ML18178A140

Response to Public Comments on Draft RIS 2018-XX, Clarification of the Requirements for Reactor Vessel Upper Head Bare Metal Visual Examinations.

ML18178A140
Person / Time
Issue date:	06/26/2018
From:	Stephen Cumblidge Division of Materials and License Renewal
To:	Steve Ruffin Division of Materials and License Renewal
Benney B
Shared Package
ml18178a133	List: ML18178A140 ML18178A230 RIS 2018-06, Clarification of the Requirements for Reactor Vessel Upper Head Bare Metal Visual Examinations
References
Download: ML18178A140 (9)

Text

/ra/

Federal Register

Comment No.1-1 1-1: The consensus of the TGHSNA is that the RIS 2018-38 does not reflect the scope of ASME Code Case N-729-4 with respect boric acid deposits found during general visual examinations performed such as part of the boric acid program. Leakage from sources other than the scope of the Case should be resolved by the corrective action program. The Code Case words direct the user to determine to source of leakage and remove extraneous boric acid. The RIS 2018-38 restricts cleaning until the source of the leakage has been confirmed not to be from the head penetrations. Boric acid deposits from other sources are not considered relevant indications under the scope of N-729-4.

Comment No. 2-1 The first sentence in the second paragraph under "Summary of Issue" as written implies that "relevant conditions" at or near a nozzle annulus necessarily must be concluded to trigger supplemental examination per 3142.2 or nozzle repair per 3142.3(b). Instead, as stated in the first sentence of the next paragraph, 3142.1(b)(1) requires further evaluation to determine the source of the leakage. I suggest clarifying the first sentence in the second paragraph under "Summary of Issue" as follows:

Consistent with the definition of "relevant conditions," areas of corrosion, boric acid deposits, or discoloration at or near a nozzle annulus in all cases, and irrespective of the material from which the affected components are fabricated, are potentially "relevant conditions indicative of possible nozzle leakage" according to ASME Code Case N-729-4, Subsections 3142.1(b) and (c).

Comment No. 2-2

The final sentence (beginning "If the source of relevant condition of possible nozzle leakage cannot be determined ... ") in the third paragraph under "Summary of Issue" is unclear as written and may lead to unnecessary confusion. For example, the sentence confuses "relevant conditions indicative of possible nozzle leakage" with "relevant conditions" as defined in 3140 of the code case. The purpose of the further evaluation of the source of the leakage is to determine whether there are "relevant conditions indicative of possible nozzle leakage." In addition, the sentence should specifically cite 3142.3(b) as 3142.3(a) is applicable only if the further evaluation shows "relevant conditions not indicative of possible nozzle leakage." I suggest clarifying the final sentence in the third paragraph under "Summary of Issue" as follows (with suggested deletions shown using strike throughs):

If the source of relevant condition of possible nozzle leakage cannot be determined by examining the as-found condition of the relevant conditions (e.g., by assessment of boron deposit tenacity using light cleaning methods or by boron deposit chemical analysis), either because the boric acid deposits were tightly adhered to the surface, or because evidence of the relevant condition was removed by aggressive cleaning methods, the requirements of ASME Code Case N-729-4, Subsection 3142.2 or Subsection 3142.3 (b) must be met.

Tightly adherent boron deposits not removed using light cleaning methods are evidence that the

deposits formed during plant operation. Removal of deposits using aggressive cleaning methods without first examining the as-found condition precludes a meaningful further evaluation of the source of the leakage.

Comment No. 3-1

This paragraph of the draft RIS references relevant sections in the ASME Code Case under 3141 and 3142.

Code Case Section 3140 broadly addresses lnservice Visual Examinations (VE) and Section 3142 provides Acceptance criteria for Visual Examination findings. Three acceptance approaches are identified:

• 3142.1 - Acceptance by VE

• 3142.2 - Acceptance by Supplemental Examination

• 3142.3 - Acceptance by Corrective Measures or Repair/Replacement Activity

However, the subject paragraph of the draft RIS only addresses acceptance under 3142.2 and 3142.3. Excluding discussion of acceptance by visual examination from this paragraph seems to imply a Code Case interpretation that a "relevant condition" cannot be dispositioned as "not indicative of nozzle leakage" under 3142.1, without resorting to non-visual supplemental examinations.

Recommendation: Revise the draft RIS to acknowledge all three acceptance methods for dispositioning "relevant conditions" which are addressed within the Code Case.

Comment No. 3-2

Code Case Section 3140 generally addresses Inservice Visual Examinations and 3141(c) defines "relevant *conditions" that require further evaluation. The determination whether a "relevant condition" is or is not "indicative of nozzle leakage" is made in accordance with guidance in 3142.1(b). This section invokes 3142.3 regarding correcting the source of any leakage, requires cleaning to allow adequate examination and evaluation of degradation, and invokes 3142.2 Supplemental Exams IF the VE indicates the relevant condition is "indicative of possible nozzle leakage".

However, in the draft RIS, the first sentence of the subject paragraph appears to directly conclude that any areas meeting the 3141(c) definition of a "relevant condition" are "relevant conditions of possible nozzle leakage" with reference to 3142.l(b). As described above, 3142.l(b) prescribes an evaluation process, it does not specify or imply the conclusion that all "relevant conditions" are "relevant conditions of possible nozzle leakage." This portion of the draft RIS appears to overstate and very conservatively interpret the referenced portion of the

Code Case.

Recommendation: Revise the draft RIS to clearly acknowledge that "relevant conditions" must be evaluated in accordance with the guidance in Section 3142.l(b) to determine whether the condition is or is not "indicative of possible nozzle leakage."

Comment No. 4-1 Under the second paragraph in the Summary of Issue section, the NRC states the following:

"An indication that the leakage may have come from a component not subject to the visual examination does not remove the possibility that some or all of the leakage possibly came from a nozzle. If the licensee fully removes the deposits using aggressive cleaning methods, such as high-pressure water/steam or power washing, an adequate examination and evaluation to determine the source of leakage is no longer possible." Exelon is requesting further clarification concerning the use of aggressive cleaning methods after determining the leakage source. The statement above, as written, indicates that it would not be acceptable to use aggressive cleaning on the head after the leakage source has been identified to preclude future corrosion and provide a cleaner surface free of obstructions for future examinations. Exelon believes that it should be acceptable to leave the head in as clean a condition as possible post examination.

Comment No. 4-2

Exelon requests that the NRC define "light cleaning methods." The use of this term in the draft RIS seems to be rather vague. Does this mean dry air only? Can water be used to clean the surface?

Comment No. 4-3

-Exelon recognizes that leakage from above the reactor head that collects in the Control Rod Drive Mechanism (CRDM) nozzle annulus region could mask a leak from the nozzle itself. However, if it is very clear that the leakage has come from sources other than the nozzle, regardless whether a sample could be obtained for chemical analysis or not, the requirements of the Code Case N-729-4 to perform a subsequent Visual Examination (VE) of previously obscured surfaces after cleaning prior to return to service and again in the subsequent refueling outage (ASME Code Subsection 3142.1 (b}(2}) should be adequate to validate that the external leakage did not mask a nozzle leak. Operating Experience (OE} through the numerous reactor head examinations throughout the industry over the years has shown that the likelihood of a CRDM nozzle leak progressing from initial leakage to a critical flaw size that could lead to possible nozzle ejection is extremely low-

Comment No. 4-4 The draft RIS does not allow alternatives for new replacement reactor heads that contain corrosion resistant material. Exelon considers this interpretation to be particularly over conservative for replaced reactor heads made from Pressurized Water Stress Corrosion Cracking (PWSCC) resistant material (e.g., Alloy 690 material} where the likelihood of cracking developing in the nozzles or attachment welds is extremely low.