ML101520112

Response to Request for Additional Information 50.55a Relief Request

ML101520112
Person / Time
Site:	Davis Besse
Issue date:	05/28/2010
From:	Lentz T FirstEnergy Corp
To:	Michael Mahoney Plant Licensing Branch III
mahoney, m NRR/DORL/LPLIII-2 415-3867
Shared Package
ML101520113	List: ML101520112 ML101520114 ML101520116
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

Penetration

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

penetration welds.

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

1. 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