ML19296B151
| ML19296B151 | |
| Person / Time | |
|---|---|
| Site: | Shoreham File:Long Island Lighting Company icon.png |
| Issue date: | 02/13/1980 |
| From: | Bordenick B, Hoefling R NRC OFFICE OF THE EXECUTIVE LEGAL DIRECTOR (OELD) |
| To: | Atomic Safety and Licensing Board Panel |
| References | |
| NUDOCS 8002200170 | |
| Download: ML19296B151 (33) | |
Text
I ENCLOSURE 1 UNITED STATES SSINS:
6820 NUCLEAR REGULATORY COMMISSION Accession No.-
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 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 have revealed cracks naar the 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 4
B,C as helium and lithium concentrations grow.
Once primary coolant penetrates tBe 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).
Itwasfurtherfoundwithsimilarcrackingbutwithlessthan50percentlocal y
depletion of B
, that leaching did not occur even though primary coolant had penetrated the cladding.
The cracking ar.d boron loss shorten the design life of the control blade.
According to the GE criteria the end of design life is reached when the reactivity wgthofthebladeisreducedby10 percent,whichcorrespondsto42 percent B
depletionaveragedoverthetopquarterofthecontrolflade.
Because of the 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.
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30%20o170
IE Bulletin No. 79-26 Date: November 20, 1979 Page 2 of 4 Because the locations of limiting Linear Heat Generation Rate (LHGR), CPR, and Average Planar LHGR (APLHGR) are not in controlled cells, local power limit monitoring is not affected by boron loss.
GE has evaluated the potential effect of boron loss on shutdown capability, CPR reduction and the consequences of control rod drop accidents.
GE's evaluation isbaseg0 n the het cell result that no boron loss is observed until 50 percent local B depletion is attain g.
For each B C tube, complete loss of B C was g
assumed when the calculateo B ygepletionexceeded50percentlocally.4For any blade expected to geach a B depletion greater than 34 percent d:..:..g a cycle, GE assumed a 8 depletion distribution typical of blades at the previously defined end of design life.
Based on these evaluations GE arrived at the following conclusions:
(a) Control rod drop accident consequences are not sufficiently sensitive to small reductions in scram reactivity to be affected by boron loss before the end of design life of the blades involved.
[
(b)
If no more than 26 percent of the control blades have experienced a 10 percent reduction in projected worth taKing boron loss into Consideration, there is a negligible effect on transient CPR reduction and MCPR limits.
(c)
If any control blades have experienced more than 10 percent reduction in projected worth, taking boron loss into consideration, the shutdown margin should be demonstrated to be at least the sum of the shutdown margin required by Technical Specifications plus an increment sufficient to account for the potential for boron loss.
We have examined the bases for GE's conclusions, including the hot cell tests and the calculational assumptions.
The preferredgction is to replace all blades expected to have greater than 34 percent B depletion averaged over the upper one-fourth of the blade.
Hgever,basedonourreviewwebelieve the relation between boron loss and B depletion (i.e., the observations to dgeshowthatboronlossdoesnotoccuruntil50percentlocaldepletionof B
) is st.fficiently understood to justify BWR operation on an interim basis provided the following actions have been taken by licensees.
(
l IE Bulletin No. 79-26 Date: November 20, 1979 Page 3 of 4 Action to be Taken by Licensees:
For all BWR power reactor facilities with an operating license:
1.
Theoperatinghistoryo{0the reactor is to be reviewed to establish a record of tne current B depletion averaged over the upper one-fourth of the blade for every control blade; the record is to be maintained on a continuing basis.
This action is required on all reactors whether shut-down for refueling or operating.
10 2.
Identify any control blades predicted to have greater that 34 percent B depletion averaged over the upper one-fourth of the blade by the next refueling outage.
a.
Describe your plans for replacement of identified control blades.
b.
Describe measures which you plan to take justifying continued operations until the next refueling specifically addressing (1) any blade with greater than 42 percent depletion averaged over the upper one-fourth of the blade; and (2) the condition where you find greater than 26
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percent of the control blades calculated to have greater than 34 percent depletion averaged over the upper one-fourth of the blade.
3.
At the next ccid shutdown or refueling outage, conduct shutdown margin tests to verify that:
a.
full withdrawal of any control blade from the cold xenon-free core will not result in criticality; and b.
compliance with the shutdown margin requirement in a manner that accommodates the baron loss phenomenon (i.e., by including a plant specific increment in the shutdown margin that takes the potential loss of boron from control blades identified from evaluation of Item 1 into consideration).
4.
Perform a destructive examination of the most highly exposed control blade at the end of the next cycle and provide results of the examination within one calender year after removal of the blade.
The results to be reported should include:
a.
Tube number or identification.
b.
The evaluation g each crack in the tubing.
Thecalulatedg0 depletion versus elevation for each tube, c.
d.
The measured B loss versus elevation for each tube.
The maximum local depletion for tubes having no cracks.
e.
f.
The maximum local depletion for tubes having no loss of boron.
I IE Bulletin No. 79-26 Date: November 20, 1979 Page 4 of 4 Alternately, the results of a destructive examination of a blade of similar fabrication and operational history may be provided within one 10 year of the date of issuance of this Bulletin.
If the highest local S depletion is less than 50 percent, this examination can be deferred until the next refueling.
5.
Submit within 45 days of the date of issuance of this Bulletin, a written report of the findings as to Items (1) and (2).
For facilities in a refueling outage, and all other facilities at their next refueling outage, submit the written report on Item (3) within 30 days after plant startup following the outage.
A written report on Item (4) is requested within one year after removal of a control blade for destructive examination Reports should be submitted to the Director of the appropriate NRC Regional Office and a copy should be forwarded to the NRC Office of Inspection and Enforcement, Division of Reactor Operations Inspection, Washington, D.C.
20555.
For all BWR facilities with a construction permit and all other power reactor facilities with an operating license or construction permit, this Bulletin is i
for information only no written response is required.
Approved by GA0 B180225 (R0072); Clearance expires 7/31/80.
Approval was given under a blanket clearance specifically for identi7ied generic problems.
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ENCLOSURE 2 I
IE Bulletin No. 79-26 Date:
November 20, 1979 Page 1 of 1 RECENTLY ISSUED IE BULLETINS Bulletin Subject Dats Issued Issued To No.
79-22 Possible Leakage of Tubes 9/5/79 Each Licensee who of Tritium Gas Used in Receives Tubes of Timepieces for Luminosity Tritium Gas in Timepieces for Luminosity 79-14 Same as Title 79-14 9/7/79 Same as 79-14 (Supplement No. 2) 79-23 Potential Failure of 9/12/79 All Power Reactor Emergency Diesel Generator Facilities with an Field Exciter Transformer OL or CP 79-24 Frozen Lines 9/27/79 All Power Reactor
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Facilities which have tither OLs of cps and are in late stage of construction 79-13 Cracking in Feedwater System 10/17/79 All PWRs with an OL and (Rev. 2)
Piping Designated Applicants (for Action), All Other Power Reactor Facilities with an OL or CP (for Information) 79-17 Pipe Cracks in Stagnant 10/29/79 All PWRs with an Borated Water Systems at OL (for Action).
PWR Plants All other Power Reactor Facilities with an OL or CP (for Information) 79-25 Failures of Westinghouse 11/2/79 All Power Reactor BFD Relays in Safety-Related Facilities with an Systems OL or CP (for Action) 79-02 Pipe Base Plate Designs Using 11/8/79 All Power Reactor (Rev. 2)