ML18040B189

Selected Operating Reactors Issues:Stability Calculations for Grand Gulf 1 & Susquehanna 2 Bwrs

ML18040B189
Person / Time
Site:	Grand Gulf, Susquehanna, 05000000
Issue date:	08/31/1987
From:	Marchleuba J OAK RIDGE NATIONAL LABORATORY
To:	Huang T Office of Nuclear Reactor Regulation
Shared Package
ML18017A037	List: ML18017A036 ML18040B189
References
CON-FIN-A-9478 ORNL-NRC-LTR-87, ORNL-NRC-LTR-87-08, ORNL-NRC-LTR-87-8, NUDOCS 8710070152
Download: ML18040B189 (58)

Text

ENCLOSURE ORNL/NRC/LTR-87/08 Contract Program:

Selected Operating Reactors Issues Subject of Document:

Stability Calculations for the Grand 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 Nuclear Reactor Regulation Prepared for U.S. Nuclear Regulatory Commission Office of Nuclear Reactor Regulation under DOE Interagency Agreement 0544-0544 A1 NRC FIN No. A9478, Project 2

Prepared by Instrumentation and Controls Division OAK RIDGE NATIONAL LABORATORY operated by MARTIN MARIETTA ENERGY SYSTEMS, INC.

for the U.S.

DEPARTMENT OF ENERGY under Contract No. DE-AC05-840R21400

LIST OF FIGURES.

TABLE OF CONTENTS Page LIST OF TABLES

~

~

~

~

~

~ vii INTRODUCTION 1.1 Objectives 1.2 Main results 1

1 1

2.

GRAND GULF-1 CALCULATIONS 2.1 Beginning-of-cycle calculations

2. 1. 1 Modelled conditions 2.1.2 Results 2.2 End-of-cycle calculations 2.2.1 Modelled conditions 2.2.2 Results 2.3 Sensitivity study 2

3 3

7 12 12 15 19 3.

SUSQUEHANNA-2 CALCULATIONS 3.1 Modelled conditions 3.2 Results 23 23 25 4.

DISCUSSION OF RESULTS 25 REFERENCES 29 APPENDIX A.

SAMPLE LAPUR INPUTS

~

31 APPENDIX B.

DESCRIPTION OF MODELLED OPERATING CONDITIONS 43

LIST OF FIGURES Figure Page Degree of control, radial power, and axial power distributions for test control GGTP4 5

2 ~

3.

Calculated close-loop reactivity-to-power transfer function for test 'point GGTP4 9

Calculated closed-loop reactivity-to-power transfer function for test point GGTP4 10 Measured core-plate-pressure-drop-to-power transfer function for test point GGTP4 11 5.

Degree of control, radial power, and axial power distributions for end-of-cycle conditions modelled in Grand Gulf-1 13 6.

7 ~

Comparison between closed-loop reactivity-to-power transfer functions of test point GGTP4 calculated for beginning and end-of-cycle conditions.

17 Comparison between open-loop power-to-void-reactivity transfer functions of test point GGTP4 calculated for beginning and end-of-cycle conditions 18 8.

Calculated constant-decay-ratio lines for end-of-cycle conditions in Grand Gulf-1 21 9.

Calculated closed-loop reactivity-to-power transfer function 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-reactivity transfer function for test point SUSTLO 27 33 35 38 40 B.l.

BE 2.

Degree of control, radial power, and distributions for test point GGTP1 Degree of control, radial power, and distributions for test point GGTP2 axial power axial power 45 46

B.3.

B.4.

B. 5.

Degree of control, radial power, and axial power distributions for test point GGTP4 Degree of control, radial power, and axial power distributions for test point GGTP6 Degree of control, radial power, and axial power distributions for test point GGTPB 47 48 49 B.6.

Degree of control, radial power, and axial power distributions for 8 x

8 fuel in test point SUSTLO.

50 B.7.

B. 8.

B.9.

Degree of control, radial power, and axial power distributions for 9 x

9 fuel in test point SUSTLO.

Degree of control, radial power, and axial power distributions for 8 x

8 fuel in test point SUSSLO.

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

51 52 53

Table LIST OF TABLES Page 1.

Modelled operating conditions for beginning of cycle in Grand Gulf-1 2.

Calculated density reactivity coefficients for beginning of cycle in Grand Gulf-1 7

3.

Comparison between measurements and LAPUR calculations for beginning of cycle in Grand Gulf-1 4.

Calculated density reactivity coefficients for beginning of cycle in Grand Gulf-1

~

~

15 5.

Comparison between LAPUR calculations for beginning and end of cycle in Grand Gulf-1 15 6.

Sensitivity of decay ratio to input parameters of beginning-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 conditions in Grand Gulf-1 22 9.

Modelled operating conditions for beginning of cycle in Susquehanna-2 24 10.

Calculated density reactivity coefficients for beginning of cycle in Susquehanna-2 24 11.

Comparison between measurements and LAPUR calculations for beginning of cycle in Susquehanna-2 25

1.

INTRODUCTION The objective of the present report is to document the results of a series of stability calculations performed using the code LAPUR-IV for various conditions in the Grand Gulf-1 and Susquehanna-2 boiling water reactors (BWRs).

The main purpose of these calculations was to verify whether LAPUR could reproduce accurately the results obtained during two recent stability tests conducted 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 the calculated 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 trends similar 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 to characterize the results of the present benchmark as inconclusive.

1n addition, EOC conditions were analyzed for the Grand Gulf-1 reactor 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 beginning of cycle.

For instance, with the nominal conditions of test GGTP6, the LAPUR code calculates a decay ratio (DR) of 0.89 at EOC compared with 0.42 at beginning of cycle.

Note, though, that the conditions used for the EOC calculations are very conservative.

Based on our engineering

judgment, we would not expect 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 of calculations 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 operating conditions 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 natural circulation.

~

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 conditions The second reload core of Grand Gulf-1 contains 800 fuel assemblies 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 freshly loaded and had an approximate exposure of 500 MWd/MT at the time of 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 axial dependence of the thermal power and the percentage of control rods inserted.

A representative case for the beginning of cycle calculations is presented in Fig. 1, which corresponds to test point GGTP4 (59% power, 39% flow). It can be observed in this figure that, for these beginning-of-cycle conditions, the axial power shape is fairly uniform and symmetrical.

The radial power distribution, although slightly skewed, shows that the value of the 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 the process computer values, which are known to underestimate the actual flow at conditions close to natural circulation.

Test point Table 1.

Modelled operating conditions for beginning of cycle in Grand Gulf-1 (MW)

(Mlb/h)

(psi)

('F)

Gain r

GGTP1 1997 44.4 GGTP2 2363 50 '

GGTP4 2257 44.3 GGTP6 1698 29.8 GGTPB 1745 33.6 992 1000 998 986 988 509 509 506 498 501

-0'9

-0 21

-0'9

-0.82

-0'7 0.22 0'6 0.22

-0 ~ 32 0 ~

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

by gH/Wo, whereore. height, Wo = core;;;flow;.

~ = Time-constant in s...

488 GGTP4 488 68 E

D 388 E0 388

~ 288 188

~ 288 x

188 28 8.8 8.5 1.8 1.5 RELATIVE PONER 8

5 18 15 CONTROLLED CHANNELS (X) 8 8 8 5 1 8 1 5 RELATIVE POWER (a) Axial power shape (b) Percentage of controlled channels (c) Radial power shape Fig. 1.

Degree of control, radial power, and axial power distributions 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 of control.

To calibrate this cross section set, keff calculations are performed at nominal conditions and at similar conditions with a +50-psi-pressure increase.

The DRC calculated by LAPUR is adjusted 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 of 13.47 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 test points at the same fuel exposure and similar control rod positions.

4 Table 2.

Calculated density reactivity coefficients for beginning of cycle in Grand Gulf-1 Test point Density reactivity coefficient

(%ok/k / ap)

GGTP1 GGTP2 GGTP4

+50 psi GGTP6 GGTPB

13. 33 13.34 13.65 13.16 13.17 13.04 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 in Table 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 in the 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 for benchmarking purposes is limited to the detection of only gross errors in modelling technique.

Table 3.

Comparison between measurements and LAPUR calculations for beginning of cycle in Grand Gulf-1 Test Power Flow Deca atmo atu a f e enc point (4)

(4)

Measured LAPUR Measured LAPUR GGTP6 GGTPB GGTP4 GGTP1 GGTP2 0.35 0.37 0.32 0'1 0'2 44 27 0'7 0'5 46 30 0.40 0.36 59 39 0.43 0.40 52 39 0.44 0.40 62 45 0.44 0.43 For illustration purposes, Figs.

2 and 3 present the calculated closed-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'was

shown, 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 188 z

X 18 1 FREQUENCY (Hz)

Fig. 2.

Calculated closed-loop reactivity-to-power transfer function for test point GGTP4.

9

18-1 18 2

-188

-278 i8 2 18 1 FREQUENCY'(Hz)

188, Fig. 3.

Calculated. open-loop. reactivity-'to-power transfer:,"';,;"

function for. test point GGTP4.'l 10

181 z

5 4.

4I zCK 18-2 Ctl fail W

8

-98 2

18 IB FRKOUENCY (HZ)

Fig. 4.

Measured core-plate-pressure-drop-to-power transfer function 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 is precisely the determination of the most unstable operating conditions during the core cycle.

In this calculation, we used operating conditions corresponding to a reactor with all control rods out and with mostly depleted fuel.

The nominal power for these 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 of 1.8 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 the nominal 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

488 GGEOC4

8. 18 58 388 I-288

~ ILI 188

8. 85 C0 P. 00 C3 UI

-8. 85 48 M

38 UJ 28 18 8

-8. 18 8 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 of cont,rolled channels (c) Radial power shape Fig. 5.

Degree of control, radial power, and axial power distributions for end of cycle conditions modelled in Grand Gulf-1.

margins (i.e., higher DR).

The fraction of controlled channels is zero, and this increases the DRC, which also has a negative effect on the reactor stability.

The main cases analyzed corresponded to the power, flow,. pressure and inlet temperature conditions of the beginning-of-cycle tests (Table 1).

We labeled these new conditions GGEOC1 through

GGEOC6, where the last digit indicates the corresponding test point conditions at beginning of cycle.

Different axial or radial power shapes were not available for the several test cases.

For that reason, the power distributions of the nominal case (60% power, 394 flow) were used for all calculated conditions 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 decrease in'oids to 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 reactivity coefficients for beginning of cycle in Grand Gulf-1 Test point GGEOC1 GGEOC2 GGEOC4

+50 psi GGEOC6 GGEOCB Density reactivity coefficient

(%ok/k / ap) 9.38 9.38 9'8 8.42 9'1 9.28 2.2.2 Results The main results of the EOC calculations are presented in Table 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 calculations for beginning and EOC in Grand Gulf-1 Test Power Flow point (4)

(4)

EOC BOC EOC BOC GGTP6 GGTPB GGTP4 GGTP1 GGTP2 44 46 59 52 62 27 29 39 39 45 0.89 0'0 0'3 0.30 0'2 0'2 0'2 0'2 0'8 0'2 0 ~ 40 0'2 0.51 0'9 0.54 0'5 0'6 0'0 0'0 0'3 aBOC = Beginning of cycle; EOC = End of cycle.

15

J I

The comparison in Table 5 indicates that, as expected, conditions at EOC in Grand Gulf will be more unstable than at beginning of cycle.

The DRs increase approximately by a factor of two, but still the expected values are below 1.0, indicating stable operation.

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 several channel types: the DRC of the high-power fresh fuel is very high (approximately 30), while the DRC of some of the old fuel is f negative, because old fuel assemblies are so burned out that they behave as if they had their control rods inserted.

Due to this disparity of cross sections, this condition is rather hard to model.

Although LAPUR performs an optimal adjoint weighing scheme 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 beginning versus the EOC.

The main difference results on the higher resonance frequency and sharper phase break indicating that the EOC condition is the less.stable.

16

181 IJI CD I

z 188 F

,-C C 18-1

IIOC,

-45 18 18 1

FREQUENCY (Hz)

Fig.

6.

Comparisc.n between closed-loop reactivity-to-power transfer functions of test point GGTP4 calculated for beginning and end-of-cycle conditions.

18-1 18-2

-188

-278 18 2 18-1 FREQUENCY.(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 stability parameters 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 to changes in density reactivity coefficient and recirculation loop parameters.

Table 6.

Sensitivity of decay ratio to input parameters of beginning-of-cycle calculations for Grand Gulf-1 DRC Gain r

Test oint GGTP1 GGTP2 GGTP4 GGTP6 GGTPB 1.0 1.0 0.7

1. 0 0 ~ 8 1.0 0.9 1.0 1

~ 1 1 ~ 0 1 ~ 2 1.0 1 ~ 3 1 ~ 0 1 '

0.4 1 '

0 '

1.0 1.3 1.0 1.6 1 '

1 '

1 '

1 '

1.0 1.0 1.0 1 '

1.0 1.0 1 '

0 '

1.0 1.0 1.0 1.0 1.0 1.0 1 ~ 0 1 ~ 0 1.0 1 ~ 0 1.0 0 '

0 '1.3 1.6 0.0 0.0 0.18 0.07 0.10 0'4 0'2 0.27 0.32 0.13 0'5 0'0 0.22

0. 16

0. 17 0'8 0'8 0'4 0.09

0. 12 0.04 0.06 0.09 0.16 0.19 0'3 0.09 0.11 0.14 0.15 0.11 0'2 0'3 0 ~ 13

0. 10 0.07 0.22 0'9 0.13 0'7 0.28 0.33 0.39 0.16 0.19 0'5 0.28 0.20 0'1 0.23 0.23 0'8 0.11 0'2 0'0 0.27 0.34 0.49 0'6 0.63 0.28 0'5 0'7 0'2 0'9 0'1 0'1 0'1 0'4 0'7 0.32 0.14 0.20 0.26 0.38 0.45 0.51 0.22 0.27

, 0'7 0.40 0.29 0.31 0'2 0'2 0.26 0.14 aDRC = Density reactivity coefficient; r = Time constant in S

~

19

Table 7.

Sensitivity of decay ratio to input parameters of end-of-cycle calculations for Grand Gulf-1 8'*

DRC Gain r

Test oint GGTP1 GGTP2 GGTP4 GGTP6 GGTPB 1.0 0.7 0.8 0.9 1 ~ 1 1 '

1 '1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1 ~ 0 1.0 1.0 1.0 1.0 1 '

1.0 1.0 1.0 1 '

1 '

1.0 1.0 1 '

1.0 0 '

1.0 0.7 1 '

1 '

1 '

1.6 1.0 1.0 0 '

1.0 0.7 1.0 1 '

1 '

1.6 1.0 0 '

0.0 0.0

0. 30

0. 13

0. 18 0 ~ 24 0.36 0.42 0.48 0'1 0.26 0.34 0.37 0.30 0.30 0.29 0.28 0'9

0. 15 0.22 0'8 0'2 0'7 0'6 0.32 0.37 0'6 0'8 0.24 0'7 0'1 0.22 0'1 0.20 0'0 0'2 0'3 0.30 0'8 0'5 0'0 0'7 0'4 0'0 0.47 0.58 0.63 0.53 0.53 0'2 0'0 0'0 0'1 0'9 0.63 0'2 0'1 0'7 1'4 1'0 0'5 0.82 0.95

1. 01 0'8 0.89 0'8 0.86 0.83 0'3 0.70 0.44 0.53 0.62 0'8 0'5 0'2 0.57 0.64 0.76 0.80 0.70 0.71 0'0 0'8 0.66 0'60 DRC = Density reactivity coefficient; r = Time constant in s 1.

In addition to the above sensitivity study, we have mapped the decay ratio as a function of power and flow for EOC conditions in the 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 lines of 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 for end-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 the Grand Gulf-1 reactor will be within the stable domain of operation 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 0.21 and an oscillation frequency of 0.47 Hz.

This DR is less than half the one calculated with the EOC power shape and of the same.

order as the DR at beginning of cycle.

This.result indicates that 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 reactor data supplied by ANF and the Pennsylvania Power and Light Company.

3.1 Modelled conditions The second reload core of Susquehanna-2 contains 764 fuel assemblies of which 8 are "Type 3" General Electric (GE) 8 x

8 fuel assemblies, 432 are "Type 6" GE 8

x 8 assemblies, and the remaining 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 operating conditions 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 the November 9, 1986, test under single-loop operating conditions.

Table 10 contains the calculated density reactivity coefficients for both conditions.

The input parameters for test SUSTLO can be found in Appendix A.

Table 9.

Modelled operating conditions for beginning of cycle in Susquehanna-2 Test Power Flow Pressure Inlet temp.

point (MW)

(Mlb/h)

(psi)

( F)

Recirc.

loo Gain 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 is normalized by gH/Wo, where H = core height, Wo ~ core flow;

= Time constant in s Table 10.

Calculated density reactivity coefficients for beginning of cycle in Susquehanna-2 Test point Density reactxvity coefficient (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 in mind, the benchmarking of LAPUR calculations versus the Susquehanna-2 test results is inconclusive, in the sense that both 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 exclusively on this benchmark are not possible.

Table 11.

Comparison between measurements and LAPUR calculations for beginning of cycle in Susquehanna-2 Test oint Deca ratio Measured LAPUR atu a

re e c Measured LAPUR SUSTLO SUSSLO 0.33 0.37 0 ~ 20 0.23 0'9 0 ~ 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 tests are inconclusive.

Given the low decay ratios observed in the tests and the errors involved in both measurements and 25

181 UJ CI X

188 I:

18 1

-45

-98 2

18 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

-278 18-2 18 1 FREQUENCY (Hz)

Fig. 10.

Calculated open-loop power-to-void-reactivity transfer function for test point SUSTLO.

27

calculations, one must conclude that satisfactory agreement is found 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 relatively large range of operating conditions and fuel types covered in the tests.

The modelling of end-of-cycle conditions in the Grand Gulf-1 reactor 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 of these calculations, we would not expect the DR to be higher than 0.7 should a second series of tests be conducted at the end of the cycle 2.

'I

~c'c4

~

<( i5y 28

REFERENCES 1.

J.

March-Leuba, and D. N. Fry, "Grand Gulf-1 and Susquehanna-2 Stability Tests."

Oak Ridge National Laboratory Letter Report.

ORNL/NRC/LTR-87/Ol (1987).

2.

F.

B. Woffinden and R.

O. Niemi, "Low-Flow Stability Tests at 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-Loop Operating Conditions." Nucl. Technol.

74, 38 (1986).

4.

J.

March-Leuba and P. J.

Otaduy, "The Importance of Momentum Dynamics 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-03

3. 870K-01

l. 159K-01

-5. 900K-04 2.082E-01 4.607K-01

-1.499E-03 2

1.365K 00 3.227K 01 9.940K-03 4.030K-01 1.220K-01

-6.600K-04

2. 157K-01

4. 608K-01

-l.860E-03 2

1 1.360E 00 3.184K-01 7.530E-03

3. 888K-01

1. 163K-01

-5. 700K-04 2.093E-01

4. 451K-01

-l. 537K-03 2

1.367K 00 3.201K-01 1.010K-02 4.046K-01 1.225K-01

-6.600K-04 2.164K-01 4.448K-01 1.912K-03 3

1 1.365K 00 2.990K-01 7.270K-03 3.959K-01 9.014K-02

-5.800K-04 2.264K-01 4.472K-01

-1.398K-03 2

l. 372K 00

2. 998K-01 Q. 910K-03

4. 121K-01 Q. 655E-02

-6. 700K-04

2. 331E-01

4. 448E-01

-1. 813K-03 3

NO.

OF STEAH)>>

7.3 SIGA2 4. 501K-02 3.047K-05

-3.676K-03 5.593K-02 1.428K-03

-3.765E-03 4.922K-02

-l.943K-04

-4. 514E-03 6.092K-02 8.846K-04

-5. 071K-03 5.987K-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-03 3.554K-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 SIGR1-2 1.994K-02

-l. 441K-02 5.643K-04 1.725E-02

-l. 438E 02 9.586E-04 1.980K-02

-1.442E"02 6.095K-04

1. 712E-02

-1. 438K-02

l. 010K-03 2.006K-02

-1.456E-02 4.702K-04 1.'730K-02

-1. 453E-02 9.044E-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 88 J>>

1 IBT>> 3 IX>>...

0 0

28 52 FUEL TYPE PER BUNDLE (IBT)

AND HEIGHT (ZXS) IN CH IBT>>

1 NZX>>

1 ZXS 411.29 1

IBT>> 2 NZX>>

1 ZXS>>

411. 29 2

IBT>> 3 NZX 1

ZXS>>

411.29 3

0 248 164 0

0 20 Fig. A2.

LAPURW sample input Zest GGTP4 (cont.).

36

APPENDIX B DESCRIPTION OF MODELLED OPERATING CONDITIONS 43

5 488 GGTP1 488 68 E0 388 E0 388

~ 288 Z

188

~ 288 X

188 W

28 C3 8.8 8.5 1.8 1.5 RELATIVE POWER (a) Axial power shape 8

5 18 (b)

Per cent,age of cont,rolled channels 15 CONTROLLED CHANNELS (X) 8.8 8.5 1.8 1.5 RELATIVE POWER

~

(c) Radial power shape Fig. Bl.

Degree of control, radial power, and axial power distributions for test point GGTPl.

488 GGTP2 488 68 388 E0

~ 288 (3

~ Ld Ch Z 188 E0 388

~ 288 LLJ 188 28 8.8 8.5 1.8 1.5

.-- RELATIVE POWER (a) Axial power shape 8

5 (b) Percent,age of cont,rolled channels 18 15 CONTROLLED CHANNELS (X) 8.8 8.5 1.8 1.5 RELATIVE POWER (c) Radial power shape t

Fig. B2.

Degree of control, radial power, and axial power distributions for test point GGTP2.

488 GGTP4 488 68 388 388

~ 288 V

188

~ 288 188 28 8.8 8.5 1.8 RELATIVE POWER 8

5 8

15 CONTROLLED CHANNELS (X) 8 85 18 15 8.

RELATIVE POWER

~

(a) Axial power shape (b) Percent,age of cont, r oiled channels (c) Radial power shape Fig. B3.

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

488 GGTP6 488 68 388 388

~ 288 C3

c. lV 00 188 t

~ 288 ILI 188 28 8.8 8.5 1.8 1.5

. RELATIVE POWER (a) Axial power shape 8

5 18 15 CONTROLLED CHANNELS (X)

(b)

Per cent,age of cont.rolled channels 8.8 8.5 1.8 1.5 RELATIVE PONER (c) Radial power shape Fig. B4.

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

488 GGTPB 488 68 388 388 0

r

~ 288

- C3.,;

"-'188

~ 288 188 z

28 8.8 8.5 1.8 1.5 RELATIVE PONER (a) Axial power shape 8

5 18 15 CONTROLLED CHANNELS (X)

(b) Percent.age of cont,r oiled channels 88.8 8.5 1.8 1.5 RELATIVE POWER (c) Radial power shape Fig. B5.

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

. 488 SUSTLO 488 88 C0 388 E0 388 68

~ 288 C3 188

~ 288 C3 UJ 188 M

48 CC 28 88 85 18 15 RELATIVE POWER (a) Axial power shape 8

18 28 38 48 58 CONTROLLED CHANNELS (X)

(b) Percent.age of cont.rolled channels 8.8 8.5 1.8 1.5 RELATIVE POWER (c) Radial power shape e

'ig.

B6.

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

488 SUSTLO 488 88 E

D 388 E0 388 68

~ 288 (3

~ hJ 188

~ 288 188 48 28 8.8 8.5 1.8 1.5 RELATIVE POWER 8

28 48 88 68 CONTROLLED CHANNELS (X) 8.8 8.5 1.8 1.5 RELATIVE POWER

~

(a) Axial power shape (b)

Per cent,age of cont,rolled channels (c) Radial power shape Fig. B7.

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

488 SUSSLO 488 88 388 C0 388 68 i 288

~ ill 188

~ 288 188 48 28 8.8 8.5 1.8 1.5 RELATIVE PONER (a) Axial power shape 8

18 28 38 CONTROLLED CHANNELS (X)

(b)

Per cent,age of cont,rolled channels 8.8 8.5 1.8 1.5 RELATIVE PONER (c) Radial power shape Fig.

B8.

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

488 SUSSLO 488 88 E0 388 388 68

~ 288 C3

~ LIJ 4l Z 188

~ 288 188 48 Z

28 8.8 8.5 1.8 1.5 RELATIVE POWER (a) Axial power shape 8

18 28 38 48 CONTROLLED CHANNELS (X)

(b)

Per centage of controlled channels 8.8 8.5 1.8 1.5 RELATIVE POWER

~

(c) Radial power shape Fig. B9.

Degree of control, radial= power, and axial power distributions 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.

Eads D.

N. Fry J.

March-Leuba R.

S.

Stone R.

S. Wiltshire M. 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 Library Y-12 Document Reference Department Z&C ZPC Laboratory Records Department Laboratory Records Department, RC ORNL Patent Section EXTERNAL DISTRIBUTION 18.

S. Bajva, Division of Engineering and Systems Technology, Office of Nuclear Reactor Regulation, U. S. Nuclear Regulatory Commission, P<<522, Washington DC 20555 19.

T. L. Huang, Division of Engineering and Systems Technology, Office of Nuclear Reactor Regulation, U. S. Nuclear Regulatory Commission, P-1022, Washington DC 20555 20.

J.

B. Henderson, Division of Engineering and Systems Technology, Office of Nuclear Reactor Regulation, P-1022, U. S. Nuclear Regulatory Commission, Washington DC 20555 21.

L. E. Philips, Division of Engineering and Systems Technology, Office of Nuclear Reactor Regulation, U. S. Nuclear Regulatory Commission, P-1022, Washington DC 20555 22.

NRC Central File 55

l t

E k

4