ML20236V521

Requests Addl Info on Proposed License Amend Re RCS Flow Monitoring

ML20236V521
Person / Time
Site:	South Texas
Issue date:	07/29/1998
From:	Alexion T NRC (Affiliation Not Assigned)
To:	Cottle W HOUSTON LIGHTING & POWER CO.
References
TAC-M99245, TAC-M99246, NUDOCS 9808040009
Download: ML20236V521 (5)

Text

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e Mr. William T. Cottle . July 29, 1998 President and Chief Executive Officer STP Nuclear Operating Company South Texas Project Electric Generating Station P. O. Box 289 Wadsworth, TX 77483

SUBJECT:

REQUEST FOR ADDITIONAL INFORMATION ON PROPOSED LICENSE AMENDMENT REGARDING REACTOR COOLANT SYSTEM FLOW MONITORING, SOUTH TEXAS PROJECT, UNITS 1 AND 2 (STP) (TAC NOS.

M99245 AND M99246)

Dear Mr. Cottle:

The Nuclear Regulatory Commission staff is reviewing STP Nuclear Operating Company's (STPNOC's) August 6,1997, application for a license amendment to allow the use of elbow taps to measure reactor coolant system flow rate.

Based on its review, the staff has determined that additionalinformation is needed, as discussed in the enclosure.

Sincerely, ORIGINAL SIGNED BY: ,

Thomas W. Alexion, Project Manager Project Directorate IV-1 Division of Reactor Projects Ill/IV Office of Nuclear Reactor Regulation I

Docket Nos. 50-498 and 50-499

Enclosure:

Request for AdditionalInformation j cc w/ encl: See next page DISTRIBUTION: kcpr' Es- "-

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NUCLEAR REGULATORY COMMISSION WASHINGTON, D.c. 3080H001 s.,*****/ July 29, 1998 Mr. William T. Cottle President and Chief Executive Officer STP Nuclear Operating Company South Texas Project Electric Generating Station P. O. Box 289 Wadsworth, TX 77483

SUBJECT:

REQUEST FOR ADDITIONAL INFORMATION ON PROPOSED LICENSE AMENDMENT REGARDING REACTOR COOLANT SYSTEM FLOW MONITORING, SOUTH TEXAS PROJECT, UNITS 1 AND 2 (STP) (TAC NOS.

M99245 AND M99246)

Dear Mr. Cottle:

The Nuclear Regulatory Commission staff is reviewing STP Nuclear Operating Company's (STPNOC's) August 6,1997, application for a license amendment to allow the use of elbow taps to measure reactor coolant system flow rate.

Based on its review, the staff has determined that additionalinformation is needed, as discussed !

in the enclosure.

Sincerely, i j

([?O '

@V l Thomas W. Alexion, Project Manager Project Directorate IV-1 Division of Reactor Projects lil/IV Office of Nuclear Reactor Regulation Docket Nos. 50-498 and 50-499

Enclosure:

Request for Additional Inforination cc w/ encl: See next page i

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1 I

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Mr. William T. Cottle STP Nuclear Operating Company South Texas, Units 1 & 2 cc:

Mr. David P. Loveless Jack R. Newman, Esq. j Senior Resident inspector Morgan, Lewis & Bockius  !

U.S. Nuclear Regulatory Commission 1800 M Street, N.W. I P. O. Box 910 : Washington, DC 20036-5869 Bay City, TX 77414 Mr. Lawrence E. Martin l

A. Ramirez/C. M. Canady Vice President, Nuc. Assurance & Licensing

! City of Austin STP Nuclear Operating Company '

l Electric Utility Department P. O. Box 289 721 Barton Springs Road Wadsworth, TX 77483 l Austin, TX 78704 l

Ofhce of the Govemor Mr. M. T. Hardt ATTN: John Howard, Director Mr. W. C. Gunst Environmental and Natural k City Public Service Board Resources Policy P. O. Box 1771 P. O. Box 12428 ]

4 San Antonio,TX 78296 Austin, TX 7S711 Mr. G. E. Vaughn/C. A. Johnson Jon C. Wood Central Power and Light Company Matthews & Branscomb P. O. Box 289 One Alamo Center Mail Code: N5012 106 S. St. Mary's Street, Suite 700 Wadsworth, TX 74483 San Antonio, TX 78205-3692 INPO Arthur C. Tate, Director Records Center Division of Compliance & Inspection 700 Galleria Parkway Bureau of Radiation Control Atlanta, GA 30339-3064 Texas Department of Health 1100 West 49th Street Regional Administrator, Region IV Austin, TX 78756 U.S. Nuclear Regulatory Commission 611 Ryan Plaza Drive, Suite 400 Jim Calloway Arlington, TX 76011 Public Utility Commission of Texas Electric Industry Analysis D. G. Tees /R. L. Balcom P. O. Box 13326 Houston Lighting & Power Co. Austin, TX 78711-3326 P. O. Box 1700 Houston,TX 77251 Judge, Matagorda County .

Matagorda County Courthouse 1700 Seventh Street Bay City, TX 77414 I

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REQUEST FOR ADDITIONAL INFORMATION

1. Section 3.4.2, Elbow Tap Flow Measurement Procedure, of Attachment 5 of the August 6,1997, submittal defines the baseline elbow tap flow coefficient (B) and the future cycle elbow tap flow coefficient (K) as the elbow tap AP (inches water) multiplied by the cold leg water specific volume (v).

a. The use of the terminology " flow coefficient" to define the AP measurement values is very confusing because the elbow tap " flow coefficient" normally refers to the constant C in the elbow tap equation, Q = C (AP)", whereas AP is a variab!e as a function of volumetric flow rate Q. For example, in the September 18,1997, response to Questions 5 and 30 regarding the need to provide the values of correlation coefficients for each of the three elbow taps in each loop, it says that flow coefficients for each elbow tap measurement are not necessary.- It is not clear whether the " flow coefficients" here refers to the term "AP x v" or the " correlation. coefficient K" referred to in Question 30. Please clarify the confusion, and, if necessary, use an altemate terminology, other than flow coefficient, to define "AP x v."

b. The definition in Equations 1 and 2 (in Section 3.4.2 of the August 6,1997, submittal) that B (or K) = AP x v (where AP is in inches H2 0, and B and K are in inches H2O

• ft8/lb) is not consistent with the basic elbow tap flow equation volumetric flow rate Q= C x (AP)".

Explain why B and K are defined as they are, and not as B (or K) = AP.

c. There appears to be an inconsistency in Table 3.6-2 (of the August 6,1997, submittal) in that the heading states,

• Differential Pressures in inches of Water" whereas the footnote indicates that the Average op is in pjj with the Flow Coefficient B in inches

• ft'/#. Clarify if the average Ap is 485.32 psi or 485.32 inches H2 0. Does this impact your response to item 1.b above?

2. In the elbow tap flow measurement procedure in Section 3.4.2 (of the August 6,1997, ,

submittal), the future cycle reactor coolant system (RCS) flow will be calculated from the {

baseline calorimetric measured RCS flow multiplied by the " ratio of future cycle flow," R,  !

which is defined in Equation 3 to be the square root of the ratio the average AP (times specific volume) of all elbow taps from the future cycle to that of the baseline cycle, i.e. 1 I

(K/B)".

a. Because of the variations in the elbow tap flow coefficients (note that the flow coefficient

)

here is C in the basic elbow tap equation, not B or K as defined in Equations 1 and 2 in  !

Section 3.4.2) and the op's for different elbow taps in the cold legs, what is the mathematical basis for the use of the average Ap of all elbow taps in defining the ratio of l future cycle flow, R? Provide the mathematical derivation to show correctness of "R" as defined in Section 3.4.2, using the average Ap of all elbow taps.

)

b. As the flow coefficient (C) for each elbow tap i should remain constant, the volumetric flow ratio should be equal to the square root of the Ap ratio between two cycles, which I should be anticipated to be the same for all elbow taps. Would it be more appropriate mathematically to use the average value of the flow ratios (i.e., square root of Ap ratio) of all elbow taps to define the

• ratio of future cycle flow", R7 If not, why not? (Note that the December 9,1997, response to Question 11 showed that the difference between the total RCS flo.y based on individual elbow taps and flow t'ased on the average elbow tap Ap is i

ENCLOSURE l

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negligible (0.01%) based on one cycle's data. But this is not mathematically demonstrated to be the case for all conditions.)

c. To provide a 95/95 probability / confidence of the value of R, would it be more appropriate to adjust the Tuture cycle flow ratio," R, by taking into to account the distribution of the Ap ratios among the elbow taps as the equation below? If not, why not?

R = R,- K(95,95,N) o where, R, = I R /N R, = (Apr / Ap ),u2, i = 1,2,....N (Note that Ap's are in inch of water. If Ap's are in psi, then it will be multiplied by the specific volume of water)

N = total number of elbow taps = 3 x number of cold legs o = standard deviation of R,'s K(95,95,N) = factor for one-sided tolerance limit for 95% probability at 95% confidence level for a sample size of N.

K(95,95,12)= 2.736 K(95,95,9) = 3.031

3. Tables A-4 and A-5 of the August 6,1997, submittal provide the cold leg elbow tap flow uncertainty for QDPS/ Process computer and low flow reactor trip, respectively. Are the instrumentation uncertainty values sufficient to bound the uncertainties of the elbow tap measurement instrument, including the larger drift effects, due to absence of current normalization of elbow tap measurement against the precision heat balance measurement at the beginning of each cycle? Provide corrected uncertainty values, if necessary, and the basis for the uncertainty values.

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