05000331/LER-1996-001, :on 960325,determined That Degradation in Scram Insertion Times Occurred.Caused by Adhesion Between Viton SSPV Exhaust Valve Diaphragm & SSPV Seat.Replaced Viton SSPV Diaphragms W/Buna-N
| ML20136G161 | |
| Person / Time | |
|---|---|
| Site: | Duane Arnold  |
| Issue date: | 03/10/1997 |
| From: | Sueper L, Van Middleswort IES UTILITIES INC., (FORMERLY IOWA ELECTRIC LIGHT |
| To: | Beach A NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| References | |
| LER-96-001, LER-96-1, NG-97-0448, NG-97-448, NUDOCS 9703170221 | |
| Download: ML20136G161 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| 3311996001R00 - NRC Website | |
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UTILITIES March 10,1997 NG-97-0448 Mr. A. Bill Beach Regional Administrator Region III U. S. Nuclear Regulatory Commission 801 Warrenville Road Lisle, IL 60532
Subject:
Duane Amold Energy Center Docket No: 50-331 Op. License No: DPR-49 Licensee Event Report #96-01, Rev. 2 File:
A-118a Gentlemen:
Please fmd attached a copy of the subject Licensee Event Report. In accordance with Boiling Water Reactor Owners' Group recommendations, this revision documents the replacement of the Viton control rod drive (CRD) scram solenoid pilot valve diaphragms with diaphragms made from Buna-N and the suspension of augmented CRD scram time testing. No new commitments are made by this letter.
Sincerely, l
Y Gary Van Middlesworth I
Plant Manager - Nuclear p g,d d iI k
cc:
Director of Nuclear Reactor Regulation Document Control Desk U. S. Nuclear Regulatory Commission Mail Station Pl-37 Washington, D. C. 20555-0001 NRC Resident Inspector - DAEC DOCU 1mnnmn 9703170221 970310 l}El,E%E!ElEEEEEE PDR ADOCK 05000331' S
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NRC FORM 3C6 U.S. NUCLEAR REGULATORY CoMMISSloN APPROVED BY oMB No. 3150-olo4 (4 951 EXPtRES 04/30/98 ESTIMATED 8URDEN PER RESPONSE TO COMPLY WITH THIS MANDATORY fNFORMAtl0N C3tLECTf0N REQUEST: 50.0 HR3. REPORTED LES3ONS LE ARNED ARE INCORPORATED INTO j
LICENSEE EVENT REPORT (LER)
EA'Es"!EVSl0RMYr'5EN!C!ROsTiNEEtNT!!!NC Yr^!s U S. NUCLEAR REGULATORY COMMISSION. WASHINGTON. DC 20555 0001. AND TO THE PAPERWORK REDUCTION PROJECT Q15001041. 0FFICE OF MANAGEMENT AND OUDGET.
(See reverse for required number of WAsMiNGTcN. 0C 20503.
digits / characters for each block)
FACIUTT NAME ele DUUEti NUmstn (Z)
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Duane Arnold Er.ergy Center 05000-331 1OF3 1
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Cora Average Control Rod Scram Time to Notch Position 46 Exceeding Technical Specification Limit f
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At 0230 on March 25,1996, with the plant at 60% power, scram time testing was completed on all (89) control rods which indicated that the core average scram insertion time to rod position 46 had exceeded the Technical Specification limit of 0.35 seconds. In addition, the average scram insertion times to notch 46 for the three fastest control rods in any two-by-two (2X2) array also exceeded the Technical Specification limit of 0.37 seconds. The average scram insertion time requirements, both for the core average and the average of the i
three f astest control rods in any 2X2 array, were met for rod positions 38,26, and 06. No individual control i
rod scram insertion time exceeded the Technical Specification limit of 7.00 seconds to rod position 04.
1 I
The testing was performed in response to industry operating experience which indicated possible degradation over time of the scram insertion times of control rods equipped with Viton scram solenoid pilot valve (SSPV) l diaphragms. The Viton SSPV exhaust diaphragms were replaced with new Viton diaphragms on 87 control rods and post maintenance scram time testing was performed. The as-left core average scram insertion time to notch position 46 was 0.32 seconds. The plant continued to perform periodic testing until the Viton diaphragms were replaced with Buna-N during the 1996 refueling outage. There was no effect on the safe operation of the plant.
NRC FORM 36614-951
Am d
.u.S. NUCLEAR REGULATORY Commission 1499*
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION i
i i
FACILITY NAME (1) oOCKET LER NUMBER (6)
PAGE (3)
)
YEAR auUtN HAL MtV" 2
OF 3
NUMBER NUMBER li Duane Amold Energy Center 05000-331 96 -- 001 02 4
I TEXT Uf more space os recurred use additional copies of NRC Form 366A) (17)
Description of Event
I In April of 1995, Viton scram solenoid pilot valve (SSPV) diaphragms were installed in all 89 control rods at the Duane Arnold Energy Center (DAEC) as a replacement for Buna-N diaphragms because of their expected increased qualified life. Beginning in late 1995, the industry began to report increased 5% (approximately equal to rod position 46 at the DAEC) scram insertion times during periodic testing. The DAEC does not have i
Technical Specification requirements to perform periodic testing, s
On March 18,1996, the DAEC initiated scram insertion time testing on all (89) control rods in response to industry operating experience indicating that control rods with Viton SSPV diaphragms may experience 1
i degraded performance over time. Each control rod was individually scrammed and its Viton SSPV exhaust i
diaphragm ('118' valve) was replaced if the scram insertion time to rod position 46 exceeded 0.35 seconds.
Those control rods that had new diaphragms installed received as-left scram insertion time testing. After the testing on a!! 85 t,etrol rods was complete on March 25, it was determined that the as-found core average scram insertion time to rod position 46 was 0.393 seconds which exceeded the Technical Specification 3.3.D.1 limit of 0.35 seconds. This represented a 0.063 second increase over the core average rod position 46 scram insertion time testing performed approximately one year earlier, in addition, it was determined that I
the Technical Specification 3.3.D.2 limit of 0.37 seconds for the average insertion time to rod position 46 for the three fastest control rods in any 2X2 array had also been exceeded.
J The average scram insertion time Technical Specification requirements, both for the core average and the j
average of the three fastest control rods in any 2X2 array, were met for rod positions 38,26, and 06.
The maximum as-found scram insertion time to rod position 46 was 0.450 seconds. The minimum as-found scram insertion time to rod position 46 was 0.320 seconds. The as-left core average scram insertion time i
was 0.324 seconds, i
Cause of Event
The degradation in the scram insertion times appears to be attributable to adhesion between the Viton SSPV
'118' exhaust valve diaphragm, and the SSPV seat.
Analysis of Event
The Technical Specification 3.3.D.1 limit on the core average scram insertion time to rod position 46 l
provides an indicator of the performance of the control rod (i.e. beginning of rod motion). However, the amount of negative reactivity inserted into the reactor at rod position 46 is not significant and is not an input into any plant transient or accident analysis. Generic analysis performed for BWR/2-5 reactors has shown that core average scram insertion times to rod position 46 as high as 0.490 seconds does not result in unacceptable consequences as long as the core average scram insertion times for the other Technical
)
Specification rod positions (i.e. 38,26, and 06) are met. The as-found core average insertion times for these Technical Specification required rod positions were all within the specified limits. The DAEC's plant specific anatysis is based on control rod insertion to rod position 38 within specified times. Therefore the plant was within analyzed conditions at all times.
NRC FORM 3f6A U.s. NUCLEAR REGULAYoRY CoMMISSloN (499, LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACluTY NAME (1)
DOCKET LER NUMBER (6)
PAGE (3) ygAR auutm at nev'"
3 OF 3
NUtalER NUMBER Duane Arnold Energy Center 05000-331 96 -- 001 02 l
TEXT ut more space os recurred, use soditional copies of NRC Form 366A) (11)
Corrective Actions
The Viton diaphragms which were installed to replace those that had degraded were themselves susceptible to degradation over time. Therefore, periodic augmented SSPV testing continued to be performed to meet the BWROG Regulatory Response Group (RRG) interim recommendations. Augmented testing ceased when the DAEC shut down in October,1996 for its refueling outage at which time the Viton SSPV diaphragms were replaced with Buna N. Buna-N has been successfully used in this application previously and is not susceptible to the type of degradation which contributed to the increase in scram times.
A. Previous Similar Events
No LERs had been written concerning degradation of the Viton diaphragms since their installation.
B. LEES System and Component Codes:
Control Rod Drive--AA Hydraulic Control Unit--HCU Scram Solenoid Pilot Valve-FSV C. The SSPVs are dual-type ASCO solenoid valves (GE part number 107E6022P001).
This event is being reported voluntarily.