ML19253C144
| ML19253C144 | |
| Person / Time | |
|---|---|
| Site: | Columbia, Washington Public Power Supply System, Satsop  |
| Issue date: | 11/20/1979 |
| From: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| To: | Strand N WASHINGTON PUBLIC POWER SUPPLY SYSTEM |
| References | |
| IEB-79-26, NUDOCS 7911300042 | |
| Download: ML19253C144 (1) | |
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UNITED STATES E ' *,,, 7 NUCLEAR REGULATORY COMMISSION g
REGION V g?
.j 1990 N. CALIFORNI A BOULEV ARD o, '
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SUITE 202, WALNUT CREEK PLAZA
- ,e e WALNUT CREEK, CALIFORNI A 94596 t
November 20, 1979 Docket Nos. 50-397, 50-460, 50-503 50-509, 50-513 Washington Public Power Supply System P. O. Box 968 Richland, Washington 99352 Attention:
Mr. N. 0. Strand Managing Director Gentlemen:
The enclosed IE Bulletin No. 79-26 is forwarded to you for information.
No written respor a is required.
If you desire additional information regarding this matter, please contact this office.
Sincerely, s1% h L p L R. H. Engelken Director
Enclosures:
1.
List of Recently Issued IE Bulletins cc w/ enclosures:
M. E. Witherspoon, WPPSS A. D. Kohler, WPPSS J. P. Thomas, WPPSS W. J. Talbott, WPPSS G. C. Sorensen, WPPSS 1443
?58 79118 00 d b
s U!lITED STATES SSIflS:
6820 NUCLEAR REGULATORY COMMISSION Accession fio.:
0FFICE OF INSPECTION AND EtiFORCEMErlT 7910250475 WASHINGTON, D.C.
20555 November 20, 1979 IE Bulletin No. 79-26 BORON LOSS FROM BWR CONTROL BLADES Description of Circumstances:
The General Electric Company (GE) has informed us of a failure mode for control blades which can cause a loss of boron poison material.
Hot cell examinations of both foreign and domestic blades t3ve revealed cracks near the upper end of stainless steel tubing and loss of baron from the tubes.
The cracks and boron loss have so far been ggnfined to locations in the poison tubes with more than 50 percent Baron-10 (B
) local depletion.
Observed crack sizes range from a quarter to a half inch in length and from one to two mils in width.
GE has postulated that the cracking is due to stress corrosion induced by solidification of baron carbide (B C) particles and swelling of the compacted g
B C as helium and lithium concentrdtions grow. Once primary coolant penetrates thecladding(i.e.,thecrackinghasprogressedthroughthecladdingwallandthe helium-lithium pressures are sufficient to open the 15ack), b r n is eached out of the tube at locations with more than 50 percent B local depletion (local depletion is considered to be twice the average depletion).
It was furtygr found with similar cracking but with less than 50 percent local depletion of B, that leaching did not occur even though primary coolant had penetrated the cladding.
The cracking and boron loss shorten the design life of the control blade.
According to the GE criteria the end of design life is reached when the reactigty worth of the blade is reduced by 10 percent, which corresponds to 42 percent B depletion averaged over the top quarter of the control glade.
Because of the l
leaching mechanism, GE has reduced the allowance for B depletion averaged over the top quarter of the control blade from the 42 percent value to 34 percent.
The safety significance of boron loss is its impact on shutdown capability and scram reactivity. Although shutdown capability is demonstrated by shutdown margin tests after refueling, the calculated control blade worths used in the tests are based on the assumption that no boron loss has occurred.
Reduction in scram reactivity due to boron loss could increase the severity of Critical Power Ratio (CPR) reductions during the plant transients and could increase the consequences of control rod drop accidents.
Because the locations of limiting Linear Heat Generation Rate (LHGR), CPR, and Average Planar LHGR (APLHGR) ar monitoring is not affected by b DUPLICATE DOCUMEN9 4 4 3 2 5 9 Entire document previously entere
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