ML22220A129
| ML22220A129 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 10/25/2022 |
| From: | Mahesh Chawla Plant Licensing Branch IV |
| To: | |
| Lingam S | |
| References | |
| EPID L-2021-LLE-0021, NRC-2022-0139, 87 FR 65618; 10/31/2022 | |
| Download: ML22220A129 (17) | |
Text
[7590-01-P]
NUCLEAR REGULATORY COMMISSION
[Docket No. 50-483; NRC-2022-0139]
Union Electric Company, dba Ameren Missouri
Callaway Plant; Unit No. 1
AGENCY: Nuclear Regulatory Commission.
ACTION: Exemption; issuance.
SUMMARY
- The U.S. Nuclear Regulatory Commission (NRC) is granting exem ptions
from certain portions of the acceptance criteria for emergency core cooling, and the
general design criteria for emergency core cooling, containment heat removal, and
atmosphere cleanup to allow the use of a risk-informed analysis to evaluate the effects
of debris in containment following a loss-of-coolant accident f or the Callaway Plant, Unit
No. 1 (Callaway) located in Callaway County, Missouri. The exe mptions are in response
to a request dated March 31, 2021, from Union Electric Company, doing business as
Ameren Missouri (the licensee) related to the licensees propos ed approach to resolve a
generic safety concern for pressurized water reactors associate d with potential clogging
of emergency core cooling and containment spray system strainer s during certain design
basis events.
DATES: The exemptions were issued on October 21, 2022.
ADDRESSES: Please refer to Docket ID NRC-2022-0139 when contacting the NRC
about the availability of information regarding this document. You may obtain publicly
available information related to this document using any of the following methods:
- Federal Rulemaking Website: Go to https://www.regulations.gov and
search for Docket ID NRC-2022-0139. Address questions about Docket IDs in
Regulations.gov to Stacy Schumann; telephone: 301-415-0624; em ail:
Stacy.Schumann@nrc.gov. For technical questions, contact the i ndividual listed in the
For Further Information Contact section of this document.
- NRCs Agencywide Documents Access and Management System
(ADAMS): You may obtain publicly available documents online in the ADA MS Public
Documents collection at https://www.nrc.gov/reading-rm/adams.ht ml. To begin the
search, select Begin Web-based ADAMS Search. For problems wi th ADAMS, please
contact the NRCs Public Document Room (PDR) reference staff at 1-800-397-4209,
301-415-4737, or by email to PDR.Resource@nrc.gov. The request for the exemptions
was submitted by letter dated March 31, 2021, as supplemented b y letters dated
May 27, 2021, July 22, 2021, August 23, 2021, October 7, 2021, January 27, 2022,
March 8, 2022, May 26, 2022, and September 8, 2022. For the co nvenience of the
reader, instructions about obtaining materials referenced in th is document are provided
in the Availability of Documents section.
- NRCs PDR: You may examine and purchase copies of public documents,
by appointment, at the NRCs PDR, Room P1 B35, One White Flint North, 11555
Rockville Pike, Rockville, Maryland 20852. To make an appointm ent to visit the PDR,
please send an email to PDR.Resource@nrc.gov or call 1-800-397-4209 or 301-415-
4737, between 8:00 a.m. and 4:00 p.m. Eastern Time (ET), Monday through Friday,
except Federal holidays.
FOR FURTHER INFORMATION CONTACT: Mahesh Chawla, Office of Nuclear
Reactor Regulation, U.S. Nuclear Regulatory Commission, Washing ton, DC 20555-
0001, telephone: 301-415-8371, email: Mahesh.Chawla@nrc.gov.
I. Availability of Documents
The documents identified in the following table are available to interested
persons through one or more of the following methods, as indica ted.
2 DOCUMENT ADAMS ACCESSION NO.
Ameren Missouri, letter to U.S. Nuclear Regulatory ML21090A184 (Package)
Commission, "Callaway Plant, Unit 1, Request for License Amendment and Regulatory Exemptions for a Risk-Informed Approach to Address GSI-191 and Respond to GL 2004-02 (LDCN 19-0014)," dated March 31, 2021.
Ameren Missouri, letter to U.S. Nuclear Regulatory ML21147A222 Commission, Callaway Plant, Unit 1, Supplement to Request for Licence Amendment and Regulatory Exemptions for a Risk-Informed Approach to Address GSI-191 and Respond to GL 2004-02 (LDCN 19-0014), dated May 27, 2021.
Ameren Missouri, letter to U.S. Nuclear Regulatory ML21203A192 (Package)
Commission, "Callaway Plant, Unit 1, Supplement to Request for License Amendment and Regulatory Exemptions for a Risk-Informed Approach to Address GSI-191 and Respond to GL-2004-02 (LDCN 19-0014), dated July 22, 2021.
Ameren Missouri, letter to U.S. Nuclear Regulatory ML21237A135 (Package)
Commission, Callaway Plant, Unit 1, Transmittal of Documents Identified from NRC Audit of License Amendment Request Regarding Risk-Informed approach to Closure of Generic Safety Issue 191 (EPID L-2021-LLA-0059), dated August 23, 2021.
Ameren Missouri, letter to U.S. Nuclear Regulatory ML21280A378 (Package)
Commission, "Callaway Plant, Unit 1, Third Supplement to Request for License Amendment and Regulatory Exemptions for a Risk-Informed Approach to Address GSI-191 and Respond to GL-2004-02 (LDCN 19-0014)
(EPID L-2021-LLA-0059 and EPID L-2021-LLE-0021),"
dated October 7, 2021.
Ameren Missouri, letter to U.S. Nuclear Regulatory ML22027A804 (Package)
Commission, "Callaway Plant, Unit 1, Fourth Supplement to Request for License Amendment and Regulatory Exemptions for a Risk-Informed Approach to Address GSI-191 and Respond to GL-2004-02 (LDCN 19-0014) (EPID L-2021-LLA-0059 and EPID L-2021-LLE-0021)," dated January 27, 2022.
Ameren Missouri, letter to U.S. Nuclear Regulatory ML22068A027 (Package)
Commission, "Callaway Plant, Unit 1, Fifth (Post-Audit)
Supplement to Request for License Amendment and Regulatory Exemptions for a Risk-Informed Approach to Address GSI-191 and Respond to GL 2004-02 (LDCN 19-0014) (EPID L-2021-LLA-0059 and EPID L-2021-LLE-0021)," dated March 8, 2022.
3 DOCUMENT ADAMS ACCESSION NO.
Ameren Missouri, letter to U.S. Nuclear Regulatory ML22146A337 (Package)
Commission, "Callaway Plant, Unit 1, Response to Request for Additional Information Regarding Request for License Amendment and Regulatory Exemptions for Risk-Informed Approach to Address GSI-191 and Respond to Generic Letter 2004-02 (LDCN 19-0014)
(EPID L-2021-LLA-0059 and EPID L-2021-LLE-0021),"
dated May 26, 2022.
Ameren Missouri, letter to U.S. Nuclear Regulatory ML22251A343 Commission, "Callaway Plant, Unit 1, Correction of Text Contained in Enclosures Provided with Supplements to Request for License Amendment and Regulatory Exemptions for a Risk-Informed Approach to Address GSI-191 and Respond to Generic Letter 2004-02 (LDCN 19-0014) (EPID L-2021-LLA-0059 and EPID L-2021-LLE-0021)," dated September 8, 2022.
SUPPLEMENTARY INFORMATION: The text of the exemption is attached.
Dated: October 25, 2022.
For the Nuclear Regulatory Commission.
/RA/
Mahesh L. Chawla, Project Manager, Plant Licensing Branch IV, Division of Operating Reactor Licensing, Office of Nuclear Reactor Regulation.
4 Attachment - Exemption.
NUCLEAR REGULATORY COMMISSION
Docket No. 50-483
Union Electric Company
Callaway Plant, Unit No. 1
Exemptions
I. Background
Union Electric Company, doing business as (dba) as Ameren Misso uri (the
licensee), is the holder of Renewed Facility Operating License No. NPF-30, which
authorizes operation of the Callaway Plant, Unit No. 1 (Callawa y). The license provides,
among other things, that the facility is subject to all rules, regulations, and orders of the
U.S. Nuclear Regulatory Commission (NRC) now or hereafter in ef fect. The facility
consists of a pressurized-water reactor (PWR) located in Callaw ay County, Missouri.
In 1996, the NRC identified Generic Safety Issue (GSI)-191, As sessment of
Debris Accumulation on PWR Sump Performance, associated with t he effects of debris
accumulation on PWR sump performance during design-basis accide nts. As part of the
actions to resolve GSI-191, the NRC issued Generic Letter (GL) 2004-02, Potential
Impact of Debris Blockage on Emergency Recirculation during Des ign Basis Accidents
at Pressurized-Water Reactors, dated September 13, 2004 (ML042 360586), to holders
of operating licenses for PWRs. In GL 2004-02, the NRC staff re quested that licensees
perform an evaluation of their emergency core cooling systems ( ECCS) and containment
spray system (CSS) recirculation functions considering the pote ntial for debris-laden
coolant to be circulated by the ECCS and the CSS after a loss-o f-coolant accident
(LOCA) or high energy line break inside containment and, if app ropriate, take additional
5 actions to ensure system function. GL 2004-02 required that lic ensees provide a written
response to the NRC, pursuant to Title 10 of the Code of Federal Regulations (10 CFR)
Section 50.54(f), describing the results of their evaluation an d any modifications made,
or planned, to ensure the ECCS and CSS remain functional.
II. Request/Action
By application dated March 31, 2021, (Agencywide Documents Acce ss and
Management System (ADAMS) Accession No. ML21090A184), as supple mented by
letters dated May 27, 2021, July 22, 2021, August 23, 2021, Oct ober 7, 2021,
January 27, 2022, March 8, 2022, May 26, 2022, and September 8, 2022
(ML21147A222, ML21203A192, ML21237A135, ML21280A378, ML22027A804,
ML22068A027, ML22146A337, and ML22251A343, respectively), the licensee, pursuant
to 10 CFR 50.12, Specific exemptions, requested exemptions fr om certain
requirements of 10 CFR 50.46, Acceptance criteria for emergenc y core cooling systems
for light-water nuclear power reactors, and 10 CFR Part 50, Ap pendix A, General
Design Criterion (GDC) 35, Emergency core cooling; GDC 38, C ontainment heat
removal; and GDC 41, Containment atmosphere cleanup, to allo w use of a risk-
informed methodology instead of the traditional deterministic m ethodology, to resolve the
concerns associated with GSI-191, and respond to GL 2004-02 for Callaway.
Specifically, the licensee requested exemptions from 10 CFR 50. 46(a)(1)(i),
which, in part, requires the ECCS cooling performance to be cal culated in accordance
with an acceptable evaluation model as described in 10 CFR 50.4 6(a)(1), and for
postulated LOCAs of different sizes, locations and other proper ties sufficient to provide
assurance that the most severe LOCAs are evaluated. The NRC sta ff interprets the
Section 50.46(a)(1) requirement to calculate ECCS performance f or other properties as
requiring licensees to consider the impacts of debris generatio n and transport in
6 containment. The most significant form of debris in nuclear pow er reactor containments
is piping and component insulation that can become debris durin g LOCAs, transport and
accumulate in the sumps, and clog the sumps strainers, thus cre ating resistance to
coolant flow. Fibrous debris from this insulation can also ente r the reactor core and
directly impede heat transfer from the fuel to the coolant.
The approval of a risk-informed methodology would require exemp tions from
10 CFR 50.46(a)(1)(i) and GDCs 35, 38, and 41 because the NRC h as interpreted these
regulations as requiring a deterministic approach and bounding calculation to show
compliance with ECCS and CSS performance criteria in 10 CFR 50. 46(b) and GDCs 35,
38, and 41. Issuance of exemptions is an appropriate means to g rant relief from the use
of a deterministic approach to show compliance with these requi rements.
The licensees 10 CFR 50.46 deterministic analysis considered t he debris in
containment and demonstrated that the debris loading could prev ent acceptable ECCS
and CSS operation and core cooling for certain pipe ruptures. B ased on its analysis, the
licensee concluded that the amount of debris in the Callaway co ntainment would need to
be reduced to demonstrate compliance with 10 CFR 50.46 criteria using a deterministic
analysis for certain large-break LOCA sizes because, for those breaks, the plant-specific
testing threshold for generation and transport of debris was ex ceeded.
Additionally, the licensees deterministic in-vessel analysis w as limited to breaks
that could generate and transport to the strainers fibrous debr is amounts in excess of the
plant-specific tested debris limit for the strainers. This valu e was chosen because it also
represents the deterministic limit for strainer failure for pip e breaks. Therefore, any break
that generates and transports more than the amount of fibrous d ebris bounded by plant
testing is already assumed to cause strainer failure and increa se core damage
frequency. Because these large breaks are already assumed to co ntribute to plant risk
7 because of strainer failure, there is no need to evaluate them for risk contribution due to
in-vessel failure. Other debris types were bounded by the strai ner evaluation and are not
critical to the in-vessel analysis. Therefore, all cases where core damage might occur
due to debris arriving at the core are already covered by scena rios that cause strainer
failure and do not need to be counted as additional increases i n risk.
The licensee requested exemptions from the requirement to use a deterministic
analysis for specific scenarios of LOCA breaks producing and tr ansporting debris in
excess of the plant-specific tested debris limits. Since it det ermined that the probability of
consequences from debris effects is very low, the licensee requ ested exemptions to
allow the use of a risk-informed analysis to show adequate assu rance of ECCS and CSS
functionality, in accordance with the criteria in Regulatory Gu ide (RG) 1.174, Revision 3,
An Approach for Using Probabilistic Risk Assessment in Risk-In formed Decisions on
Plant-Specific Changes to the Licensing Basis, dated January 2 018 (ML17317A256).
RG 1.174 was developed in consideration of the Commissions Pol icy Statements on
safety goals1 and the use of probabilistic risk assessment methods in nuclear regulatory
activities.2 Therefore, RG 1.174 provides an acceptable method for licensee s and NRC
staff to use in assessing the impact of licensing basis changes when the licensee
chooses to use risk information.
The requirements in GDC 35 require, in part, that the ECCS safe ty system
functions adequately to transfer heat from the reactor core fol lowing a LOCA and in the
presence of a worst single failure, at a rate such that (a) fue l and clad damage that could
1 Commissions Safety Goal Policy Statement, Safety Goals for the Operations of Nuclear Power Plants; Policy Statement, published in the Federal Register on August 4, 1986 (51 FR 28044), as corrected, and republished, on August 21, 1986 (51 FR 30028).
2 Use of Probabilistic Risk Assessment Methods in Nuclear Activities; Final Policy Statement, August 16, 1995 (60 FR 42622).
8 interfere with continued effective core cooling is prevented an d (b) clad metal-water
reactor is limited to negligible amounts. The licensee stated i n its application dated
March 31, 2021, that the function of the ECCS emergency sump is assumed to fail for
scenarios where debris exceeds the amount determined in accepta ble plant-specific
testing. Failure of the sump and strainers results in loss of c ooling to the core. The
licensee requested exemptions from the requirements of GDC 35, which requires the
use of a deterministic approach, for those LOCA breaks that exc eed the plant-specific
testing debris threshold. The licensee requested exemptions fro m the deterministic
requirements of GDC 35, to allow the use of a risk-informed ana lysis, in accordance with
the criteria in RG 1.174, to show that the risk from debris eff ects is very low.
The requirements in GDC 38 require containment heat removal, ra pid reduction
of containment pressure and temperature, and maintenance of pre ssure and
temperature at an acceptably low level following a LOCA, and in the presence of a single
failure, to preserve containment function. The licensee propose d that exemptions be
granted from the requirements in GDC 38 that specify the use of a deterministic
approach. The request applies only to those LOCA breaks that ex ceed the plant-specific
testing debris threshold. Current Callaway design basis calcula tions are based on the
containment cooling system (cont ainment fan coolers) functionin g in conjunction with the
CSS and ECCS, both of which can be affected by debris. Using de terministic
assumptions, the licensees analysis and testing does not assur e that the emergency
sump strainers will be available to support the CSS and ECCS fu nction considering the
effects of debris produced by those breaks that can generate an d transport debris
amounts greater than the plant-specific testing threshold. The licensee requested
exemptions from the deterministic requirements of GDC 38 to all ow the use of a risk-
informed analysis, in accordance with the criteria in RG 1.174, to show that the risk from
9 debris effects is very low.
The requirements in GDC 41, require, in part, containment atmos phere cleanup
to control substances that may be released into the reactor con tainment, to reduce the
concentration and quality of fission products released to the e nvironment following
postulated accidents, and to control the concentration of hydro gen or oxygen and other
substances in the containment atmosphere following postulated a ccidents, assuming a
single failure. The licensee stated that using deterministic as sumptions, its analysis and
testing cannot demonstrate that the emergency sump strainers wi ll be available to
support the CSS function considering the effects of debris prod uced and transported by
breaks not bounded by acceptable plant-specific testing. The li censee requested
exemptions from the deterministic requirements of GDC 41 to all ow the use of a risk-
informed analysis, in accordance with the criteria in RG 1.174, to show that the risk from
debris effects is very low.
III. Discussion
Pursuant to 10 CFR 50.12, the Commission may, upon application by any
interested person or upon its own initiative, grant exemptions from the requirements of
10 CFR Part 50, when (1) the exemptions are authorized by law, will not present an
undue risk to public health or safety, and are consistent with the common defense and
security; and (2) when special circumstances are present. Under 10 CFR 50.12(a)(2)(ii),
special circumstances are present when [a]pplication of the re gulation in the particular
circumstances would not serve the underlying purpose of the rul e or is not necessary to
achieve the underlying purpose of the rule.
The licensee proposed to use a risk-informed methodology instea d of a
deterministic approach to account for the effects of debris in containment for portions of
the LOCA analysis applicable to breaks that exceed the Callaway plant-specific debris
10 testing threshold. The licensees methodology, termed Risk over Deterministic, or
RoverD, divides the loss of core cooling design-basis analysis into two portions: the
deterministic analysis and the risk-informed analysis. The risk-informed analysis is
used by the licensee for breaks that generate and transport deb ris exceeding the plant-
specific testing threshold. These breaks result in fibrous debr is estimated to arrive in the
ECCS sump post-LOCA in amounts that are equal to or greater tha n the amount of fiber
used in acceptable strainer testing. The acceptable limit was d etermined using testing
methods intended to determine the maximum ECCS strainer head lo ss for the tested
condition.
Also, the licensee evaluated the in-core aspects of fibrous deb ris to prevent
adequate fuel cooling. The licensee found that for in-vessel ef fects, all breaks that
generate and transport fibrous debris amounts less than the str ainer acceptance
criterion can be evaluated deterministically and shown to have acceptable outcomes.
Therefore, the in-vessel effects do not contribute to changes i n core damage frequency.
For ECCS and CSS analyses other than the postulated large-break LOCAs that
generate less than the strainer acceptance limit, the licensee applied a deterministic
methodology. If the exemptions were granted for these postulate d breaks, the
requirement to use a deterministic methodology for all other po stulated LOCA breaks
would continue to apply.
A. The Exemptions are Authorized by Law
The exemptions would allow the use of a risk-informed methodolo gy to show
compliance with 10 CFR 50.46(a)(1)(i), and GDCs 35, 38, and 41 of Appendix A to
10 CFR Part 50, when considering debris in containment generate d and transported by
those breaks that exceed the plant-specific testing threshold. These regulations were
11 promulgated under and are consistent with the Commissions auth ority under
Section 161 of the Atomic Energy Act of 1954, as amended. Becau se the application of
a risk-informed methodology to show compliance with 10 CFR 50.4 6, and GDC 35, 38,
and 41 of Appendix A to 10 CFR Part 50, would not violate the A tomic Energy Act of
1954, as amended, or the Commissi ons regulations, the exemptio ns are authorized by
law provided all requisite findings are made.
B. The Exemptions Present no Undue Risk to Public Health and Safety
The provisions of 10 CFR 50.46 and GDCs 35, 38, and 41 of Appen dix A to
10 CFR Part 50 establish criteria for the emergency core coolin g, containment cooling,
and containment atmosphere cleanup system performance. As part of the amendment
request, the licensee submitted exemption requests to change it s design-basis analysis
specified in the Updated Final Safety Analysis Report (UFSAR) t o allow use of risk-
informed and deterministic methodologies to specifically accoun t for the impacts of
debris in containment. The licensee justified its use of the ri sk-informed approach by
stating that the proposed risk-informed approach meets the key principles in RG 1.174,
Revision 3, in that it is consistent with defense-in-depth phil osophy, maintains sufficient
safety margins, results in a small increase in risk, and is mon itored by the licensee using
performance measurement strategies.
Additionally, the licensee stated that the proposed exemptions, to allow use of
the risk-informed method, are consistent with Key Principle 1 i n RG 1.174 that requires a
proposed change to the licensing basis (or amendment) to meet c urrent regulations
unless the change is explicitly related to requested exemptions. The probabilistic risk
analysis results provided by the licensee and evaluated by the NRC staff in its safety
evaluation, showed that the increase in risk associated with de bris generation and
transport on ECCS and CSS function following postulated LOCAs i s very small, in
12 accordance with the criteria in RG 1.174.
The NRC staff concluded that the risk is consistent with the gu idance in
RG 1.174 and with the Commission policy statements on safety go als and the use of
probabilistic risk assessment met hods in nuclear regulatory act ivities; therefore, the
requested exemptions present no undue risk to public health and safety.
C. The Exemptions are Consistent with the Common Defense and Se curity
The requested exemptions would allow the licensee to use a risk -informed
methodology to resolve a generic safety concern for PWRs associ ated with potential
clogging of the ECCS and CSS strainers during certain design-ba sis events. The change
is adequately controlled by safety acceptance criteria and tech nical specification
requirements and is not related to security issues. Because the common defense and
security is not impacted by the exemptions, the exemptions are consistent with the
common defense and security.
D. Special Circumstances
Under the regulations in 10 CFR 50.12, the Commission may grant exemptions
from the requirements of 10 CFR Part 50 provided certain findin gs are made; namely,
that special circumstances are present, the exemptions present no undue risk to public
health and safety, the exemptions are consistent with the commo n defense and security,
and the exemptions are authorized by law. The exemptions would allow the use of a
risk-informed methodology to show compliance with 10 CFR 50.46( a)(1)(i), and
GDCs 35, 38, and 41 of Appendix A to 10 CFR Part 50, specifical ly for the analyses of
debris in containment impacting emergency cooling function duri ng postulated large-
break LOCAs that exceed the plant-specific testing threshold.
The licensee requested exemptions citing the special circumstan ces criteria of
10 CFR 50.12(a)(2)(ii), because compliance in the particular ci rcumstances would not
13 serve the underlying purpose of the rule or is not necessary to achieve the underlying
purpose of the rule. The licensee cited these special circumsta nces for all of the
requested exemptions.
The licensee stated that an objective of each of the regulation s for which
exemptions are proposed is to maintain low risk to the public h ealth and safety through
the adequate functioning of the ECCS and CSS safety systems. Th ese systems must be
supported by adequate functioning of the containment sumps. The regulations in
10 CFR 50.46(a)(1)(i) and GDCs 35, 38, and 41 of Appendix A to 10 CFR Part 50 are
met when the licensee can demonstrate, using a bounding calcula tion or other
deterministic method that the ECCS and CSS are capable of funct ioning during design
basis events. The licensee stat ed that its risk-informed analys is to show adequate
functioning of ECCS and CSS, considering the impacts of debris during certain LOCA
events, demonstrates that the ECCS and CSS systems will operate with a high degree
of reliability. The licensee stated that special circumstances exist because the underlying
intent of the regulations, to ensure adequate protection of pub lic health and safety is met
when applying a risk-informed approach to address GSI-191 and r esponding to
GL 2004-02. Further, it states that the risk-informed approach is consistent with
RG 1.174 and supports operation of those functions with a high degree of reliability.
Thus, the licensee concludes tha t the underlying intent of each regulation is met, and the
special circumstances described in 10 CFR 50.12(a)(2)(ii) apply to each of the
exemptions proposed by the licensee.
The NRC staff evaluated the licensees application, as suppleme nted and
discussed the details of its evaluation of the risk-informed ap proach in an NRC safety
evaluation available under ADAMS Accession No. ML22220A132. Alt hough
10 CFR 50.46(a)(1) requires a deterministic approach, the GDCs do not specify that a
14 risk-informed methodology may not be used to show compliance; h owever, because the
NRC has interpreted each of these regulations as requiring a de terministic approach,
exemptions are an appropriate means to grant the licensee relie f to use an alternative
approach. The underlying purpose of each regulation is to prote ct public health and
safety in the event of a LOCA by establishing criteria for emer gency core cooling,
containment cooling and containment atmosphere cleanup system p erformance. In its
safety evaluation, the NRC staff concluded, in part, that the l icensee adequately
demonstrated that the change in risk attributable to debris tha t exceed the plant specific
threshold is very small and meets the risk acceptance guideline s in RG 1.174. The NRC
staff also concluded that the analysis is consistent with defen se-in-depth philosophy,
maintains sufficient safety margins, results in a small increas e in risk, and is monitored
by the licensee using performance measurement strategies. There fore, the licensees
use of the risk-informed analysis meets the underlying requirem ents of 10 CFR 50.46
and GDCs 35, 38, and 41 of Appendix A to 10 CFR Part 50, to ens ure that a licensee
demonstrates that the ECCS and CSS will provide adequate coolin g for the reactor core
and containment and provide containment atmosphere cleanup duri ng design-basis
accidents considering the impacts of debris, since it meets the guidelines in RG 1.174.
Based on the above, the NRC staff concludes that special circum stances under
10 CFR 50.12(a)(2)(ii) exist because compliance with the determ inistic requirements of
10 CFR 50.46(a)(1)(i), and GDCs 35, 38, and 41 of Appendix A to 10 CFR Part 50 is not
necessary to achieve the underlying purpose of each rule.
E. Supplemental Information
For more technical details, refer to the SE associated with th ese exemptions
under ADAMS Accession No. ML22220A130 (enclosure 2).
15 F. Environmental Considerations
Pursuant to 10 CFR 51.21, Criteria for and identification of l icensing and
regulatory actions requiring environmental assessments, the NR C has prepared an
environmental assessment (EA) and finding of no significant imp act (FONSI)
summarizing the findings of its review of the environmental imp acts of the proposed
action under the National Environmental Policy Act (NEPA). The NRC staff determined
that special circumstances under 10 CFR 51.21 exist to warrant preparation of an EA
and FONSI because Callaway is proposing a risk-informed approac h to resolve GSI-191
as recognized in Staff Requirement Memorandum SECY-12-0093, Closure Options for
Generic Safety Issue-191, Assessment of Debris Accumulation on Pressurized-Water
Reactor Sump Performance, dated December 14, 2012 (ML12349A378 ). Because this
action uses risk information to justify exemptions from determi nistic regulations, the NRC
staff considered preparations of an EA and FONSI to be a pruden t course of action that
would further the purposes of NEPA. Based on its review, the NR C concluded that an
environmental impact statement is not required and that the pro posed action will have no
significant impact on the environment.
The NRC published a final EA and FONSI on the proposed action i n the Federal
Register on August 29, 2022 (87 FR 52816).
IV. Conclusions
Accordingly, the Commission has determined that, pursuant to 10 CFR 50.12,
exemptions are authorized by law, will not present an undue ris k to the public health and
safety, are consistent with the common defense and security, an d special circumstances
are present pursuant to 10 CFR 50.12(a)(2)(ii). Therefore, the NRC hereby grants Union
Electric Company, dba Ameren Missouri, one-time exemptions from 10 CFR 50.46(a)(1),
16 and 10 CFR Part 50, Appendix A, GDCs 35, 38, and 41 to allow th e use of a risk-
informed methodology in lieu of a deterministic methodology to show conformance with
the ECCS and CSS performance criteria accounting for debris in containment for those
breaks that exceed the plant-specific Callaway testing threshol d.
Dated at Rockville, Maryland, this 21 st day of October 2022.
For the Nuclear Regulatory Commission.
/RA/
Gregory F. Suber, Deputy Director, Division of Operating Reactor Licensing, Office of Nuclear Reactor Regulation.
17