ML20117J107
| ML20117J107 | |
| Person / Time | |
|---|---|
| Site: | 05200003 |
| Issue date: | 08/30/1996 |
| From: | WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP. |
| To: | |
| Shared Package | |
| ML20117J100 | List: |
| References | |
| PROC-960830, NUDOCS 9609100170 | |
| Download: ML20117J107 (154) | |
Text
i L
l l l Replacement Instructions l
for the l
AP600 Emergency Response Guidelines Background, Book 1 l Section AE-1: Loss of Reactor or Secondary Coolant 1
1 REMOVE INSERT
! Title pg. Rev.1,7/28/95 Title pg. Rev.1 A, 8/96 l Page 2-1 Rev.1, 7/28/95 Pages 2-1 to 2-58 Rev.1A, 8/96 O l i
4 r
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'O DOC 052 03 DR PDR A
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O l l
s BACKGROUND INFORMATION FOR ;
AP600 EMERGENCY RESPONSE GUIDELINE i
AE-1 AP600 LOSS OF REACTOR OR SECONDARY COOLAhT l Rev.IA (
August,1996 l l
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O m:wp600co64wue-l.wpf;Ib 080796 REVISION: lA
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l TABLE OF CONTENTS Section Page
1.0 INTRODUCTION
1-1
2.0 DESCRIPTION
2-1 2.1 Case 1: 0.5 Inch Diameter Cold Leg LOCA Without Operator Action 2-3 I 2.2 Case 2: 1.0 Inch Diameter Cold Leg LOCA Without Operator Action 2-14 2.3 Case 3: 2.0 Inch Diameter Cold Leg LOCA Without Operator Action 2-26 j 2.4 Case 4: 2.0 Inch Diameter Cold Leg LOCA With RNS Injection 2-41 l 2.5 Case 5: Large Double-Ended Cold Leg LOCA Without Operator Action 2-50 3.0 RECOVERY / RESTORATION TECHNIQUE 3-1 3.1 High Level Action Summary 3-1 3.2 Key Utility Decision Points 3-3 4.0 DETAILED DESCRIPTION OF GUIDELINE 4-1 ;
4.1 Detailed Description of Steps, Notes, and Cautions 4-1 4.2 Step Sequence Requirements 4-30
5.0 REFERENCES
5-1 0l l
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9 m:\ap600\2064w\ac-1.wpf:IM80796 il REVIslON: lA
2.0 DESCRIPTION
This section provides transient descriptions for a Loss of Reactor Coolant Accident (LOCA). The following cases are included:
l Case 1. 0.5 inch diameter cold leg LOCA without operator action Case 2. 1.0 inch diameter cold leg LOCA without operator action Case 3. 2.0 inch diameter cold leg LOCA without operator action Case 4. 2.0 inch diameter cold leg LOCA with RNS injection included Case 5. large double-ended cold leg LOCA without operator action t
This spectrum was selected to illustrate most of the phenomena of interest for a LOCA. The operator typically does not know the break size, so the focus is on the Reactor Coolant System (RCS) l response and the symptoms and indications the operator could use for accident mitigation.
l The first four cases were modeled using Transient Real-time Engineering Analysis Tool - Advanced l
Numerics (TREAT-AN), an interactive computer simulation program capable of modeling the l
! essential features of the primary and secondary systems of a Pressurized Water Reactor (PWR). The AP600 TREAT-AN model includes many of the control systems of interest for modeling automatic and manual (operator) actions considered in the AP600 Emergency Response Guidelines (ERGS).
The large LOCA case (Case 5), taken from the AP600 Standard Safety Analysis Report (SSAR), was l
modeled with COBRA-TRAC.
The first two TREAT-AN cases (0.5 in. and 1 in. LOCAs) consider the response of the RCS for small LOCAs that do not cause actuation of the Automatic Depressurization System (ADS) within the time frame expected for transition to AES-1.2, AP600 POST-LOCA COOLDOWN AND DEPRESSURIZATION. Operator recovery actions for these two cases are then considered in the l AES-1.2 background document.
The third case (2 in. LOCA without operator action) resembles the 2 in. cold leg LOCAs included in the AP600 SSAR modeled with NOTRUMP (Section 15.6.5). The TREAT-AN simulation, however, uses "best" estimate assumptions (e.g., charging flow, nominal set-points, etc.). The fourth case is a restart variation of Case 3 that includes RNS injection prior to ADS Stage 4. It is not required that the operator take this action since the passive systems used in the AP600 design are adequate to safety shutdown the plant and provide core cooling. RNS injection followed by recirculation, l
l however, provides a more op+.imal recovery for the larger LOCA sizes. Operators of current f operating plants are also familiar with this mode of recovery.
l l
The last case was modeled with COBRA-TRAC and was extracted from Section 15.6.5 of the SSAR.
, This case is included primarily for operator information. A large LOCA would be beyond the I- operator's capability to control during the injection phase of the accident. However,it would be mwm2064ww.1.wpr:it>.os27% 2-1 REVislON: lA l
l possible to use RNS injection (followed by recirculation) for this case, similar to Case 4. Although ADS is not required for Case 5, it is likely all four stages of ADS would be actuated.
Guideline AE-1 is also used for a secondary break after faulted Steam Generator (SG) isolation and prior to transition to AES-1.1, AP600 PASSIVE SAFETY SYSTEMS TERMINATION. An example secondary break case with these actions included is provided in the background document for AE-2, l
AP600 FAULTED STEAM GENERATOR ISOLATION.
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2.1 CASE 1: 0.5 Inch Diameter Cold Leg LOCA Without Operator Action In this section, the response of a typical small LOCA (0.5 in. diameter) cold leg LOCA is described.
The break is assumed located near the bottom of cold leg 1 A and h'as an effective area of 0.196 sq. in. For this size opening, the break flow is beyond the capability of makeup (chemical and volume control system (CVS)) to maintain RCS inventory without reactor trip. The time table of events for this case is given in Table 2-1. Transient plots of interest are discussed below and are provided in Figures 2-1 through 2-7.
The pressurizer level response for this 0.5 in. LOCA case is shown in Figure 2-1. As a result of break flow, the level decreases at a constant rate until makeup is automatically initiated (at approximately 400 seconds - see Figure 2-5). I ressurizer level continues to decrease at a reduced rate since the makeup flow compensates for about half the inventory lost out the opening. This trend continues until reactor trip (after 1100 seconds). Soon after reactor trip, pressurizer level decreases off span low primarily as a result cf the abrupt decrease in RCS average temperature (see Figure 2-3).
Later in the transient, makeup flow becomes greater than the break flow; however, pressurizer level remains off span due to the cooldown and the resulting RCS shrink caused by passive residual heat removal (PRHR) actuation. PRHR is actuated as a result of core makeup tank (CMT) actuation due to the Low-2 pressurizer level signal (this signal is modeled at 10% pressurizer level).
Figure 2-2 illustrates the RCS and SG pressure response for this case. Makeup flow and pressurizer heaters are able to maintain RCS pressure relatively constant prior to reactor trip. After reactor trip and CMT actuation, the pressurizer heaters cut out and the PRHR outlet valves open. RCS pressure then decreases at a faster rate. The rate change between 1500-1600 seconds occurs as the pressurizer surge line empties allowing the pressurizer steam to condense in the subcooled hot leg in loop 1.
The SG pressures remain less than the RCS pressure for the duration of the transient modelei Apart from brief operation of the steam dump valves, the SGs are not required to relieve steam for decay heat removal because PRHR is in service. Steamline isolation and Startup Feedwater (SFW) isolation also occur due to the low cold leg temperature signal (modeled at 514'F).
The hot leg and two of the cold leg temperatures (I A and 2A) are shown in Figure 2-3. The temperatures in cold legs IB and 2B are similar to those in cold legs lA and 2A, respectively. Prior i to reactor trip, the temperatures are relatively constant in the two hot legs (600 F) and four cold legs l (530*F). After trip, the temperatures in loop 1 decrease due to the PRHR cooldown. During this cooldown, a 40 to 50 F temperature difference is maintained between the hot leg and cold legs in loop 1 (loop modeled with the PRHR). Decay heat removal occurs primarily via natural circulation in this loop, with energy transfer to the PRHR and ultimately to the in-containment refueling water storage tank (IRWST).
The flow in loop 2 is predicted to slow down and essentially stops once the hot leg temperature in the loop decreases to about 480*F. The flow stagnation in loop 2 is predicted to occur because the m:\ap6000064w\ae.l.wpf;lt4807% 2-3 REVislON: lA
i SGs become a heat source during the transient, so there is an opposing driving head for reverse flow that can offset that for forward flow usually associated with natural circulation. If the opposing driving head becomes equal to that for forward flow, flow slowdown or stagnation can occur. A characteristic of stagnation is that the cooldown for the hot leg in the affected loop lags that of the active loop. If sufficient flow is maintained, the hot legs and core exit would all be approximately the same temperature. The cold leg temperatures in loop 2 initially stay relatively constant after reactor trip since their temperatures are determined by the SG temperature. After stagnation occurs, i
! the cold legs may mix with the water in the downcomer, which is approximately the same temperature as that of the active loop cold legs, or the cold leg water could stay at a higher temperature, closer to the inactive SG temperature. Had the stagnation not occurred, the cold leg temperature and SG temperatures in the inactive loop would become the same as the hot leg / core exit temperatures. The flow stagnation predicted by TREAT-AN is a result of a small driving head pressure difference (on the order of 0.1 psi) that can become either negative (or remain positive) depending upon the amount of cooldown or temperature response of the inactive SG.
The above characteristics of temperature trends are an indication of either flow circulation or stagnation (the lack of flow circulation). The flow rates due to natural circulation are typically less than 10% of normal flow with the reactor coolant pumps running. These rates could be too small to observe with accuracy on any available flow instrumentation. The operator would have to rely on the i temperature indications as an indication of the asymmetric flow behavior. It is important to note that the operator would be expected to transition to AES-1.2 for this case regardless of the flow conditions in loop 2. Therefore, the prediction of flow stagnation in loop 2 would not impact the overall results of the analysis.
Figure 2-4 shows the RCS subcooling based on the core exit temperature. This parameter is used by the operator as one of several to determine whether or not termination of passive safety systems can be performed per AES-1.1, AP600 PASSIVE SAFETY SYSTEMS TERMINATION. Although subcooling is more than 100 F for most of the simulation. AES-1.1 would not be implemented since pressurizer level remains off span low, and RCS pressure is slowly decreasing.
The makeup flow and break flow rates are illustrated in Figure 2-5. After 2600 seconds, makeup flow, approximately 27 lbm/sec or 200 gpm, is higher than break flow. However, pressurizer level remains off span low due to the cooldown.
Additional inventory is also added to the RCS from the CMTs. The upper curve in Figure 2-6 shows the injection flow from CMT-A. The lower curve is the flow through its cold leg balance line. The corresponding flow components for CMT-B are nearly the same. The CMTs remain full for the l
duration of the transient consideird, so the volume flows in the injection and recirculation lines are l approximately the same (initially about 0.9 ft'/sec). There is a net addition to the RCS from the CMTs since the colder borated water in the injection line is more dense. As the CMTs heat up due to balance line flows, the driving head density difference decreases and the flows become more nearly equal.
m:\ap600\2064w\ae-l .wpf:l tr080796 2-4 REVIsloN: lA
Figure 2-7 illustrates the flow through the PRHR heat exchanger. After the RCPs coast down, the flow decreases from approximately 90-100 lbm/sec for most of the transient, to approximately 80 lbm/sec at the end. PRHR outlet water, at approximately 150 F return temperature, plus makeup and CMT injection flows continue to cool the RCS, but at a decreasing rate. The initial RCS cooldown is approximately 100 F in the first half hour following reactor trip and CMT/PRHR actuation. The cooldown slows to less than 100 F per hour at the end of the transient modeled.
This transient illustrates the RCS response for a typical small LOCA with break flow beyond the capability of makeup. However, the inventory loss is slow enough that the CMTs do not drain and ADS is not actuated during the one hour time frame considered. The operator would likely take action to establish SFW while in AE-0, AP600 REACTOR TRIP OR SAFETY INJECTION.
However, this action would not significantly change the response of this transient since the RCS cooldown is being controlled by the PRHR, CMTs, and makeup. Since pressurizer level remains off span low and RCS pressure is slowly decreasing, the operator would not transition to AES-1.1, AP600 PASSIVE SAFETY SYSTEMS TERMINATION. Instead, near the end of AE-1, the operator would transition to AES-1.2, AP600 POST LOCA COOLDOWN AND DEPRESSURIZATION, since RCS pressure is above the shutoff head pressure for RNS injection (modeled at 160 psig) and ADS is not actuated. The background document for AES-1.2 will consider recovery actions for this case.
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mAap600\2064-\ae-l.wpf:Ib 080m 2-5 REVislON: lA
TABLE 21 TIME TABLE OF EVENTS FOR 0.5 INCH COLD LEG LOCA WITHOUT OPERATOR ACTION EVENT / AUTOMATIC ACTIONS >
Time (sec)
Full power operation 0 - 10 0.5 in. diameter cold leg LOCA in CL-1 A (loop with PRHR) 10 Pressurizer level reaches 40%, makeup initiated at - 100 gpm 380 Makeup and pressurizer heaters maintain RCS pressure above 2100 psia 400 - 1100 LOW-2 pressurizer level signal 1106 (CMT and PRHR initiation, RCP trip signal, makeup realigns to BAT)
Over-power AT reactor trip signal 1116 Reactor trip folicwed by turbine trip, steam dump valves open 1119 RCPs trip and begin coastdown 1124 MFW isolation on LOW-1 Tavg 1135 SI actuation and steamline isolation on LOW-2 Tcold (defeats SFW) 1148 Makeup flow near maximum (- 200 gpm), exceeds break flow - cooldown shrink > 2600 prevents recovery of pressurizer level End of transient modeled, RCS subcooling > 100'F, 3600 pressurizer level off-span low, RCS pressure ~ 1000 psia and slowly decreasing l
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m:WO64w\ae-l.wpf:Ib 0807% 2-13 REVISION: 1A
I 2.2 CASE 2: 1.0 Inch Diameter Cold Leg LOCA Without Operator Action This section describes the response of a 1.0 inch diameter LOCA. It is also modeled at the bottom of cold leg 1 A. The effective area is 0.785 sq. in., four times larger than that previously considered in l Case 1 (0.5 in. cold leg LOCA). The tin.e table of events for a 1.0 inch LOCA case is presented in Table 2-2. Transient plots are discussed below and provided in Figures 2-8 through 2-16.
The pressurizer level response for the 1.0 in. LOCA case is shown in Figure 2-8. As a result of the increased break flow, pressurizer level decreases several times faster than in Case 1. The level indication goes off span low approximately 200 seconds after reactor trip and SI actuation. By 400 seconds, the pressurizer and surge line are completely empty.
The RCS and accumulator pressure response for this case are displayed in Figure 2-9. CVS makeup and pressurizer heaters are no longer capable of maintaining RCS pressure constant prior to trip for this 1.0 in. LOCA case. As a result, reactor trip followed by SI actuation occur due to low l pressurizer pressure. RCS pressure continues to decrease as the system drains. The accumulators start to inject at approximately 1800 seconds when RCS pressure decreases to 714.7 psia or 700 psig.
The RCS and SG pressures are illustrated in Figure 2-10. For this scenario, the RCS pressure decreases below the SG pressures by approximately 600 seconds. The SGs are also a heat source for l this case since PRHR is in service and provides cooling. The break and injection flows also remove some of the core decay heat and RCS sensible heat.
At approximately 450 seconds, the upper head starts to drain (see Figure 2-11). This occurs when the RCS pressure decreases below 1100 psia, corresponding to a saturation temperature of 556*F. This is the approximate hot leg / core exit temperature that mixes with the upper head after the RCPs trip and have coasted down. The rate of RCS depressurization is reduced as the upper head flashes and starts to drain, as is evident in Figures 2-9 and 2-10.
An additional decrease in the RCS depressurization rate can be noted at approximately 800 seconds.
At this time, RCS pressure is reduced to 900 psia, corresponding to a saturation temperature of 532*F. This is the approximate temperature in the inactive loop SG (loop 2 - loop without PRHR).
As shown in Figure 2-12, the U-tubes in the loop 2 SG start to drain. By 1400 seconds, the tubes are drained and the SG channel head starts to drain. By 2000 seconds, the level in this loop has ;
I decreased to approximately 27 ft, about one foot above the top of the hot leg as modeled in TREAT-AN. AP600 has hot leg level indication normally used during shutdown that spans from the bottom of the hot legs to the top of the bend at the SG inlet connection. It is possible that the operator would be able to observe some of the SG channel head draindown with the hot leg level instrumentation.
Figure 2-13 shows the loop I hot leg, cold leg, and RCS saturation temperatures. The PRHR flow rates are similar to those for the 0.5 in. cold leg LOCA, so the RCS cooldown in loop 1 is similar.
m:\ap6000064w\ae-l.wptib.o80796 2-14 REvlslON: lA i
The loop remains subcooled for the duration of the transient modeled. The loop I hot leg l
j temperature is approximately the same as the core exit temperature. Cooldown of the loop 2 hot leg temperature lags loop 1. The loop 2 hot leg temperature then becomes equal to the saturation temperature after the SG 2 U-tubes have drained.
l l
l The amount of RCS subcooling based on the core exit thermocouples is illustrated in Figure 2-14.
l Although subcooling is maintained for the duration of the transient analyzed, it is comparable to typical RCS subcooling uncertainties (e.g.,30 F) for much of the transient. Because of the reduced RCS pressure, the RCS subcooling is considerably less than in the previous 0.5 in. cold leg LOCA case (see Figure 2-4).
The break flow and makeup flow are illustrated in Figure 2-15. The break flow remains considerably higher than the makeup flow. The net addition from the CMTs is only 10 lbm/sec (similar to Figure 2-6); consequently, the system inventory cannot be maintained even with the additional water from the accumulators.
As the system slowly drains and RCS pressure decreases below 500 psia, the top of the CMTs reach l
l saturation and start to drain. This occurs late in the transient as illustrated in Figure 2-16. Since the RCS pressure decreases slowly after 2700 seconds and the top of the CMTs are at slightly different temperatures, the two CMTs start to drain at different times. CMT-B starts to drain first, at approximately 2700 seconds, when the top part of this tank (10% of the CMT volume) reaches approximately 440 F. CMT-A drains later, at about 3500 seconds, when the top of this CMT reaches saturation at 425 F.
The CMTs drain less than 2 feet during a one hour long transient. With timely operator actions, the ADS setpoint (68% CMT level) is not reached and ADS would not be actuated. As in the previous 0.5 in. LOCA case, the operator would likely restore start-up feedwater (SFW) (while still in AE-0) and then transition to AES-1,2, POST LOCA COOLDOWN AND DEPRESSURIZATION This transition would still be taken since RCS pressure is above the shutoff head pressure for RNS injection (about 160 psig or 175 psia) and ADS has not actuated. The background document for i AES-1.2, therefore, will consider the 1.0 in, cold leg LOCA with operator actions included.
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1 usp6ooco64wwe.i.wptib-os27% 2-15 REVISION: lA
TABLE 2 2 TLTIE TABLE OF EVENTS FOR 1.0 INCH COLD LEG LOCA WITHOUT OPERATOR ACTION EVENT / AUTOMATIC ACTIONS Time (sec) l Full power operation 0 - 10 1.0 in. diameter cold leg LOCA in CL-1 A (loop with PRHR) 10 l
Pressurizer level reaches 40%, makeup initiated at - 100 gpm 110 LOW-1 pressurizer pressure reactor trip signal 173 Reactor trip followed by turbine trip 175 LOW-2 pressurizer pressure signal, SI actuation 183 1 (MFW isolation, CMT initiation, PRHR initiation, RCP trip signal) !
RCPs trip and begin coastdown 199 LOW-2 Tcold signal, SI plus steamline isolation (defeats SFW) 237 Upper head starts to drain 450 l
SG No. 2 U-tubes start to drain 800 l
SI accumulators start to inject 1820 CMT-B starts to drain - 2700 1
CMT-A starts to drain - 3500 l
l End of transient modeled, ADS not actuated (CMT-B level drop < 2 ft), RCS 3600 subcooling < 20*F, RCS pressure - 320 psia O
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50 ---
E i-T -Lf 2 L o 0 0 1000 2000 3000 4000 l
Figure 215. Makeup and Break Flow Rates for a 1.0 Inch Cold Leg LOCA Without
! Operator Action m:po64wsac 1.wpt:tb-oso796 2-24 REVISION: lA t
I
i l
l l
l \
l l
l l
CWT-A LeyeI CMT-B Level
,56 ,
~
v 54 _
e -
i
> 52 x
._J 's s
' ,50 , ' -
m -
~
48 x -
~
46 w -
2
- i i i i i i o 44 e i e i e i i ie e 0 1000 2000 3000 4000 Time (S) l l
4
(
Figure 2-16. CMT Mixture Level Response for a 1.0 Inch Cold Leg LOCA Without Operator Action m:\ap60Mw\ne-l.wpf:lbG0796 2 25 REVISION: lA l
l 2.3 CASE 3: 2.0 Inch Diameter Cold Leg LOCA Without Operator Action This section describes the response of a small LOCA (2.0 in. diameter), also modeled at the bottom l
l of cold leg 1 A. The effective area is 0.022 sq. ft. (3.2 sq. in.), four times larger than that previously considered in Case 2 (1.0 in. cold leg LOCA) and sixteen times larger than in Case 1 (0.5 in. cold leg LOCA). The timetable of events for this case is presented in Table 2-3. Transient plots are discussed below and provided in Figures 2-17 through 2-27. It should be noted that this case i resembles the 2 in. cold leg LOCA cases performed with NOTRUMP and described in Section 15.6.5 l of the AP600 SSAR. Both codes have similar parameter trends and phenomena; differences are mainly in the timing of events and are generally attributed to modeling differences (for example, conservative design basis assumptions for NOTRUMP and better estimate assumptions for l TREAT-AN).
! The pressurizer level response for this 2.0 in. LOCA case is shown in Figure 2-17. As a result of the increased break area and break flow, pressurizer level decreases several times faster than in Case 2.
The level indication goes off span low at 60 seconds, after reactor trip and SI actuation. At l approximately 80 seconds, the pressurizer and surge line are completely empty. Unlike the previous l cases, however, the pressurizer fills after 1100 seconds as a result of ADS actuation. It remains filled I
for most of the remaining transient until the Stage 4 hot leg valves open, after 2000 seconds. It then decreases as inventory is expelled from the hot legs.
l The RCS pressure response fol this case is displayed in Figure 2-18. RCS pressure decreases more O
rapidly than in the previous 1.0 in. LOCA case. 'niis results in reactor trip followed by SI actuation due to low pressurizer pressure. RCS pressure continues to decrease to approximately 1000 psia and stays relatively constant as the upper plenum and hot legs drain (see Figure 2-19). After 600 seconds, the top of the CMTs, fed by the hot water from the cold legs in loop 2, reach saturation and begin to drain. About two minutes later, the RCS pressure has decreased to 714.7 psia (700 psig) and the accumulators start to inject. The CMTs continue to drain until ADS Stage 1 actuation occurs at 68% CMT volume, corresponding to a CMT level decrease of about 7 ft. After ADS actuation, RCS pressure decreases at a faster rate. The ADS Stage 1 valves open at approximately 1050 seconds.
The Stage 2 and 3 valves are set to open based on timers, assumed at 70 seconds and 190 seconds, respectively, after the stage 1 valves start to open.
Once the ADS Stage I through 3 valves open, RCS pressure is reduced to less than 100 psia.
Finally, after 2010 seconds, RCS pressure has decreased to less than 29 psia (14 psig), thus making it possible for the IRWST to gravity feed into the DVI lines The CMTs continue to drain (to 20%
CMT volume) causing the ADS Stage 4 hot leg valves to open at 1980 seconds.
It should be noted that in the NOTRUMP analysis of two similar 2 in. LOCA cases described in Section 15.6.5 of the SSAR, actuation of ADS Stage 4 at 20% CMT level was required, along with an additional delay of about 500 seconds to allow sufficient RCS depressurization for IRWST gravity injection. The TREAT-AN analysis estimates decay heat, which is approximately 20-30% less than mAap600\2064w\ae-1.wpf:lt 0827% 2-26 REvlsioN: lA
l 120% ANS-5.1-1971 used in the NOTRUMP analysis. This reduction in the decay heat is likely the reason the times for IRWST injection differ. Otherwise, the trends modeled in the NOTRUMP and TREAT-AN analyses are reasonably close. For example, in the NOTRUMP analysis, the times to ADS Stage 4 are 2100 seconds, versus 1980 seconds in the TREAT-AN analysis.) l i
1 The upper plenum / core mixture level is illustrated in Figure 2-19. The mixture level remains above 24 feet for the duration of the transient. It is above the bottom of the hot legs in the TREAT-AN model. The top of the active fuel is approximately 19 feet, so the core is covered with at least 5 feet of mixture during this transient. AP600 has hot leg level instrumentation, used primarily during shutdown, extending from the bottom, to a few feet above the top of the hot leg at the SG inlet connection. Therefore, it is likely that the upper plenum / core level trend shown in Figure 2-19 will be evident to an operator monitoring the hot leg level instrumentation.
l The hot leg and cold leg temperatures in loop 1 are illustrated in Figure 2-20. The hot leg l temperature reaches saturation early, at approximately 100 seconds, and remains at saturation for the entire event. The cold legs in loop I continue to be cooled by PRHR until 600 seconds and makeup until 1100 seconds. The PRHR flow is reduced at approximately 600 seconds as the inlet piping starts to drain and then briefly recovers. Makeup flow is maintained at a rate of approximately 28 lbm/sec (200 gpm) for much of the early portion of the transient. Makeup flow is stopped shortly after ADS actuation. In the post-CMT actuation mode of operation, makeup flow is automatically terminated when pressurizer level increases to approximately 20%. At a maximum rate of 28 lbm/sec prior to 1100 seconds, makeup flow is small in comparison to the break flow shown in Figure 2-21.
Figure 2-22 shows the CMT levels and Figure 2-23 shows the injection flow and balance line flow for CMT-A. The flow response for CMT-B is similar. During the water recirculation mode of l
( operation, prior to 600 seconds, the CMTs remain full and inject approximately 50 lbm/sec of cold borated water. About 40 lbm/sec of warm water from the cold legs in loop 2 is recirculated to the l top of the CMTs through each respective balance line. After the top of the CMTs reach saturation and stan to drain, the injection flow approximately doubles and the balance line liquid flow decreases to zero. The reduction in CMT injection between 1100 and 1600 seconds is caused by interaction with the high flow from the accumulators (see Figure 2-24). Near the end of the transient, the CMTs {
empty and the injection flow decreases to zero. !
i Figure 2-25 shows the flow through stages 1 through 3 of the ADS. It takes several minutes for the valve opening sequence to be completed. After the valves are fully open, the combined flow area for all Stage I through 3 valves is approximately 0.65 sq. ft. The ADS l-3 flow is initially vapor until the pressurizer fills. The flow rate peaks at 400-500 lbm/see and then decreases as the RCS is funher depressurized.
l l The CMTs continue to drain until the level reaches 35 feet, which is the 20% level set-point for f Stage 4 actuation, at approximately 1980 seconds. The associated hot leg valves then open resulting in additional " break" flow as in Figure 2-26, and RCS depressurization. The combined flow area of m%p600co64**ispf:Hro8D96 2-27 REvlsioN: lA
I 1
the Stage 4 valves is more than 1.0 sq. ft., sufficient to cause additional RCS depressurization and I thereby allow IRWST gravity injection flow, as in Figure 2-27.
l The TREAT-AN simulation was stopped at 2500 seconds. After that time, inventory will be i maintained in the RCS due to gravity injection from the IRWST, as demonstrated in the NOTRUMP analysis. Hours later, the IRWST will drain down and the water level in containment will rise until water is able to recirculate through the sump screens and back into the IRWST injection lines.
Ultimately, the RCS sensible heat and core decay heat is given up to reactor containment which can be cooled over time by the passive containment cooling system (PCS).
As noted in the previous cases analyzed, the operator would likely take action to establish SFW while in AE-0, prior to transition to AE-1. Restoration of SFW would not significantly affect this transient since this action by itself would not change the secondary side pressure, which partially controls RCS pressure during the first 10 minutes of the transient. As the system drains, the SGs become decoupled and no longer influence the response of the RCS. Therefore, none of the actions taken in AE-0, and the early part of AE-1, will affect the RCS response for this case until ADS is actuated.
For a break as large as a 2.0 in. cold leg LOCA, it would be difficult to avoid ADS Stage 1, and Stages 2 and 3, since these stages are actuated on timers. However, it should be possible to establish injection using the Normal Residual Heat Removal pumps (RNS injection) prior to ADS Stage 4.
This essentially prevents creation of a large LOCA in the hot legs and allows the operator flexibility in recovering the plant with pumped injection as opposed to gravity feed. The action is included in AE-1 and a demonstration of it is presented in Case 4 which follows.
l l
I I
O mAap600\2064w\ae-l.wpf;lb482396 2-28 REVislON: lA
O TABLE 2 3 TIME TABLE OF EVENTS FOR 2.0 INCH COLD LEG LOCA WITHOUT OPERATOR ACTION EVENT / AUTOMATIC ACTIONS Time (sec)
Full power operation 0 10 2.0 in. diameter cold leg LOCA in CL-1A (loop with PRHR) 10 LOW-1 pressurizer pressure reactor trip signal 46 Reactor trip followed by turbine trip 48 LOW 2 pressurizer pressure signal, SI actuation 50 (MFW isolation, CMT initiation, PRHR initiation, RCP trip signal)
RCPs trip and begin coastdown 67 Upper plenum starts to drain 120 CMTs start to drain 630 !
SI accumulators start to inject 740 ADS Stage i valves start to open 1050 ADS Stage 2 valves start to open 1120 ADS Stage 3 valves start to open 1240 l
ADS Stage 3 valves fully open 1320 Si accumulators stop injecting (nearly empty) 1600 f ADS Stage 4 valves open 1980 Gravity injection from IRWST starts (RCS pressure < 29 psia) 2010 l CMTs empty 2350 End of transient modeled, ADS fully actuated, gravity injection from IRWST, 2500 upper plenum / core level stable near bottom of hot legs I
!O l
m:WO64w\ae l.wpf.lb-0823% 2-29 REVISION: 1A
9 Pressurizer Level 120 100 ,
I n .
M _
v 80 e
o .
S
(.
' 60 m
N L .
2 t m 40 m .
CL -
20
_ l 0
O 500 1000 1500 2000 2500 Time (s)
Figure 217. Pressurizer Level Response for a 2.0 Inch Cold Leg LOCA Without Operator Action m:\ap600C064w\ae la.wpf:lb-0823% 2-30 REVISION: lA
O RCS Pressure 2500 _
^
o 2000 m :
- n. _
v 1500 _
i O
v e
m 1000 l gn =
l m :
e -
6- 500 ~
s Q- _
~
0 0 500 1000 1500 2000 2500 Time (S) l O Figure 2-18. Reactor Coolant System Pressure Response for a 2.0 Inch Cold Leg LOCA Without Operator Action m:WW>4wk-la.wpf:lt482796 2-31 REVISION: lA
f i
l 9
Upper Plenum / Core Level l
30 1 m
I v 28
- > 26 _
'w
^
~
9%,,% e 23 -
x 22 _
E _
20 0 500 1000 1500 2000 2500 Time (S) i l
l Figure 219. Reactor Upper Plenum / Core Mixture Level Response for a 2.0 Inch Cold Leg LOCA Without Operator Action m:\ap6000064w\ae - l a.wpf: l b-082396 2-32 REVISION: lA
l Hot Leg 1
Cold Leg 1A i
RCS Saturation
! l i
700
^
_g i
1 600 -
v
- (
l e 500 Eh,
\
l u :
-N I\ I 4\
o 400
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l o : "gl 's., ,) ',
l e 300 _ x N
- a - l
{
E : ,. 3 /'JW I
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,k,., ..n. m.et i tlb. yy, sy ,
l W -
- 1 J
~ ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' '
100 I O 500 1000 1500 2000 2500 l Time (s) l l
Figure 2-20. Reactor Coolant Loop 1 Temperature Response for a 2.0 Inch Cold Leg LOCA Without Operator Action atup60cco64wwe ta.wpt:1b-osu96 2-33 REVISION: lA
1 0
l Liquid l
Vapor }
m 800 o -
c) -
m -
l
)600
.c gn 400 -
v
/
o -
LA- -
\
u 200
~
O o
D 1
- 0
' ' ' ' ' ' ' ' ' d i i i i 0 500 1000 1500 2000 2500 ;
Iime (S)
Figure 2 21. Liquid and Vapor Break Flow Rates for a 2.0 Inch Cold Leg LOCA Without Operator Action mhpun2064wue-la.wpr:ib-o823% 2-34 REVISION: 1A
m i
L )1 CMT-A Leve!
l
CMT-B Level l
m 55 ,
~
- l
_ l
~
50 \
~
a
- 45 .
, ~\
O e
~
$ 40 -
~
~
x _
- E 35 _
w -
=E
~ ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' '
30 0 500 1000 1500 2000 2500 Time (S)
/)s Figure 2 22. CMT Mixture Level Response for a 2.0 Inch Cold Leg LOCA Without Operator Action P
m:\ap6000064w\ae.ltwpf:lb-0823% 2-35 REVISION: 1A
O CMT-A injection
CMT-A Bolonce Line
_ 150
- o -
~
E 100 -
.c p
v -
+ I I m 50
, _ y-Jt-_ _4 j o - p \
- _ i
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U ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' '
-50 0 500 1000 1500 2000 2500 Iime (S) 1 i
(
Figure 2-23. CMT-A Injection and Balt.nce Line Flow Rates for a 2.0 Inch Cold Leg LOCA Without Operator Action 9 '
m:\ap600\2064w\ae la.wpf:lb-0823% 2-36 REVISION: lA
l l
4 I
, 1 l
l l
i l
1 1 Accumulator A j
Acc umu l a t o r B l m 300 _
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- 1 o -
E 50 l
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4 ~ ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' '
0 0 500 1000 1500 2000 2500 Time (S) i i
t i Figure 2 24. SI Accumulator Flow Rates for a 2.0 Inch Cold Leg LOCA Without Operator Action m:\ap6000064whe la.wpf:Ib-0823% 2 37 REVISION: lA
l l
l O l
l l
Liquid
Vapor m 500 -
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s - i E 400 c : I E 300 I 'd I 7 200
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m -
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- I, m - s 0
~ ' ' ' ' ' ' ' ' ~' ' ?# k ' " "" ' ' ~ * - ' '--
0 500 1000 1500 2000 2500 Time (s)
Figure 2-25. ADS Stage 1 Through 3 Flow Rates for a 2.0 Inch Cold Leg LOCA Without Operator Action mAap600C064w\ae-la.wpf:Ib-o823% 2-38 REVISION: lA
i l
l From Hot Leg 1
- - - - F r om H o t Leg 2 m 700 _
$ 2
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3 500 _
=
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l 300 -
+
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4 W1 5200 o : i I f 3- 'gb l 100 'l l m : f-j
,e i i } 'ti es -
4 ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' '
0 O 500 1000 1500 2000 2500 Time (S) l
% ADS Stage 4 Flow Rates for a 2.0 Inch Cold Leg LOCA Without Operator Figure 2-26.
Action l
I mMp600\2064w\ac la.wpf.lb-o823% 2-39 REVISION: lA
I
\
l O
1 i
1 ,
l l
l l
To DVI Line A
To DVI Line 8 200 N -
l E l 2 -
- 150
~
C 7 100
~
2 -
= 50 o -
n E
m -
0 0 500 1000 1500 2000 2500 Time (s) l l
l i
Figure 2 27. IRWST Gravity Injection Flow Rates for a 2.0 Inch Cold Leg LOCA Without Operator Action m.\ap60m2064w\ac-la wpf:lb-0823% 2-40 REVISION: lA
( l l
2.4 CASE 4: 2.0 Inch Diameter Cold Leg LOCA With RNS Injection This section describes the response of the 2.0 in. cold leg LOCA with RNS injection prior to ADS Stage 4. The action is assumed to be taken at 1500 seconds,180 seconds (3 minutes) after the Stage 3 valves are fully open (see Table 2-3 or Table 2-4). All other events or automatic actions prior to this are assumed to be the same as previously described for Case 3. The revised timetable of events for l
this restart simulation is provided in Table 2-4. Transient plots of interest can be found in Figures 2-28 through 2-33.
When RNS injection is started, the RCS pressure is approximately 60 psia (Figure 2-28), considerably less than the shutoff head pressure of the RNS pumps, which is about 160 psig or 175 psia with full IRWST. At this RCS pressure, one pump is capable of injecting about 800 gpm (more than 100 lbm/sec) to each of the DVI lines (see Figure 2-33). Since 200 lbm/sec is several times the core boil-off flow, the RCS inventory should recover after initiation of RNS injection due to RNS injection I alone. Each accumulator and its associated CMT inject about 200 lbm/see per DVI line, until the l accumulators stop injecting at 1600 seconds. The RCS inventory would be expected to recover rapidly l for this case due to the additional flow.
1 As expecteu the level in the upper plenum / core region recovers quickly as shown in Figure 2-29.
The upper plenum stays full even after the accumulators stop injecting their water contents.
( Eventually subcooling is restored in the hot legs and at the core exit. As shown in Figure 2-30, the core exit temperature is approximately the same as the hot leg temperature in loop 1. As noted previously, the operator should be able to observe this level increase on the hot leg level instrumentation and the increase in subcooling on the core exit, or hot leg, subcooling indication.
The CMT levels continue to decrease immediately after RNS injection is started, and decrease at a faster rate after the accumulators stop injecting (see Figure 2-31). Eventually the RNS injection flow refills the RCS sufficiently so that the CMT injection essentially stops and CMT levels stabilize. This occurs around 2000 seconds when the CMT levels are at 38 feet. It is several feet higher than the setpoint for ADS Stage 4 actuation, which is 20%, or approximately 35 feet level in the TREAT-AN model. Since there are check valves in the injection lines, the only mechanism for CMT refill is via the cold leg balance lines that connect to the top of the CMTs. The TREAT-AN model predicts some j refill via this mechanism, although this is a slow process and the cold leg balance line flows are oscillatory, but positive. It is possible that some of the steam in the CMTs will condense due to the cold thick metal in the CMTs. Metal heat transfer is not modeled in the CMTs in the TREAT-AN l example. This would permit some depressurization of the CMTs and additional flow through the balance lines, allowing the CMTs to refill faster. The effect was noted in the OSU one-quarter scale long term cooling tests (see specifically Section 6 of WCAP-14292, Rev.1).
Since the RNS injection flow helps reduce the steaming rate from the core, the RCS pressure is V slightly lower than in the previous Case 3. This allows additional flow via IRWST gravity injection (Figure 2-32) to supplement the flow from RNS injection (Figure 2-33). The flow rates of the two maap600co64wsae-ia.wpf.ib-oso7% 2-41 REVISION: lA J
components are comparable, if it is assumed simultaneous IRWST gravity feed is used. (Note: the isolation valves for IRWST gravity feed are opened by manual operator action. Automatic actuation signals due ADS Stage 4 would not be present for this event.)
The analysis for Case 4 demonstrates that for a typical small LOCA that is large enough to actuate ADS Stages I through 3, the operator should have sufficient time to establish RNS injection and stabilize CMT levels prior to opening of the ADS Stage 4 hot leg valves. It is appropriate to include this action to establish RNS injection in AE-1 after confirming the ADS Stage 1-3 sequence has been completed and the RCS is sufficiently depressurized. Based on the upper plenum / core level response, it is appropriate to include a contirmency plan to actuate ADS Stages 1 through 3 followed by RNS injection, if level goes off-span low on the hot leg level instrumentation and the CMT level has not yet reached the low-l ADS setpoint of 68%. RNS injection is clearly effective in providing core cooling for the 2 in. LOCA scenario. Furthermore, this action of recovery is familiar to the reactor operators at plats currently in operation.
After the IRWST is drained down, it is possible to recirculate the water spilled to containment in a manner also similar to that used in current operating plants (except to the DVI lines instead of the cold legs). The RNS, instead of PCS, provides long term cooling for this mode of operation. For the 2 in.
LOCA scenario, it is expected that the operator would establish RNS recirculation after several hours since it would take that long to drain the IRWST at the anticipated RNS flow rates.
O gi m:wp600co64wue.itwpt.lu)807% 2-42 REvlslON: lA )
~._ss.-_
Table 2-4 Time Table of Events for 2.0 Inch Cold Leg LOCA With RNS Injection Event / Automatic Actions Time (sec)
Full power operation 0 - 10 2.0 in. diameter cold leg LOCA in CL-1 A (loop with PRHR) 10 LOW-1 pressurizer pressure reactor trip signal 46 Reactor trip followed by turbine trip 48 l
LOW-2 pressurizer pressure signal, SI actuation 50 (MFW isolation, CMT initiation, PRHR initiation, RCP trip signal)
RCPs trip and begin coastdown 67 Upper plenum starts to drain 120 CMTs start to drain 630 SI accumulators start to inject 740 ADS Stage i valves start to open 1050 l
ADS Stage 2 valves start to open 1120 f ADS Stage 3 valves start to open 1240 ADS Stage 3 valves fully open 1320 Operator initiates RNS injection 1500 SI accumulators stop injecting (nearly empty) 1600 Gravity injection from IRWST starts 1650 (isolation valves assumed open)
CMTs reach minimum level (~ 45%) and start to refill 2000 End of transient modeled, ADS Stages 1-3 actuated, RNS injection 3000 established, core subcooled i
l m:\ap6000064w\ae-l a.wpf: l b-0807% 2-43 REVistoN: lA
O!
I 1
l \
l l
l RCS Pressure 1 2500 -
^
o 2000 k
)
m :
c.
_A v 1500
-)
m 1000 (' '
O m -
m :
a> _
u 500 s o- :
0 0 500 1000 1500 2000 2500 3000 Time (S) l l Figure 2-28. Reactor Coolant System Pressure Response for a 2.0 Inch Cold Leg LOCA With RNS Injection mAapan2064.\ae ta.wpr:Imo796 2-44 REVISION: 1A
O Upper Plenum / Core Level 30
~
m
~
~
~
~
v 8 ii
- > 26 ^
'w l
- - p C)1 24
~
u ~
m l e
~
i x 22 l
l ~
l .._
~
- s _
20 0 500 1000 1500 2000 2500 3000 l
Time (S) l l 1
l 1
O O Figure 2-29. Reactor Upper Plenum / Core Mixture Level Response for a 2.0 Inch Cold Leg LOCA With RNS Injection i m:hpmA2064w\ae-lawpf:ll>48N 2-45 REVISION: lA i
)
l l
l
[
l O
Hot Leg 1
Cold Leg 1A l ----RCS Saturation 700
- L m
L 600 $
v
- ( ^
o 500 ,,
' : \ 4\
l l
3 : (s I \
}
~ 400 '
' 3
' Y)'
's -fi e 300 [ , s a : b i
E _
'g +-- ------
e 200 ^
',6, \jy'Ii
/ ) 'l '
t l
g :
" ' ' ' ' ' ' ' ' ' ,,7T-
100 ;
0 500 1000 1500 2000 2500 3000 Time (s) l l
l l
Figure 2-30. Reactor Coolant Loop 1 Temperature Response for a 2.0 Inch Cold Leg LOCA With RNS Injection m:bp60m:064wue-ta.wpt:1b-oso796 2-46 REVISION: lA
O i
I i
CMT-A LoveI
' - - - - C M T-B Level 55 _
~
^
-: e ~
- 50
\
v ~_
a) -
u 45 O
_s _
e _
~
x 40 y
\_ ._
H 35 2 -
~
O _
~ ' ' ' ' ' ' ' ' ' ' ' ' ' ' '
30 O 500 1000 1500 2000 2500 3000 Time (S) 4 O Figure 2-31. CMT Mixture Level Response for a 2.0 Inch Cold Leg LOCA With RNS Injection
=\np6mm>4w\ae la.wpf:lN 2-47 REVISION: lA
1 I
l 1
l l
t l
l l
I l
l To DVI Line A j
To DVI Line B 200 e -
N -
E
- 150
=
o -
l C -
100 ,
~
l
~
l 2
= 50 l o -
~
E a -
l - ' ' ' ' ' ' ' '- '
0 .
l 0 500 1000 1500 2000 2500 3000 l Time (s) I i
l l
l i
i 1
1 l
l l Figure 2 32. IRWST Gravity Injection Flow Rates for a 2.0 Inch Cold Leg LOCA With RNS Injection
! m:bp60000Mw%la.wpf:lb o80796 2-48 REVIslON: lA i
O l
To CVI Line A To DVI Line B 200 a -
N -
E -
f 150 i
m -
Q V
d 100
- ~
c o -
u -
.1e 50 -
v>
z -
" ' ' ' ' iii iie i i i i i 0
0 500 1000 1500 2000 2500 3000 Time (s) l l
1
!O 4
Figure 2-33. RNS Injection Flow Rates for a 2.0 Inch Cold Leg LOCA With RNS Injection f
mWO64ww-1L*P ;1b-080796 2-49 REVISION: lA
2.5 CASE S: Large Double Ended Cold Leg LOCA Without Operator Action In section 15.6.5 of the AP600 SSAR, NOTRUMP analysis for the following small LOCA cases are presented:
- spurious ADS actuation a double-ended DVI line break 2 in. cold leg LOCA in loop with PRHR (loop 1) 2 in. cold leg LOCA in loop with CMT balance line (loop 2)
- double-ended CMT balance line break With the exception of the DVI line break, the RCS response for the above cases are all similar and feature ADS Stage 4 actuation in the 1600 to 2200 second time frame, followed by IRWST injection a few minutes later. Based on similarities between the TREAT-AN and NOTRUMP analyses for Case 3 and the TREAT-AN results for the corresponding case with RNS injection (Case 4), it is reasonable to expect that the operator could establish RNS injection after the ADS Stage 1 through 3 sequence is completed. If this action is performed quickly enough, it may be possible to prevent actuation of the Stage 4 hot leg valves to avoid making the LOCA significantly larger.
For the double-ended DVI line break and for LOCAs that are significantly larger, it may not be feasible to expect the operator to establish RNS injection prior to ADS Stage 4 actuation. ADS Stage 4 occurs at approximately 10 to 20 minutes for these cases, the fastest time (500 seconds) being that for the DVI line break. By the nature of this failure, the CMT injecting to the broken DVI line is rapidly depleted for this case. For these larger breaks, it is still reasonable to assume the operator will establish RNS injection followed by recirculation to aid in recovery. The importance of performing this action prior to Stage 4 is primarily an economic one and not as significant since there is already a large failure to deal with.
As an information aid to the operator, the response of a large LOCA is briefly described in this section. A double-ended cold leg LOCA from Section 15.6.5 of the AP600 SSAR, designated as the CD (discharge coefficient) = 0.8 DECLG (double-ended cold leg guillotine) is selected.
This case was simulated with WCOBRAC/ TRAC. A time table of events is provided in Table 2-5.
Transient plots of interest are presented in Figures 2-34 through 2-39.
As a result of the large break, there is an immediate rapid pressurization of containment causing a SI signal due to high-1 containment pressure at 1.2 seconds. CMT and PRHR actuation then occur followed by delayed RCP trip. Core shutdown occurs due to voiding, and no credit is taken for the control rods to shutdown the reactor in the SSAR. In reality, the rods should fall into the core.
The RCS depressurizes rapidly (see Figure 2-34) as initial inventory is depleted due to the break flow.
As a result a result of the blowdown, the core uncovers and begins to heat up. A typical clad temperature heatup transient at the 8.5 ft elevation,1.5 ft above the core mid-plane, is shown in maap60m2064wsae-i a.wpr:i b-oso796 2-50 REVm oN: IA
Figure 2-35. To limit the clad temperature excursion, in which peak temperature occurs at 6 seconds, water from the upper head is able to penetrate into the core region until approximately 20 seconds.
The fuel is then uncovered (Figure 2-37) and begins to heat up again.
By 15 seconds, the SI accumulators start to inject at a high flow (Figure 2-36), shutting off flow from the CMTs. Some accumulator water is bypassed to the break. By 19 seconds, accumulator water begins to flow into the lower plenum region and subsequently starts to refill the downcomer (see Figure 2-38). At 39 seconds, the lower plenum fills to the point where water begins to reflood the core from below and reduce the void (steam) fraction in the core region. As time passes, core cooling improves significantly and the cladding temperature begins to decrease as the core water level increases.
After the accumulators have injected their water, the CMT injection flows increase (Figure 2-39). The CMT operate at high injection > 100 lbm/sec per CMT, until ADS is actuated. The analysis was stopped at 500 seconds. Had the analysis continued, ADS actuation followed by IRWST gravity injection would occur. This phase of the transient would be similar to that described previously for Case 3,2 in. cold leg LOCA without operator action. Section 15.6.5 of the SSAR also discusses the long term cooling portion for both small and large LOCA cases.
1 Similar to Case 4, it is likely that the operator would establish RNS injection followed by recirculation O. for the large LOCA. The approximate response for the large LOCA case with this action assumed, sometime after 500 seconds, would likely resemble the Case 4 analysis except the events for the large j
LOCA would occur roughly 1000 seconds earlier.
O f mAap600\2064w\ac-Ia.wpf:1b-080796 2-51 REVISION: 1A
1 l
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i TABLE 2-5 TLME TABLE OF EVENTS FOR LARGE DOUBLE ENDED COLD LEG LOCA WITIIOUT OPERATOR ACTION (CD=0.8 CASE TAKEN FROM SSAR TABLE 15.6.8)
EVENT / AUTOMATIC ACTIONS Time (sec)
Full power operation <0 Double-ended LOCA in one of the loop 2 cold legs, CD = 0.8 0 (loop with cold leg balance line)
SI signal due to containment high-l pressure 1.2 l
PRHR, CMT isolation valves open 2.4 Calculated peak clad temperature occurs 6.0 Si accumulator injection begins 14.9 l
RCP trip occurs 17.4 End of blowdown 35.0 Bottom of core recovery 39.0 SI accumulators stop injecting (empty) - 270 End of transient modeled: - 500 core cooled (< 300'F),
each CMT injecting at rate > 100 lbm/sec, ADS and IRWST gravity injection will follow O
m:\ap600\2064w\ac-l b.wpf: I b-o80796 2-52 REVISION: l A
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-20 0 20 40 60 80 Time (Seconds) l
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l Figure 2-35. CD = 0.8 DECLG Break Transient PCT at 8.5 ft Elevation, Rods I thru 5 9
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> 0 l l
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Time (Seconds) l Figure 2-37. CD = 0.8 DECLG Break Transient Core Region Collapsed Level From Core Bottom (taken from Section 15.6.5 of the AP600 SSAR) i m:wp600co64wsae.lb.wpf:Ib.0807% 2-56 REVISION: lA
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(taken from Section 15.6.5 of the AP600 SSAR) Gravity Injection Flow map 600co64wsae-1b wpf:1b-oso7% 2-58 REVISION: 1A
rep lacement Instructions O for the AP600 Emergency Response Guidelines Background, Book 1 Section AES-1.1: Passive Safety Systems Termination REMOVE INSERT Title pg., Rev.1,7/28/95 Title pg., Rev.1 A, 8/96 Pages 2-1 to 2 '24, Rev.1, 7/28/95 Pages 2-1 to 2-24, Rev.1 A, 8/96 l
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1 BACKGROUND INFORMATION i
FOR i 1
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AP600 j EMERGENCY RESPONSE GUIDELINE 1
AES-1.1 AP600 PASSIVE SAFETY SYSTEMS TERMINATION Rev.1A ;
August,1996 l
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m:\ap600\2064w\aes t -l a.wpf: l b-0827% REVISION: lA
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1 TABLE OF CONTENTS Section Page
1.0 INTRODUCTION
1-1
2.0 DESCRIPTION
2-1 2.1 Case 1: Spurious Safety Injection Actuation Without Operator Recovery Actions 2-1 2.2 Case 2: Spurious SI Actuation with AES-1.1 Operator Recovery Actions 2-4 3.0 RECOVERY / RESTORATION TECHNIQUE 3-1 3.1 High Level Action Summary 3-1 3.2 Key Utility Decision Points 3-4 4.0 DETAILED DESCRIIrrION OF GUIDELINE 4-1 4.1 Detailed Description of Steps, Notes, and Cautions 4-1 4.2 Step Sequence Requirements 4-33 9
9 m:\ap6000064wbes t . l a.wpf: l b-o82796 ij REVISION: 1A
2.0 DESCRIPTION
Guideline AES-1.1, AP600 PASSIVE SAFETY SYSTEMS TERMINATION, providas instructions for securing the passive safety systems for transient events in which these systems are inadvertently actuated but no longer required. A typical example of a transient event of this type is spurious safety injection (SI) actuation. Once specified reactor coolant system (RCS) subcooling, inventory, and heat sink criteria are satisfied, the AES-1.1 guideline allows the operator to isolate the core makeup tanks (CMTs) and passive residual heat removal (PRHR) heat exchanger and use the steam generators (SGs) and other nonsafety, elated systems and equipment to maintain stable plant conditions.
The AES-1.1 guideline is also used for very small loss-of-coolant accidents (LOCAs), LOCAs that can be isolated, or following a secondary break. For the secondary break, transition to the AES-1.1 guideline would be made from AE-1, AP600 LOSS OF REACTOR OR SECONDARY COOLANT, once RCS pressure is stable or increasing after the faulted steam generator has been isolated and completed its depressurization. An example case for this situation is included in the background document for AE-2, AP600 FAULTED STEAM GENERATOR ISOLATION. Application of AES-1.1 to very small LOCAs would be similar to that described below for the spurious safety injection event, except that additional inventory from the chemical and volume control system (CVS) makeup pumps would be required to keep up with the RCS leakage. Allowing for a reduction in RCS pressure f below its nominal value (2250 psia), and assuming a maximum charging flow of 200 gpm, the maximum break size for which AES-1.1 recovery could be considered (without loss of RCS subcooling and pressurizer level) would be roughly 0.5 in. diameter. Recovery analysis for the 0.5 in. LOCA included in the background document for AES-1.2, AP600 POST LOCA COOLDOWN AND DEPRESSURIZATION illustrates that recovery using AES-1.1 would be possible for this break case.
Since the accident cases are addressed elsewhere, this background document focuses on transient events in which the passive safety systems are actuated. As a typical example, spurious safety injection actuation is considered.
2.1 CASE 1: Spurious Safety Injection Actuation Without Operator Recovery Actions To illustrate a typical application of the AES-1.1 guideline, a spurious safety injection actuation event has been analyzed both with and without operator recovery actions. These two cases are described in greater detail below. The Transient Real-time Engineering Analysis Tool- Advanced Numerics (TREAT-AN) computer program was used to simulate these two thermal hydraulic transients.
The analysis for CASE 1 (without operator action) is similar to a LOFTRAN analysis presented in Chapter 15 of the AP600 SSAR. In the TREAT-AN simulation, however, "best-estimate" assumptions are used and many of the plant control systems of interest have been included.
%./
m:\ap600\2064w\aest la.wpf:lb-0827% 2-1 REVislON: lA
For this scenario, the reactor is assumed to be operating near full power (1933 MWt ) for an extended period of time; that is, long enough to establish an equilibrium level of decay heat (approximately 7% of full power). A spurious safety injection signal is then assumed to occur at 10 seconds. The time table of events for the TREAT-AN simulation is provided in Table 2-1, and parameters of interest are l
illustrated in Figures 2-1 through 2-7. l l
Within several seconds after the safety injection signal, a series of automatic actions occur. These :
include CMT actuation, main feedwater isolation, reactor trip, and turbine trip. These are directly I caused by the safety injection signal. As a result of CMT actuation, the PRHR heat exchanger outlet I valves open, pressurizer heaters cut out (tum off), and, following a time delay, the reactor coolant i pumps (RCPs) trip at 29 seconds.
Immediately following the reactor trip, the condenser steam dump valves operate to control the average RCS temperature to the no-load value (545*F). As a result of the PRHR cooldown, however, the cold leg temperatures in loop 1 (see Figure 2-4) continue to decrease and at 67 seconds reach the low Ta setpoint (514 F). This causes isolation of the main steamlines and startup feedwater. From this time on, the plant is stabilized by the passive safety systems.
The PRHR flow (approximately 90 lbm/see following RCP coastdown and relatively constant for the duration of the transient) transfers the residual heat from the RCS to the in-containment refueling water storage tank (IRWST). The CMTs operate in a recirculation mode with approximately 100 lbm/sec total injection flow and 80 lbm/see total cold leg recirculation (balance line) flow-during the first 1000 seconds of the transient (see Figure 2-6). As the water density in the CMTs becomes more nearly equal to that of the RCS, the CMTs loose their driving head and these flows decrease.
The difference between the two curves of Figure 2-6 represents the net addition to the RCS from the CMTs. This inventory addition causes the RCS pressure and pressurizer level to increase to close to their initial values as the RCS cooldown due to the PRHR begins to slow down. At the end of the 5000 second transient analyzed, the RCS average temperature is reduced to approximately 430 F.
As a result of the heat transfer from the PRHR heat exchanger, the bulk IRWST temperature is l
calculated to increase from 95 F to 128'F, an increase of 33*F (Figure 2-7). This is based on an assumed IRWST water volume of approximately 500,000 gallons. (Note: the minimum IRWST volume in the proposed Technical Specifications is 400,000 gallons). Eventually after several hours, the IRWST will begin to boil. Although this is an acceptable consequence, boiling of the IRWST is not likely to occur since the operator can align the normal residual heat removal system (RNS) to cool the IRWST and thereby prevent boiling. Timely operator action to terminate the passive safety systems per AES-1.1 would be even more likely and limit the IRWST heatup to only a few degrees.
This case is described in CASE 2 that follows.
l l
O' mAap600\2064w\aes t - l a.wpf: l b-082796 2-2 REVISION: lA
O TABLE 21 Time Table of Events for Spurious Safety Injection Actuation Without Operator Recovery Actions Event / Automatic Actions Time (sec)
Full Power Operation 0 - 10 Spurious Safety Injection Actuation 10 CMT Actuation, Main Feedwater Isolation, Reactor Trip, Turbine Trip 12 (on S-signal)
PRHR Actuation (on CMT signal) 14 RCP Trip (delayed, following S-signal) 29 Low T (514'F) in CLs I A, IB (causes startup feedwater steamline 67 isolation)
End of Transient Modeled 5000 (d .
O m:kp60(A20Mw\aes t - l a.wpf: I b-082796 2-3 REVISION: lA
2.2 CASE 2: Spurious SI Actuation With AES 1.1 Operator Recovery Actions The initial conditions and early automatic actions for this case are the same as those modeled for the previous case without operator actions. For CASE 2 with operator actions, however, it is assumed that the operator follows the Emergency Response Guidelines (ERGS) and terminates the passive safety systems in an orderly fashion per AES-1.1, AP600 PASSIVE SAFETY SYSTEMS TERMINATION. After termination of PRHR cooling and CMT injection, the steam generators (SGs) are used for decay heat rema i.1 and the chemical and volume control system (CVS) is used for inventory and reactivity control. The TREAT-AN computer program is used for this "best-estimate" simulation of the primary and secondary systems. The containment response and many balance-of-plant support systems (including the component cooling and service water systems) are not modeled explicitly in TREAT-AN, so typical time delays to account for operation of this equipment is included in the simulation. The time table of events for this scenario is provided in Table 2-2 and figures of interest are presented in Figures 2-8 through 2-17.
l Because of human intervention, the operator action times assumed in Table 2-2 are not unique.
Realistic operator action times are considered to illustrate typical use of the ERGS and to demonstrate
! feasibility for stopping PRHR cooling and CMT injection and stabilizing the plant using nonsafety-l related systems.
1 In this scenario, it is assumed that the operators perform a verification of the automatic passive safety ,
systems features and by 300 seconds reach the step to check RCS cold-leg temperatures in AE-0, AP600 REACTOR TRIP OR SAFETY INJECTION. At this time, the cold-leg temperatures in loop 1 are less than 500 F due to the PRHR cooldown (see Figure 2-11). However, since SG narrow range levels are off span low [startup feedwater flow (SFW) is isolated due to low Ta], PRHR is not l isolated at this time. One hundred twenty seconds later (several steps later in AE-0), startup feedwater flow is restored to both intact SGs. Pressurizer level (Figure 2-10) is above the CVS level l control band used following CMT actuation (10 to 20 percent), so the makeup pumps are not started.
The operators then verify operation of balance-of-plant support systems and fan coolers and confirm that there is no accident in progress (i.e., no secondary break, LOCA, or SG tube rupture). At 600 seconds, the criteria for termination of passive safety systems are confirmed allowing transition to AES-1.1, AP600 PASSIVE SAFETY SYSTEMS TERMINATION. These criteria include stable (or )
l increasing) RCS pressure (Figure 2-8), pressurizer level on span (Figure 2-10), adequate RCS l
subcooling (Figure 2-15), and heat sink. For confirmation of the latter criterion, startup feedwater flow is aligned to both SGs and the PRHR heat exchanger is still in service (Figure 2-14). The SG narrow range levels are also ready to come on span (Figure 2-13).
The actions modeled and summarized in Table 2-2 reflect a relatively straightforward application of '
AES-1.1. Most of these actions are simple ones typically requiring only one or two minutes to perform. Following the steps to reset safety injection and reset containment isolation, these actions i include closing the outlet valves to the CMTs and PRHR (to isolate these systems) and placing letdown in service. When components are realigned to their pre-safety injection configuration, RCS l
m:\ap600\2064 wsaes t . l a.wpf: I b-0828% 2-4 REvlslON: 1A
_ _ _ _ _ _ _ _ . . _ _ = . . _ _ _ _ . . _ _ _ . _ _ _ _ _ _
i makeup flow is established at a rate less than letdown, since pressurizer level is near the top of the
" normal" or pre-safety injection control band (i.e., near 50 percent). After this action, RCS temperatures are stabilized by dumping steam from the SGs using the SG power-operated relief valves (PORVs) and then controlling secondary pressure near 750 psia. (Note: Steam dump to condenser had been isolated by the low Ta signal. If steam dump to condenser were used, additional time delay would need to be included to re-open the MSIVs and re-establish steam dump to condenser. The RCS response with steam dump to condenser in operation would otherwise be the same as that modeled here using the PORVs.) After RCS temperatures are stabilized at approximately 515'F average temperature, pressurizer heaters are operated to stabilize RCS pressure near 2100 psia. Note that the operator could elect to allow RCS temperatures to heat up closer to no-load conditions (545 F average temperature) and pressure to stabilize near the nominal value (2250 psia). However, in this scenario, it is assumed that the operator uses the nonsafety-related systems to limit any subsequent heatup and pressurization after terminating the passive safety systems.
1 At 1500 seconds transient time the operator restarts the 1 A reactor coolant pump (RCP) followed by ,
the IB RCP one minute later. These RCPs provide normal pressurizer spray. Figure 2-16 illustrates )
the hot leg flows in the two loops showing reverse flow in loop 2 after the RCPs in loop 1 are :
restarted. Following a slight RCS depressurization and drop in pressurizer level upon restart of the )
RCPs, pressure is stabilized at 2060 psia. RCS makeup flow is also increased to match letdown (100 gpm) and control pressurizer level near 46 percent. By 2100 seconds, SG narrow levels have increased to approximately 50 percent and startup feedwater flow is reduced to control levels near this value. Because the majority of the decay heat is removed by SG 1, (in loop with higher flow), the startup feedwater flow needed to match decay heat is apportioned as approximately 200 gpm to SG 1, but only 50 gpm to SG 2.
The transient is stopped at 2400 seconds with RCS pressure and temperatures stable at approximately 2060 psia and 515 F, respectively, and pressurizer level stable near 46 percent. RCS makeup and letdown are in service to maintain RCS inventory and reactivity control; pressurizer heaters and normal spray are available to maintain RCS pressure control; and SG cooling is provided for decay heat removal. Note that by completing passive safety systems termination in the time frame considered in this scenario, the IRWST heatup is limited to only 8 F (from 95 F to 103*F, see Figure 2-17). This modest increase should make it possible for a quick return to power once the cause of the spurious safety injection is identified and corrected.
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TABLE 2-2 Time Table of Events for Spurious Safety Injection Actuation With AES-1.1 Recovery Actions Event / Automatic Actions Time (see)
Full Power Operation 0 - 10 Spurious Safety injection Actuation 10 CMT Actuation Main Feedwater Isolation, Reactor Trip, Turbine Trip (on 12 S-signal)
PRHR Actuation (on CMT signal) 14 RCP Trip (delayed, following S-signal) 29 Low T,. (514'F) in CLs I A, IB (causes startup feedwater, steamline 67 isolation)
Operator completes safety injection verifications, checks RCS temperatures 300 Operator blocks low T,,, initiates startup feedwater (270 gpm per SG) 420 AES-1.1 entry conditions satisfied - transition from AE-0 600 Operator isolates CMTs (early steps of AES-1.1) 720 Letdown established at 100 gpm 780 Operator isolates PRHR 840 RCS makeup flow established at 50 gpm 900 i
SG PGRVs used to stabilize temperature 960 i CMT block removed, pressurizer heaters energized 1140 Operator restarts RCP 1A 1500 i
Operator restarts RCP IB 1560 j RCS makeup flow increased to match letdown, RCS pressure stabilized 1740 ;
Startup feedwater reduced to maintain SG levels, match decay heat 2100 i 1
i e i i
i m:\ap6000064w\aes t -l a.wpf: I b4827% 2-6 REVISION: 1A
TABLE 2-2 (Cont.)
Time Table of Events for Spurious Safety Injection Actuatica With AES-1.1 Recovery Actions Event / Automatic Actions Time (sec)
End of transient modeled, plant stabilized (end of AES-1.1) 2400 l RCS pressure = 2060 psia, SG pressures = 750 psia (
RCS temperature = 515'F, pressurizer level = 46%
RCS subcooling = 120*F, startup feedwater operating, SG NR levels = 50% l RCS makeup flow = Letdown = 100 gpm RCPs IA and IB operating l
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m:\ap600L"WAw\aest 1twpf:Ib-0827% 2-7 REVISION: lA
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RCS Pressure 2400 2300
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Figure 2-1. RCS Pressure Response for Spurious SI Without Operator Recovery Actions 9
m:\ap600\2064w\aest la.wpf.lb-082'196 2-8 REVISION: 1A
O SG 1 Pressure e e SG 2 Pressure 1200 1100
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" 900 N
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r 800 700 O 1000 2000 3000 4000 5000 Time (s)
O Figure 2-2. SG Pressure Response for Spurious SI Without Operator Recovery Actions mWO64wbl-la.wpf:1b-0827% 2-9 REVISION: lA
O Pressurizer Level 80 70 m
y 60 w .
4) h
$ 50 , f i 40 30 O 1000 2000 3000 4000 5000 Time (s)
O Figure 2-3. Pressurizer Level Response for Spurious SI Without Operator Recovery Actions m:Vp600\2064w\aes1 Itwpf:Ib-082796 2-10 REVISION: 1A
_ - . . . - . = . - - . . . . . . . . _ _ - . . - . _ . . - . . . - - - . . . _ .
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400 O 1000 2000 3000 4000 5000 Time (s) i i
lO Figure 2-4. Loop No.1 Temperatures for Spurious SI Without Operator Recovery Actions m:\np60m2064-\aes t -l a.wpf: 1b-0827% 2-11 REVISION: 1A
O Core Exit
- eDowncomer 650 600
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500 E - N e .-
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400 O 1000 2000 3000 4000 5000 Time (s) l l
l Figure 2-5. RCS Vessel Temperatures for Spurious SI Without Operator Recovery Actions m:bp600'.2064w\aes1 Ia.wpf:1b-082796 2-12 REVISION: 1A
l j
O l CMT Injection (A+B)
. . CMT Bolonce Line (A+B) 200 i
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150 l
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i -50 i 0 1000 2000 3000 4000 5000 Time (s) 4 4
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- Figure 2-6. CMT Flow Rates for Spurious SI Without Operator Recovery Actions m:\ap600co64 wues t -l awpr:I b-082796 2-13 REVISION: 1A 4
1 1
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l l
l IRWST Bulk Temp.
150 140 1
l m -
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100 90 O 1000 2000 3000 4000 5000 Time (s)
O Figure 2-7. IRWST Bulk Temperature for Spurious SI Without Operator Recovery Actions m:\ap6000064w\aes t - I twpf; 1 b-082796 2-14 REVISION: lA
l O
RCS Pressure 2400 2300 m
O
" 2200 m.
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2100 U _
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4 a _
2000 1900 O 500 1000 1500 2000 2500 Time (s)
O Figure 2-8. RCS Pressure Response for Spurious SI With AES-1.1 Recovery Actions m:\ap6000064w\aest la.wpf:lmn96 2-15 REVISION: lA
l l
l l
l i
l SG 1 Pressure
- a SG 2 Pressure 1200 1100 m
o -
1 1000
- r i m i
- s
[ 900 800
[ : __ _
700 O 500 1000 1500 2000 2500 Time (s) l l
O Figure 2-9. SG Pressure Response for Spurious SI With AES.I.1 Recovery Actions m:\ap6002064w\aest la.wpf:lb42796 2-16 REVISION: 1A
Pressurizer Level 80 70 l
^
60 kt v
O -
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40 30 O 500 1000 1500 2000 2500 Time (s)
O Figure 2-10. Pressurizer Level Response for Spurious SI With AES-1.1 Recovery Actions rn:\ap600\2064w\aes t -l a.wpf:1 b4827% 2-17 REVISION: 1A
P I
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l Hot Leg 1 l s ; Cold Leg 1A l 2 ; Cold Leg 18 650 l
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450 400 0 500 1000 1500 2000 2500 Time (s) l l
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O Figure 2-11. Loop No.1 Temperatures for Spurious SI With AES-1.1 Recovery Actions m:\ap600\2064w\aes t -l a.wpf: l b-0827% 2-18 REVISION: lA
1 Core Exlt
. .Downcomer 650 600 m
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O Figure 2-12. RCS Vessel Temperatures for Spurious SI With AES-1.1 Recovery Actions
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SG 1 NR Level e SG 2 NR Level 100 80 ,
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O Figure 213. Steam Generator Level Response for Spurious SI With AES-1.1 Recovery Actions i
m:up600co64wuest ta.wpf:1b-082796 2-20 REVISION: 1A
O PRHR inlet Flow
- aSFW to SG 1
- ;SFW to SG 2 200 m
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x 0 -
0 0 500 1000 1500 2000 2500 Time (s)
O Figure 2-14. SFW and PRHR Flow Rates for Spurious SI With AES-1.1 Recovery Actions atup600eo64wuest.la.wpt:1b-082796 2-21 REVISION: 1A
O Core Exit Subcooling 200 150 m
v
~
o
- s
- 100 0
6 C1.
E e
W 50 0
O 500 1000 1500 2000 2500 Time (s)
O Figure 2-15. Core Exit Subcooling Response for Spurious SI With AES.I.1 Recovery Actions m:\ap600\2064wWsi lawpf:lb-082796 2-22 REVISION: lA
/ w, b
Hot Leg i e aHot Leg 2 12000 10000 m
o o 8000 m
N E
.o 6000
- v m
o 4000 L .
c.
o 2000 o _
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= 2 l 0
-2000
~
0 500 1000 1500 2000 2500 Time (s)
O j Figure 2-16. Hot Leg Flow Rates for Spurious SI With AES 1.1 Recovery Actions I
mMp60m2064wws1 1a.wpc1b-082796 2-23 REVISION: 1A l l
i
O IRWST Bulk Temp.
150 140 m -
u_ 130 v _
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a> 110 H _
100 90 0 500 1000 1500 2000 2500 Time (s) i Figure 2-17. IRWST Bulk Temperature for Spurious SI With AES-1.1 Recovery Actions e
m:\ap60(A2064w\aes1 1a.wpf:1b-082796 2-24 REVISION: 1A
Replacement Instructions for the AP600 Emergency Response Guidelines Background, Book 1 Section AES-1.2: Post Loss-of-Coolant Accident Cooldown and Depressurization l
l REMOVE INSERT l Title pg., Rev.1,7/28/95 Title pg., Rev.l A, 8/96 l Page 2-1, Rev.1,7/28/95 Pages 2-1 to 2-37, Rev.l A, 8/96
{
O lO l
l O
l l
l BACKGROUND INFORMATION !
FOR l AP600 EMERGENCY RESPONSE GUIDELINE ;
l l
l AES-1.2 AP600 POST LOSS OF-COOLANT ACCIDENT COOLDOWN AND DEPRESSURIZATION l l Rev.1A 1
! August,1996 l
l l
l 1
l i
i !
l m \ap60m2064w\aest-2.wpf:lb-082996 REVISION: 1A
TABLE OF CONTENTS
(
Section h
1.0 INTRODUCTION
1-1
2.0 DESCRIPTION
2-1 2.1 Case 1: 0.5 Inch Diameter Cold Leg LOCA with AES-1.2 Recovery Actions 2-4 2.2 Case 2: 1.0 Inch Diameter Cold Leg LOCA with AES-1.2 Recovery Actions 2-20 3.0 RECOVERY / RESTORATION TECHNIQUE 3-1 3.1 High Level Action Summary 3-1 3.2 Key Utility Decision Points 3-4 4.0 DETAILED DESCRIPTION OF GUIDELINE 4-1 4.1 Detailed Description of Steps, Notes, and Cautions 4-1 4.2 Step Sequence Requirements 4-44 5.0 FOLDOUT PAGE 5-1 l
\
O m:\ap600(2064 w\aes t -2.wpf:l t482996 11 REVISION: 1A
2.0 DESCRIPTION
As a demonstration of guideline AES-1.2, AP600 POST LOSS-OF-COOLANT ACCIDENT (LOCA)
COOLDOWN AND DEPRESSURIZATION, this section presents results for two small LOCA recovery cases:
. Case 1: 0.5 inch diameter cold leg LOCA with AES-1.2 recovery actions
. Case 2: 1.0 inch diameter cold leg LOCA with AES 1.2 recovery actions These cases had previously been analyzed without operator actions for one hour transient tinas in the Section 2 background information for guideline AE-1, LOSS OF REACTOR OR SECONDARY COOLANT. As in the corresponding AE-1 background document, the AES-1.2 recovery cases were also modeled using Transient Real-time Engineering Analysis Tool- Advanced Numerics (TREAT-AN) version, an interactive computer simulation program capable of modeling the essential features of the primary and secondary systems of a pressurized water reactor (PWR). The AP600 TREAT-AN model includes rnany of the control systems of interest for modeling automatic and manual (operator) actions considered in the AP600 emergency response guidelines (ERGS).
For both of the above cases, reactor trip and safety injection occur because chemical and volume control system (CVS) makeup, and pressurizer heaters are not able to maintain reactor coolant system (RCS) inventory and pressure. After SI actuation, the core makeup tanks (CMTs) along with the ;
makeup pump add inventory to the RCS and the passive residual heat removal (PRHR) heat exchanger remove heat from the RCS. With PRHR cooling, the RCS initially cools down until the cold leg temperatures reach the low Teold setpoint for SI actuation modeled at 514'F. This also results in main steam isolation valve (MSIV) closure and isolation of all feedwater, including startup feedwater (SFW). Apart from nonsafety related CVS flow, the plant response is determined by the behavior of the passive systems. With continued inventory depletion, actuation of the automatic depressurization system (ADS) may occur. ADS actuation would be more likely for the one inch break case since the CMTs were starting to drain after one hour. For a smaller opening case (like the 0.5 in. break case),
the RCS could remain at relatively high pressure; that is 1000 psig for a prolonged period of time, until the supply of CVS makeup (BAT) is depleted. If this were to occur, ADS would occur several hours later.
Although the passive safety systems alone allow or provide for adequate recovery for these small LOCA cases, a more optimal recovery scheme considers restoration of the steam generators for cooling and temperature control versus PRHR and CVS makeup followed by normal residual heat removal (RNS) for inventory control (RNS injection) or additional cooling (RNS recirculation or closed loop cooling for very small breaks). The steps in.AES-1.2 are structured to accomplish this more optimal recovery, that is, to provide a safe and efficient means to cooldown and depressurize the RCS to cold shutdown conditions using some of the nonsafety related equipment in the AP600 plant.
O mAap600\2064w\aest.2.wpf:lb 082996 2-1 REvlsloN: lA
)
1 Some of the actions in the ERGS that influence the RCS response modeled in TREAT-AN are summarized below. Action times, setpoints, and flow rates noted here are not required but are considered typical for modeling for the recovery scenarios that follow.
- Verify SFW Flow - After the immediate actions in AE-0, AP600 REACTOR TRIP OR SAFETY INJECTION, and prior to PRHR isolation, the operator establishes SFW flow at the rate of 270 gpm (35 lbm/sec) to each steam generator (SG), the assumed capacity of each SFW pump.
This action is assumed to be performed three to five minutes following reactor trip. SFW flow is later controlled in AE-1 and AES-1.2 to maintain SG level on span in the narrow range (greater than 5 percent), provided the SG is intact.
- Check RCS Makeup Status - Various checks in AE-0, AE-1, and AES-1.2 confirm proper operation of the CVS makeup pump during post-CMT operation. It is assumed that the makeup pump is left in automatic control, starting when pressurizer level decreases to 10 percent and stopping when pressurizer level increases to 20 percent. When the CVS makeup pump is aligned for charging, the nominal flow rate is approximately 100 gpm at nominal RCS pressure (2250 psia), increasing to a maximum of 200 gpm at reduced RCS pressures (below 1000 psia). When alig"d for auxiliary spray, the flow rate is reduced to half that assumed in the charging mode (that is,100 gpm maximum), to reflect the expected reduction of flow when redirected to the l
auxiliary spray lines.
= Check if RCS Cooldown and Depressurization is Required - This AE-1 check determines whether 9
or act the operators transition to AES-1.2 or remain in AE-1 and prepare for recirculation. The trans'. tion to AES-1.2 is taken provided ADS has not actuated and the RNS pump is not injecting flow. The RCS pressure is above the shutoff head pressure of the RNS pump and modeled at 175 psia. As a typical but not required time, the transition to AES-1.2 is assumed to be 10 to 15 minutes following reactor trip.
- Check if PRHR Should be Isolated - This action is performed early in AES-1.2 provided SFW is running (ur oreviously restored) or SG NR level has recovered above 5 percent. A typical time assumed to perform this action is 15 minutes after reactor trip.
- Initiate RCS Cooldown to Cold Shutdown - Approximately 1 to 2 minutes after PRHR is isolated, the operator begins a controlled cooldown at a maximum rate of 100 F/hr using the SG PORVs for steam relief and SFW for feed. Steam dump to condenser is assumed not available due to MSIV closure. Initially, the cooldown rate based on the cold leg temperatures is maintained less than the maximum 100 F/hr rate since PRHR causes an initial cooldown prior to its isolation.
. Depressurize the RCS to Refill the Pressurizer - A few minutes after the cooldown is started, the CVS makeup pump is aligned to auxiliary spray as described above and used to depressurize the RCS. As the RCS pressure decreases, the break flow will be reduced and this should allow the RCS to refill until pressurizer level comes on span, that is, greater than 5 percent.
mAap600\2064w\aest 2.wpf:Ib-o82996 2-2 REVISION: lA I
L_____________________
E
- Check if CMT Injection Should be Isolated - Provided ADS has not actuated, CMT injection can be stopped once RCS subcooling becomes greater than uncertainties (greater than 30 F assumed) and pressurizer level is on span (greater than 5 percent). A subsequent step in AES-1.2 confirms )
l adequate RCS subcooling and inventory control; otherwise, CMT injection is re-initiated. RNS injection can also used to avoid the need for CMT injection once RCS pressure is reduced to less ;
than the shutoff head pressure of the RNS pumps. l
be greater than uncertainties (greater than 30 F) and pressurizer level on span (greater than 5 percent). RCPs I A and IB are then started to provide normal pressurizer spray. This step is considered only for the 0.5 in. LOCA case. 1
use pressurizer normal spray to depressurize the RCS to minimize RCS subcooling and break flow.
The depressurization is stopped when subcooling decreases to less than uncertainties plus 10*F ,
margin (that is,40*F), or the pressurizer fills to a high level. This occurred only for the 0.5 in. :
LOCA case.
l
- Check if SI Accumulators Should be Isolated - Near the end of the AES-1.2 guideline, the !
l l operator is instructed to isolate the SI accumulators if RCS subcooling is greater than uncertainties (30 F) and pressurizer level is on span (greater than 5 percent). An alternate accumulator isolation l criterion based on hot leg temperatures less than a specified value (300-400*F) is also to be used to avoid or limit nitrogen injection into the RCS.
- Check if RNS Can be Placed in Service - Once RCS pressure decreases to less than 450 psig and temperatures are less than 350*F, the RNS can be placed in service to continue the cooldown to cold shutdown (less than 200 F). This assumes RNS is not being used in the injection mode to supply inventory to the RCS.
The decision on whether or not to align RNS cooling would not have to be made until late in the transient (after several hours or more), thus allowing the operators and plant support staff sufficient time to evaluate the various long term cooling options for the specific event in progress. After this step, the operator transitions to the beginning of the AES-1.2 guideline and continues the RCS cooldown and depressurization to cold shutdown.
In the following two sections, simulations of the AES-1.2 recovery actions for the 0.5 in, and 1.0 in.
LOCAs cases are presented.
l lO m \ap600\2064w\aest-2.wpf:lt>.082996 2-3 REVisloN: 1A l
l
2.1 Case 1: 0.5 Inch Diameter Cold Leg LOCA with AES 1.2 Recovery Actions In this section, the response of a typical small LOCA (0.5 in. diameter) cold leg LOCA is described, including operator recovery actions taken per AES-1.2. The break is assumed located near the bottom of cold leg 1 A and has an effective area of 0.196 in2 . For this size opening, the break flow is beyond the capability of charging (CVS makeup) to maintain RCS inventory without reactor trip.
Recall that this case had previously been analyzed without operator actions in the background information for AE-1, AP600 LOSS OF REACTOR OR SECONDARY COOLANT. Reactor trip followed by SI actuation occurred at approximately 20 minutes. At the end of the one hour transient simulated for AE-1, RCS pressure was approximately 1000 psia, RCS subcooling based on the core exit thermocouples was 100*F, and the core exit and hot leg temperature in the active loop was 440*F.
The system was slowly stabilizing following PRHR cooldown and charging flow from the CVS makeup pump exceeded break flow. Level was still off span low in the pressurizer due to the initial inventory loss and PRHR cooldown shrink.
The scenario presented in this section is identical to the previous one in AE-1 up until 1380 seconds.
Beginning at that time, it is assumed that the operator restores SFW according to AE-0, AP600 REACTOR TRIP OR SAFETY INJECTION. This action is followed by most of the remaining actions described above in Section 2.0. The time table of events for this TREAT-AN simulation is given in Table 2-1. Transient plots of interest for this recovery scenario are given in Figures 2-1 through 2-11.
The pressurizcr level response for this 0.5 in. LOCA case is shown in Figure 2-1. As previously noted, charging is initially not able to compensate for the inventory loss from the break, so l pressurizer level continues to decrease and shrinks off span after reactor trip. By 2000 seconds, l charging flow equals break flow but level remains off span low due to the PRHR cooldown. After 2200 seconds, level returns on span in the pressurizer as the RCS is depressurized using auxiliary l spray. The makeup flow is reduced when the CVS pump is realigned to auxiliary spray. However, the break flow decreases during the depressurization. The pressurizer refill is aided by net addition from the CMTs, the SI accumulators, and also because of the formation of a steam bubble in the reactor vessel head. After pressurizer level reaches 20%, the initial depressurization is stopped. The CVS pump is then re-aligned to provide makeup, operating when pressurizer level decreases to 10%
and stopping once pressurizer level reaches 20%. Several times during the transient, pressurizer level exceeds 20% when the operator uses normal pressurizer spray to depressurize the RCS.
It should be noted that in this simulation, the pressurizer level drops several percent after RCPs l A and IB are restarted (at 3000 seconds). A pressurizer level drop is expected if the upper head is voided when the RCPs are restarted since the increased flow to the upper head will help collapse the voids in that region. In the TREAT-AN simulation, the amount of upper head void collapse is underestimated since the upper head is modeled using a single node (with one flow path in and one flow path out of the upper head region). In a more realistic (multi-node upper head) model, the upper nrup60m2064wues t.2.wpf Ib.082996 24 REVistoN: lA l
l
head voids would fully collapse and pressurizer level could drop off span low for this scenario. Since the CVS makeup capacity exceeds break flow for this scenario, pressurizer level would retum on span, so this under-prediction of the upper head void collapse does not significantly impact the simulation.
The operator, however, should be aware that there could be a larger decrease in pressurizer level associated with upper head void collapse once the RCPs are restarted.
Figure 2-2 shows the RCS and SG pressures. Prior to 2000 seconds, these parameters are not significantly different from the corresponding ones in the AE-1 simulation. After 2000 seconds, PRHR is isolated and the operator initiates a natural circulation cooldown using SFW and the SG PORVs on both steam generators. As the RCS is first depressurized using auxiliary spray at 2180 seconds, RCS pressure decreases by approximately 300 psi. Thereafter and up to 6000 seconds, RCS pressure is maintained roughly 200 psi higher than the SG pressures as the operator attempts to maintain RCS subcooling greater than uncertainties during the cooldown and depressurization transient.
The RCS and SG pressures become more nearly equal later in the transient, reaching approximately 200 and 100 psia respectively, near the end of the transient modeled.
The hot leg and two of the cold leg temperatures (I A and 2A) are shown in Figure 2-3. The )
temperatures in cold legs 1B and 2B are similar to those in cold legs l A and 2A, respectively. Prior to reactor trip, the temperatures are relatively constant in the two hot legs (600 F) and four cold legs j (530*F). After trip, the temperatures in loop 1 decrease due to the PRHR cooldown. During this
! cooldown, a 40 to 50*F temperature difference is maintained between the hot leg and cold legs in loop 1 (loop modeled with the PRHR). Decay heat removal occurs primarily via natural circulation in I
this loop, with energy transfer to the PRHR and ultimately to the In-containment Refueling Water Storage Tank (IRWST). As previously explained for the AE-1 simulation, the flow in loop 2 is predicted to slow down since the SG in this loop is a heat source during the PRHR cooldown. After the SGs are depressurized to begin the operator initiated cooldown, natural circulation flow is re-l established in this loop and the two hot leg temperatures become equal. With both loops participating in the cooldown and assuming a best estimate decay heat for the TREAT-AN simulation, the delta-T between the hot and cold leg temperatures decreases to about 30 F. The loop temperatures then become approximately the same after the RCPs I A and IB are stalted (at 3000 seconds). During the first two hours of the cooldown (prior to 8200 seconds), the time-averaged cooldown rate for the cold legs is less than the recommended maximum rate of 100 F/hr. After this time, the RCS temperatures are less than 350 F and the RNS could be aligned for service to continue the cooldown to cold shutdown.
The hot leg loop flow rates are illustrated in Figure 2-4. After RCP trip and during the initial PRHR cooldown, the flow rate in loop 1 exceeds that in loop 2. The two become about equal during the SG natural circulation cooldown. The flow then reverses in loop 2 after the RCPs in cold legs I A and IB are started. These RCPs are restarted to provide forced circulation and pressurizer normal spray.
f Figure 2-5 shows the RCS subcooling based on the core exit temperature. This parameter is used,
! along with pressurizer level, to determine whether or not termination of passive safety systems can be I
m$ap600\2064w\aest-2.wpf:Ib 082996 2-5 REVislON: IA
i J i
l performed. RCS subcooling is more than 100 F early in the transient. As noted previously, the l
target subcooling to exceed uncertainties was assumed to be 30 F for this simulation. Apart from the )
initial depressurization using auxiliary spray (when RCS subcooling decreased to 20*F), the simulated values typically ranged from 30 to 50 F.
The CVS makeup and break flow rates are illustrated in Figure 2-6. When the operator aligns charging flow to auxiliary spray at 2180 seconds, the CVS makeup rate is reduced to approximately j i
14 lbm/sec (100 gpm). After the CVS pump is realigned to provide makeup (at 200 gpm), it operates intermittently when pressurizer level decreases to 10 percent and stopping when level reaches 20 percent. Note that at the end of the transient, it is assumed that the operator throttles the CVS makeup flow to 100 gpm since the break flow is reduced by the AES-1.2 recovery actions. )
l l
Additional inventory is also added to the RCS from the CMTs. The upper curve in Figure 2-7 shows j the injection flow from CMT-A. The lower curve is the flow through its cold leg balance line. The l corresponding flow components for CMT-B are nearly the same. The CMTs remain essentially full l
for the duration of the transient considered, so the volume flows in the injection and recirculation lines are approximately the same (initially about 0.9 ft'/sec). There is a net addition to the RCS from the CMTs since the colder borated water in the injection line is more dense. As the CMTs heat up due to balance line flows, the driving head (density difference) decreases and the injection flows become more nearly equal to the balance line flows. CMT injection is isolated at 2700 seconds after the l operator verifies that RCS subcooling exceeds uncertainties (30 F) and pressurizer level is on span {
(>5%). The CVS pump continues to provide makeup and boration for the remainder of the transient.
Figure 2-8 illustrates the flow through the PRHR heat exchanger prior to isolation and the SFW flow restored to SGs 1 and 2. These parameters are used as indications of an RCS heat sink. After the RCPs coast down, the PRHR flow is approximately 100 lbm/sec until isolated. The hot leg flow in loop 1 is about an order of magnitude higher. Water from the PRHR outlet (at approximately 150*F return temperature), plus charging and CMT injection flows cool the RCS approximately 80 F in the first 15 minutes following reactor trip and CMT/PRHR actuation. The cooldown rate is reduced as the SGs are placed in service to perform the controlled RCS cooldown to cold shutdown. After the SG level returns on span in the narrow range as shown in Figure 2-9, the SFW and SG PORV flow rates shown in Figure 2-10 become roughly comparable or at least to the same order of magnitude. Note that after RCPs l A and IB are restarted, the steam flow and SFW requirements in loop 1 become about three times that in loop 2, that is, most of the heat is being removed from the SG in the loop with the operating RCPs.
The pressurizer spray flow rates are illustrated in Figure 2-11. Although auxiliary spray is limited to 100 gpm, it is effective in depressurizing the RCS over a period of several minutes since the temperature of the spray water is relatively low in comparison to the pressurizer steam temperature.
The normal pressurizer spray flows from RCP 1 A and IB are considerably higher and l depressurizations take longer (when compared to the depressurization using auxiliary spray). Normal I
spray is found to be effective in reducing RCS pressure for this case down to the 200 psia range (or m$ap60o(2064wbes t -2 mp f: l b-082996 2-6 REVISION: lA
lower). The RCPs would need to be tripped at pressures somewhat below this due to NPSH concerns.
Auxiliary spray (or one ADS Stage-1 valve) would then be used for further RCS depressurization.
The simulation for the 0.5 inch diameter cold leg LOCA is stopped once it is demonstrated that RNS cut-in conditions are achieved and ADS actuation is not likely to occur. It is feasible for this scenario to align RNS in the closed-loop cooling mode of operation, cooldown the RCS to cold shutdown
(< 200 F) and gradaally reduce RCS pressure to atmospheric to minimize the break flow and CVS makeup flow.
l O i 1
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m:\ap600\2064w\aes t -2.w ,f: I b-082996
, 2-7 REVISION: lA
TABLE 2-1 Time Table for Events for 0.5 Inch Cold Leg LOCA With AES-1.2 Recovery Items Event / Automatic Actions Time (sec)
Full power operation 0 - 10 0.5 in. diameter cold leg LOCA in CL-1 A (loop with PRHR) 10 i I
LOW-2 pressurizer level signal 1106 l (CMT and PRHR initiation, RCP trip signal, charging realigns to BAT)
Reactor trip on over-power AT, followed by turbine trip 1119 l
RCPs trip and begin coastdown 1124 I
SI actuation and steamline isolation on LOW-2 Tcold (defeats SFW) 1148 Operator restores SFW per AE-0,270 gpm (35 lbm/sec) per SG 1380 Operator isolates PRHR per AES-1.2 2000 l Operator initiates RCS cooldown at < 100'F/hr using SG PORVs 2060 Operator realigns CVS pump to auxiliary spray for RCS depressurization 2180 - 2400 SI accumulators start to inject 2200 Operator controls SFW to control SG level 2520 - end Operator isolates CMT injection 2700 O.l l
CVS makeup pump automatically operates to increase pressurizer level 2950 - 3350 Operator starts RCP 1 A followed by RCP IB 3000,3060 Operator uses normal pressurizer spray to depressurize RCS (to 550 psia) 3300 Operator isolates SI accumulators 3600 l 1
CVS makeup pump automatically operates to increase pressurizer level 4000 - 4300 ;
1 Operator uses normal pressurizer spray to depressurize RCS (to 500 psia) 4200 l l CVS makeup pump automatically operates to increase pressurizer level 4650 - 4850 1
Operator uses normal pressurizer spray to depressurize RCS (to 400 psia) 4800 1 CVS makeup pump automatically operates to increase pressurizer level 5450 - 6050 Operator uses normal pressurizer spray to depressurize RCS (to 300 psia) 6000 l
CVS makeup pump automatically operates to maintain pressurizer level 6500 - 9000 Operator reduces makeup to 100 gpm due to reduce inventory loss 6600 - 6660 Operator uses normal pressurizer spray to depressurize RCS (to 220 psia) 7200 End of transient modeled, RNS cut-in conditions achieved: 9000 RCS pressure = 220 psia, RCS subcooling = 50*F RCS temperature < 330'F Pressurizer level = 10 '7c m:\ap600\2064w\aest 2.wpf:Ib-082996 2-8 REVISION: 1A l
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e Figure 2 4. Ilot Leg Flow Rates for a 0.5 Inch Cold Leg LOCA With AES-1.2 j Recovery Actions I
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I Figure 2-6. Makeup and Break Flow Rates for a 0.5 Inch Cold Leg LOCA With AES-1.2 Recovery Actions abr&WO64w\aest-2.wpf:1b-082m 2-14 REVISION: lA
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'O Figure 2-9. Steam Generator Level Response for a 0.5 Inch Cold Leg LOCA With AES-1.2 Recovery Actions i
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Figure 2-11. Pressurizer Spray Flow Rates for a 0.5 Inch Cold Leg LOCA With AES-1.2 Recovery Actions m-\ap600G064w\aes t -2.wpf: l b-0829% 2-19 REVISION: 1A
1 l
2.2 Case 2: 1.0 Inch Diameter Cold Leg LOCA with AES-1.2 Recovery Actions This section describes the response of a small LOCA that is slightly larger (1.0 in. diameter) with l
AES-1.2 recovery actions considered. The beak is also modeled at the bottom of cold leg 1 A and has an effective area of 0.785 in2 , four times larger than that previously considered in Case 1: 0.5 in. Cold Leg LOCA with AES-1.2 Recovery Actions.
This case had also been analyzed previously without operator actions in the background information for AE-1, AP600 LOSS OF REACTOR OR SECONDARY COOLANT. Reactor trip followed by SI l actuation occurred due to low RCS (pressurizer) pressure at approximately three minutes. At the end of the one hour simulation for AE-1, RCS pressure had decreased to 320 psia, still above the shutoff head pressure of the RNS pumps. The RCS was subcooled with the exception of the upper head and U-tubes of the inactive loop SG; the core exit subcooling was about 15'F, corresponding to a core exit l temperature of 420 F. The CMTs were starting to drain but levels were above the low-l level for l
ADS actuation. SI accumulator and CMT injection helped to maintain RCS inventory above the top i of the hot legs and the break flow (approximately 50 lbm/sec) was somewhat beyond the capacity of CVS makeup (approximately 28 lbm/see or 200 gpm). PRHR was in service to provide cooling, l however, break flow and injection flow from the various sources also provided significant energy removal. With additional depressurization, it could be possible maintain inventory with CVS makeup alone and thereby prevent further draining of the CMTs and subsequent actuation of the ADS. Since AE-1 instructions would direct the operator to transition to AES-1.2 at some time during this transient, a simulation of this 1.0 in. LOCA case with the AES-1.2 recovery actions is considered in this case description.
l The scenario presented in this section is identical to the previous one in AE-1 up until 475 seconds or five minutes after trip. At that time, it is assumed that the operator restores SFW according to AE-0, AP600 REACTOR TRIP OR SAFETY INJECTION. Remaining operator actions assumed in this TREAT-AN simulation are as described in Section 2.0 and are listed in the time table of events in Table 2-2. Transient plots are discussed below and provided in Figures 2-12 through 2-23.
The pressurizer level response for the 1.0 in. LOCA case with AES-1.2 actions is shown in Figure 2-12. As a result of the increased break flow, pressurizer level decreases several times faster than in Case 1. The level indication goes off span low at around 200 seconds after the reactor trip and SI actuation. By 400 seconds, the pressurizer and surge line are completely empty and remain that way until the operator aligns charging (CVS makeup) to auxiliary spray to depressurize the RCS. This action is taken at 1500 seconds. By 1600 seconds, pressurizer level has increased to 20% because of l the reduced break flow, injection from the SI accumulators and CMTs, and void formation in the upper plenum. The depressurization with auxiliary spray is then stopped and the CVS pump is aligned to provide makeup if pressurizer level decreases (i.e., to 10% for post-CMT operation). By 1950 seconds, the 10% level setpoint is reached and the CVS pump operates to provide raakeup at a l
l rate of 200 gpm (28 lbmhec). Further action to depressurize the RCS to restore pressurizer level is I
not attempted since the RCS subcooling remains less than uncertainties (<30 F) for the duration of the mAap600(2064wMt.2.wpf:lb-0829% 2-20 REvlslON: lA
l
!h transient. Since ADS (Stages 1 through 3) is eventually actuated for this case, the pressurizer level becomes high near the end of the transient.
Figure 2-13 shows the RCS and SG pressures for the 1.0 in. LOCA recovery simulation. The RCS inventory loss in this case is slow enough that RCS pressure can be controlled by the secondary side pressure. Adjusting for the time shift (due to the earlier reactor trip time), the secondary side pressure j for this case resembles that previously modeled for the cooldown for the 0.5 in. LOCA case j (Figure 2-2). The RCS pressure is very close to the secondary side pressures in this 1.0 in. LOCA case since the RCS becomes saturated soon after the RCS cooldown and depressurization actions are taken, that is, after 1500 seconds. In the previous 0.5 in. LOCA case, the operator was able to maintain roughly 30 to 50 F subcooling during most of the natural circulation cooldown, so RCS pressure stayed roughly 200 psi higher than SG pressure for most of that transient. Near the end of the 1.0 inch LOCA case, ADS is actuated and RCS pressure becomes less than the SG pressures.
The hot leg and two of the cold leg temperatures (I A and 2A) are shown in Figure 2-3. The temperatures in cold legs IB and 2B are similar to those in cold legs l A and 2A, respectively. Prior to reactor trip, the temperatures are relatively constant in the two hot legs (600 F) and four cold legs (530*F). After trip, the temperatures in loop 1 decrease due to the PRHR cooldown. During this initial cooldown, a 30 to 40 F temperature difference is maintained between the hot leg and cold legs i in loop 1 (loop modeled with the PRHR). Decay heat removal occurs primarily via natural circulation l Q in this loop, with energy transfer to the PRHR and ultimately to the In-containment Refueling Water Storage Tank (IRWST). By 1400 seconds, the PRHR is isolated and the SG secondary (SFW and SG PORVs) are used for cooldown. The hot legs become saturated after 1500 seconds and later become subcooled (after 3000 seconds) as the cooldown progresses. Since the SG pressures are similar to those of Case 1, the cold leg temperatures behave in a similar manner.
The response of the upper plenum level is illustrated in Figure 2-15. Initially the upper plenum is full and the core exit region is subcooled as shown in Figure 2-16. Soon after the initial depressurization is performed at 1500 seconds, the RCS subcooling goes to zero and the upper plenum level drops to the top of the hot legs. Despite reaching saturation (between 1500 to 3000 seconds), natural circulation flow can be maintained in each loop because of the secondary side depressurization as shown in Figure 2-17. Natural circulation flow is maintained until ADS is actuated late in the transient.
The CVS makeup and break flow rates are illustrated in Figure 2-18. Between 1500 to 1600 seconds, the CVS flow is re-directed to auxiliary spray (at 100 gpm or 14 lbm/sec) to depressurize the RCS and recover pressurizer level. After 1950 seconds and until after ADS actuation (6000 seconds), the CVS j makeup pump operates at 200 gpm (28 lbm/sec) and compensates for most of the RCS break flow.
With added inventory from the accumulators and CMTs, the 1 inch LOCA size is likely a " transition" break size with respect to ADS actuation, that is, for smaller LOCAs (such as the 0.5 inch LOCA) g
- ij ADS actuation would not be expected within the time frame taken for AES-1.2 recovery actions. For
! larger LOCAs (such as the 2 in. LOCA - see AE-1 background information), it would be difficu't to maap6m206.t.smi-2.wpr:ib-082996 2-21 Revision: lA
avoid ADS. The 1.0 in. LOCA is in between and ADS actuation may or may not occur, depending on ,
makeup capability and operator actions to cooldown and depressurize the RCS.
The upper curve in Figure 2-19 shows the injection flow from CMT-A. The lower curve is the flow through its cold leg balance line. The corresponding flow components for CMT-B are similar. The CMTs remain full until 2600 seconds and prior to this they operate in a water recirculation mode. In this mode, there is net addition to the RCS of about 5 to 10 lbm/sec from each CMT since the colder borated water in the injection line is more dense. As the CMTs heat up due to balance line flows, the top portion of the tank reaches saturation and they start to drain.
Figure 2-20 illustrates the flow through the PRHR heat exchanger prior to isolation, along with the SFW flow restored to SGs 1 and 2. These parameters are used as indications of an RCS heat sink.
After the RCPs coast down, the PRHR flow is approximately 100 lbm/sec until isolated. Water from the PRHR outlet (at approximately 150*F retum temperature), plus charging and CMT injection flows cool the RCS approximately 80 F in the first 15 minutes following reactor trip and CMT/PRHR actuation. The cooldown rate is reduced as the SGs are placed in service to perform the controlled RCS cooldown to cold shutdown. Since the break also removes energy from the RCS, the amount of SFW used is smaller than in the previous 0.5 in. LOCA case (Figure 2-8). The SG NR level response for the two cases can be compared in Figure 2-21 (1.0 in. LOCA) and Figure 2-9 (0.5 in. LOCA).
Prior to ADS actuation (which cools down SGI), these SG NR levels are approximately the same (20 to 40%).
The level responses for both CMTs are shown in Figure 2-22. The CMTs start to drain at around 2600 seconds when the hot water from the cold leg balance lines of loop 2 heats the top of the CMT volume to saturation. Upon further cooldown and depressurization, CMT-A reaches the low-l ADS actuation setpoint at approximately 6000 seconds. The behavior of CMT-B is similar.
Figure 2-23 shows the flow through ADS stages I through 3. These flows are similar to those determined for the 2.0 in. cold leg LOCAs described in Section 15.6 of the AP600 SSAR and also in Cases 3 and 4 of the AE-1 background information. After the operator confirms actuation of ADS Stages 1 through 3, instructions in AES-1.2 direct the operator to align RNS injection. The RNS injection flows are shown in Figure 2-24. This action to establish RNS injection is similar to corresponding instructions in AE-1. Recovery would be similar to that described in Case 4 of the AE-1 background information (2.0 in. LOCA with RNS injection).
l l To summarize the results based on the simulations for Cases 1 and 2, although the passive safety l systems alone allow or provide for adequate recovery for these small LOCA cases, a more optimal recovery scheme per AES-1.2 considers restoration of the steam generators for cooling and temperature control (versus PRHR) and CVS makeup followed by normal residual heat removal (RNS) for inventory control (RNS injection) or additional cooling (RNS recirculation for larger breaks or closed loop cooling for very small breaks). The steps in AES-1.2 are structured to accomplish this more optimal recovery, that is, to provide a safe and efficient means to cooldown and depressurize the m:\ap6000064w\aes 1 2.wpf. l b-082996 2-22 REVisloN: 1A I
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( RCS to cold shutdown conditions using some of the nonsafety related or conventional equipment in the AP600 plant. For small LOCAs less than approximately 1.0 in. equivalent diameter, it should be possible to perform the AES-1.2 recovery actions without automatic actuation of ADS. For larger break sizes, ADS actuation is more likely to occur and recovery actions consistent with those in AE-1 have been included in AES-1.2. The operator of course has no direct indication of the break size.
However, various symptoms (such as, RCS pressure and subcooling) direct the operator to perform the j appropriate actions.
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m:\ap6000064w\aest.2.wpf:Ib-082996 2-23 REVISloN: ]A
TABLE 2-2 Time Table of Events for 1.0 Inch Cold Leg LOCA With AES-1.2 Recovery Actions Event / Automatic Actions Time (sec) 1 Full power operation 0 - 10 1.0 in. diameter cold leg LOCA in CL-1 A (loop with PRHR) 10 LOW-1 pressurizer pressure reactor trip signal 173 LOW-2 pressurizer pressure signal, Si actuation 183 (MFW isolation, CMT initiation, PRHR initiation, RCP trip signal)
RCPs trip and begin coastdown 199 LOW-2 Teold signal, SI plus steamline isolation (defeats SFW) 237 Upper head starts to drain 450 Operator restores SFW per AE-0,270 gpm (35 lbm/sec) per SG 475 i I
SG No. 2 U-tubes start to drain (recover after cooldown started) 800 l Si accumulators start to inject 1050 ,
1 Operator isolates PRIIR per AES-1.2 1375 l Operator initiates RCS cooldown at < 100*F/hr using SG PORVs 1380 Operator realigns charging to auxiliary spray for RCS depressurizadon 1500-1600 Upper plenum drains to top of hot leg 1520 CVS makeup pump automatically operates to increase pressurizer level 1950 Operator stops SFW to control SG level 2400 l CMTs start to drain 2600 Upper plenum level recovers 3000 RCS core exit subcooling > O'F 4600
~
Operator reinitiates SFW to SGs 1 and 2 (50% of full flow) 5000 ADS Stage 1 valves start to open 6000 ADS Stage 2 valves start to open 6070 ADS Stage 3 valves start to open 6190 ADS Stage 3 valves fully open 6270 Operator establishes RNS injection using one pump 6500 End of transient modeled 6800 O
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l Figure 2-13. Reactor Coolant System and Steam Generator Pressure Response for a 1.0 Inch Cold Leg LOCA With AES-1.2 Recovery Actions l
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Figure 2-15. Reactor Upper Plenum / Core Mixture Level Response for a 1.0 Inch Cold Leg LOCA With AES-1.2 Recovery Actions m:\ap600\2064wties t -2.wpf: l b482996 2-28 REVISION: lA
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Figure 219. CMT-A Injection and Balance Line Flow Rates for a 1.0 Inch Cold Leg LOCA With AES-1.2 Recovery Actions m:\ap60(A20Mw\aes t -2.wpf;1b482996 2-32 REVISION: lA
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Figure 2-24. RNS Injection Flow Rates for a 1.0 Inch Cold Leg LOCA with AES-1.2
! Recovery Actions l
mWO64wWst-2.wpf:Ib.082996 2-37 REVISION: 1A
Replacement Instructions for the AP600 Emergency Response Guidelines Background, Book 1 Section AE-2: Faulted Steam Generator Isolation REMOVE INSERT l
Title pg., Rev.1,7/28/95 Title pg., Rev.1 A, 8/96 l Page 2-1, Rev.1,7/28/95 Pages 2-1 to 2-18, Rev.1A, 8/96 l l l
lO i
i O
O BACKGROUND INFORMATION FOR AP600 EMERGENCY RESPONSE GUIDELINE I
AE-2 AP600 FAULTED STEAM GENERATOR ISOLATION Rev.1A l l
August 1996 I
j 3 i O
m \ap60cco64ww2.wpf;1b480796 REVISION: 1A
TABLE OF CONTENTS Section Pm
1.0 INTRODUCTION
1-1
2.0 DESCRIPTION
2-1 3.0 RECOVERY / RESTORATION TECHNIQUE 3-1 3.1 High-Level Action Summary 3-1 3.2 Key Utility Decision Points 3-3 4.0 DETAILED DESCRIPTION OF GUIDELINE 4-1 4.1 Detailed Description of Steps, Notes, and Cautions 4-1 4.2 Step Sequence Requirements 4-11
5.0 REFERENCES
5-1 O
O m:\ap6002064w\ae-2.wpfatro80796 ii REVislON: lA
2.0 DESCRIPTION
Guideline AE-2, AP600 FAULTED STEAM GENERATOR ISOLATION, is intended to identify and isolate a loss of secondary-side coolant resulting from a fault in a main steamline, main feedwater line, or in any piping system that interconnects with the secondary-side pressure boundary (for example, startup feedwater system or blowdown piping). The consequences of a break in any of these piping systems vary depending upon initial power level, size and location of the break, and equipment availability (safety or non-safety related) at the time the failure occurs.
The generic Westinghouse Owners Group (WOG) background document for the Emergency Response Guideline E-2, FAULTED STEAM GENERATOR ISOLATION, provides a review for the following three categories of faults:
- Small secondary break ;
- Intermediate secondary break
- Large secondary break As described, the small secondary-side break does not cause reactor trip, and the description provided also applies to AP600. Therefore, this description is repeated below with minor modification. I For the remaining two categories, this section describes the response for an intermediate secondary l I
break (0.6 sq-ft steamline break) specifically for the AP600 Considered are the operator recovery actions taken per the following AP600 guidelines:
- AE-0, AP600 REACTOR TRIP OR SAFETY INJECTION
- AE-2, AP600 FAULTED STEAM GENERATOR ISOLATION
- AE-1, AP600 LOSS OF REACTOR OR SECONDARY COOLANT l
- AES-1,1, AP600 PASSIVE SAFETY SYSTEMS TERMINATION The response to a large secondary-side break upstream of the main steam isolation valve (MSIV) would be similar to that of an interrr.ediate secondary break except that the steam generator (SG) blowdown would be somewhat faster. The flow restrictor at the outlet nozzle of each SG restricts the effective area of a large double-ended break to less than 1.4 sq-ft after the MSIVs close, so it is sufficient for demonstrating the recovery actions taken in the AP600 ERGS to restrict the focus to the 0.6 sq-ft case. The AP600 SSAR also contains analyses for a large steamline break in Section 15.1.5 and a stuck-open SG relief or safety valve in Section 15.1.4. The concem for these cases is the potential return to criticality and resulting high heat flux in a localized area of the core near the postulated " stuck rod." These cases are performed at zero-power. (For the analysis in this section, the reactor is initially at full power.) A large feedline break at full power is also analyzed in Section i 15.2.8 of the AP600 SSAR. Following the cooldown, this feedline break case is analyzed from the j perspective of a longer term heatup event.
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Small Secondary Break For this category of breaks, normal plant control systems are capable of maintaining nominal or near nominal operating conditions. For a small steamline break, the system transient response would be similar to a step load increase. The secondary system would indicate an increase in load with a resultant decrease in primary system average temperature and pressure. The control rods would withdraw from the core in an effort to restore the primary average temperature if the rod control system was in an automatic mode of operation. Because of the apparent increased load, the steam flow from the steam generators would increase in at least one loop, depending upon the location of the break. If the break occurred in the steam header, all loops would experience increased steam flow. Because of the increased steam flow, the feedwater control valves would modulate to a more open position in an attempt to maintain s:eam generator water level. As a result, the main feed flow would be increased in at least one loop, or both loops if the break is in the steam header. Another indication of this type of break would be a decreasing water level in the condenser hotwell.
Similar system characteristics would be obtained if a small feedline break occurred such that the normal plant control systems could maintain near nominal operating conditions. For this break, the feedwater control valve in at least one loop, depending upon the location of the break, would modulate to a more open position in an attempt to compensate for the flow out the break and to maintain steam generator water level The steam flow in the other loop would remain approximately normal. Again, the water level in the condenser hotwell would decrease slowly.
For either of the above scenarios, a containment temperature and/or pressure increase might be observed if the break occurred inside containment. If the break was outside containment, an audible or visual confirmation of the break might be possible.
For this size of break, an automatic reactor trip or safety injection would not be expected to occur and, therefore, guideline AE-2 would not be implemented.
Intermediate or Laree Secondary Break The intermediate or large steamline break is categorized by a decreasing steamline pressure in at least one loop, depending upon the location of the break. If the break occurred in the steam header, both loops would experience decreasing pressure. The control systems would be unable to compensate for the increased steam load and a decreasing steam generator water level and a decreasing primary average temperature would result. The control rods would commence stepping out of the core in an attempt to maintain nominal primary system average temperature.
However, due to the decreasing primary temperature, a primary pressure decrease would occur.
These trends would continue until such a time that the operator manually tripped the reactor or until a low steamline pressure setpoint or a low pressurizer pressure setpoint was reached. In either case, a safety injection signal and a reactor trip signal would be generated and result in subsequent turbine mAap600\2064w\ae.2.wpf;1b-0807% 2-2 REVisloN: lA
i l
l trip, feedwater isolation, and steamline isolation. If the break occurred upstream of the MSIV, the l
steam generator associated with the faulted loop would blow down to atmospheric pressure. If the break occurred downstream of the MSIV, the transient would be terminated following MSIV closure.
The system process parameter trends that are used to identify a faulted SG are an uncontrolled 1 pressure decrease in at least one steamline or a SG that is completely depressurized. Other symptoms include increased main feed flow to at least one steam generator, decreasing primary average temperature, and decreasing SG water level in at least one steam generator.
As an example for AP600, an intermediate (0.6 sq-ft) steamline break case is considered in this l section. The fault was selected on SG Number 2, that is, in the loop without passive residual heat removal (PRHR). A similar recovery strategy would be used if the opposite SG contained the break. )
Since flow restrictors limit the maximum break size to 1.4 sq-ft for AP600, the response for a large l steamline break would be similar except the faulted SG would blow down at a rate approximately double that described here.
Because of human intervention, the times used for modeling the operator actions are not unique.
Rather, they represent reasonable but not required times to complete the major actions described, that is, to identify and isolate the faulted SG per AE-0 and AE-2. After this, the operator is directed to l E-1 and waits until the faulted SG dries out and the criteria for termination of the passive safety I systems (core makeup tank (CMT) injection, PRHR cooling) are satisfied. In AES-1.1, the passive systems are stopped and chemical and volume control system (CVS) makeup and letdown are used for inventory control. Temperature control is reestablished using the intact SG, with startup feedwater (SFW) for feed and the SG power-operated relief valve (PORV) for steam relief.
The 0.6 sq-ft steamline break case described here was modeled using Transient Real-time Engineering Analysis Tool - Advanced Numerics (TREAT-AN), an interactive computer simulation program capable of modeling the essential features of the primary and secondary systems of a pressurized .
water reactor (PWR). The TREAT-AN model includes many of the control systems of interest for l modeling automatic and manual (operator) actions considered in the AP600 ERGS. The time table of events for this case is provided in Table 2-1. Transient plots of interest are provided in Figures 2-1 through 2-12.
As a result of the failure, the SG pressures in both steam generators begin to decrease, SG 2 at a somewhat faster rate than SG 1. After the compensated pressure in SG 2 reaches the low steamline pressure setpoint (modeled at 614.7 psia, based on a lead / lag controller), safety injection (SI) is actuated and the MSIVs close. The pressure in this SG continues to depressurize all the way to atmospheric pressure (Figure 2-1). After the MSIVs close, SG 1 repressurizes and is eventually controlled near 1050 psia, the setpoint for the SG PORV. Later in the transient, the SG 1 PORV is controlled to stabilize reactor coolant system (RCS) temperature per AES-1.1.
O maap600s2064wsae-2. pt:ib-0827% 2-3 REVislON: 1A
As a result of the steamline break, the RCS cools down and pressurizer level goes off span low early in the transient (Figure 2-2). The CMTs inject and the CVS makeup pump operates to restore inventory. As SG 2 completes its blowdown and the RCS begins to heat back up, pressurizer level returns on span. The RCS pressure response shown in Figure 2-3 has a similar trend, decreasing early in the transient during the rapid cooldown and then increasing after 500 seconds as the faulted SG completes its depressurization. As prerequisites for AES-1.1 entry, the RCS pressure should be stable or increasing and the pressurizer level greater than the low-level setpoint for starting RCS makeup. For post-CMT operation, this latter setpoint is assumed to be 10 percent. This setpoint could be higher for adverse containment conditions, thus delaying entry into AES-1.1. However, this potential delay would not change the overall recovery strategy simulated.
Figures 2-4 and 2-5 illustrate the hot leg and cold leg temperatures for loops 1 and 2, respectively.
During the initial cooldown, the cold leg temperatures in the faulted loop 2 decrease to 350 F, within approximately 300 seconds. This temperature is considerably less than that in the hot legs as well as the cold legs of loop 1, even though the loop 1 cold legs are cooled by PRHR and CVS makeup.
After the faulted SG completes its cooldown, the loop 2 temperatures become the same as the core exit and loop I hot leg temperatures. Long-term decay heat is removed via natural circulation in loop 1, and the delta-T in this loop becomes approximately 40 F.
The RCS subcooling based on the core exit thermocouples (TCs) is provided in Figure 2-6. At the time assumed for AES-1.1 entry (1000 seconds), the RCS subcooling exceeds 200 F. At the end of the transient, the RCS subcooling is maintained at approximately 175*F.
The SFW and PRHR inlet flows are illustrated in Figure 2-7. As a result of CMT actuation, the PRHR outlet valves open, and flow through the PRHR heat exchanger provides an additional heat sink for the RCS. However, since the hot leg flow in loop 2 through the faulted SG is significantly higher (Figure 2-8), the flow through loop 1 and the amount split off to the PRHR heat exchanger do l
not have a significant impact on the initial RCS cooldown. In AE-0, prior to diagnosis of the secondary-side break, it is conservatively assumed that the operator establishes SFW at the rate of 270 gpm (approximately 35 lbm/sec) per SG at 420 seconds. The pressure in SG 2 is less than 100 psia at this time, so it is likely the operator would not establish SFW to this SG based on the note in AE-0: "SFW flow should not be reestablished to a depressurized SG unless needed for RCS cooldown." Approximately 600 seconds later, it is assumed that the operator isolates SFW to SG 2 l
as part of the AE-2 faulted SG isolation steps. The MSIVs are closed as a result of low steamline pressure (or low T ). Main feedwater and blowdown are isolated as a result of SI cr PRHR actuation. Later in the transient, as part of the AES-1.1 actions, PRHR is isolated and SFW to SG 1 is controlled to maintain level on span in the narrow range (Figure 2-9). This SG is used to stabilize RCS temperature and for long-tenn decay heat removal.
The makeup and letdown flows are illustrated in Figure 2-10. In the post-CMT mode of operation, CVS makeup is alignec to the boric acid tank (BAT) and automatically operates once pressurizer r
level decreases below the low-level setpoint (modeled at 10 percent). Once pressurizer level increases l
l m:wp6 coco 64wue-2.wpt:1b-082796 24 REVISION: lA
i 1
to the high-level setpoint (modeled at 20 percent), the CVS pump stops. This occurs at i approximately 1050 seconds. Later in the transient, makeup is operated in its " normal" (non-SI) mode and contreihd to approximately match letdown (about 100 gpm).
The injection and cold leg balance line (recirculation) flows for CMT-A are shown in Figure 2-11.
The cto espondir.g flows for CMT-B are similar. The CMTs stay full for this transient, so the volumetric flows for these two components are about the same. There is a net addition to the RCS from the CMTs (the difference between the two curves) since the cold borated injection water is more l dense than the water recirculated from the cold leg balance lines ofloop 2. The CMTs are assumed to be isolated per AES-1.1 at 1200 seconds (20 minutes). )
The break flow fism the main steamline is shown in Figure 2-12. Initially, this flow rate exceeds 1000 lbm/sec, comparable to the normal main steam flow from this SG. Depending upon the actual location of the break, this flow rate may or may not be observable on the steamline flow instrumentation available to the operator. By 500 seconds, most of the initial blowdown is over, which explains why the cold leg temperatures in loop 2 have stopped cooling down (Figure 2-5).
Since the flow in this loop is relatively high, the cold leg temperatures in this loop recover to match the hot leg soon after SFW is isolated.
This example illustrates how the AP600 ERGS could be used to isolate or confirm isolation of a faulted steam generator in AE-2. A transition to AE-1 is then taken and the operator remains in l
AE-1 until the criteria are satisfied for termination o' the passive safety systems per AES-1.1. The actions taken in AES-1.1 are similar to those protously considered for the spurious SI actuation event (see AES-1.1 Background Document) axcept that only the intact SG is restored and used for l
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mNwXA2064w\ae 2.wpf:Ib-080796 2-5 REVislON: lA l
1 TABLE 2-1 l TIME T. ALE OF EVENTS FOR A 0.6 SQ-FT STEAMLINE BREAK WITH OPERATOR ACTIONS EVENT / AUTOMATIC ACTIONS TIME (SEC)
Full power operation 0 - 10 0.6 sq-ft steamline break occurs in SG 2 (loop without PRHR) 10 SI actuation on low compensated steamline pressure (CMT followed by PRHR actuation, MSIVs close, RCP trip signal with delay) 16 Rods fully inserted following reactor trip 18 RCPs trip and begin coastdown 33 Pressurizer level reaches 10%, makeup automatically started at -160 gpm 190 Pressurizer level off-span low 250 Operator establishes SFW per AE-0 (flow assumed to both SGs) 420 Operator stops SFW to SG 2, re-confirms necessary isolations per AE-2 600 SG 2 completely depressurized 700 Pressurizer level returns on span 850 Pressurizer level reaches 10%, transition to AES-1.1 1000 Operator isolates CMTs 1200 Operator establishes letdown at - 100 gpm 1300 Operator isolates PRHR 1420 Operator operates SG 1 PORV to stabilize temperature 1600 Operator controls makeup to match letdown at - 100 gpm 1750 End of transient modeled:
RCS pressure = 1900 psia, pressurizer level = 25%
SG 1 NR level = 55%, RCS subcooling = 175'F Hot leg / core exit temperature = 455'F 3000 l
l m:\ap6000064w\ae-2.wpf:lb-0807% 2-6 REVISION: lA
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l SG 1 Pressure (Intact)
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0 0 500 1000 1500 2000 2500 3000 Time (s) l
< Figure 2-1. Steam Generator Pressure Response for a 0.6 sq ft Steamline Break with AP600 ERG Recovery Actions nt\ap600do64ww-2.wpf:lt>-oso796 2-7 REVISION: lA
O Pressurizer Level 100 M
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O i RCS Pressure 2300 _
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I Figure 2 3. Reactor Coolant System Pressure Response for a 0.6 sq ft Steamline Break with AP600 ERG Recovery Actions Pressure m:\ap600\2064w\ac-2.wpf:lb-0807% 2-9 REVIslON: lA
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I Figure 2-4. Loop No.1 Temperatures for a 0.6 sq ft Steamline Break with AP600 l
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O b Figure 2-5. Loop No. 2 Temperatures for a 0.6 sq ft Steamline Break with AP600 ERG Recovery Actions m:\aA064ww.2.wpf:1b-080796 2-11 REVISION: lA
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O PRHR inlet Flow SFW to SG 1 (Intact)
SFW to SG 2 (Foulted) 200 o
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O Figure 2-7. SFW and PRHR Flow Rates for a 0.6 sq ft Steamline Break with AP600 ERG Recovery Actions maap600co64wsae-2.wpub-oso7% 2-13 REVISION: 1A
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Figure 2 8. Hot Leg Flow Rates for a 0.6 sq.ft Steamline Break with AP600 ERG l Recovery Actions m:\ap6000064w\ac-2.wpf:IM80796 2-14 REVISION: lA
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O SG 1 NR Level
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O Figure 2 9. Steam Generator Level Response for a 0.6 sq.ft Steamline Break with AP600 ERG >very Actions m:\ap600C064w\ae 2.wpf:lb480796 2 15 REVISION: 1A
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Figure 210. CVS Makeup and Letdown Flows for a 0.6 sq ft Steamline Break with AP600 ERG Recovery Actions mnap60m2064.\ae-2.wpr:lt480796 2 16 REVISION: 1A
O CMT-A injection
CMT-A Bolonce Line m 60 _
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O Break Flow m 1200 -
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0 O 500 1000 1500 2000 2500 3000 Time (s) l l
l Figure 2-12. Main Steamline Break Flow Rate for a 0.6 sq-ft Steamline Break with AP600 ERG Eecovery Actions m:\ap60m2064wsae-2.wpu b-oso7% 2 18 REVISION: 1A I
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