ML20091H745

Forwards Response to 840515 Questions Re Traversing in-core Probe (TIP) Sys.Process Computer Sys OD-2 & Recalibr of Individual Local Power Range Monitors Using TIP Sys Described

ML20091H745
Person / Time
Site:	Hatch
Issue date:	05/25/1984
From:	Gucwa L GEORGIA POWER CO.
To:	Stolz J Office of Nuclear Reactor Regulation
References
NED-84-264, TAC-53398, NUDOCS 8406050276
Download: ML20091H745 (3)

Text

Georgia Power Company a i* 333 Piedmont Avenue i

A!!anta. Georgia 30308 Telephone 404 526-6526 Ma+ng Addrew Post Office Bo,r 4545 Atlaata. Georg a 30302 L Georgia Power L T. Gucwa the sout?vo eittfoc sp, tem Manager Nuclear Engineering and Chief Nuclear Er:g1neer NED-84-264 May 25, 1984 Director of Mclear Reactor Regalation Attention: Mr. John F. Stolz, Chief Operatirg Reactors Branch No. 4 Division of Licensirg U. S. N2 clear Regulatory Comnission Washirgton, D. C. 20555 NRC DOCKER 50-366 OPERATIN3 LICENSE NPF-5 EIMIN I. HA'ICH NUCLEAR PLANE UNIT 2 RESPONSE 'IO NRC STAFF QUESTIONS ON TIPS SYSTEM Gentlemen:

On May 15, 1984 a teleconference was held between members of the NRC staff, Georgia Power Ccxnpany (GPC) m clear Generation Ergineering, and Southern Conpany Services M2 clear Safety and Riel. 'Ihe subject of the discussion was the Plant Hatch Unit 2 Traversirg Incore Probe (TIP) system.

The NRC staff reglested that GPC provide a written description of how irxlivichal Local Power Range mnitor (LPRM) strings are recalibrated using the TIP system and the process conputer program known as "OD-2". That information is provided in the erclosure to this letter, j The erclosare contains no proprietary information, therefore this aabnittal may be placed in the public document room without exception.

Sincerely yours,

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y[.L.T.G2 cwa CBS/mb l l

xc: J. T. Beckham, Jr. '

H. C. Nix, Jr.

J. P. O'Reilly (NRC- Region II)

Senior Resident Inspector

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DESCRIPTION OF FUNCTION FOR PROCESS OCMPUIER PROGRAM OD-2 4

Process caputer progra OD-2, "Specified LPM Substitute Value and Base

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Distribution," is -intended to be used for individual lpm strings which either need re-establishnent of BASE, BASLP, and C values, or need substitute values for failed or drifted lpm chmbers. %e BASE values, used in the power distribution calculations, represent the axial distribution of TIP-machine independent and core-power-independent TIP signals'in a given TIP channel at the ' elevations of the center of the fuel segments. BASLP contains the BASE values at the lpm elevations. %e process cmputer lpm calibration constant C relates the LPM reading, taken at the time of the last TIP' traverse .in that string, to the machine-normalized TIP reading at the LPBM elevation at that time.

If- the core power distribution changes significantly, or if one or more LPMs drift or fail, the axial distribution for see locations based upon the lpm readings may deviate from the stored BASE distributions for those locations by more than an acceptable mount. In that case, the accuracy of the axial power shape determination would be affected. %e power distribution calculation (Program P-1) will identify such an occurrence and will type an edit- giving the string coordinates in which new BASE distributions are required, and a " criticality code" assessing the seriousness of the need.

%e method of OD-2 is (1) to insert the TIP probe into the channel having the failed sensor - (or sensors), or into a channel requiring a new BASE distribution; (2) determine a new TIP machine normalization factor A(M) which makes the newly-normalized TIP signals best match the calibrated signals fra the LPMS in that string which are unfailed and which have not been diagnosed as having " drifted; and (3) apply that normalization factor to the TIP readings to obtain a .new BASE distribution and new full-power-adjusted substitute LPBM readings for the traversed channel. If all the chambers in the string in question are either failed or drifted, the TIP probe must first be run into a different channel containing - sme

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unfailed and undrifted chmbers to determine an updated TIP normalization factor A(M) . his factor will then be used following the subssluent traverse of the channel containing all failed or drifted LPMs.

Note that this method involves the assmption, not required when performing a whole-core calibration, that the average LPFM error in the traversed string is zero. More specifically, it is assmed that the_ machine normalization constant A(M), calculated frm the unfailed and undrifted chambers in the given string, is the see value that would be calculated if a similar traverse were made of any other string serviced by that particular machine.

5/25/84 G

r Description of Function for Process Cmputer Progra OD-2 Page 'IWo

'Ihe method of determination of the new machine normalization constant A(M) forces the average of the deviations between the calibrated lpm readings (for unfailed LPINs) and the normalized TIP readings at the elevations of LPIEs to zero. Individual deviations will, however, be non-zero, due to "ncrmal" error sources such as small power level fluctuations during the course of the TIP traverse or errors in the calculated cmpensation for exposure-dependent LPIN sensitivity loss.

Cmpensation is made for these small deviations by calculating new process cmputer LPIE calibration constants (C-values) for any unfailed LPINs in the traversed string.

'Ihe - calibration constants (Cs) for all LPINs besides those in the traversed channel reain unaffected by use of program OD-2. Changing the machine normalization constant A(M), therefore, caly affects the Cs for the LPIN string traversed and has no other effect on calibration constant.

Also, use of progra OD-2 will not affect results frm PlB, the backup thermal limits calculation, because machine normalization factors and LPIE calibration constants are not involved in that calculation.

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5/25/84 l

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