ML20072F279
| ML20072F279 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 03/14/1983 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20072F272 | List: |
| References | |
| NUDOCS 8303230449 | |
| Download: ML20072F279 (3) | |
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDVENT NO. 26 TO FACILITY OPERATING LICENSE DPR-77 AND AMENDMENT N0.15 TO FACILITY OPERATING LICENSE DPR-79 TENNESSEE VALLEY AUTHORITY INTR 000CTIOJ{
In a letter dated Augu'st 16, 1982, TVA requested changes to the rod position indication (RPI) system Technical Specification (TS 3.1.3.3) for Sequoyah Nuclear Plant Units 1 and 2.
The subject of the W analog rod indication system has been under review for some time because of calTbration problems encountered at Sequoyah and other plants that utilize this system.
The RPI system was originally installed 50 that there would be an accurate means of telling the location of individual control rods during power operation in order to avoid misaligned rods.
The Westinghouse safety analysis shows that a control 14 steps is acceptable.
Since there is a 12 step uncertainty, rod misalignment of 2
this leaves a requirement for no more than a 112 step indicated misalignment.
Thus the present Technical Specification requires individual control rods to be aligned with their banks within +12 steps in all modes.
The RPI system was not originally intended to be used in tee shutdown modes.
1 Calibration of the RPI system has been a problem both during power operation and in the shutdown modes. Var 10us solutions to the calibration problems for Modes 1 and
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2 (power operation) have been worked out and presently the licensees have the 112 step accuracy requirement for Modes 1 and 2.
The RPI for each individual rod is calibrated at beginning of cycle at operating j
temperature.
The calibration of the RPIs is highly temperature sensitive.
Thus as the reactor cools down in Modes 3, 4 and 5, the hot calibration becomes inaccur-i ate and may be off as much as 60 steps (total rod is 228 steps).
Thus the Tecnnical Specification which states that the RPIs and group demand counters must agree within 112 steps cannot be met as the plant cools down unless there are calibrations as a function of temperature, l
If the plants wanted to operate in Modes 3, 4 and 5 only with all the rods fully inserted, the Technical Specification could be met because it does not apply to rods t
i fully inserted, hrever, many plants prefer to operate with the shutdown banks j
" cocked" in order to have reactivity available if needed.
They cannot meet the 112 l
step accuracy unless they recalibrate as temperature decreases, t
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. EVALUATION To prevent inadvertent criticality from Hodes 3, 4 and 5, the licensee is required to maintain the reactor in a sub-critical condition with k 0
This is accon-plished thru boron concentration and insertion of control fbb<s. 99.
Calculation of the necessary boron concentration takes into account the position of the control rods.
While it would be extremely useful to have the RPI system indicating rod positions, it is not possible to use the system accurately in Modes 3, 4 and 5.
yestinghouse has proposed a specification which requires only the group demand counters be operable and capable of determining rod position for Modes 3, 4 and 5.
In this way the analog systen is used for the Modes 1 and 2 where it was intended to be used and is not required for Modes 3, 4 and 5.
The group demand counters have proven to be extremely reliable over the 15 years they have been used.
They have proved to be the most accurate means of determining rod position and are in fact used to calibrate the RPIs.
In addition, meeting the requirement that keff(0.99 f r Modes 3, 4 and 5 provides margin to inadvertent critical ity.
Based on our review the staff finds that the safety consideration of maintaining adequate sub-criticality can be accomplished by requiring that the group denand counters be used for rod position indication.
The requirement to maintain a 12 step accuracy with the RPIs is not necessary. Therefore, TVA's proposed Technical Speci-fication change is acceptable.
ENVIRONMENTAL CONSIDERATION We have determined that the acendment does not authorize a change in effluent types or total amounts nor an increase in power level and will not result in any signif-icant environmental impact.
Having made this determination, we have further con-cluded that the amendment involves an action which is insignificant froa the stand-point of environmental impact and, pursuant to 10 CFR G51.5(d)(4), that an environ-nental impact statement or negative declaration and environmental impact appraisal need not be prepared in connection with the issuance of this amendment.
CONCLUSION We have concluded, based on the considerations discussed above, that: (1) because the amendment does not involve a significant increase in the probability or con-sequences of accidents previously considered, does not create the possibility of an accident of a type different from any evaluated previously, and does not OFFICE)
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. involve a significant decre,ase in a safety margin, the amendment does not involve a significant hazards consideration, (2) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner.
and (3) such activities will be conducted in compliance with the Commission's regu-lations and the issuance of this amendment will not be inimical to the common defense and security or to the health and safety of the public.
Date: March 14, 1983 Principal Contributors: Margaret Chatterton, Core Performance Branch, DSI Melanie Miller, Licensing Branch No. 4,DL Carl Stahle, Licensing Branch No. 4. DL l
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