ML19057A438
| ML19057A438 | |
| Person / Time | |
|---|---|
| Site: | NuScale |
| Issue date: | 02/26/2019 |
| From: | NRC |
| To: | NRC/NRO/DLSE/LB1 |
| References | |
| Download: ML19057A438 (5) | |
Text
NuScaleDCDocsPEm Resource From: Chowdhury, Prosanta Sent: Tuesday, February 26, 2019 11:48 AM To: NuScaleDCDocsPEm Resource
Subject:
March 5, 2019, Public/Closed Meeting on NuScale EPZ Sizing Methodology Topical Report_NRC Staff Talking Points (Public)
Attachments: NuScale EPZ TR Meeting_03-05-2019_NRC Staff Talking Points.pdf 1
Hearing Identifier: NuScale_SMR_DC_Docs_Public Email Number: 27 Mail Envelope Properties (DM6PR09MB2748835BBC51E6812E3DC0C99E7B0)
Subject:
March 5, 2019, Public/Closed Meeting on NuScale EPZ Sizing Methodology Topical Report_NRC Staff Talking Points (Public)
Sent Date: 2/26/2019 11:47:35 AM Received Date: 2/26/2019 11:47:39 AM From: Chowdhury, Prosanta Created By: Prosanta.Chowdhury@nrc.gov Recipients:
"NuScaleDCDocsPEm Resource" <NuScaleDCDocsPEm.Resource@nrc.gov>
Tracking Status: None Post Office: DM6PR09MB2748.namprd09.prod.outlook.com Files Size Date & Time MESSAGE 3 2/26/2019 11:47:39 AM NuScale EPZ TR Meeting_03-05-2019_NRC Staff Talking Points.pdf 325615 Options Priority: Standard Return Notification: No Reply Requested: No Sensitivity: Normal Expiration Date:
Recipients Received:
NRC Staff Talking Points for March 5, 2019, Public Meeting on TR-0915-17772, Methodology for Establishing the Technical Basis for Plume Exposure Emergency Planning Zones at NuScale Small Modular Reactor Plant Sites, Revision 1 STAFF CONCERNS
- 1. PRA Acceptability: The methodology described in this topical report (TR) is based on the Combined License Applicants (COL) probabilistic risk assessment (PRA), but the existing review guidance for a COL PRA (Standard Review Plan Chapter 19.0 and Interim Staff Guidance DC/COL-ISG-028) is not sufficient to demonstrate the PRA is acceptable for use in risk-informed applications. Using the COL PRA to size the plume exposure emergency planning zone (EPZ) would be a first-of-a-kind use for a COL PRA and a first-of-a-kind review for the staff.
Proposed Resolution: Include a condition of use in the TR or Safety Evaluation Report (SER) that the COL applicant that references this TR will demonstrate their PRA is consistent with RG 1.200. NUREG-1855 shall be used to address the impact to the screening process from the parameter and model uncertainties associated with a new, un-built design.
- 2. Screening of Seismic Events: The methodology described in this TR uses a seismic screening based on 1.67 times the ground motion acceleration of the design-basis safe-shutdown earthquake while all other hazards are screened on core damage frequency (CDF). Per the TR methodology, all structures in rev. 2 of the NuScale Design Certification (DC) would screen out, but if the CDF screening was applied using the seismic CDFs from the NuScale SAMDA analysis, the events would screen in.
Proposed Resolution: Include a condition of use in the TR or SER requiring the COL applicant that references this TR to perform a seismic PRA and screen seismic sequences with same process as other hazards.
- 3. Severe Accident Phenomena: Statements in the LTR, sections 3.4.3, Final Classification of Accidents by Severity, and 3.8.2, Severe Accident Phenomena, describe severe accidents as not physically credible. This phrase is being removed from the NuScale Chapter 19 DC in response to request for additional information (RAI) 9138 (Steam Explosion), RAI 9043 (In-Vessel Retention), and RAI 9108 (Screening of Severe Accident phenomena from the Containment Event Tree) because of large uncertainties associated with these phenomena. These uncertainties make severe accidents physically credible, they will not lead to a large release.
Status: This cannot be resolved with a condition of use.
February 26, 2019 Page 1 of 3
- 4. Level 2 Risk: The Commission goals for advanced light water reactors include two risk metrics, CDF and large release frequency (LRF). The TR methodology screens on CDF, but does not consider LRF unless the event screens into the defense in depth process.
Proposed Resolution: Include a condition of use in the TR or SER requiring the COL applicant that references this TR to consider risk insights from the Level 2 PRA (i.e.,
Table 19.1-27 in rev. 2 of NuScale DCA)
- 5. Module Drop: In NUREG-0396, it was demonstrated that credible accidents meet the early phase protective action guides (PAGs) and less credible accidents show substantial reduction in early severe health effects. In contrast, the methodology in this TR compares less severe accidents to the early phase PAGS and more severe accidents to 200 rem whole body acute dose. The implied assumption is that less severe accidents are more frequent. However, in rev. 2 of the NuScale DC, module drop is the dominant and most likely cause of CDF. Because module drop may or may not result in an intact containment, the methodology evaluates the intact containment event to PAGs and non-intact containment to 200 rem even though it appears both events have the same frequency. Additionally, not all events that should be evaluated against the PAGs are identified in the PRA. For example, module drops during refueling may not lead to CDF (because fuel is exposed to reactor pool) or LRF (because of reactor pool scrubbing), so these events are not identified in the PRA. As such, they wont be pulled into this TR methodology despite their potential for a small release. The staff also seeks to understand if module drop events that impact adjacent modules are considered as correlated failures between modules (3.7.2) or shared system failures (3.7.3)
Status: This cannot be resolved with a condition of use.
- 6. Defense in Depth Attribute Ranking: DiD approach uses rigid dividers and Low DiD bins are based on minimum acceptable risk metrics. The low DID attribute values are not characteristics of certified ALWR designs and/or Commission expectations in SECYs or in the Advanced Reactor Policy Statement1 that new reactors are an improvement over existing designs. Staff seeks to understand how the following Low values were set:
x Containment Isolation Response Low requirement of only check valves appears to be inconsistent with intersystem loss-of-coolant accident guidance in SECY-93-087 x Sequences LRF > 1E-6 per module year is inconsistent with SECY-91-06 LRF Goals of total LRF < 1E-6 x Sequence CDF considering only safety-related systems (focused PRA) >
1E-3/year per module year seems inconsistent with Adv Rx Policy Statement 1
In the Policy Statement on the Regulation of Advanced Reactors, 60612 Federal Register / Vol. 73, No. 199 /
Tuesday, October 14, 2008, Regarding advanced reactors, the Commission expects, as a minimum, at least the same degree of protection of the environment and public health and safety and the common defense and security that is required for current generation light-water reactors (LWRs). Furthermore, the Commission expects that advanced reactors will provide enhanced margins of safety and/or use simplified, inherent, passive, or other innovative means to accomplish their safety and security functions.
February 26, 2019 Page 2 of 3
x Safety system response to detect and control initiating event - active system with manual control seems inconsistent with Adv Rx Policy Statement x Time to the beginning of core damage less than one hour seems inconsistent with Adv Rx Policy Statement Status: This cannot be resolved with a condition of use.
February 26, 2019 Page 3 of 3