ML20198P356
| ML20198P356 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 11/03/1997 |
| From: | Jeffery Wood CENTERIOR ENERGY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 2495, NUDOCS 9711070102 | |
| Download: ML20198P356 (4) | |
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l f401 H Unte F50ute 2 419-249-2300 John K.Wooti j
Oak He**s OH 43449 FAX: 4193214137 Vit,e Psesrx t. Nuclear e
i De+ Bene License Number NPF-3 Serial Number 2495 Docket Number 50 346 I
November 3. 1997
- United States Nuclear Regulatory Commission Document Control Desk Washington, D. C. 20555 0001
Subject:
Request for Interpretation of Schedule Requirements Regarding Technical Specification Surveillance Tests Conducted on a Staggered Test Basis Ladies and Ocntlemen:
The purpose of this letter is to request an NRC interpretation of schedule requirements regarding Technical Specification surveillance tests conducted on a " Staggered Test Basis" for the Davis-Besse Nuclear Power Station (DBNPS), Unit Number 1, Occrating License Number NPF-3. The details of this request are provided in the Enclosure. A response is requested by June 1,1998.
Should you have any questions or require additional inforn ation, please contact Mr. James L. Freels, Manager - Regulatory Affairs, at (419) 321-8466.
Ve truly yours.
Ww-h M lilaj c Q\\
Enclosure cc:
A. B. Beach, Regional Administrator, NRC Region 111
(
S. J. Campbeli, DB-1 NRC Senior Resident inspector A. G. Ilansen, DB-1 NRC/NRR Project Manager t
Utili.ty Radiological Safety Board lllRElR,lRI,Ey!g iT=P M i M L
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i Docket Number 50 346 License Number NPF-3 Serial Number 2495 Enclos'ure PageI l
Request for Interpretation of Schedule Requirements Regarding Technical Specincation Surveillance Tests Conducted on a Staggered Test Basis Backcround:
The Davis Besse Nuclear Power Station (DBNPS) Technical Specifications (TS) Definition 1.21 states as follows:
A STAGGERED TEST B ASIS shall consist of:
a.
A test schedule for n systems, subsystems, trains or designated components obtained by dividing the specified test interval into n equal subintervals, b.
T he testing of one system, subsystem, train or designated components at the beginning of each subinterval.
There are no TS Bases associated with the Definitions Section of TS, however, the intent of i
performing testing on a staggered basis is to limit the length of time that a common cause system failure could go undetected.
Section 4.0.2 of the DBNPS TS states as follows:
Each Surveillance Requirement sh.,ll be performed within the specified time interval with a maximum allowable extension not to exceed 25 percent of the specified surveillance interval.
The associated Bases for DBNPS TS Section 4.0.2 states, in part:
The provisions of this specification provide allowable tolerances for perfonning surveillance activities beyond those specified in the nominal surveillance interval. These tolerances are necessary to provide operational flexibility because of scheduling and performance considerations. Tht: phrase "at least" associated with a surveillance frequency does not negate this allowable tolerance value and permits the performance of more frequent surveillance activities.
The allowable tolerance for performing surveillance activities is sufficiently restrictive to ensure that the reliability associated with the surveillance activity is not significantly l
degiaded beyond that obtained from the nominal specified interval. It is not intended that l
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O Docket Number 50-346 License Number NPF-3 Serial Number 2495 Enclos'ure Page 2 the allowable tolerance be used as a convenience to repeatedly schedule the performance of surveillances at the allowable tolerance limit.
i Explanation ofIssue:
The issue of interpretation is how to apply the maximum alloivable extension provisions of TS Section 4.0.2 to surveillance testing conducted on a STAGGERED TCST BASIS. To illustrate the issue, assume a typical four channel instrumentation functional unit, v>ith channel functional testing required to be performed at least once per 31 days on a STAGGERED TEST B ASIS.
Using the above example, under TS Definition 1.21, the 31 day specified test interval is divided into four equal subintervals of 7.75 days, and one channel is tested at the beginning of each subinterval As a practical matter, at the DBNPS, such a channel functional test would typically be scheduled once a week on the same day of the week, with each channel being tested every 4 weeks. In the event that the channel functional test schedule is disrupted, for whatever reason, and it becomes necessary for the provisions of Specification 4.0.2 to be applied, there are differing interpretations as to how this should be done.
One interpretation is that the 25% allowance must be applied to the subinterval time frame.
Under this interpretation, if last week's channel functional test (for channel "x") was completed at arbitrary time "zero", then this week's channel functional test (for channi "y") must be completed no later than 125% of the 7.75 day subinterval, or by day 9.6875.
A differing interpretation is that the 25% allowance may be applied to the 31 day interval for the particular channel of interest, irrespective of the test completion history for the other channels.
Under this interpretation, the maximum allowable extension for any channel is 125% of 31 days, or 38.75 days from the last performance of the channel functional test for that same channel.
The first interpretation ensures that if the channel "y" test is completed at day 9.6875, that time will be within 125% of 31 days since the last performance of the channel "y" test, even if each test in the past month utilized N 15% allowance. This method also ensures a relatively unifonn test spacing over the 31 da-
. vat, regardless of whether the 25% allowance is used, llowever, this method is potentially o ly conservative in the sense that if each of the three previous channels were completed on the nonnal 7 day schedule, and the need arose to use the maximum 9.6875 day allowance for channel "y", then channel "y" testing would be required to be completed within 30.6875 days ( 3 x 7 + 9.6875 days) of the last performance of the channel "y" test. Or, if each of the three previous channels were completed on a 7.75 day schedule, and the need arose to use the maximum 9.6875 day allowance for channel "y", then channel "y" testing would be required to be completed within 32.9375 days ( 3 x 7.75 + 9.6875 days) of the last performance of the channel "y" test. In either case, the current channel "y" test would be required to be completed well within the 38.75 day limit, were the extension applied to the 31 day interval, as would be allowed by the second interpretation. The end result is that, under the i
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o Docket Number 50-346 License Number NPF-3 Serial Number 2495 Enclos'ure Page 3 first interpretation, a channel may need to be declared inoperable and placed in a tripped condition earlier than under the second interpretation. This could place the plant in a less reliable configuration since under a typical 2 out of 4 actuation logic, a spurious signal in a second channel could cause inadvertent initiation of a protective action, for example a reactor trip or a Safety Features Actuatien System actuation, llo'vever, while the second interpretation potentially allows a greater time margin to perfonn a test,it does not ensure that testing is uniformly spaced. Under the above example, a series of channel functional tests for each of four channels could be conducted with three 7 day cubintervals and one 17.75 day subinterval.
Reauest for Interoretation:
The DBNPS surveillance test program is presently being conducted under the more conservative scheduling approach of applying the 25% maximum allowable extenr. ion of TS Section 4.0.2 to the STAGGERED TEST B ASIS subinterval, liowever, as described above, this approach may be overly conservathe and could result in equipment being prematurely declared inoperable, potentially placing the plant in a less reliable condition.
For this reason, the DBNPS requests a written response from the NRC on the appropriate t.pplication of the 25% maximum allowable extension of TS Section 4.0.2 to TS surveillance testing performed on a STAGGERED TEST BASIS,