ML20029D628
| ML20029D628 | |
| Person / Time | |
|---|---|
| Site: | Braidwood  |
| Issue date: | 05/02/1994 |
| From: | Dyer J Office of Nuclear Reactor Regulation |
| To: | AFFILIATION NOT ASSIGNED |
| References | |
| NUDOCS 9405090093 | |
| Download: ML20029D628 (6) | |
Text
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May 2, 1994 Docket No. 50-456 Morris Daily Herald ATTN: Legal NM ices (Joan) 1804 N Division Morris, Illinois Legal Notices:
Enclosed is a Public Notice for the Braidwood Nuclear Plant, Unit 1, that we would like published on Tuesday, May 3,1994, in the Morris Daily Herald.
After publication, please send a copy of the proof of run to my attention.
Please note that the enclosed Public Notice and Advertising Order were faxed to you on Saturday, April 30, 1994, and these hard copies are for confirmation only.
If you have any questions, please call me at (301) 504-1995.
Sincerely, ORIGINAL SIGNED BY:
James E. Dyer, Director Project Directorate III-2 i
9405090093 940502 Division of Reactor Projects-- III/IV/V yDR ADOCK 0500 6
Office of Nuclear Reactor Regulation
Enclosures:
I.
Public Notice 2.
Advertising Order DISTRIBUTION:
iDocket File-NRC & Local PDRs (without Enclosure 2)
PDIII-2 Reading JDyer IDI:NTICAL LETTER SENT TO:
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l-PUBLIC NOTICE 4
NRC STAFF CONSIDERING LICENSE AMENDMENT REQUESTS FOR BRAIDWOOD UNIT 1 The U.S. Nuclear Regulatory Commission (NRC) has received an application dated April 25, 1994, and supplements from Commonwealth Edison Company (Ceco, the licensee) for emergency amendment to Facility Operating License No. NPF-72 for the Braidwood Nuclear Plant, Unit No.1, located in Will County, Illinois.
1 If approved, the amendment would implement a 1.0 volt steam generator i
(SG) tube interim plugging criteria (IPC) for tha tube support plate elevation 2
outer diameter stress corrosion cracking (0DSCC) for a limited period during 4
Cycle 5.
1 The NRC has determined that the licensee used its best efforts to make timely application for the proposed changes and that exigent circumstances do exist and were not the result of any fault of the. licensee.
Ceco had no reason to anticipate the extensive number of tubes that would require plugging / repairing at the tube support plates due to ODSCC under the current Technical Specifications (TSs). After identifying the number of tubes requiring repair, Braidwood management considered various repair strategies that could be performed within the current Braidwood licensing basis.
The i
licensee determined that these repair options were unacceptable because they would create operational limitations (unit derating) and may impact future tube repair efforts.
Subsequently, Braidwood management decided to apply an l
NRC approved IPC methodology to the inspection results. The licensee reviewed the number of tubes to be repaired using the existing TS criteria for tube repair and the number required by the IPC methodology and discussed its
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findings with the NRC.
Based on its analysis, the. licensee has proposed to incorporate a 1.0 volt criterion into the Unit 1 SG inservice inspection and repair program for its current Unit I refueling outage.
Currently, the i
licensee has plugged all tubes with indications greater than 2.7 volts and all confirmed indications greater than 1 volt.
i The licensee has evaluated the requested amendments against the standards in 10 CFR 50.92 and the NRC staff has made a proposed (preliminary) determination that the requested amendments involve no significant hazards considerations. Under NRC regulations, this means that operation of the facility in accordance with the proposed amendments would not (1) involve a 1
significant increase in the probability or consequences of an accident 4
previously evaluated; (2) create the possibility of a new or different kind of accident from any accident previously evaluated; or (3) involve a significant reduction in a margin of safety. The licensee's analyses are summarized below:
Incoroorate 1.0 Volt Criterion 1.
The proposed change does not involve a significant increase in the probability or consequences of an accident previously evaluated.
d The proposed license amendment request to implement SG 'IPC. for Braidwood, Unit 1, Cycle 5 meets the requirements of Regulatory Guide (RG) 1.121 by demonstrating that tube leakage is acceptably low and tube burst is a
highly improbable event during normal operation or a main steam line break t
(MSLB) event over tha limited time period of this license amendment.
Under accident conditions, conservatively assuming main steam line break (MSLB), significant margins exist for free span burst considerations for voltage growth in excess of 95% cumulative probability.
For the largest confirmed indications left-in service, the projected voltage at 95% growth is 2.6 volts at the end-of-cycle (E0C) 5, compared to the 4.54 volts structural limit for a free span burst pressure of 1.43 times the steam line break pressure differential.
Even at 99% cumulative probability, the observed voltage growth is bounded by 2.7 volts and the structural limit is satisfied for the 1.0 volt rotating pancake coil (RPC) confirmed indications left in service.
In addition, the following analyses were done to provide assurance that there are additional margins provided by the following considerations:
A demonstration of limited tube support plate (TSP) displacement was done which reduces the likelihood of a tube burst.
Limited TSP displacement would also reduce leakage compared to free span indications.
l The Electric Power Research Institute (EPRI) Performance Demonstration Program analyzed the performance of some 20 eddy current data analysts evaluating data from a unit with 3/4" inside diameter and 0.049" wall thickness tubes.
This data demonstrated the voltage dependence of the probability of detection (P0D) and argues for a P0D of greater than 0.6 for ODSCC indications larger than 1.0 volt.
CECO's risk evaluation of the operability of Braidwood, Unit 1, Cycle 5 compared core damage frequency, with containment bypass, with and without the IPC applied at Braidwood Unit 1.
The total Braidwood core damage frequency is estimated to be 2.74E-5 per reactor year with a total contribution from containment bypass sequences of 2.9E-8 per reactor year in the current individual plant evaluation (IPE).
l Operation with the requested IPC resulted in an insignificant increase in the MSLB with containment bypass sequence frequency.
The analyses presented above apply to a full cycle of operation.
Because plant operations approved by the proposed amendment would be for a significantly shorter period, the probability of an accident is much less than that calculated for the full cycle.
To support the restart and limited operation of Braidwood Unit 1, reactor coolant system (RCS) dose equivalent (DE) Iodine 131 (I-131) will be limited to 0.35 microcuries per gram (uc/gm).
Therefore, since implementation of the 1.0 volt IPC for a limited time period for Braidwood, Unit 1, Cycle 5 does not adversely affect steam generator tube integrity and results in acceptable dose consequences for a 1
. worst case postulated accident, the proposed license amendment request does not result in any increase in the probability or consequences of an accident previously evaluated within the Braidwood Updated Final Safety Analysis Report.
2.
The proposed change does not create the possibility of a new or different kind of accident from any accident previously evaluated.
The proposed steam generator tube interim plugging criteria does not introduce any significant changes to the plant design basis.
Use of the criteria does not provide a mechanism which could result in an accident outside the tube support plate elevations; no 0DSCC is occurring outside the thickness of the tube support plates. Neither a single or multiple tube rupture event would be expected in a steam generator in which the IPC has been applied.
CECO will implement a maximum leakage rate limit of 150 gallons per day (gpd) through any one SG to help preclude the potential for excessive leakage during all plant conditions.
The RG 1.121 criterion for establishing operational leakage rate limits that require plant shutdown are based upon 1
leak-before-break considerations to detect a free span crack before potential i
tube rupture during faulted plant conditions.
The 150 gpd limit will provide 1
for leakage detection and plant shutdown in the event of the occurrence of an unexpected single crack resulting in leakage that is associated with the i
longest permissible free span crack length.
Since tube burst due to ODSCC is precluded during normal operation due to the proximity of the TSP to the tube and the potential exists for the crevice to become uncovered during MSLB conditions, the leakage from the maximum permissible crack must preclude tube l
burst at MSLB conditions. Thus, the 150 gpd limit provides for plant shutdown prior to reaching critical crack lengths for MSLB conditions.
3.
The proposed change does not involve a significant reduction in a margin of safety.
Upon implementation of RG 1.121 criteria, even under the worst case postulated accident conditions, the occurrence of ODSCC at the TSP elevations is not expected to lead to a steam generator tube rupture event during normal or faulted plant conditions.
The distribution of crack indications at the TSP elevations are confirmed to result in acceptable primary-to-secondary leakage during all plant conditions for the limited time period of this license amendment and that radiological consequences are not adversely impacted, Loss of Corlant Accident (LOCA) coincident with a Safe Shutdown Earthquake (SSE) on the SG (as required by GDC 2), may cause a tube collapse in the SGs at some plants. A number of tubes have been identified, in the
" wedge" locations of the SG TSPs, to represent a potential for tube collapse during a LOCA + SSE event.
These tubes have been excluded from application of the voltage based SG TSP IPC.
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.. i Addressing RG 1.83, " Inservice Inspection of PWR Steam Generator Tubes,"
Revision 1, July 1975, considerations, implementation of the bobbin coil probe voltage based IPC of 1.0 volt is supplemented by: enhanced eddy current inspection guidelines to provide consistency in voltage normalization, a 100%
eddy current inspection sample size at the tube support plate elevations, and RPC inspection requirements for the larger indications left in service to characterize the principal degradation as ODSCC.
Implementation of the SG TSP IPC will decrease the number of tubes which must be repaired. Therefore, the margin of flow that would otherwise be reduced in the event of increased tube plugging would be maintained.
If the proposed determinations that the requested license amendments involve no significant hazards considerations become final, the NRC will issue the amendments without first offering an opportunity for a public hearing. An opportunity for a hearing will be published in the ff eral Reaister at a later d
date and any hearing request will not delay the effective date of the amendments.
If the NRC staff decides in its final determinations that the amendments do involve a significant hazards consideration, a notice of opportunity for a prior hearing will be published in the Federal Reaister and, if a hearing is granted, it will be held before the amendment is issued.
Comments on the proposed determinations of no significant hazards considerations may be telephoned to James E. Dyer, Director, Project Directorate III-2, by collect call to 1-(301)-504-1995 or submitted in writing 1
to the Rules and Directives Review Branch, Division of Freedom of Information l
and Publication Services, Office of Administration, U.S. Nuclear Regulatory Commission, Washington, DC 20555. All comments received by close of business on May 5, 1994, will be considered in reaching a final determination. Copies of the applications may be examined at the NRC's Local Public Document Room, located at Wilmington Township Public Library, 201 S. Kankakee Street, Wilmington, Illinois 60481, and at the Commission's Public Document Room, the Gelman Building, 2120 L Street, NW, Washington, DC 20555.
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