ML19210E551
| ML19210E551 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 11/20/1979 |
| From: | Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | Woolever E DUQUESNE LIGHT CO. |
| References | |
| NUDOCS 7912050233 | |
| Download: ML19210E551 (1) | |
Text
UNITED STATES
$ "f) 4,( [oj NUCLEAR REGULATORY COMMISSION
,x
./.:: p REGION I s.g' f*,
g 631 PARK AVENUE 0,
,o KING OF PRUSSIA, PENNSYLVANIA 19406
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Docket No. 50-412
'20 0 73 Duquesne Light Company ATTN:
Mr. E. J. Woolever Vice President 435 Sixth Avenue Pittsburgh, PA 15219 Gentlemen:
The enclosed IE Bulletin 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, k W.% N.
w h yce H. Grier Bo rector
Enclosures:
1.
List of Recently issued IE Bulletins CONTACT:
D. L. Caphton (215-337-5266) cc w/encls:
R. J. Washabat j, Quality Assurance Manager 1500 124 233 4
p m 20so
4 ENCLOSURE 1 UNITED STATES SSINS:
6820 NUCLEAR REGULATORY COMMISSION Accession Mo.:
0FFICE OF INSPECTION AND ENFORCEMENT 7910250475 WASHINGTON, D.C.
20555 IE Bulletin No. 79-26 Date: November 20, 1979 Page 1 of 4 BORON LOSS FROM BWR CONTROL BLADES Description of Circumstances:
The General Electric Company (GE) has informed us at 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 cracks near tne upper end of stainless steel tubing and loss of boron from the tubes.
The cracks and boron loss have so far been ggnfined to locations in the poison tubes with more than 50 percent Boron-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 boron carbide (B C) particles and swelling of the compacted g
8 C as helium and lithium concentrdtions grow.
Once primary coolant penetrates 4
tne cladding (i.e., the cracking has progressed through the cladding wall and thehelium-lithiumpressuresaresufficienttoopenthecrack),ggronis leached out of the tube at locations with more than 50 percent B local depletion (local depletion is considered to be twice the average depletion).
Itwasfurtherfundwithsimilarcrackingbutwithlessthan50percentlocal 1
depletion of 8
, 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 tne end of design life is reached when the reactivity wggthofthebladeisreducedby10 percent,whichcorrespondsto42 percent B
depletion averaged over the top quarter of the control glade.
Because of y
the leaching mechanism, GE has redu ed 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 calcu tests are based on the assumption that in scram reactivity due to boron loss c DUPLICATE DOCUMENT Power Ratio (CPR) reductions during the the consequences of control rod drop ac Entire document previcesly entered into system under:
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1500 125 No. oc gmes:
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