ML20205K614
| ML20205K614 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 04/30/1999 |
| From: | HOLTEC INTERNATIONAL |
| To: | |
| Shared Package | |
| ML20205K607 | List: |
| References | |
| HI-971843(NP), HI-971843-R02, HI-971843-R2, NUDOCS 9904130298 | |
| Download: ML20205K614 (47) | |
Text
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lioltec Center,555 Lin( oln Drive West, Marlton, NJ 08053 H O L T E C-Telephone (609) 797-0900 I ax (609) 797-0909 INTERNATIONAL LICENSING REPORT FOR RECLASSIFICATION OF DISCHARGE IN MILLSTONE POINT UNIT 3 SPENT FUEL POOL for NORTHEAST UTILITIES l
by HOLTEC PROJECT NO: 70911 IlOLTEC REPORT NO: HI-971843 REPORT CATEGORY: 1 l
REPORT CLASS: SAFETY RELATED COMPANY PRIVATE l
This document version has all proprietary information rernoved and has replaced those sections, figures, and tables with highlight ng and/or notes to designate the i
removal of such information. This document is to be used only in connection with the performance of work by lloltec Internat anal or its designated subcontractors.
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Reproduction, publication or presentation, in whole or in part, for any other purpose by any party other than the Client is expressly forbidden.
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9904130298 990405 #
PDR ADOCK 05000423 P
PDR.
1 IIOLTEC REPORT: 111-971843
SUMMARY
OF REVISIONS LOG REVISION 0 Title Page 1
QA and Administrative Log 1
Review and Certification 1 og 1
Summary of Revisions Log 1
Table of Contents 1
List of Figures 1
Text and Tables 31 Figures 12 REVISION 1 Pool building ambient temperature changed from 98 F to 108 F. All pages re-issued as Revision 1. Number of pages unchanged.
REVISION 2 l
Editorial correction on page 23. Number of pages unchanged.
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Report 111 -971843 Revision 1 1
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l TAllLE OF CONTENTS
1.0 INTRODUCTION
.....I 2.0 1 UEL POOL COOLING SYSTEM DESCRIPTION................
.3 3.0 DISCIIARGE SCENARIOS AND PROBLEM DESCRIPTION.....
.... 7 l
4.0 SOLUTION METilODOLOGY......
.. 12 4.1 Introduction.........
12 1
4.2 Ilackground Decay lleat Load Calculations......
... 12 l
4.3 Maximum Decay IIcat Load Limits.......
.14 4.4 Transient llulk Pool Temperatures..
16 5.0 R E S U LT S.............................................
.. 22 5.1 Decay lleat Input
. 22 5.2 Determination of Maximum Decay lleat input.
.. 22 5.3 Minimum lloid Time Results....
23 5.4 Pool lleat-Up During loss of Cooling
.. 23 j
5.5 Partial Core Discharge (Case 3 Scenario) Results
. 24 6.0 REl:ERENCES..............
.... 31 1
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1 LIST OF FIGURES Figure 3.1:
Millstone Unit 3 Spent Fuel Pool Scheduled Full Core Discharge Scenario (Case 1)
Figure 3.2:
Millstone Unit 3 Spent Fuel Pool Unscheduled Emergency Full Core Discharge Scenario (Case 2)
Figure 3.3:
Spent Fuel Pool Cooling Model Figure 5.1:
Post-Shutdown Decay lleat Generation Due to Most Recently Discharged Full core (Case 1 Scenario)
Figure 5.2:
Post-Shutdown I)ecay lleat Generation Due to Most Recently Discharged Full core and Previous Shutdown Partial Core (Case 2 Scenario)
Figure 5.3:
Total System Cooling Capacity at 150 F Ilulk Pool Temperature as a Function of CCP Temperature Figure 5.4:
Millstone Unit 3 Fuel Pool Minimum In-Core lloid Time Figure 5.5:
Bulk Pool Transient Temperature Plot (Case 1 Scenario)
Figure 5.6:
Ilulk Pool Transient Temperature Plot (Case 2 Scenario)
Figure 5.7:
CCP Outlet Temperature as a Function of the SFP Temperature (Clean Unplugged Exchanger)
Figure 5.8:
Cooldown Curve for Case 1 Scenario After a 4-Ilour Loss of Pool Cooling Figure 5.9:
Cooldown Curve for Case 3 Scenario After a 4-Hour Loss of Pool Cooling i
1(eport 111-97 i 843 llevision 1 111 l
t 1.0 INTitODilCTION Millstone Point Unit 3 (MP3) is a Westinghouse-supplied PWR reactor rated at 3411 MW (thermal). MP3 is located at a three reactor unit site on the sou'^ ern coast of Connecticut in the town of Waterford. The plant began commercial operation in 1985.
In its first ten years of operation, MP3 underwent five refuelings leading to a total accumulated fuel inventory of 416 assemblies (Table 3.1). An extensive system-wide enhancement program undertaken after the fifth refueling outage has kept the plant offline since March 1996. Th~
current schedule is for the restart of MP3 in early 1998. A projected discharge schedule is presented in Table 3.2.
NU has decided to classify full-core offload into the pool at scheduled outages as a " normal" discharge. The object of this report is to set down the analyses carried out to determine the restrictions on fuel transfer to the pool which must be applied administratively.
In order to render the evaluations independent of the refueling cycle, the analyses performed herein assume that the inventory of the spent fuel in the pool corresponds to the end-of-the-licensed life of the MP3 reactor. The " background" heat load in the MP3 pool is maximized by assuming a theoretical maximum quantity of fuel stored in the pool from prior discharges. By assuming an artificially large quantity of fuel stored in the pool from prior discharges, the
" background" heat load in the pool is maximized.
l As is true in all northern plants in the country, the plant cooling water temperature varies within a wide range throughout the year at MP3, resulting in a corresponding seasonal variation in the component cooling water (CCP) heat removal capability. The CCP temperature is controh J by Itepoi1111-971843 llevision i 1
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a temperature control valve with a setpoint adjustable over the entire allowable range. 'lhe analyses performed and reported in this 1.icensing Report, there fore, treat the component cooling water temperature t, as a system variable. 'Ihe thermal problem seeks to determine the elapsed time T, to complete full-core transfer to the pool (with the origin of the time coordinate at reactor i
shutdown) as a function of t, such that the maximum pool bulk temperature remains below the newly prescribed conservative limit. T he function representation of T, vs. t, will enable MP3 to plan fuel transfer at outages (schedcled and unscheduled) with absolute assurance that the pool bulk temperature limit committed to in this license submittal will not be violated. To ensure that a comfortable margin in the calculated results exists, several conservative assumptions have been made, among them the assumption that 77 tubes are plugged (removed from service) in each cooler when, in fact, no tubes have been plugged so far. A listing of conservative assumptions l
which innate the computed pool bulk temperature is provided in a later section of this report.
As an auxiliary to the bulk pool temperature analyses, pool heat-up rate in the wake ofpostulated loss of all forced cooling paths is also determined for all postulated discharge scenarios. These calculations serve to provide a qualitative evaluation of the feasibility of implementing alternative ameliorative cooling measures after loss of all forced cooling paths.
The analysis methodologies and computer codes utilized in this analysis have a long history of usage in prior licensing applications. Table 4.1 provides a listing of recent license applications where these analysis methodologies have been used. A11 analyses documented in this report were carried out by lioltec International of Marlton, New Jersey, as a consultant to the plant's operator, Northeast Utilities (NU).
Under separate work efforts NU and lloltec International are developing a multi-campaign capacity expanion of the MP3 fuel pool to deal with the projected loss of full-core-reserve Report 111-971843 Revision i f
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capacity in about the year 2001. The implementation of the multi-campaign pool capacity expansion will increase the installed capacity, which will, nevertheless, remain below the inventory assumed herein (3048 assemblies). All analyses have been performed under lloltec international's 10CFR50 Appendix B QA program.
l 2.0 FUEL, POOL, COOL ING SYSTEM DESCRIPTION l
L The fuel pool cooling and purification system removes decay heat from spent fuel stored in the fuel pool and provides adequate cooling of water in the fuel pool. Two 100% capacity fuel pool i
cooling pumps and two 100% capacity fuel pool coolers are provided to ensure 100-percent l
redundant cooling capacity. This portion of the system is Seismic Category I and Safety Class j
- 3. The spent fuel pool water flows from the fuel pool discharge through either of the two fuel j
pool cooling pumps and through 'he tubeside of either fuel pool cooler, and then returns to the fuel pool. Table 2.1 lists the performance characteristics of the fuel pool cooling system. Cooling l
for the fuel pool coolers is provided by the reactor plant component cooling water system.
i Each pipe which enters the fuel pool has a vent hole drilled into the pipe to act as a anti-l siphoning device or terminates at an elevation above these vent holes. These provisior s prevent siphoning of the fuel pool water to less than 10 feet above the spent f"el. One pump and one cooler are sufficient to maintain the bulk pool temperatures to a maximum of 150 F for any long-term period. The bulk peak temperature of the spent fuel pool is limited to 200 F for structural qualification of the spent fuel pool.
Following a design basis accident with loss of power, the reactor plant component cooling water system is not available to cool the spent fuel pool coolers until approximately four hours after the accident. Power from the emergency generators is not immediately available due to loading 1(eport 111-971843 itevision 1 3
I considerations. Pool cooling will be reinitiated at this time.
Redundant safety grade fuel pool temperature indication is provided on the main control board.
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Redundant safety class 3 level instruments are located in the fuel pool which indicate both locally and in the control room. They are set to provide indication before the water level falls below 23 feet above the top of the fuel racks. Piping penetrations are at least i1 feet above the top of the spent fuel so that failure ofinlets, outlets, or accident piping leaks cannot reduce the water below this level.
Normal makeup water to the spent fuel pool is the primary grade water system. Should primary grade water be unavailable, makeup water can be provided from the refueling water storage tank, a Seismic Category I source 130th of these systems connect to the spent fuel pool through the non-nuclear safety purification system. Water can also be provided from the hose station of the fire protection system near the spent fuel pool. As an additional safety feature for the unlikely event of failure of the sources above, a Seismic Category 1, Safety Class 3 flow path is provided from the service water system.
The fuel pool has redundant safety grade low level lights and temperature indicators provided in the main control room. Non-safety grade level indication is provided locally and high and low level alarms are provided both locally and in the main control room.
l.ocal temperat ure indicators are provided on each fuel pool cooler outlet. Fuel pool cooler outlet high temperature is alarmed locally and in the control room. Fuel pool cooler outlet flow is indicated, and low flow alarmed, locally. Fuel pool cooler instrumentation is non-safety grade.
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L The fuel pool cooling pumps have control switches and indicating lights in the main control room. The discharges of a!! pumps have local pressure indicators. Upon a high temperature at
'he pool, the standby fuel pool cooler is started manually. The cooling pumps can be operated manually either from the control room or the switchgear. The purification pumps are operated i
locally.
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Table 2.1 FUEL POOL COOLING AND PURIFICATION SYSTliM PRINCIPAL COMPONENT DESIGN CHARACTERISTICS Fuel Pool Cooling Pumps Quantity 2
Capacity (gpm) 3,500 l
IIcad (ft)
I15
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Design pressure (psig) 200 Design temperature ( F) 200 Fuel Pool lleat Exchangers Quantity 2
Design heat load per exchanger (Btu /hr) 27.7 x 10
Reactor plant component cooling water flow per exchanger (gpm) 1,800 Reactor plant component cooling water inlet temperature (*F) 95 Reactor plant component cooling water outlet temperature ( F) 126 Fuel pool cooling flow (gpm) 3,500 Fuel pool water inlet temperature
( F) 140 Fuel pool water outle: temperature ( F) 125 Tubeside design pressure (psig) 150 j
l Design temperature ( F) 200 Report 111-971843 Revision 1 6
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l 3.0 I)lSCllAltGli SCl!NAltlOS ANI) Pitolli, lim I)liSCillPTION The Millstone Unit 3 spent fuel pool is designed to meet the following post-reactor shutdown fuel discharge scenarios.
l Case 1: Scheduled Full-Core Offlog One full core (193 assemblies) is off-loaded to the pool aller one year of operation at full power.
Figure 3.1 pictorially depicts this discharge case.
Case 2: Unscheduled Emergency Full-core Offload One full core (193 assemblies) is offloaded to the pool after a previous outage lasting for 10 days with 36 days of operation at full power. Figure 3.2 depicts this discharge case.
Case 3: Partial Core Discharee This case is for a partial core discharge of up to 97 assemblies into the pool followed by loss of cooling for 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. The temperature and decay heat loads in the pool at the start of loss of i
cooling correspond to the time at 600 hours0.00694 days <br />0.167 hours <br />9.920635e-4 weeks <br />2.283e-4 months <br /> after reactor shutdown. Cooling water temperature is assumed to be at an operating high temperature of 95 F.
In Case 1 and Case 2 discharge scenarios it must be demonstrated that peak bulk pool temperatures do not exceed 150 F temperature limit when normal cooling is operational with component cooling water (CCP) supplied to fuel pool heat exchanger. One fuel pool pump and one heat exchanger are assumed to be normally available for removing decay heat from the Report 111-971843 llevision 1 7
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Millstone Unit 3 fuel pool for all scenarios. The two 100% capacity fuel pool cooling pumps and two 100% capacity fuel pool coolers are able to provide completely redundant cooling capacity.
The CCP system, following a design basis accident, is not available to cool the fuel pool for fbur hours. In the event of loss of pool cooling, it must be demonstrated that the bulk pool temperature shall not exceed 200'F during this four-hour post LOCA heat up of the pool.
1 in Table 3.1 (from Reference 6.4), the Millstone Unit 3 pool existing fuel discharge data is presented. The existing fuel pool inventory of 416 fuel assemblies is ihr cycles 1 through 5 of reactor operation. The last (cycle 5) discharge occurred on 4/14/95. Future projected fuel discharges (from Reference 6.4) at bounding average batch burnup is presented in Table 3.2. The last (cycle 20) End of Cycle (EOC) full-core discharge is projected to occur after approximately two years of reactor operation at full power in February 2026. For consarvatism, the EOC full-core discharge is assumed to occur on March 1,2025, one year after the previous discharge. The freshly discharged assemblies fuel burnup, consistent with a 24-month operating cycle, is conservatively assumed at bounding average batch burnup levels. In addition to fuel pool inventory from Millstone Unit 3 fuel discharges (1,960 fuel assemblies), storage of up to 1.088 fuel assemblies transferred from Unit I and Unit 2 pools is also considered. Adding in the heat load simulating discharges of Unit I and Unit 2 fuel is conservative, since Unit 3 is not currently licensed to store any Unit I or Unit 2 fuel in the Unit 3 spent fuel pool. This heat lead is being added in case, at some future time, authorization to store Unit 1 or Unit 2 tuel in the Unit 3 pool is requested. The old Unit I and Unit 2 fuel assembly decay heat characteristics are not deemed to be limiting, compared to Millstone Unit 3 fuel.110 wever, for conservatism, it is assumed that the transferred fuel assemblies will be equivalent to 10-year old Unit 3 fuel at bounding average burnup level prescribed for projected discharges. At the EOL, up to 2,855 old fuel assemblies will be stored in the Unit 3 pool prior to a full-core discharge. Including the freshly discharged Iteport 111-971843 itevision 1 8
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full core, a maximum of up to 3,048 fuel assemblies will be stored in the Unit 3 pool. The fuel I
inventory information is used to compute the Unit 3 pool decay heat burden by llollec's QA validated DECOR computer code [ Reference 6.1]. The DECOR computer program is based on the ORNL's ORIGEN2 code for perfonning irradiated fuel source term computations.
Figure 3.3 depicts a fuel pool cooling model for performing Millstone Unit 3 thermal-hydraulic computations. The decay heat input to the pool from the fuel inventory (old fuel or freshly discharged fuel) is removed by 'he fuel pool heat exchanger and by pool surface evaporation cooling mechanisms. The maximum pool decay heat load occurs at the end of fuel transfer as depicted in Figures 3.1 and 3.2 fbr Case 1 and Case 2 discharge scenarios. The 150 F maximum bulk pool temperature limit shall be demonstrated by limiting the maximum decay heat load to Millstone Unit 3 pool to within the heat removal capacity of the cooling system. The l
methodology for performing these calculations is presented in Section 4.
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l Table 3.1 MILLSTONE UNIT 3 lilSTORICAL FUEL DISCilARGE DATA Ave Disch Number of Shutdown Discharge Number Aserage llurnup MtU per Assemblies Date Cycle llatch Disch w/o (Mwd /MtU)
Assem in SFP 10/31/87 I
A 65 2.42 20570 0.4614 B
10 2.90 21585 0.4613 75 5/11/89 2
B 45 2.90 32?86 0.4613 C
40 3.40 32576 0.4613 160 2/2/91 3
B 9
2.90 38739 0.4613 C
24 3.40 41566 0.4613 DI 46 3.50 35994 0.4621 239 7/31/93 4
D1 9
3.50 47885 0.4621 D2 4
3.80 50174 0.4623 El 32 4.10 43915 0.4627 E2 23 4.50 41683 0.4616 307 4/14/95 5
E2 21 4.50 44142 0.4616 FI 32 4.20 44722 0.4639 F2 56 4.50 42111 0.4630 416 l
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Table 3.2 MILLSTONE UNIT 3 96 FEED EQUILIBRIUM CYCLE PROJECTED FUTURE DISCllARGE SCENARIO Discharge Cycle Number Average Ase Disch Mtu per Number of Shutdown Cycle EFPD Disch w/o Burnup Assembly Assemblics Date (Mwd /MtU) in SFP Oct-1998 6t 564 97 5.0 60000 0.455 513 Oct-2000 7
644 96 5.0 60000 0.455 609 Sep-2002 8
644 97 5.0 60000 0.455 706 I
Sep-2004 9
644 96 5.0 60000 0.455 802 Aug-2006 10 644 97 5.0 60000 0.455 899 Jul.2008 11 644 96 5.0 60000 0.455 995 Jul-2010 12 644 97 5.0 60000 0.455 1092 J
Jun-2012 13-644 96 5.0 60000 0.455 1188 Jun-2014 14 644 97 5.0 60000 0.455 1285 May-2016 15 644 96 5.0 60000 0.455 1381 May-2018 16 644 97 5.0 60000 0.455 1478 Apr-2020 17 644 96 5.0 60000 0.455 1574 Mar-2022 18 644 97 5.0 60000 0.455 1671 Mar-2024 19 644 96 5.0 60000 0.455 1767 Feb-2026 20 644 193 5.0 60000 0.455 1960 1
Due to delay in Unit 3 startup, the discharge date will be delayed.
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4.0 SOI,lJTION MIiTIIODol A)GY l
4.1 Introduction l
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This section provides a summary of the methods, models, and analyses to demonstrate the adequacy of the Millstone Unit 3 spent fuel pool cooling systems to meet the applicable bulk pool temperature limits criteria discussed in Chapter 3. Similar methods of therr.tal-hydraulic analysis have been used in numerous other rerack licensing projects (see Table 4.1).
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4.2 Backcround Decav Ileat Load Calculations The decay heat load calculation is conservatively performed on ORNL's ORIGEN2 computer code implementation on Iloltec's QA validated DECOR code. Tables 3.1 and 3.2 show the past and future projected discharges in the Millstone Unit 3 pool. For conservatism, all iteport lll 971843 llevision i 12
l calculations are performed assuming that the pool has accumulated conservatively bounding fuel inventory based on Unit 3 96-1;eed Equilibrium Cycle Discharge projections and provision ihr t
up to 1,088 old fuel assemblics transferred from Unit 1 and Unit 2 pools to Unit 3. The 96-Feed 1
Equilibrium Cycle Discharge projection, therefore, produces the largest End-of-Life decay heat burden to the Unit 3 pool. Since the decay heat load from old assemblies attenuates very slowly with time, it is assumed to remain constant Ihr the duration when the discharge scenarios described in Chapter 3 are considered.
l A total of 2,855 fuel assemblies will be stored in the Unit 3 pool from previous discharges prior to a full-core discharge of fresh fuel at the end of life. Including fresh and old discharges, bounding decay heat from up to 3,048 fuel assemblies in the fuel pool is considered. To render a conservatively bounding estimate of the decay heat, the following assumptions are included in the analysis:
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Note that two other studies by NU [ Reference 6,4] have demonstrated that fewer i
assemblies will be in the pool at the end oflife.
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r 4.3 hkiximum 1)ecav Ileat 1 oad I.imits The heat input to the spent fuel pool is the sum of a constant background decay heat (from previously discharged assemblies) and a time varying decay heat input from freshly discharged assemblies. This is expressed in the fellowing equation:
Q, (T) = P,, + Q(T)
[Eq. 4.1]
1 where:
Qi(T) =
time dependent heat inpet to spent fuel pool constant background decay heat P
=
com time dependent heat input from freshly discharged assemblies Q(T)
=
time after reactor shutdown T
=
A key characteristic of the decay heat input from freshly discharged assemblies is that the heat emittance exponentially attenuates with time. Consequently, the maximum heat load to the spent fuel pool occurs at the instant of end of fuel transfer to the pool (see Figure 3.1). If this maximum decay heat load is conservatively applied as a constant heat load to the fuel pool, then, at steady state conditions, the decay heat input will equal heat output from all sources of cooling to the pool. The heat output from the pool is given by the following equation:
Qo = Qux + Qn. + O + Qn + Qw
[Eq. 4.2]
c where:
Qo = total heat output from the spent fuel pool Qnx = pool temperature dependent heat removal by spent fuel heat exchangers to CCP system Qn = pool cooling by surface evaporation Repon 111-971843 Revision i 14 m
F Q, =
pool surface cooling by natural convection Qx = pool surface cooling by radiation Qw= heat conduction through pool liner and concrete walls in this evaluation, heat losses by natural convection, radiation, and wall conduction are 1
conservatively neglected. Therefore, at postulated steady state conditions, the following relationship must be satisfied:
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O.mn (T ) = Onx + Q
[lig. 4.3]
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where Qtm, (r,) is the maximum decay heat input limit to the pool at the end of fuel transfer (T,).
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4.4 Transient llulk Pool Temperatures In this section, we present the methodology for calculating the bulk pool temperature as a function of the time coordinate. The method used to calculate the rate of pool water temperature rise and the time-to-heat up, when all forced cooling paths are unavailable, is also presented.
In order to perform a conservative analysis, the heat exchangers are assumed to be fouled to their design maximum. Thus, the temperature effectiveness, p, for the heat exchanger utilized in the analysis, is the lowest postulated value calculated from heat exchanger thermal-hydraulic codes.
The temperature effectivenees p is assumed to remain constant for the duration of the bulk temperature variation considered in this analysis.
The mathematical formulation can be explained with reference to the simplified heat exchanger alignment of Figure 3.3. Referring to the spent fuel pool cooling system, the governiiQ differential egaation can be written by utilizing conservation of energy:
C dT = P,,ns Q(t) - Q ;y (T,t,) - Qnx
[Eq. 4.5]
+
i dT where:
C:
Thermal capacity of the pool (net water volume times water density and times heat capacity), Btu / F Q(T):
lleat generation rate from recently discharged fuel, which is a specified function of time, T, Btu /hr.
Pcon,=pP,:
Ileat generation rate from "old" fuel, Btu /hr. It is also termed as long-term decay heat load. (P, = average assembly operating power, Btu /hr. and p is dimensionless decay heat power)
Q,n:
lleat removal rate by the heat exchanger, Btu /hr.
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4 0: v (T,t,):
lleat loss to the surroundings, which is a function of pool temperature T and ambient temperature t, litu/hr.
o Qux is a nonlinear function of time if we assume the temperature effectiveness p is constant during the calculation. Qux can, however, be written in terms of effectiveness p as follows:
Qux = W, C, p (T - t )
[Eq. 4.b]
i t' - t' p =.I,' - t;
[Eq. 4.7]
where:
W(:
Coolant flow rate,Ib./hr.
C:
Coolant specific heat, Btullb. F.
p:
Temperature effectiveness of heat exchanger.
T:
Pool water temperature, F t,:
Coolant inlet temperature, F t:
Coolant outlet temperature, F o
Qty is a nonlinear function of pool temperature and ambient temperature. Qty contains the heat evaporation loss through the pool surface. Natural convection and radiation from the pool Report 111-971843 Revision i 17
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surface and heat conduction through the pool walls and slab are conservatively neglected. The evaporation heat less can be expressed as (Reference 6.2):
g A, lP(T) - P '(t,)]
[Eq. 4.8]
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2 a:
evaporation constant, lBru/ft -hr-psi]
n A,:
pool surface area, [ft.2]
T, t : the temperature of pool water and building ambient air, 17 o
P:
saturation pressure of water at bulk pool temperature T, [ psi]
P':
saturation vapor pressure of water at ambient building temperature, [ psi]
The nonlinear single order differential equation (4.1) is solved using lloltec's QA validated numerical integration code "BULKTEM" [ Reference 6.3].
The next step in the analysis is to determine the heat-up time if all forced cooling paths become unavailable. Clearly, the most critical instant ofloss-of-cooling is when pool water temperature has reached its maximum value. It is assumed that no makeup water is added to the pool. The governing enthalpy balance equation for this condition can be conservatively expressed as:
dT C
- P,ns Q (t;ns) - Qn.
[Eq. 4.9]
+
y di I
where T is the time coordinate measured from the instant maximum pool water temperature is reached and I,n,is the time coordinate measured from the instant of reacto shutdown to when maximum pool water temperature is reached. T is the dependent variable (pool water i
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temperature). For this evaluation, the time T,,,., is conservatively assumed to be the end of fuel transfer at which instant the pool decay heat is at its maximum value. Note that the heat input to the pool is conservatively assumed to be constant after loss of pool cooling. The time to heat up to maximum 200 F temperature is determined by integrating the !!quation 4.9.
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l Table 4.2 1
TilERMAL-IlYDRAULIC DATA FOR MILLSTONE UNIT 3 i
SPENT FUEL POOL ANALYSIS i
Parameter Value Reactor power 3,41 l MW (thermal)
Core size 193 assemblies Fuel transfer rate 3 assemblies per hour Pool thermal capacity 3.845 x 106 Blu/ F 2
Pool area 2,231 ft CCPHow 900,000 lbs/hr CCP temperature 95 F (max.)
Exchanger tubes plugged assumption 77t Pool Building Ambient Temperature 108 F t
No tubes have been plugged.
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5.0 R ESI11ll'S 5.1 Decav 11 eat input Based on existing and projected fuel discharge data for the Millstone Unit 3 spent fuel pool (Tables 3.1 and 3.2), the background decay heat load at the End-of-Life is provided in Table 5.1.
For the Case 2 back-to-back discharge scenario, the partial core discharge is excluded from the list of background or constant decay heat fuel assemblies list. Consequently, the total background decay heat load is expected to be lower for this case. The partial core discharge is included in the list of freshly discharged fuel assemblies which is discussed next. The time varying decay heat input from freshly discharged fuel assemblies is given in Figures 5.1 and 5.2.
The burnup level of the most recently discharged assemblies for Case 2 scenario from the refueled reactor is lower due to a short 36-days operation at full power. The decay heat input for Case I scenario is therefore conservatively higher compared to the Case 2 scenario. Therefore, the Millstone Unit 3 full-core discharge is the limiting scenario for demonstration of thermal-hydraulic adequacy of fuel pool cooling system.
J 5.2 Determination of Maximum Decav Ileat Innut The evaporative cooling from Millstone Unit 3 pool surface as a function of pool bulk temperature is provided in Table 5.2.
The rate of heat removal by the fuel pool heat exchanger is a function of the bulk pool and CCP temperatures. At the bulk pool long-term temperature limit of 150 F, heat removal capacity in the range of 80 F to 95*F (max) inlet CCP temperature is also provided in Table 5.3. The maximum decay heat input line obtained from the sum of cooling rates by fuel pool exchanger and evaporative cooling is provided in Table 5.3. The decay heat input is limited to 36.08 million Repon 111-971843 Revision 1 22
Iltu/hr at the maximum 95"F CCP temperature. The maximum permissible limit is higher under improved fuel pool exchanger performance at lower CCP temperature. At 80 F CCP inlet temperature, the decay heat input limit is up to 45.41 million litu/hr. This information is also depicted graphically in Figure 5.3.
5.3 Minimum lloid Time Results The minimmn in-core hold time results are summarized in Table 5.4. After the maximum decay heat input limit to the fuel pool is established, the corresponding fresh core discharge decay heat input limit at the end of fuel transfer is obtained by subtracting the constant background decay heat input. The second column in Table 5.4 provides this result for the limiting Case I scenario as a function of CCP inlet temperature, after removing the background contribution (obtained from Table 5.1). The minimum end of transfer time after which the full-core decay heat load limit shall not be exceeded is obtained by interpolating the time-dependent decay heat data depicted in Figure 5.1. The minimum in-core hold time provided in the last column is obtained by subtracting 64 hours7.407407e-4 days <br />0.0178 hours <br />1.058201e-4 weeks <br />2.4352e-5 months <br /> transfer time (193 assemblies transferred at three assemblies per hour) 1 from the end of fuel transfer time. The minimum hold time is 285 hours0.0033 days <br />0.0792 hours <br />4.712302e-4 weeks <br />1.084425e-4 months <br /> after reactor shutdown if the CCP inlet temperature is 95 F. The hold time requirement is as low as 101 hours0.00117 days <br />0.0281 hours <br />1.669974e-4 weeks <br />3.84305e-5 months <br /> if the CCP inlet temperature is 80 F. Figure 5.4 depicts this information graphically. The bulk pool transient temperature profiles during fuel transfer are shown in Figures 5.5 and 5.6 for Case 1 and Case 2 scenarios, respectively. The CCP outlet temperature variations during the transient are depicted as a function of the spent fuel pool bulk temperature in Figure 5.7.
5.4 Pool Heat-t Ip Durine 1.oss of Cooling From Table 5.3, the maximum decay heat input to the pool at the end of fuel transfer is Report 111-971843 Revision i 23
determined to be in the range of 36.08 million Btu /hr to 45.41 million Btu /hr, depending upon
(
the CCP inlet temperature. A loss of forced cooling is postulated to occur at the end of fuel transfer with the bulk pool at 150 F temperature limit. The post-loss ofcooling fuel pool heat-up is summarized in Table 5.5 for several CCP inlet temperature levels. The heat-up calculation includes a conservatively credited evaporative cooling effect evaluated at 150 F bulk temperature applied to the entire range of temperature rise from 150 F to 200 F. The evaporative cooling contribution increases rapidly waa increasing temperature. The most limiting loss of coolant heat input to pool occurs at the highest maximum decay heat input limit corresponding to 80 F CCP temperature. In this case, the heat-up time from 150 F to 200 F is greater than 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. The cooldown transient after forced cooling is restored is depicted in Figure 5.8 for the Case I scenario at 95 F CCP inlet temperature.
5.5 Partial Core Discharge (Case 3 Scenario) Results In this case, a partial core of 97 fuel assemblies is transferred to the p, ol. The decay heat loads and pool bulk temperature data 600 hrs after reactor shutdown is provided in Table 5.6. The CCP
]
inlet temperature for this scenario is 95 F. The evaporative cooling rate corresponding to the coincident bulk temperature is 0.73 Million Btu /hr. Therefore, the rate of bulk temperature rise
)
for the case of a loss in forced cooling (obtained by applying Eq. 4.9 reported earlier) is 5.3 F/hr. Ilence, the maximum bulk temperature at the end of a 4-hour loss of forced cooling is 148.8 F. The cooldown transient after forced cooling is restored is depicted in Figure 5.9.
l Report 111-971843 Revision 1
l l
Table 5.1 MILLSTONE UNIT 3 POOL END-OF-LIFE' 13ACKGROUND DECAY llEAT l
Number of Assemblics Decay IIcat (Blu/hr)
Previously Discharged 0.496 x 106 (up to 4/14/95):
416 l
Projected Future 10.648 x 10(Case 1 Scenario) l Discharge:
1351 from Unit 3 9.143 x 106 (Case 2 Scenario) i 1088 from Units 1 & 2" 6
Total:
2855 11.144 x 10 (Case 1 Scenario) 9.693 x 106 (Case 2 Scenario)
EOL full-core discharge is consen atively postulated to occur 1-year after end of Cycle 1
19 on March 1,2025.
Fuel assemblics transferred from Units 1 and 2 are modeled as 10-year old PWR fuel at 60,000 MWD /MTU burnup. The decay heat load to pool from the transferred fuel is 3.8 Million Btu /hr.
Report 111971843 Revision 1 25
)
i j
Table 5.2 MILLSTONII UNIT 3 POOL SUltFACE EVAPORATION IIEAT LOSSt llulk Pool Temperature Evaporation IIcat Loss
(*F)
(Iltu/hr) 150 1.88 x 10
(
t 2
Pool surface area is 2231 ft, and pool building is at 108*F and 100% humidity.
Report 111-971843 Revision 1 26
f:
l Table 5.3 MAXIMUM DECAY llEAT INPUT' TO MILLSTONE UNIT 3 POOL AT 150 F IlULK TEMPERATURE Maximum Decay CCP lleat Removal by IIcat Removal by lleat Temperature Pool Exchanger Evaporation input
( F)
(Btu /hr)
(Btu /hr)
(Btu /hr) 95 34.20 x 106 1.88 x 106 36.08 x 10
90 37.31 x 106 1.88 x 105 39.19 x 10' 85 40.42 x 106 1.88 x 10
42.30 x 106 6
6 80 43.53 x 10 1.88 x 106 45.41 x 10 t
CCP flow = 900,000 lbs/hr, heat exchanger effectiveness (with 77 tubes plugged) =
0.691 i
Report 111-971843 Revision 1
I l
1 l
l l
Table 5.4 MINIMUM llOLD TIME RESULTS (LIMITING CASE 1 SCENARIO)
CCP Maximum Full Core Minimum end-Minimum Temperature Decay IIcat Discharge of-transfer lloid Time
( F)
Input Decay IIcat time (hrs)
(Blu/hr)
(Btu /hr)
(hrs) 95 36.08 x 106 24.94 x 10 349 285 6
90 39.19 x 10^
28.05 x 10^
264 200 85 42.30 x 10 31.16 x 10 206 142 6
6 80 45.41 x 10 34.27 x 106 165 101 6
l l
1 Repon 111-971843 Revision 1 r
28
+1
r l
f l
l l
l Table 5.5 4
MILLSTONE UNIT 3 FUEL POOL INCREMENTAL llEAT-UP IIISTORY UNDER LOSS OF COOLING Time to IIeat Up CCP Temperature Maximum Decay Evaporation From 150 F to
( F)
IIcat Input Cooling Rate 200 F (llrs) l (Blu/hr)
(Btu /hr) 95 36.08x 10*
1.88x 10
5.62 90 39.19x106 1.88x10' 5.15 85 42.30x106 1.88x106 4.75 l
'80 45.41x106 1.88x106 4.41 l
l j
Report 111-971843 Revision 1 29 i
f-l l.
l l
Table 5.6 MILI51ONE UNIT 3 BULK POOL CONDITIONS 600 llRS AFTER RliACTOR SilUTDOWN (CASE 3 SCENARIO)
Parameter Value Total Decay lleat Load 21.1x10" litu/hr Evaporative Cooling 0.73x106 Iltu/hr Bulk Pool Temperature 127.6 F CCP Inlet Temperature 95 F Report 111-971843 Revision 1 30
t 6.0 RiiFliRENCliS
[6.1] "QA Documentation for DECOR", llottec Report !l1-971734"
[6.2] "An improved Correlation for Evaporation I rom Sn
- liuel Pools", lloltec Report i11-971664.
[6.3] "QA Documentation for IlULKTEM", lloitec Report 111-951391.
[6.4] NU Internal Memorandum,"l;uel Input fbr Millstone Unit 3 Spent Fuel Pool Ileat Load Analysis", from K.J. Connor to R.W. Sterner, August 20,1997. (NE-97-F-199,25212-ER-97-0150).
i Report 111-971843 Revision 1 31
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