ML19253C138
| ML19253C138 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 11/20/1979 |
| From: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| To: | Goodwin C PORTLAND GENERAL ELECTRIC CO. |
| References | |
| IEB-79-26, NUDOCS 7911300034 | |
| Download: ML19253C138 (1) | |
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'o UNITED STATES 8'
NUCLEAR REGULATORY COMMISSION
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REGION V t
8 1990 N. CALIFORNIA EOULEVARD o
Eo" SUITE 202, WALNUT CREE K PLAZA
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WALNUT CREEK, CAltFORNIA 94596 November 20, 1979 Docket No. 50-344 Portland General Electric Company 121 S. W. Salmon Street Portland, Oregon 97204 Attention: Mr. Charles Goodwin Assistant Vice President Gentlemen:
The enclosed IE Bulletin No. 79-26 is forwarded to you for information.
No written response is required.
If you desire additional information regarding this matter, please contact this office.
Sincerely, lC qc5b----
R. H. Engelken Director
Enclosures:
1.
List of Recently Issued IE Bulletins cc w/ enclosures:
C. P. Yundt, PGE F. C. Gaidos, PGE 1443 249 (D
OM-7911300
UtlITED STATES SSIriS:
6820 tiUCLEAR REGULATORY COMMISSI0tl Accession tio.:
0FFICE OF If1SPECTI0rl AliD EriFORCEMEllT 7910250475 WASHIfiGT0il, D.C.
20555 flovember 20, 1979 IE Bulletin tio. 79-26 BOR0:1 LOSS FROM BWR C0!! TROL BLADES Description of Circumstances:
The General Electric Company (GE) has informed us tf a failure mode for control blades which can cause a loss of boron poison material.
Hot cell examinations of both foreign and domestic blades have revealed r. racks near the upper end of stainless steel tubing and loss of boron from the cubes.
The cracks and boron loss have so far been ggnfined to locations in th; poison tubes with more than 50 percent Bo.on-10 (B ) local depletion. Obse ved 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 boron 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-lithiumpressuresaresufficienttoopentheggack),boronisleachedout 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 furtggr found with similar cracking but with less than 50 percent locci 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 quartar 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 cargin 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 loce. ions of limiting Linear Heat Generation Rate (LHGR), CPR, and Average Planar i.HGR (APLHGR) are no
+
monitoring is not affected by boron DUPLICATE DOCUMENT 1443 250 Entire document previously entered into system under:
ANO No. of pages:
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