ML20056D961

SER Accepting Licensee 930325-0429 Submittals of Technical Info to Support Continued Operation of Facility for Remainder of Fuel Cycle 7

ML20056D961
Person / Time
Site:	Catawba
Issue date:	07/30/1993
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20056D960	List: ML20056D959 ML20056D961
References
NUDOCS 9308190082
Download: ML20056D961 (11)

Text

.

.. [FM RicNo  !

[ ( MI ' ,i J UNITED STATES

.gp j NUCLEAR REGULATORY COMMISSION gv j f WASHINGTON, D.C. 20555 @ 01 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION DUKE POWER COMPANY. ET AL.

CATAWBA NUCLEAR STATION. UNIT 1 DOCKET NO. 50-413

1.0 INTRODUCTION

By letter dated August 24, 1992, as supplemented September 2, 4, 17, and 23, ,

1992, Duke Power Company, et al. (the licensee), submitted a request for -

changes to the Catawba Nuclear Station, Units 1 and 2, Technical l Specifications (TSs). The requested changes revised TS Sections 3/4.4.5 and

~

3/4.4.6, and associated Bases 3/4.4.5, 3/4.4.6.2, and 3/4.4.8 allowing the '

implementation of an interim steam generator tube plugging criteria for defects located at the tube support plate (TSP) elevations. The. amendments reduced the allowed primary-to-secondary operational leakage from any one steam generator from 500 gallons per day (gpd) to 150 gpd. The total allowed primary-to-secondary operational leakage through all steam generators was also reduced from 0.5 gallons per minute (720 gpd) to 0.4 gallons per minute (576 gpd). The charges were applicable for Unit I fuel Cycle 7. The supplemental submittals provided clarifying information to the original submittal.

The staff reviewed the above submittals as documented in the issuance of the 1 amendment package dated September 25, 1992 (Reference 1). The staff concluded that the proposed interim tube repair limits and leakage limits would ensure adequate structural and leakage integrity of the steam generator (SG) tubing at Catawba Unit 1, consistent with applicable regulatory requirements, until

~

May 1, 1993. The staff concluded that a mid-cycle inspection was warranted for the reasons cited in Reference 1. The staff concluded that-a mid-cycle i inspection was necessary by May 1,190.' to ensure that the proposed 1.0 volt interim limit would provide- a comparable level of conservatism as compared to the interim limits approved for plants with 7/8-inch outside diameter (OD) SG tubing. The NRC staff found the_ proposed changes to the TSs to be acceptable.

By letter dated March 25, 1993, as supplemented by letters dated April 8, 21, 22, 28, and 29, 1993, the licensee submitted a request ( References'2-7) l

~ intended to support continued operation of Unit 1 for the remainder of Cycle  ;

'7 . This request provides, in part, additional information on margins to tube ~

burst, bobbin coil voltage normalization, and main steam line break-(MSLB) leakage.

t 93082900e2 93073o PDR ADOCK 05000413 P ppg

2.0 BACKGPOUND l

. The modi'ications to the tube repair limits, as documented in Reference 1, i included a one volt repair criterion for axially oriented outside diameter i stress corrosion cracking (0DSCC) flaws confined to within the thickness of j the tube support plate (TSP) in lieu of the depth-based limit of 40%. The i staff review concluded that the interim tube repair limits and leakage limits i would ensure adequate structural and leakage integrity of the SG tubing at i Catawba Unit 1, consistent with applicable regulatory requirements, until May  ;

1, 1993. The staff concluded that a mid-cycle inspection was necessary to  ;

ensure that the proposed 1.0 volt interim limit would provide a comparable level of conservatism to other plants, with 7/8-inch OD tubing, that had implemented similar SG tube repair criteria. The specific reasons cited by the staff for the mid-cycle inspection requirement are outlined below

:

1. For Farley and Cook, the allowable end-of-cycle (EOC) voltage consistent  :

with the most limiting Regulatory Guide 1.121 criterion on burst is 6.2 l volts. This is based on burst pressures evaluated at the lower 95% l prediction interval as a function of voltage. For Catawba, the ,

allowable EOC voltage is 3.5 volts if no correction factor is applied to ,

the Belgian data as is discussed in Section 4.2. Thus, the 1 valt  ;

3 criterion for Farley and Cook provides a 5.2 volt allowance to i accommodate voltage measurement uncertainty and voltage growth between  !

i inspections, whereas a 1 volt limit for Catawba provides only a 2.5 volt  !

4 allowance. [

2. Voltage measurement uncertainties are larger at Catawba than was the -

case for farley or Cook, primarily due to the fact that a probe wear i standard was not used at Catawba. The voltage measurement uncertainties  !

. at Farley were estimated te be 0.16 volts and 0.25 volts when evaluated  !

at the 90% and 99% cumulative probability values, respectively. These l compare to voltage measurement uncertainty estimates at Catawba of 0.22  ;

volts and 0.42 volts, respectively. I

3. Bounding values of voltage growth observed during previous cycles at d Farley and Cook were 2.6 volts and 0.8 volts, respectively, based on the  ;

most recent information available at the time the staff approved the 1 j r volt interim plugging criteria (IPC) for these units (WCAP-12871, Rev. 2 l and WCAP-13187). The staff's SERs noted that even if bounding values of f voltage measurement uncertainty and voltage growth are simultaneously i applied to a 1.0 volt indication being accepted for continued service,  !

the resulting E0C voltage would be 3.9 volts for Farley and 2.0 volts  !

for Cook, significantly less than the allowable E0C voltage of 6.2 volts. Pending completion of the lead plant alternate plugging criteria (APC) review, the staff cited this as'a basis for approving the interim 1 volt limit. For Catawba, the bounding value of voltage growth during  ;

the past operating cycle was 2.3 volts. Applying this value to a 1 volt l indication being accepted for continued service leads to.an EOC voltage of 3.3 volts which is close to the allowable EOC voltage of 3.5 volts.

However, application of a voltage measurement uncertainty of greater than 0.2 volts and a voltage adjustment of approximately 0.5 volts for the increased length of Cycle 7 compared to Cycle 6 would increase this j i

i 1

l l

bounding estimate to beyond the allowable EOC voltage. The staff '

further notes that a 3.6 volt indication was actually found at Catawba  !

during the current outage.  :

i

4. The staff concluded that a mid-cycle inspection may reasonably be i

~

expected to verify the growth of indications to values significantly [

less than 3.5 volts and that this should confirm a level of conservatism i consistent with that which is inherent in IPCs that have been approved  !

for other plants. l f

The staff also cited the lack of unadjusted 3/4-inch OD pulled tube data used i in the development of the burst pressure / bobbin voltage correlation as another i reason for the mid-cycle inspection requirement. E a

3.0 EVALUATION f 3.1 Tube Intearity Issues The purpose of the Technical Specification tube repair limits is to ensure r that tubes accepted for continued service will retain adequate structural and  !

leakage integrity during normal operating, transient, and postulated accident  !

conditions, consistent with General Design Criteria 14, 15, 31 and 32 of 10 7 CFR Part 50, Appendix A. Structural integrity refers to maintaining adequate margins against gross failure, rupture, and collapse of the steam generator  !

(SG) tubing. Leakage integrity refers to limiting primary-to-secondary j leakage to within acceptable limits. The traditional strategy for  ;

accomplishing these objectives has been to establish a minimum wall thickness  !

requirement in accordance with the structural criteria of Regulatory Guide 1.121, " Basis for Pitgging Degraded PWR Steam Generator Tubes." Allowance for eddy current measurement error and flaw growth between inspections has been added to the minimum wall thickness requirements (consistent with the t Regulatory Guide) to arrive at a depth-based repair limit. Enforcement of a minimum wall thickness requirement would implicitly serve to ensure leakage j integrity (during normal operation and accidents), as well as structural  !

integrity. It has been recognized, however, that defects, especially cracks, l will occasionally grow entirely through-wall and develop small leaks. For-  !

this reason, limits on allowable primary-to-secondary leakage have been j established in the Technical Specifications to ensure timely plant shutdown f before adequate structural and leakage integrity of the affected tube is  ;

impaired. [

The interim tube repair limits for Catawba Unit I consist of voltage amplitude.  !

criteria rather than the _ traditional depth-based criteria. Thus, the repair  !

criterion represents a departure from the past practice of explicitly  :

enforcing a minimum wall thickness requirement.

The industry-wide data base from the pulled tube examinations show that for j bobbin indications at or near 1,0 volt (i.e., the IPC repair limit) maximum  ;

crack depths range between 20% and 98% through-wall.. The likelihood of l

, through-wall or near through-wall crack penetrations appears to increase with  ;

increasing voltage amplitude. For indications at or near 2.0 volts, the' t

'l

{

t

4 maximum crack depths have been found to generally range between 50% and 100%

through-wall. Clearly, many of the tubes which will be found to contain "non-

~

repairable" indications under the proposed interim criteria may develop through-wall and near through-wall crack penetrations during the upcoming cycle, thus creating the potential for leakage during normal operation and ,

postulated MSLB accidents. The staff's evaluation of the proposed repair criteria from a structural and leakage integrity standpoint is provided in +

Sections 3.2 and 3.3, respectively. ,

3.2 Structural Inteority >

In support of the 1.0 volt repair limit approved in Reference 1, the licensee developed a burst strength / bobbin voltage correlation to demonstrate that bobbin indications satisfying the 1.0 volt interim repair criterion would retain adequate structural margins during Cycle 7 operation, consistent with  ;

the criteria of Regulatory Guide 1.121. The correlation was developed from both pulled tube data and laboratory tube specimens containing ODSCC flaws-produced in model boilers. The bobbin voltage data used to construct the  ;

burst pressure / bobbin voltage correlation were normalized to be consistent with the calibration standard voltage set-ups and voltage measurement -

procedures described in WCAP-13494. The normalization was performed to ensure

• consistency among the voltage data in the burst pressure / bobbin voltage ,

correlation and consistency between the voltage data in the correlation and  :

the field voltage measurements at Catawba Unit 1.

In support of a mid-cycle SG tube inspection, the staff noted in Reference 1 that there was a lack of unadjusted 3/4-inch OD pulled tube data in the burst pressure / bobbin voltage correlation. The licensee has provided.in Reference ,

2, an updated data base for the burst pressure / bobbin voltage correlation .

which no longer contains the " adjusted" data points associated with tubes that '

had experienced " incomplete bursts" during destructive examination. In addition, this updated data base has been supplemented with 5 additional pulled tube data points from 3 pulled tubes from Catawba Unit 1. The revised burst pressure / bobbin voltage correlation includes the burst pressure versus-field bobbin voltage data (pre-pull values) for 10 pulled tubes (14 TSP i intersections) which includes the 3 pulled tubes (5 TSP intersections) from Catawba Unit 1.

he staff also noted in Reference I that there was an inadequate technical basis to support a voltage cross-calibration factor of 1.5 for the Belgian data points in the burst pressure / bobbin voltage correlation. A cross-calibration factor is necessary since the Belgians use different probes,

. equipment, calibrations and frequencies than that used in the development of the. burst pressure / bobbin voltage correlation developed by Westinghouse. .The- j staff had assumed a cross-calibration of 1.0 for the Belgian data points until '!

a complete evaluation had been performed by the licensee. In Reference 2, the ,

- licensee submitted an evaluation which supports the use of a cross-calibration factor of 1.7 for the Bd gian pulled tube data points. The staff has  ;

concluded that a correction factor of 1.7 for the Belgian pulled tube data.is appropriate for supporting this IPC proposal. However, the staff is i considering a draft recommendation developed by the IPC task group that the ,

industry be requested to further confirm this factor based on an analysis of j b

e scaled EDM notches or from an analysis of actual field tube data to support its use for any future, less restrictive APC proposal.

i h

The staff notes that the proposed burst pressure / bobbin voltage correlation submitted by the licensee has excluded one data point from the correlation.

This data point was excluded based on the fact that this specimen had multiple indications around the tube circumference thereby increasing the bobbin i voltage while the burst pressure remained high as it was controlled by the limiting single crack (i.e., high bobbin voltage with correspoading high burst pressure). The staff notes that there was no specific error in either the burst pressure test or voltage measurement for this outlier and, therefore, removal cf the data point from the correlation limits the distribution of error for the regression fit. Unless the test itself can be shown to be invalid, then the regression model (specifically the distribution for the  !

error term) must be changed to account for these outliers. Otherwise the prediction intervals may be too narrow and the voltage thresholds and '

probability of burst calculations that use this model will be non-conservative.

As a result of recent staff efforts in addressing the issue of voltage-based SG tube repair criteria, the staff has concluded that for Catawba, assessment  ;

l of tube structural strength could be achieved by a deterministic analysis l which adjusts the beginning-of-cycle (BOC) voltage by the 95% cumulative i probability values for eddy current measurement uncertainty and flaw growth.  ;

The resultant E0C voltage is then used to determine the burst pressure of the l tube from the lower 95% prediction interval of the burst pressure versus  !

bobbin voltage correlation. The results of the deterministic analysis must i ensure that the structural requirements of Regulatory Guide 1.121 are  !

satisfied.  !

For the proposed 1.0 volt IPC, the projected deterministic E0C voltage is 1.92 volts assuming the 95% cumulative probability values of voltage measurement ,

uncertainty and voltage growth. Using the lower 95% prediction interval curve  ;

for burst pressure as a function of voltage, the maximum allowable E0C voltage  !'

, that will satisfy the limiting burst pressure criterion in Regulatory Guide l.121 is approximately 4.35 volts. This voltage value assumes the 1.7 i

! correction factor for the Belgian voltages in the burst pressure / voltage ,

Eorrelation and also assumes inclusion of the outlier in the data base.  ;

For any specific individual tube, voltage measurement uncertainty and/or voltage growth may exceed the value assumed in the above deterministic analysis since the deterministic analysis does not consider the full tails of 1 the voltage measurement uncertainty and voltage growth distributions. I Similarly, burst pressure for some tubes may be less than the 95% lower l

, prediction interval values in the burst pressure / bobbin voltage correlation. 1 These distrioution tails may involve sizable numbers of tubes in cases such as Catawba where thousands of tubes with indications are being accepted for continued service. To directly account for these uncertainties, Monte Carlo methods have typically been used to demonstrate that the probability of burst during MSLB accidents is acceptably low for the distribution of voltage

, indications being left in service. Under this approach, the'B0C indications left in service are projected to the EOC by randomly sampling the probability 1

A

t distributions for NDE uncertainties and voltage growth per cycle. For each E0C Monte Carlo sample of bobbin voltage, the burst pressure / bobbin voltage correlation is randomly sampled to obtain a burst pressure. A number of Monte Carlo samples (e.g., 100,000) are performed for the entire B0C distribution. i The probability of tube burst at MSLB is obtained as the sum of the samples l resulting in burst pressures less than the MSLB pressure differential of 2650  :

psi divided by the number of times the distribution of indications left in  !

service is sampled. This kind of Monte Carlo analysis was performed for the  ;

distribution of indications that were left in service belu the 1.0 volt ,

interim repair limit at the BOC 7 at Catawba Unit I as noted in Reference 1.  !

This analysis indicated that implementation of a 1.0 volt repair criterion at this time would yield a conditional probability of burst of'l.1x10'5, given a MSLB. The staff concurs that this is an extremely low probability, three orders of magnitude less than the value considered in a staff generic risk assessment for SGs (NUREG-0844). j As part of the IPC approved in Reference 1, the licensee was allowed to leave tubes with bobbin indications greater than the 1.0 volt interim limit in

• service provided that the bobbin voltage was less than the proposed full APC i voltage limit and provided that the RPC inspection found no detectable  ;

degradation at this location. However, in the analyses provided in Reference  !

1, these tubes were not included in the B0C voltage distribution. The staff  ;

notes that the normal eddy current flow produced by the bobbin probe and the  !

RPC probe is different and therefore they have different sensitivities to  !

. different shapes and locations of defects. Subsequent review of this approach by the IPC task group has lead to the tentative conclusion that such tubes ,

should be included in the probabilistic tube burst assessments. In addition, i the IPC task group has also tentatively concluded that the probabilistic tube i burst assessments to support IPC implementation should also account for non- l detected ODSCC that remains in service by adjustment of the B0C distribution ~

by the probability of detection (i.e., divide the number of tubes that were detected in each voltage interval by an appropriate probability of detection .

(e.g., 0.6) and subtract the number of tubes repaired in each voltage interval '

to obtain the POD adjusted BOC voltage distribution).  :

i The value for the conditional probability of burst referenced above (i.e., )

l.1x10'5) was determined from the original burst pressure versus bobbin  !

Voltage correlation submitted to support the issuance of Reference 1 (i.e.,  ;

WCAP 13494). The staff estimates, however, that using the updated data base j (with the outlier included), adjusting the BOC distribution to include the  ;

, tubes that were left in service based on the lack of RPC confirmation of the J bobbin indication, and adjusting the BOC distribution by the probability of detection would result in a probability of tube rupture given a MSLB of approximately 4x10'5 .

3.3 Leakane Intearity A number of the indications satisfying the proposed interim 1.0 volt . repair limit can be expected to have, or to devr'7, through-wall and/or near through-wall crack penetrations during t.4 next cycle, thus creating the potential for primary-to-secondary leakage during normal operation, transients, or postulated accidents.

The staff finds that adequate leakage I

.I

~ ._ . . _ . . -- - - --

4 b

integrity during normal operating conditions is assured by the Technical  ;

Specification limits on allowable primary-to-secondary leakage. Adequate j leakage integrity during transients and postulated accidents is demonstrated  :

by showing that for the most limiting accident, assumed to occur at the end of the next cycle, the resulting leakage will not exceed a rate that will result in off-site dose limits being exceeded.

As the basis for estimating the potential leakage during MSLB accidents, Westinghouse has correlated leakage test data obtained under simulated MSLB conditions with the corresponding bobbin voltage amplitudes. For 3/4-inch OD

• tubing, the correlation is based on 37 data points from laboratory tube ~

i specimens containing ODSCC flaws produced in a model boiler facility. The correlation is based on a linear regression fit of the logarithms of the corresponding leak rates and voltages. The leak rate data exhibits  ;

considerable scatter relative to the mean correlation. Thus, prediction intervals for leak rate at a given voltage have been established to statistically define the range of potential leak rates. As part of the on- <

going review of the APC, the staff has further reviewed the correlation of the leak rate data to bobbin voltage. The staff has tentatively concluded that no y proven relationship between leakage rate and voltage presently exists and that }

the proposed approach fails to account for non-detected ODSCC that remains in service. However, the staff has tentatively concluded that a voltage-based j approach can be used if these non-conservatisms are accounted for and  !

sufficient conservatisms are included in the analysis. Therefore, at the j staff's request, the licensee has provided a calculation of potential MSLB leakage by a methodology designed to address the staff concerns. The methodology is as follows:

l. An EOC voltage distribution is determined by randomly sampling the-BOC voltage distribution, the NDE measurement uncertainty i distributions (i.e., analyst variability and probe wear), and the voltage growth distribution. The BOC distribution includes all indications regardless of RPC confirmation.

2. For each indication, the maximum likelihood probability of leakage is determined from the probability of leakage versus bobbin voltage correlation.

3. For each E0C voltage, the number of detected indications is divided by the probability of detection (i.e., 0.6) to determine the number ,

of E0C indications in each voltage interval adjusted for the probability of detection .(i.e., n i ). ,

4. The number of potentially leaking tubes at a given EOC voltage is -

determined by multiplying the probability of detection (P0D) adjusted number of indications at a given voltage ~ (i.e., n,) by. the ';

maximum likelihood probability of leakage for that voltage (i.e., '

P,). The number of potentially-leaking tubes at _each voltage interval is then summed to determine the total number of potentially leaking tubes (i.e., n = Zn ii P ).

5. The total MStB leak rate at 2560 psi is calculated per the following i

4 l

r l

equation: I Qr " D# + 1.645*o*/n i where n is the total number of potentially leaking tubes for the EOC distribution indications adjusted for the POD, o is the estimated i standard deviation in the population leak rate from the specimen measurements, and g is the mean of the experimental leak rate data.

In addition, the staff has performed a more conservative analysis for calculating MSLB leakage which differs slightly from the above methodology. ,

In particular, the total MSLB leak rate at 2560 psi is calculated by the following methodology:

1. An E0C voltage d' Sution is determined as follows: 1) the number !

of indications a r, i each voltage interval during the inservice  ;

inspection regardiesa of RPC confirmation is adjusted by a POD of  ;

0.6 to obtain a POD adjusted distribution of indications, and 2) the '

number of indications that were repaired in each voltage interval '

during the outage are subtracted from the number of indications in l that voltage interval in the P00 adjusted distribution of '

indications. The resultant POD adjusted B0C distribution of 4 indications is randomly sampled along with the NDE measurement ,

uncertainty distributions, and the voltage growth distribution in  ;

order to obtain an E0C voltage distribution.

2. For each indication, the maximum likelihood probability of leakage is determined from the probability of leakage versus bobbin voltage correlation.

3. The number of potentially leaking tubes at a given E0C voltage is l determined by multiplying the projected E0C number of indications at a given voltage (i.e., n )i by the maximum likelihood probability of leakage for that voltage (i.e., Pi ). The number of potentially leaking tubes at each voltage interval is then summed to determine the total number of potentially leaking tubes (i.e., n = En ii P ).

r

4. The total MSLB leak rate at 2560 psi is calculated per the following equation:

Q = ng + 2*[no2 + ng2_p2 Zni P 1 i 3

]5 where n is the total number of potentially leaking tubes for the E0C distribution indications adjusted for the P0D, o is the estimated standard deviation in the population leak rate from the specimen measurements, y is the mean of the experimental leak rate data, n i is the number of tubes with a given EOC voltage, and iP is the maximum likelihood probability of leakage for a given E0C voltage.

The intent behind this methodology for calculating MSLB leakage is to provide an estimate of the expected total lea *K rate during MSLB conditions that will bound the actual observed leak rate in 98 cases out of 100. '

i i

i 0-l l

The licensee's calculation of potential MSLB leakage based on the above i methodology (i.e., Q = ng + 1.645*o*/n) resulted in a MSLB leakage value of 3 l The staff's  !

calculation (i.e., Q, = ng + 2*[no2.7gallonsperminute(gpm)forthelimitingSG(j].g.S 2 + np .y En iP ) for potential MSLB leakage resulted in a MSLB leakage value of approx,imately 3.6 gpm for the ,

limiting SG (i.e., SG C).

J 4.0 RADIOLOGICAL CONSE0VENCES l

By letter dated April 29, 1993, the licensee presented a compilation of all . )

the steamline break (SLB) calculations completed to date by the licensee. The  !

licensee submitted these analyses in support of not performing a mid-cycle 3 inspection of SG tubes as discussed above. ,

These calculations were intended to provide a " reasonable estimate" of the total primary to secondary leakage rate that can be expected during a  !

postulated steam line break event. The licensee concluded that an upper 95% i confidence bound leakage rate of 2.73 gallons per minute .(gpm) in steam  ;

generator considering all of the test data. However, in its evaluation of the 1 information presented by the licensee, Materials and Chemical Engineering Branch, (EMCB) concluded that, based on its evaluation the estimated primary-to secondary leakage during a postulated MSLB.at the end of fuel Cycle 7 for 1 Catawba Unit 1 is 3.6 gpm vice the 2.73 gallons per minute assumed by .the licensee in its evaluation. In addition, 3

the staff used the licensing basis i value for X/Q of 3.8 x 10 sec/m in performing its evaluation, compared to

~

the value of 4.78 E-04 sec/m3 assumed by the licensee.  :

i Finally, Duke Power's evaluation considered both the pre-existing iodine spike .j case and an event generated spike case. In this evaluation, the licensee  ;

calculated exclusion area boundary thyroid doses, assuming a 2.73 gpm primary .;

to secondary leak rate, of 11.88 and 7.36 rem (respectively) for the pre-existing and event generated iodine spike cases.

The staff has independently calculated the radiological consequences of a ' l postulated steam line break assuming staff-calculated primary to secondary leak rate values and the licensing basis value for x/Q. The staff and the ricensee both used the dose conversion factors for iodine isotopes set forth  ;

in ICRP 30 as well as the breathing' rates set forth in Regulatory Guide 1.4. 1 Table 1 presents the staff calculated thyroid doses for both the pre-existing  :

spike case and the event generated. spike case. The ' principal differences  !

i betweenthestaffcalculatednumbersandthosepresentedbytgelicensee.arise from the site boundar value -

Duke Power, 3.8 X 10'y sec/m, of X/Q assumed assumed by the staff) and (4.78 the Xdifferent 10 sec/m.

leak assumed by-t rates assumed (2.73 gallons per minute (gpm) assumed by the licensee, 3.6 gpm i assumed by the staff). In addition, the value for .X/Q at the low population '

3 zone (LPZ)usedbythe1(censeewas6.85X10~5 sec/m compared to the staff '!

value of 2.7 X 10'5 sec/m . ,l l

y -. -

r *r ,

a

_ 10 -

TABLE 1 3.6 gpm Increased Primary to Secondary Leak Rate CALCULATION TYPE THYROID DOSE THYROID DOSE WHOLE-BODY DOSE (REM) PRE- (REM) EVENT- (REM)

ACCTSENT SPIKE GENERATED IODINE .

CASE SPIKE l EAB (2 HOUR) 12.5 1.8 s0.1 LPZ (8 HOUR) 3.6 0.5 s0.1 As can be seen from this Table, calculated thyroid doses are within the exposure guideline values of 10 CFR 100 for the pre-existing iodine spike case and, thus, satisfy the acceptance criteria of Standard Review Plan 15.1.5 Appendix A " Radiological Consequences of Main Steam Line Failures Outside i Containment of a PWR."

Similarly, calculated doses for the event generated spike case are also shown  ;

in this Table. Calculated thyroid doses for the event generated spike case are less than a small fraction of the exposure guideline values of 10 CFR 100 and satisfy the acceptance criteria of Standard Review Plan 15.1.5. Appendix A.

Based on the foregoing, it is concluded that the radiological consequences of a main steam line break (MSLB) outside containment for Catawba Unit 1 at the end of Cycle 7 are acceptable.

5.0 CONCLUSION

S Based on the above evaluation, it can be concluded that adequate structural and leakage integrity of the SG tubing at Catawba Unit 1, consistent with applicable regulatory requirements, can be ensured for the remainder of fuel  ;

Cycle 7. l t' 1 Principal Contributors: K. Karwoski K. Eccleston i Date: July 30, 1993 i

l

a f

i REFERENCES I

(1) Letter, R. E. Martin, NRC, to M. S. Tuckman, DPC, dated September 25,  ;

1992, issuing Amendments 102 and 96 changing the TS to allow the i implementation of interim steam generator tube plugging criteria (IPC)  ;

for the tube support plate elevations.

(2) Letter, H. S. Tuckman, DPC, to NRC dated March 25, 1993, providing .

additional analyses and data to further support IPC as set forth in the i enclosed reports WCAP-13494, Revision 1, " Catawba Unit 1 Technical ,

Support for SG Interim Plugging Criteria for Indications at Tube Support  !

Plates" (Proprietary) and its non-proprietary- version, WCAP-13495,  ;

Revision 1.  :

(3) Letter, M. S. Tuckman, DPC, to NRC dated April 8, 1993, providing MSLB  :

dose analysis results and the Westinghouse report NSD-SGD-0784.

]

(4) Letter, M. S. Tuckman, DPC, to NRC dated April 21, 1993, providing l revision 1 to the Westinghouse report NSD-SGD-0784.

l (5) Letter, M. S. Tuckman, DPC, to NRC dated April 22, 1993, providing- i Addendum 1 to Catawba Unit 1 USNRC Requested SG Tube Leak Rate  :

Evaluation, in report NSD-SGD-0792. l (6) Letter, M.S. Tuckman, DPC, to NRC dated April- 28, 1993, providing i presentation materials from a meeting with the NRC staff on April 1, t 1993 in WCAP-13701," Catawba Unit 1 Steam Generator Tube Interim Plugging i Criterion Mid-Cycle Outage Assessment Presentation Materials" and its '

non-proprietary version, WCAP-13702.  :

(7) Letter, M. S. Tuckman, DPC, to NRC dated April 29, 1993, providing a compilation of. previously submitted SLB leakage calculations' as set forth in WCAP-13715, "NRC Requested Catawba 1 S/G Leakage Evaluation" l (Proprietary) and its non-proprietary version, WCAP-13716. j i

t' f

i I

l l

t

..