ML20076L580

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

ML20076L580
Person / Time
Site:	Crane
Issue date:	07/14/1983
From:	GENERAL PUBLIC UTILITIES CORP.
To:
Shared Package
ML20076L576	List: ML20076L574 ML20076L580
References
RTR-NUREG-0630, RTR-NUREG-630 NUDOCS 8307190238
Download: ML20076L580 (18)

Text

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1' BOUNDING ANALYTICAL ASSESSMENT OF l

NUREG 0630 MODELS ON LOCA kW/ft LIMITS 2.

9 m

• "w-f m

y

CONTENTS Page 1.

I NTR OD UC T IO N..........................

1-1 2.

SUMMARY

AND C0fC LUS ION...............

2-1 3.

METH O D OF A NAL YS I S.......................

3-1 4

RESULTS OF ANALYSIS 4-1 4.1.

Impact of NUREG-0630 on LOCA Limits 4-1

4. 2.

Impacts of NUREG-0630 With FLECSET on LOCA Limits 4-2 R EF E R E NC E S...........................

A-1 List of Tables Table 4-1.

LOCA Limit NUREG-0630 Impact Sensitivity Study at 2-ft Core Elevation, 8.55-ft2 DEPD, CD = 1.0 4-4 4-2, 177-FA Lowered-Loop Plant LOCA Limits 4-5 List of Figures Figure 4-1.

Large Break Analysis Code Interfaces 4-6 4-2.

B&W Model and ORNL Correlation of Rupture Temperature as i

a Function of Engineering Hoop Stress and Ramp Rate.....

4-7 4-3.

B&W THETA Model and Composite NUREG Correlation of r

f Circumferential Burst Strain as a Function of Rupture l

Temperature.........................

4-8 t

4-4.

B&W Model and Composite NUREG Correlation of Reduction in I

Assembly Flow Area as a Function of Rupture Temperature...

4-9 4-5.

Hot Spot Clad Temperature Vs Time With NUREG-0630 -

l 13.5 kW/ft at 2-ft Core El evation..............

4-10 l

4-6.

Hot Spot Clad Temperature Vs Time With NUREG-0630 and FLECSET - 14.0 kW/f t at 2-ft Core Elevation.........

4-11

- iii -

1.

INTRODUCTION During a postulated loss-of-coolant accident (LOCA), when the reactor cool-ant pressure drops below the fuel rod internal pressure, the fuel cladding may swell and rupture for particular combinations of strain, fuel rod inter-nal pressure, cladding temperature, and material properties of the clad-ding.

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

Appendix K of 10 CFR 50.46 requires that the cladding swelling and rupture calculations be based on applicable data in such a way that the degree of swelling and incidence of rupture are not underestimated.

In order to es-tablish an industry data base, the NRC has sponsored several recearch pro-grams on cladding behavior during and after a LOCA.

NUREG-06301 is based on this research.

It contains revised models for cladding rupture, strain, and blockage during and following a LOCA which differ from present B&W eval-uation models.

Irch utility. with a B&W designed NSS was requested to provice ' supplemental ECCS calculations assessing the impact of NUREG-0630 models.

A. study was j

l undertaken to detennine the impact of NUREG-0630 implementation on LOCA limits for B&W lowered-loop 177-fuel assembly plants operating at power levels up to 2772 MWt.

The FLESSET reflood heat transfer correlation was also used. as a compensating model to offset any NUREG-0630 LOCA kW/ft limit penalty.

l-1-1 i

i

be sufficient margin to satisfy the 2200F limit required by 10 CFR 50.46.

Therefore, no LOCA limit penalty is imposed at the 8-and 10-ft core eleva-tions.

For the 6-ft core elevation, however, the peak ruptured node clad-ding temperature 2 was calculated to be 2090F, There may not be enough clad temperature margin to neet the 2200F requirement of 10 CFR 50.46.

Use of FLECSET may not produce a sufficiently low peak clad temperature to compen-sate the 0.5 kW/ft' penalty on the LOCA limit at the 6-f t core elevation.

The 4 through 10-ft LOCA limtis, based on NUREG-0630 and the compensating model, FLECSET, are determined by comparisons to the results at the 2-ft core elevation and the case analyses.2 The analyses were performed for the beginning-of-life (80L) conditions at which the average fuel temperature is at its maximum value.

At higher burn-ups, the lower fuel temperature will result in a LOCA kW/ft margin when com-pared to BOL.

A summary of the key results at the 2-ft core elevation comparing the base case 2,3 with a case utilizing boundary NUREG-0630 models and a second case which included bounding NUREG-0630 models and use of FLECSET, is shown in Table 4-1.

The 177-FA lowered-loop plant LOCA limits at each elevation are listed separately in Table 4-2.

l l

2-2

W 2.

SUMMARY

AND CONCLUSION An ECCS bounding analysis was performed to determine the impact of the NUREG-0630 on B&W 177-fuel assembly (FA) lowered-loop plants operating LOCA limits.

The break analyzed was an 8.55-f t2 double-ended cold leg rupture at the RC pump discharge with a discharge coefficient of CD = 1. 0 The LOCA limit was calculated for the 2-ft core elevation.

Previous experience has demonstrated this core elevation to be the most sensitive with respect to clad swelling and rupture phenomena which are affected by the NUREG-0630 model s.

The implementation of bounding NUREG-0630 models without the use of compen-sating models will result in a 0.5 kW/ft penalty on the LOCA limit at the a

2-ft elevation.

NUREG-0630 mainly affects the LOCA limits of the lower core elevations which are limited by the ruptured node temperatures.

The 0.5 kW/ft penalty was also assigned to the LOCA limits at the 4-and 6-ft el evations.

The. LOCA limits at the 8-and 10-ft elevations are limited by the unruptured node temperature, and enough margin between the peak calcu-lated temperature and the 2200F limits exists that use of NUREG-0630 models will not impose any penalty at these elevations.

Implementation of bounding NdREG-0630 models with the FLECSET reflood heat transfer correlation as a compensating model resulted in a kW/ft penalty on the LOCA limit at the 2-ft core elevation.

An engineering assessment was performed for the 4 through 10-ft LOCA limits.

For the 4-ft core eleva-tion, there is no penalty due to the implementation of NUREG-0630 for the following reasons:

(1) based on previous LOCA analyses 2, the peak ruptured node cladding temperature was calculated to be 1899F; therefore, sufficient margin ~ exists to meet the 10 CFR 50.46 criteria of 2200F, and (2) the FLECSET compensating model results in a higher allowable kW/ft limit, thus L

'resulting in no impact to the LOCA limit at the 4-ft core elevation For i

the 8-and ft core elevations, the peak ruptured node cladding tempera-

. ture2 was found to be 1664 and 1560F, respectively.

There is considered to 2-1

3.

METHOD OF ANSLYSIS The analytical methods used in the study are the same as those described in the B&W ECCS evaluation model topicals, BAW-10103A, Rev. 34 and BAW-10104, 5

3, except for the modifications due to NUREG-0630 and FLECSET imple-Rev.

mentation which are explained in the foll owing paragraphs.

Figures 4-2 through 4-4 show the NUREG-0630 bounding parameters.

The major impact on the base case LOCA limit analysis 2, was the implementa-tion of the NUREG-0630 data in the ECCS large break evaluation model.

The modifications due to NUREG-0630 are:

1.

The NUREG-0630 rupture temperature as a function of engineering hoop stress correlation with a heating ramp of 0*C/s, shown in Figure 4-2, was used.

This ramp rate represents a bounding value for rupture data.

2.

The NUREG-0630 strain versus temperature data are contained in a fast and a slow ramp rate correlation.

The circumferential strain model, Figure 4-3, used in the analysis bounds the composite of the slow and the fast ramp models.

3.

The NUREG-0630 coolant flow blockage data, Figure 4-4, is derived from burst strain data and, therefore, also bounds the conposite of the slow and fast ramp models.

Inputs to the CRAFT 26 code are stress versus rupture temperature data and blockage based on the reduction in flow area data.

Inputs to tt.s THETAl-8 7 code are stress versus rupture temperautre data and maximum rou circumferen-tial strain data to maximize metal-water reaction.

All other input re-mained the same as the base case LOCA limit analysis.2 Two analyses were performed at the 2-ft core elevation to determine impact on the peak clad temperature due to both the implementation of NUREG-0630 3-1

bounding models and use of the FLECSET heat transfer correlation.

Previous analyses 4,5 have demonstrated that the 2-f t core elevation is the most sen-sitive with respect to clad swelling and rupture phenomena.

The first case used the large break LOCA ECCS model, Figure 4-1, from reference 2 with NUREG-0630 bounding data as input to the CRAFT 26 and THETAl-8 7 models.

The second case empl oyed the san CRAFT 2 and REFLOD modals but replaced the FLECKA correlations wi th the FLECSET model.

A new THETAl-B case was then a,alyzed at 14.0 kW/ft.

Case 1 CRAFT 26 was run at 14.0 kW/ft for the 2-ft core elevation.

REFLOD, FLECKA, and THETAl-B7 were also run at 14.0 kW/ft but did not succeed due to the ex-ceedingly high ruptured node peak cladding temperatures that resulted from the use of the NUREG-0630 models.

Both FLECKA and THETAl-B were again run 13.5 kW/ft and succeeded with a ruptured node peak cladding temperature at below the 2200F limit required by NRC criteria 10 CFR 50.46 Case 2 In an effort to reduce or eliminate the 0.5 kW/ft penalty from the implemen-tation of NUREG-0630, a computer code called FLECSET,9, developed to pre-8 dict the quench time and heat transfer coefficient for cosine and skewed power shapes, was used as a compensating mode.

FLECSET was run at 14.0 kW/ft using input on flooding rates obtained from the first bounding anal-ysis case.

An analysis using THETA 1-8 7 was perfonned to generate the hot channel response at the 14.0 kW/ft LOCA limit.

The peak cladding tempera-ture was compared to the 10 CFR 50.46 limit of 2200F. to determine accepta-bility.

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RESULTS OF ANALYSIS 4.1.

Impact of NUREG-0630 on LOCA Limits The results of this anlaysis are summarized and compared to the base case large break LOCA analysis in Table 4-1.

The maximum clad temperature was calculated as 1736 and 1692F for the ruptured and unruptured nodes, respec-tively, as shown in Figure 4-5.

These results are based on a kW/ft limit of 13.5 at the 2-f t elevation, which represents a reduction from the 14.0 kW/ft in the base case.

A LOCA case was examined at a 13.8 kW/ft limit at the 2-ft elevation but cladding temperatures fail ed to remain below the 2200F -limit when including the impact of NUREG-0630 in the analysis.

Previous analyses 4,5 have shown that the LOCA limits at the lower core ele-vations are limited by the time of rupture and the rupture node tempera-ture.

Since the NUREG-0630 impacts mainly the rupture node clad tempera-ture, the LOCA limits at the upper core elevations are not expected to be affected more than the LOCA limit at the 2-ft elevation.

Therefore, the re-sidual impact at the 2-ft elevation can be assigned to LOCA limits at the other core elevation.

As stated above, the NUREG-0630 impact was 0.5 kW/ft at the 2-ft elevation.

The LOCA limits at the 4-and 6-ft elevation can be conservatively reduced-by 0.5 kW/ft to reflect the effect 'of NUREG-0630.

The LOCA limits at the 8-and 10-ft elevations are limited by the unruptured node temperature and are not greatly affected by NUREG-0630 Also, the maximum clad tempera-tures for currently calculated LOCA limits at the 8-and 10-ft elevations l

are significantly lower than the 2200F limit which provide additional mar-gin for the effect of NUREG-0630 Therefore, the impact of NUREG-0630 will not require a reduction of LOCA limits at the 8-and 10-ft core elevations.

l 4-1

Finally, due to the burnup dependency of the average fuel temperature, the lower fuel temperature at higher burnups will compensate for the impact of NUREG-0630 It has been estimated that the LOCA limits can be restored to their original values after a specified burnup as shown in Table 4-2, 4.2.

Impacts of NUREG-0630 With FLECSET on LOCA Limits The results of this analysis are summarized and compared to both the base case 2 and NUREG-0630 case 1 analysis in Table 4-1.

The maximum clad temper-ature for the case using NUREG-0630 and FLECSET was calculated to be 1847 and 1809F for the ruptured and unruptured nodes, respectively, as shown in Figure 4-6.

These results were calculated based on a 14.0 kW/ft limit at the 2-ft core elevation.

As stated in section 4.1, there was an impact of 0.5 kW/ft for the 2, 4,

and 6-ft core elevations due to the implementatin of NUREG-0630

However, based on the results obtained from the analysis using NUREG-0630 with the FLECSET heat transfer correlation, no LOCA impact has been found at the 2-ft core elevation.

This is. because of the higher heat transfer coef-ficients generated by the FLECSET compensating model, which in turn re-sulted in a higher allowable kW/ft limit.

A 0.5 kW/ft NUREG-0630 penalty was assigned in case 1 to the 4-and 6-ft core elevations.

These elevations are also kW/ft limited by the ruptured node temperatures..The peak cladding temperature results at these respec-tive elevations were reviewed considering the improved heat transfer pre-dicted by FLECSET.

For the 4-ft core elevation, there is no impact on kW/ft limits due to the implemenation of NUREG-0630 and FLECSET for the following reasons:

(1) based on the results of reference 2, the peak rup-tured node cladding temperature was calculated to be 1899F; therefore, suf-ficient ma~rgin exists to meet the 10 CFR S0.46 criteria of 2200F, and (2) the FLECSET compensating model.is expected to a result in a higher' allow-

'i able kW/ft limit, thus resulting in no impact to the LOCA limit at the 4-tt core elevation.

However, for the 6-ft core elevation, the peak ruptured node cladding temperature was calculated to be 2090F.

There may not be enough clad temperature margin to meet the 2200F requi rement of 10 CFR 50.46 Use of F,LECSE T may not produce a sufficiently low peak clad temperature to compensate the 0.5 kW/ft penalty on the LOCA limit at the 4-2 9

4 6-ft core elevaticn.

For the 8-and 10-ft core elevations, the peak rup-

.tured node cladding temperature 2 was found to be 1664 and 1560F, respective-ly.

There is sufficient clad temperature margin to satisfy the 2200F limit required by 10 CFR 50.46 Therefore, there is no penalty on the LOCA limit ai the 8-and 10-ft core elevations as given in BAW-10103A, Rev. 3.4 9

4 4

b 4

1 4-3

Table 4-1.

LOCA Limit NUREG-0630 Impact Sensitivity Study at 2-ft Core Elevation, 8.55-ft2 DEPD, CD = 1.0 Base case 2 Case 1(a)

Case 2(b)

CRAFT run AD4ICLD AD4IDWU AD41DWU REFLOD3 run AD4IBKD AD4IVUS AD41VUS THETA 1-B run AD4ICCA AD41EVW AEKIBull CRAFT, kW/ft 14.5 14.0 14.0 TilETAl-8,1.0CA limi t 14.0 13.5 14.0 Peak temperature, 'F, un rup-1843/43.5 1692/42.5 1809/37.0 tured node / time, s Peak temperature, F, rup-1934/43.5 1736/42.0 1847/37.3 tured node / time, s Rupture time, s 21.6 22.6 17.9 End of blowdown, s 25.2 24.8 24.8 End of adiabatic heatup, s 36.0 35.5 35.5 Maximum local oxidation, %

2.14 1.52 1.67 CRAFT 2 blockage, %

58.8 67.65 67.65 (a) Case 1 includes the impact of NUREG-0630 bounding models.

(b) Case 2 includes the impact of NUR.EG-0630 bounding models and the use of FLECSET heat transfer correlation.

4-4

Table 4-2, 177-FA Lowered-loop Plant LOCA Limits Core elevation, ft 2

4 6

8 10 B AW-10103 LOCA limits,4 kW/ft 15.5 16.6 18.0 17.0 16.0 TACO 2 impact,2 kW/ft

-1.5 0

0 0

0 Base case limits,(a) kW/ft 14.0 16.6' 18.0 17.0 16.0

• NUREG-0630 impact, kW/ft

-0.5

-0.5

-0.5 0

0 Case 1(b) (base case + NUREG-0630), kW/ft 13.5 16.1 17.5 17.0 16.0

• FLECSET-of fset, kW/ft

+0.5

+0.5 0

0 0

Case 2(C) (base case + NUREG-0630 +

14.0 16.6 17.5 17.0 16.0 FLECSET), kW/ft (a)The 2-ft LOCA~ limit can be restored to 15.5 kW/ft after a burnup of 1000 mwd /mtU.

(b)LOCA limits for 4-and 6-ft core elevations can be restored 18.0 kW/ft, respectively, after a burnup of 1000 mwd /mtU.

The 2-ft LOCA limit can be increased to 15 kW/ft after a burnup of 1000 mwd /mtu and restored to 15.5 kW/ft after a burnup of 2600 mwd /mtU.

(c)The 2-and 6-ft LOCA limit can be restored to 15.5 and 1 respectively, after a burnup of 1000 mwd /mtu.

4, 4-5

Figure 4-1.

Large Break Analysis Code Interfaces INITIAL RC SYSTEM &

CORE PARAMETERS INITIAL CORE PARAMETERS lf I CRAFT MASS & ENERGY RELEASE CORE RESPONSE DURING BLOWDOWN if II. CONTEMPT CONTAINMENT PRESSURE

RESPONSE

STORED ENERGY CONTAINMENT VESSEL if

'I BACK PRESSURE gy GENERATE III

• FLECHT h(t)

REFLOD 3 FLOODING REFLOOD HEAT TRANSFER if if

'I COEFFICIENTS V THETA HOT CHANNEL RESPONSE Y

br a

pa ECHT SEASE correlation (FLECSET Code) l i f HOT PIN THERMAL RESPONSE SURFACE i

4 HEAT TRANSFER COEFFICIENT HOT CHANNEL FLUID TEMPERATURE METAL-WATER REACTION 4-6

Figure 4-2.

B&W Model and ORNI Correlation of Rupture Temperature as a Function of Engineering Hoop Stress and Ramp Rate 1200-1100-1000-o

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B&W THETA Model and Composite NUREG Correla ion of Circumferential Burst a

Strain as a Function of Rupture Temperature 120-i 100 Composite J

80' NlREG

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0630 Values g

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B&W Model and Composite NUREG Correlation of Reduction in Assembly Flow Area as a Function of Rupture Temperature 100--

B&W 80-

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NUREG E

1 0630 Values 20-1 0-600 700 8b0 900 1000 1100 1200 Temperature, C t

Figure 4-5.

Hot Spot Clad Temperature Vs Time With NUREG-0630 -

13.5 kW/ft at 2-f t Core Elevation 1000

/s

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20 40 60 80 100 120 Time, s I

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Figure 4-6.

Hot Spot Clad Temperature Vs Time With NUREG-0630 and FLECSET - 14.0 kW/ft at 2-ft Core Elevation 2000 n

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4 1600 i

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REFERENCES 1.

D. A.

Powers and R. O. Meyer, Cladding Swelling Models for LOCA Anal-ysis, NRC Report NUREG-0630, April 1980, 2.

M.A.

Haghi, et al., TACO 2 Loss-of-Coolant Accident Limi t Analyses fo r 177-FA Lowered-Loop Plants, BAW-1775, Babcock & Wil cox, Lynchburg, Virginia, February 1983, 3.

TAC 02 - Fuel Pin Performance Analysis, BAW-10141P, Babcock & Wi l cox,

Lynchburg, Virginia, August 1979 4.

B.

M.

Dunn, et al.,

ECCS Analysis of B&W's 177-FA Lowered-Loop NSS, BAW-10103A, Rev. 3, Babcock & Wilccx, Lynchburg, Vi rginia, July 1977.

5 B.

M.

Dunn, et al.,

B&W's ECCS Evaluation Model, BAW-10104, Rev.

3, Babcock & Wilcox, Lynchburg, Virginia, August 1977 6.

J. J. Cudlin and M.

I. Meerbaum, CRAFT 2 - FORTRAN Program for Digital Simulation of a Multinode Reactor Plant During Loss of Coolant, NPGD-TM-287, Rev. AA, Babcock & Wilcox, Lynchburg, Virginia, June 1982.

7 R.

H.

Stoudt, et al.,

THETA 1-B - Computer Code for Nuclear Reactor l

Thermal Analysi s, NPGD-TM-405 Rev.

L, Babcock - & Wilcox, Lynchburg, Virginia, March 1982.

- 8.

N. Lee, S. Wong, H. C Veh, and L. E. Hochreiter, "PWR FLE CHT SEASET Unblocked Bundle, Forced and Gravity Reflood Task Data Evaluation and i

Analysis Report, NUREG/CR-2256 (EPRI NI-2013 or WCAP-9891), November 1981.

l

'9.

G. P. Lilly, et al., PWR FLECHT Skewed Profile Low Flooding Rage Test Series Evaluation Report, WCAP-9183, November 1977 A-1 t

.