ML24120A350
| ML24120A350 | |
| Person / Time | |
|---|---|
| Issue date: | 05/01/2024 |
| From: | Mike Franovich NRC/NRR/DRA/ARCB |
| To: | |
| References | |
| Download: ML24120A350 (37) | |
Text
Information Sharing Public Meeting Update to Regulatory Guide 1.183, Revision 1, Alternative Radiological Source Terms for Evaluating Design Basis Accidents at Nuclear Power Reactors May 1, 2024 ADAMS Accession No. ML24120A350
Introductions
Please ensure to identify yourself before speaking throughout the meeting.
3 ADAMS ML24120A350 NRC Opening Remarks Michael Franovich, Director Division of Risk Assessment Office of Nuclear Reactor Regulation
Agenda
- Background
- Methods of Stakeholder Involvement
- Schedule
- Workshop Overview/Takeaways
- Priorities
- Selected Topics for Discussion 4
Background - What/Why Revision 0 - Implementing guidance for 10 CFR 50.67, Accident Source Term Identified the significant attributes of an acceptable accident AST based largely on NUREG-1465, Accident Sources Terms for Light-Water Nuclear Power Plants (1995) provides assumptions and methods that are acceptable to the NRC staff for performing design basis radiological analyses using an AST Revision 1 - Incorporated improved understanding of source term behavior and expanded applicability to higher burnups Revision 2 -
Safely enable applicability to higher burnups and increased enrichments Address implementation issues Refine conservatisms and allow flexibility in analysis approaches Maintain adequate protection and reflect NRC commitments to Principles of Good Regulations See supplementary slides for additional information on RG process.
Background (Contd)
Increased Enrichment Rulemaking
- Docket ID NRC-2020-0034, www.regulations.gov
- Regulatory Basis comment period ended on January 22, 2024
- Alternative 2 for Control Room Dose Criteria proposed changes to criteria
- Staff has been developing draft guidance in case this alternative is selected
- Per NRC policy to reduce the cumulative effects of regulation, implementing guidance should be developed with proposed rules
- Important Point - Rulemaking is separate from guidance development 6
ADAMS ML24120A350 Stakeholder engagement for the rulemaking is through Regulations.gov.
Stakeholder Involvement
- Staff aiming to be responsive to feedback
- Public Workshops and Information Meetings
- 3 Workshops (1/9/24, 2/13/24 and 3/8/24)
- 2 Information Meetings
- Contact Project Leads
- Meeting Feedback
- ACRS Briefings - approximately October/November 2024
- Draft Guide Comment Period - approximately June 2025
- Relationship with Proposed Increased Enrichment Rulemaking
- Docket ID NRC-2020-0034, www.regulations.gov
- Comment period on Proposed Increased Enrichment Rulemaking Regulatory Basis ended on January 22, 2024 7
8 ADAMS ML24120A350 Project Schedule Milestone Tentative Completion Public Workshops* and Information Meetings**
January 2024 - June 2024 DG Internal Review begins June 2024 DG Internal Review completed October 2024 Pre-Decisional DG Publicly Available to Support ACRS Briefings October/November 2024 ACRS Briefings (Staff to respond as needed)
October/November 2024 Increased Enrichment Proposed Rule package to Commission (will include DG referenced in SECY paper)
December 2024 DG Available for Public Comment via Proposed IAW Increased Enrichment Rulemaking SECY June 2025 (Estimated)
- The term Workshop means a Comment-Gathering Meeting as described in the NRCs policy statement on public meetings (see 86 FR 14964)
- The term Information Meeting means NRC will inform attendees and allow questions (see 86 FR 14964)
Workshop Review Opportunities for staff and external stakeholders to present ideas and draw attention to issues Great participation from external stakeholders
- ~100 participants Substantive discussions and opportunity for participation early in the regulatory process 9
Workshop Review (Contd)
Staff takeaways
- Clarification needed on the purpose of the maximum hypothetical accident
- Desire for clarification of certain case-by-case reviews
- Industry Priorities:
10 ADAMS ML24120A350
NRC Priorities for RG 1.183 Update Ensuring adequate protection and meeting commitment to the Principles of Good Regulation Changes that implement Increased Enrichment Rulemaking Develop guidance for pathway specific source terms Address potential implementation issues
- Staff Items (e.g., items related to DPO 2020-002 and DPO 2021-001)
- Resolve version consolidation/backfit question
- Steam Line and Containment Removal Coefficients
- Non-LOCA Release Fractions
- Non-LOCA FFRD
- Clarification of Environmental Qualification (EQ)
Process improvements
- Refine Conservatisms
- Added Flexibility 11 ADAMS ML24120A350
Priority Mapping NRC Priorities Adequate protection/POGR Changes to enable Increased Enrichment Rulemaking Develop implementing guidance for pathway specific source terms Address potential guidance implementation issues Select DPO Items Version consolidation/backfit?
Non-LOCA Release Fractions Non-LOCA FFRD EQ Process improvements Refine Conservatisms Flexibility 12 ADAMS ML24120A350
Selected Topics for Discussion 13 ADAMS ML24120A350
Insight into Guidance Development Process
- Process
- Staff makes technically sound recommendations to management
- Management approves recommendations to Commission
- Commission can approve/deny/set different course
- Staff is still finalizing recommendations to management
- Diversity in thought and positions among staff
- Free and open exchange of views and ideas
- NRC Policy on Differing Views (ML17065A327) provides multiple options for Staff 14 ADAMS ML24120A350
Topics Considered during Staff Technical Discussions 15 ADAMS ML24120A350
- Clarify purpose and objectives of DBA analyses
- Additional guidance for MSIV leakage
- Reinforce the information needed to enable staff reviews, include reference to 57 FR 35455, to (application and licensing basis information)
- Clarify the role that risk insights can play in DBA analyses
- Clarify the applicability of older guidance
- Clarify iodine removal rate in containment
- Enhance focus on overall intent of regulations related to DBA analysis
- Other DPO 2021-001 items
- Potential allowance to move FHA related T.S. to licensee-controlled documents
- Allowance for plant-specific control room occupancy factors consistent with facility specific staffing plans
- Clarify guidance on application of single-failure criteria in analyses
- Clarify guidance on crediting safety-related ESFs to mitigate the source term
- Allow credit for operator actions to purge the control room atmosphere
- Establish consistency with SRP regarding sensitivity and uncertainty analyses
- Update chemical speciation of the source term to be consistent with SAND2023-01313 Potential approaches to establishing graded, risk-informed approaches to control room dose criteria
- Changes to regulatory acceptance criteria for pre-accident iodine spike analysis
- Eliminating pre-accident iodine spike analysis
- Expanding BWR rod-drop condenser guidance to MHA
- Eliminating FHA analysis
- Applicability of new CR dose criteria should be for MHA only
- Allowance for crediting safety-related systems in evaluation of post-accident containment pressure response
- Other DPO 2020-002 items
- Thermal hydraulic conditions that should be assumed in the reactor/steam lines for source term analysis
Control Room Dose Criteria Update Alternative 2 in the Increased Enrichment Rulemaking* Regulatory Basis Document
- Considers updating the control room dose acceptance criteria for design basis accident analyses
- One option being considered is to use a risk-informed, graded-approach to determining criteria that applies to a facility Staff is drafting methodology to propose to the Commission
- Applicable criteria include consideration of facility risk profiles
- Further discussion expected during June 2024 public meeting Draft implementing guidance will be provided to the Commission to support decision-making with respect to Increased Enrichment Rulemaking 16 ADAMS ML24120A350
- Docket ID NRC-2020-0034, www.regulations.gov
Pathway-Specific Source Term Analysis Update 17 ADAMS ML24120A350
Proposed BWR Pathway-Specific Source Term 18 ADAMS ML24120A350 2 to 4 SRVs per MSL 3 RCIC (MSL A) 10 HPCI (MSL B)
MSIV #1 MSIV #2 TSV to TCVs and turbine Vented to environment Condenser Containment boundary RPV steam dome All 4xMSLs modeled separately The release fractions in the steam line are for the green portion (downstream of first SRV, upstream of MSIV)
Airborne aerosols only, already takes into account the removal of fission products Time averaged over each phase duration (i.e. gap, early in-vessel, etc.)
RADTRAD would take this as a constant concentration over the gap and early in-vessel phases Steamline Release Phase Gap Release*
0.0h - 0.7h Early In-vessel* 0.7h -
7.4h Noble Gases 2.9e-5 1.1e-3 Halogens 5.6e-6 5.1e-5 Alkali Metals 5.1e-6 1.3e-5 Te Group 3.2e-6 2.7e-5 Ba/Sr Group 6.1e-7 2.4e-7 Ru Group 2.2e-11 2.4e-7 Mo Group 3.3e-9 3.0e-6 Lanthanides 3.6e-16 1.0e-11 Ce Group 3.7e-16 8.4e-12
- inventory fracon held constant across the phase duraon Information presented Jan 9 public workshop
19 ADAMS ML24120A350 Total Containment Source Term Containment Source Term (ST)
Radionuclide Group Containment (SAND2023 Table 5-16)
Halogens 6.00E-02 Alkali Metals 6.00E-03 Te Group 3.80E-02 Radionuclide Group Steam Line (Preliminary Follow-on Calcs)
Halogens 5.1E-05 Alkali Metals 1.3E-05 Te Group 2.7E-05 No proposed change to process in calculating the dose.
Steam line ST table already takes FP deposition into account so credit should not be taken for deposition between the reactor vessel and first MSIV during early in-vessel phase.
Possible approaches after early in-vessel phase:
1.
Keep concentration constant 2.
Apply a removal rate informed by additional analyses Proposed BWR Pathway-Specific Source Term (Contd)
Proposed BWR Pathway-Specific Source Term (Contd) 20 ADAMS ML24120A350 Model MELCOR model is the same as used for the SOARCA studies (NUREG/CR 7110 and 7155)
Reference:
J. Barr, S. Basu, H. Esmaili and M. Stutzke, Technical Basis for the Containment Protection and Release Reduction Rulemaking for BWRs with Mark I and Mark II Containments, Office of Nuclear Regulatory Research, US NRC, NUREG-2206, March 2018.
Case selections:
Note:
- 1) Two cases with water injection and five cases without water injection are selected.
Option Case 0
4 72 0
4 16 SP CST 230 240 No Yes 15 5
21' Throttle
@ 21 '
Continuo us Thermal seizure -
fraction open Seizure on #
cycles?
Open Cycle (10/20 psid)
Initial Switchov er PCPL PSP Yes No 1
1 X
X X
X X
X X
100%
Enabled X
WW X
X 1
3 X
X X
X X
X X
No Disabled X
WW X
X 2A 10 X
X X
X X
X X
X X
100%
Enabled X
WW DW X
X 2A 11 X
X X
X X
X X
X X
100%
Enabled X
WW DW X
X 2B 18 X
X X
X X
X X
X X
100%
Enabled 10/10 WW DW X
X 2B 16 X
X X
X X
X X
X X
100%
Enabled 20/-
WW DW X
X 2A 42 X
X X
X X
X X
X X
No Disabled X
WW DW X
X Notes 0 DC power means there is no RPV pressure control, so should start like a SBO and remains so 10/10 means both WW and DW cycle at 10 psid 20/- means allow WW cycling at 20 psid but DW is not cycling and remains open WW Level Control Injection Allow SRV stuck Mode Setpoint (psig)
Allow after RCIC Injection @ LH Location Setpoint Fail @ 700F DW Head Seal Availability (hr)
RCIC Availability (hr)
RCIC Suction Failure Temp (F)
Open SRV after RUN MATRIX REV 9 (10/15/2014) - Mark I Pre Core Damage Post Core Damage DC Power RCIC Operation Anticipatory Venting Flex Operation SRV Operation Containment Venting
Proposed BWR Pathway-Specific Source Term (Contd) 21 ADAMS ML24120A350 0
200 400 600 800 1000 1200 1400 1600 1800 0
10 20 30 40 50 60 70 80 Temperature [K]
time [hr]
Cases with water injection Cases without water injection Maximum MSL wall temperatures
Proposed BWR Pathway-Specific Source Term (Contd) 22 ADAMS ML24120A350 Total halogens time-averaged airborne concentration 1.0E-12 1.0E-11 1.0E-10 1.0E-09 1.0E-08 1.0E-07 1.0E-06 1.0E-05 1.0E-04 1.0E-03 1.0E-02 1.0E-01 1.0E+00 Concentrations (fraction of inventory/m3) in MSLs, early in-vessel phase in MSLs, VB to 48 hrs in MSLs, 48 to 72 hrs in containment, early in-vessel phase in containment, VB to 48 hrs in containment, 48 to 72 hrs Note: The hollow marks indicate the cases where water injection to the RPV dome shroud did not occur 1.0E-12 1.0E-11 1.0E-10 1.0E-09 1.0E-08 1.0E-07 1.0E-06 1.0E-05 1.0E-04 1.0E-03 1.0E-02 1.0E-01 1.0E+00 Concentrations (fraction of inventory/m3) in MSLs, early in-vessel phase in MSLs, VB to 48 hrs in MSLs, 48 to 72 hrs in containment, early in-vessel phase in containment, VB to 48 hrs in containment, 48 to 72 hrs
Proposed BWR Pathway-Specific Source Term (Contd) 23 ADAMS ML24120A350
-10.0
-8.0
-6.0
-4.0
-2.0 0.0 2.0 0.0E+0 2.0E+4 4.0E+4 6.0E+4 8.0E+4 1.0E+5 1.2E+5 1.4E+5 1.6E+5 1.8E+5 ln (Conc/Conc0) (-)
Time (sec)
Regression of Concentrations of Halogens and Alkali Metals in MSLs Halogens Alkali Metals Regression: ln(conc/conc0) =-3.4E-5*t, (R square = 0.810)
Proposed BWR Pathway-Specific Source Term (Contd) 24 ADAMS ML24120A350 2 to 4 SRVs per MSL 3 RCIC (MSL A) 10 HPCI (MSL B)
MSIV #1 MSIV #2 TSV to TCVs and turbine Vented to environment Condenser Containment boundary RPV steam dome All 4xMSLs modeled separately MSIV Volume Between SRV and MSIV Steamline post-MSIV Use existing methodology (akin to RG1.183 rev1) 1.0E-44 1.0E-40 1.0E-36 1.0E-32 1.0E-28 1.0E-24 1.0E-20 1.0E-16 1.0E-12 1.0E-08 1.0E-04 1.0E+00 0
1 10 100 1000 Fraction of inventory (-)
Time (hr)
Halogens Fractional Inventory in MSLs During Each Accident Phase Gap release Early in-vessel After VB: Airborne removal coefficent = -3.4E-5 (1/s)
Non-LOCA Gap Release Fractions for RG 1.183, Revision 2 See ADAMS Accession No. ML24120A351 25 ADAMS ML24120A350
Clarification on MHA The maximum hypothetical accident (MHA) is a design basis accident (DBA)
Title 10 of the Code of Federal Regulations, (CFR) sections 50.34, 52.17, 52.47, 52.79, 52.137, and 52.157 describe the minimum technical information that applicants must include in support of applications for the Commissions approval of construction permits, operating licenses, early site permits, standard design certifications, combined licenses, standard design approvals, and manufacturing licenses.
These regulations require an analysis and evaluation of the major structures, systems, and components (SSCs) of the facility that bear significantly on the acceptability of the site under specified radiological consequence evaluation factors.
These regulations require that applicants demonstrate that the facility design can accommodate a substantial fuel melt source term released into containment without exceeding applicable regulatory requirements.
The NRC staff considers the required substantial fuel melt accident (MHA) described in these regulations to be a design basis accident and should be analyzed using appropriately conservative assumptions.
26 ADAMS ML24120A350
Pre-Accident Iodine Spike Analysis Maximum hypothetical accident (MHA) acceptance criteria (25 rem TEDE) should only be applied to MHA analyses Two approaches under consideration by staff:
- Lower acceptance criteria in RG to well within the MHA acceptance criteria
- Experience has shown that these analyses results are significantly lower than the acceptance criteria
- Potential backfitting/forward-fitting issue
- Eliminating the acceptance criteria in RG to model a pre-accident spike in accidents that use reactor coolant source activity as the source term
- When long-term reactor coolant activity limits are exceeded, the plant will be in a limiting condition of operation (typically 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />)
- Staff is reconsidering the appropriateness of requiring accident analyses to assume a limiting condition for operation condition 27 ADAMS ML24120A350
Fuel Handling Accident Consider Eliminating Fuel Handling Accident Analysis Operating Experience Considerations Experience demonstrates no radiological release when fuel assemblies have been dropped NUREG-1774 none of the fuel assembly drop or fuel handling events resulted in radiation exposure or risk to personnel Reconsideration of conservatisms Two accident phases Source Term - assume 100% of gap activity released from 1 entire fuel assembly (some analyses include additional release from another impacted assembly)
Transport - Using a science-based transport model developed by the staff, even with the very conservative 100% gap release source term the calculated doses are minimal Revised methodology described in RG 1.183, Revision 1 Regulatory experience has demonstrated that for certain facilities this analysis may challenge the control room dose acceptance criteria Because of the significant level of conservatism assumed, not because of actual risk Currently, the only DBA that applies during shutdown conditions Staff recognizes that the risk during shutdown is the loss of Residual Heat Removal 28 ADAMS ML24120A350
Best Estimate Plus Uncertainty Properly applied, can provide a more realistic representation of uncertainty and thus enhancement of analyses Most difficult aspects
- Modeling appropriate parameters
- Selection/development of representative distributions Distributions should encompass entire range of values for parameter
- Extrapolation of data should not be used
- Triangular distributions in not adequately representative Descriptive statistics should be provided with submittals 95th percentile values should be used when demonstrating compliance with acceptance criteria 29 ADAMS ML24120A350 Use of Best Estimate plus uncertainty will be evaluated on a case-by-case basis.
Feedback and Discussion 30 ADAMS ML24120A350
Comments and Input from the Public 31 ADAMS ML24120A350
Supplementary Slides 32 ADAMS ML24120A350
33 ADAMS ML24120A350 Project Plan and RG Process Overview
- Background on RGs
- Purpose and benefit
- Management of updates
- Withdrawal of RGs
- Purposes for updating RG 1.183, Rev. 1
- Project Schedules
ADAMS ML24120A350 Regulatory Guides - Background
- Purpose
- Assist stakeholders in understanding and complying with NRC rules and regulations
- Describe methods NRC staff have determined to be acceptable (but not required) for meeting regulations
- Provide for licensing efficiency and regulatory stability
- RGs do not impose requirements 34
35 ADAMS ML24120A350 Regulatory Guides - Background
- Benefit - If not required, why do we have them?
- Conserves resources and simplifies approval process because the guide describes ways the staff has already determined to be acceptable to meeting regulations
- Relieves burden of demonstrating that approved methods satisfy applicable NRC requirements
- In safety evaluations, the staff recognizes that approved methods were used by applicant/licensee and evaluates the outcome of those methods
- Without RG, licensee must first establish that a method is acceptable
36 ADAMS ML24120A350
- Update Process Highlights
- Identifying the need for new guidance
- Development of the technical basis
- Development of the Draft Regulatory Guide
- Development of supporting documents
- RGs that support rulemakings
- Internal and external review
- Publication (Pre-decisional Draft, DG and Final RG)
Regulatory Guides - Background
ADAMS ML24120A350 Regulatory Guides - Background
- Withdrawal of RGs (per Management Directive 6.6)
- NRC determines that guidance has been relocated
- NRC determines guidance is no longer an acceptable means of complying with the applicable requirements
- If pursued, a backfit assessment should be performed and shared via Federal Register notice
- If the NRC staff determines that withdrawing the RG would constitute backfitting but cannot justify the backfitting, then the NRC staff cannot withdraw the RG
- Withdrawal of previous versions can be done especially if guidance is no longer an acceptable means of compliance 37