ML20050B257
| ML20050B257 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 03/29/1982 |
| From: | Kay J YANKEE ATOMIC ELECTRIC CO. |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| References | |
| FYR-82-36, NUDOCS 8204050148 | |
| Download: ML20050B257 (2) | |
Text
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United States Nuclear Regulatory Commission N&
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Attention:
fir. Dennis M. Crutchfield, Chief Operat ing Reac tors Branch #5 4,\\
Division of Licensing
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,Dl Ref e rence s :
(a)
License No. DPR-3 (Docket No. 50-29)
(b) USNRC Let ter to YAEC, dated Februa ry 18, 1982 (c) YA FC Le t t e r t o USNRC, d a t ed lia rc h 26, 1981 (FYR 81-52),
Attachment D (d) USNRC Let ter to YAEC, dated July 22, 1981.
(e) Technical Speci f icat ions, Yankee Nuclear Power Station (Docket No. 50-29).
Su bjec t :
Boron Dilution Event in Mode 6 De a r S i r :
Pursuant to the NRC's request in Reference (b), the following information is provided to supplement the results of the Mode 6 Boron Dilution Event, which were originally submitted in Reference (c) for the Core XV reload and subsequently approved by the NRC in Reference (d).
The Core XV Perf ormance Analysis, Peferenta (c), states for any postulated boron dilution event while in Mode 6 (refueling mode:
loops i solated, upper head d ra i ned), that:
"...the operat or has greater t han 20 minutes to acknowledge the event and take corrective action.
Twenty minutes is ample time f or the operator to acknowledge the audible count rate signal and high neutron fluy level recorder alarm.
The operator can then take correct ive action to terminate the dilution by isolating the I mary makeup wa ter sou rce by closing valves or s t o ppi ng the (
rging pumps.' [ Re f e re nc e (c), pp. 78, 79]
Specifically, the elapsed time f rom event initiation until loss of shutdown margin via dilution was stated in Table 7-5, Reference (c) to be
- 21. 5 m i n.
es.
The reason t ila t this result is known to be conservat ive i nc lude s, but is not limited to, the following:
(1) The assumed values of inverse boron worth include a conservatism of 10%.
This results in a more rapid loss of available shutdown margin than could reasonably be expected during a boron dilution event.
f00l 8204050148 820329 h
DR ADOCK 05000029 C
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U. S. Nuclear Regulatory Commission Ma rch 29,1982 Attention:
Mr. Dennis M. Crutchfield Page 2 D
(2)
The cycle-dependent administratively prescribed boron concentration for Mode 6-refueling is based upon analytical assumptions that are more conservative than the actual conditions for which the Mode 6 Surveillance Requirement 4. 9.1.1 of Ref erence (e) applies.
The cycle-dependent value of boron concent ration during refueling is based upon a calculated 7% Ao shutdown margin that is subject to an uncertainty of + 2% Ap, which is consistent with the Surveillance Requirement that a measured 5% Ap shutdown na rgin must exist. The calculated shutdown margin, from which the boron concentration during refueling is determined, conservatively assumes that the most react ive cont rol rod is fully withdrawn (2.67% Ap a ll owa nc e ).
This measured shutdown margin prescribed by th Surveillance Requirement, however, is based upon an all-rods-in condition even though a control rod is moved to establish the neutron multiplication necessary for the required inverse-count rate measurement.
If the excess conservatism were renoved in the analysis of a Mode 6 boron dilution event, the time interval to loss of shutdown margin would exceed 30 ninutes.
The interval for operator termination of this event of 21. 5 minutes, reported in Table 7-5 of Ref erence (c) for Core XV, is considered to be a highly conservative result.
This conservatism is the product of a Technical-Spec if icat ions-based analysis for an administrative 1y-controlled mode of operation f or which nunerous safeguards are imposed.
Therefore, no changes to the Technical Specifications will be necessary prior to the next entry into Mode 6 - refueling to ensure that a 30 minutes response interval is available.
Very truly yours, YANKEE ATOMIC ELECTRIC COMPANY J. A. Kay Senior Engineer - Licensing JAK: dad
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