ML101520112
ML101520112 | |
Person / Time | |
---|---|
Site: | Davis Besse |
Issue date: | 05/28/2010 |
From: | Lentz T A FirstEnergy Corp |
To: | Michael Mahoney Plant Licensing Branch III |
mahoney, m NRR/DORL/LPLIII-2 415-3867 | |
Shared Package | |
ML101520113 | List: |
References | |
Download: ML101520112 (6) | |
Text
From:talentz@firstenergycorp.comSent:Friday, May 28, 2010 11:56 PM To:Mahoney, Michael Cc:phlashley@firstenergycorp.com; kmnesser@firstenergycorp.com;
kwbyrd@firstenergycorp.com; apwise@firstenergycorp.com;
ctdaft@firstenergycorp.com; gmwolf@firstenergycorp.com
Subject:
FENOC Follow-up Clarifications for the Davis-Besse RPV Head
Nozzle 50.55a Request Attachments:20100528093714771.pdf; 20100526154647573.pdf; Nozzle 4
- 52M Deposit
Depth.pdfFollow Up Flag:Follow upFlag Status:FlaggedADAMSAccessionNumber:ML101520088 Mike: In response to the telecon conducted on May 24, 2010, FENOC provides the following
clarifications regarding the subject relief request. :
- 1. The NRC has received the proprietary calculations that were submitted by FENOC on May
17, 2010 and they have been forwarded to the appropriate technical
reviewers. No further
action is required by FENOC.
- 2. As a result of a question from the NRC Special Inspection Team it was discovered that the
post-weld PT examinations for ten nozzles did not have sufficient
coverage in bands of the
examination area due to the field of view on the camera vs the spacer
size used. This post weld
PT examination overlap issue affected nozzles. 10, 24, 28, 43, 51, 55, 58, 59, 61 and 67.
This is documented in the site corrective action program under FENOC CR
10-77201 (Areva CR 2010-3544). As a result, the post weld PTs for these
nozzles are being
reperformed. For nozzles 51, 55, 58, 59, 61 and 67, since abrasive
water jet machining
remediation has already been completed, the PT will now be performed
after water jet
remediation. This is contrary to the process overview provided in our
April 1, 2010, 10 CFR
50.55a request. Specifically, on page 4 of 20 of the Enclosure, FENOC
provided an overview of
the basic steps of the repair process. Step 6 and 7 will now be
reversed for these six nozzles.
As discussed on the telecon yesterday and, in part, in our April 16, 2010 response to RAI
Question 2(4), the order of these two steps can be interchanged, as the
material removed by the
water jetting is minimal (approximately 0.030 inches) and the abrasive
water jet machining
remediation will not interfere with the subsequent surface examination (i.e., the abrasive water jet machining remediation is not considered a peening process).
- 3. As provided in our May 17, 2010 response to RAI Question 3(2), the examination area for the
preservice examination following repair and for future inservice
inspections shall include the
wetted surface of the new weld from the toe of the weld up through 0.5
inches above the rolled
region of the nozzle remnant. In accordance with Figure 3 of Attachment
1 of the April 1, 2010
relief request, during the post-weld PT examination following repairs, the examination includes
the area 1/2 inch below the toe of the weld. This PT will also serve as
the preservice
examination.
As noted in the 50.55a request, FENOC plans to use a surface examination method for future
inservice inspections. If PT is used, the examination will be in
accordance with Code Case N-
729-1 and the 50.55a request. In addition, the DB "ISI database" has
been updated (see
attached) to ensure the PT will include the area 1/4 inch below the toe
of the weld. If other
surface or volumetric examination techniques (e.g. eddy current or UT)
are developed and
qualified per Code Case N-729-1, the qualified examination area would
include, as a minimum
the wetted surface of the new weld from the toe of the weld up through
0.5 inches
above the
rolled region of the nozzle remnant.(See attached file: 20100528093714771.pdf)
- 4. As requested, the subject DB nozzle 4 repair weld NDE results are attached.(See attached file: 20100526154647573.pdf)
Subsequent to the May 24, 2010 telecon, the NRC provided the following additional question via
email on May 25, 2010 (question highlighted in
bold): By letters dated April 1, 2010 and May 17, 2010, the licensee submitted the half nozzle repair
relief request for the control rod drive mechanism (CRDM) nozzles at Davis Besse. In response to RAI Question number 2 in to the May 17, 2010, submittal, the licensee stated that
Code Case N-416-3 will be
used to satisfy pressure testing requirements subsequent to the CRDM
nozzle repair. In the
teleconference dated May 24, 2010, the licensee indicated that it will
perform a visual (VT-2)
examination from outside the service structure of the reactor pressure
vessel without any direct
view of the surface of the head in the areas that were repaired during
the system leakage test.
In general, the NRC accepts this type of indirect visual (VT-2)
examination. However, it may not be appropriate for Davis-Besse CRDM nozzle repairs based on the following:
- 1) A larger number of repaired CRDM nozzles increases possibility
for fabrication defects that may be missed by nondestructive
examination.
- 2) Several unsuccessful repairs on CRDM nozzle 4 create the
possibility for unforeseen fabrication defects.
- 3) Inability of a visual (VT-2) examination from the outside
service structure to detect small leakage from a through-wall
fabrication defect in a repaired nozzle.
For these reasons, the staff requests a direct viewing of the bare metal head surface through
one or more access hole penetrations during the system leakage test to
provide an additional
defense in-depth and increase confidence in these nozzle repairs.
Alternatively, the licensee
needs to justify why the proposed indirect visual (VT-2) examination is
acceptable.
- 5. As noted in the 50.55a request, the CRDM nozzle repair weld is a partial penetration weld.
ASME Code NB-5245 requires a progressive surface examination of partial
In lieu of the progressive surface examination, a surface examination
and an ultrasonic
examination, qualified to detect flaws in the new weld and base material
is performed on the
partial penetration weld as described in the 50.55a request, Figure 3.
This UT examination, exceeds construction code requirements and along
with the liquid
penetrant examination of the weld area provides a high degree of
confidence in the integrity of
the repair weld.
Pressure testing requirements will be met by the completion of a VT-2 examination that will be
conducted in accordance with the requirements of IWA-5000 and Code Case
N-416-3 which is
endorsed in NRC Regulatory Guide
1.147 Revision 15 with no conditions noted. IWA-5000 permits a VT-2
visual examination with
insulation installed. As specified in IWA-5242, the VT-2 examination
will be conducted at the
lowest elevation where leakage may be detectable. Examination of the
surrounding area such
as floor areas, equipment surfaces or underneath components is required.
A remote VT-2
examination will be conducted by examining the refueling canal floor in
the area of the reactor
vessel flange. A direct VT-2 examination of the reactor vessel
insulation joints from under the
reactor vessel will also be performed. Together, the NDE and pressure
test visual examination
will provide a high level of confidence in the integrity of the CRDM
repairs.The CRDM penetrations are located within the service structure below the reactor vessel head's insulation package. Access to this area is available through inspection
ports, however, during the
system leakage test, the Reactor Coolant System is at normal operating
temperature and
pressure (approximately 532 degrees Fahrenheit and 2150 psig) with all
insulation in place as
permitted by IWA-5000. This insulation covers the inspection ports.
Opening the inspection
ports would require removal of the insulation and the hot inspection
ports. Air emitted from the
ports could approach 500 degrees Fahrenheit. Inspection would be
difficult and access would
require personnel to be in close proximity to the hot surfaces creating
an industrial safety hazard.
The benefit of this direct visual examination is considered to be
limited given the additional level
of NDE and pressure test visual examination noted above. However, In
addition to the VT-2
examination discussed above, FENOC intends to perform a visual
inspection for leakage from
the reactor vessel head through an inspection port to the extent that
access and environmental
conditions permit.
Why is it not necessary to perform AWJ conditioning of the repair made to CRDM penetration
- 58?6. The purpose for Abrasive Water Jet (AWJ) machining is to mitigate the initiation of
pressurized water stress corrosion cracking (PWSCC) in PWSCC susceptible
materials. Of the
three materials that are part of the RVCH CRDM penetration modification
[RVCH Low Alloy
Steel base metal (SA-533, Gr.
B, Cl 1), CRDM Nozzle (Alloy 600), and weld filler material (Alloy 52M)]
only the CRDM nozzle
Alloy 600 material is known to be susceptible to PWSCC. The weld repair
to the IDTB weld in
penetration #58 was limited to the Alloy 52M weld material. The
machining hard stop, acting as
a plug, was positioned so that the lower end extended down to just below
the upper weld toe (the
Alloy 600 / Alloy 52M interface). The position of the hard stop
prevented repair activities (cavity
grinding and post-weld grinding) from contacting the Alloy 600 nozzle
material.This response clarifies the scope of AWJ for nozzle 58 as described in the FENOC response to
RAI #3 dated April 16, 2010.
The "as-built" nozzle 4 weld plan is also attached for information:
- 7. PS0139 required five layers of Alloy 52M weld filler metal to adequately cover the Alloy 82
filler metal. The five layers of Alloy 52M was to clearly communicate to
the welding operators
the amount of Alloy 52M to be deposited over the Alloy 82 . The intention was to achieve a minimum of five layers cover of Alloy 52M over the Alloy 82 in the as-
welded condition. This
would allow for the machining and abrasive water jet material removal
operations and still
maintain a minimum of 0.125 inch thickness of Alloy 52M covering the
Alloy 82 filler metal to
avoid reactor coolant exposure of the Alloy 82 filler metal that is
susceptible to PWSCC.
The average Alloy 82 and Alloy 52M layer thickness is 0.08 inches.
Therefore, this would provide a cover thickness of Alloy 52M filler
metal of significantly more
than 0.125 in. over the Alloy 82 filler metal after final machining and
abrasive waterjet
remediation.(See attached file: Nozzle 4 - 52M Deposit Depth.pdf)
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Subject:
FENOC Follow-up Clarifications for the Davis-Besse RPV Head Penetration Nozzle 50.55a Request Sent Date:5/28/2010 11:57:19 PM Received Date:5/28/2010 11:57:20 PM From:talentz@firstenergycorp.comCreated By: talentz@firstenergycorp.com
Recipients:
Michael.Mahoney@nrc.gov (Mahoney, Michael)
Tracking Status: None phlashley@firstenergycorp.com (phlashley@firstenergycorp.com)
Tracking Status: None kmnesser@firstenergycorp.com (kmnesser@firstenergycorp.com)
Tracking Status: None kwbyrd@firstenergycorp.com (kwbyrd@firstenergycorp.com)
Tracking Status: None apwise@firstenergycorp.com (apwise@firstenergycorp.com)
Tracking Status: None ctdaft@firstenergycorp.com (ctdaft@firstenergycorp.com)
Tracking Status: None gmwolf@firstenergycorp.com (gmwolf@firstenergycorp.com)
Tracking Status: None Post Office:
FirstEnergyCorp.comFilesSizeDate & TimeMESSAGE47586495/28/2010 20100528093714771.pdf176228 20100526154647573.pdf4532624 Nozzle 4 - 52M Deposit Depth.pdf24252 Options Expiration Date:
Priority:olImportanceNormal ReplyRequested:False Return Notification:False Sensitivity: olNormalRecipients received:Follow up. Start by Tuesday, June 01, 2010. Due
by Tuesday, June 01, 2010