ML20079Q282

Bounding Analytical Assessment of NUREG-0630 on LOCA & Operating Kw/Ft Limits

ML20079Q282
Person / Time
Site:	Davis Besse
Issue date:	05/06/1983
From:	BABCOCK & WILCOX CO.
To:
Shared Package
ML20079Q276	List: ML20079Q273 ML20079Q282
References
RTR-NUREG-0630, RTR-NUREG-630, TASK-2.K.3.30, TASK-TM 77-1142162, 77-1142162-00, TAC-45817, NUDOCS 8305110443
Download: ML20079Q282 (28)

Text

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BOUNDING ANALYTICAL ASSESSMENT CF NUREG 0630 ON LOCA AND OPERATING kW/FT LIMITS B&W Document No.: 77-1142162-00 BABCOCK & WILCOX Utility Power Generation Division P. O. Box 1260 Lynchburg, Virginia 24505 8305110443 830506 PDR ADOCK 05000346 Babcock & Wilcox P PDR . m e....n ......,

CONTENTS Pace

1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1

2.

SUMMARY

AND CO NCLUS ION . . . . . . . . . . . . . . . . . . . . . . 2-1 2.1. Impact on LOCA Limits ................... 2-1

2. 2. Impact on Operating Limits of Cycle 4 of Davis-Besse . . . . 2-1

3. IMPACT OF NUREG-0630 ON LOCA LIMITS ............... 3-1 3.1. Method of An alys i s . . . . . . . . . . . . . . . . . . . . . 3-1

3. 2. Base Case ......................... 3-1 3.3. Resul t s and Di scu s sion . . . . . . . . . . . . . . . . . . . 3-2 4 IMPACT OF NUREG-0630 ON NORMAL OPERATING TECHNICAL SPEC IF IC ATION L IMITS . . . . . . . . . . . . . . . . . . . . . . . 4-1 4.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4-1 4.1.1. Co re El eva ti on . . . . . . . . . . . . . . . . . . . 4-1 4.1. 2. Burnup Dependencies ................ 4-2 4.2. Impact on Operating Limits of Cycle 4 of Davis-Besse . . . . 4-3 4.3. Operational Considerations . . . . . . . . . . . . . . . . . 44

5. R EF E R E NC E S . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1 l

List of Tables l l'

Table 3-1. NUREG-0630 LOCA Limit Impact at 2 ft Core Elevation 8.55 ft2 DEPO, CD = 1.0 . ................... 3-S 3-2. 177-FA Lowered-Loop Plant LOCA Limits for BOL . . . . . . . . . 3-6 4-1. LOC A kW/ f t C ri t e ri a . . . . . . . . . . . . . . . . . . . . . . 4-5

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List of Figures Figure Page 3-1. B&W Model and ORNL Correlation of Rupture Temperature as a Function of Engineering Hoop Stress and Ramp Rate . . . . . . . 3-7 3-2. B&W THETA Model and Composite NUREG Correlation of Circum-ferential Burst Strain as a Function of Rupture Temperature . . 3-8 3-3. B&W Model and Composite NUREG Correlation of Reduction in Assembly Flow Area as a Function of Rupture Temoerature . . . . 3-9 34 Hot Spot Clad Tempe rature Vs Time . . . . . . . . . . . . . . . 3-10 4-1. Axial Power Shapes Compared to LOCA Limits .......... 4-5 4-2. LOCA Limit Effect on Permissible Axial Dower Shapes . . . . . . 4-6 4-3. 80C and EOC Axial Power Shace Comparison ........... 4-7 4-4 Steady State Power Peak Vs EFPD . . . . . . . . . . . . . . . . 4-8 4-5. Four Pump Operating Limits, Davis-Besse Cycle 4 NUREG-0630. . . 4-9 4-6. APSR Position Limits, Davis-Besse Cycle 4 NUREG-0630. . . . . . 4-10 4-7 Imbalance Limits, Davis-Besse Cycle 4 NUREG-0630 ....... 4-11 l

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1. INTRODUCTION During a postulated loss-of-coolant accident (LOCA), when the reactor coolant pressure drops below the fuel rod internal pressure, the fuel cladding may swell and rupture for particular conbinations of strain, fuel rod internal pressure, cladding temperature, and material properties of the cladding.

Reactor thermal and hydrodynamic behavior during a LOCA depend on the type of accident, the time at which swelling and rupture occur, and the resulting coolant flow blockage.

Appendix K requires that the cladding swelling and rupture calculations shall be based on applicable data in such a way that the degree of swelling and in-cidence of rupture are not underestimated. In order to establish an industry data base, the NRC has sponsored several research programs on cladding behav-ior during and after a LOCA. NUR EG-06301 is based on this research. It con-tains revised models for cladding rupture, strain and blockage during and following a LOCA which differ from present B&W evaluation models. The NRC re-quires compliance to NUREG-0630.

This study was undertaken to determine the impact of NUREG-0630 on LOCA lim-its and plant operating technical specification limits for B&W raised-loop 177-fuel assembly plant operating at 2772 MWt. This report summarizes the re-sults of this analysis for the Davis-Besse plant with specific operating lin-its for the Davis-Besse cycle 4 reload.

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2.

SUMMARY

AND C0fCLUSION 2.1. Imoact on LOCA Limits An ECCS bounding analysis was perfomed to detemine the impact of the NUREG-0630 on B&W 177-FA raiseed-loop Davis-Besse plant operating LOCA lim-its. The most limiting break size and location used for this analysis was an 8.55 ft2 double-ended cold leg break at the RC pump discharge with a dis-charge coefficient of 1.0. The LOCA limit was evaluated for the 2 ft core elevation, as previous experience has demonstrated this core elevation to be the most sensitive with respect to clad swelling and rupture phenomena.

A 2 ft LOCA limit analysis was perfomed at 15.5 kW/ft. No mid-bl owdown rup-ture occurred. Therefore, since NUREG-0630 primarily af fects the ruptured node, the impact due to NUREG-0630 was not realized. It should be noted that evaluations between the two LOCA limits of 16.5 kW/ft (reported in BAW-10105 2 ) and 15.5 kW/ft were not perfomed. Since NUREG-0630 and TAC 023 were implemented simultaneously, the detemination of the respective LOCA limit impacts have been based upon engineering judgment and analysis per-fomed on the 177-FA lowered loop plants. The resulting impact due to TAC 02 has been estimated to be a 0.5 kW/ft reduction from the 16.5 kW/ft LOCA limit reported in BAW-10105. An additional 0.5 kW/ft reduction due to NUREG-0630 established the revised 2 f t LOCA limit for the Davis-Besse plant at 15.5 kW/ft.

The impacts at the other lower core elevations are based upon both the re-sults of this analysis at the 2 ft elevation and the results of the TAC 02 177-FA lowered-loop LOCA limit analysis.4 It is estimated that the 4 ft and 6 ft LOCA limits reported in BAW-10105 will not be affected by the implenenta-tion of TACO 2, but will be affected by the implementation of NUREG-0630. The interim LOCA limits are considered to be valid at the 4 ft and 6 ft eleva-tions (16.8 kW/ft and 18.0 kW/ft, respectively), as these elevations have been shown to be ruptured - node sensitive.

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The LOCA limits at the 8 ft and 10 f t elevations are limited by the unrup-tured node temperature, and enough margin exists such that NUREG-0630 and TACO 2 will not impose any affect at these elevations.

The analysis was performed for the BOL conditions at which the average fuel temperature is at its maximum value. At higher burnups the lower fuel temper-ature will compensate for the impact of NUREG-0630 and no penalty will be re-qui red. A summary of the LOCA limits is given in Table 4-1. It should be noted that the revised LOCA limits at the 4, 6, 8 and 10 ft elevations were based on the results of the 2 ft analysis and conclusions drawn from the TAC 02 177-FA lowered-loop analysis.

2.2. Impact on Operating Limits of Cycle 4 of Davis-Besse The implementation of the NUREG-0630 limits would impact only the imbalance limits, restricting the negative imbalance by 2.5". The control rod and APSR position limits would not be affected by cycle 4.

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3. IMPACT OF NUREG-0630 AND TAC 02 ON LOCA LIMITS 3.1. Method of Analysis The analytical metnoos usec in the study are tne same as those descriced in I the B&W ECCS evaluation nodel topicals, BAW-10104, Rev. 3 5ex cep*. f o r the l

modifications due to NL' REG-0630 and TAC 02 which are explained in section 3.2.

1 3.2. Base Case A bounding analysis inclementing NUREG-0630 ructure data and f 3CL) MCO2 fuel data was perfomed at the 2 ft core elevation. The 2 ft core elevation was chosen based on the results of the 177-F A LL TAC 02 LOCA limits analysis ahich showed the LOCA limit at the 2 ft elevation to be the most sensitive with re-spect to the TAC 02 fuel model.

The assumptions for establishing the base case for the 177-FA RL analysis were detemined by drawing conclusions from similar studies performed for the 177-FA lowered-loop plants. The following conclusions have been assumed:

1. The TACO 2177-F A LL LOCA limit analysis, which re-analyzed the three worst break cases reported in BAW 10103, found the worst break type to be the same as that reported in BAW-10103 (8.55 ft ,2 DEPD, CD = 1.0).

Since the LOCA limit analysis for the 177-FA RL plant reported in BAW-10105 shows the 8.55 2ft , DEPD, CD = 1.0 case to be the most limit-ing, it is estimated that the implementation of TAC 02 and NUREG-0630 would not alter the worst break type.

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2. The TAC 02177-F A LL LOCA limits analysis showed the greatest impact to exist at the 2 ft core elevation. It was, therefore, estimated that the implementation of TACO 2 for the 177-FA RL analysis would, similar to the lowered-loop analysis, show the greatest LOCA limit impact to exist at the 2 ft core elevation.

From the above stated conclusions it was estimated that the impact analysis, due to NUREG-0630 and TACO 2, should be performed by modeling an 8.55 ft DEPD, CD = 1.0 break at the 2 ft core elevation. The ECCS base case used for this analysis was the same as that used for the S AW-10105 analysis with modifica-tions due to NUREG-0630 rupture data and inclementation of TAC 02 fuel data.

The modifications due to NUREG-0630 are as follows:

1. The NUREG-0630 rupture temperature as a function of engineering hoco stress correlation with a heating ri a of 0 C/s, shown in Figure 3-1, was used. This ramp rate represents a btunding value for rupture data.

2. The NUREG-0630 strain versus temperature data is contained in a fast and a slow ramp rate correlation. The circumferential strain model, Figure 3-2, used in the analysis bounds the composite of the slow and the fast ramp models.

3. The NUREG-0630 coolant flow blockage data, Figure 3-3, is derived from burst strain data and, therefore, also bounds the composite of the slow and fast ramp models.

Inputs to the CRAFT 2 6 code are stress versus rupture temperature data and blockage based on the reduction in flow area data. Inputs to the THETA 1-87 code are stress versus rupture temperature data and maximum rod circumferen-tial strain data to maximize metal-water reaction. The methodology for im-plementing the tac 02 code is described in section 4.2.2 of reference 4 3.3. Results and Discussion Table 3-2 summarizes the results of the LBLOCA analysis with the bounding values of NUREG-0630 compared to the base case as reported in BAW-10105. The maximum clad temperatures were cal culated to be 1887.1 F ar,1 1747.2 F for the unruptured and ruptured nodes, respectively. These results are based on a 15.5 kW/ft limit at the 2 ft elevation.

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l l The LOCA limit penalty, due to the implementation of NUREG-0630 and TAC 02, with respect to the 16.5 kW/ft limit reported in BAW-10105 was determined to be 1.0 kW/ft. Penalties of 0.5 kW/ft were attributed to both NUREG-0630 and TAC 02. These respective LOCA limit penalties were estimated based upon con-clusions drawn from a similar 177-FA lowered loop NUREG-0630 analysis. The lowered-loop NUREG-0630 analysis determined the maximum NUREG-0630 impact to

! be 0.5 kW/ft. It is estimated that the maximum lowered-loop NUREG-0630 penal-ty should also apply to the 177-FA raised loop plant. Thus, one half of the l 1.0 kW/ft penalty has been attributed to NUREG-0630. The resulting 0.5 kW/f t i has been attributed to the use of TACO 2 fuel parameters.

I The NUREG-0630 and TAC 0 impacts at the 4, 6, 8, and 10 ft elevations for the l

177-FA raised-loop plant have been estimated based upon the results of the l 177-FA lowered loop (TACO 2 and NUREG-0630) analyses, and the results of this analysis at the 2 ft elevation.

Previous analyses have shown that the LOCA limits at the lower core eleva-tions (2, 4, and 6 ft) are limited by the time of rupture and the rupture node temperature, whereas the LOCA limits at the upper core elevations are limited by the unruptured node temperature. Since NUREG-0630 impacts the rup-tured nede, the LOCA limits at the upper core elevations are not expected to be affected by NUREG-0630, whereas the LOCA limits at the lower core eleva-tions are expected to be affected by NUREG-0630, whereas the LOCA limits at the 8 and 10 ft elevations are not.

The lowered-loop analysis showed no LOCA limit penalty to exist at the 4, 6, 8, and 10 ft elevations as a result of the implementation of TAC 02. It is estimated that the implementation of TACO 2 to the raised loop plant would, similar to the lowered-loop analysis, result in no LOCA impact at the 4 through 10 ft elevations.

. is estimated that since NUREG-0630 impacts the ruptured node temperature, the 177-FA RL LOCA limits at the 4 ft and 6 ft elevations are not affected more than the LOCA limit at the 2 ft elevation. Therefore, the interim LOCA limits are considered to be valid at the 4 ft and 6 ft elevations (16.8 kW/ft and 18.0 kW/ft, respectively), as these elevations have been shown to be rup-1 tured node sensitive. The LOCA limits at the 8 and 10 ft elevations are re-qui red.

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Due to the burnup def endence of the average fuel temperature, the lower fuel temperatures at higher burnups will compensate for the affects of NUREG-0630 and TACO 2. It has been estimated that the LOCA limits can be restored to their original values after a burnup of 1000 mwd /mtU as shown in Table 3-1.

A summary of the latest 177-FA raised-loop plant LOCA analysis showing the in-pact of TACO 2 and NUREG-0630 separately is shown in Table 3-2.

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Table 3-1. 177-FA Raised-Loop Plant LOCA Limits for BOL l

Core elevation, ft 2 4 6 8 10 BAW-10105 limits, kW/ft 16.5 17.2 18.4 17.5 17.0 Impact of NUREG-0630 with TAC 02 -1.0* (-0.4) (-0.4) ( 0) ( 0) 15.5 16.8 18.0 17.5 17.0 Note: LOCA limits for 4 and 6 ft elevation can be restored to 16.5, 17.2, and 18.4 kW/ft, respectively, after a burnuo of 1000 mwd /mtU.

• It is estimated that the impact for TACO 2, if taken alone is 0.5 kW/ft at the 2 ft core elevation.

( ) Extrapolated by comparison with TAC 02 impacts on 177 F A lowered-loop plants and the 1.0 kW/ft calculated penalty at the 2 ft core elevation.

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Table 3-2. NUREG-0630 LOC A L Elevation 8.55 f tgmit Impact DEPD, CD =at 1.02 ft Core Base Case BAW-10105 NUREG-0630 CRAFT run T0416J8 ACLYEKS, ACLYAVI THETA 1-B Run T116IAX AD4IHQA CRAFT, kW/ft 16.5 15.5 THETA 1-B , kW/ft 16.5 15.5 Peak temperature, F, unruptured 2057.0/ 1887.1 F/

node / time, s 37.5 29.0 Peak temperature, F, ruptured 2135.0/ 1747.2 F/

node / time, s 40.5 39.5 Rupture time, s 13.12 23.0 End of blowdown, s 24.9 22.5 End of adiabatic heatup, s 34.1 31.9 Maxinun local oxidation, % 4.01 1.54%

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4. IMPACT OF NUREG-0630 ON NORMAL OPERATING TECHNICAL SPECIFICATION LIMITS 4.1. Introduction 4.1.1. Core Elevation Control rod position, APSR position, and imbalance alarm limits are estab-lished to prevent the LOCA kW/ft criteria from being exceeded during nornal operation. Figure 4-1 shows how this is accomplished. The Interim LOC A kW/ft limit is shown as a function of axial height along with typical SCC axial power shapes which include all of the uncertainties normally applied in defining the Technical Specification Limits. The uncertainties and their ap-plication are described more fully in section 4 of Topical Report BAW-10122.

l It should be noted tnat the radial peaking factors which these shap9s inher-ently include are cycle dependent. The nominal axial power shape represents hot f ull power steady-state conditions. When something occurs to shift the power toward the bottom of the core (a more negative imbalance) such as APSR withdrawal, control rod insertion, xenon shift, etc., the power shape changes from the nominal . The limits on imbalance and rod position are defined when the shape reaches the LOCA kW/ft criteria as shown in Figure 4-1.

The values of the LOCA kW/ft criteria used in the analysis of the NUREG-0630 impact on operation are given in Table 4-1. The LOCA kW/ft limit at the 2 ft elevation is the most influential in determining the operational impact for two reasons. First, moderator temperature effects on reactivity and control rod insertion from the top of the core cause the core to have a greater pro-pensity toward large negative imbalances than toward large positive imbalanc-es. As Figure 4-1 shows, the power is shifted toward the 2 ft elevation and away from the higher elevations at the limiting negative imbalance condition.

Secondly, due to the value of the 1.0CA limit at the 4 ft and higher eleva-tions being significantly higher than the value at the 2 ft elevation, the 4-1 Babcock & Wilcox

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distance between the limit and the axial power shape is less for the 2 ft ele-vation. This generally ensures that the limiting condition will be caused by a power distribution wnose peak reaches the LOCA kW/ft limit at or near the 2 ft elevation, while some distance remains between the power shape and the limit for all other, higher elevations.

The effect of a reduction in the LOCA kW/ft criteria is shown in Figure 4-2.

The limiting power shape as defined by the NUREG-0630 LOCA criteria is more restricted than that defined by the present Interim LOCA criteria. To fur-ther restrict the power shapc to meet the tighter LOCA criteria, the allow-able control rod position, APSR position, and/or imbalance must be further restricted.

4.1.2. Burnuo Decendencies For a given period in cycle life, the initial conditions for the LOCA are pre-served by a set of Technical Specification limits consisting of full length control rod position, Axial Power Shaping Rod position, axial imbalance, and quadrant power tilt limits. B&W presently furnishes a minimum of three dif-ferent sets of these limits to cover the entire cycle. The applicability of each set is for a specific range of EFPDs. The present interin LOCA limits require the first set to cover from 0 to 50 EFPD. Other sets are provided which cover 50 EFPD to middle-of-cycle and middle to end-of-cycle. As dis-cussed in section 3, NUREG-0630 only impacts the LOCA kW/ft criteria for fuel burnups below 1.000 mwd /mtU. As shown in the BOL and EOL comparison in Figure 4-3, burnup generally reduces the power peaking. This decrease in peaking is illustrated in another form in Figure 4-4, which shows the total peak from the nominal depletion versus EFPD. The nominal peak, representing the gener-al trend in present fuel cycles, is highest in the first 25 EFPD. This type of burnup dependent peaking behavior contributes to the fact that the first set of limits is the most restrictive.

The NUREG-0630 LOCA limits, if implemented, would replace the Interim Limits.

The main difference between these two sets of limits is a 0.5 kW/ft reduction at the 2-ft level. In cycle 4, the limiting assemblies exceed 1000 mwd /mtu at about 25 EFPD. After 25 EFPD (aoproximately) FAC LOCA limits would be valid. This is typical for most reloads, whether L3P or out-in shuffle pat-terns are used.

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4.2. Impact on Operating Limits of Cycle 4 of Davis-Besse Estimated rod index, APSR and imbalance coerating limits are shown in Figures 4-5, 4-6, and 4-7 for Davis-Besse, cycle 4 The solid lines in these figures represent limits based on the Interim LOCA kW/ft limits, and the dashed lines those based on NUREG-0630 LOCA kW/ft limits. The implementation of the NUREG-0630 limits would impact only the imbalance limits, restricting the negative imbalance by 2.5%. All limits shown in these three figures are pre-liminary as the reload analysis for cycle 4 is currently in progress.

4.3. Operational Considerations The general impact of the reduced LOCA kW/ft limits is the reduction in the imbalance limits as discussed above. This results in a loss in operational fl exibil ity. Since insertion of the regulating rods forces the core imbal-ance to become more negative, the alarm limit will be approached as the rods insert. Therefore, the regulating rod position must be controlled more care-fully to maintain axial imbalance within the more restrictive limits.

This will in turn increase feed and bleed requirements. Since NUREG-0630 only impacts very low burnup fuel, this increase will be small because the higher critical boron concentration at BOL, when the fuel is fresh, requires less bleed volume exchange to change reactivity by a given amount. The types of operation affected will include large load reduction transients, runbacks and subsequent power escalation, and power escalation after a reactor trip or extended shutdown.

The use of NUREG-0630 limits would allow the final acceptance criteria kW/ft limits to be used earlier than the current interin kW/ft limits do. These wider limits would become effective at about 25 EFPD.

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Table 4-1. LOCA kW/ft Criteria Core elevation, NUREG-0630 Interim ft 0-1000 mwd /ntu 0-50 EFPD FAC 10 17.0 17.0 17.0 8 17.5 17.5 17.5 6 18.0 18.0 18.4 4 16.8 16.8 17.2 2 15.5 16.0 16.5 Babcock & Wilcox 4-4 * "co=="2 ce='*av

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l S. REFERENC ES 1 D. A. Powers and R. O. Meyer, " Cladding Swe1 ling Models for LOCA Analysis,"

NRC Report NUREG-0630, April 1980.

2 W. L. Bloomfield, et al. , "ECCS Evaluation of B&W's 177-FA Raised-Loco NSS, BAW-10105, Rev. 1, Babcock & Wil cox, July 1975.

3 TAC 02 - Fuel Pin Perfomance Analysis, BAW-10041, Babcock & Wilcox, August 1979.

4 M. A. Haghi, et al. , " TACO 2 Loss of Coolant Accident Linit Analyses for 177-FA Lowered Loop Plants," BAW-1775, February 1983.

5 B. M. Dunn, et al. , "B&W's ECCS Evalut ticn Model," BAW-10104, Rev. 3, Babcock & Wilcox, August 1977.

6 J. J. Cudlin, M. I. Meerbaum, " CRAFT 2 - Fortran Program for Digital Simula-tion of a Multinode Reactor Plant During Loss of Coolant," NPGD-TM-2B7, Rev. AA. Babcock & Wilcox, Lynchburg, Virginia, June 1982.

7 R. H. Stoudt, et al. , " THETA 1-B - Computer Code for Nuclear Reactor Thermal Analysis," NPGD-TM 405, Rev. L, Babcock & Wilcox, Lynchburg, Vi rginia, March 1982.

5-1 Babcock & Wilcox

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