ML20094P526
| ML20094P526 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 06/30/1984 |
| From: | Brandon R, Gridley R GENERAL ELECTRIC CO. |
| To: | |
| Shared Package | |
| ML112991291 | List: |
| References | |
| NEDO-30477, NEDO-30477-R01, NEDO-30477-R1, NUDOCS 8408170262 | |
| Download: ML20094P526 (27) | |
Text
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NEDO 30477 REVISION 1 DRF E12 00088 83NED139R1 l
Cl.ASSI JUNE 1984 l
i SAFETY ANALYSIS OF THE RHR INTERTIE LINE MONTICELLO. NUCLEAR GENERATING PLANT i
l I
l
NEDO-30477 Revision 1 DRF E12-00088 83NED139R1 Class I June 1984 SAFETY ANALYSIS OF THE RHR INTERTIE LINE, MONTICELLO NUCLEAR GENERATING PLANT l
l Approved:
.2.
/c 7/is/a4 Approved:
1 */d -9 RdJ. Brandon,' Manager' '
R. If. GrlTiley, Manager j
Application Engineering Fuel and Services Licensing NUCLEAR ENERGY BUSINESS OPERATIONS + GENERAL ELECTRIC COMPANY SAN JOSE, CALIFORNIA 95125 GENER AL $ ELECTRIC
NEDO-30477 Revision 1 DISCLAIMER OF RESPONSIBILITY Neither the General Electric Company nor any of the contributors to this document makes any warranty or representation (express or implied) with respect to the accuracy, completeness, or usefulness of the information contained in this document or that the use of such information may not infringe privately owned rights; nor do they assume any responsibility for liability or damage of any kind which may result from the use of any of the information contained in this document.
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NEDO-30477 Rsvisien 1 l
CONTENTS Pj!ge 1.
INTRODUCTION 1-1 2.
DISCUSSION 2-1 2.1 One Recirculation Pump Mode 2-1 2.2 Two Recirculation Pump Mode 2-1 3.
SAFETY EVALUATION 3-1 3.1 Emergency Core Cooling System Analysis 3-1 3.1.1 LPCI Effects 3-1 i
3.1.2 Blowdown Effects 3-1 3.2 containment Analysis 3-4 3.3 Flow Bias Systems Analysis 3-4 3.4 LPCI Loop Selection Logic 3-6 3.5 Jet Pump Vibration 3-6 3.5.1 Zero Flow Condition 3-7 1
3.5.2 Jet Pump Riser Brace Vibration 3-7 3.5.3 Jet Pump Flow Rates 3-8 3.6 Jet Pump Surveillance 3-8 4.
CONCLUSIONS 4-1 4.1 ECCS Performance 4-1 4.2 Containment Response 4-1 4.3 Flow Bias APRM Scram and Rod Blocks 4-1 4.4 LPCI Loop Selection Logic 4-1 4.5 Jet Pump Vibration-4-1 4.6 Jet Pump Surveillance 4-2 5.
REFERENCES 5-1 i
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NEDO-30477 R; vision 1
' TABLES Table Title Page 3-1 Monticello DBA Analysis with the Limiting Single Failure of the LPCI Injection Valve 3-9 3-2 MAPLHGR Multiplier Versus Core Flow Adjustment for Open Intertie Line at Full Power 3-11 3-3 Containment Analysis Results 3-13 o
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NEDO-30477 Rivision 1 ILLUSTRATIONS Figure Title Page 1-1 RHR Intertie Modification 1-3 3-1 MAPLHGR Multipliers With and Without Intertie Line 3-15 3-2 ARTS MAPFACp Limits for 4-in. Intertie Open (A =9, 6 -13) 3-17 y
2 3-3 Containment Pressure Response 3-19 3-4 Containment Temperature Response 3-21 3-5 Flow Bias System Adjustments for RHR Intertie Operation 3-23 l
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c' NED0-30477 RXvi21:n 1 1.
INTRODUCTION A proposed modification to the Monticello Nuclear Generating Plant will be the addition of a 4-in. nominal pipe size line which connects the Residual Heat Removal (RHR) System suction and discharge lines inside the drywell.
Since these RHR lines are connected to the recirculation loops, the pipe will also connect the recirculation loops as shown in Figure 1-1.
This line with its associated valves is called the RHR intertie line.
The purpose of this report is to document the safety analyses performed to evaluate the effect of this line.
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NEDO-30477 R;vicion 1 2.
DISCUSSION 4
The RHR intertie will be added to minimize the potential for RHR and Recirculation System steam condensation water hansaers when the RHR System is put into operation for shutdown cooling. The intertie will allow circulation of reactor water through idle portions of the piping during depressurization to prevent accumulation of steam in the piping loops. The line will have three remote, manually operated gate valves to route flow through the piping.
Valves A and B will be normally closed and, if opened, will be signalled to close on indication of a loss-of-coolant accident (LOCA). Valve C will be a normally open remote manual valve. During shutdown and before depressurization, the valves will be opened and will remain open until RHR shutdown cooling is started. The intertie will have two basic operating modes, presented in Subsections 2.1 and 2.2.
I 2.1 ONE RECIRCULATION PUMP MODE In some unusual cases, such as in the case of a pump seal failure, it is necessary to shut down with only one recirculation pump operating.
In this mode, the operating loop will circulate water through the RHR piping and the idle recirculation loop piping. The flow can be selectively routed by opening or closing valves A, B or C (Figure 1-1).
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2.2 TWO RECIRCULATION PUMP MODE i
The flow will be directed from both recirculation pump discharge lines through the RHR discharge lines and back through the RHR suction line. This will be the normal mode of operation with Valves A, B and C open.
2-1/2-2
NED0-30477 Revision 1 3.
SAFETY EVALUATION 3.1 EMERGENCY CORE COOLING' SYSTEM ANALYSIS A cross connection between the RHR loops also connects the recirculation loops. Such a connection has two important characteristics with respect to a recirculation line break, If open, the intertie line would divert some low pressure coolant a.
injection (LPCI) flow from the unbroken loop to the broken loop.
b.
The intertie would allow blowdown from the unbroken loop before LPCI injection occurs.
3.1.1 LPCI Effects The current worst single failure for the Emergency Core Cooling System (ECCS) analysis is failure of the LPCI injection valve to open. As such, no credit is taken for LPCI flow in the design basis accident (DBA) analysis.
Addition of the intertie line without automatic isolation would make it neces-sary to redefine the worst single failure which might no longer be LPCI injec-tion valve failure. Consequently, Isolation Valves A and B receive automatic closure signals to assure that LPCI flow to the vessel is not affected.
3.1.2 Blowdown Effects For LOCA analyses, the peak cladding temperature (PCT) is the primary measure of ECCS performance. The PCT for a BWR during a LOCA is generally governed by the time the core is uncovered.
In large LOCAs, however, some core heat-up can occur because of early boiling transition (i.e., the transi-tion from nucleate to film boiling).
The potential for early boiling transi-tion is a function of the initial core power and flow conditions.
3-1
NEDO-30477 Revision 1 To account for potential early boillag transition during a LOCA due to reduced initial core flow, the current Monticello Technical Specifications include a set of maximum average planar linear heat generation rate (MAPLHGR) multipliers. These MAPLHCR multipliers are a function of reduced core flow and prevent the PCT limit (2200*F for Monticello) from being exceeded during a LOCA.
3.1.2.1 Analyses of ECCS Performance The proposed intertie can have two effects on ECCS performance:
An increase in the DBA break size could change the core uncovery a.
and recovery time during a postulated LOCA.
b.
An additional flow path between the broken and unbroken recircula-tion loops during a postulated LOCA may change core flow and cause earlier boiling transition.
Valves A and B automatically isolate the intertie line, but were assumed to remain open in evaluation of the DBA (Recirculation Line Break with failure of the LPCI injection valve).
3.1.2.2 Effect of Intertie on DBA Break Size Since the intertie valves are assumed to be open at the time of a pos-tulated LOCA, the effect of the proposed intertie on the DBA break size requires re-evaluation with the NRC approved ECCS evaluation models.
The intertie is a 4-in. line with a flow area of 0.08 ft2 If this flow area is added to the former maximum flow area, the new 100% DBA break size becomes 4.09 ft2 The additio~n of the intertie flow area increases the maxi-mum flow area by about 2%.
An analysis was performed using the new maximum flow area in the ECCS evaluation models. The results of the analysis are shown in comparison with 3-2
NEDO-30477 Rtvision 1 the previous reload results in Table 3-1.
The difference in the time of core uncovery is less than 1 second.
I The limiting break size from the most recent analysis (Reference 1) is the 2
34% DBA break size (1.36 ft ) which would have the same uncovery and recovery time with or without the intertie.
3.1.2.3 Effect of Additional Flow Path on Core Flow and Time to Boiling Transition The postulated open intertie line flow path will split off some recircula-tion drive flow from the unbroken recirculation loop if a LOCA occurs in the opposite loop. The effect of the additional flow path on core flow requires analyses similar to the reduced core flow analyses performed in References 2, 3 and 4.
The primary effect of an additional flow path is to reduce core flow during the early portion of a postulated DBA, resulting in more rapid core heat-up due to early bailing transition.
I 1
l A set of MAPLHGR multipliers to take into account the effects of early boiling transition were developed for a representative BWR/3 plant similar to Monticello.
Since the representative plant has a 100% DBA break size of 4.34 ft2 (8% larger than Monticello) and a lower rated core flow, the MAPLHGR multipliers are conservative and bounding for Monticello.
These current multipliers are shown in Figure 3-1.
There are two reduc-tions in the MAPLHGR multiplier at 90 and 70% rated core flow, respectively.
A reduction in the core flow would have an effect on the range of the MAPLHGR multipliers as indicated by A and A in Figure 3-1 and the corresponding 1
2 Average Power Range Monitor (APRM), Rod Block Monitor (RBM) and Technical Specification Improvement (ARTS) (Reference 5) flow limits (Figure 3-2).
The magnitudes of both A and A are governed by the minimum flow area y
2 in the path between the unbroken and broken recirculation loops. Variour, minimum flow areas or flow area reductions were evaluated, assuming that the reduction occurred between Valve B and Location D in Figure 1-1.
The bounding results for the different A's are given in Table 3-2.
For example, with no 3-3
NEBO-30477 Revision 1 flow reducer (i.e., for a full NPS 4-in, line), the A and A increase by 9 y
2 and 13%, respectively.
3.2 CONTAINMENT ANALYSIS The DBA break size will determine the rate of energy release (break flow) to the containment during a postulated LOCA. An increase in DBA break size of 0.08 ft due to the intertie line could thus affect the peak drywell pres-sure and temperature.
The ef fect of increased DBA break size on peak containment pressure and temperature was analyzed. The models and initial conditions assumed in the analysis are consistent with those previously established in the plant unique load definition report (Reference 6), except that the DBA break size is 2
increased to 4.09 ft, compared to the current licensing basis of 4.01 ft The results of the analysis are given in Table 3-3 and are shown in Figures 3-3 and 3-4.
Following the rupture of the recirculation line, sub-cooled liquid will be discharged to the drywell causing pressurization. The peak drywell pressure and temperature occur during the subcooled liquid blow-down phase when mass and energy release into the drywell is maximized.
The increased DBA break size has the potential of increasing the subcooled liquid flow through the break and can result in slightly higher peak drywell pressure and temperature; however, the higher peak vahes are both still below design bases (Reference 7).
The pool swell loads on the torus shell and internals increase by less than 1% because of the increased drywell pressure.
Therefore, the RHR intertie line piping will have negligible impact on the containment loads.
3.3 FLOW BIAS SYSTEMS ANALYSIS The flow bias scram and rod blocks are based on the drive flow to the jet pumps assuming a constant value for the drive flow to core flow ratio (M-Ratio).
If the M-ratio changes as it does in single-loop operation, the flow bias sys-tem must be adjusted to account for the change. When the RHR intertie is open, 3-4
NEDO-30477 Rtvision 1.
the measured drive flow will be greater than the actual drive flow since flow is diverted to the intertie after the flow is measured (Figure 1-1).
The flow bias systems will then allow higher rod block or flux limits than should be allowed for the actual drive flow.. Consequently, the flow bias system must be adjusted if the intertie is open at high power (Reference 8).
Hydraulic evaluations show c drive flow reduction for two-pump operation of 3.7% per loop or 7.4% total.
For one-pump operation, 9% is diverted with 5.3% driving the nonoperating loop jet pumps, which will reduce the jet pump backflow and increase core flow. Consequently, about 4% drive flow per loop is lost when the intertie is open.
l The adjustment for the change in the drive flow / core flow relationship is similar to the type of adjustment that must be made for single-loop opera-tion. The equations for the flow referenced scram and rod block are Scram
= 0.58 W(DRIVE) + 62%
Rod Block = 0.58 W(DRIVE) + 50%
where W(DRIVE) = percent of drive flow needed for 100% core flow operation l
i In this case, since 8% drive flow is lost, W(DRIVE) = W(MEASURED) x (0.92) and the equations are Scram
= 0.53 W(MEASURED) + 62%
Rod Block = 0.53 W(MEASURED) + 50%
The highest power level allowable without adjusting the flow bias system is the lowest power level at which a rod block should occur. This lowest power level is determined by the intersection of the minimum pump speed curve and the rod block line (Figure 3-5).
In this case, the RHR intertie open minimum pump speed curve is 8% less than the minimum speed intertie closed curve and is calculated by subtracting 8% of the difference between the minimum pump speed core flow and the natural circulation core flow. The intersection of 3-5
NEDO-30477 Revision 1 the intertie open curve with the rod block is at 65% power; consequently, tht flow bias system must be adjusted if the intertie is opened above 65% power.
Since the RBM flow bias trip settings will be changed to a thermal power bias when the ARTS (Reference 5) improvements are implemented, no changes to the RBM will be needed.
e Normally, the intertie would be opened only during shutdown from hot standby to a cold depressurized condition since the intertie is only needed in that period to avoid RHR water hammer.
Since it is not necessary to adjust the flow bias systems for this low power mode of operation, the Technical Specifications could be modified either to limit the thermal power at which the intertie may be opened or to identify the power level above which the flow bias systems must be adjusted if the intertie is opened.
3.4 LPCI LOOP SELECTION LOGIC To assure selection of the unbroken recirculation loop, Monticello has operating procedures to limit the amount of speed mismatch between the two recirculation loops. Operation of one recirculation pump with the intertie open also produces a high flow mismatch between the two loops. This operation will not affect loop selection since the logic will trip the operating pump and wait for pump coastdown before selecting a loop when operating with one recirculation loop.
3.5 JET PUMP VIBRATION During initial plant startup testing, it was found that high jet pump vibration occurred during unbalanced speed (flow) operation (Reference 9).
The highest vibration occurred at the point where there was zero flow in the low speed loop jet pumps, since their developed head was not sufficient to overcome the lower plenum pressure established by the high speed jet pumps.
In one-pump operation with the intertie open, there is low flow in the inactive loop and high flow in the active loop, which is a similar condition and raises concerns about the potential for component failures.
3-6
NEDO-30477 R:vicion 1 3.5.1 Zero Flow Condition During initial plant startup testing, the zero flow point occurred with a 94%/25% jet pump drive flow ratio. Since the intertie produces a 91%/5.3%
drive flow ratio in one-pump operation, the idle loop jet pumps should be in reverse flow, not in the high vibration, zero flow condition.
3.5.2 Jet Pump Riser Brace Vibration The jet pump riser brace is the component that is the primary concern during unbalanced flow operation. The startup vibration program measured both the tangential motion of the riser pipe and the radial motion of the jet pump. The vibration test report for Monticello gives the following peak vibra-tion for constant flow hot (530*F) and cold (120'F) tests. The results are presented in percent of the steady-state criteria that were developed assuming 40 years of continuous operation.
Percent of Steady-State Criteria Riser Pipe Cold Balanced / Unbalanced 50/83 Hot Balanced / Unbalanced 25/91 Jet rump Cold Balanced / Unbalanced 30/17 Hot Balanced / Unbalanced 6/20 The highest vibration occurred during a one-pump trip transient for less than 1.5 seconds where 100% of criteria was reached during hot testing (higher values of 112% and 150% were reached for cold one-pump trip tests where jet pump cavitation occurred since the jet pump net positive suction head avail-able was not sufficient to support one-pump operation at 65% speed). These test results indicate that unbalanced operation would not be expected to 3-7
WED0-30477 Revision 1 cause jet pump or riser brace failure, although it is not a desirable area to operate within if avoidable.
In addition, the operational duration for one-pump intertie open will be one or two orders of magnitude less than 40 years in a 40-yr lifetime.
Such a duration would be acceptable at the highest steady-state vibration levels observed during startup testing.
3.5.3 Jet Pump Flow Rates The highest vibration occurred during startup testing at loop drive flow ratios of 94 to 91% versus 25 to 27%. The maximum expected flow for intertie line operation is 30%, while the flow rate in the inactive loop is 500 gpm which corresponds to about 2% flow. This produces at least 67% less velocity and 90% less kinetic energy (proportional to velocity squared) into the system.
Consequently, the applied forces will be significantly less than those encountered during startup testing, which implies that the vibration ampli-tudes will also be significantly reduced.
3.6 JET PUMP SURVEILLANCE Jet pump surveillance depends upon acquisition of a " normal" operational data base for each mode of operation. The surveillance criteria remain the same whatever the mode of operation. The " normal" data base against which the surveillance data is compared changes depending on the mode of operation.
Jet punp surveillance for the intertie open case may not be needed since the plant would already be proceeding to shut down.
If the intertie were open at power, it would be necessary to acquire a surveillance data base the first time that mode of operation was implemented.
3-8
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NEDO-30477 Revicion 1 Table 3-1 MONTICELLO DBA ANALYSIS WITH THE LIMITING SINGLE FAILURE OF THE LPCI INJECTION VALVE No Intertie With Intertie 2
Break Size 4.01 ft 4.09 ft Core Uncovery Time 19.74 see 19.48 see Time of Rated Core Spray 31.6 sec 31.37 see Core Recovery Time 193.92 sec 193.95 see l
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NEDO-30477 Rr, vision 1 Table 3-2 MAPLHGR MULTIPLIER VERSUS CORE FLOW ADJUSTMENT FOR OPEN INTERTIE LINE AT FULL POWER Adjustment to Core Flowa f r Applying Multiplier Flow Through Area of Flow Open Intertie (41 percent (A2 Percent 2
Reducer (ft )
Line (gpm) of rated) of rated) 0.08 4947 9
13 No reducer (4-in. i.d.)
0.034 2108 3.6 5.4 (Reduce to 2.5-in. i.d.)
0.02 1237 2.3 4
(Redued to 2-in. i.d.)
asee Figure 3-1: 41 is adjustment at 90% core flow; A2 is adjustment at 70% core flow.
3-11/3-12
NEDO-30477' R;vici:n 1 Table 3-3 CONTAINMENT ANALYSIS RESULTS No Intertie With Intertie 2
2 Break 4.01 ft 4.09 ft Peak Drywell.
41.4 42.3 Pressure (psig)
Peak Drywell 281 282 Temperature ('F) 3-13/3-14
NEDO-30477 Revision 1 1.1 1.0 CURRENT g
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MAPLilGR Multipliers With and Without Intertie Line 3-15/3-16
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Ap Bp Ap Bp 102.5 0.4698 0.6557 0.4861 0.6784 NOTE: OS4 MULTIPLIER NECESSARY 107.0 0.4421 0.6533 0.4574 0.6758 BELOW 99% CORE FLOW IF 112.0 0.4074 0.6581 0.4214 0.6807 RATED OPERATING LIMIT < 1.28 117.0 0.3701 0.6656 0.3828 0.6886 0.5 30 40 50 60 70 80 90 100 110
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NEDO-30477 Revision 1 140 FLOW REFERENCED FLUX SCRAM LINE (0.58 Wo + 62%)
APRM ROD BLOCK LINE (0.58 Wo + 50%)
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Flow Bias System Adjustments for RilR Intertic Operation 3-23/3-24
NEDO-30477 Revision 1 4.
CONCLUSIONS A safety analysis of the proposed RHR intertie line at the Monticello Nuclear Generating Plant was performed.
The results of this assessment are summarized in Subsections 4.1 through 4.6.
4.1 ECCS PERFORMANCE At full reactor power, the effect of the 2% increase in break area during the blowdown phase of the DBA can be conservatively accounted for by applying a 0.94 MAPLHGR multiplier for operation between 99 and 83% core flow and a 0.91 MAPLHGR multiplier for core flow below 83.0%.
If a flow area reducer is used in the intertie line, it is likely that a more detailed analysis would show that the current MAPLHGR limits are adequate.
4.2 CONTAINMENT RESPONSE A 2% increase in the DBA break area has a negligible effect on peak containment pressure and temperature and also on core uncovery and recovery during a postulated LOCA.
4.3 FLOW BIAS APRM SCRAM AND ROD BLOCKS It will be necessary to adjust the flow bias systems if the intertie line is opened above 65% power.
4.4 LPCI LOOP SELECTION LOGIC The intertie line will not prevent selection of the unbroken recircula-tion loop.
4.5 JET PUMP VIBRATION The intertie line is not expected to increase the potential for com-ponent failures.
4-1
7,..
NEDO-30477 Rivicirn 1 4.6 JET PUMP SURVEILLANCE Operation of the intertie line, except during shutdown, will make it necessary to acquire a new surveillance data base for that mode of operation.
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NEDO-30477 R;visi:n 1 5.
REFERENCES 1.
"LOCA Analysis Report for Monticello Nuclear Generating Plant," General Electric Company, NEDO-24050,*Rev. 1, December 1980.
2.
Letters, A. J. Levine (GE) to Z. R. Rosztocy (NRC), " Additional Effects of Core Flow on Loss of Coolant Accident 'LOCA' Analysis," August 24, 1976, Nov. 4, 1976, and March 9, 1977.
3.
Letters, R. L. Gridley (GE) to D. G. Eisenhut (NRC), " Review of Low Core Flow Effects on LOCA Analysis for Operating BWR's - Revision 2",
May 8, 1978.
4.
D. G. Eisenhut (NRC) to R. L. Gridley (GE), " Safety Evaluation Report on Revision of Previously Imposed MAPLHGR (ECCS-LOCA) Restrictions of BWR's at less than Rated Flow," May 19, 1978.
5.
" General Electric BWR Licensing Report: Average Power Range Monitor, Rod Block Monitor and Technical Specification Improvement (ARTS) Program for Monticello Nuclear Ger erating Plant," General Electric Company, i
NEDC-30492-P Class III. April 1984.
6.
" Mark I Containment Pr< gram Plant Unique Load Definition, Monticello Nuclear Generating Plan *," General Electric Company, NED0-24576-1, October 1981.
l 7.
Monticello Nuclear Generating Plant Technical Specifications, Northern States Power Company Docket No. 50-263, License No. DPR-22, Rev. 67, April 17, 1983.
8.
"Monticello Nuclear Generating Plant Residual Heat Removal System Intertie Line Evaluations" General Electric Company, NSEO 62-0783, July 1983.
9.
"Monticello Vibration Measurements", General Electric Company, 383HA732 Rev. O Class II, October 19, 1972.
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