ML20129E487
| ML20129E487 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 09/25/1996 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20129E466 | List: |
| References | |
| NUDOCS 9610010092 | |
| Download: ML20129E487 (4) | |
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M Eig UNITED STATES 1
,j NUCLEAR REGULATORY COMMISSION WASHINGTON. D.C. 30M6 0001
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1 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION l
RELATED TO AMENDMENT NO.148 TO FACILITY OPERATING LICENSE NO. DPR-28 i
VERMONT YANKEE NUCLEAR POWER CORPORATION s
VERMONT YANKEE NUCLEAR POWER STATION i
l DOCKET NO. 50-271
1.0 INTRODUCTION
]
By letter dated June 28, 1996, as supplemented by letter dated August 30, 1996, the Vermont Yankee Nuclear Power Corporation (the licensee) submitted a request j
1 for changes to the Vermont Yankee Nuclear Power Station (VYNPS) Technical 4
Specifications (TSs). The proposed changes would increase the required shutdown j
margin to allow the highest worth control rod to be determined by calculation as well as by testing.
In addition, the licensee proposed to relax the action i
requirements in the event the required shutdown margin is not met. Appropriate editorial changes and minor editorial corrections to the affected specifications were also proposed. The August 30, 1996, letter provided clarifying information that did not change the scope of the June 28, 1996, application or affect the initial proposed no significant hazards consideration determination.
The safety objective of establishing shutdown margin limits is to ensure that i
inadvertent criticalities and potential control rod drop accidents (CRDAs) will not cause significant fuel damage, which could result in undue release of radioactivity.
Consequently, to prevent significant fuel damage in the event of j
an inadvertent criticality or a CRDA, the TS require maintaining the shutdown
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margin within the established limit whenever fuel is present in the reactor vessel.
1 2.0 EVALUATION The licensee has proposed to increase the current limit of 0.25 percent &/k on shutdown margin in TSs 4.3.A.1, 4.12.D.1, and 4.12.D.2 to 2 0.28% M /k with the highest worth rod determined by test, as currently done, and 2 0.38% M /k with i
the highest worth rod determined analytically. The new limits would be given in the limiting condition for operation (LCO), TS 3.3.A.1, rather thaa in the associated surveillance requirement, TS 4.3.A.1, as currently done.
would specify the same shutdown margin limits by referencing TS 3.3.A.1.
The higher value of 0.38% M/k provides conservative margin in consideration of the additional uncertainty that is introduced when the highest worth rod is not l'
determined by actual measurement.
However, as the licensee pointed out in its j
submittal, this provision will provide additional flexibility in refueling outage operations which require a shutdown margin demonstration. This flexibility in performing maintenance eliminates, for example, the need to completely remove all fuel from a maintenance cell to perform a control rod drive replacement.
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9610010092 960925 PDR ADOCK 05000271 P
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in turn will reduce the number of tiines a fuel bundle is handled and thus the likelihood of a fuel handling event. The proposed increase is acceptable because it offers additional assurance that significant fuel damage will not occur in the event of an inadvertent criticality or a CRDA, and because of the potential benefit to safety from the added flexibility in performing maintenance.
The licensee proposed the following additional changes to accompany the increased shutdown margin limits.
l (a)
In the event the shutdown margin required by TS 3.3.A.1 is not met, TS 3.3.F specifies that "an orderly shutdown shall be initiated and the reactor shall be in the cold shutdown condition within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />." These I
action requirements are replaced by the following less restrictive action requirements in revised TS 3.3.A.1:
"With the required shutdown margin not met during power operation, either restore the required shutdown
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margin within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, or be in hot shutdown within the next 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />."
The 6-hour allowance to restore the required shutdown margin is i
s acceptable, considering that the reactor can still be shut down, assuming i
3 no failures of additional control rods to insert, and the low probability of an event occurring during this interval.
The 12-hour allowance is reasonable, based on operating experience, to reach hot shutdown from full power conditions in an orderly manner and without challenging plant q
systems, and is therefore acceptable. There is no need to further cool down the plant to cold shutdown, as currently required, because in hot shutdown the plant is already in a safe condition.
Therefore, deleting 3
j the cold shutdown requirement is acceptable.
(b)
The applicability requirements of TS 3.12.0, " Control Rod and Control Rod Drive Maintenance," and TS 3.12.E, " Extended Core Maintenance," are i
revised as follows.
i (1) TS 3.12.D states that "A maximum of two non-adjacent control rods 1
separated by more than two control cells in any direction may be withdrawn from the core for the purpose of performing control rod and/or control rod drive maintenance" provided certain conditions are satisfied. The preceding words given in italics are replaced with the words "One control rod" thus limiting the application of this LC0 4
to the performance of maintenance on one control rod and its associated control rod drive mechanism at a time.
The conditions that must be satisfied to perform control rod maintenance under this LC0 are also revised.
The first condition specified by TS 3.12.0 contains the following statement, "The refueling interlock which prevents more than one control rod from being withdrawn may be bypassed for one of the control rods on which maintenance is being performed." This bypass allowance is deleted.
This is acceptable because the revised LC0 only allows one control to be withdrawn at a time for maintenance, making the bypass allowance unnecessary.
The second and third conditions, as revised, only l
I je i
l l
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_3 contain minor editorial changes consistent with the change in the LC0 l
applicability.
In addition, the wording of the third condition, TS 3.12.D.3, is simplified to be consistent with the wording of similar i
condition in TS 3.12.E.2, regarding source range monitor operability.
These editorial improvements are acceptable because they are purely administrative.
(2) TS 3.12.E states that "# ore than two control rods may be withdrawn from the reactor core" provided certain conditions are satisfied.
The preceding words given in italics are replaced with the words "One or more" thus adding to the applicability of this LC0 the withdrawal i
of one control rod for extended core maintenance. Also, the words "or removed" are inserted following the word withdrawn to change the j
LCO to state that "One or more control rods may be withdrawn or removed from the reactor core" provided certain conditions are 2
satisfied. This last change only clarifies the intent of the current i
LC0 and is consistent with plant practice. Thus, it does not remove or add any restrictions. Therefore, it is an acceptable administrative change.
As revised, both TS 3.12.D and 3.12.E appear to apply whenever maintenance on just one control rod is needed. However, the conditions that must be satisfied to perform such maintenance under i
these two LCOs make it clear that maintenance under TS 3.12.0 is not to be conducted in conjunction with other core alterations associated with refueling; such a situation is covered by TS 4.12.E.
Overall, the preceding changes to TS 3.12.D and 3.12.E result in more restrictive TS controls over control rod and control rod drive maintenance. The conduct of maintenance on two control rods j
simultaneously may no longer be accomplished under the conditions and surveillances specified in TS 3/4.12.0, but under the more restrictive conditions and surveillances of TS 3/4.12.E.
The procedural controls imposed by the requirements of these TSs, such as placing the reactor mode switch in the refuel position, verification of the required shutdown margin, source range monitor operability, j
and refueling interlock operability, will prevent the reactor from becoming critical during control rod maintenance and during refueling i
operations. Thus, the proposed changes to TS 3/4.12.0 and 3/4.12.E will result in increased safety margins and are, therefore, acceptable.
The licensee also proposed changes to the Bases for TS 3.3.A.1, 3.3.E, 3.12.D, and 3.12.E to address the proposed changes discussed above and to replace the unit "Ak", that occurs in several places in the specifications and the Bases, with the correct unit for reactivity "Ak/k." The staff has reviewed the proposed Bases changes and has no objection to them.
i The staff notes that the proposed changes are consistent with corresponding provisions in Specifications 3.1.1, " Shutdown Margin," 3.10.3, " Single Control Rod Withdrawal-Hot Shutdown," 3.10.4, " Single Control Rod Withdrawal-Cold
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_4 Shutdown," and 3.10.6, " Multiple Control Rod Withdrawal-Refueling," in NUREG-1433, " Standard Technical Specifications, General Electric Plants, BWR/4,"
Revision 1, dated April 1995.
3.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Vermont State official was notified of the proposed issuance of the amendment. The State official had no comments.
4.0 ENVIRONMENTAL CONSIDERATION
The amendment changes requirements with respect to installation or use of facility components located within the restricted area as defined in 10 CFR Part 20 and changes surveillance requirements.
The NRC staff has determined that the amendment involves 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 Commission has previously issued a proposed finding that the amendment involves no significant hazards consideration, and there has been no public comment on such finding (61 FR 20860). Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in cacaection with the issuance of the amendment.
5.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that:
(1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor:
C. Harbuck Date:
September 25, 1996
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