ML20083D758
| ML20083D758 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 09/27/1991 |
| From: | Broughton T GENERAL PUBLIC UTILITIES CORP. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| C311-91-2053, NUDOCS 9110010222 | |
| Download: ML20083D758 (50) | |
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.,.,u; Nuclear GPU Nuclest Corpotetton o
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n Hot.te 441 South Middletown, Fennt>lvanta 170's 010 t 717 94. 7621 TELEX % 2386 Writet's Direct Dial Number (717) 948-8005 I
Septa ber 27, 1993 C311-91-2053 U. S. Nuclear Regulatory Commission Attn:
Document Control Desk Washington, DC 20555
Dear Sir:
Subject:
Three Mile Island huclear Station, Unit 1 (1MI-1)
Operating License No. DPR-50 Docket No. 50-289 Reactor Building Integrated Leak Rate Testing (ILRT) in Accordance with 10 CFR 50, Appendix J 1his letter provides additional supporting information to demonstrate the validity of pressurizing the secondary side of the Once Through Steam Generators (OTSGs) during an ILRT. As noted in the NRC's letter of March 26, 1991, GPU Nuclear intends te perform future ILRT with 45 psig nitrogen pressure applied to the shell side of the OTSGs. The objective of maintaining a secondary side pressure or blanket during the ILRT is to minimile the introduction of oxygen in order to avoid its corrosive effects on the internal surfaces of the steam generators.
Potential paths for oxygen intrusion during ILRT are the steam generator instrument root valves (skin valves), and the manway/handhole gaskets, which are not considered to be containment boundary components.
it is reasonable to assume, following a loss of Coolant Accident (LOCA), that the Emergency feedwater (EfW) System will maintain the OTSG secondary side in a water-filled condition of approximately 75-85% of the operating range level. This would not only reduce containment atmosphere inleakage but would provide for significant scrubbing of any containment atmosphere inleakage and reduce the associated source term should the secondary sidn pressure not remain above containment pressure during a LOCA.
Secondary side leakage paths into the containment which develop during plant operation are programmatically identified and repaired. During hot shutdown I
plant conditions, GPU Nuclear performs a walkdown at approximately 900 psig secondary side 3ressure.
Any leaks that are identified are scheduled for repair during tie outage whethar or not an ILRT is planned.
It is noteworthy that the steam generators and associated skin valves were designed to prevent leakage under conditions of internal pressurization. There were r:0 requirements that steam generators be designed to prevent leakage at a negative pressure with respect to reactor building pressure.
H 10010222 91on7 PDR ADOCK 05000289 P
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GPu Nuciear cowanon is a subscary of Generai puboc umes corporw;n g
Document Control Desk C311-91-2053 Page 2 To further substantiate the validity of maintaining a secondary sido pressure or nitrogen blanket during performance of the ILRT, an analysis was conducted to demonstrate that the OTSGs would remain pressurized during design basis LOCAs.
Enclosed is the GPUN analysis evaluating steam generator ) essure versus time for large brctk LOCAs in which the steam generator tu>es fill with steam.
TMs. condition occurs for all large breaks below the top of the OTSG; i.e., nearly the entire RCS piping. A cold leg break was modeled because this break location produces the maximum containment pressure, for the various design basis cold leg break LOCAs analyzed, it is clearly demonstrated that the presture differential between the steam generators and the containment atmosphere never exceeds-2-4 psi below containment pressure.
The OTSG's are raintained at least 5 psi below containment pressure during the ILRT.
Therefore the current ILRT method adequately demonstrates the leak tightness of the OTSG for all LOCAs below the top of the OTSG.
A hot leg break LOCA above the top of the OTSG was also analyzed because it results in the lowest 0150 shell pressure.
As the OTSG tubes fill with water, this significantly reduces primary to secondary heat transfer. With minimal heat transfer across the tubes, the pressure rapidly drops to atmospheric.
The analysis predicts a peak differential pressure of approximately 35 psi where the shell side pressure is below that of the containment.
The differential pressure between the OTSG shell and containment returns to within 5 psi in-approximately 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, when containment pressure has dropped to below 5 psig.
Because the ILRT does not test the leak integrity of the OTSG at a differential pressure greater than 5 psi, more inleakage to the OTSG could occur for this 6 hour6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> period than would be experienced during the ILRT.
Ilowever, we have estimated that the volume of this inleakage will not be sufficient to displace the steam line volume inside containment during this period. Moreover, even if the inleakage and any contained radioactive material were to reach the steam piping in the intermediate building, there would be very little potential for leakage because the steam lines depressurize to atmospheric pressure and because this piping represents an additional substantial holdup volume for any activity. Therefore, any radioactivity in the steam lines would be reduced by 1) decay due to holdup,
- 2) partitioning due to the water in the OTSG, as well as 3) condensation and plateout on the internal piping surfaces.
in summary, GPU Nuclear has concluded that preventing oxygen intrusion into t
the CTSG with a secondary side nitrogen pressure or blanket provides a net inprovnent in plant safety by avoiding the corrosive effects of oxygen on the internal surfaces of the steam g(nerators without adversely impacting the validity of the ILRT.
This conclasion is supported by analysis of cold leg break LOCAs which has demonstrated that TMI-l OTSGs remain pressurized to within 5 psi of containment atmosphere pressure. Adequate programs are in place to ensure that OTSG secondary side leak paths are identified and l
repaired in a timely fashion.
These programs, in conjunction with the l
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Document Control Desk 0311-91-2053 Page 3 mitigating factors described above for the hot leg LOCA, would minimize the potential for significant post-LOCA transfer of contaminants to the environment.
Therefore, the OTSG secondary side boundary components are not included as part of the containment integrated leak rate test boundary.
Sincerely, Ll w T. G. B ton Vice President and Director, IMl-1 Enclosure DJD/amk cc:
Region I Administrator TM1-1 Senior Pcoject Me ger THI Senior Resicent inspector t
l I
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' ANALYSIS OF OMO DEpRESSURIZATION DM10NG A LARGIL11R11AK_LOfA 1.0 flLQILLSiSTEllihiliNI During a Laige Dreak LOCA the Reactor Duilding (RB) could pressurire to a maximum of 50.6 psig. The offsite dose consequences are calculated for an assumed leak rate from the containment. Therefore, the RB is pressurized to 50.6 psig to verify that the containment leak rate does not exceed the assumed value. The NRC indicates that the Integrated Leak Rate Test (ILRT) boundary should include the outside of the steam generator (SG) shell and the Main Steam, hiain Feedwater and Emergency Feedwater lines. Occause the NRC wants this boundary included in the ILRT they believe that the SGs should be depressurized during the test. Pressurizing the steam generators to within a few psi of containment pressure reduces the potentialleakage through the secondary system. This analysis investigates whether the SGs remain pressurized during a LBLOCA.
The SG willinitially remain at a greater pressuie than the RB during a Large Urcak LOCA because of both automatic and manual action to isolate major steam loads and reduce EFW Gow. Ilowever,if no manual actions are taken and SG pressure drops below RB pressure, steam in the tubes of the SG will be condensed and heat will be transferred to the steam and water on the secondary side of the tubes. This heat transfer will maintain SG pressure within a few psi of containment pressure.
The primary side invemory should not impact the transient as long as sufficient steara condensing surface area exists inside the tubes. liowever, the RCS refills to the elevation of the break.
In the case of a hot leg break at an elevation above the SG upper tube sheet the RCS would refill, including the SG tubes, eliminating the steam condensing surface area inside the tubes. Ileat transfer can still occur between the liquid in the tubes and the liquid and steam on the outside of the tubes.
This calculation will evaluate SG pressure versus time for various LDLOCAs using the RELAP5 Mod 2 B&W rycle 36.04 computer code. This vers'on of the computer code was chosen because of extensive benchmarks against plant transient data and Multi Loop Integral System Test (MIST) facility data by the B&W Owr.er's Group.
The purpose of this analysis is also to investigate OTSG depressurization sersus containment pressure during a LBLOCA.
2.0 f_\\SSUMPTIONS 2.1 The RCS inventory is released to the RB rapidly, pressurizing the RB to approximately 50.6 psig. Subsequently, containment pressure is reduced by building spray and/or fan coolers within a short period of time. An existing plant specific RB pressure versus time boundary condition will be applied for this analysis.
2.2 Main Feedwater (MFW) flow is automatically stopped when the main block l
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$1YS1LQF OTSG DEPRESS _URIZATION DURING A LAl[QE BREAK 10CA valves close on trip confirmed logic and the main and startup regulating valves close on ICS cross limits and rapidly decreasing demand. The hiFW main and startup regulating valves remain closed becaus: SG level remains above the low level setpoint throughout the event. Finally, the htFW main and startup block and regulating valves automatically close when SG pressure drops below 600 psig.
Therefore, MFW Oow to the OTSGs will be terminated when the reactor & turbine trip for this analysis.
2.3 Emergency Feedwater (EFW) starts automatically when the Reactor Coolant Pumps are manually tripped on loss of subcooling margin (SCM) (ATP 12101, Reactor Trip; ATP 1210 2, Loss of 25'F Subcooled Margin).
Additionally, EFW I automatically actuated when RB pressure exceeds 4 psig. The lleat Sink Protection System (LISPS) raises SG level to 50% in the operate range. The operators manually raise SG level control setpoint to 75 85% in the operate range (ATP 12101, Reactor Trip; ATP 1210 2, twss of 25'F Subcooled Margin: ATP 1210-10. Abnormal Transient Procedures Rules, Guides and Graphs). EFW flow is limited by the cavitating venturis
. to a total of approximately 1180 gpm. Also, the operators manually reduce flow to the minimum required during a loss of SCM (125 gpm/SG) to minimize the SG depressurization (ATP 1210 10). When the LPI flow rate is stable at 1000 gpm (or more) per injection line the operators are allowed to secure EFW to the OTSG (ATP 1210-7, large Break LOCA Cooldown).
Finally, the operator is required to feed and steam the OTSGs as necessary to minimize the tube to shell differential temperature (ATP 1210 7). For this analysis EFW will be initiated 10 seconds after the reactor and turbine trip and raise SG level to 85% OR level. Flow will be maintained at 590 gpm until the level setpoint is reached. Flow will be limited to 125 gpm for one hot leg break case.
2.4 The steam loads during a LBLOCA would be the turbine driven EFW pump, Gland Seal Steam (GSS), idling MFPs, and Main Steam Relief Valve (MSRV) Post Support Heating. Based on the SG pressure response the operators would secure the turbine driven EFW pump, which is not required for primary to secondary heat removal, or supply steam from the auxiliary boiler to reduce the steam loads. The GSS and MFP turbine steam loads are isolated by the operator when the MSIVs are closed (ATP 1210-7). For this analysis the turbine driven EFW pump, one idling MFP md GSS will be modelled as a constant steam load on the SG. For the hot leg break cases this steam load will be isolated at 10 minutes by closing the MSIV. The MSRV Post Support Heating steam-load will be mc'delled as a pressure dependent steam load.
Specific s: cam flows are established in the Calculations section.
2.5 The RCS and RB portions of an input deck will be modelled as time-dependent volumes connected to a single SG. Refer to Figures 1 & 2. The 5/30/91 Page 2 of 47
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' ANALYSIS OF OTSG DEPRESEU10ZeJ10N DURINGJtLARGEllimi}LlaCA Initial primary side boundary conditions will be full power, full 00w It is assumed that at the start of the LOCA the RCS flow will coast down to nro in I second. At the same time the RCS pressure response verus time will be modelled using a characteristic LilLOCA response. The break to be useilis 2
an 8.55 ft cold leg break at the RCP d4 charge (Figure 5). This boundtry condition is assumed to be valid until RCS pressure equalizes with containment pressure (at approximately 24 seconds). The pressure pmfile is
~,
also applied to the hot leg break cases. For both hot and cold leg breaks the blowdown is complete within approximately 25 seconds. Derefore, there would be little difference to the thermal hydraulic response of 'this model.
After this time the containmem pressure versus tim; tesponse will be modelled using a bounding LDLOCA response. Further d.iscussict, or the model is included in the Calculation section.
3.0 CALCULATIONS 3.1 A single, stand alone steam genciatur model was developed for RELAPS, Mod 2, including both primary and secondary volumes. Additionally, the heat structures for the shell, shrouds and tubes are included. The initial full flo v, pressure and temperature conditions are maintained for the first 10 seconds of each computcr run.
3.2 For the time from 10 to 34 seconds (24 seconds) the RCS boundary condition was derived from the core pressure versus time response attached aa Figure 5 (Figure 61 of Reference 6.1). As discussed abose this pressurc.esponse is 2
characteristic of an 8.55 ft cold leg break. The boundary conditions is specified as saturated steam for which no temperature is specified. This RCS pressure boundary condition is included as Table 1 for reference.
3.3 RCS Pressure Boundary Condition: Five cases will be run with different boundary conditions for RB pressure and control of primary side level.
3.3.1 Case 1: Once RCS pressure equalizes with containment pressure (after 34 seconds of transient time) the RCS boundary condition is derived from the containment pressure response shown in Figure 7.
2 This RB pressure vs time trace is for a 8.55 ft LDLOCA with two fan coolers and 1500 spiti of spray tiow (Fig. 6.H-11 of reference 2), This pressure response was chosen because of the fairly rapid depressurization. The pressure response is included as Table 2 for reference.
3.3.2 Case 2: Once RCS pressure equahres with containment pressure (after 34 seconds of transient time) the RCS boundary condition is derived from the containment ptessure response shown in Figure 6.
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1 MLY.SLS OF QIl10 DEPRESSURIZATION DMPELA.LMEiE_LlBEAK LOCA 2
This RB pressure vs time trace is for a 8.55 ft cold leg LBLOCA with trace fan coolers and no spray flow (Fig. 6.B.14 of icference 2). This f
pressure response was chosen because the rate of RU depressurization is slower than the one used for Case 1. He pressure response is included as Table 3 for reference.
3.3.3 Case 3 5: The hot leg bounday connections and pressure response for these cases are the same as those of case 2.
3.4 Two hot leg inlet volumes are used to model the event for all three cases.
Refer to Figures 1 and 2. Volume 109 & Junction 609 establish the normal full flow, full power condition. The flow is reduced to zero over 1 second through this path. Volume 108 & Junction 608 establish the RCS pressure versus time boundary condition. After 10 seconds of steady state operation the time dependent pressure is reduced as discussed above.
This depressurization accounts for the blowdown of the RCS and subsequent reduction of containment pressure.
The hot leg boundary condition is specified as saturated steam.
3.5 Cold 1.cg Boundary Conditions:
3.5.1 Case 1: The second set of primary boundary conditions consists of time dependent volume 122 and time dependent junction 622. Refer to Figure 1.
RCS temperature, pressure and flow are maintained constant at the full flow, full pcwer condition for the first 10 seconds.
Then the flow through the junction is reduced to zero over i second.
After one second into the blowdown (11 seconds transient time) no more flow is allowed to pass through the cold leg junction (J622).
Water will collect on the priman side of the steam generator tubes as the steam condenses.
3.5.2.Cuc_2: The second set of primary boundary conditions consists of two time dependent volumes, a single junction aad a time dependent junction. Refer to Figure 2. Volume 123 and junction 623 establish the full Dow, full power boundary condition to the cold leg for the first 10 seconds. Then the now through this junction is reduced to zero over 1 second. This is the same method employed in Case 1.
An additional bounday condhion la app!!cd to the cold leg. Volume -
122 and junction 622 establish the same time dependent primary pressure response as does the hot leg boundary candition (V109, J609).
Unlikc casc 1, f!cw is a!!cwcd to pass through a ;old leg junction.
However, after the transient starts no difference in pressure is maintained between the hot and cold leg boundan conditions.
Therefore, little or no water will collect on the primary sido of the SG
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4 ANALYSIS OFIEDiO_ del'REMUR1ZNrION DURING A.lARGE_IlRFAK.1DfA as the steam condenses. Finaliy, the water at the cold leg junction is maintained slightly subcooled. The temperatures of the Guid are specifed but have no impact on the analysis because now will be out of the tubes and into the cold leg time dependent junction.
3.5.3 fue_3
Except for a slight modification to the pressure boundary condition the cold leg connections for this case are the same as those of case 2. Again, flow is allowed to pass through cold leg junction 622.
Ilowever, the input control gards of case 2 were increased by 5 psi for times greater than or equatio 34 seconds. Ilecause of the simplistic nature of this change the control cards are not included.
Tins adjustment maintains a difference in pressure between the hot and cold leg boundary conditions. Theiefore, approxirnately 160 inches of water should collect on the primary side. This is characteristic of a cold leg break. Table 4 compares the hot and cold leg boundary conditions.
3.5.4 Cases 4 f: Except for a slight modification to the pressure boundary condition the cold leg connections for this case are the same as those of cases 2 and 3. Again, now is allowed to pass through cold leg junction 622.
Ilowever, the input control cards of case 2 were inc* cased in pressure to refill the primary volumes as would be expected for a hot leg break. This adjustment establishes a difference in pressure between the hot and cold leg boundary conditions.
Tlierefore, the water level should rise on the primary side. A table comparing the hot and cold leg boundary conditions is included below for reference.
The RCS refill rate was based on single failure assumptions in that one LPI and one llPI pump were used. The LPI How rate was assumed to of 7.9 ft'gpm and the llPI now rate was assumed to be 550 gpm be 3000
/sec). No throttling other than to' limit nows to these values is assumed until the RCS refills. The RCS is assumed to be void of
!! quid at the end of blowdown leaving a volume of approximately 12000 ft' to fill.
The core flood tanks dump almost immediately adding appriximately 14000 gal (1870 ft'). This leaves 10130 ft' to fill at 7.9 ft'/see over approximately 1280 sec. It is assumed that no liquid enters the loops until the vessel is refilled and that no liquid flashes during the refill.
This will take approximately 270 see after the CITs empty. (4000 ft' -
2 1870 ft' = 2130 ft) at 7.9 ft /sec).
For this analysis it was assumed that the loops and therefore the SG tubes will start to fill at approximately 275 sec after the start of the i
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' ANALYSIS.,OF OTEO DEPRESSMlUZAQQN D_UltlNG A.1ARGE_lulEAtLLQCA break and fills at a linear rate until 1235 ee after the break (960 see to fill the SG tubes).
De refill of the OTSG tubes will be accomplished by linearly increasing the differential pressuro between the hot and cold leg junctions. 52 ft of level head corresponds to approximately 22 psi at standard conditions. He results can be seen in Table 5.
3.6 hiain Steam System input & Boundary Conditions 3.6.1 The main steam portion of the input deck is about the same as a standard Th11 1 REIAPS, hiOD2 deck, except that only the lines from a single 50 are included. Also, the two main steam lines from the SG have been combined into one line. The post trip steam loads discussed in section 2.4 above are included as boundary conditions. Refer to Figure 3 for the hiain Steam System hiodel.
'.6.2 Cans 1 3: A time dependent junction applies a steam now boundary condition based on steam pressure. The assumed steam loads are included as Table 6.
The steam loads listed in Table 6 are at 900 psia and total 27.5 lbm/sec. The total steam load will be conservatively set at 30 lbm/see with 20 lbm/see being helc constant with pressure and 10 lbm/sec decreasing linearly with pressure. The same steam load is applied to all three cues.
3.6.3 Cases 4 5: The steam loads were reevaluated for the hot leg break eases. Three of the four loads would be isolated by the hiain Steam isolation Valves (MSIV) when they are closed by the operators in accordance with step 2.9 of ATP 1210 7, "Large Break LOCA Cooldown." It is usumed that the htSIVs are closed at 10 minutes.
Therefore, single junction 667 was converted back to a motor operated valve. Time dependent junction 676 was modified to maintain a i
constant 30 lbm/sec of steam flow until volume 568 depressurizes after the hiSIV closes. The higher now rate of this steam load is based on higher steam requirements for the idling h1FP Each hiFP requires approximately 60000 lbm/hr on minimum recirculation. A new time dependent junction (J767) was developed for the hiSSV steam post heating steam ioad (refer to Figure 3).
The Dow rate for this load was set at 7 lbm/see based on the above information. Since there is no pressure regulator the steam now was reduced linearly as SG pressure decreases.
3.7 Emergency feedwater (EFW) is assumed to automatically start and feed the OTSG to 50% on the operate range and the operator increases the setpoint 5/30/91 Page 6 of 47
- ANALYSJE,QF OTSG DEPRESSURIZATION DUIUNG A LARGE UREAK.LOCA to 75 85% on the operate range. For all cases once the level setpoint is reached the EFW system adds EFW to maintain the level at 350 inches.
3.7.1 Cases 1 4: The EFW flow is initiated at 590 gpm (82.5 lbm/sec) and maintained until the SG level reaches 350 inches (approximately 85%
operate range level).
3.7.2 Osd: The EFW flow is initiated at 125 gpm (17.4 lbm/sec).
4.0 EUMMARY QE.llESULTS The results are included as Figures 8 27. The figures for each case are discussed below followed by a comparison of the five cases.
4.1 Case 1: Figures 8 and 11 show the RCS/RB pressure and SG pressure response versus time. The SG pressure remains greater than RCS/RB pressure for approximately 600 seconds (10 minutes). Ileat transfer from the primary to the secondary side of the SG tubes holds SG pressure within 2 3 psi of RCS/RB pressure. Figure 9 shows the rapid blowdown of mass in the primary and the subsequent increase in level to approximately 180 inches as the steam in the tubes condenses. No flow is allowed to pass through the cold leg after 11 seconds. The increase of SG level to setpoint over approximately 1500 seconds can be seen on Figures 9 and 10. EFW increnses to full fkw (Figure 10) and stays on until the SG level setpoint is reached
4.2 D3r_2
Figures 12 and 15 show the RCS/RB pressure and SG pressure response versus time. The SG pressure remains greater than RCS/RB pressure for greater than 600 seconds (10 minutes). Heat transfer from the primuy to the secondary side of the SG tubes holds SG pressure within 2 4 psi of RCS/RB pressure. Figure 13 shows the rapid blowdown of rnass in the primary and the subsequent increase in level to approximately 5 inches as the steam in the tubes condenses Since flow is allowed to pass through the cold leg and no pressure difference is maintained between the hot leg and cold legs only a small amount of water collects on the side of the tubes. The increase of SG Ievel to setpoint over approximately 1500 seconds can be seen on Figures 13 and 14.
EFW increases to full flow to raise SG level (Figure 14) and stays on until the level setpoint is reached.
4.3 Case 3: Figures 16 and 19 show the RCS/RB pressure and SG pressure response versus time. 'lhe SG pressure remains greater than RCS/RB pressure for approximately 150 seconds (2.5 minutes). Figure 17 shows the rapid blowdown of mass in the primary and the subsequent rapid increase in level to approximately 160 inches. This rapid increase in level is from subcooled liquid flowing up from the cold leg because of the 5 psi pressure 5/30/9t Page 7 of 47
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' ANALYSIS.DF OTSG D%ESSURIZA'110N DlJR[EG A LARGlijREAK LOCA diffe mee between the hot leg and cold legs, ne pressure difference is maintairmd after 34 seconds of transient time. His large now of subcooled liquid from the cold leg rapidly cooled and reduced pressure in the SG.
liowever, subsequent heat transfer from the primaty to the secondary side of the SG tubes maintained SG pressure within 3 4 psi of RCS/RB pressure.
The increase of SG level to setpoint over approximately 1500 seconds cun be seen on Figures 17 and i8. EFW increases to full now to raise SG level (Figure 18) and stays on until the level setpoint is reached. The rapid decrease in SG pressure reduced the steaming rate from the SG. Therefore, SG level reached setpoint at approximately 1000 seconds, i
4.4 f,.ng_3: Figure 20 shows the RCS/RB boundary condition pressure and SG pressure response versus time.
The SG pressure remains greater than RCS/RB pressure for approximately 300 seconds (5 minutes). Figure 21 shows the rapid blowdown of mass in the primary and the subsequent controlled increase in level until the SG tubes are full. The increase in level is from subcooled liquid nowing up from the cold leg because of the increasing pressure difference between the hot leg and cold legs. The change ir pressure difference can be seen in Figure 23. The Dow of subcooled liquid from the cold leg contributes to the rapid cooldown and depressurization of the SG.
However, subsequent heat transfer from the primary to the secondary side of the SG tubes maintained SG pressure within 4 - 5 psi of RCS/RB pressure until approximately 1200 seconds. At that time the SG tubes are filled with liquid and heat transfer from the primary to the secondary is lost. The SG depressurizes fairly quickly by transferring heat to the subcooled water on the RCS side of the tubes.
The increase of SG level to setpoim over approximately 1100 seconds can be seen on Figures 21 and 22. EFW increases to full flow to raise SG level (Figure 22) and stays on until the level setpoint is reached. The rapid decrease in SG pressure reduced the steaming rate from the SG. Therefore, SG level reached setpoint at approximately 1100 seconds. Additionally, the rate of level rise increases at 610 seconds when the MSIV closes to isolate a majority of the steam loads.
4.5 f.ne_5: Figure 24 shows the RCS/RB boundary condition pressure and SG pressure response versus time. The SG pressure remains greater than RCS/RB pressure for approximately 500 seconds (8.3 minutes). Figure 25 shows the rapid blowdown of mass in the primary and the subsequent controlled increase in level until the SG tubes a:u full. The increase in level is from subcooled liquid Dowing up from the cold leg because of the increasing pressure difference between the hot leg and cold legs. The change in pressure difference can be seen in Figure 27. The Dow of subcooled liquid from the cold leg cont ibutes to the rapid cooldown and depressurization of the SG. lieat transfer from the primary to the secondary side of the SG tubes 5/30/91 Page 8 of 47
ANALYSIS OF OTSQ.DfEESSIBlZATION DURING A lARGE lllWAK10CA is unable to maintain SG pressure within 4 5 psi of RCS/RB pressure.
50 level does not increase significantly during the transient (Figures 25 and 26). The reduced EFW Gow (Figure 25) is not sufficient to make up for steam flow until the MSIV closes at 600 seconds. SG pressure is held to within approdmately 15 20 psi of RB/RCS pressure until the SG tubes fill with liquid. At apprmimately !?00 seconds heat transfer from the primary to the secondary is lost. The SG depressurires fairly quickly by transferring heat to the subcooled water on the RCS side of the tubes.
4.6 fnmparison of Results:
4.6.1 Cases 1 3: Steam generator pressure dropped rapidly during the RCS blowdown. The rapid depressurization is because of significant heat transfer from the SG to the reactor coolant, continuous (eeding with EFW and contbuous steam loads. In Case 3 the rapid rate of pressure drop in the SG is aggravated by the insurge of a large amount of subcooled liquid from the cold leg. When SG pressure dropped below the RCS pressure, heat transfer occurred from the primary to the secondary. The amount of water present on the primary side of the SG tubes had no perceptible impact on the pressure difference between the SG and RCS/RB volumes. Primary to secondary heat transfer maintained SG pressure within approximately 2 - 4 psi of RCS pressure for all three cases.
4.6.2 Cases 4 - 5: Steam generator pressure dropped rapidly during the RCS blowdown. The rapid depressurization is because of significant heat transfer from the SG to the reactor coolant, continuous feeding with EFW and continuous steam loads. The OTSG depressurizes more rapidly at a high EFW flow. Some of the effect can be attributed to steam condensation on the secondary side of the SG which lowers pressure because of the cooler bulk temperatute, Additionally, less water accumulates on the secondary side of the tubes because of the lower flow rate and relatively high steam flow. The heat transfer coefficient of steam (on the outside the tubes in the lower level /EFW flow case) is less than heat transfer coefficient of water (on the outside of the tubes in the higher level /EFW flow case). Therefore, there is insufficient heat transfer to hold up SG pressure.
5.0 CONCLUSION
The Integrated Leak Rate Test of the containment is performed at 50.6 psig. The results of this calculation indicate that the steam generators remain within 3 - 4 psi of the RB pressure for more than one hour after a classical large break LOCA occuring at the reactor vessel inlet or outlet nozzles. Additionally, the results are l
5/30/91 Page 9 of 47
ANALYSIS OF OTSG DEPRESS _URIZATION DURING A LARGEllEliAK LOCA approximately the same unless the break were to occur at a high level in the hot leg.
Rapid depressurization of the SG could occur within approximately 1800 2000 seconds.
In a hot leg break (Case 4 and 5) the differential pressure would be a maximum approximately 35 psi. This pressure difference decreases to only a few psi over several hours.
The offsite dose consequences are calcuated using the conservative assumption that the leakrate remains constant for the drst 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. Then the leak rate is assumed to decrease by half and remaining constant for 30 days. Based on the conservative nature of the offsite dose calculation the amount of leakage through the secondary system would be small in comparison and well within the bounding analysis.
Additionally, the GG would partition some of the activity because the water level is raised above the instrument lower taps, the most likely source of leakage. Steam condensation may maintain the instrument sensing lines connected to the upper taps at least partially full of water. Also, the plant was not designed such that the instrument line isolation valves would have to prevent backleakage through the valve packing.
6.0 REEERENCES 6.1 Babcock & Wilcox,"ECCS Analysis of B&W's 177 FA Lowered Loop NSS,"
Topical Report BAW 10103A, Rev 3, July 1977.
6.2 GPUN, " Final Safety Analysis Report", Update 8, Chapters 6B & 14 5/30/91 Page 10 of 47 l
, ANAL,XSIS OF OTSRDEl'Rl!SSUltlZATj0N DUltlNG A IAltGli llJlERLQfa Tall! II 1 Transient Time Time Since Pressure (sec) lireak (see)
(psia) 10.0 0.0 2145.0 10.1 0.1 1600.0 15.0 5.0 1200.0 20.0 10.0 1050.0 25.0 l'i.0 750.0 30.0 20.0 350.0 33.0 23.0 100.0 34.0 24.0 65.0 JhllLIO Transient Time Time Since Pressure (see)
Ilreak (see)
(psia) l 34.0 24.0 65.0 110.0 100.0 65.0 l
210.0 200.0 61.0 510.0 500.0 51.0 1010.0 1000.0 40.0 2010.0 2000.0 27.0 4010.0 4000.0 18.5 10010.0 10000.0 22.0 r
1 r
l l
5/.10/91 Page 11 of 47
, ANALYSIS 012 OTSG DEPRESSUltlZATION DUltlNG A I ARGILilJtEAK l OSA TAlli.E 3 Transient Time Time Since Pressure (see)
Ilreak (sec)
(psl:i) 34.0 24.0 66.0 110.0 100.0 66.0 210.0 200.0 62.0 510.0 500.0 58.0 1010.0 1000.0 54.0 2010.0 2000.0 49.0 4010,0 4000.0 41.0 10010.0 10000.0 29.0 TAllt.E 4
'I ransient ' lime Time since 11r Hot leg ColJ l cg Cold l eg Temi crature (wc)
(uc) l'rruure l'reuure (l')
(Imia)
(Fsia) 10.0 0.0
_ 2145 0 21MO
$35 0 10.1 0.1 IMoo IMo D
$mo 13.0 3.0 12fnD 12(no
$15.0 20.0 10.0 1050.0 10500 5050 25.0 15 0 750.0 750.0 470.0 30.0 20.0
- 150 0 140 4C0 0 33.0 23.0 1(nu 100 0 Xc0
'A 24 0 (A0 71.0 2WO
!)0.0 1(n0 (40 71.0 250.0 210D 2J00 62.D 67.0 220
$ s
$@0 SAO 610 2$0 0 4010.0 10(n0 54.0 59.0 2MO 2010.0 2000 0 49.0
$4 0 200.0 40100
- 000 ':
41.0 460 2CnD 100100 luano 29 0 M0 200 0
., u-5/30/91 Page 12 of 47
ANAL,YSIS OF OTSG DEPRESSURIZATION DURING A 1.Allf.iE BREAK LOCA TAllLE_5 Transient lime litra %nce isreak flot 14g udJ Irg Cold leg Ternperaturc (sec) tuc)
Prtuure Preuure (l')
Qua)
Osia) 10.0 0.0 2145.0 2130 0 SA5 0 10.1 0.1 1&OO leduo SMO 15.0 50 1Ano 12(u0 515.0 20 0 10.0 1050.0 1050 0 505 0 25.0 15.0 750.0 750.0 470.0 3u.0 20.0
.B0 0 1%.0 4(n0 110 23 0 1(*10 100.0 A00 34 0 24.0 66 0 66 0 1% 0 110.0 100.0 (AD (40 250 0 210,0 2(o 0 62.0 62.0 1% 0 285 0 275.0 83
61.0 150 0
$10.0 VOO
$8 0 63 2 250 0 1010.0 1000 0 54 0 70.6 250 0 1245.0 1235.0 St.e 74 8 250 0 2010.0
%In0 49.0 71.0 2tulo 4010.0 4(inD 41.0 63.0 200 0 10010.0 1(KKnD 29 0
$l.0 200.0 r
i 5/30/91 Page 13 of 47
ANALYSIS OF OTSG DEPRESSURIZATION DURING A LARGE BREAK LQCA TABLE 6 Steam Load Total Flow Rate Flow Rate per (Ibm /hr) 013G (lbm/sec)
Idling M tin Feedwater 60000.0 8.4 Pumps Fully Loaded Turbine 27700.0 3.9 Driven EFW Pump Gland Seal Steam (GSS) 30000.0 8.3
5/30/91 Page 14 of 47
. ~........ - - -. -...
i ANALYSIS OF OTSG DEPRESSURIZATION DURING A LARGE BREAK LOCA i
FIGURES 1-7 MODEL DIAGRAME RB/RCS HOT LEG BOUNDARY CONDITIONS I
e
$/30/91 Page 15 of 47-
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r RELAPS STAND ALONE STEAM GENERATOR HOT LEG 108 t
IEFW 109 J609 lJ608 Y m
110 163 JB67 164 110 :2:
162
_164 2
g SECONDARY PRIMAAY 2
$wi 161 SIDE 164 SIDE 110 3
3 A
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164 M
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4
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110 lM 158 J66f 151
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110 $
157 151 7
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b 5/30/91_
Page 16 of 47 4W**f?'MT tr ?
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n ANALYSIS OF OT5G DEPRESSURIZATION DURING A LARGE BREAK LOCA ElqUP2 2 RELAPS STAND ALONE OTSG TWO LOWER VOLUMES HOT LEG 108 109 608 m
110 '
163 J664 164 110 kh 162 164 2
gj 58CONDARY PRIMARY a
]4 SIDE SIDE 110 j
161 164 110 (g 160 4
kh 164
%[g 159 5
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2 110 156 151 3
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10 110 $
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110 152 151 J652 7
12 123 WISIJ622 122 COLO LEG 5/30/91 Page 17 of 47 J
ANALYSIS OF OT5G DEPRESSURIZATION DURING A IARGE BREAK LOCA UGURE 3 MAIN STEAM SYSTEM MODEL TSV J665 J666 J667 J668/
J569g SG v165 v166
_D=0 vi67
-M D=1 yggg C751 V568 4,C750 V998 J676 J767 Notes:
1.
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modelled as valves.
2.
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3.
C751, J767 & V997 only included in cases 4 & 5.
5/30/91 Page 18 of 47
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5/30/91 Page 19 of 47 l
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l FIGURES e.11 CASE 1 RESULTS 4
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4 ANALYSIS OF OTSG DEPRESSURIZATION DURING A LARGE BREAK LOCA i
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- ANALYSIS OF OTSG DEPRESSUllZAllON DURING A LARGE BREAK LOC 6 FIGURES 16 - 19 CASE 3 RESULTS h
5/30/91 Page 33 of 47
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ANALYSIS OF OTSG DEPRESSURIZATION DURING A LARGE BREAK LOCA FIGUPE 17 CMIL2 TMl $TAND ALCNE SC NC153.1P. SCONE 06 g
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ANALYSIS OF OTSG DEPRESSURIZATION DURING A LARGE BREAK LOCA FIGURE 19 CASE 3 iM1 STAND AL0tE 50 NC153.TP. SCONE 06 i
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Page 38 of 47
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ANALYSIS OF OTSG DEPRESSURIZATION DURING A LARGE BREAK LOCA T.LGURE U CASE 4 1M1 STFNO PLCNC 50 NC153.TP.SCHLO2C 8
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