ML20078L639
| ML20078L639 | |
| Person / Time | |
|---|---|
| Site: | Braidwood  |
| Issue date: | 11/23/1994 |
| From: | Saccomando D COMMONWEALTH EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM), Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 9411300315 | |
| Download: ML20078L639 (7) | |
Text
/^N Crmm::nwnith Edison l
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1400 Opus Place Downers Grove, Illinois 60515 November 23,1994 i
Office of Nuclear Reactor Regulations U.S. Nuclear Regulatory Commission Washington, D.C. 20555 Attention:
Document Control Desk
Subject:
Braidwood Unit 1 Mid-Cycle Inspection Plans NRC Docket Number 50-456
References:
1.
D. Saccomando letter to NRC transmitting request for Interim Plugging Criteria for Braidwood Unit 1 dated April 25,1994 2.
R. Assa letter to D. Farrar transmitting Safety Evahation for Use ofInterim Plugging Criteria for Braidwood Unit i dated August 18,1994 3.
G. Dick letter to D. Farrar transmitting Safety Evaluation for j
Use ofInterim Plugging Criteria for Byron Unit 1 dated j
October 24,1994 4.
H. Pontious Letter to NRC transmitting response to Safety Evaluation for Use ofInterim Plugging Criteria for Byron Unit 1 dated November 23,1994 I
Reference 2, transmitted Nuclear Regulatory Commission (NRC)'s Safety Evaluation Report (SER) for the Use ofInterim Plugging Criteria for Braidwood Unit 1. In the SER, the Staff required Braidwood Station to perform a mid cycle steam generator (SG) tube inspection on Unit 1. Additionally Reference 2 requested that Braidwood Station submit plans for assessing the mid-cycle inspection data at least 60 days prior to the planned shutdown.
In order to develop a comprehensive plan, Braidwood performed a plant specific comparison of the Draft IPC Generic Letter requirements and the currently approved Cycle 5 Braidwood requirements. This comparison is included as Attachment A. It should be noted, that if the IPC Generic Letter is finalized prior to the Braidwood mid-cycle inspection, an assessment of the need for further revision of data analysis guidelines will be performed.
The following is a description of the Unit 1 SG mid-cycle tube inspection outage scope and the methods which will be used to collect, analyze, and assess the SG tube inspection data.
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Document Control Desk November 23,1994 Inspection Scope: Braidwood will perform a bobbin coil inspection of 100% of the Unit 1 SG hot leg tubing through the top support plate on the cold-leg side, and at least 20% of the tubing will be examined full length. This is consistent with the Draft Interim Plugging Criteria (IPC) Generic Letter requirements. A 0.610" bobbin probe will be used to inspect all SG tube support plate intersections where IPC will be applied. All SG support plate indications with flaw-like bobbin coil signal amplitudes greater than 1.0 volt, will be inspected by a 3-coil Rotating Pancake Coil (RPC) probe.
Braidwood Station is aware that there is an industry concern that Primary Water Stress Corrosion Cracking (PWSCC) can occur at dented support plate intersections. To address this concern Braidwood will implement the following augmented inspection program during the Unit 1 SG mid-cycle tube inspection.
This program is consistent with that approved for Byron Unit 1 as described in their Safety Evaluation Report (Reference 3).
RPC inspection will be performed on all dents located at tube support plate intersections identified during the SG tube IPC inspection that have bobbin coil voltage amplitudes greater than 5.0 volts. In addition,20% of the dents located at tube support plate intersections having bobbin coil voltage amplitudes between 2.5 and 5.0 volts will be inspected using RPC.
The 20% sampling program will be expanded to 100% of the dent indications found during the IPC inspection if any dents examined by RPC confirm PWSCC indications.
All RPC confirmed indications will be plugged or repaired.
The NRC will be promptly notified if any PWSCC indications are identified at the tube support plate intersections.
The data analysts will be informed of the potential for PWSCC at dented support plates. The analysts will also be instructed to report occurrences of PWSCC to Braidwood Station management immediately.
Inspection Guidelines: The eddy current data analysis guidelines as revised fbr the Byron Unit 1 Fall 1994 refuel outage, will be used for the Braidwood Unit 1 mid-cycle SG tube inspection. These analysis guidelines have been submitted to the NRC and are discussed in Reference 3. Comed realizes that there are several outstanding technical issues with respect to inspection icnlo\\bwd\\sixdayrl
Document Control Desk November 23,1994 guidelines which will be resolved between the industry and the NRC p.:or to issuing the final generic letter on IPC. If the IPC Generic Letter is issued in its final form prior to the Braidwood Unit 1 mid-cycle inspection Comed will assess this information and make revisions to the eddy current data analysis guidelines if it is deemed necessary.
Methodolocv for Braidwood Leakage Calculation: Comed will use a method for determining the primary-to-secondary SG tube leakage during a postulated main steam line break which involves a Monte Carlo technique which accounts for the regression parameter uncertainties. This methodology has been reviewed and accepted by the NRC as documented in Reference 3, and was used during the Byron Unit 1 Fall 1994 outage. The leakage calculation will include the time interval between the mid-cycle inspection and the next refueling outage (AIR 05) which is currently scheduled for September 1995. Leakage calculations based on the actual measured end-of-cycle voltage distribution will also be performed. If this calculation indicates that the leakage would have exceeded the leakage limit postulated during a MSLB, the Staff will be notified prior to returning the steam generators to service and provided with the safety assessment of the results.
1 l
Methodolocv for Braidwood Co.Dditional Probability of Burst Calculatiom: Comed will use the conditional probability of burst calculation identified in Section 5 of WCAP-14046, "Braidwood Unit 1 Technical Support for Cycle 5 Steam Generator Interim Tube Plugging Criteria," revision 1. Full Monte Carlo analysis will be l
performed. This analysis will account for parameter uncertainty per the methods described in WCAP-14046. The Probability of Burst will be calculated for the time l
interval between the mid-cycle inspection and the next refueling outage, A1R05. If the calculated probability of burst based on end-of-previous cycle voltage distribution exceeds the Draft IPC Generic Letter requirement of 1E-2, the Staff will be notified prior to returning the steam generators to service and will be provided a safety assessment of the results. This assessment will include both probabilistic and deterministic information to support justification of Braidwood Unit 1 operation until its next scheduled refuel outage. Additionally, as requested by the Staff during the Byron Unit 1 Fall 1994 outage, Braidwood will also calculate the beginning-of-cycle probability of burst. This information will be used fbr comparison against probability of burst projections.
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I Document Control Desk November 23,1994 1
Ihttabase for Leak and Burst Correlations: The database which will be used to support the leak and burst assessments for the Braidwood Unit 1 SG mid-cycle tube inspection is the same as that used for the Fall 1994 assessment of Byron Unit 1. The Staff has reviewed and accepted this data base as documented in Reference 3. If data from the recent Byron tube pull is available, and it meets the data exclusion criteria, it will also be included in the database.
1 Calculation of Offsite and Comtrol Room Doses: As transmitted in Reference 1, 1
Braidwood Station determined the offsite dose associated with the MSLB primary-to-secondary leakage limit. The Draft IPC Generic Letter has an additional requirement to determine the control room doses. Braidwood Station will complete this evaluation prior to the Unit 1 mid-cycle inspection Tubes Excluded by Combined LOCA + SSE Event: As required by Reference 3 for Byron Station, Reference 4 transmitted a schedule to submit a plant-specfic analysis of the effects on certain SG tubes of the loads from a safe shtdown earthquake in combination with a postulated loss-of-coolant accident.
Assessment ofIndication Voltage Growth Rates: Braidwood will compare the eddy current indication growth rates calculated during the mid-cycle inspection (based on a linear scaled factor), to that seen during previous outages. This comparison will be used to assess the effectiveness of the various programs which have been put in place to mitigate degradation.
Pull Tubns: Braidwood does not plan on removing any tubes from the SGs during the mid-cycle inspection. Braidwood removed 4 tubes from the Unit 1 SGs during the fourth refueling outage, which fulfills all Draft IPC Generic 1,etter requirements until the sixth refueling outage.
Please address any questions that you may have to this office.
5 Sincerely, C.-
j f
A&
'M V
Denise-M. Saccomando l
Nuclear Liwnsing Administrator Attachment cc:
J. Martin, Regional Administrator, RIII R. Assa, Braidwood Project Manager, NRR S. DuPont, Senior Resident Inspector, Braidwood Office of Nuclear Safety-IDNS k:nio\\bwd\\swdoyr)
ATTACHMENT A DRAFT GL SECTION(S)
SUMMARY
OF DRAFT GL REQ
SUMMARY
OF CURRENT BRWD REQ DISCUSSION 1.b.4 Repair criterio do not apply to flow Not specificotty oddressed.
To date Bnad has not found indicottons in distr!bution intersections.
this region. IPC criteno will not be opplied to this oreo. thus Broidwood will meet the
.Drott GL requirement..... _
2
. Burst probability criterio limit is 1E-2.
. Burst probobilty criterio hmit is 2.5 E-2 For the Broidwood Mid-Cycle inspection the Draft GL requirement of 1 E-2 will be used as the acceptance criterio.
2.o.1 and 'Certain teok/ burst dato exclusions
'The calculations used in the Brwd IPC WCAP exclude IThe data bop; Athich wid be used to
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2.b.3(2) should not be taken and the VC this doto point. The Braidwcod SER which oppoved support the Braidwood mid-cycle leak Summer dato point should have o the use of IPC for Cycle 5 included this dato point.
'and burst assesment is the some os that
- MSLB lookrate of 24761/hr, pending used for the Byron L' nit 1 Fall 1994 outage.
NRC review.
The Commission hos reviewed and accepted this doto base os
.do.comented in referenc_e _2.
2.b.2(2)
. Growth rotes are to be taken from Braidwood growth rotes were obtained by Braidwood will meet this Draft Generic the most limiting of the lost 2 comparison of the dato from the previous outage Letter requirement as written.
inspections if both employed IPC (A1R03), to to the current outoge (AlR04). IPC guidelines or from the current guidelines were employed during A1R04 and data inspection if it is the first to employ IPC from the previous outoge was corrected for guidelines. Negative growth roias calibration differences.
shou!d be included as zero in the
~ distribution
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2.b 4 Co!culate Offsite and Control Room 'The Brwd specifid MSLB leakrate limit is estbblished ~ 'Braidwood wi:1 evoIuoteihe control room Doses every cycle based on based on 0.35 micro-curies /cc and 10CFR100 doses prior to comp letion of the mid-calculated MSLB leckrote and
, requirements. Control Room doses were not
. cycle inspection, thus meeting the Drott reduced lodine timits to meet 10 CFR specifcolly addressed GL requirements.
- 100 requirements. _ _.. _ _ _
3 Inspection criteria should be
,_ Byron /Brwd inspection guidelines are consistent with Braidwood will emp!oy the inspection consistent with the VC Summer the Cotowba Appendix A guidelines and the EPRI
.guidehnes used by Byron during their Fall
' Appendix A guidelines.
APC guidelines,
'1994 outoge. These guidelines have been submitted to the NRC for information and are discussed in reference 2.
Page1 i
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ATTACHMENT A DRAFT GL SECTION(S)
SUMMARY
OF DRAFT GL REQ
SUMMARY
OF CURRENT BRWD REQ DISCUSSION 3 o.1 and inspection scope is to be 100% of hot TS requires 100% of hot leg tubes to the lowest cold Braidwood wiil meet the Draft GL Model IS teg tubes and a 20% random sample leg intersection with ODSCC.
requirements during the mid-cycle 4 4.5.2 of cold leg tubes inspection.
3.b.1
~A!! indications greater than 1.0 volt ICurrent requirement cons for' RPC of o!! indicotions
~Braidwood will meet the Drott GL
~
hmit are subject to RPC inspection.
between 1.0 and 2.7 volts. During AlR04 Brwd on requirements by performing RPC indications were RPC inspected regardless of inspection on oil TSP indications greater voltage.
than 1.0 volt during the mid-cycle inspection I equirement does not ' ffect Byron or 3 b 2 and ' Tubes with copper deposits at
~ Copper is not found ot' Byron or Brwd R
e 3 b.3 intersections should be RPC inspected Brwd but is specifically addressed in the and any indications detected should dato onolysis guidelines.
be repaired.
~
1.b'2.1 b13, ' Tubes with dents > 5.0 v6fts and with Tubes with dents > 5 0 volts and with large mixed
'Braidwood will meet'the Draft GL 3 b 2. 3 b 4 large mixed residuals are excluded residuals are required to be inspected by RPC.
requirement. Affected tubes with RPC and 3 b.5 from IPC requirements. Snould be flow indicottons wiU be repaired.
inspected. and any indicotions should result in tube repair.
3.c.2 Bobbin coil calibration is to be setup Current requirement cotts for calibration of 4-20% TW Braidwood will defer implementation of on 4-100% through-won (TW) holes.
- holes consistent with the Appenoix A guidelines. The this requirement pending resolution of Brwd calibration standards are normalized to o industry comments. Converting to 4-100%
laborotory standard.
- TW holes would result in o loss of
- comparison basis to other plants and Braidwood history.
3c3
'New probe variability to be within +- 'Not specifico!!y mentioned f6r new probes.
'~ ' 'Braidwood will defer implementation of 10%
this requirement pending resolution of industry comments.
3c4
'For probes ihot do not meet wear
'During A1R04 pr6be wear limit was +- 15%. For probes'Broidwo6d wilidefer implementation of
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measurement criterio, oil tubes that did not meet this criterio. indications measured this requirement above what was done inspected since the lost successful since the lost acceptable probe woor measurement during our AlR04. pending resolution of co;ibration should be reinspected with that were within 5%. required reinspection.
industry coniments.
o new calibrated probe.
O Page 2
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