ML20149J136

Responds to NRC Questions Concerning Rev 2 to License Amend, Communicated by Ltr to Util Dtd 970710.Staff Questions Have Been Reproduced Together W/Util Responses in Encl Attachment

ML20149J136
Person / Time
Site:	Monticello
Issue date:	07/16/1997
From:	Hill W NORTHERN STATES POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
TAC-L97781, NUDOCS 9707280068
Download: ML20149J136 (49)

Text

Northem States Power Company Monticello Nuclear Generating Plant 2807 West Hwy 75 Monticello, Minnesota 55362 9637 July 16,1997 US Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 MONTICELLO NUCLEAR GENERATING PLANT Docket No. 50-263 License No. DPR-22 Response to Request for Additional Information Regarding Revision 2 to MNGP License Amendment Dated January 23,1997 (TAC No. 97781)

This letter provides responses to Staff questions concerning Rev. No. 2 to the subject license amendment which were communicated by letter to NSP dated July 10,1997. The Staffs questions have been reproduced together with NSP's responses in the enclosed attachment. The information provided herein augments, and in some cases, supersedes previous Information provided to the Staff. Therefore, NSP requests that this letter be considered as part of the subject license amendment.

This letter contains the following new NRC commitments.

1) NSP commits to finalize the containment analysis and associa'ed NPSH evaluation for the long term case prior to plant startup. These analyses will be availab!e for inspection onsite. Changes to the requested long-term containment overpressure table, if any, will be promptly reported to the Staff prior to startup.

/

2) NSP commits to submit a revision or supplement to Exhibits D and E of the subject license amendment request to include the time extension data herein within 90 days of plant startup.

4 I ZEJ[

/

3) NSP commits to incorporate the staff's SER regarding containment overpressure into Section 5.2 of the MNGP USAR within 90 days of the date of plant startup. The revised Section 5.2 willinclude the approved containment overpressure and the respective time periods.

4) Prior to startup, NSP commits to adding a Caution in the EOPs to include NPSH considerations for precsure control while venting to control primary containment pressure.

5) Prior to startup, NSP commits to change the Primary Containment Pressure EOP NPSH Caution statement to include the Core Spray pumps.

50100 9707280068 970716 PDR ADOCK 05000263 P

PDR f

,l.hll mun m muccmumenmcmn.we

6) Prior to startup, NSP commits to revise the EOPs to require manualisolation of torus and drywell sprays prior to the point where primary containment pressure would not provide adequate NPSH for the ECCS pumps.

7) NSP commits to process a 50.59 evaluation to change the EOP definition of adequate core cooling to 2/3 core height within 180 days of the plant startup date. The corresponding EOP changes and the required operator training will also be completed in this time period.

Please contact Joel Beres, Licensing Engineer, at (612) 295-1436 if you require further information.

l L

William J. Hill Plant Manager Monticello Nuclear Generating Plant c:

Regional Administrator - 111, NRC NRR Project Manager, NRC Sr. Resident inspector, NRC State of Minnesota, Attn: Kris Sanda J. Silberg, Esq.

Attachments:

Affidavit to the US Nuclear Regulatory Commission Response to Request for Additional Information 2

UNITED STATES NUCLEAR REGULATORY COMMISSION NORTHERN STATES POWER COMPANY MONTICELLO NUCLEAR GENERATING PLANT DOCKET NO. 50-263 Response to Request for Information Recarding Revision 2 to MNGP License Amendment Dated January 23,1997 (TAC No. 97781)

Northem States Power Company, a Minnesota corporation, by letter dated July 16,1997 provides its response for the Monticello Nuclear Generating Plant to U.S. Nuclear Regulatory Commission (NRC) letter dated July 10,1997, with the subject " Request for Additional Information on Revision No. 2 to License Amendment Request Dated January 23,1997, Entitled ' Update of Design Basis Accident Containment Temperature and Pressure Response'(TAC No. M97781)." This letter contains no restricted j

or other defense information.

NORTHERN STATES POWER COMPANY By

/ddn

]

^

William J. ! ill #

~

Plant Manager Monticello Nuclear Generating Plant On this Ib day ofMy

\\D before me a notary public in and for said County, personally appeared William b. Hill, Plant Manager, Monticello Nuclear Generating Plant, and being first duly swom acknowledged that he is authorized to execute this document on behalf of Northem States Power Company, and that to the best of his knowledge, information, and belief, the statements made in it are true.

9 r'

Mamuel I. Shirey

~^^^^^^^^^^^^^^^^^^^^^ ^^^ ^ ^^^

- -. SHIREY SAMUEL 1 Notary Public - Minnesota i

Sherbume County NommuC WINNESOM My Commission Expires January 31,2000

..['_{....p.,,

,7g;y,.3hacooj cc

Response to Request for AdditionalInformation 1,

Page A-5 of the June 19,1997 submittalstates that 'the figures in Exhibit E demonstrate graphically the amount of containment pressure required and the minimum con:ainment pressure i

available to supply the required NPSH[ net positive suction head] for the emergency core cooling system (ECCS) pumps in the limiting pump combinations evaluated." These evaluations are for both short and long-term penods under minimum containment pressure conditions. For the short-term case, please state the requested overpressure and respective time periods to ensure that no cavitation of the ECCS pumps occurs. This request should be in the submittal and shown graphically on the figures in Exhibit E. Examples of such requests are available in the recent.

requests from the licensees of Dresden and Pilgrim Nuclear Power Stations.

NSP requests authonzation for containment overpressure of 2.0 psig for the time period between i

10 and 600 seconds. The minimum wetwell pressure available for C_.se No. 2, short-term case utilizing a power of 1880 MWt, is 2.34 psig at approximately 480 seconds. The wetwell pressure required to ensure adequate NPSH for the most limiting ECCS pump is 1.37 psig. The requested pressure was chosen to be below the minimum available pressure and slightly above the pressure required for adequate NPSH. The margin between the requested pressure and the pressure required for adequate NPSH is anticipated to sufficiently bound the containment overpressure required to account for head loss associated with debris loading per IEB 96-03.

Figure E.1 has been revised to graphically show the requested containment overpressure and is attached.

1/14/91 Jta J:\\ LICENSE \\JCEL\\ LETTERS \\CNTMT1.00C

CONTAINMENT PRESSURE FOR NPSH SHORT-TERM ANALYSIS - LPCI LOOP SELECT FAILURE 24 i

23 22 21 20

-g 19 l

e j

S 18 E

I 17 g

i C-l 1

................L,.......

1......

.g i

13 l

12 -

l 11 10 10 100 1000 l

TIME (sec)

Wetwell Pressure

-e--

B" CS NPSH Pressure

---

Atmospheric Pressure A

• B" RHR NPSH Pressure Requested Containment Overpressure l

l FIGURE E.1

i 2,

For the long-term case, the submitted analysis does not extend to the time when the required i

containment overpressure for the core spray pumps retums to atmospheric conditions. Please extend the analysis to show this point. Also, state the requested overpressure and respective time periods to ensure that no cavitation of the ECCS pumps occurs. This request should be in the submittal and shown graphically on the figures in Exhibit E.

General Electric has completed a preliminary analysis which extends long-term Case No. 3 past the time when the required containment overpressure for the core spray pumps retums to l

atmospheric conditions. This analysis is complete to the extent that the analytical output can be used to examine the effect of the extension on containment pressure. No changes to the requested overpressure for the time extension are expected when the analysis is completed.

NSP commits to finalize the containment analysis and associated NPSH evaluation prior to plant startup. These analyses will be available for inspection onsite. Changes to the requested overpressure as listed in the table below, if any, will be promptly reported to the Staff prior to startup. NSP also commits to submit a revision or supplement to Exhibits D and E of the subject license amendment request to include the time extension data herein within 90 days of the date of plant startup.

Monticello requests authorization for containment overpressure for the limiting long-term case as listed in the table below. The minimum containment pressure available for the limiting long-term case, Case No. 3 of Exhibit D as modified by the extended analysis with containment leakage, are also provided for the time periods specified. Since the analysis was extended out to 5 days, the Technical Specification containment leakage rate was conservatively considered irrespective of the containment pressure (1.2 w/o for the entire 5 day duration) in the evaluation. The pressure required for adequate NPSH was evaluated for this extend period. The requested pressure was chosen to be below the minimum containment pressure available and slightly above the pressure required for adequate NPSH. As in the short term case, the margin between the requested pressere and the pressure required for adequate NPSH is anticipated to bound the additional i

pressure that will be required when debris loading per IEB-96-03 is addressed.

Time (seconds)

Requested Containment Minimum Containment Overpressure (psig)

Pressure Available (psig) 600 - 2,000 2.0 4.60 2,000 -10,000 4.0 4.53 10,000 -16,000 5.3 5.67 16,000 - 55,000 6.1 6.21 55,000-69,000 5.6 5.71 69,000 - 85,000 5.0 5.10 85,000 - 110,000 4.2 4.30 110,000 -140,000 3.3 3.49 140,000 -200,000 2.3 2.37 200,000 -330,000 1.0 1.12 Although Case 3 represents the limiting case for requested overpressure, it is noteworthy that the minimum containment pressure available for the other long term cases evaluated in Exhibit D is less than that for Case No. 3 due to containment cooling equipment availability. The containment pressure required for adequate NPSH, however, is also less.

7/14/97 JIB J i \\ LI CEN$ E\\.10CL\\ LTTTER3 \\CNTMT1. 00C

f Figure E.2 has been revised to graphically show the requested containment overpressure with respect to time and is attached, i

l l

l i

i i

1 l

7/14/91 Jta Js\\LICEN$t\\JotL\\LETTLAS\\CNTNT1. Doc 1

CONTAINMENT PRESSURE REQUIRED FOR NPSH DIESEL GENERATOR FAILURE (NO OFFSITE POWER) 24 23 j

22

[I l i

s s,_

l f

19 m-'i j

j' I

I I

$ 18 -

/

I l

m i

E 17 -

/

I S

/

I I

I i

@ 16 --

/

f m

/

/

t 15 --

/

j/

j l

f..._....

/

i i

13 i;

12 -

A l

1 i

\\

11 i

to I

i l

I 100 1000 10000 100000 1000000 TIME (sec)

Wetwell Pressure

--m-B" CS NPSH Pressure

---

Atmospheric Pressure

- A

• B* RHR NPSH Pressure Requested Containment Overpressure FIGURE E.2

l 3.

On page A-2 of the submittal, the licensee proposed to change section 3.7.A of the Bases to the following:

For an initialmaximum suppression chamber water temperature of 90cF and conditions which lead to minimum containment pressure, adequate net positive suction head (NPSH) is maintained for the core spray, RHR, and HPCI pumps underloss of coolant accident conditions.

The staff believes that when the amendment request is approved that the approved containment overpressure and respective time periods should be stated in section 3.7.A of the Bases. This should avoid any confusion in the future regarding Monticello's credit for use of containment overpressure.

The staff-approved limits on containment overpressure will be added to the Technical Specification bases by cross-referencing Section 5.2 of the MNGP USAR. The applicable Technical Specification bases page (p.176) has been revised to reference this section of tho i

USAR and is attachedl. In addition, NSP commits to incorporate the staffs SER regarding containment overpressure into Section 5.2 of the MNGP USAR within 00 days of the date of plant -

startup. The revised Section 5.2 willinclude the approved containment overpressure and the respective time periods.

-l l

s 7/14/91 JEB Ja\\LICENSEUCCL\\ LETTER $\\CNTNT3.00C

Bases continued-Vent system downcomer submergence is three feet below the minimum specified suppression pool water level. This length has been shown to result in reduced postulated accident loading of the torus while at the same time i

assuring the downcomers remain submerged under all seismic and accident conditions and possess adequate condensation ef fectiveness. '"

The maximum temperature at the end of blowdown tested during the Humboldt Bay"' and Bodega Bay

• tests was 1700F and this is conservatively taken to be the limit for complete condensation of the reactor coolant, although condensation would occur for temperatures above 1700F.

Experimental data indicate that excessive steam condensing loads can be avoided if the peak temperature of the suppression pool is maintained below 1600F during any period of relief valve operation with sonic conditions at

~

the discharge exit.

Specifications have been placed on the envelope of reactor operating conditions so that the reactor can be depressurized in a timely manner to avoid the regime of potentially high suppression chamber loadings.

In addition to the limits on temperature of the suppression chamber pool water, cperating procedures define the action to be taken in the event a relief valve inadvertently opens or sticks open.

This action would include:

(1) use of all available means to close the valve, (2) initiate suppression pool water cooling heat exchangers, (3) initiate reactor shutdown, and (4) if other relief valves are used to depressurize the reactor, their discharge shall be separated from that of the stuck-open relief valve to assure mixing and uniformity of energy insertion to the pool.

For an initial maximum suppression chamber water temperature of 90* F and conditions which lead to minimum containment pressure, adequate net positive suction head (NPSH) is maintained for the core spray, RHR, and HPCI pumps under loss of coolant accident conditions. Analyses were performed for a broad range of pump combinations and failure modes to define the minimum amount of containment pressure available to provide adequate NPSH in the short and long term.

Refer to Section 5.2.3.3 of the USAR for a discussion of these analyses and figures which demonstrate graphically the amount of pressure required and the minimum containment pressure available to supply i

the required NPSH for the emergency core cooling pumps in the limiting pump combinations evaluated. No pump cavitation will occur over either the short or long term periods under conditions resulting in minimum containment pressure.

(1) Robbins, C.H.

" Tests of Full Scale 1/48 Segment of the Humboldt Bay Pressure Suppression Containment

• GEAP-3596, November 17, 1960.

(2) Bodega Bay Preliminary Hazards Summary Report, Appendix 1, Docket 50-205, December ~28, 1962.

(3) General Electric NEDE-21885-P, " Mark I Containment Program Downcomer Reduced Submergence Functional Assessment Report," June, 1978.

3.7 BASES 176 REV

4 4.

For the long-term NPSH case, what factors contribute to the relatively high requirement of containment overpressure in comparison to other BWRs of the same vintage? The staff has recently approved credit forlong-term containment overpressure on the order of 2.5 psig.

However, the calculations presented in the submittalimply that Monticello will need approximately S. 7 psig to meet the long-term NPSH requirements.

The major factors that contribute to the required containment overpressure in comparison to other BWRs of the same vintage are RHR heat exchanger capacity and containment spray temperature.

l The Table below provides a comparison of Monticello with Dresden.

Parameter Monticello Monticello Dresden 1 pump,1 1 pump,1 2/17/97 pump,1 division pump,2 Submittal Case 3 of divisions Exhibit D Case 6 of Exhibit D RHR/LPCI Flow 4000 8000 5000 i

(gpm)

RHRSW/CCSW Flow 3500 7000 5000 (gpm) l Max. SW Temp (*F) 90 90 95 Heat Exchanger"U" 180 180 197.9 2

2 Value BTU /hr-ft *F BTU /hr-ft *F-BTU /hr-ft' *F Heat Exchanger *K*

143.1 286.2 281.7 Value BTU /sec *F BTU /sec *F BTU /sec *F Heat Transfer Rate, Q 53.6E6 BTU /hr 82.4E6 BTU /hr 78.1E6 BTU /hr at Peak Pool Temp (PPT) '

Peak Pool Temp, 194 169 172 PPT (*F)

Wetwell Pressure @

6.67 psig 3.49 psig 2.9 psig PPT Approximate 167.2 148.7 140.7 Containment Spray Water Temperature

('F)-

Vapor Pressure of 5.62 3.60 2.95 Containment Spray Water, psia Monticello's ECCS capability is restricted by EDG ! imitations. In addition, the heat removal capability of the Dresden ECCS configuration with one LPCI pump, one CCSW pump and one RHR heat exchanger is approximately two times greater than Monticello's containment heat removal capability with the same r, umber of pumps and heat exchangers. Therefore Dresden's peak pool temperature and containment spray temperature is less than Monticello's.

A comparison of Dresden with Monticello's Case 6, with an ECCS configuration of two RHR pumps, two RHRSW pumps and 2 RHR heat exchangers, provides a similar comparison of heat exchanger capacities. Variations exist with respect to containment air and water volumes and with U16/91 JE5 J r \\ LICENSE \\JOEL\\LETTEM \\CNTNT1. DOC

decay heat assumptions between the two plants. As can be seen, Dresden's w2well pressure is lower. A major reason for this difference is that containment spray temperatuns is 8'F lower for 1

Dresden when compared with Case 6.

)

't 2

't 4

L t/14/97 Jts J:\\LICENst\\JotL\\ LETTERS \\CNTHT1.coC I

5.

In Appendix A of Exhibit D, it is stated that the 'HXSIZ" code can only model the long term response for only the DBA-LOCA and only with assumptions which maximize drywell and suppression chamber airspace pressure. State andjustify the differences between using the SHEX code to analyze for minimum versus maximum containment pressure.

The differences between using e.e SHEX code to analyze for minimum versus maximum containment pressure are defined in Table A-1 in Exhibit D of the subject license amendment (hereafter referred to as Exhibit D). Table A-1 provides information on Case A-1 and Case 3 of analysis described in the submittal. Case A-1 uses assumptions based on maximizing containment pressure for the DBA-LOCA analysis. Case 3 uses assumptions based on minimizing containment pressure for the DBA-LOCA analysis when done as an input for ECCS pump NPSH. Additional discussion of the assumptions used are provided in Exhibit D, Section 3.

A justification for the values used is provided below.

PARAMETER CASE A-1 CASE 3 JUSTIFICATION initial Drywell 15.7 psia 14.26 psia The assumption in case A-1 is based on Pressure maximizing the amount of non-condensable gases in containment by using 1 psi greater Initial than a nominal value of atmospheric pressure.

Suppression This is typical of historical analysis done at Chamber MNGP in the past.

Airspace Pressure Case 3 uses an assumed initial drywell pressure of 14.26 psia to minimize the amount of non-condensable gases in con'.ainment. This is the historical minimum average local atmospheric pressure at Monticello. See Exhibit D, Section 3.1, Assumption 9 and Section 3.2.

Initial Drywell 20 %

100 %

The assumption in case A-1 is based on Relative maximizing the amount of non-condensable Humidity gases in containment by minimizing the amount of condensable water vapor.

Case 3 assumed an initial condition of 100%

humidity to maximize the amount of condensable water vapor and thereby minimize 4

i the amount of non-condensable gases. See Exhibit D, Section 3.1, Assumption 10 and Section 3.2.

Containment Suppression Containment The use of suppression pool cooling in Case A-Cooling Mode Pool Cooling Sprays 1 without the use of containment sprays will minimize the cooling applied to the containment atmosphere. The higher gas temperature that results willincrease containment pressure accordingly.

The use of containment spray with 100% mixing efficiency was used in Case 3. This will result in significant cooling of the containment airspace based on the temperature of the spray water as 1/16/97 JE9 J r \\ LICEN5E\\J0EL\\LEffEAS \\CNTM71. DOC

i PARAMETER CASE A-1 CASE 3 JUSTIFICATION 1

l it leaves the RHR heat exchanger. See Exhibit l

D. Section 3.2, Analysis Assumption 1.

Heat and Mass Thermal Heat and Case A-1 assumes that the suppression Transfer Equilibrium Mass chamber air space is always at equilibrium with between the and Saturated Transfer the suppression pool and at saturated Suppression Conditions calculated conditions after the start of the accident. This Pooland imposed mechanis-maintains the gas temperature, and associated i

l Suppression tically gas pressure, at a higher value than would be Chamber Air expected if a realistic modelwas used. In j

Space addition, maintaining the air at saturated conditions conservatively maximtzes gas pressure.

Case 3 uses a mechanistic evaluation of heat and mass transfer mechanisms between the suppression pool and the supp ession chamber air space. This approach reduces air space temperature and humidity and results in a conservatively lower air space pressure for the calculation of minimum pressures. See Exhibit D, Section 3.1, input 5.

Thermal Mixing 100 %

20%

Case A-1 does not use containment spray. The Efficiency break flow is assumed to mix with 100%

Between Break efficiency with the drywell atmosphere.

Flow and Drywell Atmosphere Case 3 does use containment spray with an assumed thermal mixing efficiency of 100% with the drywell atmospiere. Since the containment spray flow will be at a lover temperature than the break flow, use of a low mixing efficiency for the DBA accident break flow is conservative.

Containment spray flow will tend to reduce drywell temperatures and pressures. See Exhibit D Section 3.2, Analysis Assumption 3.

GE conducted a manual calculation ta provide additional support to the benchmarking analysis of Exhibit D for the minimum pressure case. The calculational methodology is similar to that provided by Commonwealth Edison fce the Dresden Unit as described in their letter of March 12, 1997 to the NRC,"Dresden Nuclear Power Station Units 2 and 3, AdditionalInformation Regarding Application for Amendment to Facility Operating Licenses DPR-19 and DPR-25, Appendix A, Technical Specifications, Section 3/4.7.K, " Suppression Chamber,' and Section 3/4.8.C," Ultimate Heat Sink." The GE calculation, GLN-97-025, is attached.

The manual calculation evaluates suppression chamber pressure for SHEX with the use of containment sprays. It uses the suppression pool temperature and wetwell airspace volume taken directly from the SHEX output as a starting point. This is a reasonable assumption since the suppression pool temperature response for SHEX was shown to be consistent with previous l

analysis approved by the NRC as demonstrated in Exhibit D, Appendix A. Wetwell airspace volume is simply the initial wetwell airspace volume reduced by the volume of water added to the i

l l

mm, m m am um m m mc u.wc l

suppression pool by the feedwater system and the water lost from the vessel (the vessel is assumed to be reflooded to two-thirds core height inside the shroud following the break).

Wetwell airspace temperature was assumed to be equal to containment spray temperature which was equal to the RHR heat exchanger outlet temperature. Drywell temperature is based on a mass average temperature of the mass flows into the drywell with accounting for break flows and containment spray temperatures. Drywell and wetwell pressures are based on ideal gas laws to obtain the air partial pressures plus vapor pressures based on saturated conditions. Use of containment sprays during the event insures that the use of saturated conditions is reasonable.

For Exhibit D, Case 3, the manual calculation resulted in a wetwell pressure of 20.9 psia at the peak suppression pool temperature of 194.2*F at approximately 33500 seconds. The SHEX model predicts a wetwell pressure of 21.1 psia at 33500 seconds. Based on the similar outcome of SHEX with the independent calculation and the benchmarking analyses provided in Exhibit D, it is reasonable to conclude that the SHEX model provides accurate results for the case where containment sprays are in service in order to calculate minimum containment pressures.

1/16/97 JE8 Js\\LICIHSE\\JOEL\\ LETTER 3\\CNTNT1.D3C

~

GENuclear Energy Y?u$ Y.?$J:se C.U:::

July 10,1997 cc: MSE GLN-97-025 P. Tobin A.V. Wojchouski GE Mr. S. J. Hammer D.C. Pappone Northern States Power Company S. Mintz Monticello Nuclear Generating Plant E. G. Thacker 2807 West Highway 75 Monticello, MN 55362-0637

Subject:

Benchmark Calculation for SHEX Minimum Containment Pressure (GE Proposal No. 523-1HBYF-EKI)

References:

1. FAX, S.J. Hammer (NSP) to P.T. Tran (GE-NE), " Draft RAI for Monticello Regarding NPSH License Amendment." dated July 7,1997.

2. GE Report, GE-NE-T2300731-2,"LOCA Containment Analyses for Use in Evaluation of NPSH for the RHR and Core Spray Pumps," June 1997.

Dear Steve,

This letter provides the benchmark calculation justifying the use of the SHEX code for analyzing events which minimize the containment pressure. The benchmark calculation was requested in response to Question 5 in Reference 1 in order to support the NRC review of the containment pressure and temperature analyses submitted in Reference 2.

The benchmark calculation for the wetwell pressure agrees quite well with the SHEX results (within one percent).

Please do not hesitate to call us if you have additional questions on this subject.

Sincerely, hVrCI %./

P.T. Tran Monticello Power Rerate Project Manager M/C 172, Tel. (408) 925-3348

Atly 10,1997 Page 2 of 8 GLN-97-025 BENCHMARK CALCULATION FOR SHEX MINIMUM CONTAINMENT PRESSURE i

The following calculation of the suppression chamber pressure can be used to benchmark the SHEX results for containment pressure calculations with containment sprays. This calculation uses the suppression pool temperature and wetwell airspace volume taken directly from the SHEX output. It has been demonstrated in Appendix A ofReference I that the suppression pool temperature calculated with the SHEX code is consistent with the suppression pool temperature calculated using the current USAR license basis code (HXSIZ) for Monticello. The other inputs are obtained from the plant configuration and initial plant operating conditions.

The evaluation below is best used near the time of peak suppression pool temperature when quasi-equlibrium conditions exists in the drywell and wetwell. The wetwell airspace volume was taken from SHEX as a matter of calculational convenience. The wetwell airspace volume is simply the initial wetwell airspace volume reduced by the volume of water added to the suppression pool by the feedwater system and the water lost from the vessel (the vessel is assumed to be reflooded to two-thirds core height inside the shroud following the break). Note that air capacitance effects and heat transfer lag times are not considered in this calculation. However, as demonstrated below, the calculated values closely match the SHEX calculated results.

ASSUMPTIONS:

1. Saturated conditions exist in the drywell and wetwell at the time of peak suppression.

pool temperature.

100% humidity in the drywell (dw) and wetwell (ww)

Pv,dw = Psat (Tdw)

Pv,ww = Psat(Tww) where:

Pv,dw is the partial pressure of the vapor in the drywell, psia Pv,ww is the partial pressure of the vapor in the wetwell, psia Psat is the saturation pressure at the airspace temperature, psia Tdw is the drywell airspace temperature, F Tww is the wetwell airspace temperature, *F

July 10,1997 Page 3 of 8 GLN-97-025

2. The drywell temperature is based on mass average temperature ofinflows to drywell and take into account the thermal mixing efficiency of the break flow with the drywell atmosphere.100% thermal mixing of the drywell spray flow is assumed. The core j

spray system is the only system injecting into the vesssel during this time period and l

the level in the vessel has stabilized at two-thirds core height inside the shroud.

l Therefore, the break flow is equal to the core spray flow rate. The break flow temperature is equal to the pool temperature plus the addition of the core spray pump heat and the core decay heat. The drywell spray temperature is equal to the heat exchanger outlet temperature. The heat exchanger outlet temperature is based on an energy balance on the flow through the RHR system (pool temperature coming in plus the pump heat minus the heat removed through the heat exchanger).

Tdw = mass weighted average temperature of break flow and spray.

=(f*mbreak'Tbreak + mspray*Tspray)/(f*mbreak+mspray) where:

Tdw is the drywell temperMure, *F fis the thermal mixing c ficiency for break flow, unitiess mbreak is the break flow hom the vessel, Ibm /sec Tbreak is the temperature of the break flow from the vessel, F mspray is the drywell spray flow rate, Ibm /see Tspray is the temperature of the drywell spray flow, *F using the assumptions described above, mbreak = mes Tbreak = Tpool + (Qdecay+Qcspump)/mes Tspray = Tpool + QRHRpump/ mRHR*c

+ (-K(Tpool + QRHRpump/ mRHR*c -Tsw))/(mRHR*c) where:

Tpoolis the suppression pool temperature, F mes is the core spray flow rate, Ibm /sec Qdecay is the core decay heat, Btu /sec Qespump is the core spray pump heat, Btu /sec

(

K is the RHR heat exchanger coefficient, Btu /sec-F Tsw is the service water temperature, *F QRHRpump is the RHR pump heat. Btu /sec mRHR is the RHR system flow rate, Ibm /sec i

c is the heat capacity of water = 1 Btu /lb *F l

l July 10,1997 Page 4 of 8 GLN-97-025

3. The wetwell airspace temperature is based on the spray temperature. The spray temperature is equal to the heat exchanger outlet temperature. The heat exchanger outlet temperature is based on an energy balance on the flow through the RHR system (pool temperature coming in plus the pump heat minus the heat removed through the heat exchanger).

Tww = spray temperature Tww = Tpool + (-K(Tpool + QRHRpump/ mRHR*c -Tsw))/(mRHR*c)

+ QRHRpump/ mRHR*c

5. The wetwell pressure is obtained with the ideal gas laws to obtain the air partial pressure plus with the assumption saturated conditions in the wetwell airspace to obtain the vapor pressure (see Assumption 1).

Pww = Pa,ww + Psat (Tww) where:

Pa,ww is the partial pressure of air in the wetwell, psia

6. The drywell pressure is obtained with the ideal gas laws to obtain the air partial pressure plus with the assumption saturated conditions in the drywell airspace to obtain the vapor pressure (see Assumption 1).

Pdw = Pa,dw + Psat (Tdw) i where:

Pa,dw is the partial pressure of air in the drywell, psia

7. The drywell pressure is equal to the wetwell pressure minus the wetwell-to-drywell vacuum breaker setpoint pressure full open pressure difference.

Pdw = Pww - APvb where:

APvb = vacuum breaker full open pressure differential setpoint, psi

6. The total air in drywell and wetwell is assumed to be constant during the event (no containment leakage or generation of noncondensables is assumed).

Ma.dw + Ma,ww = (Ma,dw + Ma,ww) initial = Ma, initial. total

July 10,1997 Page 5 of 8 GLN-97-025 where:

Ma,dw is the mass of air in the drywell, Ibm Ma,ww is the mass of air in the wetwell, Ibm Ma, initial, total is the total initial air mass in the containment, Ibm

't 4

6

(

July 10.1997 Page 6 of 8 j

GLN-97-025 l

ANALYSIS:

With the above assumptions, two equations for two unknowns can be set up. The two unknowns are the air mass in the wetwell Ma.ww and the air in the drywell Ma,dw.

(1)

Pww - Pdw ^ APvb or [Pa,ww + Psat (Tww)] - (Pa,dw + Psat (Tdw)] = APv6 (l')

Ma.ww + Ma,dw = Ma. initial total

'(2)

From ideal gas law Eq.I' is rewritten as:

((Ma ww *R*(Tww+460)]Nww +Psai(Tww)} - ([Ma.dw R*(Tow +460)]Ndw + Psat(Tdw)}

= APvb (1a) where:

3 Vww is defined as the wetwell air space volume, ft Vdw is defined as the drywell air space volume, ft' Solving Equations la and 2 for Ma,ww yields:

Ma,ww = IPsat(Tdw)- Psat(Tww) + APvbl + IMa initiattotal*R*(Tow &460VVdw]

(3) i (R*(Tdw+460Ndw + R*(Tww + 460)Nww]

I-where:

R is the gas constant for air = 53.34 ft-lbf/lbm *R I -.

The wetwell pressure at the time of the peak pool temperature is obtained by using Ma.ww

'k from Equation 3 as input to Equation 4 to obtain Pa,ww.

se

~ \\;

Pww = Ma,ww*R*Tww/Vww + Psat(Tww)

(4)'

f

. July 10,1997 Page 7 of 8 GLN-97-025 i

EXAMPLE -

The example below is for Case 3 of GENE-T2300740-2 (135'F initial DW temperature) at the time of peak pool temperature.

~

Tpool

- = 194.2 F at 33546 sec K ~

= 143.1 Btu /sec *F l

.Tsw-

= 90 F Q RHRyump

= 600 hp = 424 Btu /sec Q cspump

= 800 hp = 566 Btu /sec.

mRHR

= 555.81bm/sec mspray,dw

= 528 lbmisec :

mspray,ww

= 28 lbm/sec mes

= 375.3 lbm/sec Qdecay

= 1.39e4 Bru/sec f

= 0.2 APvb

= 0.242 psi -

Vdw

= 134,200 ft' Vww

= 97,950 (Case 3 at time ofpeak suppression pool temperature).

Ma, total

= 14225 lbm (SHEX initial air mass total based on 135'F -

initial DW temp) -

From Assumption 3:

Tww = Tspray = (194.2) + [-143.l(194.2+(424/555.8* 1)-90)]/(555.8* 1)

+(424/555.8* l) = 167.9'F For comparison, the value for Tww from SHEX is 169'F.

Psat(167.9'F) = 5.71 psia.

R From Assumption 2:

Tbreak = (Qdecay+ Qcspump)/(mes*c) + Tpool

= (566+1.39e4)/(375.3* 1)+194.2 = 232.7'F Tdw = [(0.2*232.7*375.3)+(l67.9*528)]/(528+0.2*375.3)= 176.0 F i-For comparison, the value for Tdw from SHEX is 178'F.

l-t Psat(176.0 F) = 6.87 psia

j July 10,1997 Page 8 of 8 l

GLN-97-025 d

l From Eq.3:

Ma,ww =[(6.87 - 5.71 + 0 242)*144+f(14225*S3.34)*(176.0+460)1/134.2001

[53.34 * (176.0+460)]/134.200+53.34 * ( 167.9+460)/97950)]

-= (201.9 + 3595.9)/(0.253 + 0.341) = 6393.6 lbm For comparison, the value for Ma,ww from SHEX is 6516 lbm.

From Eq. 4:

Pww = (1/144)* [6393.6

• 53.34 * (167.9+460)/97950] + 5.71 = 20.9 osia For comparison, the value for Pww from SHEX is 21.1 osia.

From Eq.1 -

Pdw = 20.9.- 0.2' 2 = 20.7 nsia 4

For comparison, the value for Pdw from SHEX is 21.0 nsia.

- Conclusion The calculated value of the wetwell pressure is within one percent (0.2 psi) of the SHEX

- value.

J REFERENCES 1.

GE-NE-T2300731-2,"Monticello Nuclear Generating Plant LOCA Containment Analyses For Use in Evaluation of NPSH for the RHR and Core Spray Pumps,"

June 1997.

6:

Please specify under what conditions that the containment venting is allowed by the plant procedures, and discuss the ramifications for the adequacy of NPSH during containment venting.

There are two reasons the EOPs require primary containment venting: 1) to control primary containment pressure and 2) to control primary containment hydrogen and oxygen concentrations.

The EOPs require venting primary containment to stay below the containment design pressure of 56 psig. Prior to startup, NSP commits to adding a Caution in the EOPs to include NPSH considerations for pressure control while ventirig to control primary containment pressure.

Venting for hydrogen control woc!d not be necessary in the design basis events described in the license amendment request The hydrogen controlleg of the EOPs is entered if either the drywell or torus hydrogen concentration reaches the minimum detectable level (1%). For a containment hydrogen concentration of 1% to occur, additional failures of the ECCS beyond that assumed in the design basis event analysis must be assumed.

If a event beyond the design basis occurs and detectable hydrogen is indicated, the hydrogen control leg instructs the operator to initiate the Combustible Gas Control System (CGCS). Either train of the fully redundant and safety-related CGCS is designed to maintain combustible gas concentrations below the deflagration limits. As long as either train of the CGCS is operable, manual venting of the containment would not be necessary.

If offsite release rates are expected to stay below the LCO limits, the operators are permitted to

- vent and purge primary containment concurrently with operating CGCS to restore and maintain drywell hydrogen concentrations below the minimum detectable level. The initiating event that resulted in the hydrogen generation, however, would necessarily include fuel failure, and the venting would be precluded by virtue of the LCO limitation.

Given the above, NPSH is not adversely affected by the hydrogen control EOP because a condition that would require venting would necessarily involve an incredible sequence of multiple failures beyond the design basis of the plant.

1/16/97 JE8 J i \\ LI CEN$ t \\ JCCL\\ LE TTERS\\CNTMT1. COC

- ~.. -. _. _ -

7.

At what containment pressure do the EOPs (emergency operating procedures] require manual 1

initiation and manual shutoff of containment sprays.

The EOPs require manualinitiation of torus sprays before drywell pressure reaches 12 psig and manual initiation of drywell sprays when drywell pressure exceeds 12 psig. Manual isolation of drywell sprays is required when drywell pressure drops below 2 psig, and manualisolation of torus sprays is required when torus pressure drops below 2 psig.

I Cautions that wam the operator that exceeding NPSH limits may damage RHR equipment already exist in the MNGP EOPs. Prior to startup, NSP commits to change the Primary Containment Pressure EOP NPSH Caution statement to include the Core Spray pumps. NSP also commits to revise the EOPs to require manualisolation of torus and drywell sprays prior to the point where primary containment pressure would not provide adequate NPSH for the ECCS pumps. To the extent possible, changes will be equivalent to the Dresden EOP changes.

1

]

i m.,,,

. mmm.m-mmm-u.-

)

~. - - -. - -

i 8.

Provide your verification that equipment quali5 cation (EQ) evaluation included an analysis which i

. confirmed that all accident and post accident temperature and pressure (notjust peak) were i

bounded. Provide a representation of EQ test profile curve to demonstrate that the EQ test prohle

?

continues to bound the new containment response profile resulting from the reanalysis.

A.

EQ and NPSH Cases y

Temperature The peak containment accident temperatures are generated in the drywell. Plot one is the composite of the drywell temperatures for cases 1 through 7 of Exhibit D. Plot 2 Nws cases 1 i

and 2. Plot 3 shows case 3. Plot 4 shows cases 4 and 5. Plot 5 shows cases 6..d 7. All of l

these cases are for NPSH analysis, which minimizes the containment pressure response. These plots clearly show that the existing EQ temperature profile bounds the containment reanalysis for NPSH considerations.

Pressure The peak containment accident pressures are generated in the dntwell. In order to evaluate the pressure profiles, a dryweil pressure envelope was developed using data from General Electric Report NEDO-30485 using a local atmospheric pressure of 14.26 psia. Plot 6 is the composite of the drywell pressures for cases 1 through 7 of Exhibit D. Plot 7 shows cases 1 and 2. Plot 8 shows case 3. Plot 9 shows cases 4 and 5. Plot 10 shows cases 6 and 7. All of these cases are for NPSH analysis which minimizes the containment pressure. These plots clearly show that the existing EQ pressure profile bounds the containment reanalysis for NPSH considerations.

B.

SHEX Benchmark Analyses and 1880 MWt Case The SHEX benchmark analyses in Exhibit D describes and compares containment responses using different computer codes and different decay heat models. These analyses used input assumptions that maximize the containment responses for temperature and pressure. The containment response profiles resulting from this benchmark analysis have been plotted, along with the bounding profiles for Environmental Qualification. A new case, the power rerate 1880 MWt case, was also plotted with the profiles for Environmental Qualification.

Temperature Plot 11 is the composite of the drywell temperatures for cases contained in Table A-4 of Exhibit D and the 1880 MWt rerate case. Plot 12 shows cases A-1 and A-2. Plot 13 shows the 1880 MWt rerate case. Plot 14 shows cases 1 and A2. Plot 15 shows all cases with a DBA temperature envelope. All of these cases are with assumptions that maximize the containment response. As can be seen, not all portions of the temperature response are contained within the EQ profile. In order to evaluate the differences, a drywell DBA temperature envelope was developed. The DBA temperature envelope was constructed by choosing points that assured all the containment DBA temperature profiles were bounded. An equivalent integrated temperature evaluation for EQ.

equipment in containment was calculated using the Arrhenius methodology. The results from MNGP Calculation CA 97-176 show that the equivalent temperature exposure time for the EQ temperature profile exceeds the equivalent temperature exposure time for the DBA temperature profile. Therefore, the existing EQ temperature profile bounds the DBA temperature profile generated for the containment reanalysis.

1/14/97 JEB Ja\\ LICENSE \\JoEL\\ LETTER 3\\CNTMT1. DOC l

Pressure Plot 16 is a composite of the drywell pressures for cases contained in Table A-4 of Exhibit D and the 1880 MWt case. Plot 17 shows cases A 1 and A-2. Plot 18 shows the 1880 MWt rerate case.

Plot 19 shows cases 1 and A.2. Plot 20 shows all cases with a revised pressure envelope. All of these cases are with assumptions that maximize the containment pressure response. As can be seen not all portions of the pressure response are contained within the EQ pressure profile.

The qualification of equipment inside containment for the effects of pressure were reviewed. The environmentally qualified equipment inside containment was verified to be qualified to a pressure that substantia!!y bounds the peak containment pressure,(53 to 122 psig vs. 42.3 psig). NSP has obtained an opinion from a noted EQ expert and has determined that it is reasonable to conclude that failure modes caused by pressure are a function of the peak pressure and the rate of pressurization / depressurization. See also Equipment Qualification Reference Manuai, EPRI, 1992, page 3-12. In addition, the failure modes and rnechanisms caused by pressure are not time dependent aging effects. See Section 6.3.3 of IEEE-323-1983, Standard for Qualifying Class 1E Equipment for Nuclear Power Generation Stations.

Given the above, the equipment inside containment has been qualified for the failure modes and mechanisms associated with pressure and is qualified in accordance with the requirements of 10 CFR 50.49. A revised pressure envelope is shown on plot 20.

1/14/97 JE8 J i \\ LICENS E \\ JOE t\\ LETTER 3 TCNTMT I. DOC

PLOT 1 -

MONTICELLO DRYWELL TEMPERATURE ENVELOPE 350 II l

1 E-u 300 7

j g

iv--g N

4,sik; -

\\

r 250 y/

3

\\

)g/

j s

f

--m--EQ ENVELOPE

{

k 5l,

}\\

- - - CASE 1 y 200-

,,/

I h

\\

---

CASE 2

[

k

[

\\

- - - - CASE 3

~'

g j/

17

)

.~

1 s

_.. - CASE 4 E

/

Y

--iq CASES u

.ad:'

150-L q

s 2

Q.

N se

- - - CASE 6

...... CASE 7 100-50 -

0 O.1 1

10 100 1000 10000 100000 1000000 10000000 TIME (seconds)

PLOT 2 MONTICELLO DRYWELL TEMPERATURE ENVELOPE 350 g

i 300-

/.

/

se--$

/

\\

s

\\

250

/

r e

s.

v

/

g C

\\

Y 200

\\

M

(

\\

-e-EO ENVELOPE E

/

\\

--- CASE 1 q

/

W

...... CASE 2 g"150

/

%-- qs F

i 100 50 0

0.1 1

10 100 1000 10000 100000 1000000 10000000 TIME (seconds)

4 PLOT 3 MONTICELLO DRYWELL TEMPERATURE ENVELOPE 350 I1 I

ll' l l

1 l

m--u 300

/

7

-f g

IF--$

/

L N

t

\\

N 250 i

s r

t g

N W 200-

) !"

\\

i m

N\\.

f

-m-EO ENVELOPE s

s g

.s

..l q-

-.--CASE 3 m

/

s

,_ A

$150-N

/

--se m

1 p

I s

100 --

f l

50 0

0.1 1

10 100 1000 10000 100000 1000000 10000000 TIME (seconds) t w-

m.

PLOT 4 t.

MONTICELLO DRYWELL TEMPERATURE ENVELOPE I

5 i

l I

i l

l 1

j I

IF-o 300 F

n---g

\\

g f

s 250

/

\\

k

/

s

/

1\\

g

/

N g 200 j

\\

-m-EO ENVELOPE S

/

\\

- - - - CASE 4

[

k s

CASES su

/

.i

-l%

t

$150-L Sq

- g i

\\

t 100 l

50 -

0 0.1 1

10 100 1000 10000 100000 1000000 10000000 TIME (seconds) b

PLOT 5

+

MONTICELLO DRYWELL TEMPERATURE ENVELOPE 350

[

I l1 5--n 300 sF-3 j

\\

_..A.

t 250 -

/

N N

/

l N

/

us 200-

-e' 3

\\

cc 4

s

-e-EO ENVELOPE g

N 3

\\

- - - CASE 6

.e

$ 150 -- /'y.e

)

Ik tc

...... CASE 7 ur M

, 1A

?

us s,

qu I

100 l

f 50 0

0.1 1

10 100 1000 10000 100000 1000000 10000000 I

TIME (seconds) t

EP O

LEVN1 2 3 4 S 6 /

EE EEEEE E SS S S SSS QAAAAAAA ECCCCCCC 000 i

0 t

0 1

~

s N

I~;

/ ~~,6'.

E 0

P 0

O 0

s:

s' 0

L s

1 E

s V

s' r

N E

=

E

=

R U

0 S

=

0 S

0

-s.k1 1

E i

R 4

6 P

NN 2

T NN 3

s'

<\\k O

L L

L

)

P E

s d

W

\\

n N

y o

Y 0 c R

k 0 es

\\

1 D

(

\\

\\

E O

h M

L I

T L

e E

C h

I

/,

T N

O 0

1 M

's

/ //

/ j s

/ I N

p/!

f

/

1

/

l

/

l

/

/

1 0

0 0

0 0

0 0

6 5

3 2

1

_5m8 EUmuE t

PLOT 7 MONTICELLO DRYWELL PRESSURE ENVELOPE N

-- s

/

N 50 -

/

/

~- s s

/

/

s

/

/^N N

Q

/

Y-N s,

N g

h

[

\\. EQ ENVELOPE E 30 -

/

\\'

K CASE 1

- - - - - - CASE 2 uJ i

g t

tr s

G-i

/

s*

/

n e

20

/

I

/

(

l W

t 10 -

l 0

0.1 1

10 100 1000 10000 100000 TIME (seconds) i b

PLOT 8 t

MONTICELLO DRYWELL PRESSURE ENVELOPE 60 t

i

~ -

l/

N 50 -

~~

j N

40-

/

b

\\

/

w v---m s

j

\\

\\

8

/

us

,/

)

t s

,/

til

-e-EQ ENVELOPE i

CASE 3 l

y l

\\

cc

/

\\

i.

E

'I

/

g N

/

11

/

s

____-_/^'

20

- s

/

i 10 -

I O

{

0.1 1

to 100 1000 10000 100000 r

TIME (seconds) i I

m

PLOT 9 1

MONTICELLO DRYWELL PRESSURE ENVELOPE 60 r-N

/

50 -

-.'N s

/

-.. ' i

/

s 40 -

N

/

N sn

/

~

E

/

-e-EO ENVELOPE ui

/

- - - CASE 4

'\\

E 30 -

3

/

g j/

---

CASES W

/

E N

I

\\

EL i

/

/

II

\\

20 -

/

, = :.:- s s

/

'" ~~- Z:

10 0

0.1 1

10 100 1000 10000 100000 TIME (seconds)

=

PLOT 10 3

MONTICELLO DRYWELL PRESSURE ENVELOPE -

so

/

50 -

/

/

N

/

~-1

/

x 40-

/

\\

/

/\\

/

\\

\\

E

/

\\

--m-EO ENVELOPE

/

CE 30

/

h

- - - - CASE 6 k

CASE 7 m

/

/

\\

m

/

I

\\

L i

/

s

/

IB-20

/

, g

/

l

-,-ce-

%Q 10 0

0.1 1

10 100 1000 10000 100000 TIME (seconds) 4 2

m m

PLOT 11 MONTICELLO DRYWELL TEMPERATURE ENVELOPE -

350-

-is l

300

/

f

- ;;kni:;_: g

'- -i

\\hs

/

\\

d g

r[

-b-A'-

250 -

f

\\

4 t -[...-M-9. WI-its

)

/

\\

\\

/

p,}g s

j

\\

h

-m-EO ENVELOPE g 200

/

'/

\\

\\

\\ '-

--- CASE 1-REF.A-1

[

/

\\

'4 CASE A-1 sQN

- - - - - CASE A-2 E

i

' N:-N

- - - - CASEA.2-REF.A-1 150 2

s tu

'1ll

- - - - 1880-DBA l

' il 100 I

50 I

0

'l O.1 1

10 100 1000 10000 100000 1000000 10000000 TIME (seconds) s

PLCT 12 MONTICELLO DRYWELL TEMPERATURE ENVELOPE 350 g

~

~

E-u

/

300-f N

N

~'

j f

/

\\

N 250

~~

f

/

\\f f

7

\\

~

s

\\

W 200

/

/

\\

-e-EO ENVELOPE E

y CASE A-1

-k cc

/

N

- - - - - - CASE A-2 w

$150-/

._b

,_ill Wv i

100 50 i

1 0

0.1 1

10 100 1000 10000 100000 1000000 10000000 TIME (seconds)

PLOT 13 MONTICELLO DRYWELL TEMPERATURE ENVELOPE 350 j

g ii--u 300 I

....,!!~ 3

^

l N

250-s

/

g

,/

\\

N g 200-j

\\

S

\\

-e-EO ENVELOPE s

N 15-

- - - - 1880-DBA us

/

t

$ 150 -

,/

-b us

'1B p

I d

100 50 -

0 0.1 1

10 100 1000 10000 100000 1000000 10000000 TIME (seconds)

PLOT 14 MONTICELLO DRYWELLTEMPERATURE ENVELOPE 1

l l ll it-u 300-f

• d e

s, tv\\

250-

' [

\\

j

$' \\

s

/

i

- 's t

\\

l E

\\

I j

200

\\

@'q

--m-EQ ENVELOPE f

Q

--- CASE 1-REF.A-1

/

M

- - - - CASEA.2-REF.A-1 e,

$150 s

au

'S F

i 100 50 0

0.1 1

10 100 1000 10000 100000 1000000 10000000 TIME (seconds)

PLOT 15 MONTICELLO DRYWELL TEMPERATURE ENVELOPE 350 g

15-ai 300

)

I

$m.

.,Ap, e

a

\\

l

\\y q f

g a

L

[

[

-$g k.

250 L

j r..

ym, sm, j

a e

\\

f N

\\

--45-EO ENVELOPE C

s

\\

s

)

\\

\\

2.

DBA ENVELOPE tu 200-g

/

\\

Qm

--- CASE 1 REF.A-1

/

f

/

F r

N t

CASE A-1

k

"'y

.... -. CASE A-2 i

/

$ 150 -

- - - - CASEA.2-REF.A-1 N

I

- -- 1880-DBA I

100 50 L

0 0.1 1

10 100 1000 10000 100000 1000000 10000000 TIME (seconds)

=

PLOT 16 MONTICELLO DRYWELL PRESSURE ENVELOPE 60

-- A

//

. / 3 N

50 f \\ 's

. N

/

s s 2

~

.y, 3

.rj

, \\

\\

40

/

.N h

{

/l,

/f V.

g.

y%.,

s e

t

[

I i

- i O

EQ ENVELOPE

' q.,p

//

g j

[

'/

U~

CASE 1-REF.A-1

~

4

[

f,'

n' A

N

- - - CASE A-1

~

'\\

$ 30 f

s\\

- - - - - - CASE A-2

//

g f

s \\ '.

- - - - CASEA2-REF.A-1

\\

E g[

/

(

- - - - 1880-DBA s

f[

N-20-g il r

10 O

0.1 1

10 100 1000 10000 100000 1000000 TIME (seconds)

- - ~. -

-w.-

--,n-n---

PLOT 17.-

MONTICELLO DRYWELL PRESSURE ENVELOPE 60 N

/

,-g 50 -

/

\\

N--..N

\\

/

\\

N

/

,I

\\

%"* *,6g,,

/

• =,,

\\

e 40-f 4

\\

1

<c t

, \\

/.r g

g, s

/

[

-.s s

EO ENVELOPE y

$ 30 -

h K

- - - CASE A-1

/

\\

' s

- - - - - - CASE A-2 s

s m

l

\\

E 0-

/

N s

/

t>

20

/

/

/

/

10 -

0 0.1 1

10 100 1000 10000 100000 TIME (seconds)

_,___..m_

PLOT 18 L

MONTICELLO DRYWELL PRESSURE ENVELOPE 60 g

D l

- ~

y

~~.

~

\\

50 -

/

- --~x l

s. _

. W s

/

./

N 40

./

k y

/

R

--~.

m f

a.

-s y

\\

EQ ENVELOPE 30

- - - - 1880-DBA m

g E

G-N

./

s s

)

20 -

t' 10 0

0.1 1

10 100 1000 10000 100000 TIME (seconds) m am---

' PLOT 19 MONTICELLO DRYWELL PRESSURE ENVELOPE i

s i

t f

,, 'N s

50

/,

--..N

.s i

//

(;

7 i

f.

/

f ', \\

40 -

l N

s s

Q

's, \\

\\

q j

s

/

t f

.j-'

\\

EQ ENVELOPE

\\

E 30 -

~~~ $

- - - - - - CASE 1-REF.A-1 3

/

\\

m CASEA2-REF.A-1 s

us m

s n.

s q

g o

-.y 20-N t

.t 10 -

l O

t 0.1 1

10 100 1000 10000 100000 1000000 F

TIME (seconds).

1 i

PLOT 20 MONTICELLO DRYWELL PRESSURE ENVELOPE 60

=

llll t,

l N

,~:::js

i

• (W's

' s

'N-.

50

~ 's s-y\\'

s

\\

. ;.y.g 7

,g.

y

~

~

-)

i

..'.,s N

s,

N 1

//

k 40 X

g N

EO ENVELOPE

=

d,/

f i,

b

,-1 J,

.. k.f A

NEW EQ ENVELOPE

~

E 4

.'.)'

k---

Qg 8*

6 CASE 1-REF.A-1 Y) 5N ';l'

- - - CASE A-1 30 3

\\

- - - - - - CASE A-2

.j

\\

\\

n.

\\

N

- - - - CASEA.2-REF.A-1 s

\\

//

\\

\\

_. _.1880-DBA s

f,'!

20 p g

i

/

10 g

i 0.1 1

10 100 1000 10000 100000 1000000 TIME (seconds)

l l

9.

For Case 3 the GE analysis assumes that after 10 minutes, one of the RHR pumps is tumed off to allow start of a RHRSWpump. The remain.hg RHR pump is aligned to containment spray mode. One core spray (CS) pump would be injecting into the vessel.

Based on our review of the applicable sections of the EOPs, the staff came to the following conclusions. In EOP Section C.S.1-1100, the operators are instructed to maintain level between

+9 and 48 inches. Under this scenario however, this band is not achievable. The next allowable band is top of active fuel, -126 inches. The EOPs instruct the operators to establish two injection paths (CS and RHR with a heat exchangerin LPCI[ low pressure coolant injection] mode under this scenario). Again, the levelbandis not attainable. The operators wouldproceedinto C.5-2004, 'Drywell Flooding."

Concurrently with the Reactor Pressure Vessel Pressure / Level Control, the operatom would be entering Primary Containment Contml, C.5.1 1200. The torus temperature and drywellpressure branches instruct the operators to place RHR in torus cooling mode only if not required for core cooling. A RHR pump will be placed in drywell sprayAorus cooling mode onlyif the pressure cannot be maintained below 56 psig. (in Figure B-6 of the submittal, pressure is less than 40 psia.)

Therefore, it appears that there may be some discrepancies between assumptions made in the GE analysis and EOPs. The staff believes this question also applies to Cases 4 and 6.

The ECCS NPSH concerns are obviated by other limiting factors under the required EOP mitigation sequence. The Drywell Flooding leg of the EOPs instructs the operator to flood the drywell with LPCI using the Condensate Storage Tank (CST) suction path. The CSTs would provide adequate NPSH for the RHR pumps. In addition, flooding is accomplished using significantly colder sources of water. Under the EOP flooding instructions, only one core spray pump is left with a suction path from the torus. Because of the increase in torus level, decrease in torus water vapor pressure, and the reduction in friction head loss from flow reduction with only one pump, it is reasonable to conclude that core spray pump NPSH would not be a concem for this scenario.

In addition to NPSH concems, the EOPs as written would continue to assure adequate core cooling and primary containment integrity, albeit by a different mitigation path than that described in the design basis event analyses.

Design basis event analyses are based on a set of deterministic assumptions. The EOPs are not wholly predicated on such assumptions and were developed to provide the best operational guidance based on the symptomatic conditions available to the operator for a full spectrum of plant conditions and events. The MNGP EOPs are in compliance with Rev. 4 of the Emergency Procedure Guidelines.

NSP does, however, recognize a salien? difference between the plant licensing basis and the EOPs which causes the level bands iden ified by the staff to be unattainable. This is due to the inconsistency between the licensing basia definition for the required reactor water level to achieve adequate core cooling (2/3 core height) anC the EOP definition (top of active fuel). The differences in the design basis accident analyds assumptions and the EOP actions for suppression pool cooling are caused by this incorsistency. The complete and definitive method of addressing Question 9 is to change the EOP defdtion of adequate core cooling to coincide with the licensing basis definition of adequate core cooling. This action would be consistent with the original and current licensirig basis of the plant. It would also serve to eliminate the 7/16/91 JE9 J a \\ LICENSE \\JOCL\\ LETTER $\\CNTMT1. DOC l

l discrepancies between the design basis accident assumptions for the accidents described in the license amendment and the EOPs. Moreover, it represents a movement toward additional safety as operators would now be instructed to maintain primary containment integrity in a more controlled manner and not continue injecting into the core with an ECCS pump that would be much better employed in a containment cooling capacity.-

In order to make the EOPs reflect the current licensing basis of the plant and to enhance the overall safety of the plant, NSP commits to process a 50.59 evaluation to change the EOP definition of adequate core cooling to 2/3 core height within 180 days of the plant startup date.

The corresponding EOP changes and the required operator training will also be completed in this j

time period. Implementation will be completed when all of the 50.59 requirements are satisfied.

l i

I 7/16/97 JE8 Ji\\ LICENSE \\JOEL\\LF.TTERS\\CNTMT1. DOC I