ML20214W473
| ML20214W473 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 06/09/1987 |
| From: | Tiernan J BALTIMORE GAS & ELECTRIC CO. |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| NUDOCS 8706160038 | |
| Download: ML20214W473 (47) | |
Text
_
BALTIMORE GAS AND ELECTRIC CHARLES CENTER P. O. BOX 1475 BALTIMORE, MARYLAND 21203 JOSEPH A,TIERNAN Vice PRES! DENT NUCLEAR ENEROY June 9,1987 U. S. Nuclear Regulatory Commission Washington, DC 20555 ATTENTION:
Document Control Desk
SUBJECT:
Calvert Cliffs Nuclear Power Plant Unit Nos.1 & 2; Docket Nos. 50-317 & 50-318 RETRAN Review - Submittal of Additional Information
REFERENCES:
(a)
Letter from Mr. S. A. McNeil (NRC), to Mr. 3. A. Tiernan (BG&E),
dated November 20, 1986, Request for Additional Information -
RETRAN Review (b)
Letter from Mr. 3. A. Tiernan (BG&E), to NRC Document Control Desk, dated February 24,1987, same subject Gentlemen:
In Reference (a), you requested additional information regarding Topical Report A-85-11 (RETRAN Computer Code, Reactor System Transient Analysis Model Qualification) which was submitted in January 1986. We provided a response in Reference (b). A conference call between NRC staff and Baltimore Gas and Electric (BG&E) Company was held on April 28, 1987, to discuss the RETRAN Topical Report and our response to the request for additional information.
The attached letter incorporates the additional information requested during this conference call.
Should y3u have any questions regarding this matter, we will be pleased to discuss them with you.
M' ggO 0706160038 870609' Very truly yours, PDR ADOCK 05000317 A
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JAT/LSL/ dim Attachments
- (pel cc D. A. Brune, Esquire
- 3. E. Silberg, Esquire el g R. A. Capra, NRC k
S. A. McNeil, NRC (3 copies)
W. T. Russell, NRC T. Foley/D. C. Trimble, NRC
r ATTACHMENT' RETRAN REVIEW - ADDITIONAL INFORMATION (June 1987)
The following responds to your request for additional information regarding Topical Report A-85-11 (RETRAN Computer Code,. Reactor System Transient Analysis Model Qualification).
These responses are the same as our February 24,1987 submittal except where annotated in the margins. References forwarded on February 24,1987 have not been attached to this submittal.
1.
BG&E used the RETRAN-02/ Mod 03 computer code which has not been generically approved by the NRC._
Discuss the differences between this code and the RETRAN-02/ Mod 02 code (which is the NRC approved version) and the impact of these differences on transient and accident analyses.
Response
The NRC Safety Evaluation Report (SER) (Reference (1) for RETRAN states that RETRAN-02/ Mod 02 was the code reviewed. As a result of code errors identified during the review process, the SER for RETRAN-02/ Mod 02 states:
"The staff requires that these errors be corrected in the approved versions of RETRAN-01 and RETRAN-02 prior to safety related application of these codes. Code modi!! cations should be corrected according to established error reporting and control change procedures. No analyses in support of licensing actions should be submitted utilizing uncorrected versions of the code."
RETRAN-02/ Mod 03 is the E!ectric Power Research Institute (EPRI)/ Utility Group for Regulatory Action (UGRA) revised version of RETRAN-02/ Mod 02 with the identified errors corrected. The NRC was notified in letters from both Mr. L. 3. Agee (EPRI) and Mr. T. W. Schnatz (UGR A) to Mr. C. O. Thomas (NRC) (attached References (2) and (3)).
As stated in Mr. Schnatz's letter, no significant differences were noted when 10 sample problems were rerun with RETRAN-02/ Mod 03 and compared to the results of RETRAN-02/ Mod 02 (see EPRI NP-1850 CCM-A, Vol. 3). Finally, the RETRAN-02/ Mod 02 document, EPRI NP-1850-CCM, was modified to EPRI NP-1850-CCM.A_,as required by NUREG-0390 and represents RETRAN-02/ Mod 03.
The above status of RETRAN-02/ Mod 03 is also discussed in attached References (4) and (5).
2.
Provide the data and comparison which support BG&E's conclusion that the use of a single node for the secondary side of the steam generator will produce acceptable results. In addition, provide and justify the types of transients for which such a single node secondary volume is valid. -
e ATTACHMENT RETRAN REVIEW - ADDITIONAL INFORMATION (June 1987)
Response
The statement of acceptable results for a single node steam generator (SG) secondary side is made on page 13 of the BG&E Topical Report (Reference (6))in discussing the RETRAN one loop model. It should first be noted that the two loop and four loop models, discussed on BG&E Topical Report pages 16-20, utilize a four node recirculating SG secondary side model.
The BG&E Topical Report presents two analyses using the one loop model with a single node SG secondary. The first analysis, four pump coastdown from 20% power (Sec. 4.2), is not affected by the secondary side. The dominant parameter of interest is transient primary coolant system flow rate. The second analysis, cooldown to residual heat removal entry (Section 5.2), compares primary pressure and temperature and secondary side pressure for 11500 seconds with a similar TRAC model calculation.- RETRAN results closely follow the TRAC calculation results. The TRAC model uses 26 calculation mesh cells for the SG secondary side. This excellent comparison between RETRAN and TRAC substantiates the adequacy of the RETRAN single node SG secondary side.
The major disadvantage of a single node secondary volume is that a discrete mass and energy distribution is homogenized. This distorts the SG downcomer level and riser region heat transfer coefficients. Instead of a subcooled downcomer fluid approaching saturation in the riser region, the single node models the entire secondary side as a saturated fluid.
Also, tube bundle region velocity is not correctly simulated in a single node because of recirculation. Even adjusting flow area to account for the recirculation ratio would only be valid at a single power level because the recirculation ratio varies with power.
Therefore, a single node SG secondary is valid whenever accurate level prediction is not necessary or, very large changes in secondary inventory and changes in heat transfer mode on the tube bundle (i.e., counter current flow, primary side condensation) are not expated.
The Calvert Cliffs Updated Final Safety Analysis Report (FSAR) Chapter 14 Safety Analyses were evaluated to determine appropriate RETRAN SG secondary side noding for each transient. The Loss of Coolant Accident (LOCA), Boron Dilution, Containment /
Subcompartment Pressurization, Radiological Release and Turbine Missile Events are not included in this evaluation since RETRAN would not be used for these analyses. It should be noted that this evaluation is based on a best estimate RETRAN calculation, not the licensing level analysis presented in the Updated FSAR.
The Calvert Cliffs Updated FSAR Chapter 14 transients for which RETRAN could be used can be divided into the following four categories differentiated by the nature of the initiating event:
1.
Primary Coolant System Flow Disruption 2.
Reactor Core Reactivity Perturbation 3.
Change in Secondary System Heat Removal 4.
Loss of Primary Coolant System Inventory (Non-LOCA) n q
ATTACHMENT RETRAN REVIEW - ADDITIONAL INFORMATION (June 1987)
The primary coolant system flow disruption events are the Loss of Flow (LOF) and Seized Rotor (SR) transients. These transients are analyzed for a short time period (10-20 seconds). These events are primarily concerned with the effect of sudden Reactor Coolant System (RCS) flow reduction on Departure From Nucleate Bolling Ratio (DNBR) and fuel failure. Key parameters are transient core flow reduction, core reactivity variables, and initial conditions. The LOF and SR transient time of interest is small compared to RCS toop transit time and therefore secondary side coupling effects are not important. A single node model of the SG secondary side would be sufficient for these transients.
Reactor core reactivity perturbation transients in the Updated FSAR include: Control Element Assembly Drop (CEAD), Control Element Assembly Withdrawal (CEAW) and Control Element Assembly Ejection (CEAE). All of these events cause a core power change by either inserting positive or negative reactivity and the CEAD/CEAE also increase local power peaks. The time period of interest for these events are: CEAD (300 seconds), CEAW (50 seconds), CEAE (5 seconds). The key consequences of these transients are minimum DNBR and minimum fuel failure fraction. The most sensitive parameters i
affecting results are core reactivity coefficients / constants, and fuel rod power distribution.
The CEAE and CEAW occur over a short time period where secondary system changes do not significantly affect the core response. Since the CEAE and CEAW transients are analyzed over a short time period as related to the loop transit time and the effects of secondary side heat removal, a single node SG secondary RETRAN model would be adequate for these events.
The CEAD assumes constant secondary side steam flow resulting in a slow RCS cooldown and depressurization (20 psi drop in 300 seconds and 6%
core power variation).
The CEAD does not result in a reactor trip, so there is no associated turbine trip to perturb the secondary side. Although CEAD occurs over a longer time period, the slow system response and implicit full power steam flow conditions during this event also allow the use of a RETRAN single node SG secondary model for CEAD. Finally, the nature of these events (i.e., a core reactivity change initiating local and/or core wide power fluctuations) further substantiates the accuracy of a single node secondary side model.
The following Updated FSAR Chapter 14 transients involve changes in secondary side heat removals o
Excess Load (EL) o Loss of Load (LOL) o Loss of Feedwater (LOFW) o Feedwater Malfunction (FWM) o Loss of AC (LOAC) o Main Steam Line Break (MSLB) o Feedwater Line Break (FWLB)
These transients are analyzed over a time period ranging from 100 to 1800 seconds in the Updated FSAR. They can be categorized as either excess secondary side (S.S.) heat removal or reduced secondary side heat removal as delineated below: P
. m.
r ATTACHMENT RETRAN REVIEW - ADDITIONAL INFORMATION (June 1987) -
UPDATED CALVERT CLIFFS EXCESS S.S.
REDUCED S.S.
FSAR CH.14 TRANSIENT HEAT REMOVAL HEAT REMOVAL EL X
LOL X
LOFW X
FWM X
LOAC X
MSLB X
FWLB X
The excess secondary side heat removal events are initiated by failures which cause either an increase in main steam flow rate or increased feedwater flow / reduced feedwater temperature. The reduced secondary side heat removal events involve degraded main steam flow, feedwater flow or SG inventory. Both events result in rapid wide fluctuations in SG pressure, level, enthalpy, and heat transfer. These secondary side transients create a core-power steam-flow mismatch with an accompanying change in primary coolant system pressure and temperature.
A multiple noded SG secondary side model is required for accurate simulation of level, rapid change in secondary side inventory, and heat transfer mode.
Therefore, the excess / reduced secondary side heat removal transients in the Calvert Cliffs Updated FSAR Chapter 14 should be modelled with a RETRAN multiple node SG secondary side for best estimate calculations.
The two loss of primary coolant system inventory events are the Steam Generator Tube Rupture (SGTR) and Reactor Coolant System Depressurization (RCSD). The RCSD is only analyzed over a 20 second period and is principally (concerned with the minimum tran DNBR, and peak Linear Heat Generation Rate LHGR) occurring from reduced RCS pressure prior to reactor trip. Since the time of minimum DNBR and peak LHGR occur prior to reactor (and turbine) trip, there is no effect on the key results of this transient from the secondary side. Therefore, because the time of interest is small compared to loop transit time and the secondary side of the SG is at steady state conditions during this time, a single node SG secondary is sufficient to model the RCSD.
The SGTR is analyzed over 1800 seconds during which there is a significant flow of primary coolant through the ruptured tube to the SG secondary. This causes a rapid drop in RCS pressure and significant changes in SG pressure and level. To properly model the local effects of ruptured tube flow, changes in SG secondary side enthalpy, flow rates, level, and pressure, a multi-noded RETRAN SG secondary model should be used for the SGTR.
In summary, the following table delineates the Calvert Cliffs Updated FSAR Chapter 14 transients and which RETRAN SG secondary side model would be used for best estimate calculations.
4
r ATTACHMENT RETRAN REVIEW - ADDITIONAL INFORMATION (June 1987)
RETRAN SG SECONDARY SIDE MODEL CH.14 UPDATED FSAR EVENT, SINGLE NODE MULTIPLE NODE RCSD X
LOF X
SR X
CEAD X
CEAW X
CEAE X
EL X
LOL X
LOFW X
FWM X
LOAC X
MSLB X
SGTR X
FWLB X
3.
Justify the use of a single node non-equilibrium pressurizer regarding rapid insurge and outsurge transients.
Response
The RETRAN non-equilibrium model is used in the single node representation of the pressurizer.
This model effectively breaks the node into two mass and energy conservation regions (llquid and vapor) which are not required to be at the same temperature. This allows the model to effectively track a varying mixture level. During insurge transients, the liquid region will subcool due to the incoming hot leg fluid.
Although the basic single node non-equilibrium model (which assumes complete instantaneous mixing of the liquid region) may not be accurate for a rapid insurge/outsurge transient, a longer term insurge or outsurge transient can be acceptably modeled. This is because homogeneous mixing of the incoming fluid with the pressurizer fluid does occur for the longer term transient.
To overcome the limitation of the single node model described above, RETRAN can use a Temperature Transport Delay Time Model (TTDT) In conjunction with a single node non-equilibrium pressurizer to properly simulate a rapid insurge and outsurge transient. This model tracks the movement of a temperature front to the pressurizer volume and allows the user to divide a single node into multiple mesh intervals for simulating a slug of lower / higher temperature fluid moving within a node. A more detailed explanation of the TTDT Model can be found in the RETRAN-02 Report, EPRI NP-1850-CCM A Vol. 3, page IV-52 and Vol.1, Rev. 2, page Vil-13.
Finally, as indicated on page 27 of the BG&E Topical Report, a RETRAN two-node pressurizer without TTDT, as compared to a single node pressurizer without TTDT, had no significant effect on Pressurizer Pressure and Level response for a typical rapid insurge/outsurge transient. -
r-ATTACHMENT RETRAN REVIEW - ADDITIONAL INFORMATION (June 1987) 4.
For the Multiple Secondary Side Malfunction (MSSM) event, BG&E assumes three heat transfer slabs transferring thermal energy to a single hydraulle node in the pressurizer.
Discuss the effect of not subdividing the hydraulic node in the pressurizer in light of the temperature stratification of the fluid in the pressurizer.
Response
RETRAN 02 Mod 3 is basically a one dimensional homogeneous computer code. The pressurizer is a region of the primary coolant system where two water phases (liquid and vapor) can exist at different temperatures during a transient.
To simulate this thermodynamic state, a number of models are included to compensate for the homogeneous assumptions in RETRAN. The non-equilibrium model allows the liquid and vapor states in a single node to exist at different temperatures, but at the same pressure.
However, this model assigns the same temperature for all of the vapor space with another single value of temperature for all of the liquid space. During rapid insurge transients, thermal stratification occurs in the pressurizer liquid space resulting in a temperature gradient, induced by the colder hot leg and surge line fluid.
The RETRAN TTDT model was developed to follow a front of different temperature fluid as it moves within a node. Use of the TTDT model ensures that no mixing of incoming fluid is allowed, but rather maintains the integrity of incoming fluid as a front that displaces the warmer fluid in the pressurizer. In reality, neither complete mixing nor zero mixing occur in the pressurizer liquid during rapid insurge events due to local flow effects. Multiple pressurizer nodes are useful when used in conjunction with the TTDT model. Without TTDT, each volume homogeneously mixes all fluid and, because of very low form loss coefficient, and geometric inertia, flow between nodes is almost instantaneous.
Other important pressurizer heat transfer processes during rapid insurge and/or outsurge events include condensation /cyaporation at the liquid-vapor interface, heat loss to the pressurizer wall, and steam condensation onto spray droplets. Although RETRAN 02 Mod 3 models each of these processes, the models are limited in scope and accuracy. The RETRAN Interface Heat Transfer Coefficient (IHTC) applies a single constant value of IHTC to the liquid-vapor interface surface area. In reality, this value would change during an insurge-outsurge transient as would the heat transfer area due to liquid surface turbulence and time varying liquid surface / vapor enthalples. Similarly, heat transfer to the walls and spray droplets is modelled with correlations that approximate, but do not accurately represent these actual rnechanisms.
RETRAN 02 Mod 3 uses bubble velocity gradient and spray rainout velocity as a means of simulating phase separation in the liquid region and spray heat transfer. Careful selection of the aforementioned RETRAN 02 Mod 3 pressurizer model parameters can result in a reasonable simulation of many transients. In some cases (e.g., IHTC), use of an unrealistic value will provide good results by compensating for oeficiencies in other models (e.g., wall heat transfer).
Another effect that is not modelled by RETRAN 02 Mod 3 in the pressurizer is the presence and effect on wall heat transfer and pressure response of non-condensible gases in the vapor space. The primary coolant contains dissolved gases, some naturally present and some injected for oxygen scavenging (e.g., Hydrogen).
The saturation temperature condition, high elevation, and use of heaters drive non-condensible gases out of solution into the vapor space. These gases blanket part of the wall surfaces -. -
e ATTACHMENT RETRAN REVIEW - ADDITIONAL INFORMATION (June 1987) acting as an insulator thereby reducing heat transfer and also act to increase pressurization during an insurge event.
The selection of three heat transfer slabs in the pressurizer was based on RETRAN input requirements for a minimum number of " stacked" heat conducters in a single volume, and engineering judgement on heat transfer modeling of these conductors. For the Multiple Secondary Side Malfunction event, the single hydraulle node was subdivided into two nodes as part of the sensitivity study (Sec. 4.1.4 of the BG&E Topical Report) with no significant effect on Pressurizer Pressure or Level response (Item 3 on page 27 of the BG&E Topical Report). The large flow area, small pressure loss coefficient, and small inertia of the junction connecting these two nodes allow almost instantaneous temperature changes for both nodes.
However, using the TTDT model (see answer to question 3) allows for effective tracking of a temperature front as it enters the pressurizer without homogeneously mixing it throughout the node.
The MSSM event was rerun using the TTDT model with 20 mesh intervals (recommended in the RETRAN-02 input manual). Key results were compared with the case reported in the BG&E Topical Report (without the TTDT model) and measured plant data and are summarized below.
Parameter Plant Data Topical Report Case TTDT Model Case Peak Pressurizer 2306 2338 2310.7 Pressure (psla)
Time of Peak (sec.)
48 51 31 Peak Pressurizer 254 244.4 246.3 Level (inches)
Time of Peak (sec.)
60 66 66 The above data shows that the TTDT model reduced peak pressure from 2338 psia to 2310.7 psia which is closer to the measured 2306 psla. Also, the TTDT model increased peak level by about two inches closer to plant data. A comparison of pressurizer liquid space temperatures (during the insurge segment of the transient) between the two RETRAN cases shows that the TTDT case was a maximum of 0.5 F cooler (at 73 seconds) than the base case without the TTDT model.
BG&E plans to use the TTDT model whenever a similar phenomena is expected to occur in the pressurizer.
5.
Based on our review of Section 4.1 of the topleal report, we have identifled several anomalles. Provide explanations for the following anomalless (a)
BG&E had postulated that "possibly higher run-out auxillary feedwater (AFW) pump i
flow rates and lower post trip main feedwater (MFW) temperatures caused more j
rapid cooldown af ter 160 seconds in plant data." However, we note that the plant data show the SG21 lovel pegged at about 200 sec and that differences in level in i
I l l
I' ATTACHMENT RETRAN REVIEW - ADDITIONAL INFORMATION (June 1987)
SG21 existed from about 70 seconds, not 160. The RETRAN calculation of levelin SG21 lagged the actual refill data by roughly 20 seconds throughout the transienti (b)
The slope difference in the Steam Generator Level between the RETRAN calculation and the plant data for SG22 resulted in a difference in dry out time of about 40 seconds (c)
The effect on the transient of the broader spike in RETRAN analysis.
(d)
What happened in the plant data at approximately 140 seconds following the event?
Why was this transient curve not followed by the RETRAN calculations? Is it related to dryout of the steam generator? Would a more detailed steam generator secondary side nodalization give better results?
Responset (a-b)
Steam Generator Level is based on wide and narrow range taps on the SG downcomer which are connected to a reference leg. The RETRAN model explicit-ly includes the actual tap locations in calculating SG Level. RETRAN calculates SG Level by applying a correction factor to the calculated differential pressure using the Bernoulli Equation, and by accounting for the applicable downcomer fluid density, tap clevation, flow rates and flow area.
Since the four node RETRAN SG secondary model has only one node for the downcomer, the average downcomer thermodynamic properties are used in this correction factor.
The reported SG Level plant data is actually provided by one of six separate instrument channels for each SG. Combustion Engineering (CE) has identitled significant differences between individual channel level indications and has postulated that this channel discrepancy may be attributable to o
Flow perturbations from uneven local downcomer flow rate distribution and eddy currents (including the effect of asymmetric SG shroud cutouts for hand-hole / tap locations),
inconsistent / erroneous individual instrument channel corrections, and o
o Variations in reference leg temperatures which affect the correlation of reference leg level to SG Level.
Combustion Engineering has determined that the measured SG Level must be corrected to account for power dependent velocity head (from constricted shroud-to-shell area near the taps), contraction friction losses, and power dependent SG pressure. CE has only provided corrections for steady state power operation at different SG Pressures, power level, and reference leg temperature.
The difference in dryout time is really only a difference in reaching the lower tap of the SG Level measurement instrumentation.
This tap is well above the tubesheet.
-8
ATTACHMENT RETRAN REVIEW - ADDITIONAL INFORMATION (June 1987) l l
l In summary, the plant measured SG Level may significantly differ from actual level due to numerous Instrumentation errors (channel differences) and the presence of physical phenomena in the downcomer and reference leg that are not accounted for by the level indication. Some of these phenomena are not modeled by RETRAN. A more detailed nodalization of the SG downcomer region may improve RETRAN calculated level.
However, in light of the uncertainty of measured level and the significant increase in computer run time previously experienced with more detailed SG nodalization, a more detailed SG nodalization would not be practical.
(c)
The broader SG pressure spike in the RETRAN analysis results in a slightly larger l
steam flow rate out the Atmospheric Dump Valves (ADVs) and Turbine Bypass Valves (TBVs). Up until about 30 seconds, RETRAN SG Pressure is lower than plant data. From about 70 seconds to 120 seconds, RETRAN SG Pressure is greater than plant data. The maximum difference of about 30 psi (out of 900 to 1030 psla) and relatively short time for this difference does not significantly affect primary coolant system thermal-hydraulle response as evidenced by the excellent comparison of this calculation to plant data.
(d)
At approximately 140 seconds, SG Pressure dropped to 870 psia, the setpoint at which all TBVs should have closed, but one stuck open. No other information on j
the position of this stuck-open TBV was avallable except that it was identified and isolated at about 300 seconds. As discussed on pages 24 and 23 of the BG&E Topical Report, the RETRAN model assumes that the TBV was half open. Some RETRAN sensitivity studies and examination of SG Pressure response indicated l
that the stuck-open TBV position was more likely varying between 140 and 300 seconds. The complexity and the consuming nature associated with arbitrarily l
using different time dependent TBV areas to better " match" plant data was deemed impractical in light of the reasonably close agreement from the half open l
TBV assumption.
In response to the April 28, 1987 conference call with the NRC and its contractor, the following detailed evaluation of the multiple secondary side malfunction is presented.
An analysis of the RETRAN curves in Figures 4.1-3 through 4.1-7 of the topical report Indicates several common trends in the data. Four basic trends noted for pressurizer pressure and level, hot and cold leg temperature, and SG pressure are delineated below:
1.
These parameters start to increase in the time frame of 20-30 seconds af ter the start of the event.
l 2.
A peak value occurs between $3 and 70 seconds af ter which the parameter rapidly l
decreases.
l l
3.
A discernible change in slope is evident between 120 and 130 seconds. This change is in the direction of a reduction in the rate of decrease.
4.
A minimum value is reached for pressurizer pressure and level between 244 and 258 seconds for hot leg temperature at 210 seconds for steam generator secondary side I
pressure at 310 seconds. Af ter this minimum, these parameters increase slightly.
l 9
____ __ _ _ ~
ATTACHMENT l
RETRAN REVIEW - ADDITIONAL INFORMATION (June 1987)
Pressurizer pressure and level, hot and cold leg temperature and SG secondary side pressure are all affected by the mismatch betwcan core power and main steam flow that occurs during this transient. Figure A5-1 was developed which presents a comparison of core power and total main steam flow power. The core power is based on the measured plant data for this event which was input to the RETRAN model. The total main steam flow power is the sum of the RETRAN calculated steam flows to the turbine stop valve (TSV), condenser (TBVs), and atmosphere (ADVs) and Safety Rellet Valves (SRVs) which is l
normalized to the normal 100% power steam flow rate.
The initial core power reduction from 20 to 62 seconds in Fig. A5-1 was due to operator action (emergency boration and CEA insertion) to attempt to match decreasing main l
feedwater flow. At 62 seconds, the reactor tripped on low SG level causing the drop in core power down to decay heat levels. The steam power reduction from 20 to 62 seconds was also a result of operator action to match reducing feedwater flow and prevent reactor trip. Upon reactor trip at 62 seconds, rapid TSV closure and ADV opening cause the steep decline in steam flow power shown in Fig. A5-1. Within a few seconds, the TBVs and SRVs open resulting in an increase in steam flow power until peaking at 68 seconds. At 68 seconds, total steam flow power exceeded core power. Atter 68 seconds, steam flow dropped (SRV closed at 82 seconds and ADV closed at 133 seconds). ADV closure caused the slope change in the steam flow curve. All but one TBV closed at 133 seconds which also contributed to this slope change. Finally, Isolation of the open TBV at 310 seconds is reflected by the step drop in steam flow.
In comparing the relative magnitude and direction of the difference between the core power and steam flow power curves in Fig. A5-1, the four aforementioned trends can be explained.
Wherever the core power curve is greater than steam power, inadequate secondary heat removal is occurring and the primary system will heatup/ pressurize along with the secondary side. A larger dif ference (in corc/ steam power mismatch) results in an increasing slope.
Conversely, a higher steam power curve will cause a reduction in primary and secondary temperatures and pressures. The increase of pressurizer pressure and level, hot and cold leg temperature and SG pressure commencing at 20-30 seconds (Trend 1) is due to the core-steam mismatch that begins at this time. From 20 to 62 seconds, this dif ference becomes larger.
This mismatch is directly coupled to the thermodynamic parameter response (i.e., primary system pressure, level, temperature and l
secondary side pressure response).
l On reactor trip at 62 seconds, Fig. A5-1 shows a small time period in which the mismatch is even greater.
This imbalance in heat removal causes the peaks (Trend 2) in l
thermodynamic parameters.
Since the thermal lag and transit time for the primary coolant system is much greater than the secondary side, the secondary side pressure peak l
has a sharper peak. The thermal capacity of the primary coolant system and hydraulle response of the pressurizer steam space reduce the primary system peak. The subsequent rapid decrease noted in Trend (2) results from the opening of the SRVs and TBVs which l
causes steam flow power to rise above the core power. The large difference between core and steam power results in the significant drop in thermodynamic parameters until 120-130 seconds when the TBYs and ADVs closure changes the slope of steam flow power. This l
change in steam flow power slope coincides with a concurrent chango in slope of the decreasing primary and secondary system parameters (Trend 3). The remaining steam flow path af ter 133 seconds is solely the stuck open TBV which had unknown translent flow characteristics until isolated. -
r ATTACHMENT RETRAN REVIEW - ADDITIONAL INFORMATION (June 1987)
Figure 4.1-8 of the RETRAN Topical Report presents SG narrow range response calculated by RETRAN as well as plant measured data for this event. RETRAN calculated both SG levels to drop until about 85 seconds when SG 21 level began to increase. The SG 21 level reached the upper limit of the narrow range at about 210 seconds where it remained for the balance of the RETRAN analysis time (360 seconds). The RETRAN calculated SG 22 level continued to drop until reaching the lower limit of the narrow range at about 118 seconds. At about 200 seconds, SG 22 level increased above this lower limit and reached an equilibrium value of about -90 inches where it remained for the balance of the RETRAN anlaysis.
To analyze the trends in RETRAN calculated SG level response, two graphs were developed from the RETRAN output. Figures A5-2 and A5-3 present a comparison of RETRAN calculated individual SG feedwater flow rates with total and one half of total main steam flow rate.
The one half steam flow rate comparison is an estimate of individual SG steam flow rate.
As in Figure A5-1, the relative difference between the feedwater and steam flow curves constitutes the basis for the translent SG level response in Figure 4.1-8.
Figure A5-1 represents a system transient energy balance whereas Figures A5-2 and A5-3 depict the SG secondary side mass balance. Whenever the steam flow exceeds feedwater flow, the SG level would be expected to decrease (assuming that no competing thermodynamic effects are occurring) and conversely, an Imbalance in which feedwater flow exceeds steam flow would result in an increasing SG level.
The initial drop in SG 21 and SG 22 levels until 85 seconds is explained by the fact that in both Figures A5-2 and AS-3, steam flow is greater than both feedwater flows during this time period. The SG 22 Feedwater flow curve crosses the steam flow curve and thereaf ter exceeds it at about 85 seconds. The continually dropping SG 21 feedwater flow curve stays below the steam flow curve until about 200 seconds. This substantiates the drop in SG 22 level to the lower level limit until 200 seconds.
At about 200 seconds, the SG 22 auxillary feedwater flow becomes approximately equal to the one half steam flow rate. Review of the limited RETRAN major edits providing Individual SG steam !!ows Indicated that, during this time period, only about one third of the total steam flow was coming from SG 22. This would place the SG 22 feedwater flow curve above the steam flow curve in Figure A5-2 which explains the return in level for this SG at about 200 seconds. The higher SG 21 feedwater flow (as compared to steam flow) af ter about 85 seconds is the reason for the SG 21 level rising to the upper limit and staying there throughout the RETRAN analysis.
6.
The statement that the " difference in SG pressure response accounts for dif ferences in primary coolant systems cooldown af ter 160 sec"is not exactly accurate. The dif ferences in secondary side pressure began at roughly 70 seconds and the large change in slope in secondary pressure data at roughly 110 seconds was not matched by the RETRAN calculation of the SG Fressure although the general characteristics of the SG Fressure was followed. Explain the sources of all the significant deviations and justify the differences between the RETRAN calculation and the plant data. -
ATTACHMENT RETRAN REVIEW - ADDITIONAL INFORMATION (June 1987)
Response
Steam Generator Pressure response during this event is due to the following factors:
1.
Pre-trip reactor power level and steam flow rate to the turbine 2.
Timing of the TSVs closure and the TBVs and ADVs opening 3.
The magnitude and enthalpy of the MFW 4.
The stuck-open TSV area 5.
Additional steam flowpaths.
Of the above factors, only reactor power level and MFW flow were measured parameters.
All other factors were accounted for by deducing their values from other data and plant experience. Uncertainties in these factors can affect RETRAN calculated SG Pressure well in excess of the relatively small differences shown in Figure 4.1-7 of the BG&E Topical Report. It should also be noted that the differences between RETRAN calculated SG Pressure and plant data are bounded by the Instrument tolerance delineated in Table 4.1-2 of the BG&E Topical Report.
7.
Expand your discussions of the RETRAN model sensitivity study to support your conclusion stated on page 27 of the report. In particular, did BG&E perform sensitivity studies to determine what happened on the secondary side and its impact on the primary side? If not, then discuss the secondary side flow data and the RETRAN modeling thereof, and justify any differences by discussion of their impact upon the overall transient results.
Response
The conclusions on page 27 of the BG&E Topical Report were specifically made regarding pressurizer modeling sensitivity studies and their effect on transient Pressurizer Pressure and Level response.
A sensitivity study of secondary side effects on the primary side was performed in examining the performance of the TSVs, TSVs, ADYs, and Turbine Governor Valves 1
(TGVs). These four secondary side valve systems directly affect the steam flow rate and l
associated primary system pressure, level, and temperature response. During the early stages of this analysis, a number of RETRAN runs were made in which the timing and/or position of these valves were varied.
Prior to the reactor trip on low SG level at 62 seconds, the transient TGV steam flow rate (as the operators attempted to match decreasing reactor power down to 70%) had a strong effect on the magnitude and time of peal < Pressurizer Pressure, and Level, SG Pressure, and Hot and Cold 1.cg Temperature. As stated on page 24 of the BG&E Topical Report, the measured first stage turbine pressure and its relationship to turbine intet steam flow rate was used to deduce the TGV position.
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i ATTACHMENT RETRAN REVIEW - ADDITIONAL. INFORMATION (June 1987)
Upon reactor trip, the TSVs close and the TBYs and ADVs open. The time delays of both the TBVs and ADVs opening and the TSVs closing were found to directly affect the slope of decreasing Primary Pressure, Temperature, Pressurizer Level, and SG Pressure and Level during the first 120 seconds. Best estimate time delays were used for the final analysis reported in Figure 4.1-3 through Figure 4.1-8. At 120 seconds, SG Pressure dropped to 870 psia, the programmed value below which all TBVs should have closed. Af ter this time, the ysition of the stuck-open TBVs affected the primary system pressure, level, and temperature response as well as the SGs Pressure and Level.
Without any direct measurement of the stuck-open TBV position, a large number of possible transient positions could be postulated. The final analysis of the BG&E Topical Report assumes a half-open TBV until isolation at 300 seconds.
8.
What input loss coefficients were adjusted to establish initial conditions in the transient of four pump coastdown from 20% power? Were any reverse flow loss coefficients used for the reactor coolant pumps? If the reverse flow coefficients were used, describe what caused the steep changes in flow data at roughly 45 sec? Were the same coefficients used in Section 4.37 Was there a change in flow regime which caused the flow meter to give a different correlation? If the plant data is correct as plotted, why was the slope change not followed by RETRAN7 Pina!!y, provide estimates of the natural circulation that is predicted by RETRAN and compare RETRAN's estimates with the expected values.
Responset input loss coefficients were not used to establish initial conditions. Rather, the initial conditions for the four pump coastdown from 20% power were established by the use of the initial pressure in each designated volume of the primary coolant system. When initial pressures are input, RETRAN calculates loss coefficients. The pressure drops are based on four pump operation at 100% power. The difference in RCS density between 100% and 20% power, which affects the total primary loop pressure drop by 2%, was accounted for by appropriately adjusting the overall loop pressure distribution. This best estimate pressure distribution was provided by CE to BG&E for the Pressurized Thermal Shock LPTS) project and was used by the Los Alamos National Laboratory in the TRAC model of Calvert Cliffs.
Although no forward pressure loss coefficients were input for the primary system, the RCP reverse flow loss coefficient provided by CE was used and is the same loss coefficient used in Sections 4.3 and 4.4.
This is discussed further in the response to question 9.
We have concluded that the steep change in flow data at 45 seconds shown in Figure 4.21 is an error in the measurement data. This is based on discussions with both CE and Byron-Jackson (the RCP manufacturer) as well as an evaluation of the four pump coastdown data for other plants.
This steep flow change can not be justified by the basic physical phenomena affecting flywheel equipped centrifugal pump coastdown.
The RETRAN estimate of natural circulation is addressed in Section 4.5 and further l
discussed in the answer to question 11.
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I ATTACHMENT RETR AN REVIEW - ADDITIONAL INFORMATION (June 1987) 9.
BG&E states that sensitivity studies were performed to adjust the downcomer cross-flow and RCP reverse flow coefficients. Although the cross-flow takes place across a large area, perhaps the flow modeling is inaccurate and/or incomplete due to failure to model cross-flows in the above core region. Explain how the flows in the above core region were modeled; and justify BG&E's modeling of the cross-flow. Provide detailed results from sensitivity studies of variation of cross-flows and reverse flow coefficients. Provide plots to accompany the analysis and discussions on comparison of RETRAN results with the measured plant data for each of five combinations of RCP operation (4,3,2 in the same loop, 2 in opposite loops, and 1 RCP running). Explain how flow rates of various cross-flows were determined for the calculations, including the bypass flows which " flows circumferencially around the downcomer and out the cold leg nozzle (s) in the reverse direction through the shutdown RCP(s) to the steam generator outlet plenum."
Compare the predicted flows in these various combinations with vendor computations and explain any significant differences. Provide the data that are availabic to verify the
" actual flow path" for reduced RCP operation configurations. Describe how the RCP locked rotor reverse flow coefficient was determined.
Response
Flows in the "above core regions" are modeled by dividing this region of the Reactor Vessel into four volumes. These four volumes and their respective RETRAN model node numbers (BG&E Topical Report Figure 3.3-1 or Figure 3.4-1) are: Upper Plenum A (25),
Upper Plenum B (26), CEA Shrouds (27) and Upper Head (28). RETRAN junction flow paths are provided to allow flow from each Upper Core (19 and 20) and Core Bypass (8) volume to the two upper plenum and CEA shroud volumes. Also, cross-flow between the two upper plenum volumes is provided in the RETRAN model. Finally, the upper head can receive (and provide) flow to both the upper plenum and the CEA shroud volumes. Thus, the "above core region" cross-flow is modeled by the following flow paths:
1.
Cross-flow between two separate upper plenum volumes 2.
Flow from both upper core volumes to the CEA shrouds which flow to the upper head. The upper head then has flow paths to both upper plenum volumes.
Both core bypass and upper plenum bypass (i.e., CEA shrouds) flow rates were also provided by CE during the PTS CE (see answer to Question 8) project. Using the known pressure distribution provided by and the flow rates, RETRAN calculated all pressure loss coefficients in the "above core region" cross-flow junctions except the upper plenum cross-flow junction.
This junction, initially set at zero flow, requires an input loss coefficient. The input loss coefficient was calculated using the geometry for flow across a bank of tubes (l.c., CEA shrouds). This is described in the 11andbook of liydraulle Resistance by I. E. Idel'Chlk (Reference (9)).
The upper plenum cross-flow loss coefficient was varied by 50% with no significant effect on the resulting loop flow spilts. As stated on page 51 in the BG&E Topical Report, varying tle downcomer cross-flow loss coefficient from.02 to 13.2 and varying the RCP locked rotor reverse flow coef ficient by 14% had no significant (l.c., less than 1%) effect on the magnitude of the flow split..
ATTACHMENT RETRAN REVIEW - ADDITIONAL INFORMATION (June 1987)
No plots are provided of results because the measured plant data for the flow through each cold leg (flow sp!!t) is a steady state value (provided in Table 4.3-1 of the BG&E Topical Report). The RETRAN calculations require 50 to 140 null transient seconds (depending on the particular case) to reach a steady state when initialized with no pumps running and followed by a start of one to three pumps.
Flow rates for various cross-flow paths are directly calculated by RETRAN and are provided as specific junction flow rates.
For example, the core bypass flow rate is provided in the downcomer uoss-flow junction No. 5 of the RETRAN Calvert Cliffs i
Nuclear Power Plant (CCNPP) model.
CE has informed us that no vendor computations are available for comparison for these RCP flow split tests. The data that substantiates " actual flow path"is the flow direction for each cold leg reported in the test results.
The RCP locked rotor reverse flow coefficients were provided by CE.
These flow coefficients were determined from predicted "K" factor curves based upon 1/3 scale model l
test results and homologous pump data. These coefficients have also been compared to full scale test data.
CE uses these same coefficients in analyzing the locked rotor accident in the Calvert Cliffs FSAR for reload analysis.
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- 10. With regard to the translent of one pump coastdown from 80% power, discuss the h. sis for adjustment of reactor coolant pump (RCP) moment of inertla and torque includ.ng the uncertainty of such pump information. Were any cross-flow sensitivity studies performed for the one RCP coastdown transient? The transient computation seems to substantially over-predict the flow reduction in the shutdown loop. Identify and describe the likely sources of over-prediction. What results are obtained without cross-flow and with nominal reverse flow coefficients? Why does plant data show nearly Instantaneous pressurizer response while RETRAN seems to show no response for approximately 3 sec? Describe why, even though both the Hot 1.eg Temperature and the SG Pressure increase for about 5 seconds immediately following the RCP trip, and the Cold I.eg Temperature remains constant, neither the primary nor the secondary side pressures immediately increase in the RETRAN calculations. Describe and quantify to the extent feasible the differences in the results between the case in which BG&E adjusted the RCS total flow to match Hot and Cold I.cg Temperatures, and the case using the initial conditions described in Sections 4.3 and 4.4.
1
Response
The RCP moment of inertia and torque were varied by 10% to determine the effect of the parameters on RCS flow coastdown. The RCP manufacturer, Byron Jackson, has stated that the nominal values for Calvert Cliffs' RCP moment of inertia and torque are calculated (by Byron Jackson) from RCP design data and are expected to have an uncertainty of no more than 3% Therefore, the 10% variation of these parameters was intended to envelope actual uncertaintles in these values provided by the RCP vendor.
As presented in Table 4.4-1 of the BG&E Topical Report, the base case without the downcomer cross-flow coefficient and a realistic RCP reverse flow loss coefficient was compared to a case which used these coefficients.
Downcomer cross flow and RCP,
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l ATTACHMENT l
RETRAN REVIEW - ADDITIONAL INFORMATION (June 1987) reverse flow had no significant effect on RCS flow except at 18 seconds when these refinements resulted in a higher flow (79.1% versus 78% for the base case and 80% for plant data) which compared more closely with measured data. Varying the downcomer cross-flow loss coefficient had no significant effect on the RCS flow coastdown.
The RETRAN transient computatloa, for the base case with downcomer cross-flow and RCP reverse flow model coefficients, under-predicts RCS total flow (i.e., over-predicts flow reduction in the shutdown loop) by 0.4% to 3.9% During the 60-second period of Interest, RCS flow measurement accuracy is k2% in addition, the plant data presented l
for this event was taken from a plot in which visual data discrimination due to the plot grid size is approximately kl%
In light of the aforementioned uncertaintles, the differences in predicted flow coastdown is not considered " substantial." Possible sources of this difference in flow coastdown include differences in actual RCP moment of inertia and torque, measurement Instrumentation accuracy, and time lag.
Results without cross-flow and with nominal reverse flow coefficient are reported as the
" base case" in Table 4.4-1 The five second difference between RETRAN pressure / temperature results and data is due to the imposition of a five second delay of the TBVs and ADVs opening in the RETRAN model.
This delay was based on previous experience with the TBVs and ADVs performance. A new case was run with instantaneous opening of the TSVs and ADVs. The results are overlayed on Figures 4.4-2, 4.4-3, and 4.4-4, from the BG&E Topical Report (attached Figures A10-1 through A10-3). These figures show that faster TBV and ADY opening results in RETRAN Pressurizer Pressure and Level, and flot and Cold Leg Temperatures comparing closer to plant data in both magnitude and timing.
l Another case with instantaneous TSV closing, but five second delayed TBV/ADV opening, l
was run and also showed a closer comparison with SG Pressure (overlayed on Figure 4.4-5 of the BG&E Topical Report and shown on attached Figure A10-4). It should be noted that i
the RETRAN simulation of this event did not allow a reactor trip (and concurrent turbine trip) until actuated by the low RCS flow signal which did not occur until about 2.5 seconds.
Any SG Pressure variation prior to 2.5 seconds would not be calculated.
In those cases in which RCS flow was adjusted to match llot and Cold Leg Temperature, l
the flow adjustment was less than 1% of the Initial conditions described in Section 4.3 and 4.4 and had no significant of feet on other parameters.
l 11.
It appears that the RETRAN calculation for a totalloss of flow transient from 40% power was initiated with a slightly different flot Leg Temperature from the plant data. Was there any difficulty in initializing the calculation at 40% power?
Were any loss coefficients adjusted in setting up initial conditions? If so, how did they compare to adjustments in Sections 4.3 and 4.47 What happened in the steam generator at 10 seconds (see Figures 4.5-2, 3, and 5) and why wasn't it modeled in RETRAN? (We note that there l
was relatively poor transient computation of temperatures between 10 and 60 seconds I
because of these differences.) Slnce the time between 60 seconds to 130 minutes is considered to be the more important period, provide transient curves for that period. The transient curves of primary flow and pressure are in agreement but do not agree for the liot and Cold Leg Temperatures and SG secondary side pressure. What is the reason to i
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ATTACHMENT RETRAN REVIEW - ADDITIONAL INFORMATION (June 1987) cause this effect and why did the secondary side not have a stronger coupling to the primary side?
Response
The measured total loss of flow test initial Hot Leg Temperature was 555 F; whereas, the RETRAN calculated initial Hot Leg Temperature was 554.4 F.
Small differences in temperature, flow or power instrumentation accuracy (see Table 4.1-2 of the BG&E Topical Report) could account for this difference. Further refinement of this model, to exactly match the measured Hot Leg Temperature, was deemed to be unnecessary because this small difference does not significantly affect the important results of this test (i.e.,
the onset and magnitude of natural circulation flow).
Loss coefficients were not adjusted in setting up initial conditions since the CCNPP model was initiated with a pressure distribution obtained from CE (discussed in our response to question 8). This pressure distribution, based on 100% power, was adjusted to account for density dif ferences associated with 40% power.
Performance of the TBVs and ADVs was not available in the startup test report. RETRAN assumes normal full power operation of these valves (i.e., quick opening TBVs and ADVs with the ADVs closing at 870 psla). In the past, slow opening times for TBYs have occurred at Calvert Cliffs. A slow opening TBV would cause the higher peak pressure (at 10 seconds) shown in Figure 4.5-5. Without the test specific ADV/TBV performance data, it was impossible to more accurately simulate SG Pressure response.
Reference 12 states: " Natural circulation was verified about five (5) minutes af ter the trip. Verification was based on the behavior of the Reactor Coolant System (RCS) hot and cold leg temperatures (T HOT and T COLD, respectively). Indication that cooler water from the cold leg was reaching the hot leg was signalled by the decrease in T HOT which was a good indication that suf ficient natural circulation was indeed occurring." RETRAN calculated hot leg temperature also decreased at this time.
As previously discussed, a lack of information on TSV and ADY performance affected RETRAN's results of Hot and Cold Leg Temperature and SG Pressure. However, during the 60 second post-trip period, there is a strong coupling between the secondary and primary side data. The higher SG Pressure peak shown in plant data is reflected in the faster hot leg cooldown since a larger ADV and TBY flow would result from higher SG Pressure. Also, the delayed SG Pressure peak in plant data (as compared to RETRAN)is reflected in a delayed Cold Leg Temperature peak.
It should be noted that although other parameter results for 60 seconds were presented for this test, the principal objective of this test and the reason for performing a RETRAN analysis was to compare tne onset and magnitude of natural circulation af ter a trip from 40% power. RETRAN's calculation of natural circulation showed the onset at about the same time as data (five minutes) and the magnitude (i.e., ratio of natural circulation flow rate to reactor thermal power)In close agreement with measurements...
ATTACHMENT RETRAN REVIEW - ADDITIONAL INFORMATION (June 1987)
- 12. One of the objectives of this BG&E Topical Report is to present BG&E's capability in modeling control systems. Since it is apparent that the major reason for disagreement between TRAC and RETRAN results in the differences in the ADV modeling, BG&E should match the ADV control system used in TRAC and rerun the calculation.
BG&E states that in spite of the fact that " primary pressure compares very well, RETRAN predicts the pressurizer to empty while TRAC does not" and that "this is consistent with previous comparison." If this difference is present in the revised calculation, then explain why one code predicts the pressurizer to empty and the other does not.
Response
There are tuo important differences between the results of the RETRAN and TRAC calculations. The first is that RETRAN calculates the pressurizer to empty and TRAC does not. The second is that RETRAN calculates a more restrictive cooldown than TRAC.
RETRAN predicted the pressurizer to empty because charging was not restored to maintain level. The assumption (for RETRAN) was that charging would be permanently realigned to provide for auxiliary pressurizer spray. However, in the TRAC analysis, charging was assumed to be restored for level control. RETRAN was subsequently rerun assuming rntoration of charging and the results accurately matched the TRAC Pressurizer Level performance (i.e., the pressurizer does not empty). Results for this revised RETilAN case are presented in Figures A12-1 to A12-2 for primary / secondary pressure and pressurizer !cvel.
The more reitrictive cooldown is explained in the BG&E Topical Report. For the pur of respondinj to the above question, a less restrictive ADV model (geometry) pose was substituted for the best-estimate ADV model and consequently, TRAC calculated temperatures were reproduced (Figure Al2-3). It should be noted that no changes to the l
ADV control system were required to resolve the differences between the TRAC and RETR 4N results.
13.
Provide detailed transient curves of RETRAN and TRAC secondary flows, pressures, and temperatures. Correlate to the transient curves for the secondary side with parameters on the primary side. Explain why the PORY reaches its setpoint about 500 seconds earlier than the TRAC predictions. Explain why itETRAN aredicts that the pressurizer water level will rise to the top of the pressurizer 1250 secones before the TRAC predicted time.
In addressing the differences between results, explain the impact that the noding may have in computing downcomer temperature. It seems un!!kely to us that these differences are caused by the coarse RETitAN noding in the downcomer (2 vs $4). Discuss the cross-flow between nodes in the TRAC nodalization, and provide the theoretical foundation for the statements that imply cross-flow would increase with increasing nodalization. In addition, explain why increasing the number of nodes in the secondary side of the SG was not considered as an option to reduce the vold formation in the upper tube volumes. -
ATTACHMENT RETRAN REVIEW - ADDITIONAL INFORMATION (June 1987) l Psponse Reference 35 (NUREG/CR-4109) from the BG&E Topical Report only presents TRAC calculated results for SG mass inventory and steamline flow rate for this transient.
Therefore, to provide a comparison of SG secondary parameters, RETRAN calculated results are overlayed on these figures from NUREG/CR-4109 (attached Figure A-13-1).
The RETRAN calculated SG mass inventory closely agrees with TRAC results with the overfed SG Inventory rising to about the same peak value and the other SG inventory dropping to the same lower value of Inventory. Steamline flow rates also closely agree with RETRAN slightly over-predicting peak flow, but following the same transient behavior and reflecting the initial runaway MFW until 303 seconds when MFW pumps trip off.
Cooling due to the high steamline flow rate between about 100 and 400 seconds caused the large Pressurizer Pressure and Level, Hot Leg Temperature and Downcomer Temperature drop during this same time period. Similarly, the rapid drop in steamline flow rate after 400 seconds resulted in the later increase of these parameters.
The earlier PORY setpoint pressure and Pressurizer Level rise to the top are attributed to two factors. First, the TRAC model of Calvert Cliffs did not allow backup pressurizer heaters to reactivitate after pressurizer liquid level returned above a programmed level setpoint even though the actual CCNPP control system has this feature. Los Alamos National Laboratory acknowledged this error on page 23 of NUREG/CR-4109. The BG&E RETRAN model does have this feature which became activated at about 450 seconds for this transient. Therefore, the RETRAN simulation included a 1200 kw backup heater input to the pressurizer after 450 seconds which was erroneously omitted from the TRAC model. This additional input increased Pressurizer Pressure.
The second factor which caused the more rapid RETRAN Pressurizer Pressure and Level rise is the large difference in liigh Pressure Safety injection (HPSI) flow rate between RETRAN and TRAC. As shown is Figure 5.3-1 of the BG&E Topical Report, RETRAN calculated Pressurizer Pressure is lower than TRAC Pressurizer Pressure until about 1000 seconds. During this time period, RETRAN Pressurizer Pressure is as much as 300 psi tower than TRAC due to the selection of a large value of IHTC. This lower pressure results in a much higher HPSI flow rate until the 1275 psia HPSI shutoff head is reached at about 900 seconds in the RETRAN analysis. The higher HPSI flow rate which occurs over this 800 second time period is responsible for the more rapid Pressurizer Level rise.
Since the TRAC model uses six circumferential cells (one for each reactor vessel nozzle) and nine axial levels as compared to RETRAN's two nodes, a much larger combination of mixing flowpaths are available in the TRAC model. This transient is asymmetric since one loo) experiences a much more rapid cooldown and higher flow rates than the other. This difference in loop flow and temperature (Figures 3.3-4 and 5.3-5 of the BG&E Topical Report) will create a significant cross-flow within the downcomer.
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Several factors differentiate the cross-flow calculated between TRAC and RETRAN.
l TRAC uses a three dimensional flow solution (r,Q,z) method as compared to RETRAN's one dimensional flow method. TRACs flow solution method coupled with a larger number of nodes allows greater mixing. It was also apparent in performing this comparison that -
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ATTACHMENT RETRAN REVIEW - ADDITIONAL INFORMATION (June 1987) l the TRAC report (NUREG/CR-4109) does not identify which downcomer node temperature is reported. For PTS purposes, a node adjacent to the highest neutron flux core midplane may have been selected which is several levels down from the cold leg nozzle location.
With the finer TRAC nodalization, a downcomer node location several levels below the nozzle allows cross-flow mixing from the adjacent warmer downcomer and cold leg nodes. This detall was not included in the RETRAN model. Finally, the TRAC model allows leak flow from the reactor vessel upper head to the upper downcomer. This flowpath, which would increase downcomer temperature, was not included in the RETRAN model.
Increasing the number of nodes in the secondary side of the SG was not considered because the extremely large computer run time for this transient (greater than 10 cpu hours) greatly restricted the number of sensitivity studies and model changes.
Previous experience with increasing SG secondary nodalization has also resulted in further increases in computer run time. Since the model changes in the SG tube volumes allowed RETRAN to simulate SG reverse heat transfer and upper tube volding, the cost versus benefits of further SG nodalization studies was not justifiable.
- 14. Describe any differences between the BG&E RETRAN model and the RETRAN model used in initial analysis of L6-1 and L6-3 by EPRI as presented to the ACRS on January 14, 1981.
Responses As a contractor to EG&G Idaho, Intermountain Technologies incorporated (ITI) developed pretest RETRAN models for the L-6 series of LOFT tests (Reference (10)). Energy incorporated (EI), as a contractor to EPRI, took the ITI models and modified them to match actual plant initial and boundary conditions, and then performed post-test analyses. The results were presented to the ACRS by EPRI on January 14,1981. Some further refinements were made to the models by El and the results were printed in the May 1983 issue of Nuclear Technology (Reference (11)).
l As stated in the BG&E Topical Report, the model which served as the starting point for i
BG&E was an L6-5 RETRAN-01 model supplied by El. This was the original RETRAN LOFT model created for EG&G (documented in Reference (10)). When comparing the BG&E model to the El model, we are really only comparing the modifications BG&E and El cach made to the original L6-5 model. The models were found to be similar, with only a few significant differences. The basic geometry and material detall are nearly identical.
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The only important exception is the inclusion of heat slabs in the BG&E model pressurizer (an option not available to El at the time they modified the ITI models).
The control systems are also similar. Although the ordering of the control cards is somewhat different and some trip actions have slightly different set points, the fundamentals of the control systems are the same. (Additional detall will be given on secondary controls in our answer to question 15.)
Boundary conditions and initialization schemes are slightly different. BG&E and El both chose to input primary system pressure in the pressurizer (El used 2144 psla and BG&E used 2142 psla). The BG&E model input primary pressure and temperature Information l l
ATTACHMENT l'
RETRAN REVIEW - ADDITIONAL INFORMATION (June 1987) into the Hot Leg volume 31; whereas, the El model input temperature into the Cold Leg volume 46. Both models had secondary pressure and temperature input to the Steam Dome volume 61 (BG&E used 779 psia and 610 F with a mixture level of 2.0 feet, while El used 0
779 psia and 600 F with a mixture level of 1.7 feet). No steady state equilibrium outputs i
were available to BG&E using the El input. The BG&E method results in a steady null transient equilibrium response.
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- 15. Verify the slip impact on secondary swell level by plotting results with an infinite bubble rise model in the steam generator secondary side. Compare the results from an infinite bubble rise model with results from a single node secondary side model.
Explain significantly greater depressurization ar.d why the main steam flow control valve (MSFCV) was open 40% longer than the test, and provide the transient curve of experimental and predicted flowrates. Describe the control system which governs the MSFCV operation in the experiment and how this was simulated by RETRAN. The depressurization computed by RETRAN was 50-60% larger than the test result, therefore, it appears to be not merely due to 40% longer opening of the MSFCV.
Response
The L6-3 transient was rerun without slip and used only the bubble rise models to provide phase separation. The level calculated is presented as Figure A15-1. The liquid level is calculated as an equivalent liquid level for the composite of volumes 75 and 61. For the slip case, af ter MSFCV closure, fluid drains rapidly from the steam dome volume 61 to the riser volume 62. The no-s!!p case does not allow the fluid to drain properly and so liquid mass is retained in volume 61. The equivalent liquid level calculation finds less mass in the composite volume for the slip case and results in a lower (and more accurate) level calculation. A single node secondary model does not accurately predict the level.
The significantly greater primary depressurization seen in the L6-1 simulation is principally due to the pressurizer modeling and not to any effects from the seconpagy.
The L6-1 pressurizer model uses a very high value for the IHTC (27500.0 BTU /HR-FT - F) in order to correctly calculate the rising pressure, liquid level, and spray effectiveness.
As stated in the BG&E Topical Report, this modeling gives good results for rapid insurge transients. Unfortunately, the L6-1 transient has a rapid pressurizer insurge followed by an equally ryd outsurge. For rapid outsurge transients, small values of IHTC (e.g.,400.0 BTU /HR-FT - F) are more appropriate. RETRAN does not allow a varying IHTC.
The large value of IHTC used to properly calculate the insurge conditions caused excessivt energy transfer from the steam space. This resulted in a lower pressure which caused too much pressurizer liquid to flash during the depressurization/outsurge portion of the 3
transient. This resulted in a greatly depressed Pressurizer Pressure. Tpis effect was l
verified by rerunning the L6-1 transient with a value of 10.0 BTU /HR-FT - F for IHTC.
Pressurizer Pressure and Level results have been plotted and are attached as Figures A15-l 2 and A15-3. As shown in these figures, pressure and (to a lesser extent) level more closely track plant data during the outsurge portion og the transient than the original calculation which used an IHTC of 27500 BTU /HR-FT - F.
However, with the lower values of IHTC, pressure and level are poorly modeled during the insurge, causing a r ggt g glgn high pressure to occur at 11.6 seconds (about 10 seconds earlier than g -
ATTACHMENT RETRAN REVIEW - ADDITIONAL INFORMATION (June 1987)
The model used for the BG&E Topical Report represents a compromise which, because of its importance, was biased toward accurately predicting the time of reactor trip. A model using a modified MSFCV control system was run to establish the effect of the 40% longer opening of the MSFCV on the depressurization.
The result indicated no change in calculated pressure when the difference in MSFCV open time was reduced by 50%
The principal element of the LOFT secondary side model is the MSFCV. The MSFCV operates automatically to provide SG overpressure protection and to limit primary system cooldown af ter a reactor trip. The valve opens and closes at a stem rate of 5% per second. The valve will begin to close should pressure drop below 920 psig and a reactor trip has occurred. The valve stops closing when pressure climbs to 930 psig. If the steam pressure reaches or exceeds 1020 psig, the valve will start opening. The valve will stop opening when pressure drops below 1010 psig. The control system used in the BG&E RETRAN LOFT model accurately reproduces this design behavior.
Stem position is converted to flow area using data supplied in the base L6-5 decl<. This relationship is also shown in Table 2 of Reference (10).
As stated, the MSFCV position is driven by a simple open or stop-open, close or stop-close logic based on reaching certain secondary pressure setpoints. The data reported in our BG&E Topical Report was based on using design setpoints from all our control systems. In many cases, the use of a setpoint slightly lower or higher than the design value, but still within the range of instrument or measurement uncertainty, will result in substantial differences in the sequence and timing of events.
The sensitivity of the LOFT results to variations in setpoints was not examined for the BG&E Topical Report. However, by carefully examining the figures for MSFCV valve position and secondary pressure as given in BG&E Topical Report Reference 40, doubt is cast on the design values for MSFCV operation. It appears that the " actual" setpoints were as follows: start opening 1017 psia, stop opening 984 psla, start closing 958 psia, stop closing 966 psia. L6-1 was rerun with these setpoints and secondary pressure is shown in Figure A15-4. Since all the setpoints are for lower pressures, the sequence of MSFCV actions have been accelerated in time.
Although no further sensitivities were examined, we believe that RETRAN would better reproduce the LOFT secondary pressure curves by using setpoints between the original design values and the above " actual" values. The best result would be obtained by lowering the start opening setpoint sufficiently to show the reopening of the MSFCV seen in the test data. This is what El did for their LOFT analyses presented in Nuclear Technology (attached Reference (11)). As requested, the mass flow rate through the MSFCV is plotted against test data for the original L6-1 analysis and is shown in Figure A15-5.
- 16. (LOFT-6-3) Modeling of the secondary side appears to be inadequate (see Figure 6.4-1, 2, and 5), causing primary side behaviors to differ from the test data. Explain and justify the secondary side modeling including a thorough explanation of why RETRAN calculates i
"somewhat higher terminal steam flow and feedwater flow."
i 1
1 - -
ATTACHMENT RETRAN REVIEW - ADDITIONAL INFORMATION (June 1987)
Response
RETRAN very accurately calculates Hot Leg Temperature as seen in Figure A16-1. BG&E Topical Report Figure 6.4-5 gives an unrealistic impression-of the accuracy of the RETRAN calculated L6-3 primary temperatures.
Steam generator primary side inlet plenum temperature was presented because it was the first primary side temperature presented in the LOFT data book (BG&E Topical Report Reference 40). There are many possible influences on the SG inlet plenum temperature which could cause it to lag behind Hot Leg Temperature. The placement of the measuring instrument in the LOFT facility is one example.
Another possibility is the local effects due to the proximity to the downcomer and tube regions.
Pressurizer Pressure was improved by adding the TTDT option (20 mesh intervals). The revised Pressurizer Pressure calculation is shown in Figure A16-2. Given the accurate calculation of Hot Leg Temperature and Pressurizer Pressure, we conclude that the RETRAN model adequately calculates primary system parameters.
The L6-3 SG levelis also predicted quite well. The BG&E Topical Report Figure 6.4-2 was plotted by hand from RETRAN output data. The spike at 50 seconds is explained in detall in the BG&E Topical Report.
The figure exaggerates the spread in the data by representing it as a crisp line that swings down and up. A more accurate representation of the data has been plotted and presented as Figure A16-3. As can be seen, there are many possible curve fits to this data.
In the BG&E Topical Report calculation for L6-3, MFW and steam flow were allowed to attain the highest possible terminal value indicated in the LOFT data report (Figures 35-3 4
and SC-1 of BG&E Topical Report Reference 40) - about 4 lbm/s of feedwater and 1.5 i
Ibm /s steam at 200 seconds. It was recognized after the calculation that this feed flow value may not have been realistic since the feed pump discharge pressure (Figure 5S-4 of Reference 40) was given as zero. L6-3 was rerun using a more probable 0.5 lbm/s feedflow with results indicating no change in system response. This was expected since steam flow controls secondary pressure and primary to secondary heat transfer. The true steam flow i
is unknown since the flow indication seems to have pegged low and the MSFCV position (Figure 55-1) is obscured by its uncertainty band. Rather than using an iterative process to find an MSFCV position which will give an exact reproduction of LOFT results, we simply state that reduced steam flow in the RETRAN calculation would increase the rate of secondary repressurization, better matching the LOFT data.
17.
With respect to BG&E general analysis of the LOFT tests, BG&E selected two transients i
that were initiated on the secondary side. Since BG&E did not accurately model the secondary events, the primary response may be incorrectly computed. Develop secondary controls and input which accurately represent the transients conducted in the LOFT test.
Rerun these computations to obtain a valid comparison of RETRAN results with LOFT test data.
t,
i
ATTACHMENT RETRAN REVIEW - ADDITIONAL INFORMATION (June 1987)
Response
4 The answers to questions 15 and 16 include discussions of additional sensitivity runs for both transients L6-1 and L6-3. Any improvements in calculating pressures, temperatures, or levels were presented in the answers to those questions. Attached as Tables A17-1 and A17-2 are revised sequences of events for the LOFT transients which were generated during the aforementioned sensitivity runs. Improvements to those sequences of events can be attributed to minor changes in the RETRAN control setpoints i
)
1.
ATTACHMENT RETRAN REVIEW - ADDITIONAL INFORMATION (June 1987)
REFERENCES 1.
Letter from Mr. C. O. Thomas (NRC), to Mr. T. W. Schnatz (UGRA), dated September 4, 1984, Acceptance for Referencing of Licensing Topical Report EPRI CCM-5, "RETRAN -
A Program for One Dimensional Transient Thermal-Hydraulic Analysis of Complex Fluid -
Flow Systems" 2.
Letter from Mr. L. 3. Agee (EPRI), to Mr. C. O. Thomas (NRC), dated December 20,1984 3.
Letter from Mr. T. W. Schnatz (UGRA), to Mr. C. O. Thomas (NRC), dated February 4, 1985, RETRAN - A Program for Transient Thermal-Hydraulic Analysis of Complex Fluid Systems 4.
Lance 3. Agee (EPRI), "RETRAN Overview," Nuclear Technology, January 1987, Vol. 76.
5.
Thomas L. Temple (Middle South Services),"RETRAN Generic Review - A Retrospection,"
Nuclear Technology, January 1987, Vol. 76 6.
BG&E Topical Report A-85-11, RETRAN Computer Code Reactor System Transient Analysis Model Qualification, T.
L. Cook, S.
M. Mirsky, and G. R. Wisniewski, January 31,1986 7.
N. A. Smith, VEP-FRD-41, "VEPCO Reactor System Transient Analyses using the RETRAN Computer Code," March 1981.
8.
Letter to W. L. Stewart (VEPCO) from Cecil O. Thomas (NRC), dated April 11, 1985, Acceptance for Referencing of Licensing Topical Report VEP-FRD-41 9.
I. E. idel'Chik, Handbook of Hydraulic Resistance, AEC-TR-6630,1960 10.
EG&G Idaho, EGG-LOFT-5161; Best Estimate Predictions for LOFT Nuclear Experiments L6-1, L6-2, L6-3, and L6 Experiment Prediction Analysis Report, October 31,1980 11.
Miller, et al"RETRAN-02 Calculations of Operational Transients in the Loss-of-Fluid Test Facility," Nuclear Technology, May 1983, pp.181-192 12.
Baltimore Gas and Electric Company Calvert Cliffs Nuclear Power Plant Unit 1 Startup Test Report August 29,1975...
Table A-17-1 Sequence of Events for Experiment L6-l*
Time After Experiment Initiation
.RETRAN Time RETRAN Time Event seconds (seconds)
Sensitivity Run MSFCV Closing Initiated 0.0 0.0 0.0 Pressurizer Backup Heaters Off 6.1 11 7.07
- 7.07 0
11 9.47 9.47 Pressurizer Spray On 9.1 0
f 12 11.61 11.61 MSFCV Closed 11.6 0
12 17.67 18.8 Reactor Scrammed 21.8 0
Maximum PCS Pressure Reached 22.0 + 0.2 18 19.0 22.
18.61 22.1 MSFCV Opened 22.2 0
12 25 27.5 QSG < 9 core **
26.5 0
12 21.46 21.46 0
Pressurizer Spray Off 30.4 Pressurizer Backup Heaters On 32.5 11
.23.8 23.8 0
12 43.23-42.0 MSFCV Closed 40.6 0
MSFCV Opened 91.2 12 0
12 MSFCV Closed 104.4 0
Only the first 200 seconds are presented.
Pressurizer liquid level at maximum.
- RETRAN did not predict this event.
i i
-.2
Tabla A-17-2 Sequence of Events for Experiment L6-3*
RETRAN Time Event LOFT Time RETRAN Time Sensitivity Run MSFCV Opening 0.0 0.0 0.0 Feedwater Flow Increased 1.412 0.0 *
- 0.0 Pressurizer Backup Heaters On 10.2 11 0.0 0.0 Maximum Reactor Power 15.6 12 14.18 15.53 Reactor Scrammed 15.612 14.18 15.53 Feedwater Flow Terminated 16.6 12 15.0 16.6 MSFCV Start Closing 17.812 15.0 15.53 HPSI Pump A On 26.4 12 18.5 24.13 HPSI Pump B On 26.612 18.5 24.13 Minimum PCS Pressure Reached 26.812 30.5 31.0 QSG < O 33 1 1 32.25 33.0 core MSFCV Closed 36.212 34.00 36.0 HPSI Pump A Off 48.612 44.14 48.15 HPSI Pump B Off 50 12 44.14 48.15 Pressurizer Backup Heaters Off 105.4 11 Pressurizer Cycling Heaters Off 154.9 11 Only events occurring in the first 200 seconds of the LOFT Test are presented.
RETRAN Feedwater was delivered by a fill junction designed to match the LOFT data.
Pressurizer liquid level at minimum.
RETRAN did not predict this event.
FIGURE AS-l (June 1987)
OCTOBER 11,1983 EVENT COMPARISON CORE THERM AL POWER WITH MAIN STEAM FLOW POWER 15 0
~
=
CORE POWER MAIN STEAM FLOW POWER I
10 0
'N k
's L
's E
Ns <>
~
ADV OPEN i>
N TSV CLOSED I,
2 i,
l" PEAK SRV FLOW J
I 4
li 2
g Eg gs SRV CLOSED b
50 14
\\
I'I
\\
O
\\
l s
j I
\\
sh ',
s E
f
\\
\\
i>
g
\\
TSV CLDSED g
ii ADV CLOSED g
g OPEN TBV ISOLATED
\\
g
\\~~,,
7.,-3
,..7.-
O loo 200 300 360 TIME (SECONDS)
FIGURE A5-2 (June 1987)
~
OCT 11,1983 EVENT COMPARISON OF INDIVIDUAL SG FEEDWATER FLOW RATES WITH HALF OF TOTAL STEAM FLOW RATE 1.7 i
i N\\
j FW 21 N
o o o o RW 22 N
HALF STEAM I
I I
'\\
4I \\
6
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o o o o o o o o o 'o'o'o "5 o o Fo o o ovo7 o T o o 5tr Q 0 o o
O i
i i
i i.
i O
10 0 200 300.
TIME (SECONDS)
FIGUTE A5-3 OCT II,1983 EVENT COMPARISON OF INDIVIDUAL SG FEEDWATER FLOW RATES WITH TOTAL STEAM FLOW RATE 3.4 3
_ _- s i
sN FW 22 g
\\
3-s oooooo FW 21
\\
Tomt. STEAM
)
1 I
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' '===== - - - - - - -
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0 10 0 200 300 TIME (SECONDS) si
o l
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13 5
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n (3.)annivaadwal dool saa
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l i
FIGURE A-10-2 ONE PUMP COASTDOWN PRESSURIZER PRESSURE RESPONSE 2500 PLANT DATA i
2400 RETRAN RETRAN REVISED 4
g 2300 ADV/TBV/TSV
~ ~%.
' - 5' h.
0 2200 N~.N.b i
o s~
0 y
=.
21 0 0 2200 1900 0
10 20 30 40 50 60 TIME (SECONDS)-
O w
9
d N
i FIGURE A lO-3 ONE PUHP COASTDOWN PRESSURIZER LEVEL RESPONSE 300 PLANT DATA 250 RETRAN
^
RETRAN REVISED l0
^#/*/*
200
~~. 7 I
~ ~ _-,,, %, N v
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~~~~~~_%--.*5-.,__
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9 I
t i
1 I
l FIGURE A-10-4 ONE PUHP COASTDOWN STEAM GENERATOR SECONDARY SIDE PRESSURE RESPONSE 950 PLANT DATA
.N RETRAN i
925 N,\\
RETRAN REVISED ADV/TBV/TSV y
s m
900 -
o
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~
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=
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=>
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/P 'i 825 800 50 60 0
10 20 30 40 TIME (SECONDS)
I l
FIGURE Al21 (June 1987) 6 NORMAL
- 230
.___.. TRAC 5.75-RETRAN W/ CHARGING o o o o RETRAN W/0 CHARGING
- 220 5.50-
- 210 5.25-1A
\\t \\ $\\ l\\
-200 i i V
- s l '$oii;M j V V V
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1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000 TIME (S) l PRESSURIZER COLLAPSED LIQUID LEVEL, CASE 2.
FIGURE Al2 2 (June 1987)
COOLDOWN TO RHR ENTRY - PRUtARY AND SECONDARY PRESSURE RESPONSE 16 RETRAN 2100 000000 RETRAN W/ CHARGING 12 0
1400 a.
0 E
8 PRIMARY s
700 SECONDARY 0
O O
2000 4000 6000 8000 10000 12000 Time (s)
O 1
FIGURE Al2 3 (June 1987)
COOLDOWN TO RHR ENTRY - HOT LIG TEMPERATURE RESPONSE f
o 600 600
...... R ETR AN TRAC 000000 REVISED ADI 550 MODEL 520 44o
- F
'K SCO 360 450 280 400 0
2000 4000 6000 8000 10000 12000 Time (s)
. 1 l
l 1
FIGURE A-I3-I 2$o000
.Sooooo leer 4 2ecoco-Lamps N
--- RETRAN
- mosos 1
I
'N' noooo. 1 2
i
-30000o I NOTE: These tronsienis i
assumed multiple i
20000-operator / equipment f allures. See TABLE I.
-2conos i
t
e-~~~.*
googg.
..oooo 4
I o
3000 4000 sooo sooo 7000 sooo o
1000 200o O
Trne (s)
Fig. B.9.
Steam generator mass inventory--Runaway MFW to one SG from FP.
MM
,co..n
.-2000 soo-ma
-oso lll
RETRAN 7eo-.
l 9
m.
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)
i l
-ase 4,
8"~
3 l
NOTE: These transients
~
5 d
l ossumed multiple t
l operator /. equioment f
a 400-
}
f ailures. See TABLE I.
n 300- I ;;
j
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i 20o -
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soo.co.00 2000 Trne (s)
Fig. B.10.
Steamline mass flow--Runaway M7W to one SG from FP.
245 i
0
FIGURE A-15-1 LOFT TEST L6-3 LIQUID LEVEL IN STEAM GENERATOR SECONDARY SIDE 0.5 f,
i nfi WIDE RANGE j
1 RETRAN
.I 1
l O O O O.
NO SLIP I
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~
l 1
FIGURE A.15 2 LOFT TEST L6-1 PRESSURE IN PRESSURIZER 16.0
\\
TEST DATA g
i RETRAN g
I I J i lHTC 10.0 TRAPCENT STOPPED l
AT 100 SECONDS 4
Ij l l[ il
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I 118 -
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1 l
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LIQUID LEVEL IN TRESSURIZER l
1.5 TEST DATA 4.s j
RETRAN il
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4
FIGURE A-IS-4' LOFT TEST L6-1 PRESSURE IN STEAM GENERATOR DOME 8
6 6
s TEST DATA RETRAN
$ CTUAL SECONDARY
~
SETPONTS USED
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i FIGURE A 16-2 LOFT TEST L6-3 PRESSURE IN PRESSURIZER 16
=
U
~
TEST DATA RETRAN
-=
TEMR TRANSPORT DELAY MODEL 2200 15
. g. _ _ _
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-50 0
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- 130 -
e FIGURE A-16-3 1.M T TEST L6-3 LIQUID LEVEL IN STEAM GENERATOR SECONDARY SIDE 0.5 i\\
./ !
WIDE RANGE
,! 1 RETRAN l
AAAA DATA POINTS.
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