ML20248E573
| ML20248E573 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 03/28/1989 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20248E546 | List: |
| References | |
| NUDOCS 8904120287 | |
| Download: ML20248E573 (4) | |
Text
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UNITED STATES p,
NUCLEAR REGULATORY COMMISSION
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WASHINGTON, D. C. 20555
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SAFETY EVAL' ATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION J
SUPPORTING AMENDMENT N0.108 TO FACILITY OPERATING LICENSE NO. DPR-77 i
AND AMENDMENT NO. 98 TO FACILITY OPERATING LICENSE NO. DPR-79 TENNESSEE VALLEY AUTHORITY SEQUOYAH NUCLEAR PLANT, UNITS 1 AND 2 DOCKET NOS. 50-327 AND 50-328
1.0 INTRODUCTION
By submittal dated January 31, 1989, the Tennessee Valley Authority (TVA) proposed to modify Section 3.1.3, Movable Control Assemblies, of the Sequoyah Nuclear Plant (SQN) Units 1 and 2 Technical Specification (TS). The proposed changes would revise the limiting conditions for operation (LCO) 3.1.3.4, Rod Drop Time, and 3.1.3.5, Shutdown Rod Insertion Limit, to define the fully withdrawn condition for shutdown and control rods as a position within.the interval of equal to or greater than 222 steps withdrawn and equal to or less i
than 231 steps withdrawn.
Fully withdrawn is currently 228 steps.
Figure l
3.1-1, " Rod Bank Insertion Limits Versus Thermal Power Loop Operation", is also proposed to be amended to reflect the fully withdrawn interval discussed above.
TVA has also added the TS Bases with 3/4.1.3.4, " Rod Drop Time" and 3/4.1.3.5, l
" Shutdown Rod Insertion Limit " to provide the operators with an explanation for the fully withdrawn rod position range.
This is TVA's TS change number 89-15.
By letter dated March 9, 1989, TVA provided supplemental information to its application.
The information discussed the effect of the core neutron flux on the control rods being at the 222 steps as being fully withdrawn.
This information did not change the substance of the proposed action which TVA submitted in its application dated January (31, 1989 and which was noticed in the Federal Register on February 22, 1989 54 FR 7645).
The information did not affect the staff's initial determination of no significant hazards l
consideration in that notice.
2.0 EVALUATION NRC Inspection and Enforcement (IE) Information Notice (IN) 87-19, dated April 9,1987, identified a potential problem for Westinghouse Electric Corporation (_W)pressurizedwaterreactors(PWR)rodclustercontrol assembly (RCCA) guides.
A phenomenon known as fretting wear of the RCCA rodlets was noted at W PWRs.
The fretting was determined to be caused by flow-induced vibratory contact between the rodlets and the guide blocks during long periods of steady state operation.
W recommended that the RCCAs be axially repositioned during operation to slightly change the position of fully withdrawn RCCAs in order to distribute the wear.
IE IN 87-19, referenced above, supported the W fix as a mitigating step for RCCA guide block wear. TVA has proposed to change the SQN, Units 1 and 2 TS to define the fully withdrawn position of RCCAs as a range of 222 and 231 steps.
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. The current fully withdrawn RCCA position is 228 steps. TVA has stated this action will improve RCCA reliability and extend the RCCA lifetime.
i The term fully withdrawn is applied to shutdown and control banks in TS LCOs 3.1.3.4 and 3.1.3.5.
Figure 3.1-1, " Rod Bank Insertion Limits Versus Thermal Power - Four Loop Operation," indicates fully withdrawn is 228 steps. The above proposed change will redefine the term fully withdrawn in LCOs 3.1.3.4 and 3.1.3.5 and modify Figure 3.1-1 to allow axial repositioning of shutdown and control banks within the interval of 222 to 231 steps.
TVA noted in their submittal that RCCA repositioning has the potential to i
reduce control rod worth and to increase control rod drop time.
In the case of the fully withdrawn position of 222 steps TVA has calculated that the control rod worth would be reduced by 0.12-percent delta rho.
TVA states, however, this penalty would be accounted for in the TS shutdown margin requirements.
TVA has provided, as an enclosure to their January 31, 1989 submittal, a W Safety Evaluation supporting the proposed changes.
The Safety Evaluation addresses both the hardware impact and the impact on Cycle 4 specific accident analyses.
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The hardware portion of this evaluation addresses the operation of the Control l
Rod Drive Mechanism (CRDM) and the Solid State Rod Control System.
W review of l
the RCCA design and performance requirements shows that the subject repositioning
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will be totally mechanically transparent to the operation of the installed L106A j
CRDMs at SQN and will not pose a challenge to CRDM operation. At step 231, the l
RCCAs are still engaged in the top of the fuel assembly thereby allowing for smooth rod drop. The changes required to the control system, solid state logic, l
and the bank overlap switches S1 through S6, do not apply to Class 1E equipment and will not challenge safety related equipment.
W review of the RCCA repositioning impact on the postulated loss-of-coolant and related accidents were assessed for increased control rod drop time.
In the case of the fully withdrawn position of 231 steps, TVA has calculated an approximately time However, the.03 second increase is small 0.03 second increase in rod drop (appro.ximately 0.60 second).
The rod drop relative to the existing margin time assumed in these analyses is consistent with the TS LC0 3.1.3.4 limit of 2.2 seconds from the beginning of the decay of the stationery gripper coil voltage to dashpot entry.
The W and TVA Safety Evaluation conclusions for the RCCA repositioning is.that a change from the fully withdrawn position of 228 to a range of 222-231 steps does not represent an unreviewed safety question.
A similar conclusion is reached with respect to all loss-of-coolant and non-loss-of-coolant accidents l
specific to Cycle 4 operation.
For both loss-of-coolant and non-loss-of-coolant accidents, there is no effect on any existing safety analyses by the subject RCCA repositioning.
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, By telephone conference on February 27, 1989, TVA discussed the impact of increased neutron fluence on the RCCA tips since these tips would be below 228 steps for some period during each of the future fuel cycles.
The only impact noted by TVA was that the RCCAs would experience slightly increased swelling at the tips. A's justification for the acceptability of this increased swelling, TVA has stated that RCCA Control Bank "D" is normally more inserted into the core than 228 steps since its the controlling bank (particularly during beginning and middle of cycle operation) and that the remaining banks are of the same material and construction; therefore, all of the RCCA shutdown and control banks are bounded by the controlling bank D analyses in terms of rod life.
TVA provided this supplemental information in its letter dated March 9, 1989.
Based on the above, the NRC staff has concluded that repositioning the RCCAs from a fully withdrawn position of 228 steps to a step within the range of 222-231, is acceptable.
The proposed changes to TS LC0 3.1.3.4 and 3.1.3.5 to add the footnote, " fully withdrawn shall be the condition where shutdown and control banks are at a position within the interval of 222 and 23' steps withdrawn, inclusive" is found to be acceptable.
The proposed changes to Figure 3.1-1 to add an identical footnote as just quoted above, with the l
additional footnote, "There are no Rod Insertion Limits when shutdown and j
control banks are at a position within the interval 222 and 231 steps with-drawn, inclusive. The fully withdrawn position shall be specified in a reload sefety evaluation for each cycle of operation and; once specified, shall not be changed unless such change is specifically evaluated", is also found to be acceptable.
Furthermore, the proposed addition of 3/4.1.3.4 Rod Drop Time and 3/4.1.3.5 Shutdown Rod Insertion Limit to the TS bases is found to be appropriate and acceptable.
Based on the above, the staff concludes that the proposed changes in its application for TS 89-15 are acceptable.
3.0 ENVIRONMENTAL CONSIDERATION
These amendments involve a change to a requirement with respect to the' install-ation or use of a facility component located within the restricted area as defined in 10 CFR Part 20. The staff has determined that the amendments involve no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure.
The Commisssion has previously issued a proposed finding that these amendments involve no significant hazards consideration and there has been no public comment on such finding. Accordingly, the amendments meet the eli criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9)gibility Pursuant to 10 CFR 51.22(b), no environmental impact statement nor environmental assessment need be prepared in connection with the issuance of these amendments.
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4.0 CONCLUSION
The Commission made a proposed determination that the amendment involves no significant hazards consideration which was published in the Federal Register (54 FR 7645) on Februarf 22, 1989 and consulted with the State of Tennessee.
No public comments were received and the State of Tennessee did not have any ccmments.
The staff has concluded, based on the considerations discussed above, that:
will not be endangered by operation in the proposed manner, and (2) public (1) there is reasonable assurance that the health and safety of the such activities will be conducted in compliance with the Commission's regulations, and the issuance of the amendments will not be inimical to the common defense and security nor to the health and safety of the public.
Principal Contributor:
T. Rotella Dated: March 28, 1989
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