ML19321B180
| ML19321B180 | |
| Person / Time | |
|---|---|
| Site: | Clinton  |
| Issue date: | 07/18/1980 |
| From: | Koch L ILLINOIS POWER CO. |
| To: | |
| References | |
| L-14-80-(07-18), L-14-80-(7-18), U-0157, U-157, NUDOCS 8007280506 | |
| Download: ML19321B180 (5) | |
Text
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7YM U-0157 L14-80(07-18)-9 ILLINO/S POWER 00MPANY soo SOUTH 27TH STREET. DECATUR, ILUNolS 62525 July 18, 1980 Mr. James G.
Keppler Director, Region III Office rf Inspection and Enforcement U.S. Nuclear Regulatory Commission 799 Roosevelt Road Glen Ellyn, Illinois 6013V
Dear Mr. Keppler:
e
Reference:
IP Letter 6/24/80, U-0150, L.
J.
Koch to J. G.
- Keppler, NRC Region III; Subject Matter:
Extension of Time for 10CFR50.55(e) Final Report Clinton Power Station Unit 1 Docket No. 50-461 Construction' Permit No. CPPR-137 On May 27, 1980, Illinois Power Company verbally notified Mr.
H. M.
Wescott, NRC Region III, of a potential reportable deficiency per 10CFR50. 55 (e) associated with the Control Rod Drive (CRD) penetra-tions through the drywell wall.
By the referenced letter, we informed you on June 24 by interim report that our investigation of the deficiency was not completed for final reporting.
We have since concluded our investigation as summarized in the attached report and corrective action is currently underway.
We did not undertake a detailed investigation of the "reportability" of the deficiency as defined by 10CFR50.55(c) because:
(1) it would entail an extremely large number of analyses to cover all of the possible operating modes to be considered, and (2) the recommended corrective action was taken.
As the attached report indicates, CRD tube failure during normal power operation would not prevent normal control rod ' actuation and reactor shutdown, but under certain part load and reduced reactor pressure condi-tions the drive system may not function properly.
It would require expensive, time consuming analyses to evaluate each pos-sible operating scenario to determine if a reportable situation 30/7 S
/ [
80072gogg b
U-0157 Ll4-8 0 ( 07-18 ) - 9 could result.
We have concluded that it is more realistic to assume that a reportable set of circumstances could arise and to report the deficiency in accordance with the intent of 10CFR50.55(e).
All of the CRD tubes which had been adversely affected by the weld-ing are being replaced as corrective action for the deficie; y.
We trust that the information provided in the attached final report is sufficient for ycur analysis and evaluation of the deficiency and the corrective action.
Sincerely, L. J.
Koch Vice President j
LJK:nh attach.
cc:
H.
H. Livermore, NRC Resident Inspector
Attachm@nt to: U-0157 Y-5460 Ll4-80(07-10)-9 Clinton Power Station 10CFR50.55(e) Deficiency Report Control Rod Drive Penetrations Deficiency (10CFR50. 55 (e) (1) (iii) )
As a result of a cleanliness inspection of a control rod drive (CRD) penetration of the drywell (Penetration IMD-37), an area on the internal surface of Control Rod Drive Tube 2-B was found to have an area which appeared to have melted during the fillet welding pro-cess of the tube to the outside drywell plate.
Since the pipe internels were not purged with an inert gas (a purge was not a the melted area had a burnt sugar appearance (oxidized).
requirement),
Subsequently, all tubes in'the CRD penetrations were inspected.
A total of fifteen insert tubes (1 1/4-inch Schedule 80 pipe, ASME (1-inch Schedule SA-312, TP-316L) and twenty-three withdrawal tubes 80 pipe, ASME SA-312, TP-315L) were idencified by this investigation to have surface irregularities such as burn through and suck back the weld area connecting on the internal surfaces of the tubes at the tubes to the drywell penetracion plate (1/2-inch carbon steel),
and several more tubes were found to have evidence of oxidation on the internal surfaces of the tubes in the weld area.
Corrective Action Nonconformance Report (NCR). No. 3041 was initiated and forwarded to The corrective Sargent & Lundy for dispositioning the deficiency.
action was to:
Remove all tubes identified as having burn through/ suck back conditions utilizing Sargent & Lundy approved Job Instruction P-017.
a.
Clean and polish the remaining tubes utilizing a Sargent & Lundy b.
approved Job Instruction P-018.
Per the Job Instruction, the tubes were to be cleaned and polished and reinspected after thirty days.
If a sugaring or rust-like condition reappeared after cleaning, a nonconformance report was to be initiated.
Replace unacceptable CRD tubes in accordance with Sargent &
c.
Lundy approved design.
As of June This corrective action is currently being imp'.emented.
thirty-five (35) CRD tubes had been removed and the 27, 1980, The NRC installation of the replacement tubes had commenced.
resident inspector, H. H. Livermore, has performed surveillance activities on this corrective action.
To prevent recurrence of these problems in the installation of replace-ment tubes, the following actions will be taken (per Job Instruction M-009, Rev. 0):
,e 2-a.
The inside of the tubes will be purged with inert gas (i.e., argon) during welding operations.
b.
During the welding operations, the welding variables (i.e., heat j
input) will be monitored.
Safety Implications The effect of the burn through and suck back on the integrity of the j
tubes over the life of the plant is very difficult to determine.
Since the tubes are stainless steel, it is believed that any tube failrres would be in the form of cracks rather than a sudden rupture of the tube, and that all of the tubes would not fail simultaneously.
The reactor is designed so that the core system can be made sub-i critical at any time or at any core condition with the highest worth 1
control rod fully withdrawn.
Thus, any CRD tube could fail totally and the reactor could be brought.to cold shutdown (the most limiting condition with regard ts the shutdowm criteria) conditions.
_f the reactor pressure was greater than 600 psig and all of the CRD tubes identified to have burn through or suck back were to fail totally, all control rods would insert on a scram signal.
Reactor
^
pressure. mtid. cause the control rods with failed tubes to insert.
Thus, the reactor could be brought to cold shutdown conditions.
l Da: aged withdrawal tubes would not prevent a scram at any operating i
condition.
If reactor pressure was less than 600 psig and more than one insert tube failed, the potential exists that the reactor could not be brought to cold shutdown conditions without using the standby liquid control system.
If this action is undesirable, the reactor could be maintained in a stable condition at a pressure less than 600 psig and the corresponding saturated temperature.
If j
reactor pressure would rise above 600 psig, the remaining withdrawn-control rods could be inserted with reactor pressure and cold shutdown achieved.
A detailed engineering analysis has not been perfcrmed to determine what, if any, combination of insert tube failures (of those fifteen insert tubes identified) and reactor conditions would not give a cold shutdown condition without the standby liquid control system.
This is due to the cost of the analysis, the fact that all the tubes which had been adversely affected by the welding are being replaced, and such an analysis would not ser"e a useful purpose.
The corrective actions for the deficiency assure that no unsafe installation exists.
Because a detailed engineering analysis was not performed, the significance of the deficiency to the safety of the plant has.not been quantified.
In summary, due to-the items list.above:
L l
a..
Failure mode via cracks is expected and not total failure.
I
- b.. Any one rod could be fully withdrawn and the reactor could be made suberitical at all+ conditions.
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. c.
Above 600 psig reactor pressure, all control rods can be inserted even if the CRD tubes fail.
d.
The small fraction of time the reactor is below 600 psig, the reactor could be made suberitical with the standby liquid control system if necessary or reactor pressure could be increased to 600 psig and then all control rods could be inserted, e.
A stable condition below 600 psio could always be reached.
The safety significance of the deficiency is considered minimal.
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