ML20090L592
| ML20090L592 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 02/02/1976 |
| From: | Mayer L NORTHERN STATES POWER CO. |
| To: | Stello V Office of Nuclear Reactor Regulation |
| References | |
| 1098, NUDOCS 9102120449 | |
| Download: ML20090L592 (3) | |
Text
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NSF NORTHERN STATES POWtR COMPANY M I N N E A P O t.l S. M I N N E S OT A es400 a\\ hL1'.,' /,
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D ',h%.'/,8 Mr. Victor Stello, Director 1
Division of Operating Reactors U.S. Nuclear Regulatory Commission
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Washington, DC 20555
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Dear Mr. Stello:
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Nk MONTICELLO NUCLEAR GENERATING PIANT Docket No. 50-263 License No. DPR-22 Eummary Status of Fuel Report Wis report is submitted in compliance with Technical Specification 6.7.C.6,
" Summary Status of Fuel Report", which is required following each refueling.
The Monticello generator was taken off line and the reactor made subcritical on September 11, 1975. Puring the outage the remaining 268 initial core 7x7 fuel assemblies were replaced with Reload 4 8x8 fuel assemblies.
Cycle 5 commenced as the reactor was again made critical on November 16 and the gen-erator put on line on November 19, 1975.
The perfomance of fuel is monitored by the of fgas level during plant opera-tion and by fuel sipping during a refueling outage.
Previous reports referenced stack offgas levels.
Since the offgas recombiner and storage system were placed in service about one year ago, the stack emissions are so low they are no longer a good indicator of fuel performance.
The offgas activity level at the air ejector, upstream of the augmented offgas treatment system, is now used. A summary of fuel performance through Cycle 3 is documented in the April 29,1975 "Sucary Status of Fuel Report".
As reported, a thorough sip-ping program at the er.d of Cycle 3 revealed cladding perforations in a number of initial core fuel assemblies.
The offgas level was found substantially re-duced during the initial power ascension in Cycle 4.
As the cycle proceeded the offgas rate gradually increased as the high exposure initial core fuel developed additional cladding perforations.
Power was restricted during a significant portion of the cycle by offgas limitations; power was gradually reduced to 57% of rated at the end of Cycle 4.
During the recent refueling outage the remaining 268 initial core 7x7 fuel assemblies were discharged to the spent fuel pool.
Subsequent sipping in the fuel pool identified 77 leakers.
The fuel assemblies remaining in the reactor from Cycle 4 consisted of 20 7x7 assemblies of an improved design and 196 8x8 assemblies. All of the improved 7x7 fuel and a 25% sample of the 8x8 fuel was sipped with nn Icala rs identified.
To date 237 of the initial core fuel as-semblies have been classified as leakers. The number of fuel assemblies clas-sified as lenkers in each of Cycles 1 through 4 are 25, 86, 49 and 77.
(The 9102120449 760202 ~
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Mr. Victor Stello February 2, 1976 1
Cycle 2 number is an update to that reported in our " Cycle 3 Startup Report and Sum-
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mary Status of Fuel Report," reficcting additional sipping done af ter the report j
was prepared.) No replacement fuel has shown signs of cladding perforations.
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The average exposure of the 77 Cycle 4 leakers was 14,686 MWD /STU.
Based on l
limited visual inspection and previous experience at Monticello and other re-l actors, the predominant failure mechanism was concluded to be pellet-clad in-te rac tion.
In the first two months of Cycle 5 there has been no offgas increase trend as observed in previous cycles.
It is anticipated that the excellent performance of reload fuel will continue in the future and that power reductions 1
due to fuel failures will not be necessary in the future.
The exposure summary of the Cycle 4 discharge and the reload fuel as of the beginning of Cycle 5, 1
i is as follows:
Number of pxposure (MWD /STU)
Fuel Type Enrichment Assemblies Minimum Ave rage Maximum Initial Core (7x7) 2.25 w/o 268 9,139 15,310 18,358 Reload 1 (Improved 7 x 7) 2.30 w/o 20 11,693 11,775 11,879 Reload 2 (8x8) 2.62 w/o 116 4,686 6,656 8,149 Reload 3 (8x8) 2.50 w/o 80 1,560 3,258 4,168 Reload 4 (8x8) 2.19 w/o 268 0
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Yours very truly, MO-i l
L. O. Mayer, PE l
Manager, Nuclear Support Se rvices i
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J. G. Keppler G.
Cha rnof f MPCA Attn: J. W.
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ENCLOSURES:
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