ML19305E064
| ML19305E064 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 02/25/1977 |
| From: | Gower G, Roy G, Thompson D NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | |
| References | |
| FOIA-79-149 PNO-III-77-033, PNO-III-77-33, NUDOCS 8004220249 | |
| Download: ML19305E064 (2) | |
Text
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i a-u-%d te_ v cI PRELIMINARY NOTIFICATION February 25 1977 PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCLTRENCE-PNO-77-33 l
This preliminary n_otification constitutes EARLY notice of an event of i
POSSIELE safety or public interest significance. The information presented is as initially receivad without verification or evaluation and is basically all that is known by IE staff on this date.
i Facility: Horthern States Power Company, Monticello (CN 50-263)
Monticello NN
Subject:
RZACTOR PERIOD LESS THAN 5 SECONDS DURING REACTOR STARTUP During a reactor startup on February 23, 1977, at 5:15 p.m.,
(following a reactor trip 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> earlier from 100% recetor power during an ice storm) a reactor period of less than 5 seconds was obtained before the The l
reactor tripped on the lowest level (Range 1) intermediate range.
reactor was slightly supercritical (approximately 600-second period) when the controlling rod (46-26) was withdrawn one notch from position 06 to 08 (18" to 24" withdrawn), and caused the short period. All reactor protective aystems functioned as required. The licantse's review of the occurrence indicates that only the 46-26 rod moved one notch and no other rods moved and no rods were uncoupled.
Analyses performed by NSP indicates that the combination of temperature and high xenon concentration at the time of the occurrence established conditions such that criticality occurred at an unusually high reactivity worth control rod notch. A similar event occurred at Dresden Unit 2 in August 1972.
The licensee's calculations indicate the total worth of the 46-26 rod to have been 1.27% delta K/K and the worth of the rod notch from position 06 to 08 to have been 0.47% K/K.
Following tha trip, the licensea performed a post-scram review and from previous core analysis, determir.ed that the same conditions no longer existed and resuned reactor operations.
'Ihm licensee monitored air ejector off-gas activity during the subsequent startup and no abnormal conditions were acted.
CONTINUED 8004220 2$
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l FNO-77-33 Page 2 Continued Fabruary 25, 1977 j
I i
I A Region III (Glen Ellyn) inspector has been sent to review this occur-rence.
i No press release is planned by the licensee or Region III.
Region III (Glen Ellyn) received notification of this occurrence by telephone (USP) at 3:00 p.t. on February 24, 1977.
Contact:
GCGover, IE x27261 GWRoy, IE x27261 DThompson, IE x27541 i
Distribution:
Chairman Rowden Commissioner Kennedy S. J. Chilk, SECY Commissioner Gilinsky C. C. Kammerer CA G. F. Murphy, JCAE L. V. Gossick, EDO K. R. Chapean, NMSS R. G. Ryan, OSP S. H. Hanauer, EDO E. Volgenau, OIE J. A. Harris, PA E. C. Rusche, NRR H. K. Shapar, ELD T. J. McTiernan, CIA j
Transmitted: PBldg 3.'2 4_; H St. II/I_; HNBB
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