Stability Boiling Office of - nrc.gov

ENCLOSURE

ORNL/NRC/LTR-87/08

Contract Program: Selected Operating Reactors Issues

Subject of Document: Stability Calculations for theGrand Gulf-1 and Susquehanna-2 Boiling Water Reactors

Type of Document: Technical Evaluation Report

Author: Jose March-Leuba

Date of Document: August 1987

Date Published: September 1987

NRC Monitor: T. L. Huang, Office of NuclearReactor Regulation

Prepared forU.S. Nuclear Regulatory Commission

Office of Nuclear Reactor Regulationunder

DOE Interagency Agreement 0544-0544 A1NRC FIN No. A9478, Project 2

Prepared byInstrumentation and Controls Division

OAK RIDGE NATIONAL LABORATORYoperated by

MARTIN MARIETTA ENERGY SYSTEMS, INC.for theU.S. DEPARTMENT OF ENERGY

under Contract No. DE-AC05-840R21400

LIST OF FIGURES.

TABLE OF CONTENTS

Page

LIST OF TABLES ~ ~ ~ ~ ~ ~ viiINTRODUCTION1.1 Objectives1.2 Main results

111

2. GRAND GULF-1 CALCULATIONS2.1 Beginning-of-cycle calculations

2. 1. 1 Modelled conditions2.1.2 Results

2.2 End-of-cycle calculations2.2.1 Modelled conditions2.2.2 Results

2.3 Sensitivity study

2337

12121519

3. SUSQUEHANNA-2 CALCULATIONS3.1 Modelled conditions3.2 Results

232325

4. DISCUSSION OF RESULTS 25

REFERENCES 29

APPENDIX A. SAMPLE LAPUR INPUTS ~ 31

APPENDIX B. DESCRIPTION OF MODELLED OPERATING CONDITIONS 43

LIST OF FIGURES

FigurePage

Degree of control, radial power, and axial powerdistributions for test control GGTP4 . . . . . . . . . 5

2 ~

3.

Calculated close-loop reactivity-to-power transferfunction for test 'point GGTP4 . . . . . . . . . . . . 9

Calculated closed-loop reactivity-to-power transferfunction for test point GGTP4 . . . . . . . . . . . . 10

Measured core-plate-pressure-drop-to-power transferfunction for test point GGTP4 . . . . . . . . . . . . 11

5. Degree of control, radial power, and axial powerdistributions for end-of-cycle conditions modelledin Grand Gulf-1 . . . . . . . . . . . . . . . . . . . 13

6.

7 ~

Comparison between closed-loop reactivity-to-powertransfer functions of test point GGTP4 calculatedfor beginning and end-of-cycle conditions. . . . . . . 17

Comparison between open-loop power-to-void-reactivitytransfer functions of test point GGTP4 calculated forbeginning and end-of-cycle conditions . . . . . . . . 18

8. Calculated constant-decay-ratio lines for end-of-cycleconditions in Grand Gulf-1 . . . . . . . . . . . . . 21

9. Calculated closed-loop reactivity-to-power transferfunction for test point SUSTLO . . . . . . . . . . . . 26

10.

A.l. LAPURX sample input~est GGPT4

A.2. LAPURW sample input~est GGTP4

A.3. LAPURX sample input Zest SUSTLO

A.4. LAPURW sample=-input Zest, SUSTLO

Calculated open-loop power-to-void-reactivitytransfer function for test point SUSTLO 27

33

35

38

40

B.l.

BE 2.

Degree of control, radial power, anddistributions for test point GGTP1

Degree of control, radial power, anddistributions for test point GGTP2

axial power

axial power

45

46

B.3.

B.4.

B. 5.

Degree of control, radial power, and axial powerdistributions for test point GGTP4

Degree of control, radial power, and axial powerdistributions for test point GGTP6

Degree of control, radial power, and axial powerdistributions for test point GGTPB

47

48

49

B.6. Degree of control, radial power, and axial powerdistributions for 8 x 8 fuel in test point SUSTLO. . . 50

B.7.

B. 8.

B.9.

Degree of control, radial power, and axial powerdistributions for 9 x 9 fuel in test point SUSTLO.

Degree of control, radial power, and axial powerdistributions for 8 x 8 fuel in test point SUSSLO.

Degree of control, radial power, and axial powerdistribitions for 9 i 9 fuel in test point SUSSLO.

51

52

53

TableLIST OF TABLES

Page

1. Modelled operating conditions for beginning of cyclein Grand Gulf-1

2. Calculated density reactivity coefficients for beginningof cycle in Grand Gulf-1 . . . . . . . . . . ... . . . 7

3. Comparison between measurements and LAPUR calculationsfor beginning of cycle in Grand Gulf-1

4. Calculated density reactivity coefficients for beginningof cycle in Grand Gulf-1 . . . . . . . . . . . . ~ ~ . 15

5. Comparison between LAPUR calculations for beginning andend of cycle in Grand Gulf-1 . . . . . . . . . . . . . 15

6. Sensitivity of decay ratio to input parameters ofbeginning-of-cycle calculations for Grand Gulf-1 . . . 19

7. Sensitivity of decay ratio to input parameters of end-of-cycle calculations for Grand Gulf-1 . . . . . . . . 20

8. Sensitivity to power and flow for end-of-cycle conditionsin Grand Gulf-1 . . . . . . . . . . . . . . . . . . . . 22

9. Modelled operating conditions for beginning of cycle inSusquehanna-2 . . . . . . . . . . . . . . . . . . . . . 24

10. Calculated density reactivity coefficients for beginningof cycle in Susquehanna-2 . . . . . . . . . . . . . . . 24

11. Comparison between measurements and LAPUR calculationsfor beginning of cycle in Susquehanna-2 . . . . . . . . 25

1. INTRODUCTION

The objective of the present report is to document the results ofa series o f stability calculations per formed using the code

LAPUR-IV for various conditions in the Grand Gulf-1 and

Susquehanna-2 boiling water reactors (BWRs). The main purpose ofthese calculations was to verify whether LAPUR could reproduce

accurately the results obtained during two recent stability testsconducted on these two reactors. In addition, calculations have

been performed for end-of-cycle (EOC) conditions in the Grand

Gulf-1 reactor.

Satisfactory agreement was found between test data and thecalculated stability margins for both reactors. In both tests,the measured decay ratios were low, ranging between 0.2 and 0.4.The calculated values fell within that range and followed trendssimilar to those of the measured values. At one point, though,it was expected that these tests would serve as an open-

literature benchmark case for LAPUR and other codes; however,

given the low-decay-ratio values obtained from the tests,extrapolations of code accuracy at higher values cannot be made

with high confidence. Within this context, we have tocharacterize the results of the present benchmark as

inconclusive.

1n addition, EOC conditions were analyzed for the Grand Gulf-1reactor based on data supplied by System Energy Resources, Inc.(SERI), and the Advanced Nuclear Fuels Corporation (ANF). The

results of the LAPUR modelling of these conditions show that the

Grand Gulf-1 reactor should be stable at the EOC but with a

significantly reduced stability margin as compared with beginningof cycle. For instance, with the nominal conditions of testGGTP6, the LAPUR code calculates a decay ratio (DR) of 0.89 atEOC compared with 0.42 at beginning of cycle. Note, though, thatthe conditions used for the EOC calculations are veryconservative. Based on our engineering judgment, we would notexpect DRs higher than 0.7 should a new series of tests be

performed at the EOC.

1

'

2. GRAND GULF-1 CALCULATIONS

Two sets of LAPUR calculations were performed for the Grand Gulf-1 reactor. The first set corresponds to the operating conditions .

of the stability tests performed at the beginning of cycle 2 on

January 31, 1987. The objective of the second set ofcalculations was to predict the stability of this reactor under

EOC conditions, which were expected to be more unstable.

:.For all these calculations, we relied sonl nuclear and:-'operating-

data .supplied';;;by:,ANF'and.'SERI;;" Input: data, for'he beginning-'of-':: ",

cycle calculations '.are'ar;more reliable;than data .for EOC,:.

because we obtained measurements of the actual operatingconditions during the tests. Nevertheless, there are some

concerns about the accuracy of these input data; in particular,it is well known that flow instrumentation is highly conservative

(and as such, inaccurate) at flow conditions close to naturalcirculation. ~ No attempt has been made to correct the measured

flows for these calculations; thus, the calculated values of the

DR for the lower flow conditions should be expected to be

conservatively high (i.e., the actual values are expected to be

lower).

2.1 Be innin -of-c cle ca culations

2.1.1 Modelled conditionsThe second reload core of Grand Gulf-1 contains 800 fuelassemblies of which 80 are "Type 3" General Electric (GE) 8 x 8

fuel assemblies with 2% Gd, 456 are "Type 7" GE 8 x 8 assemblies

with 5% Gd, and the remaining '264 assemblies are "Type 8" ANF

8 x 8 assemblies. The average exposure of the GE fuel was

approximately 104 MWd/MT, while all the ANF fuel was freshlyloaded and had an approximate exposure of 500 MWd/MT at the timeof the tests.

The radial dependence on power and thermohydraulic

characteristics has been modelled by grouping the 800 assemblies

into six representative channel types. Appendix A contains the

radial power distributions for all the runs, along with the axialdependence of the thermal power and the percentage of controlrods inserted. A representative case for the beginning of cyclecalculations is presented in Fig. 1, which corresponds to testpoint GGTP4 (59% power, 39% flow). It can be observed in thisfigure that, for these beginning-of-cycle conditions, the axialpower shape is fairly uniform and symmetrical. The radial power

distribution, although slightly skewed, shows that the value ofthe average radial peaking factor is less than 1. 2. These two

conditions, along with the high degree of control, which reduces

the density reactivity coefficient, imply that the calculated DRs

should be small.

Table 1 summarizes the operating conditions for the test points.Note that the values given in Table 1 for the flow are theprocess computer values, which are known to underestimate theactual flow at conditions close to natural circulation.

Testpoint

Table 1. Modelled operating conditions forbeginning of cycle in Grand Gulf-1

(MW) (Mlb/h) (psi) ('F) Gain r

GGTP1 1997 44.4GGTP2 2363 50 'GGTP4 2257 44.3GGTP6 1698 29.8GGTPB 1745 33.6

9921000

998986988

509509506498501

-0 '9-0 21-0 '9-0.82-0 '7

0.220 '60.22

-0 ~ 320 ~

28'he

pressure-drop to inlet-flow transfer function is"normalized-'-'. "

by gH/Wo, where''ore. height, Wo = core;;;flow;.~ = Time- constant in s ...

488GGTP4

488 68

ED

388E0

388

~ 288

188

~ 288x

18828

8.8 8.5 1.8 1.5RELATIVE PONER

8 5 18 15CONTROLLED CHANNELS (X)

8 8 8 5 1 8 1 5

RELATIVE POWER

(a) Axial power shape (b) Percentage ofcontrolled channels

(c) Radial power shape

Fig. 1. Degree of control, radial power, and axial powerdistributions for test point GGTP4.

Probably the single most important input parameter for these

calculations is the density reactivity coefficient (DRC). The

LAPUR code estimates a one-dimensional DRC from a two-group cross

section set as a function of void, fuel type, and degree ofcontrol. To calibrate this cross section set, keff calculationsare performed at nominal conditions and at similar conditionswith a +50-psi-pressure increase. The DRC calculated by LAPUR isadjusted by a multiplier to reproduce this calibration. For the

Grand Gulf-1 conditions, the calibration supplied by ANF

corresponded to case GGTP4. At nominal conditions, keff had a

value of 1.00994, with an average void fraction of 0.402354. At+50-psi-pressure conditions, keff increased to 1.01324, with a

decrease of average void fraction to 0.377856, yielding a DRC of13.47 measured in units of %ak/k per unit void change. The LAPUR

calculated value was 13.65 at nominal conditions and 13.16 at+50-psi conditions, which yields an average DRC of 13.41; thus,the DRCs had to be corrected by a factor of less than 0.54.,Table 2 presents the nominal-condition DRCs calculated by LAPUR.

Zt can be observed that the DRCs do not vary greatly between testpoints at the same fuel exposure and similar control rod

positions.

4

Table 2. Calculated density reactivitycoefficients for beginning of cycle in

Grand Gulf-1

Testpoint

Density reactivitycoefficient

(%ok/k / ap)

GGTP1GGTP2GGTP4

+50 psiGGTP6GGTPB

13. 3313.3413.6513.1613.1713.04

The LAPUR code requires a relatively large set of input data

describing the geometry and general characteristics of the

reactor. For completeness in the documentation of these

calculations, a typical input set (for case GGTP4} is presented

in Appendix A.

2.1.2 Results

The main results of these calculations are presented inTable 3, which contains a comparison between the measured and

calculated values of the DR and frequencies of oscillation.Overall, fair agreement has been obtained between the measured

and calculated numbers. For these comparisons, it is important

to realize that, in most cases, neither LAPUR calculations nor

the measurement technique of Ref. 1 has better than a single-digit resolution. Thus, for the small range of DRs observed inthe Grand Gulf-1 tests, we can only extract information about

trends. As long as the calculated DRs are low and the trends

correspond to the measured ones, good agreement has to be

assumed. In other words, the value of the Grand Gulf-1 tests forbenchmarking purposes is limited to the detection of only gross

errors in modelling technique.

Table 3. Comparison between measurements and LAPURcalculations for beginning of cycle in Grand Gulf-1

Test Power Flow Deca atmo atu a f e encpoint (4) (4) Measured LAPUR Measured LAPUR

GGTP6GGTPBGGTP4GGTP1GGTP2

0.350.370.320 '10 '2

44 27 0 '7 0 '546 30 0.40 0.3659 39 0.43 0.4052 39 0.44 0.4062 45 0.44 0.43

For illustration purposes, Figs. 2 and 3 present the calculatedclosed-loop and open-loop reactor transfer functions,respectively, for case GGTP4. Unfortunately, the noise

measurement technique (Ref. 1) for the Grand Gulf-1 tests does

not supply a similar transfer function for comparison. It'wasshown, however, in Refs. 3 and 4 that the transfer function from

the core-plate-pressure-drop signal to the average-power-range

(APRM) signal is related to the calculated transfer function.For purposes of comparison, Fig. 4 presents 'the measured core-.,

- plate-pressure!drop. to: APRM,transfer':function,"„iwh'ich sh'ows', a',"'structure .similar to the one:'in Fig. 2.

18

LVo

188zX

18 1FREQUENCY (Hz)

Fig. 2. Calculated closed-loop reactivity-to-power transferfunction for test point GGTP4.

9

18-1

18 2

-188

-278i8 2 18 1

FREQUENCY'(Hz)188,

Fig. 3. Calculated. open-loop. reactivity-'to-power transfer:,"';,;"function for. test point GGTP4.'l10

181z5

4.

4I

zCK

18-2

CtlfailW

8

-98218 IB

FRKOUENCY (HZ)

Fig. 4. Measured core-plate-pressure-drop-to-power transferfunction for test point GGTP4.11

2.2 End-of-c cle calculations

2.2.1 Modelled conditions

For these series of calculations, we had to rely on ANF's

predictions of operating conditions at the EOC. One of the main

sources of error for predictive stability calculations isprecisely the determination of the most unstable operatingconditions during the core cycle. In this calculation, we used

operating conditions corresponding to a reactor with all controlrods out and with mostly depleted fuel. The nominal power forthese calculations was approximately 60% and the flow 39%, which

are the conditions of test GGTP4 at beginning of cycle.

For the conditions supplied by ANF, the "Type 3" fuel (GE 8 x 8

with 24 Gd) had an average exposure of 1.2 x 104 MWd/MT, the"Type 7" fuel (GE 8 x 8 with 54 Gd) had an exposure of1.8 x 10 MHd/MT, and the "Type 8" fuel (ANF 8 x 8) had

104 MNd/MT of average exposure.

Figure 5 presents the axial and radial power shapes for thenominal EOC condition (604 power, 394 flow). It can be observed;

that both power shapes are heavily skewed. In particular, the;axial power shape is extremely bottom peaked. This fact'.increases the average void fraction in the core, which greatly-reduces; the reactor's stability margin.. The; radial peaking,», " ~

factor, .which is, as high as- 1'.'4", also .forces'ower stability,'--

12

488GGEOC4

8. 18 58

388

I- 288

~ ILI

188

8. 85C0

P. 00C3

UI

-8. 85

48

M38

UJ

28

18

8 -8. 188 8 85 1 8 1.5 -8 188 8%I . 888. 858. 18

RELATIVE POWER CONTROLLED CHANNELS (X)8.8 8.5 1.8 1.5

RELATIVE PONER

(a) Axial power shape (b) Percent,age ofcont, rolled channels


Fig. 5. Degree of control, radial power, and axial powerdistributions for end of cycle conditions modelled inGrand Gulf-1.

margins (i.e., higher DR). The fraction of controlled channels

is zero, and this increases the DRC, which also has a negativeeffect on the reactor stability.

The main cases analyzed corresponded to the power, flow,. pressureand inlet temperature conditions of the beginning-of-cycle tests(Table 1). We labeled these new conditions GGEOC1 throughGGEOC6, where the last digit indicates the corresponding testpoint conditions at beginning of cycle. Different axial orradial power shapes were not available for the several testcases. For that reason, the power distributions of the nominalcase (60% power, 394 flow) were used for all calculatedconditions at EOC. For the same reason, all of these

calculations were performed assuming no control rods inserted.

According to ANF's calculations for EOC conditions, keff was

1.00068 with an average void fraction of 0.474302. With a +50-

psi-pressure increase, keff changes to 1.0043 with a decreasein'oidsto 0.437054. These numbers imply that the value of the DRC,

should be 9.83 measured in units of 4k/k per unit void change.

Table 4 presents the LAPUR-calculated DRCs for operating powers

and flows equivalent to those of the stability. tests but",under

EOC conditions:.

Table 4. Calculated density reactivitycoefficients for beginning of

cycle in Grand Gulf-1

Testpoint

GGEOC1GGEOC2GGEOC4

+50 psiGGEOC6GGEOCB

Density reactivitycoefficient(%ok/k / ap)

9.389.389 '88.429 '19.28

2.2.2 Results

The main results of the EOC calculations are presented inTable 5, which contains the calcul'ated DRs and the natural

frequencies of oscillation for conditions similar to the ones

during the stability tests. For comparison, the LAPUR-

calculated numbers at beginning of cycle (Table 3) are also shown

in Table 5.

Table 5. Comparison between LAPUR calculationsfor beginning and EOC in Grand Gulf-1

Test Power Flowpoint (4) (4) EOC BOC EOC BOC

GGTP6GGTPBGGTP4GGTP1GGTP2

4446595262

2729393945

0.890 '00 '30.300 '2

0 '20 '20 '20 '80 '2

0 ~ 400 '20.510 '90.54

0 '50 '60 '00 '00 '3

aBOC = Beginning of cycle; EOC = End of cycle.

15

J

I

The comparison in Table 5 indicates that, as expected, conditionsat EOC in Grand Gulf will be more unstable than at beginning ofcycle. The DRs increase approximately by a factor of two, butstill the expected values are below 1.0, indicating stableoperation. The main reason for the increased value of the DR

seems to be the extremely bottom-peaked axial power shape.

,An interesting result of these calculations is that the average

DRC is lower at the EOC than at the beginning of cycle (Tables 2

and 4). This effect is caused by the averaging of severalchannel types: the DRC of the high-power fresh fuel is very high(approximately 30), while the DRC of some of the old fuel is

fnegative, because old fuel assemblies are so burned out that theybehave as if they had their control rods inserted. Due to thisdisparity of cross sections, this condition is rather hard tomodel. Although LAPUR performs an optimal adjoint weighingscheme to account for spacial void feedbacks, the result, for such

a nonhomogeneous core may have poor reliability.

Figures 6 and 7 present a comparison of the reactor transfer.functions for the conditions of test GGTP4 at the beginningversus the EOC. The main difference results on the higherresonance frequency and sharper phase break indicating that theEOC condition is the less .stable.

16„

181

IJICD

I

z 188

F

,-C C

18-1

IIOC,

-45

18 18 1

FREQUENCY (Hz)

Fig. 6. Comparisc.n between closed-loop reactivity-to-powertransfer functions of test point GGTP4 calculated for beginningand end-of-cycle conditions.

18-1

18-2

-188

-27818 2 18-1FREQUENCY.(Hz)'8

Fig. 7. , Comparison'. between'pen-loop",power-to-vo'id-reactivity':.-.transfer ..functions of ..test'oint GGTP4"calculated;for,,b'eginning -.-."'~-".and end-of-cycle conditions.;

18

2.3 Sensitivit stud

Zn addition to the nominal cases presented in Sects. 2.2 and 2.3,we have performed a sensitivity study of the calculated stabilityparameters to changes in LAPUR input parameters. The main

results of this study are presented in Tables 6 and 7, which

indicate the sensitivity 'of the DR and oscillation frequency tochanges in density reactivity coefficient and recirculation loop

parameters.

Table 6. Sensitivity of decay ratio to inputparameters of beginning-of-cyclecalculations for Grand Gulf-1

DRC Gain rTest oint

GGTP1 GGTP2 GGTP4 GGTP6 GGTPB

1.0 1.00.7 1. 00 ~ 8 1.00.9 1.01 ~ 1 1 ~ 01 ~ 2 1.01 ~ 3 1 ~ 01 ' 0.41 ' 0 '1.0 1.31.0 1.61 ' 1 '1 ' 1 '1.0 1.01.0 1 '1.0 1.01 ' 0 '

1.01.01.01.01.01.01 ~ 01 ~ 01.01 ~ 01.00 '0 '1.31.60.00.0

0.180.070.100 '40 '20.270.320.130 '50 '00.220. 160. 170 '80 '80 '40.09

0. 120.040.060.090.160.190 '30.090.110.140.150.110 '20 '30 ~ 130. 100.07

0.220 '90.130 '70.280.330.390.160.190 '50.280.200 '10.230.230 '80.11

0 '20 '00.270.340.490 '60.630.280 '50 '70 '20 '90 '10 '10 '10 '40 '7

0.320.140.200.260.380.450.510.220.27

, 0 '70.400.290.310 '20 '20.260.14

aDRC = Density reactivity coefficient; r = Timeconstant in

S ~

19

Table 7. Sensitivity of decay ratio to inputparameters of end-of-cycle calculations for

Grand Gulf-1

8'*DRC Gain r

Test ointGGTP1 GGTP2 GGTP4 GGTP6 GGTPB

1.00.70.80.91 ~ 11 '1 '1.01.01.01.01.01.01.01.01.01 ~ 0

1.0 1.01.0 1.01 ' 1.01.0 1.01 ' 1 '1.0 1.01 ' 1.00 ' 1.00.7 1 '1 ' 1 '1.6 1.01.0 0 '1.0 0.71.0 1 '1 ' 1.61.0 0 '0.0 0.0

0. 300. 130. 180 ~ 240.360.420.480 '10.260.340.370.300.300.290.280 '90. 15

0.220 '80 '20 '70 '60.320.370 '60 '80.240 '70 '10.220 '10.200 '00 '2

0 '30.300 '80 '50 '00 '70 '40 '00.470.580.630.530.530 '20 '00 '00 '1

0 '90.630 '20 '10 '71 '41 '00 '50.820.951. 010 '80.890 '80.860.830 '3

0.700.440.530.620 '80 '50 '20.570.640.760.800.700.710 '00 '80.660 '60

DRC = Density reactivity coefficient; r = Timeconstant in s 1.

In addition to the above sensitivity study, we have mapped thedecay ratio as a function of power and flow for EOC conditions inthe Grand Gulf-1 reactor. The conditions of test GGTP4 have been

selected as base case for these calculations (i.e., the axial and

radial power shapes have been kept constant for this study). The

results are presented in Table 8 and Fig. 8. The predicted linesof constant DR at the end of cycle 2 are shown in Fig. 8.

20.

88

0$0.5

0.5

(>.2

68

4828 38

FLOW (X)

Fig. 8. Calculated constant-decay-ratio lines for end-of-cycle conditions in grand Gulf-l.

Table 8. Sensitivity to power and flow forend-of-cycle conditions in Grand Gulf-1

Power()

Flow Decay Oscillation(>) ratio . frequency

52

60

68

76

60

39

39

39

39

30

0. 30

0. 53

0. 67

0.82

0 '9

0.49

0.51

0.55

0.57

0.48

We observe from this table that the DR is more sensitive to, changes in flow than to changes in power. Nevertheless, these

4,q

calculations suggest that all the normal operating region of theGrand Gulf-1 reactor will be within the stable domain ofoperation at EOC conditions.

To determine the probable cause of the increase in calculated DR

at the EOC compared with the beginning-of-cycle calculations and

measurements, we performed a calculation with all the EOC

parameters for test GGTP4 except the axial power shape. With a

sinusoidal, symmetric power shape, we obtained a DR value of 0.21and an oscillation frequency of 0.47 Hz. This DR is less thanhalf the one calculated with the EOC power shape and of the same.

order as the DR at beginning of cycle. This .result indicatesthat the main reason for the decreased stability margin at'OC .in- '-Grand Gulf-1 is the!-shift in axial power» shape

toward-ai'.b'ottom-'.'..',",'eaked

distribut'ion.'.

22

3. SUSQUEHANNA-2 CALCULATIONS

LAPUR calculations were performed for the two conditions of the

stability tests performed on November 2 and November 9, 1986,

respectively.1 End-of-cycle conditions were not analyzed for the

Susquehanna™2 reactor due to lack of input data. For the

beginning-of-cycle calculations, we relied on nuclear and reactordata supplied by ANF and the Pennsylvania Power and LightCompany.

3.1 Modelled conditions

The second reload core of Susquehanna-2 contains 764 fuelassemblies of which 8 are "Type 3" General Electric (GE) 8 x 8

fuel assemblies, 432 are "Type 6" GE 8 x 8 assemblies, and theremaining 324 are "Type 12" 9 x 9 ANF assemblies. The average

exposure of the 8 x 8 fuel was 12 ' x 10 MWd/MT< while the 9 x 9

fuel had not been exposed yet.

The radial dependence of power and thermohydraulic

characteristics has been modelled by grouping the 764 assemblies

in five channel types: three of them correspond to 8 z 8 fuel and

the other two are 9 x 9 fuel. The axial and radial power

distributions are shown in Appendix A, along with the percentage

of controlled assemblies. Table 9 summarizes the operatingconditions for the two tests. Test SUSTLO corresponds to the

23

test of November 2, 1986, which was performed with the two

recirculation loops active. Test SUSSLO corresponds to theNovember 9, 1986, test under single-loop operating conditions.Table 10 contains the calculated density reactivity coefficientsfor both conditions. The input parameters for test SUSTLO can be

found in Appendix A.

Table 9. Modelled operating conditions for beginning ofcycle in Susquehanna-2

Test Power Flow Pressure Inlet temp.point (MW) (Mlb/h) (psi) ( F)

Recirc. looGain

SUSTLO 1970 46.8

SUSSLO 1834 43.9

960

955

505

500

-0.36 0.21

-0.36 0.21

The pressure-drop to inlet-flow transfer function isnormalized by gH/Wo, where H = core height, Wo ~ core flow;

= Time constant in s

Table 10. Calculated densityreactivity coefficients for

beginning of cycle in Susquehanna-2

Testpoint

Density reactxvitycoefficient

(Oak/k / ap)

SUSTLO

SUSSLO

12. 07

13.97

24

3.2 Results

The main results of these calculations are presented in Table 11,

which compares the measured and calculated values of the DRs and

frequencies of oscillation. Figures 9 and 10 present the

calculated reactor transfer functions for test SUSTLO.. Similar

arguments to those in Sect. 2.1.2 can be made with respect of the

accuracy of both the measurements and calculations. With that inmind, the benchmarking of LAPUR calculations versus the

Susquehanna-2 test results is inconclusive, in the sense thatboth DRs are low and, as such, good agreement is found between

measurements and calculations. However, extrapolations of the

accuracy of LAPUR calculations for higher DRs based exclusivelyon this benchmark are not possible.

Table 11. Comparison between measurements and LAPURcalculations for beginning of cycle in Susquehanna-2

Testoint

Deca ratioMeasured LAPUR

atu a re e cMeasured LAPUR

SUSTLO

SUSSLO

0.33

0.37

0 ~ 20

0.23

0 '90 ~ 34

0.38

0.42

4. DISCUSSION OF RESULTS

Overall, the results of the present benchmark of the LAPUR-IV

code against the Susquehanna-2 and Grand Gulf-1 stability testsare inconclusive. Given the low decay ratios observed in the

tests and the errors involved in both measurements and

25

181

UJCI

X 188

I:

18 1

-45

-98218 18 1

FREQUENCY (Hz)ie

Fig. 9. Calculated closed-loop.. reactivity-to-power;:transfer„ „

function for test point SUSTLO.26

181

18

18 2

8

-27818-2 18 1

FREQUENCY (Hz)

Fig. 10. Calculated open-loop power-to-void-reactivitytransfer function for test point SUSTLO.

27

calculations, one must conclude that satisfactory agreement isfound as long as the calculated DRs are low. This has been the

case, since both measured and calculated DR values have been less

than 0.4 for all test conditions. The present benchmark has once

more increased our confidence in the general validity of the

LAPUR code, in that if LAPUR had gross modelling errors,agreement might not have been successful over the relativelylarge range of operating conditions and fuel types covered in the

tests.

The modelling of end-of-cycle conditions in the Grand Gulf-1reactor implies that this reactor should be stable at those

conditions, but with a reduced margin as compared with beginning-of-cycle conditions. The highest calculated DR has been 0.89.

Based on our engineering judgment and the conservative nature ofthese calculations, we would not expect the DR to be higher than

0.7 should a second series of tests be conducted at the end ofthe cycle 2.

'I

~ c'c4 ~ <( i5y

28

REFERENCES

1. J. March-Leuba, and D. N. Fry, "Grand Gulf-1 andSusquehanna-2 Stability Tests." Oak Ridge NationalLaboratory Letter Report. ORNL/NRC/LTR-87/Ol (1987).

2. F. B. Woffinden and R. O. Niemi, "Low-Flow Stability Testsat Peach Bottom Atomic Power Station Unit 2 During Cycle 3."EPRI NP-972 (1981).

3. J. March-Leuba, R. T. Wood, P. J. Otaduy, and C. O. McNew,"Stability Tests at Browns Ferry Unit 1 Under Single-LoopOperating Conditions." Nucl. Technol. 74, 38 (1986).

4. J. March-Leuba and P. J. Otaduy, "The Importance of MomentumDynamics in BWR Neutronic Stability: Experimental Evidence."Trans Am. Nucl. Soc. 51, 563 (1985).

29

APPENDIX A

SAMPLE LAPUR INPUTS

31

(13)»» 2 G X SEC TABLE a*

NO. OF FUEL + GD X-SECT TYPES (NFT)»REF. MATER DENS. FOR X-SEC. (LIQUID,

NFT CTRL Dl D2 SIGA1

1 1 1.358K 00 3.208K-01 7.350K-033. 870K-01 l. 159K-01 -5. 900K-042.082E-01 4.607K-01 -1.499E-03

2 1.365K 00 3.227K 01 9.940K-034.030K-01 1.220K-01 -6.600K-042. 157K-01 4. 608K-01 -l.860E-03

2 1 1.360E 00 3.184K-01 7.530E-033. 888K-01 1. 163K-01 -5. 700K-042.093E-01 4. 451K-01 -l. 537K-03

2 1.367K 00 3.201K-01 1.010K-024.046K-01 1.225K-01 -6.600K-042.164K-01 4.448K-01 1.912K-03

3 1 1.365K 00 2.990K-01 7.270K-033.959K-01 9.014K-02 -5.800K-042.264K-01 4.472K-01 -1.398K-03

2 l. 372K 00 2. 998K-01 Q. 910K-034. 121K-01 Q. 655E-02 -6. 700K-042. 331E-01 4. 448E-01 -1. 813K-03

3 NO. OF

STEAH)» 7.3SIGA2

4 . 501K-023.047K-05

-3.676K-035.593K-021.428K-03

-3.765E-034.922K-02

-l.943K-04-4. 514E-036.092K-028.846K-04

-5. 071K-035.987K-02

-5.005K-03-l. 143K-02

7.400K-02-5.393K-03-l.271K-02

~ 4 1 ~ ~ * I *

COEFF. OF X-SEC. POLYNOHIAL EXPAN. (NCOPOL)62E-01 3.790K-02

NUSIGF1 NUSIGF2

3.084E-03 5.490K-02-1. 486K-05 7. 647E-03-6.229K-04 -5.661K-03

3.083E-03 5.841K-02-5.139K-05 6.778E-03-6.782K-04 -7.908K-03

3. 571K-03 6. 397K-02-1.429K-05 7.065K-03-6. 943K-04 -8. 132E-033.554K-03 6.855K-02

-7.023E-OS 5.599K-03-7. 581K-04 -1. 091K-02

4.984K-03 7.320E-02-2.187E-04 -4 '94K-03-9.239K-04 -1.318K-02

4.905E-03 7.928K-02-3.230K 04 -8.417E-03-1. 011E-03 -1. 622K-02

SIGR1-21.994K-02

-l. 441K-025.643K-041.725E-02

-l. 438E 029.586E-041.980K-02

-1.442E"026.095K-041. 712E-02

-1. 438K-02l. 010K-032.006K-02

-1.456E-024.702K-041.'730K-02

-1. 453E-029.044E-04

* * * * P ~ » * *NO.OF CHANN. OF FUEL TYPE (IBT),CH. TYPE (IX) AND HORIZ. NUCL. REGION (J)

J 1 IBT» 1 IX 80 0 0 0

J» 1 IBT» 2 IX»... 0 52 68 88J» 1 IBT» 3 IX»... 0 0 28 52

FUEL TYPE PER BUNDLE (IBT) AND HEIGHT (ZXS) IN CH

IBT» 1 NZX» 1 ZXS 411.291

IBT» 2 NZX» 1 ZXS» 411. 29

2IBT» 3 NZX 1 ZXS» 411.29

3

0

248164

0

0

20

Fig. A2. LAPURW sample input Zest GGTP4 (cont.).

36

APPENDIX B

DESCRIPTION OF MODELLED OPERATING CONDITIONS

43

5

488GGTP1

488 68

E0

388E0

388

~ 288

Z188

~ 288X

188

W

28C3

8.8 8.5 1.8 1.5RELATIVE POWER

(a) Axial power shape

8 5 18

(b) Per cent,age ofcont, rolled channels

15CONTROLLED CHANNELS (X)

8.8 8.5 1.8 1.5RELATIVE POWER ~


Fig. Bl. Degree of control, radial power, and axial powerdistributions for test point GGTPl.

488GGTP2

488 68

388E0

~ 288(3

~ LdCh Z

188

E0

388

~ 288

LLJ

18828

8.8 8.5 1.8 1.5—. -- RELATIVE POWER


8 5

(b) Percent,age ofcont, rolled channels

18 15CONTROLLED CHANNELS (X)



t

Fig. B2. Degree of control, radial power, and axial powerdistributions for test point GGTP2.

488GGTP4

488 68

388 388

~ 288

V188

~ 288

18828

8.8 8.5 1.8RELATIVE POWER


8 85 18 158.RELATIVE POWER ~

(a) Axial power shape (b) Percent,age ofcont, r oiled channels



488GGTP6

488 68

388 388

~ 288C3

c. lV00

188t

~ 288

ILI

18828

8.8 8.5 1 .8 1.5. RELATIVE POWER



(b) Per cent,age ofcont. rolled channels




488GGTPB

488 68

388 388

0r

~ 288- C3.,;

"-'188

~ 288

188z 28




(b) Percent.age ofcont,r oiled channels

88.8 8.5 1.8 1.5

RELATIVE POWER


Fig. B5. Degree of control, radial power, and axial powerdistributions for test point GGTPB.

. 488SUSTLO

488 88

C0

388E0

388 68

~ 288C3

188

~ 288C3

UJ

188

M48

CC

28

88 85 18 15RELATIVE POWER


8 18 28 38 48 58CONTROLLED CHANNELS (X)

(b) Percent.age ofcont. rolled channels


(c) Radial power shapee

'ig.

B6. Degree of control, radial power, and axial powerdistributions for 8 x 8 fuel in test point SUSTLO.

488SUSTLO

488 88

ED

388E0

388 68

~ 288(3

~ hJ

188

~ 288

188

48

28




(a) Axial power shape (b) Per cent,age ofcont, rolled channels


Fig. B7. Degree of control, radial power, and axial powerdistributions for 9 x 9 fuel in test point SUSTLO.

488SUSSLO

488 88

388C0

388 68

i 288

~ ill188

~ 288

188

48

28




(b) Per cent,age ofcont, rolled channels



Fig. B8. Degree of control, radial power, and axial powerdistributions for 8 x 8 fuel in test point SUSSLO.

488SUSSLO

488 88

E0

388 388 68

~ 288C3

~ LIJ4l Z

188

~ 288

188

48Z

28



8 18 28 38 48CONTROLLED CHANNELS (X)

(b) Per centage ofcontrolled channels



Fig. B9. Degree of control, radial= power, and axial powerdistributions for 9 x 9 fuel in test point SUSSLO.

Q)A I

~I

ORNL/NRC/LTR-87/08

INTERNAL DISTRIBUTION

1.2.3.4 ~

5.6.7.8.9.

10

'.E. Clapp

B. G. EadsD. N. FryJ. March-LeubaR. S. StoneR. S. WiltshireM. J. Kopp (Advisor)P. F. McCrea (Advisor)H. M. Paynter (Advisor)J. G. Pruett

11'2.

13 ~

14'5

'6

~

17 ~

J. B. Ball (Advisor)Central Research LibraryY-12 Document Reference

DepartmentZ&C ZPCLaboratory Records DepartmentLaboratory Records

Department, RCORNL Patent Section

EXTERNAL DISTRIBUTION

18. S. Bajva, Division of Engineering and Systems Technology,Office of Nuclear Reactor Regulation, U. S. NuclearRegulatory Commission, P«522, Washington DC 20555

19. T. L. Huang, Division of Engineering and Systems Technology,Office of Nuclear Reactor Regulation, U. S. NuclearRegulatory Commission, P-1022, Washington DC 20555

20. J. B. Henderson, Division of Engineering and SystemsTechnology, Office of Nuclear Reactor Regulation, P-1022,U. S. Nuclear Regulatory Commission, Washington DC 20555

21. L. E. Philips, Division of Engineering and SystemsTechnology, Office of Nuclear Reactor Regulation,U. S. Nuclear Regulatory Commission, P-1022,Washington DC 20555

22. NRC Central File

55

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tE

k

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