 9.3 It appears that some confusion exists as to whether 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.
II.           Program for Resolution
: 1. MP&L will submit a letter confirming that the small break accident and the stuck open relief value transient were treated as design basis accidents. The analyses for these transients are completed using licensing basis values for the initial conditions.
III. Schedule Item 1 will be completed for submittal on August 19, 1982.
l l
l

l Action Plan 29 I. Issues Addressed 10.1 The suppression pool may overflow from the weir wall when the                                                                             I upper pool is dumped into the suppression pool.. Alternately, negative pressure between the drywell and the containment which occurs as a result of normal operation or sudden containment pressurization could produce similar overflow. Any cold water spilling into the drywell and striking hot equipment may. produce
;                                       thermal failures.
I                       II. Program for Resolution
: 1.       An evaluation is being performed to assess changing the vacuum breaker set point from 0.5 psid to 0.15 psid.
!                             2.       The previously submitted analysis of weir wall overflow based
                                     'upon the potential change in vacuum breaker set point to control differential pressure between the containment and drywell    will                     be revised. The   revised           analysis                     should                         l demonstrate that weir wall . overflow will not occur under the most pessimistic combination of initial conditions during normal operation.
.                       III. Schedule Items 1 and 2 will be completed for submittal on August 19, 1982.
1 4
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     -,,,,..m.. -- --- - --       -. ~ . ,     y   -.----.--.-__.,-~.,-,-.,,y            - - ,     - , , . - - -      , - - _ , , , , - _ _ _ . , ,  ,-%- , . - .- - . . ,

Action Plan 30
: 1. Issues Addressed 10.2 Describe the interface requirement (A-42) (sic) that specifies that no flooding of the drywell shall occur. Describe your intended methods to follow this interface or justify ignoring this requirement.
II. Program for Resolution
: 1. MP&L will submit the wording of the requirement and the interpretation of this requirement which was used to assure that the requirement was met.
III. Schedule Item 1 will be completed for submittal on August 19, 1982.
I i

Action Plan 31
: 1. Issues Addressed 11.0 Mark III load definitions are based upon the levels in the suppression pool and the drywell weir annulus being the same.
The GGNS technical specifications permit elevation differences between these pools. This may effect load definition for vent clearing.
II. Program for Resolution
: 1.        The maximum possible differences between weir annulus level and suppression pool level will be defined. This definition will include an evaluation of changing the vacuum breaker set point per action plan 29,
: 2.         A discussion will be given of how pressure differences between the wetwell and the drywell will be controlled.
: 3.         The changes in hydrodynamic loads which may result from these maximum possible level differences will be evaluated.
III. Schedule Items 1-3 will be completed for submittal on August 19, 1982.

Action Plan 32
: 1. Issues Addressed 14.0 A failure in the check valve in the LPCI line to the reactor vessel could result in direct leakage from the 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 the containment spray.
II. Program for Resolution
: 1.         The potential effect of maximum backflow which can occur will be estimated.      This will include calculating the maximum backfiow which can occur, evaluating thermal interaction with the relatively cool RHR spray flow and estimates of the limitations on flashing created by flow through the spray nozzles.
: 2.         An evaluation of the possibility of adding interlocks to prevent simulataneous actuation of these valves will also be performed.
III. Schedule Item 1 will be completed for submittal on October 1,1982.
Item 2 will be completed for submittal on August 19, 1982.
l l
Action Plan 33 16.0 Some of the suppression pool temperature sensors are located (by GE recommendation) 3" to 12" below the pool surface to provide early warning of high pool temperature. However, if the suppression pool is drawn down below the level of the temperature sensors, the operator could be misled by erroneous readings and required safety action could be delayed.
II. Program for Resolution
: 1.         The emergency procedures will be revised to either require the operator to verify level in the suppression pool before reading suppression pool temperature or to specify which suppression pool temperature instruments can be used following an accident.
III. Schedule Item 1 will be completed for submittal on August 19, 1982.

Action Plan 34
: 1.      Issues Addressed 19.1 The chugging loads were originally defined on the basis of i
7.5 feet of submergence over the drywell to suppression pool vents. Following an upper pool dump, the submergence will actually be 12 feet which may effect chugging loads.
II. Program for Resolution
: 1.              The mass flux through the horizontal vents as a function of time during the postulated design basis accident will be established. A table showing submergence versus mass flux will be prepared.
;                                      2.              Test data will be used to demonstrate that chugging loads decrease with lower mass flux and air content.
: 3.              An evaluation will be performed to show that mass flux effects will bound any submergence effects.
1
: 4.              Arguments will be presented to show that addition of mass in the Mark III suppression pool in the low bubble velocity regions at the pool surface _ have a negligible effect on chugging loads since the chugging bubble course
:                                                      is inertia controlled.
III. Schedule j                                      Items 1-4 will be completed for submittal on October 1, 1982.
I, F
1 i

Action Plan 35 I. Issues Addressed 19.2 The effect of local encroachments on chugging loads needs to be addressed.
II. Program for Resolution
: 1. An evaluation of the         adequacy of available models to investigate the impact of longer acoustic paths on chugging load definition will be performed.
: 2. The inertial impedance effect on chugging loads will be quantified to the maximum extent possible.
III. Schedule Items 1 and 2 will be completed for submittal October 1, 1982.
4
  !                            Action Plan 36 I.               Issu'es Addressed
  .                                            20.0 During the latter stages of a LOCA, ECCS overflow from the
  ]                                                               primary system, can cause drywell depressurization and vent backflow.            The   GESSAR                           defines vent backflow vertical impingement          and drag                           loads,   to be         applied        to drywell structures, piping and equipment, but no horizontal loading is specified.
l                            11. Program for Resolution i                                                                          (" %c                                                                                                                             '
;                                              1.                 An an ysis is being completed to quanti fy the maximum cred         horizontal load component. Equipment supports will l                                                               be eva ated against the horizontal loads .to assure that the
  ;                                                               components can withstand the additional loads.                                                  Preliminary results indicate that the horizontal loads perturb the overall
]                                                                 load definition by less than 10 percent.
III. Schedule
;                                              Item 1 will be completed for submittal on October 1,1982.
t 1
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i
                                                                                                                                    ~
:                     Action Plan 37                                                                                                                                       ;
I.      Issues Addressed                                                                                                            \
s                            22.0 The EPG's currently in existence have been prepared with the' intent of- coping with 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 the expected course of the design basis accident.
II. Program for Resolution MP&L believes that the development program through which the
;                             emergency procedure guidelines have passed has adequately addressed this concern. As a result of this issue, MP&L has brought this
 ,                            concern to the attention of the BWR owners group. MP&L will pursue generic resolution of ;this issue with the BWR - owners group.
However, MP&L believes that for Grand Gulf Nuclear ' Station, this' I
issue is closed.
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P Attachment Two AECM-82/321 Action Plan       Addresses    >
NRC Question Number        MP&L Issues          Number 1          1.1, 1.2, 1.4     1.1, 1.2, 1.4 2          1.3               1.3 3          1.5               1.5 4          1.6               1.6 5          2.1, 2.2, 2.3     2.1, 2.2, 2.3 6          3.1, 3.7          3.1, 3.7, 3.11 7          3.2               3.2 8          3.4, 3.5          3.8, 3.9, 3.10 9          3.6 10          4.1               4.1 11          4.2, 9.1 '        4.2, 9.1 12          4.3               4.3, 4.10 13          4.4, 7.1          4.4, 7.1 14          4.5               4.5 15          4.6               4.6 16          4.7, 4.10         4.7 17          4.8               4.8 18          4.9, 5.3          4.8, 4.9, 5.3 19          5.1, 5.6, 9.2     5.1, 5.6, 9.2 20          5.4               5.4 21          5.5               5.5 22          5.8               5.8, 8.3 23          6.3, 6.5          6.3, 6.5 24          7.2               7.2 25          8.1               8.1 26          8.2, 8.3 27          8.4               8.2, 8.4 28          9.3               9.3 29          10.1              10.1 30          10.2              10.2 31          11.0              11.0 32          14.0              14.0 33          16.0              16.0 34           19.1             19.1 35          19.2              19.2 36          20.0 37          22.0 4

1-
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Attachment Three M                                                                          ,y
                                                  .- A E C M-82/321                          8 7           /3 .                         /          l
                                                                      ,                     ,o + 9 _ ~,                                        x t-                ,                      ,
1.8 Bechtel Drawing C-1043A which . opposedly represenWtn'e,as-built condition of the TIP platform idoes not show the platform ~ extending into the suppression- pool., This 19 not in c9reyest witN ,MPAUs                                                                                                 <
contention that the TIP platform enends jnto the poof.                                                              -," W                         '
                                                                                                                                                                              ']
Response                            .
                                                                                                                    #                                                        ?>     /
M r. Humphrey is misintcrpreting .DraNing -C-1043 A." TWe drawino '                                                                                                .
references structural detailss on another drawing which show thi }
skirt that extends frog thc? base of 'the TIP platform into the suppression pool.          These drawings reflect the as-built condition .of the plant.                               ,
                                                                                                                                                   /
                                               ,c 1.9 The presence o.f catwalks may aggr avate pool ~ swell. e adjacent open areas of the pec1 because they are altp local flow certrictions.
                                                                                     ,              ,):                            i, Response               --                                   .,
ig The su rface area of the catwalks and < as>0ciated . gratings is ap p roximately 70% open , area.                       The circumfe@ntial . catwalks /near the pool surface arce no'morg than four' feet wide. Conscquentif,      -
these gratings should ' rpt act as appreciable - obstructions to the pool swell. They will provide an effective smechani:;m foplartially breaking up the snll thds.geducinds bubble # breakthrough heic No additional effort 'need be appi(cd to resobtiod of this issub'ht.                                                               5
                                                                       ). ' f             >
3          1                   o                                         u        ,-
1.10 Even if adequate vent area' in dh'e H C U 100or 5of 1,500"'ft?*is '
provided, the distrihition of thishdyt area A hdnld' be uniform. 2 There is no analysis or tesv? data to' Wad 4fythe " effects of. non-uniformly distributed vent aireas. .
* h 7 l;                                        s
                                                                                                          ~ #</                           ,                         h
                                                                              /                   <,                                   _.
Response                        >                  ,e -          (       ,r (
7 Qi                   _
m T he potential effects of ,the existence of por..-uniform # vent eyea are negligibly small. Thq compressibility;of? aiv and;t!4 duration of the pool swell will assure that only lni.Aimal, cf,ta'niesJ in the #
3 conditions in (the wctwell and drywelP, pcgion                                           can occur.                          T his -
phe.:omena has been evaluated and bounded .in GESS AR. The results of this evaluation hhe ben reviewed with th'e, N P C. Therefore -
additional effort necdk to'be'43plie'd       i to the resolation ofl tyisi                                   e. s,su,00 lv                               ,g                                       .g, 2.4 The existing definition for!the~ preferped frequency of condensation oscillation may not be fully adequate. Large 'Yhifts in" frequency                                                                                             ^
such as those which occurred in th -1/9 scale te'sts may occur if a
                                                                                                                  ~
                                                                                                                                                                         /"
!                strong sourte,et a different frequefty' exists.                                                                               !                        j
                                 )\        ,        .d                       '[
j                             '
Response                                                                                                                                                   ' g ,.
                                        -         1                                                                                         s          ,-   ,     ..
Neither the 1/3 nor the full scale tests which were conducted tbJ                                                                                y,f,-
y define these leads 'showed any unaccc9nted for frequency shifts.                                                                                                      l
;                In addition, this issue has been thoroughly reviewed, wit;i the NR C                                                                             /
                                                                                                                                                                                    ~,'
                                                                                                                                                                                   '~
staff. MP&L is providing reference.g to correspondence vith                                                           '
the                  q,^
N RC concerning this issue.                                                   C - .c c> .t
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2.5 No assessment has been made of alternate condensation frequencies whiche may occur other than the C.0. frequency observed in the PS T F' tests.              These alternate frequencies may result from small plant 'ipecific changes such as the presence of local encroach-ments , vent acoustic treq uencies , contain ment response modes,
_ ,.                                          etc.
I

===Response===
The entensive information base which exists regarding condensation t
osci1Mt' ion frequency behavior has demonstrated the ability to
                #                        J                    'preoic't'consistant frequency content. This data base -has been R.                                  ~
                                       ,           e reviewed extensively with the NRC.                                      References identifying the
'/    '
relevant documentation' will be provided by MP&L.
      .                                              . i.
1 2                                          2.6 The pressure amplitude of condensation oscillation may change without respect to frequency.                   Plant specific geometry effects may also produce chaqges in the pressure magnitude of C.0.
Rrdonse MP&L has been ;.previously requested by the N RC to demonstrate
        ,.                                                    that condensation oscilhtion ' loads for the Grand G ulf N uclear In Station are bounded by the C.0. loads defined in GESSAR.
respengo . tc. this req uest, MP&L submitted an evaluation of the i              C . 0 / ' lod ds w hich would be produced based on plant specific
                   ,                         ;;             -ca?ctulat'ed , mass flux through the horizontal vents, air content in
                 -                           +-               the- exiting mass flux and su p pression pool temperature.                               The
                                      ,/.                 21oads caldulated using plant specific factors were bounded by the
,                                                              GESSAR C .0. loads. In addition, the GGNS suppression pool is
                                                     .,       both wider and shall,ower than the GESS AR suppression pool. T his
                                                   ,           will produce more attenuation of the C.0. loads and further assure
                                                                                         ~
4                that the plajit specific loads are bounded by the GESS AR' loads.
3.8 The RH R' heat exchanger relief valves may fail open in the shut-down cooling mode. Normally, the reactor pressure must be below 135 psig before initiation of shutdown cooling. However, there is
                                                     ~,
a booster pump in the line which may raise the pressure in the i
system to 364 pig. If the valve fails open at a lower pressure
                   ._",                                       then recloses when system pressu re drops, the valve could experience repeated actuations.

===Response===
l                                                             ~As* indicated above, the maximum pressure in the RH R system in l-                                                            the shutdowry cooling mode will be 364 psig. The only mechanism for opening the relief valve at this pressure is a single failure l
which would cause flow of subcooled liquid out of the relief valve.
i                                                              The' loads produced by an actuation of the relief valve at this
                                                        "' lower pressurei would be completely bounded by the loads which
                                 ,                            would be prodt:ced during a relief valve actuation in the steam F
                                      ' ,.. e                 condensings mode at 500 psig.                    The mass flux, input energy, and driving pressure are all significantly lower if the relief valve fails y               ".,                        openfat a pressure of 364 psig. Therefore, the analysis which
                                            /          h, MP&L is completing to quantify the loads produced by a relief vhlve a'ctuation in the steam condensing mode will bound a relief l
                                                         , valve failure. accident When the RH R system is in the shutdown
                                 /,                           coohng mo,de.
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3.9 If the RH R heat exchanger relief valve actuates with the vacuum breaker relief valve closed due to RCIC operation, the relief valve discharge line may fill completely with water.

===Response===
The con nection between the relief valve discharge line vacuum breakers and the RCIC system is isolated with two check valves.
A double failure of both check valves would have to occur before the relief valve discharge line vacuum breaker function could be impaired by operation of the RCIC system.                The connection between the RCIC system and the vacuum breaker line is shown on Figure 5.4-10 in the' G G N S FS AR. This concern is not applicable to G G N S 3.10 GE used the ANS 5 (1971) decay heat curve with a 20% margin for short term decay energy and a 10% margin for long term decay energy. Mr. Humphrey is concerned that a 20% margin should be applied throughout the transient.

===Response===
The conservatisms in decay heat margins used in long term ,
accident response have been approved by the N RC. In addition, the NRC staff is considering adopting ANSI /ANS 5.1-1979 which is essentially a lower decay heat load curve thus increasing the margin in the existing calculation. MP&L does not believe that any additional effort is required to address this concern.
5.9 Excessive localized leakage may saturate the containment heat sinks below the operating floor.        Then the heat sin ks would radiate energy back into         the    contain ment  following   termination .of containment spray.

===Response===
T he principal heat sinks in the containment below the operating floor include the drywell wall, the outer containment wall, the TIP removal area structure, the RW CU filter demineralizer room, the RWCU heat exchanger room , the pipe tu n nel, the upper pool stru ctu res , miscellaneous walls and floors.         All of these are massive structures with a very large heat capacity which would require an immense amount of energy to saturate the heat sink. If localized leakage did lead to saturation of one of these heat sinks, the amount of energy removed would decrease the severity of the containment response.        Even if this phenomena did occur, the contain ment spray system would be available to be reactivated.
MP&L is preparing detailed information on the criteria to be used for reactivating the containment sprays.          Separate information is also bein g prepared to demonstrate that the containment spray system can be cycled on and off.         Therefore, no additional effort is required.
5.10 The existing IB A analysis shows both the drywell atmosphere and su ppression pool temperatu re retu rning to 90 F within a few seconds. This does not appear correct.

===Response===
The radical drops in temperature are produced by the rapid condensation of steam in the drywell when water supplied by the ECCS begins flowing out the postulated breaks. This produces rapid steam condensation and an associated drop in temperature in the drywell.       When the steam in the drywell is quenched, the energy input to the suppression pool is largely terminated and the pool cooling system can rapidly reduce pool temperature. Thus the existing analysis is correct.
7.4 If cyclical operation of the contain ment spray is required to mitigate concerns with respect to su p pression pool temperature stratification or drywell leakage, a transient pool evaporation model             ,
will have to be licensed.                                                         I Res pons _e Such pool evaporation models exist and are utilized to perform realistic - basis assessments of containment transient responses.
Results invariably show containment responses to be lower than FSAR-basis responses which are used for design.
8.5 A technical specification limiting operation at low drywell tempera-tures should be established. T his will preclude operation with higher masses of air in the drywell than have been considered in the current licensing analysis.

===Response===
During normal power operation, the drywell temperature will never be below approximately 100 F.           The containment - and drywell tem peratu res and pressure is equalized n u merous times du ring power ascension. Thus a substantially higher drywell mass than accident analyses assume to exist will not occur. In spite of the contain ment sprays capability to mitigate potential pressu re increases, an endpoint calculation will be completed to evaluate the maximum effect of lower temperatures in the drywell.
8.6 An endpoint calculation has been completed which shows that the containment design pressure of 15 psig may be exceeded if the final containment atmosphere is saturated with water at 185 F.

===Response===
The assu mptions used to complete this en d point analysis are excessively conservative.       For exa m ple , the initial contain ment temperatu re will never approach 70"F d uring power operation .
The final conditions inside this containment will not involve air thermodynamic equilibrium with saturated water vapor at 185 F.
Containment spray would also be available to relieve containment pressu re. Furthermore, the initial pressure in the containment will not be 0.5 psig during normal operation with the containment purge.

9.4 The design basis calculations for stuck open relief valves should not rely on a manually initiated scram to occur within a short interval of the SO RV occurrence. The analyses should assume that scram is initiated when the pool temperatu re reaches 110 F or 10 minutes after occurrence of the SO RV.

===Response===
The Grand Gulf S0RV analysis does assume that a manual scram occurs when the su p pression pool tem perature reaches 110 F.
This is documented in MP&L's response to N RC question 21.7.
10.1 An additional mechanism capable of leading to ' negative pool swell has been identified. Use of drywell cooling after an upper pool dump may create a negative pressure transient sufficient to draw water over the weir wall.

===Response===
Sudden drywell cooler activation may treate a negative pressure transient in the drywell. However, MP&L is evaluating changing the normal set point of the vacuum breakers to 0.15 ,sig while the existing setpoint is 0.5 psig post LOC A.        Consequently, the weir wall overflow should not occur.
23.0 Some plants (specifically Kuo Sheng) use only one pool for upper pool dump. If the other pools are not initially full there could be excessive hold up of containment spray w hich might deplete the pool inventory and in concert with full drywell hold up could cause the su p pression pool level to fall below the minimum vent su b mergence.

===Response===
All contain ment pools dump simultaneously into the su p pression pool on the Grand Gulf Nuclear Station. Therefore, this concern is not applicable to GG NS.
4.5 Several additional factors which may aggravate suppression pool temperature stratification were identified. ^1 he extension of the TIP platform into the su p pression pool will further ag gravate su p pression    pool   temperatu re   stratification  by    restricting circulation of the upper part of the pool.
During a small break accident (SB A) the interaction of chugging from the SRVDL sleeve annular opening may mitigate chugging from the main horizontal vents. This would ' decrease pool mixing and aggravate suppression pool temperature stratification.
A SORV w hich occurs behind local encroachment could further degrade pool mixing efficiency.                                          ,

===Response===
The presence of the TIP platform will enhance radial and vertical mixing of the suppression pool by creating eddies and wakes. But circumferential circulation is less important since energy is added to the pool either uniformly through the horizontal vents or by actuating    circu mferentially  distributed relief valves.          The postulated interaction of annular vent chugging mitigation of main vent chugging induced mixing will be eliminated if MP&L seals the annular vents inside the drywell.      A single relief valve is located below the TIP platform. The encroachment does not extend near this relief valve and therefore failure of this relief valve should not adversely effect the pool mixing.
                                }}