[Federal Register Volume 87, Number 83 (Friday, April 29, 2022)]
[Notices]
[Pages 25554-25561]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2022-09171]
-----------------------------------------------------------------------
NUCLEAR REGULATORY COMMISSION
[Docket Nos. 72-1041, 50-498, and 50-499; NRC-2022-0099]
South Texas Project Nuclear Operating Company; South Texas
Project Electric Generating Station Units 1 and 2; Independent Spent
Fuel Storage Installation
AGENCY: Nuclear Regulatory Commission.
ACTION: Exemption; issuance.
-----------------------------------------------------------------------
SUMMARY: The U.S. Nuclear Regulatory Commission (NRC) is issuing an
exemption in response to a request submitted by South Texas Project
Nuclear Operating Company (STPNOC) on March 11, 2022, from meeting
certain NRC regulatory requirements for one multipurpose canister
(MPC), Serial Number 248 (MPC 248), in use at the South Texas Project
Electric Generating Station, Units 1 and 2 (STPEGS). This exemption
permits STPNOC to continue using MPC 248 to store spent fuel for the
service life of the canister, including transferring the MPC to a HI-
STORM FW overpack, without volumetric examination data from
radiographic testing for a 1-inch section of the repaired weld seam
joining the baseplate to the canister shell.
DATES: This exemption was issued on April 25, 2022.
ADDRESSES: Please refer to Docket ID NRC-2022-0099 when contacting the
NRC about the availability of information regarding this action. You
may obtain publicly available information related to this action using
any of the following methods:
Federal Rulemaking Website: Go to https://www.regulations.gov and search for Docket ID NRC-2022-0099. Address
questions about Docket IDs in Regulations.gov to Stacy Schumann;
telephone: 301-415-0624; email: [email protected]. For technical
questions, contact the individual listed in the For Further Information
Contact section of this document.
NRC's Agencywide Documents Access and Management System
(ADAMS): You may obtain publicly available documents online in the
ADAMS Public Documents collection at https://www.nrc.gov/reading-rm/adams.html. To begin the search, select ``Begin Web-based ADAMS
Search.'' For problems with ADAMS, please contact the NRC's Public
Document Room (PDR) reference staff at 1-800-397-4209, 301-415-4737, or
by email to [email protected]. For the convenience of the reader,
instructions about obtaining materials referenced in this document are
provided in the ``Availability of Documents'' section.
NRC's PDR: You may examine and purchase copies of public
documents, by appointment, at the NRC's PDR, Room P1 B35, One White
Flint North, 11555 Rockville Pike, Rockville, Maryland 20852. To make
an appointment to visit the PDR, please send an email to
[email protected] or call 1-800-397-4209 or 301-415-4737, between
8:00 a.m. and 4:00 p.m.
[[Page 25555]]
(ET), Monday through Friday, except Federal holidays.
FOR FURTHER INFORMATION CONTACT: Donald Habib, Office of Nuclear
Material Safety and Safeguards, U.S. Nuclear Regulatory Commission,
Washington, DC 20555-0001; telephone: 301-415-1035; email:
[email protected].
SUPPLEMENTARY INFORMATION:
I. Background
South Texas Project Nuclear Operating Company (STPNOC or the
licensee) is the holder of Facility Operating License Nos. NPF-76 and
NPF-80, which authorize operation of the STPEGS, respectively, in
Matagorda County, Texas, pursuant to part 50 of title 10 of the Code of
Federal Regulations (10 CFR), ``Domestic Licensing of Production and
Utilization Facilities.'' The license provides, among other things,
that the facility is subject to all rules, regulations, and orders of
the NRC now or hereafter in effect.
Under 10 CFR part 72, subpart K, ``General License for Storage of
Spent Fuel at Power Reactor Sites,'' a general license is issued for
the storage of spent fuel in an independent spent fuel storage
installation (ISFSI) at power reactor sites to persons authorized to
possess or operate nuclear power reactors under 10 CFR part 50. The
licensee is authorized to operate a nuclear power reactor under 10 CFR
part 50 and, accordingly, holds a 10 CFR part 72 general license for
storage of spent fuel at the STPEGS ISFSI. Under 10 CFR 72.212(a)(2),
(b)(3), (b)(5)(i), (b)(11) and 72.214, a general licensee may store
spent fuel in a cask, so long as it is one of the approved casks listed
in 10 CFR 72.214 and the general licensee conforms to the terms,
conditions, and specifications of the relevant certificate of
compliance (CoC) or amended CoC. Accordingly, under the terms of the
general license, the STPNOC stores spent fuel at its ISFSI using the
HI-STORM FW MPC-37 Storage System in accordance with CoC No. 1032,
Amendment No. 2. As part of the MPC storage system, the MPC (of which
the weld seam joining the baseplate to the shell is an integral part)
ensures the functions of criticality safety, confinement boundary,
shielding, structural support, and heat transfer.
II. Request/Action
In a letter dated March 11, 2022, the licensee requested an
exemption from the requirements of 10 CFR 72.154(b) as well as 10 CFR
72.212(a)(2), (b)(3), (b)(5)(i), and (b)(11). Paragraph 72.154(b)
requires the licensee to have available documentary evidence that
material and equipment conform to the procurement specifications prior
to installation or use of the material and equipment and to retain or
have available this documentary evidence for the life of the ISFSI or
spent fuel cask.
Paragraph 72.212(a)(2) limits a general license to storage of spent
fuel in casks approved under the provisions of 10 CFR part 72.
Paragraph 72.212(b)(3) requires the general licensee to ensure that
each cask it uses conforms to the terms, conditions, and specifications
of a CoC or an amended CoC listed in Sec. 72.214.
Paragraph 72.212(b)(5)(i) requires the general licensee to perform
written evaluations which establish that the relevant cask, once loaded
with spent fuel or once the changes authorized by an amended CoC have
been applied, will conform to the terms, conditions, and specifications
of a CoC or an amended CoC listed in Sec. 72.214. Paragraph
72.212(b)(11) requires, among other things, that the general licensee
comply with the terms, conditions, and specifications of the CoC or the
amended CoC, as appropriate. Section 72.214 lists the casks that are
approved for storage of spent fuel under the conditions specified in
their CoC.
The licensee loaded spent fuel in the HI-STORM FW Storage System
MPC-37, MPC 248, for storage in the ISFSI at STPEGS under CoC No. 1032,
Amendment No. 2, under its general license. Condition 6 of the CoC
states, ``Features or characteristics for the site or system must be in
accordance with Appendix B to this certificate.'' Appendix B, Section
3.3 of the CoC requires, with certain approved alternatives that are
not relevant in this case, the HI-STORM FW MPC-37 to meet the American
Society of Mechanical Engineers Boiler and Pressure Vessel Code, 2007
Edition (ASME Code). Section III, Subsection NB, of the ASME Code
requires that 100 percent of the weld seam joining the baseplate to the
shell of the canister be examined by a radiography test (RT). Further,
ASME Code Section III, Subsection NB requires, in part, that
``examination of a weld repair shall be repeated as required for the
original weld.'' Thus, in effect, the NRC staff is considering an
exemption from the requirement to repeat volumetric examination by RT
as required for the original weld on a 1-inch portion of the repaired
weld.
During a review of manufacturing documents, the manufacturer
determined that a 1-inch section of the shell-to-baseplate weld on MPC
248 was not properly digitally radiographed after a weld repair. When
notified of this issue, the licensee had already loaded MPC 248 with
spent fuel assemblies and was in the process of preparing the MPC for
long-term storage at the STPEGS ISFSI pad. The affected MPC is
currently in a safe, analyzed condition in the STPEGS Unit 1 Fuel
Handling Building cask decontamination area.
This exemption would, if granted, permit the licensee to continue
using MPC 248 to store spent fuel for the service life of the canister,
including transferring the MPC to a HI-STORM FW overpack, without
volumetric examination data from radiographic testing for a 1-inch
section of the repaired weld seam joining the baseplate to the canister
shell. In order for this exemption to exempt the licensee from all
relevant provisions, the licensee would also need an exemption from 10
CFR 72.214. As the licensee did not request an exemption from 10 CFR
72.214, as part of the NRC staff's consideration of the requested
exemption, the NRC staff will also consider granting an exemption from
10 CFR 72.214 upon its own initiative, in accordance with 10 CFR 72.7.
For brevity, whenever this analysis refers to the requested exemption
it means both the exemption requested by the licensee and the exemption
from 10 CFR 72.214.
III. Discussion
Pursuant to 10 CFR 72.7, the Commission may, upon application by
any interested person or upon its own initiative, grant such exemptions
from the requirements of the regulations of 10 CFR part 72 as it
determines are authorized by law and will not endanger life or property
or the common defense and security and are otherwise in the public
interest.
Authorized by Law
Section 72.7 allows the NRC to grant exemptions from the
requirements of 10 CFR part 72. The NRC staff has determined that
issuance of this exemption is consistent with the Atomic Energy Act of
1954, as amended, and not otherwise inconsistent with NRC's regulations
or other applicable laws. Therefore, the requested exemption is
authorized by law.
Will Not Endanger Life or Property or the Common Defense and Security
This exemption would, if granted, exempt the licensee from the
requirement to repeat volumetric examination as required for the
original weld on a 1-inch portion of the repaired weld in ASME Code
Section III, Subsection NB, which the licensee is
[[Page 25556]]
required to follow by the relevant technical specifications. If would
also, if granted, exempt the licensee from the 10 CFR 72.154(b)
requirement to have available documentary evidence that material and
equipment conform to the procurement specifications prior to
installation or use of the material and equipment and to retain or have
available this documentary evidence for the life of the ISFSI or spent
fuel cask.
The licensee supported this exemption request with a structural
evaluation for the MPC and a separate structural analysis, both of
which assumed a weld strength reduction factor of 0.8 to account for
the missing RT examination. The structural evaluation showed that MPC
248 maintains structural and confinement functions and that, even with
the 0.8 weld strength reduction factor, MPC 248 would still meet the
ASME Code, Section III, Subsection NB structural analysis requirements.
The NRC's review and evaluation of this 0.8 weld strength reduction
factor and the licensee's structural analysis for MPC 248 are found in
the Materials Review for the Requested Exemption and the Structural
Review for the Requested Exemption section of this notice,
respectively.
Review of the Requested Exemption
The HI-STORM FW storage system consists of a sealed metallic multi-
purpose canister (MPC) contained within an overpack constructed from a
combination of steel and concrete. The HI-STORM FW overpack can be
loaded with the MPC containing spent fuel using the HI-TRAC VW transfer
cask and prepared for storage while inside the 10 CFR part 50 facility.
The HI-TRAC VW transfer cask is required for shielding and protection
of the spent fuel during loading and closure of the MPC and during
movement of the loaded MPC from the cask loading area of a nuclear
plant spent fuel pool to the storage overpack. The MPC enclosure
vessels are cylindrical weldments with identical and fixed outside
diameters. Each MPC is an assembly consisting of a honeycomb fuel
basket, a baseplate, a canister shell, a lid, and a closure ring. The
number of spent fuel storage locations in an MPC depends on the type of
fuel assembly. The MPC-37 model in use at STPEGS is designed to hold 37
pressurized water reactor fuel assemblies.
The NRC has previously approved the HI-STORM FW storage system in
CoC No. 1032, including Amendment No. 2 to the CoC, which is the
version of the CoC in use at STPEGS. The requested exemption does not
change the fundamental design, components, contents, or safety features
of the storage system. The NRC staff has evaluated the applicable
potential safety impacts of granting the requested exemption to assess
the requested exemption's potential for danger to life or property or
the common defense and security; the evaluation and resulting
conclusions are presented in this notice. The potential impacts
identified for this exemption request were in the areas of materials,
structural integrity, and confinement capability. The staff did not
identify any potential impacts in the areas of criticality, shielding,
and thermal conditions.
Materials Review for the Requested Exemption: The licensee asserted
that although MPC 248 does not meet the ASME Code requirements
specified in Appendix B, Section 3.3 of the CoC, MPC 248 continues to
meet its safety functions. The licensee stated that after the
completion of spent fuel loading, drying, and closure welding of MPC
248, Holtec International, the CoC holder, informed the licensee that
MPC 248 does not fully meet the requirements in CoC Appendix B. More
specifically, the Holtec HI-STORM FW MPC design and certification is
based on compliance with ASME Code Section III, with certain approved
alternatives. Portions of ASME Code Section III, Subsection NB-5000,
require that weld repairs in the MPC confinement boundary be examined
to the same criteria as the initial welds. Section III, Subsection NB
also requires that 100 percent of the MPC shell-to-baseplate welds be
volumetrically examined using RT, in accordance with Section III, NB-
5230.
During fabrication, Holtec performed a typical weld repair of the
MPC 248 shell-to-baseplate weld after the initial digital RT
examination showed a section of the weld had lack of fusion. The weld
was excavated to remove the lack-of-fusion defect and a successful
liquid penetrant test (PT) examination of the entire excavated area was
performed. The dimensions of the excavated area are approximately 9
inches in length by 0.5 inches in width and 0.5 inches in depth
(through wall at the defect location). The licensee stated that
detailed profile dimensions of the repaired area are not available but
referred to Holtec procedures that require a 3-to-1 taper for weld
repair excavations. The weld repair was performed using an ASME Code
Section IX qualified gas tungsten arc weld procedure and successfully
passed a final PT exam. After the PT exam was completed, the unit was
reinspected using the same digital RT process used on the original
weld, but only 8 inches of the 9-inch length were examined. The missing
1-inch section is located at the end of one side of the excavated area.
The licensee stated that the RT on the original weld did not identify
weld defects on the end of the excavated area containing this 1-inch
portion, but a portion of the weld in this 1-inch section had to be
removed to access the defects in the adjacent portion of the shell-to-
baseplate weld and allow repair welding to be performed. Following
completion of the weld repair, MPC 248 successfully passed a helium
leakage test during factory acceptance testing as well as a hydrostatic
test performed at STPEGS during loading operations.
According to the licensee, the repairs along the MPC shell-to-base
plate weld were completed per Holtec's written procedures. After
completing the repairs, Holtec examined the repaired area by PT and
determined that the PT examination results met the acceptance criteria
of ASME Code Section III, NB-5350. Holtec performed the post-repair RT
examination and later determined that the RT examination which met the
acceptance criteria of ASME Code Section III, NB-5320 included only 8
of the 9 inches.
The licensee's assertion that MPC 248 continues to meet all its
safety functions is based on the following:
The weld repair was performed in accordance with all
Holtec quality procedures.
MPC 248 has 653 inches of welds in total. Holtec performed
an RT examination on all those welds except for the approximately 1-
inch section of repaired weld. This 1-inch section is approximately
0.15 percent of the MPC 248 welds. The remaining 99.85 percent of MPC
248's welds were fully inspected.
To support its weld strength reduction factor, the licensee
referenced the weld strength reduction factor of 0.8 from NRC Interim
Staff Guidance (ISG)--15, ``Materials Evaluation,'' for welded
austenitic stainless steel spent fuel storage canisters that are
examined using progressive, multiple-layer PT examinations in lieu of a
volumetric examination nondestructive examination (NDE) method that is
required by ASME Code Section III, Subsection NB.
The licensee also reviewed the requirements in several sections of
the ASME code to support its selection of the weld strength reduction
factor value from ISG-15. Specifically, the licensee reviewed the joint
efficiency values included in ASME Code Section VIII, Division 1 and
Section III, Subsection ND. The licensee also reviewed the
[[Page 25557]]
quality factor for welded joints in ASME Code Section III, Subsection
NG. The licensee also noted that the SA-240 Type 304 stainless steel
design stress values applicable to ASME Code Section VIII, Division 1
and Section III, Subsection ND are generally equal to the design stress
intensity values applicable to Section III, Subsection NB--which apply
to the weld in question--except for minor variances at 300 and 400
degrees Fahrenheit.
The licensee noted that ASME Code Section VIII, Division 1, which
governs the design and construction of non-nuclear pressure vessels,
specifies that Category C butt joints have a weld efficiency of 0.85
when subject to spot radiography, as specified in ASME Code, Section
VIII, Division 1, UW-52. The licensee noted that spot radiography
requires a minimum of one 6-inch spot to be RT examined for every 50-
foot increment of the weld. The licensee stated that the Category C
butt joints are more critical than Category C corner joints, which is
the type of joint for the weld in question. The licensee also stated
that by comparison, more than 99 percent of the MPC shell-to-baseplate
weld was examined by RT, far exceeding the requirement for spot
radiography per ASME Code Section VIII, Division 1, UW-52. Therefore,
the licensee concluded that a 0.85 value for joint efficiency is
conservative for evaluation of MPC 248, making the selected 0.8 value
even more conservative.
The licensee noted that ASME Code Section III, Subsection ND, which
applies to Class 3 nuclear components, also specifies a joint
efficiency of 0.85 for Category C butt welds subject to spot
radiography. The licensee stated that the inspection performed on the
shell-to-base plate weld for MPC 248 exceeds these minimum ASME Code
requirements for spot radiography in ASME Code Section III, Subsection
ND because more than 99 percent of the weld was examined by RT.
The licensee also compared the value of the weld strength reduction
factor from ISG-15 to the requirements of ASME Code Section III,
Subsection NG, which is applicable to core support structures of
nuclear facility components. The licensee pointed to Table NG-3352-1,
which specifies a quality factor for a welded joint of 0.75 for a full
penetration weld subjected to PT for both the root pass and the final
pass. The licensee stated that the quality factor for welded joints in
Table NG-3352-1 would be overly conservative because more than 99
percent of the shell-to-baseplate weld for MPC 248 was volumetrically
examined using RT, 100 percent of the weld received surface examination
using PT, and the weld excavation cavity at 3-to-1 taper at the 1-inch
weld location received PT. This is discussed in detail in the staff's
independent analysis in this notice.
The NRC staff reviewed the information provided by the licensee
including: (1) The licensee's comparisons of the weld strength
reduction factor to the joint efficiency values based on requirements
contained in ASME Code Section VIII, Division 1, and ASME Code Section
III, Subsection ND; and to the quality factor for welded joints in ASME
Code Section III, Subsection NG; (2) the specific requirements in those
ASME Code sections; (3) the guidance in, and applicability of ISG-15;
and (4) the information provided by the licensee regarding the weld
repair procedures and post-weld repair NDE results.
The staff determined that although the weld strength reduction
factors specified in the ASME Code sections cited by the licensee are
not applicable to the Holtec HI-STORM FW MPC-37--which was approved
using the design and construction requirements in ASME Code, Section
III, Subsection NB--the values are conservative with respect to a
possible weld strength reduction factor for MPC 248 because more than
99 percent of the shell-to-baseplate weld was examined using RT and 100
percent was examined using PT. As discussed in this notice, the staff
calculated two potential weld strength reduction factors, both are
which are conservative. Both calculated values are greater than the
licensee's 0.8 value, making the licensee's value more conservative. In
addition, the staff notes that: (1) Only the fraction of the 1-inch-
long three-to-one tapered section of the weld that was removed was not
examined by RT after the repair; (2) the portion of the 1-inch weld
that remained after excavation at the three-to-one tapered section was
volumetrically examined by RT prior to excavation and met the
acceptance criteria of ASME Code Section III, NB-5320; (3) 100 percent
of the repair weld section was successfully examined by PT both after
excavation and after repair; and (4) more than 88 percent of the
approximately 9-inch repair weld section was examined using RT.
Therefore, the staff concluded that the values of the weld strength
reduction factors derived from the ASME Code sections cited by the
licensee conservatively bound the reduction in the weld strength of the
shell-to-baseplate weld of MPC 248 as a result of possible weld defects
in the 1-inch portion of the repair weld that was not examined by RT.
The staff also reviewed the guidance in ISG-15 which states that,
if progressive surface examinations (i.e., sequential examinations
conducted as a multi-pass weld is deposited) such as multiple layer PT
or magnetic particle testing are used for a spent fuel storage canister
closure lid weld in lieu of a volumetric examination, a weld strength
reduction factor of 0.8 is to be imposed on the weld design to account
for imperfections or flaws that may have been missed by the progressive
surface examinations. The staff determined that, although the guidance
for the use of the weld strength reduction factor in ISG-15 was not
intended to be applied for an MPC shell-to-baseplate weld, the value of
the weld strength reduction factor from ISG-15 would be conservative
for the MPC 248 shell-to-baseplate weld for the same reasons provided
for the comparisons of the weld strength reduction factors from the
ASME Code sections cited by the licensee and discussed in the previous
paragraph. Therefore, the staff concluded that the values of the weld
strength reduction factor from ISG-15 conservatively bound the
reduction in the weld strength of the shell-to-baseplate weld of MPC
248 as a result of possible buried weld defects in the 1-inch portion
of the repair weld that was not examined by RT.
The NRC staff conducted an independent analysis of MPC 248
considering the MPC materials and the design of the shell-to-baseplate
weld. The staff's analysis postulated that the portion of the repaired
area of the weld that was not subjected to the post-weld repair RT
examination includes a buried weld flaw.
The NRC staff used this initial postulate because: (1) The portion
of the original weld in the 1-inch section was examined by PT after the
weld excavation's completion; and (2) the completed repair weld was
also PT-examined. Both of these examinations reveal no surface-breaking
flaws, indicating that if a flaw was to exist in that 1-inch section,
it would be a buried weld flaw. The staff determined that for the
entire shell-to-baseplate weld, the weld strength reduction factor that
would be applied to the structural analysis of such a joint to account
for a buried weld flaw per the ASME Code would be at least 0.99
because: (1) The entire section of the shell-to-base plate weld and the
section of the repair weld that was RT-examined were verified to be
free of any relevant flaws; (2) the design of the MPC shell and MPC
baseplate are sufficiently thick and provide sufficient stiffness to
the MPC shell to prevent significant stress
[[Page 25558]]
concentrations for relatively small buried weld flaws; (3) the MPC
shell, baseplate, and the shell-to-baseplate weld are all high
toughness materials that are not susceptible to brittle fracture; and
(4) MPC 248 successfully passed a helium leakage test during factory
acceptance testing and a hydrostatic pressure test during the loading
operations. This number does not credit the 1-inch section without RT.
The NRC staff calculated this number dividing the length of the section
that that did not receive RT by the total length of the shell-to-
baseplate weld and then subtracting that result from 1. This method
produces a weld strength reduction factor that is greater than .99.
Given that the licensee's selected weld strength reduction factor of
0.8 is less than this staff-calculated value, the licensee's factor
accounts for a greater reduction in weld strength due to a buried flaw.
In addition to the above analysis, the staff conducted a weld
strength reduction factor analysis using greater conservatisms.
Specifically, the staff assumed a worst-case flaw size that considered
information provided by the licensee on the results of the initial RT
of the shell-to-baseplate weld; the profile of the weld excavation and
the weld repair process; and the NDE conducted after excavation and
again after the weld repair was completed. This calculation based the
weld strength reduction factor on only the repaired weld rather than
the entire shell-to-baseplate weld. In this evaluation, the staff also
did not credit the presence of the entire 1-inch repair weld which was
not RT-examined post repair. This calculation would be conservative
relative to the actual reduction in weld strength because the 1-inch
portion of the weld that did not receive post-repair RT was initially
examined by RT per ASME Code Section III, NB-5230 and shown to meet the
ASME Code Section III, NB-5320 acceptance criteria prior to weld
excavation (as previously discussed, this section of the weld is
located within the 3-to-1 taper area). Additionally, the weld
excavation cavity and post-repair weld were both PT examined per ASME
Code Section III, NB-5230 and met the acceptance criteria of ASME Code
Section III, NB-5350. In this case, the 1-inch section is 11 percent of
the 9-inch repair section. Thus, the same calculation discussed above
produces a weld strength reduction factor of 0.89.
Given that the licensee's selected weld strength reduction factor
of 0.8 is less than both of the staff-calculated values, it would
account for a greater reduction in weld strength due to a buried flaw
than either of those values. Therefore, the 0.80 weld strength
reduction factor is conservative.
The staff's independent analyses of the weld strength reduction
factor for MPC 248 are conservative because: (1) The weld repair
procedure with the multi-pass manual gas tungsten arc weld was
developed to facilitate a weld repair, provide more control over weld
deposition, and minimize the introduction of weld flaws; (2) the 1-inch
weld is within the three-to-one taper section of the repair excavation
with sound weld metal backing based on the initial RT results and the
weld excavation cavity PT results prior to the weld repair; (3) the
post-repair weld examinations using PT and RT met the acceptance
criteria in ASME Code Section III, NB-5300; (4) any weld repair flaw
present in the non-examined RT weld repair section would be limited to
the dimensions of the weld repair in the tapered area of the
excavation; (5) based on the post-repair PT results, any flaw
introduced during repair welding would be embedded in the weld with low
stress concentration of little to no significance to structural
performance or the confinement function of the MPC; and (6) the staff's
analysis was based on a maximum of 1-inch missing weld in the MPC
shell-to-baseplate weld.
Based on the points above, any weld flaw present in the 1-inch
section that was not examined by RT after the weld repair would be a
small relative to the length of that section of the weld. The staff's
analysis is conservative because, as stated above, the analysis assumed
no credit for the entire portion of the weld that was not examined by
RT after the repair. Because the licensee's 0.8 weld strength reduction
factor is more conservative than the values of the weld strength
reduction factor the staff calculated, the staff's independent analysis
shows that the weld strength reduction factor of 0.8 used by the
licensee is sufficient to account for the possible presence of non-
surface breaking flaws in the portion of the repair weld that was not
subjected to post-repair volumetric examination. Therefore, the staff
finds the 0.8 weld strength reduction factor acceptable. The licensee's
structural analysis using this weld strength reduction factor is
analyzed in this notice.
Evaluation Findings of Materials Review: As a result of the
analyses discussed above, the NRC staff finds that the weld strength
reduction factor provided by the licensee is sufficient to account for
the presence of undetected flaws that may be present in the shell-to-
baseplate weld of MPC 248, loaded under CoC No. 1032, Amendment No. 2.
Therefore, the use of a 0.8 weld strength reduction factor in the
structural evaluation would not endanger life or property or the common
defense and security if the requested exemption were granted.
Structural Review for the Requested Exemption: The staff's
structural review focused on the re-analysis of the shell-to-baseplate
weld, as provided in Enclosure 2 (proprietary), ``HI-STORM FW MPC
Stress Analysis,'' of the exemption request, to verify that the safety
function of the MPC is maintained after considering a weld strength
reduction factor to the allowable stress values used as design
criteria. As discussed above, the licensee applied a weld strength
reduction factor in its analysis to account for imperfections or flaws
that may be missed for the 1-inch weld portion without post-repair RT.
Re-Analysis of the Shell-to-Baseplate Weld: The HI-STORM FW Final
Safety Analysis Report (FSAR), HOLTEC Report No. HI-2114830, Table
10.1.4, ``HI-STORM FW MPC NDE Requirements,'' establishes the weld
acceptance criteria that provide reasonable assurance that the weld
will perform its design function under all loading conditions as
defined in ASME Code, Section III, Subsection NB. In accordance with
Appendix B, Section 3.3, ``Codes and Standards,'' of CoC No. 1032, the
HI-STORM FW MPC-37 must meet the 2007 Edition of the ASME Code. The
ASME Code Section III, Subsection NB, states, in part, that
``examination of a weld repair shall be repeated as required for the
original weld.'' For original welds, it is required that 100 percent of
the weld seam joining the baseplate to the shell of the canister be
examined by RT. Since the unexamined portion of the repair weld is not
in conformance with the ASME Code requirements described in the CoC,
the licensee's structural evaluation seeks to demonstrate that the use
of the affected MPC 248 will not adversely impact its structural safety
function after considering a weld strength reduction factor used to
account for the non-conformance condition.
As discussed above in the materials review of the requested
exemption, the staff concluded that the licensee's weld strength
reduction factor of 0.8 (i.e., an overall 20 percent reduction in the
allowable stress) is sufficient to account for potential imperfections
or flaws that may have been missed by an incomplete RT when considering
the size of the unexamined portion of the repair weld. The licensee
applied this weld strength reduction factor to the allowable stress
intensity used in the five load cases
[[Page 25559]]
identified as the governing load combinations for the MPC 248 shell-to-
baseplate weld per the HI-STORM FW FSAR (HOLTEC Report No. HI-2114830,
Revision 5) to re-evaluate the safety factors that are available and
demonstrate that the design function will be maintained. The five load
cases are as follows: The design condition with a 120 pounds per square
inch gauge (psig) normal internal pressure only to bound short-term
normal operations (Case 1), an accident condition with a 200 psig
accident internal pressure (Case 2), a short-term MPC lifting operation
with a 120 psig operating internal pressure plus weight of the contents
(Case 3), an off-normal condition with a 120 psig off-normal internal
pressure plus bounding off-normal temperature contours (Case 4), and a
design basis short-term operation with a 120 psig internal pressure
plus bounding short-term operation temperature contours (Case 5). By
comparing the reduced allowable stress of each loading condition to the
resultant stress obtained from the finite element analysis performed by
the licensee in the structural analysis of the HI-STORM FW system
(Holtec Report HI-2094418, Revision 20), the licensee calculated a new
safety factor for each loading condition. The analysis demonstrated
that the shell-to-baseplate weld maintains a safety factor above 1.0
for all loading conditions and that sufficient design margin remains to
accommodate the resultant stress from each loading condition even with
the reduced stress allowable used to account for potential
imperfections or flaws in the repaired weld. The licensee further
stated that, in addition to the weld strength reduction factor, the
analysis also retains several conservatisms from the existing FSAR
design basis analysis, such as using bounding pressures, temperatures,
and temperature contours.
While the NRC staff is not basing its conclusions on these
conservatisms, the NRC staff notes that the use of these conservative
values in the analysis demonstrate that additional design margin
remains available to accommodate resultant stress.
Evaluation Findings of Structural Review: The NRC staff reviewed
the analysis performed in Enclosure 2 (proprietary) of the exemption
request for the MPC shell-to-baseplate weld and finds that the licensee
evaluation demonstrates that a safety factor greater than 1.0 is
maintained (i.e., calculated stresses remain below the allowable stress
intensities with the reduction factor) for all normal, off-normal, and
accident conditions after the stress allowable for each load case is
reduced by 20 percent to account for imperfections or flaws that may be
missed due to the non-conforming weld inspection. The staff notes that
the use of a weld strength reduction factor to the allowable stress
values is similar to other approved alternatives to the ASME code
examination requirements as described in NUREG-2215, ``Standard Review
Plan for Spent Fuel Dry Storage Systems and Facilities,'' to account
for imperfections or flaws that may be missed by other examinations.
While the alternatives described in NUREG-2215 are not applicable to
this weld, as discussed above in the materials section, the NRC finds
their use acceptable in this instance. During its review, the staff
also verified that the licensee has properly applied the weld strength
reduction factor of 0.8 to applicable allowable stress values for the
design criteria. The staff also notes that no potential for stress
cycling is expected at the unexamined portion of the repair. As
discussed in Section 3.1.2.5 of CoC No. 1032 FSAR, fatigue failure is
not a credible concern for the MPC since it is not an active system
(i.e., no moving parts) and is not subject to significant stress
cycling due to rapid temperature changes or significant pressure
changes. Therefore, there is no credible concern of fatigue failure if
any flaw introduced during the weld repair is considered.
As set forth above, the licensee has demonstrated that the shell-
to-baseplate weld for MPC 248, loaded under CoC No. 1032, Amendment No.
2, is capable of maintaining its structural integrity and performing
its safety function under normal, off-normal, and accident conditions.
Therefore, the staff concludes that the structural properties of MPC
248, as addressed in the exemption request, remain in compliance with
10 CFR part 72, and therefore, from a structural perspective, this
exemption, if granted, would not endanger life or property or the
common defense and security.
Confinement Review for the Requested Exemption: The licensee stated
on page 1 of Enclosure 1 of its exemption request that MPC 248
successfully passed a helium leakage test during factory acceptance
testing following completion of the weld repair, as well as a
hydrostatic test which was performed at STPEGS during loading
operations. According to the licensee, the helium leakage test
performed on MPC 248 was in conformance with the FSAR and the
applicable Technical Specifications for the HI-STORM FW storage system
and satisfied the ``leaktight'' criteria in ANSI N14.5-1997.
Evaluation Findings of Confinement Review: The staff found that,
because MPC 248 successfully passed a helium leakage test during a
fabrication acceptance test following completion of the weld repair,
the MPC meets the leaktight criteria of ANSI N14.5-1997. Further, MPC
248 passed a hydrostatic test performed at STPEGS during loading
operations, which provides further evidence of no discernable leakage
from this MPC at the time of loading. The staff therefore concludes
that MPC 248 meets the regulatory requirements for confinement in 10
CFR part 72 and, therefore, the weld repair completed on MPC 248 has
had no effect on the confinement performance of the MPC in question.
Consequently, from a confinement perspective, this exemption, if
granted, would not endanger life or property or the common defense and
security.
Conclusion Regarding Deviation from Weld Inspection Requirement: As
noted above, the NRC staff did not identify any potential effects on
criticality, shielding, and thermal conditions. Therefore, based on
that fact and the above discussions, the NRC staff concludes that an
exemption exempting the licensee from the requirement to repeat
volumetric examination for the 1-inch portion of the repaired weld, if
granted, would not endanger life or property or the common defense and
security.
Record Keeping Provision Evaluation: As noted above, the licensee
also requested an exemption from the 10 CFR 72.154(b) requirement to
have available documentary evidence that material and equipment conform
to the procurement specifications prior to installation or use of the
material and equipment and to retain or have available this documentary
evidence for the life of the ISFSI or spent fuel cask. The records
covered by the requested exemption are the records detailing the
results for the RT discussed above. As previously detailed, the NRC
staff has concluded that exempting the licensee from the requirement to
repeat volumetric examination as required for the original weld on a 1-
inch portion of the repaired weld would not endanger life or property
or the common defense and security. If not performing the RT does not
endanger life or property or the common defense and security, it
follows that not retaining records of those test results would also not
endanger life or property or the common defense and security.
Therefore, the NRC staff finds that the requested exemption from 10 CFR
72.154(b), if granted, would not
[[Page 25560]]
endanger life or property or the common defense and security.
Otherwise in the Public Interest
In considering whether granting the requested exemption is in the
public interest, the NRC staff considered the alternative of not
granting the requested exemption. If the requested exemption were not
granted, in order to comply with the CoC, MPC 248 would need to be
opened and unloaded, the contents loaded in new MPC, and the new MPC
welded and tested. This option would entail a higher risk of canister
handling accidents, additional personnel exposure, and greater cost to
the licensee. This option would also generate additional radioactive
contaminated material and waste from operations. For example, the lid
would have to be removed, which would generate cuttings from removing
the weld material that could require disposal as contaminated material.
This radioactive waste would be transported and ultimately disposed of
at a qualified low-level radioactive waste disposal facility,
potentially exposing it to the environment.
Further, data subject to the requested exemption from 10 CFR
72.154(b) is the data that comes from the test from which the licensee
is being exempted. Without the data from the test, the licensee cannot
satisfy 10 CFR 72.154(b). Thus, granting an exemption from the test
requirements but not from the record-keeping requirement would still
force the license to open and unload MPC 248, load the contents in new
MPC, and weld and test the new MPC, meaning all the potential negative
effects would still occur.
Based on the above, approving the requested exemption reduces the
opportunity for a release of radioactive material compared to the
alternative to the proposed action because there will be no operations
involving the opening of the MPC that confines the spent nuclear fuel,
potentially exposing radioactive waste to the environment. It will also
generate less radioactive waste for disposal. Thus, the proposed
exemption is consistent with NRC's mission to protect public health and
safety. Therefore, the requested exemption is otherwise in the public
interest.
Environmental Consideration
The NRC staff also considered in the review of this exemption
request whether there would be any significant environmental impacts
associated with the exemption. The NRC staff determined that this
proposed action fits a category of actions that do not require an
environmental assessment or environmental impact statement.
Specifically, the requested exemption meets the categorical exclusion
in 10 CFR 51.22(c)(25).
Granting an exemption from 10 CFR 72.212(a)(2), 10 CFR
72.212(b)(3), 10 CFR 72.212(b)(5)(i), 10 CFR 72.212(b)(11), and 10 CFR
72.214 would only relieve the licensee from the inspection requirement
found in TS 3.3 of Attachment B of CoC No. 1032. With this requested
exemption, the licensee would be exempt from the requirement to repeat
volumetric examination as required for the original weld on a 1-inch
portion of the repaired weld joining the canister baseplate to the
canister shell of the HI-STORM FW MPC 248. Granting an exemption from
10 CFR 72.154(b) only relieves the licensee from the recordkeeping
requirement associated with retaining and having available documentary
evidence of a complete volumetric examination of the subject weld. A
categorical exclusion for inspection requirements is provided under 10
CFR 51.22(c)(25)(vi)(C), and a categorical exclusion for recordkeeping
requirements is provided under 10 CFR 51.22(c)(25)(A). In both cases,
the criteria in 10 CFR 51.22(c)(25)(i)-(v) must also be satisfied.
In its review of the exemption request, the NRC staff determined,
that, in accordance with 10 CFR 51.22(c)(25): (i) Granting the
exemption does not involve a significant hazards considerations because
granting the exemption neither reduces a margin of safety, creates a
new or different kind of accident from any accident previously
evaluated, nor significantly increases either the probability or
consequences of an accident previously evaluated; (ii) granting the
exemption would not produce a significant change in either the types or
amounts of any effluents that may be released offsite because the
requested exemption neither changes the effluents nor produces
additional avenues of effluent release; (iii) granting the exemption
would not result in a significant increase in either occupational
radiation exposure or public radiation exposure, because the requested
exemption neither introduces new radiological hazards nor increases
existing radiological hazards; (iv) granting the exemption would not
result in a significant construction impact, because there are no
construction activities associated with the requested exemption; and
(v) granting the exemption would not increase either the potential for
or consequences from radiological accidents because, even with the
exemption, the canister will still be bounded by the FSAR analysis and
will remain leaktight, and the exemption creates no new accident
precursors at the STP ISFSI. Finally, as previously noted this
exemption request involves recordkeeping requirements and inspection
requirements under 10 CFR 51.22(c)(25)(A) and (C), respectively.
Accordingly, the requested exemption meets the criteria for a
categorical exclusion in 10 CFR 51.22(c)(25)(vi)(C).
IV. Availability of Documents
The documents identified in the following table are available to
interested persons through one or more of the previously described
methods.
------------------------------------------------------------------------
Document ADAMS accession No.
------------------------------------------------------------------------
South Texas Project, Units 1 and 2, ML22070B140
Docket Nos. 50-498; 50-499; 72-1041,
Independent Spent Fuel Storage
Installation, Request for Exemption
from Certificate of Compliance,
Inspection Requirement for One
Multipurpose Canister, dated March 11,
2022.
Request for Additional Information for ML22089A085
Review of the South Texas Project
Electric Generating Station
Independent Spent Fuel Storage
Installation, License No. SNM-2514,
dated March 31, 2022.
South Texas Project, Units 1 and 2, ML22091A308
Docket Nos. 50-498; 50-499; 72-1041,
Independent Spent Fuel Storage
Installation, Supplement to Request
for Exemption from Certificate of
Compliance (CoC) Inspection
Requirement for One Multipurpose
Canister, dated April 1, 2022.
Spent Fuel Project Office Interim Staff ML010100170
Guidance-15, Materials Evaluation,
Revision 0, January 10, 2001.
Issuance of Certificate of Compliance ML16280A008 *
No. 1032, Amendment No. 2 for the HI-
STORM Flood/Wind Multipurpose Canister
Storage System.
CoC No. 1032, Amendment No. 2 [Letter ML16280A017
to K. Manzione re: Issuance of
Certificate of Compliance No. 1032,
Amendment No. 2 for the HI-STORM Flood/
Wind Multipurpose Canister Storage
System].
[[Page 25561]]
Certificate of Compliance No. 1032, ML16280A019
Appendix B [Letter to K. Manzione re:
Issuance of Certificate of Compliance
No. 1032, Amendment No. 2 for the HI-
STORM Flood/Wind Multipurpose Canister
Storage System].
HI-2114830, Rev. 5, ``Final Safety ML17179A444
Analysis Report on the HI-STORM FW
FSAR MPC Storage System''.
NUREG-2215, ``Standard Review Plan for ML20121A190
Spent Fuel Dry Storage Systems and
Facilities''.
------------------------------------------------------------------------
* (Package).
V. Conclusion
Based on the foregoing considerations, the NRC staff has determined
that, pursuant to 10 CFR 72.7, the exemption is authorized by law, will
not endanger life or property or the common defense and security, and
is otherwise in the public interest. Therefore, the NRC grants the
licensee an exemption from the requirements of 10 CFR 72.212(a)(2), 10
CFR 72.212(b)(3), 10 CFR 72.212(b)(5)(i), 10 CFR 72.212(b)(11), and 10
CFR 72.214 only with regard to meeting the requirement to repeat
volumetric examination as required for the original weld on a 1-inch
portion of the repaired weld in conformance with Section III,
Subsection NB, of the ASME Code, 2007 Edition, and 10 CFR 72.154(b)
only with regard to maintaining and having available documentary
evidence of the test for the service life of the canister.
This exemption is effective upon issuance.
Dated: April 25, 2022.
For the Nuclear Regulatory Commission.
Yoira K. Diaz-Sanabria,
Chief, Storage and Transportation Licensing Branch, Division of Fuel
Management, Office of Nuclear Material Safety and Safeguards.
[FR Doc. 2022-09171 Filed 4-28-22; 8:45 am]
BILLING CODE 7590-01-P