ML22224A059
| ML22224A059 | |
| Person / Time | |
|---|---|
| Issue date: | 10/12/2022 |
| From: | Meraj Rahimi NRC/RES/DE/RGDB |
| To: | |
| Karagiannis H | |
| References | |
| NRC-2022-0052 RG 1.247 Trial | |
| Download: ML22224A059 (7) | |
Text
[7590-01-P]
NUCLEAR REGULATORY COMMISSION
[NRC-2022-0052]
Acceptability of Probabilistic Risk Assessment Results for Non-Light Water
Reactor Risk-Informed Activities
AGENCY: Nuclear Regulatory Commission.
ACTION: Regulatory guide for trial use; response to comments.
SUMMARY
- The U.S. Nuclear Regulatory Commission (NRC) is addressing co mments
received after issuing for public comment and trial use a new r egulatory guide (RG)
1.247, Acceptability of Probabilistic Risk Assessment Results for Non-Light Water
Reactor Risk-Informed Activiti es. The NRC will not make any changes to the RG as a
result of these comments.
DATES: The public comment period for RG 1.247 ended on May 23, 2022.
ADDRESSES: Please refer to Docket ID NRC-2022-0052 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-2022-0052. 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 ndividuals 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 ADAMS a ccession number
for each document referenced (if it is available in ADAMS) is p rovided the first time that it
is mentioned in this document.
- NRCs 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 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.
RG 1.247 for trial use and the regulatory analysis may be found in ADAMS under
Accession Nos. ML21235A008 and M L21235A010, respectively.
Regulatory guides are not copyrighted, and NRC approval is not required to
reproduce them.
FOR FURTHER INFORMATION CONTACT: Michelle Gonzalez, telephone:
301-415-5661, email: Michelle.Gonzalez@nrc.gov, Anders Gilbertson,
telephone: 301-415-1541, email: Anders.Gilbertson@nrc.gov, or Harriet
Karagiannis, telephone: 301-415-2493, email: Harriet.Karagian nis@nrc.gov.
These individuals are staff in the Office of Nuclear Regulatory Research at the
U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001.
SUPPLEMENTARY INFORMATION:
I. Background
The NRC has issued for trial use this new RG titled, Acceptability of Probabilistic
Risk Assessment Results for Non-Light Water Reactor Risk-Inform ed Activities, and it is
designated as trial use RG 1.247. It describes one acceptable approach for determining 2
whether a design-specific or plant-specific probabilistic risk assessment (PRA) used to
support an application is sufficient to provide confidence in t he results, such that the
PRA can be used in regulatory decision-making for non-light wat er reactors (NLWRs) for
implementing the requirements in Part 50 and 52 of title 10 of the Code of Federal
Regulations (10 CFR). In addition, this trial use RG is intended to be co nsistent with the
NRCs PRA Policy Statement and reflects and endorses, with staf f exceptions, national
consensus PRA standards provided by standards development organ izations and
guidance provided by nuclear industry organizations. As a tria l use RG, this issuance
allows early use prior to general implementation, and the guida nce may be revised
based on experience obtained by t he NRC from the implementation of the trial use RG.
The staff is planning to conduct a public meeting by the end of calendar year
2022 to obtain stakeholder feedback on the development of a dra ft guide, which will be
issued at the conclusion of the trial use period, and subsequen t final publication of
RG 1.247. The NRC will also provide an additional opportunity for formal public
comment on the planned draft RG, with feedback considered prior to final RG
publication.
II. Public Comments
This trial use RG was not published for public comment as a dra ft RG. Trial use
RG 1.247 was issued for a 60-day, post-promulgation public comm ent in the Federal
Register on March 24, 2022 (87 FR 16770). Pursuant to 10 CFR 2.804(e), the NRC
must publish in the Federal Register an evaluation of any significant comments and
describe any revisions made as a result of the comments and the ir evaluation.
The public comment period ended on May 23, 2022, and comments w ere
received from two organizations ( Nuclear Energy Institute (NEI) and X-energy). NEI and
X-energy submitted separate comments on the staff endorsement o f items HLR-HR-E 3
and HR-E4 from the American Society of Mechanical Engineers (AS ME) and American
Nuclear Society (ANS) NLWR PRA standard. The staff considers t hese comments
significant to the extent they warrant a response to clarify th e record. While the staff is
not responding in this notice to the other comments submitted i n response to the
opportunity to comment the NRC published at 87 FR 16770, the st aff will consider those
comments in preparing a draft of RG 1.247 for comment or in con sidering the experience
obtained through trial use of RG 1.247.
For items HLR-HR-E and HR-E4, the staff takes exceptions to the ASME and
ANS NLWR PRA standard regarding the treatment of errors of comm ission (EOCs) in a
PRA. The exceptions provide for consideration of EOCs that res ult in adverse safety
impacts for Compatibility Category I, (CC-I). CC-I defines the minimum capability
needed for a PRA element. In contrast, Compatibility Category II (CC-II) defines the
minimum capability needed to meet current good practice standar ds for each PRA
element. The comments indicate that these exceptions are not c onsistent with the
current PRA state of practice, which does not call for broad co nsideration of EOCs for
PRAs for LWRs as per the NRC endorsement of HR-E4 in the trial use RG. Thus, the
comment contends that broadly considering EOCs goes above and b eyond the
requirement for the current operating fleet. Although no chang es were made to the trial
use RG based on these comments, the staff provides a brief disc ussion on these
significant comments.
Specifically, the comment recommends that this exception to HR-E4 and the
HLR-HR-E be removed from the trial use RG or only be applicable for
CC-II of HR-E4, the latter of which would represent good practi ce as opposed to a
minimum capability. Another comment notes that the trial use R G 1.247 includes
additional language on the scope of such considerations; howeve r, the comment states 4
that this added language does not maintain consistency with the LWR PRA standard.
The comment supports retaining consistency with the LWR PRA sta ndard in the trial use
RG 1.247, which would call for removal of this added exception regarding consideration
of EOCs in the NLWR PRA standard.
The staff is keeping the exceptions related to EOCs in this tri al use RG, which is
based on the following consideration. The development efforts for the ASME/ANS
NLWR PRA standard relied substantially on the development effor ts for the next edition
of the ASME/ANS Level 1/large early release frequency (LERF) LW R PRA standard
and, in many cases, the NLWR PRA standard adopted the same or s imilar requirements
as the next edition of the Level 1/LERF LWR PRA standard. Howe ver, the Level
1/LERF LWR PRA standard state of practice relies on significant LWR operating
experience that facilitates a consensus to generally exclude EO Cs from LWR PRAs, but
no similar body of operating experience underlies the NLWR PRA standard.
Because there is limited operating experience regarding EOCs fo r NLWRs and
the scope of the ASME/ANS NLWR PRA standard is broader than the scope of the
ASME/ANS Level 1/LERF LWR PRA standard, EOCs may play a more im portant role in
NLWR PRA than for LWR PRA and, therefore, NLWR PRA developers w ill need to
demonstrate that EOCs are not an issue before eliminating them from consideration.
However, the staff also notes that such identification of EOCs is generally expected to
apply to a PRA developed for the operational phase of a plants lifecycle. This is based
on the premise that there is expected to be a general lack of a vailable, relevant
information that would allow meaningful identification of EOCs in pre-operational stages
of a plants lifecycle. Related staff guidance on the treatmen t of such EOCs during pre-
operational phases of a plants lifecycle is currently under de velopment.
A comment states that EOCs are already captured in FHR-A1 at CC -II for fires 5
where operating experience supports consideration of spurious s ignals. Therefore, the
comment notes that the RG 1.247 position on HR-E4 requiring EOC s at CC-I is not
internally consistent with the trial use RG position on FHR-A1 requiring EOCs only at
CC-II. The comment also states that, for non-fire hazards, spu rious signals should occur
with low frequency and would require significant operator error due to the redundancy of
information available to the operator.
The staff notes that, while the consideration of spurious signa ls as a potential
cause of an EOC is important and spurious signals may occur due to fire damage, such
spurious signals are not the only reason an EOC may occur. NUR EG-1880, ATHEANA
Users Guide, (ADAMS Accession No. ML072130359) recommends sea rching for
potential EOCs and the contexts that could cause them. However, while the staff
maintains that other sources of EOCs should be considered for i dentification in CC-I of
FHR-A1, the staff did not intend for new, undesired operator ac tions that could result
from spurious indications from fire-induced failure of a single instrument to be identified
to meet CC-I of FHR-A1. The staff would therefore not call for such identification as part
of meeting the trial use RG. The staff notes that while the co mment characterizes the
staff positions as requirements, no regulatory guide establis hes requirements. Rather,
6 the exceptions and clarifications in a regulatory guide are gui dance to an applicant
stating elements of an acceptable method for complying with NRC regulations.
Dated: October 12, 2022.
For the Nuclear Regulatory Commission.
/RA/
Meraj Rahimi, Chief, Regulatory Guide and Programs Management Branch, Division of Engineering, Office of Nuclear Regulatory Research.
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