ML20072P202

Forwards Supplemental Info to 830324 Request for Emergency Relief from Tech Specs Requiring Power Range Monitor Calibr.Justification for Relief Provided

ML20072P202
Person / Time
Site:	Hatch
Issue date:	03/25/1983
From:	Beckham J GEORGIA POWER CO.
To:	Stolz J Office of Nuclear Reactor Regulation
References
NED-83-220, TAC-49983, NUDOCS 8304040152
Download: ML20072P202 (3)

Text

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, e Georg:a Power Company 333 Piedmont Avenue Atlanta. Georg a 30308 Telephone 404 526-7020 Maihng Address' Post Off,ce Box 4545 Atlanta. Georg'a 30302 Georgia Power J. T. Beckham, Jr.

the sournem electnc system Vce President and General Manager Nuclear Generation NED-83-220 March 25, 1983 Director of Nuclear Reactor Regulation Attention: Mr. John F. Stolz, Chief Operating Reactors Branch No. 4 Division of Licensing l'. S. Nuclear Regulatory Commission Washington, D. C. 20555 NRC DOCKET 50-366 OPERATING LICENSE tFF-5

. EDWIN I. HATCH NUCLEAR PLANT UNIT 2 SLPPLEENTAL INFORMATION Gentlemen:

The attached information supplements our submittal of March 24, 1983, requesting emergency relief from Technical Specifications requiring Local Power Range Monitor calibration. This information has been previously discussed with Mr. George Rivenbark, Hatch Licensing Project Manager, and provides additional justification for emergency relief requested in our March 24, 1983 submittal.

Very truly yours,

,_ Y,.-

J. T. Beckham, Jr.

REB /mb Enclosure O Of xc: H. C. Nix, Jr. ,

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

Senior Resident Inspector 8304040152 830525 PDR ADOCK 05000366 P PDR

, o JUSTIFICATION FOR SPECIAL-CASE EXTENSION OF INTERVAL BETWEEN CALIBRATIONS FOR HATCH-2 LOCAL POWER RAtCE MONITOR (LPRM) AWLIFIER GAINS The Edwin I. Hatch Nuclear Plant Unit-2 Technical Specifications require (Table 4.3.1-1, footnote g) that "the LPRMs shall be calibrated at least once per 1000 effective full power hours (EFPH) using the TIP system." A 25% extension, to 1250 EFPH, of this surveillance interval is permitted under Technical Specification 4.0.2, page 3/4 0-1. When the core average exposure (CAVEX) reaches 14347 MWD /T, expected to occur on March 28, 1983, 1250 EFPH will have elapsed since the last LPRM amplifier gain adjustment (LPRM calibration) was performed. The following is a technical justification intended to support operation of the Hatch-2 core in mode 1 for 126.7 additional EFPH, for a total of 1376.7 EFPH since the last amplifier gain adjustment was performed.

Granting of this extension will allow the unit to operate to the date of its planned shutdown for refueling, April 4, 1983. Without the extension, the length of the refueling outage will be extended by several days at considerable cost to the consumer.

The requirement that the LPRM amplifier gains be adjusted periodically is based on two safety-related design bases of the LPRM:

1. To provide signals of sufficient accuracy to the Average Power Range Monitors (APRMs), each LPRM signal being proportional to the local neutron flux at various positions in the reactor core.

2. To provide LPRM signals to the Rod Block Monitor (RBM) to indicate changes in local, relative neutron flux during the movement of control rods.

Other uses of LPRM signals, described in Hatch-2 FSAR Section 7.6.2.1.3, are either not safety-related or are compensated for by computed gain adjustments in determination of core power distribution and related factors. (The computed gain adjustments were updated using Traversing Incore Probes (TIPS) on March 16, 1983 at CAVEX = 14174).

The number of LPRM channels available for use by each APRM is sufficient to meet the APRM requirements and is not affected by this request for extension. The extent to which each LPRM reading accurately reflects local neutron flux is indicated by the LPRMs gain-adjustment factor (GAF), as monitored daily by the plant process computer. These computed GAFs are adjusted daily to account for LPRM sensitivity changes. Also, GAFs are adjusted when a scan of the core power distribution is performed with Traversing In-Core Probes. This was performed on March 16, 1983 at CAVEX =

14174 MWD /T. An edit of the GAFs calculated at that time showed that the average GAF was 1.03, the maximum GAF was 1.14, and the minimum GAF was

.91. (A GAF of 1.00 would indicate that no LPRM amplifier gain adjustment

is requirad to cause the amplifier output to equal' the desired, correctly-calibrated value.) Previous edits of the GAFs show that little change in the detector sensitivities is occurring. For instance on January 26, 1983 the average GAF was 1.01 and the maximum was 1.13. Therefore, the maximum and average GAFs are expected to change very. little during the period of this extension, and the LPRM readings will remain close to their desired value. The 1000 EFPH calibration interval was established based on conservative rates of detector drift experienced in practice, and assumed that individual detector drifts as large as 20% are acceptable without LPRM recalibration. Any change in the APRM signal as a result of the LPRM sensitivity change is checked daily and adjusted, if necessary, to assure close agreement with core power based on a system energy balance. Operaton of the Hatch-2 core for longer than the specified period is justified in this case because detector. drifts are considerably smaller than 20% and are expected to remain so during the requested extension.

A similar argument applies in the case of the rod block monitor. When a control rod is selected, the gain of each RBM channel is normalized to an assigned APRM channel. Thus, any error in RBM response due to LPRM drift is minimized. Again, proper response of the RBM is assured by requiring accurate individual LPRM inputs, and the small GAFs recorded on March 16, 1983 verify this.

In summary, data available from a recent TIP flux map shows that all LPRM gains are presently within 14% of the correct value, with the average reading within 3% of the correct value. The observed rate of LPRM drift is small, indicating that the relative importance assigned to each LPRM will remain nearly identical as input to the safety systems affected, during the period for the proposed extension. All safety design bases defined in the FSAR for the APRM and RBM will remain unaffected during the extension.

The possibility for an accident or malfunction of a different type than any evaluated previously in the FSAR is not created, nor is the margin of safety as defined in the basis for any technical specification reduced by the proposed extension.

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