ML20040D016

Nonproprietary Version of Revision 2 to Response to Questions on Documents Supporting San Onofre Nuclear Generating Station 2 License Submittal

ML20040D016
Person / Time
Site:	San Onofre
Issue date:	11/30/1981
From:	ABB COMBUSTION ENGINEERING NUCLEAR FUEL (FORMERLY
To:
Shared Package
ML19297F285	List: ML20040D011 ML20040D013 ML20040D016 ML20040D018 ML20040D020
References
CEN-184(S)-NP, CEN-184(S)-NP-R02, CEN-184(S)-NP-R2, NUDOCS 8201290483
Download: ML20040D016 (40)

Text

r-*

i

'., eA s

l.

J Respon'se to Quest 16ns f

'on Documents. Supporting. SON.GS 2 License Submittal CEN-184(S)-NP, Rev.2-NP c

November 1981 COMBUSTION ENGINEERING, INC.

WINDSOR, CONNECTICUT Docko!hhojj, PDR

a LEGAL NOTICE This report was prepared as an account of work sponsored by Combustion Engineering, Inc. Neither Combustion Engineering l

nor any person acting on'its behalf:

A.

Makes any warranty or representation, express or implied including the warranties of fitness for a particular purpose or merchantability, with respect to the accuracy, completeness, or usefullness of the information contained in this report, or that the use of any information, apparatus, method, or process disclosed in this report may not infringe l

privately owned rights; or B.

Assumes any liabilities with respect to the use of, or fdr damages resulting from the use of, any information, apparatus, method or process disclosed in this report.

G h

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~

INDEX

~

Question I' aber Page Nunber f

~

1 1

f 1 - Supplement A 4

2 7

3 8

3 - Supplement A 10 4

14 5

18 5 - Supplement A 19 5 - Supplement B 22 6

27 7

28 8

29 9

30 10 31 10 - Supplement A 14 11 35 References 37 9

11.

4L f

l i

}

1 L

Question 1 In Table 3.2 of CEN-135(S)-P, Plant-specific constants for SONGS, the narrow-band i

and and wide-band algorithm uncertainty factors (E) and E ) are listed as 2

, respectively. However, CEN-175(S)-P Data Base Document lists the values

'l and E

• of and respectively, for Ej 2

(a) Explain the discrepancies.

(b) Describe in detail how these values are obtained.

(c) Describe how the narrow-band and wide-band ranges are determined.

Answer

1. (a) The narrow-band and wide-band algorithm unce_rtain,ty factors (E) and E )

2 were reported in CEN-135(S)-P as and respectively. These values were preliminary values calculated during"the testing of the CPC STATIC algorithm. The final values of the narrow-band and wide-band algorithm u,ncertainty factors are correctly reported in CEN-175(S)-P as and respectively. The discrepancy between the preliminary values and the final values is due to the use of quality assured input

~

~

~

data in the final calculation and the correction of some errors in the STATIC (CETOP2) coding.

(b) The narrow-band and wide-be.d algorithm uncertainty factors are obtained by performing an uncertainty assessment for CETOP2 relative to the CETOP-D code. This assessment consists of dividing the operating space into a narrow range and a wide range and comparing the overpower margin (OPM) calculated by CETOP2 to that calculated by CETOP-D for thousands of cases in each range. From the resulting error distributions 95/95 one sided tolerance factors are determined which then become the algorithm uncertainty factors. These algorithm uncertainty factors provide a 95%

t onfidence' that at least 95% of the MDNBk's calculated by CETOP2 are conservative with respect to CETOP-D.

(c) The narrow and wide range limits on the CPC operating space are determined by examining the range of the parameters expected to be observed during A00's as well as trip limits and limits of. tha range of validity of the CE-1 correlation data base. A description of the range limits is given in Table 1..

TABLE 1 CPC OPERATING RANGE FOR SONGS 2 AND 3. CYCLE 1 UNITS NARROW RANGE WIDE RANGE PARAMETER l

Ccre Power (1) 1 of full power 01 power 4130%

0 < power i 130%

i 1.28 < P1 < 2.5 1.28 < P1 < 4.28 CPC-Calculated One-Pin Radial, Peak P1' (2)

-0.3 1 ASI 1 +0.3

-0.6 1 ASI 1 +0.6 l

t Hot Pin Axial Shape Index ASI (3) 6 Ccre Flow Rate (4) 1 of 143 x 10 90% < flow < 120%

90% < flow < 120%

lbm/hr 490 1 -cold 1 585 T

Core iniet Temperature. T-cold (5)

• F 530 < T-cold 1 571 Primary Pressure, P (6) psia 1960 < P < 2415 1785 < P < 2415 A

' NOTES:

(1) CPC's have no explicit range limits on power. However, the CPC's are valid within the range j

provided. The upper limit of the range is based upon a 125% analysis setpoint for the high linear power level trip with a 5% allowance.

CPC-calculated one-pin radial peak is conservative with respect to actual one pin peak and includes (2) any penalties for CEA misoperation events.

The +0.6 ASI limits were used for The 10.3 ASI limits are based on range of validity for POIL's.

(3)

The range limits are based on values of CPC-calculated hot pTn ASI. Differences between AND-2.

the CPC-calculated values and the actual values of hot pin ASI are accommodated b) the CPC uncertainty analysis.

CPC's have no explicit range limits on flow. However, the CPC's are valid within the range i

(4)

In addition, The CPC's generate a trip if more than two pumps have speeds less than 90%.

provided.

large conservative uncertainty factors are applied to DNBR and LPD if one or more pumps have speeds less than 90%. Part-loop operation is not a design basis for 3410 MWt CPC data constant j,

j 9eneration.

(5) Narrow range based on contractual transients. Lower limit of wide range based on a low SG pressure o

l trip analysis setpoint of 695 psia minus a 30 psi allowance. Upper limit of wide range based on the SG pressure required to lift the secondary safety valves. Temperatures include a +5.0*F a

uncertainty allowance.

i

~

I 1

t a

(6) Harrow range envelopes contractual transient range. Lower limit of wide range is based on a low pressurizer trip for CPC's assumed in the safety analysis. The upper wide range limit is the Pressures include a + 40 highest pressure of the CE-1 correlation data base (Reference ?).

This uncertainty is not valid for any accident conditions resulting psi uncertainty allowance.

in an abnormal ccatainment environment.

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SUPPLEMENT A SUPPLEMENT TO THE RESPONSE TO NRC QUESTION 1 FOR SONGS 2 CYCLE 1 I

In a telephone conversation with Gene Hsii of the NRC on September #17,1981, CE was asked to provide the histograms of the error distribution for the CETOP2 vs. CETOP-D uncertainty assessment. These error distributions are used to determine the narrow and wide range algorithm uncertainty factors as described in the response to NRC question 1 for the SONGS 2 Cycle 1 license submittal.

Attached are the histogram plots for the narrow range and wide range error distribu-tions. The narrow range uncertainty analysis was performed using over 1600 cases spanning the range of operation specified in Table 1 of the response to question 1 (Reference 1). The wide range uncertainty analysis wc4 performed using over 5000 cases spanning the range of conditions specified in Table 1 of the response to question 1 (Reference 1).

REFERENCES 1.

Responses to Questions on Documents Supporting SONGS 2 License Submittal, CEN-184(S)-P.

NOTE: The OPM error presented in the attached plots is defined as,follows:

CETOP-2 OPM - CETOP-D OPM rror =

CETOP-D OPM h

m' 9

i o _

.. _ + _.

NARROW RANGE ERROR DISTRIBUTION

[EEullEllCf-------------------------

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Question 2: In table 3.2 of CEN-135(S)-P the flow starvation factors split 1 split 2) for narrow-band and wide-band (F

and F operations are listed asL, land ( lues as[)lrespectively. Howe the Data Base Documint l'sts the va i]and[ ] respectively.

(a) explain the discrepancy.

(b) describe in detail how these values are obtained.

(c) provide ficw test data to justify these values.

Response

(a) The correct flow factor is { [las shown in the data base document, CEN-175(S)-P. The[[}value was a prelimin-are estimate.

(b)and(c) The flow factor is not determined by using flow model test data in CETOP.

It is a factor which is determined by benchmarking minimum DNBR values from CETOP against Detailed TORC values for a specified range of operating conditions. Further discussion on the use of the flow factor is included in Section 5 of Reference 1.

Two flow factors are determined for SONGS; the[' 3for the narrow band and([ ]for the wider band of operating conditions.

S 4

5.-

Question 3 CEN-175(S)-P, Data Base Document, lists the BERR1 value as 1.13.

Describe in detail how this value is obtained. Is BERR1 a fixed value or an addressable constant as indicated in CEN-135(S)-P? If BERR1 is an addressable constant, will it be 1.13 for an entire cycle?

Answer The

• alue of 1.13 for BERR1 (from CEN-175(S)-P) was preliminary. The final BERR1 value for SONGS-2 Cycle 1 is 1.15.

BERR1 is an addressable constant and is utilized in accordance with Section 2.5 of CEN-135(S)-P. The present stipulations of the CE analysis for calculation of the DNBR encertainty factor (EERR1) require that the BERR1 value of 1.15 remain through-out the entire first cycle.

The details of tha methodology used to obtain the value of BERR1 is documented in the response to item 222.129 of CEN-35(A)-P. The following table provides the individual uncertainty components which were used to calculate BERR1 for SONGS-2 Cycle 1.

O e

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BERR1 RELATED UNCERTAINTIES EQUIVALENT OVERPOWER 4

UNCERTAINTY COMPONENT (i)

MGNITUDE

-MARGIN UNITS, 5 (x )

g

1) Inlet Temperature II)

2) CPC Reactor. Coolant Flow Rate

3) Reactor Coolant System Pressure 4)'Startup'ipit Acceptance

Criteria,

5) Composite Modelling Error (3)

6) Computer Processing L

L (1) Uncertainties due to off-line flow measurement. CPC-to-off-line calibration, and reactor coolant pump speed measurement.

(2) Parameter uncertainties include, rod shadowing factors, temperature shadowing factor, and boundary point power coefficients.

(3) Combines the pseudn-hot-pin synthesis error { including ex-core detector signal noise and CEA position mea:urement error), CECOR planar radial peaking measurement uncertainty 'and

• rod ' bow uncert&i6tf on radial peaking factor.

0 4

e e.

e 6

D 0

0 0

9 4

e. _. _,,. - - - -, - -.

QUESTION 3 SUPPLEMENT A SONGS-2 CYCLE 1 BERR1 CALCULATIONAL METHODOLOGY The general formula of BERR1 is defined in equation (1).

• P (I)

P)

• P2 3

BERR1

=

Where P) composite DNB modelling uncertainty'

=

state parameter fluctuation and computer processing uncertainties.

P

=

2 startup test acceptance band uncertainty, P

=

3 P combines the CPC DNB modelling error, CECOR Fxy measurement error and rod bow 3penalty. Note that the CPC DNB modelling error includes the effect of pseudo-hot-pin synthesis error, ex-core detector noise and CEA position measurement error.

1 + (Ttotal

• total}

(}

P)

=

(3)

CECOR) - CECOR *

• (

Eere Y

~

total DNB model

+ IKS

• SENS1)2 + (DF)

(4)

KStotal " EIK3DNB model)

CECOR maximum derivative (sensitivity) of DNB-OPM with respcct to Where SENS1

=

radial peaking.

rod bow penalty due t9 increased radia' peaking.

DF

=

With appropriate values of KSDNB model' ESCECOR, SENS1 and DF equation (4) becomes total "

}

~

Therefore, (6)

P)

=

and Y '

P is based on th'e combination of Y), Y ' Y, Y4 5

2 2

3 f

Where Y) =

Y2*

I l

3*

Y4=

Y5*

c-g-9

+-

.&y

-..yc.,-y-3 3

-.m---.

and Y are combined in two ways.

Po is assigned The uncertainties Y, Y

.Y, Y the maximum value ddtermined from two kypes of calculational methodst Briefly p

4 the two methods are:

j 1.

2.

l tenn (Y)) is applied deterministically In both cases, the using a sensitivity.

1 l

(7)

RSS Combination

=

of Y2-Y5

~

Multiplicative (8)

Combination of

=

'Y) - Y5 1

Where, in all cases, SENS,,x =

g SENS

=

9 1

SENS

.... SENS and Using the appropriate values of Y, Y, Y, Y, Y 5

5 (see Table 1) ln ekuations (7)S,d (8)2 $e,following rga,ts 4

T ul SENS,..... SENS an arebbtained:

RSS Combinatior, of (g)

Y)....YS (equation 7)

Multiplicative Combination (10)

=

o f Y).... Y5 (equation 8)

(11)

P 2

i Y and Y

• P conventionally combines Y6 7

8 3

Where Y 6

Y

=

7 Y

8 and Y, P is evaluated according to the tiith appropriate values of Y, Y7 8

3 6

following technique:

a i

(Y )2 + (Y )

(12)

P3 " I + E(Y )

+

7 8

6

_ _ _ _. _ _ ~._ _ _...

and Y, P leads to:

Using appropriate values for Y ' Y7 8

3 6

P3"_

3 P3*

and P from equations (6), (11) and (13)

Using equation 1 and values of P), P2 3

respectively, we have:

BERR1

_1.15

=

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et

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TABLE 1 TEMPERATURE, PRESSURE, FLOW AND DNBR MEASUREMENT AND PROCESSING UNCERTAINTIES e

. PARAMETER MAXIMUM MEAN TYPE MAGNITUDE SENSITIVITY SENSITIVITY p

~

AOPM/ PSI

~

AOPM/PS 60PM/ PSI AOPM/PS 60PM/a*F 60PM/a*

^

SOPM/a% Flow A0PM/f.'

F1 AOPM/ADNBR AOPM/AD e

M M

e g

og 5

O O

O G

e s

9 e

e -

y m--,e,,,

w m

,m,

Question 4 Provide a sensitivity study of DilBR vs. BERR1 for various ASI and flow conditions.

Answer The BERR1 term is a multiplier on the core power level used in the CP'C calculations

. of DNBR. Therefore the requested sensitivity study is actually a study of how power affects DNBR for various ASI's and flows. This, sensitivity study is g'iven below.

~

A sensitivity study of the derivative, f

• h R was perfomed using the CETOP-D SONGS-2 Cycle 1 model. This study exa_ mined the change in overpower margin relative to change in the DNBR limit from

'to for the following conditions:

Pressure:

psia

~

Inlet Temperature:

_J F

jASI ASI 405 shapes from {.

g Core Flow:

] nominal volumetric flow J

d~

A plot of f r each condition is given 'in Figure 1.

dad R This study is similar to that provided for A,fl0-2 Cycle 2 in the response to NRC

~

Question 492.66.

A sensitivity study of D:tBR vs. Power (BERRl) for various flows is also provided.

The methodology used in this study is described below.

l

1) The pressure, inlet temperature, radial peak, and ASI for this study l

were held constant at the following values.

l Pressure

.Jpsia e

Inlet Temperature -

F

~

~

~

Radial Peak l

m ASI -

The power which results in a MDNBR of approximately at

. - flow was determined.i.

Using this power and(., flow the MDNBR was calculated by CETOP2.

! t h.

2

2) Using the flow I Mlbm/ft br) a multiplier on po(er (BIRRl) is increased In 702 incremenfs until a MDNBR of approximately is reached.

These values of DNBR vs. BERR1 are plotted in Figure 2.

3) Next, the value of BERR1 is held constant at The flow is decreased until a MDNBR of approximately is obtained.'" This DNBR vs. flow sensitivity

~

is shown in Figure 3.

4) Finally, holding the flow at the value which re_sulted_in a MDNBR of in step 3, the value of BERR1 is reduced from to in intervals of 702.

i This values of DNBR vs. BERR1 at the lower flow are pl'otted on Figure 2 also.

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16-y c

--.---um

- -,w-

---

r--r ye-y

-+v--

p FIGURE 2 MDNBR vs BERR1 e

z l i 1.60 1.56 1.52 1.48 3.44 1.40 g 1.36 E*

1.32 1.28

)

1.24 1.20 1.16 l

1.12 1.10 1.04 b

1.00 -

1.00 1.04 1.08 1.12 1.16 1.20 1.24 x

BERR1

,--,p

,.,,.,.,,ry-

,,-c.-

FIGURE 3 MDNBR vs MASS FLUX t

1,38 _

1.36 1.34 1.32 1.30 1.28 1.26 1.24 1.22 1.20 1.18 1.16 1.14 i

1.12 1.10 i

1.08 1.06 1.04 -

2.32 2.36 2.40 2.44 2.48 2.52 2.56 2.60 2.64 2

MASS FLUX (M1bm/f hr) 9 -

i Question 5: CEN-175(S)-P lists the spacer grid loss coefficient as[

$)

However, the response to an NRC question (CEN-155(S)-P) indicates thattheJverall loss coefficients for HID-1 and HID-2 grids are

[

tjand(

} respectively. Explain the discrepancy.

Response

The[ land (~~ loss coefficients are evaluated based upon best estimate calculations and test data.

In the CETOP on-line program one loss coefficient was used for both grid types since one value could easily be programmed into the protection system as opposed to using nore than, one constant or Reynolds number dependent equations. The(

value was chosen instead of a best estimate value since a lower value produces slightly conservative MDNBRs. This conservatism results from the reduction in cross-flow which is associated with the use of a lower grid loss coefficient.

In addition to this conservatism, the CETOP on-line program is benchmarked to the parent design code CETOP-D, which uses more accurate grid loss coefficients. Therefore the DNBRs predicted by CETOP on-line program will be conservative due to the benchmarking and use of the(..) grid loss coefficient.

e 5..

QUESTION 5 SUPPLEMENT A

" ~ ~

Question: Explain why the lower grid loss coefficient

, used in the SONGS CETOP on-line program, produces conservative MDpBRs.

Response: The following response is given in addition to the one provided in Question 5 received by C-E 19, 1931 to verify the lower grid loss coefficient { cp August

, produces conservative hDNBRs.

The use of a higher grid loss coefficient tends to equalize the pressure differences between the hot and adjacent assemblies faster than a lower value. At the lower portion of the, core the hot assembly receives crossflows from the adjacent a'ssemblies since the adjacent assemblies are colder and have higher inlet flows. A higher grid loss coefficient in this region of the core provides more crossflow into the hot assembly to equalize the pressure differences between the assemblies.

In the upper portion of the core the flow leaves the hot assembly and hot channel due to higher temperatures in the hot assembly.

A higher grid loss coefficient will increase this crossflow.

However, the local coolant conditions in the hot channel will still be less severe than the coolant conditions that would prevail if a lower grid loss coefficient was used since there is an increase in crossflow into the hot channel from the adjacent assemblies in the lower portion 'of the core.

Therefore MDNBR calculated in the hot channel will be conservative for a lower grid loss coefficient. Several CETOP-D cases were

<... performed at..various operating conditions. as, a. function of grid loss coefficient to verify the above statement. The CETOP-D model described in Section~ 5 of CEM-160(S)-P was used in the sensitivity study. Operating conditions were chosen to consider boil'ing and non-boiling in the hot assembly and MDNBR occurring at the lower and upper portions of the core. The results in Table 1 indicate that MDNBR increaseswhen using a hicher grid loss coefficient.

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QUESTION 5 SUPPLEMENT 8

,r

Background:

'~~

A meeting was held on Nov. 16, 1981 between representatives of the NRC, C-E, and SCE. At that meeting the NRC raised a concern about the CETOP2 model used in the SONGS-2 CPC's. The NRC's concern was that the CETOP2 model did not properly model the HID-1 and HID-2 spacer grids used in the SONGS-2 core. C-E pointed out that the benchmarking process used in determining the CETOP2 algorithm pen &lty factors conservatively compensates for any effects of using grid co-efficients which are not best estimate values. At the conclusion of the meeting the NRC requested that C-E provide a study demonstrating the sensitivity of the CETOP2 model uncertainty to the grid coefficients.

Methodology:

In this study the CETOP2 model is compared with the CETOP-D model over the allow-able operating space for the SONGS-2 CPC's. The CETOP-D model uses best estimate correlations to determine the grid coefficients. Three CETOP2 models are compared with the CETOP-D model.

The first model is the CETOP2 model used in the SONGS-2 CPC's and has grid coefficients of The second CETOP2 model

~

uses grid coeffici6nis of

". The third CETOP2 model uses grid coefficients calculated from the best estimate correlations at nominal operating conditions.

The Overpower Margins (0PM) calculated using each of these CETOP2 models ire compared to the OPM calculated using CETOP-D for approximately 6800 cases.

Results:

Tablel sumarizes the results of this study by providing the statistics of the CETOP2 errer distributions.

In Table 1 the statistics are defined 'as follows:

(percent er M X = OPM CTOP2 - OPM CTOPD X 100 OPM CTOPD UF 95/95 = 95/95 probability / confidence factor (percent OPM) p,NE Xj /N (mean error) 1

f I

o$

lX,,j. p 2 (standarddeviation)

(N-1)

PF = 1 + E + UF95/95 (penalty factor) 100 The penalty factor is defined as the multiplier on the power used in'CETOP2 which will provide a 95% confidence that at least 95% of the CETOP2 calculations are conservative to CETOP-D. The statistics are provided for two regions of operating space corresponding to the Narrow band and Wide band of the CPC operating space.

In examining the sensitivity of the model uncertainty two quahtities can be used. The standard deviation of the error distribution will indicate the spread of the distribution around the mean and is a measure of the model uncertainty.

The 95/95 uncertainty factor (UF95/95) is the component of the penalty factor which compensates for the spread in the error distribution. Table 2 provides the change in the standard deviation and the 95/95 uncertainty factor in going from the on-line CETOP2 model to the other two models.

(This difference is provided in units of percent OPM and also in DNBR. The conversion of %0PM to DNBR is based on a conversion factor of -0.6 %0PM at a MDNBR of 1.20).

%DNBR

==

Conclusions:==

The results of this study indicate that the values used for the grid coefficients do not significantly impact the model uncertainty. The effects of this parameter or any other component of the CETOP2 model on the model uncertainty are con-servatively compensated for by the 95/95 uncertainty factor. Any bias in the CETOP2 model will show up in the mean error. Therefore the penalty factor, which is defined PF = 1+ E + UF will conservatively compensate the 95/95 100 on-line calculations for any bias and uncertainty in the algorithm. Thus the level of conservatism in the algorithm calculations is always maintained at least at the 95/95 prob' ability / confidence level..

Conservatisms in the CPC's The algorithm penalty factors given in Table 1 for the on-line CETOP2 model provide at least a 95% probability, at the 95% confidence level, that CETOP2 is conservative with respect to CETOP-D. The penalty factors included in the on-line data base, however, are actually for the narrow and wide bands respectively. Therefore the on-line C/C DN3R calculations are more c;nservative than the 95/95 level.

The conservatism of the CETOP2 algorithm is measured against the CETOP-D code.

However CETOP-D is forced through a benchmarking process to calculate conservative DNBR's with rest et to the Detailed TORC model. Therefore"there is conservatism in the CETOP-D calculations which is built into the benchmark process.

The SONGS-2 CPC's use a deterministic treatment of state parameter uncertainties and a calculation of the BERR1 penalty factor for system parameter uncertainties which is more conservative than the method used in other C-E plants (i.e., ANO-2 cycl e 2).

These conservatisms inherent in the treatment of algorithm and system parameter-uncertainties will result in conservative calculations of the MDNBR and therefore adequate plant protection by the CPC's.

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I Table 1 Statistics of CETOP2 Model Uncertainty l

Narrow Band (1617 cases)

CETOP2 Model E

(% OPN) 0

(% OPF))

PF UF 95/95

(%OPM)

~

Wide Band (5186 cases) 7

(%OPM) l O

I

(%OPM)

PF UF i'

(% OPM)/95 95 9

G S _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

Table 2 Change in CETOP2 Model Uncertainty Narrow Band ON-LINE ON-LINE vs vs Model Model Ao (% OPM).

(- DNBR unit:)

AUF 95/95

(- DNBR units)

Wide Band j

Ao (% OPM)

( ~ DNBR units)

A UF 95/95

( ' DNBR units) l 6

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I Question 6: Is the SONGS CETOP-D report identical to the ANO-2 CETOP-D report?

Response

The SONGS report is identical to the ANO-2 CETOP report except

g for the following differences

(a) System parameter uncertainties in SONGS CETOP-D are

~

applied deteministically instead of statistically for ANO-2.

(2) Section 5 of the SONGS CETOP-D report is slightly different since it describes thermal margin analyses for SONGS core instead of ANO-2.

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Question 7 In Appendix A of CEN-135(S )-P. CETOP-2 Functional Description, there is a dis-crepancy in the range of applicability of Martinelli-Nelson void fraction correlation between the CETOP-2 algorithm and Table 3.1.

These applicability ranges also differ from that described in TORC. Explain the discrepancy.

Answer The values of the quality ranges used in determining the void fraction correlation in CETOP-2 are the [

J. The values gi.ven in Taile 3-1

~

and on page A-7 of CEN-135 are incorrect. The correct implementation of the void fraction correlation is given on page A-26 of CEN-135(S)-P.

The pressure range for this correlation is the same as in TORC.

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Question 8

.~

Describe how the values of energy and momentum transport coefficients are obtained for SONGS CPC.

Answer The energy and monientum transport coefficients are constants used in the CETOP2 algorithm to model the enthalpy and momen,tum exchange between the buffer channel 7

. or hot channel and the hot assembly. The energy transport coefficient is deter-mined by

}.Anyuncertaintyinthe t

CETOP2 calculations due to the use of this constant energy transport coefficient are conservatively compensated by the algcrithm uncertainty factors.

The momentum transport coefficient it a constant used in the calculation of the transverse momentum exchange. The calculation of DNBR has been found to be insensitive to this coefficient. Therefore a typical value determined from TORC subchannel calculations is used. The momentum transport coefficier. is defir.ed as:

r CN

=

L Pressure Transport Coefficient l

where N

=

P..g.

Number of gaps

=

CN

=

r These transport coefficients and the sensitivity of DNBR to each is discussed in the responses to NRC questions 492.3 and 492.75 of the ANO-2 Cycle 2 licensing submittal as well as in Reference 1.

REFERENCE 1.

C. Chiu, et al., "Enthalpy Transfer Between PWR Fuel Assemblies in Analysis by the Lumped Subchannel Model", Nuclear Enoineering and Desion, 53 pp.165 -

186,(1979).

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j Ouestion 9: Provide justification for using a guide tube channel modeling for the pseudo hot channel in SONGS CPC. You must show that the--

minimum DNBR also occurs in a guide tube channel during the entire cycle if the modeling is to be used for one cycle only.

The same should be proved for the entire core life if the modeling is to be used for the entire SONGS core life.

~

Response

The response to this question is the same as that provided in Question 492.77 for ANO-2.

(Ref. 2). A copy of this response is included below for SONGS.

The MCt:F in detailed TORC will always be located in the corner guide tube channel throughout the cort life, if the following are true:

1.

The cold wall correction factor in the CE-1 correlation is used to reduce DNBR in guide tube channels.

2.

Present fuel management schemes are used to generate power distributions which produce the largest pin peaks near guide tube water holes throughout the core life.

Since the above items are true for present SONGS design analyses, MDNBR will always occur in the corner guide tube channel in detailed TORC. Therefore a best estimate model for CETOP-D or CETOP-2 should also use the corner guide tube channel as the hot channel.

If in reality MDNBR does not occur in the corner guide tube channel, the MDNBR predicted with detailed TORC (in the corner guide tube channel) will still be lower than any value in the core since the use o'f the CE-1 correlation in detailed TORC has been verified to produce conservative results relative to test measurements (Ref. 3), which included CHF occurrences in both the guide tube and matrix channels. The CETOP-D MDNBR will also be conservative relative to the actual MDNBR in the core since it is benchmarked to detailed TORC results.

However, the corner guide tube channel does not have to be modeled in CETOP-D as the hot channel since the benchmarking forces CETOP-D to be independent of the location of the hot channel and other model differences between TORC and CETOP-D. -- -

- = -

OUESTION #10 "THE DSVT (DYNAMIC SOFTWARE VERIFICATION TEST) CASE 22-4 0F THE CPC PHASE II TEST REPORT (CEN-173(S)-P) SHOWS THE SINGLE CHANNEL DNBR TRIP TIME OF 56.35 SECONDS COMPARED TO THE ACCEPTABLE TRIP RANGE OF 66.45 TO 66.75 SECONDS. THE REPORT FURTHER INDICATES.

THAT THE REASON IS BELIEVED TO BE THE DIFFERENCE IN MACHINE ROUND-OFF RATHER THAN SOFTWARE ERROR. PLEASE QUANTIFY YOUR FIND-INGS TO SHOW THAT THE ROUND-OFF DIFFERENCE CAUSES THE TRIP TIME TO BE 0.1 SECONDS OUTSIDE THE ACCEPTABLE TRIP TIME RANGE."

RESPONSE

CONSIDERABLE EFFORT WAS PUT FORTH TO MORE FULLY ANALYZE THIS

- - DYNAMIC TEST CASE, PARTICULARLY AS TO THE NATURE OF THE TRIP TIME DISCREPANCY. THERE ARE THREE POSSIBLE CAUSES OF THE DISCRE-PANT TRIP TIME-

1) SOFTWARE ERRORS IN THE CPC DESIGN CODE OR THE SPECIAL DSVT SOFTWARE WHICH OVERLAYS PORTIONS OF THE CPC EXECUTIVE, OR

2) DIFFERENCES DUE TO THE VARIATION BETWEEN THE PRECISION AVAILABLE

~~

TO THE INTERDATA 7/16 COMPUTER WHICH RUNS THE CPC SYSTEM SOFT-

~

WARE AND THE CDC-7600 (64-BIT) WHICH RUNS THE CPC FORTRAN CODE.

OR

3) ERRORS WHICH MAY HAVE BEEN MADE IN.THE RUNNING OF THE DSVT TEST CASE ITSELF.

IN ORDER TO VERIFY THAT NO SOFTWARE ERRORS EXISTED IN EITHER THE CPC SOFTWARE OR THE SPECIAL DSVT SOFTWAPE, HAND-CALCULATIONS WERE PERFORMED AT TIMES IMEDIATELY BEFORE AND AFTER THE TRIP

_ WITH KNOWN INPUTS RECORDED. THIS VERIFICATION INDICATED THAT THE DNBR VALUES BEING CALCULATED BY THE SOFTWARE PROGRAMS WERE CORRECT AND WERE GENERATING THE CORRECT TRIP RESPONSE. THE SPEC-IAL DSVT SOFTWARE WAS VERIFIED TO BE OVERWRITING PORTIONS OF THE EXECUTIVE CORRECTLY AND TO BE PERFORMAING THE TASK OF INPUT DATA

~ ~ "

INTERPOLA PION FUNCTIONALLY IDENTICALLY TO THE CPC f0RTRAN CODE.

ALL OF THIS SOFTWARE IS DEVELOPED AND TESTED IN ACCORDANCE WITH THE APPROVED CPC PROTECTION ALGORITM SOFTWARE CHANGE PROCEDURE CEN-39( A)-P, REVISION 02.

- =-

THE DSVT CASE ITSELF WAS RERUN SEVERAL TIMES DURING "HE INITIAL PHASE II TESTING PROCESS, AND EACH TIME YIELDED IDENTICAL RESULTS.

BY PROCESS OF ELIMINATION, _ AND BY CONFIRMATION OF INPUTS RECORDED IT WAS OBSERVED THAT SMALL DIFFERENCES EXISTED BETWEEN INPUTS TO

._.. THE CPC SOFTWARE AND FORTRAN CODES. BECAUSE IT HAD BEEN VERIFIED THAT THE ALGORITMS WERE FUNCTIONALLY IDENTICAL, IT WAS CONCLUDED THAT THIS DIFFERENCE MUST HAVE BEEN DUE TO THE DIFFERENCE IN MACH-

..._.____ __.__ q _

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INE PRECISION REALIZED IN INTERPOLATION OF THE PROCESS INPUTS. THIS DIFFERENCE, UNLIKE THE PROCESSOR UNCERTAINTIES FOR THE APPLICATION PROGRAMS, IS NOT CALCULATED AS PART OF THE INPUT SWEEP TESTS, AND THUS WOULD NOT HAVE BEEN FACTORED INTO THE DSVT ACCEPTANCE CRITER-IA.

~

DURING RECENT ANALYSIS TO ATTEMPT TO QUANTIFY THIS DIFFERENCE AND THUS ANSWER THE STAFF'S QUESTION, IT WAS DISCOVERED THAT A MINOR CHANGE IN HOW THE TEST CASE WAS EXECUTED RESULTED IN A TRIP.

TIME WITHIN THE FORTRAN-GENERATED ACCEPTANCE CRITERI/. IT IS NOW EVIDENT THAT WHILE SMALL INPUT DIFFERENCES ARE PRESENT AND MAY (IN SOME CASES) RESULTS IN DIFFERENT TRIP TIMES, THIS IS NOT THE SITUATION FOR TEST CASE 22-4. THE TRIP TIME WHICH RESULTED USING THE REVISED ( AND CORRECT) ETHOD WAS 66.65 SECONDS, WHICH IS WITH-IN THE DSVT ACCEPTANCE CRITERIA FOR TRIP TIMES FOR THIS TEST CASE.

A BRIEF DISCUSSION OF TEST CASE 22-4 AND THE SOURCE OF TRIP TIME DIFFERENCES FOLLOWS:

THE TRANSIENT REPRESENTED BY THIS TEST CASE RESULTS IN A DNBR TRIP BEING SET, BEING RESET AT A LATER POINT IN TIME, AND THEN EVENTUAL-ALLY BEING SET ONCE AGAIN. THE DSVT PROGRAM OVERLAYS TO THE CPC SYSTEM RESULT IN STORED AND DISPLAYED YALUES OF TIMES AT WHICH THE DNBR OR LPD TRIPS OR PRE-TkIPS CHANGED STATE. THUS FOR THIS PARTICULAR CASE IF RUN TO DURATION, THE FINAL VALUE STORED IN THE DNBR TRIP LOCATION WOULD BE THAT AT WHICH THE SECOND TRIP OCCURRED.

THE TEST APPROACH USED IN DSVT FOR CASES WHICH INYOLVE TRIP RESETS HAS BEEN TO ONLY RUN THE TEST CASE LONG EN0 UGH TO GET AN INITIAL TRIP. REASONS FOR THIS ARE THAT A TRUE TRIP WILL RESULT IN CEA INSERTIONS WHICH ARE NOT MODELLED FOR THE TEST CASE ( AND THUS THE l

TEST CASE DIVERGES FROM ACTUAL PLANT CONDITIONS UNDER THE CIRCUM-STANCES) AND ALSO BECl4JSE A COMPARIS0t/ OF THE INITIAL TRIP TIME IS THE MOST SIGNIFICANT IN ENSURING THAT POTENTIAL SOFTWARE ERRORS DO NOT EXIST WHICH MIGHT IMPACT PLANT SAFETY.

i THE ETHOD USED TO MODIFY THE LENGTH OF A TEST CASE IS TO ENTER (VIA THE OPERATOR'S MODULE) A DIFFERENT TRANSIENT LENGTH (IN SEC-ONDS) WHILE THE TEST CASE IS IN INITIALIZATION. DURING PHASE II TESTING, A TRANSIENT LENGTH OF 66.2 SECONOS WAS INITIALLY ENTERED AND FOLLOWING INITIALIZATION OF THE TEST CASE IT WAS EXECUTED.

AS THIS DID NOT THEN RESULT IN A TRIP DN LOW DNBR, THE TRANSIENT WAS THEN LENGTHENED IN 50 MSEC. INCREMENTS UNTIL A TRIP WAS OBTAI-NED AT 66.35 SECONDS. THIS THEN BECAE THE DSYT SINGLE CHANNEL RES-ULT FOR TEST CASE 22-4.

WHEN THIS TEST CASE WAS RE-ANALYZED RECENTLY AN IN.ITIAL TRANSIENT -

LENGTH OF 66.8 SECONDS WAS ENTERED THROUGH THE OPERATOR'S MODULE (0.M.), WHICH WHEN RUN, RESULTED IN A TRIP TIME OF 66.65 SECONDS.

IN FACT, AS LONG AS A TRANSIENT LENGTH OF 66.65 SECONDS OR LONGER WAS ENTERED THE SAME RESULTS WERE OBTAINED. WITH TRANSIENT LENGTHS OF LESS THAN 66.65 SECONDS, IT WAS NECESSARY TO USE THE 0.M. TO PROVIDE SUCCESSIVE 50 MSEC. INCREMENTS TO THE TEST CASE UNTIL A TRIP WAS OBTA!HED. FOR EACH OF THE5E CASES A DIFFERENT TRIP TIME WAS OBTAINED FOR EACH DIFFERENT INITIAL TRANSIENT LENGTH.

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~

FURTHER INTO THE TEST CASE TRANSIENT THAN PREVIOUSLY. THUS THE PRO-PER ETHOD OF VERIFYING TRIP TIMES FOR CASES WITH RESETS IS TO ENT-ER AN INITIAL TEST CASE LENGTH 1HROUGH THE 0.M. (DURING INITIALI-ZATION) WHICH IS SLIGHTLY GREATER THAN THE EXPECTED TRIP TIME, BUT OBVIOUSLY LESS THAN THE RESET TIME (OR ANY SUBSEQUENT TRIP TIME).-

THIS WILL ENSURE CONTINUOUS OPERATION OF THE CPC SOFTWARE THROUGH THE INITIAL TIME-TO-TRIP WHICH IS CONSISTENT WITH THAT OF THE CPC FORTRAN CODE AGAINST WHICH IT IS BEING VERIFIED. THIS HETHOD WILL BE INCLUDED AS PART OF THE DSVT PROCEDURE FOR FUTURE TESTS.

ALL 39 OTHER SONGS-2 CYCLE 1 DSVT TEST CASES WERE SUBSEQUENTLY' ANALYZED TO SEE WHETHER THE USE OF THE SO MSEC. INCREMENT THROUGH THE 0.M. WAS USED TO DETERMINE A TRIP TIME. NO OTHER CASES WERE DETERMINED TO HAVE USED THIS METHOD, THUS MAINTAINING ALL OTHER RESULTS AS VALID. THIS FURTHER ANALYSIS HAS IDENTIFIED THAT THE SOURCE OF THE PHASE II TRIP TIME DISCREPANCY WAS NOT A DIFF-ERENCE IN MACHINE PRECISION AS WAS PREVIOUSLY THOUGHT, BUT WAS RATHER THE RESULT OF A TESTING TECHNIQUE WHICH WAS NOT VALID FOR THIS APPLICATION. IDENTIFICATION OF THE CORRECT TECHNIQUE IS CONSISTENT WITH THE CPC SOFTWARE PROGRAM AND THE DSVT PRO-GRAM AND ITS APPLICATION RESULTS IN ACCEPTABLE TRIP TIMES.

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QUESTION 10 SUPPLEMENT A j

t INVESTIGATION OF SONGS-2 CYCLE 1 DSVT TEST CASE 22-4

(

i When the spare NJtton is used to single step beyond the initial run time of a test case, the scheduling of CPC application programs by

)

the DSVT sof tware differs from normal CPC operation in that the POWER and STATIC application programs are given extra time (50 msec.) to i

execute. This extra time is not accounted for in the DSVT time-of-day.

i Detailed study of test case 22-4, run at various initial starting times, i

revealed that the cause of the varying-trip times was this extra time given to STATIC to execute. The following table gives a comparison of the DSVT time-of-day when STATIC finishes execution, when UPDATE finishes its first execution after STATIC completes execution, and when the i

trip occurs.

(Note - all times are in seconds.)

Initial Run Time STATIC Completes Next UPDATE Completes Trip Time l

66.20 66.35 66.35 66.35 66.25 66.40 66.45 66.45 66.30 66.40 66.45 66.45 66.35 66.45 66.45 66.45 l

66.40 66.45 66.55 66.55 1

66.45 66.50 66.55 66.55 66.50 66.55 66.55 66.55 l

66.55 66.55 66.65 66.65 l

66.60 66.55 66.65 66.65 l

66.65 66.55 66.65 66.65 As the table shows, the trip always occurs on the next execution of 8

UPDATE after STATIC completes execution (i.e., the CPC algorithms j

always generate the trip at the same point in the same cycle).

Thus, the trip time discrepancy is caused by DSVT task scheduling differences when the spare button is used to single step a test case.

j When the initial run time is 66.65 seconds or longer the trip time is always 66.65 seconds because task scheduling is not interrupted until i

af ter the time trip. This value is thus correct and meets the acceptance criteria for this test case (66.45-66.75 seconds). The I

task scheduling difference will be modified in the DSVT sof tware for future testing.

l As a result of this investigation, it is concluded that all test cases meet the DSVT acceptance criteria on initial values and trip times for DNBR and LPD.

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QUESTION 811

" PROVIDE THE RANGES OF LIMITS ON ADDRESSABLE CONSTANTS WITH AN

- I EVALUATION OF ENTRY ERRORS AS COMMITTED IN THE MARCH 9,1981 E ETING."

RESPONSE

DISCUSSION WITH THE NRC STAFF ON THNINTENT OF THIS QUESTION INDICATED THAT THEIR CONCERN WAS PRIMARILY WITH PREVENTING INCORRECT ENTRIES OF ADDRESSABLE CONSTANTS, AND THAT AN EVAL-UATION OF THE IMPACT OF ENTRY ERRORS ( AS STATED) MIGHT NOT BE REQUIRED, PROVIDED THAT THE PROCEDURE FOR PREVENTING ENTRY ERRORS WAS CONSIDERED ACCEPTABLE.

THIS SAE CONCERN WAS VOICED DURING THE AND-2 CYCLE 2 NRC REV-IEW OF THE CPC'S AT WHICH TIME IT WAS DECIDED BY AP&L TO ATTE-MPT TO RESOLVE THE CONCERN BY INCORPORATION OF A TECH SPEC (2.2.2) WHICH REQUIRED PLANT SAFETY COMMITTEE REVIEW FOR CHANGES INVOLVING:

1) FREQUENTLY CHANGED (TYPE I) ADDRESSABLE CONSTANTS OUTSIDE OF AN " ALLOWABLE R ANGE" WHICH IS MORE RESTRICTIVE TH AN THE R ANGE

~ WHICH THE CPC CALCULATORS THEMSELVES WILL ALLOW.

2) INFREQUENTLY CHANGED (TYPE II) ADDRESSABLE CONSTANTS OTHER THAN THOSE MADE AS A RESULT OF POST-FUEL LOADING PHYSICS TESTS, OR AS REQUIRED FOR TECH SPEC COMPLIANCE.

THE TECH SPEC ITSELF WAS REVIEWED BY C-E PRIOR TO SUBMITTAL TO AND APPROYAL BY THE NRC. AP&L'S BASIS FOR INCORPORATING THE TECH SPEC WAS NOT TECHNICAL IN NATURE BUT IN ORDER TO EXPEDITE THE RESTRICTIVE LICENSING SCHEDULE.

IT WAS INITIALLY PROPOSED TO THE NRC STAFF THAT C-E WOULD PREPARE j

A SIMILAR TECH SPEC REQUIREMENT FOR SONGS-2, AND, SUBJECT TO SCE l

APPROVAL THIS WOULD BE PROPOSED TO THE NRC. BASED UPON FURTHER CONSIDERATIONS, C-E SUGGESTED AN ALTERNATE SOLUTION TO THIS CON-CERN; NAMELY THAT ADMINISTRATIVE CONTROLS ON CHANGES TO ADDRESS-ABLE CONSTANTS BE ESTABLISHED WHICH ENSURE AN ADE00 ATE MEANS OF INDEPENDENT REVIEW DESIGNED TO PRECLUDE ENTRY ERRORS.

I l

THE OBJECTIONS TO THE SOLUTION OF ACCOMODATING ADDRESSABLE CONS-'

TANT CHANGES VIA THE.mTECH SPECS ARE AS FOLLOWSr

1) CURRENTLY NO ANALOG TRIPS REQUIRE SUCH A REVIEW PROCESS, DES-PITE THE GREATER PROBABILITY AND CONSFOUENCES (IN MANY CASES) 0F ENTERING AN INCORRECT VALUE AS AN ANALOG TRIP SETPOINT.

CHANGES TO THE INTERNAL CALCULATIONS OF THE CPC'S ARE EASILY ACCOMPLISHED AND VERIFIED VIA KEYPUNCH ENTRIES AND THE OPER-ATOR'S MODULE DISPLAY, RESPECTIVELY. THIS METHOD IS CONSIDERED MORE RELIABLE THAN THAT CURRENTLY USED FOR CHANGES TO ANALOG i

TRIP SETPOINTS WHICH INVOLVE ADJUSTMENTS USING VOLTAGE REGU-LATING EQUIPMENT AND VERIFICATION USING HETERS. FURTHERNORE, i

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CHANGES TO ANALOG SETPOINTS HOLD THE POTENTIAL FOR VOLTAGE DRIFT WHICH IS OBVIOUSLY NOT A FACTOR FOR THE DIGITAL SYSTEM.

2) INCLUDING ADDITIONAL REQUIREMENTS ON ADDRESSABLE CONSTANT CHAN-GES WITHIN THE TECH SPECS WOULD ONLY SERVE TO " CLUTTER" THIS DOCUMENT WITH INFORMATION ON A MORE DETAILED LEVEL THAN REQUI-RED. THIS WOULD FURTHER AN ENVIR0titENT FOR PLANT OPERATORS.

ALREADY ENCUMBERED BY NUMEROUS TECH SPEC REQUIREMENTS, ALL OF WHICH MUST BE SIMULTANEOUSLY ADHERED TO. THE POTENTIAL FOR VIO-LATING THIS OR OTHER TECH SPECS IS THUS INCREASED. INCORPORA-ATION OF CONTROLS ON ADDRESSABLE CONSTANT CHANGES WITHIN PLANT OPERATING PROCEDURES RATHER THAN TECH SPECS TENDS TO REDUCE THE PROBABILITY OF VIOLATING AN LCO WHILE MAINTAINING AN ADEQ-UATE DEGREE OF QUALITY CONTROL.

3) ESTABLISHING SUCH A RESTRICTIVE TECH SPEC REQUIREMENT MAY INHI-BIT PLANT MANUEVERABILITY, PARTICULARLY DURING " NIGHTTIME" HOURS WHEN PLANT SAFETY COMMITTEE APPROVAL MAY NOT BE IMED-IATELY AVAILABLE. ALTHOUGH OTHER THAN MINOR CHANGES TO TYPE I AND ANY CHANGES TO 1YPE II ADDRESSABLE CONSTANTS FOR ROUTINE PLANT OPERATION WOULD GENERALLY BE ANTICIPATED WELL IN ADVANCE.

THE POTENTIAL FOR THIS NEED NONETHELESS EXISTS AND THUS IT WOULD BE ADVISASLE NOT TO INCLUDE THIS AS A REQUIREMENT.

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s

s 1.

"CETOP-D Code Structure and Modeling Methods for San Onofre Nuclear Generating Station Units 2 and 3", CEN-160-(S)-P, May,1981.

2.

" Responses to Questions on Documents Supporting ANO-2 Cycle 2 License Submittal", CEN-157(A)-P. Amendements 1-P, 2-P, 3-P, 1981.

3.

"C-E Critical Heat Flux Correlations for C-E Fuel Assemblies wi.th Standard Spacer Grids", CENPD-162-P-A, Sept.1976.,

f(

C. Chia, et al., "Enthalpy Transfer Betweer Pi!P. Fuel Assemblies in Analysis by the Lumped Subchannel flodel", i:cclear Engincaring and Design, 53 pp.165 -

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ENCLOSURE 7 4

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