ML21243A543
| ML21243A543 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 09/01/2021 |
| From: | Siva Lingam Plant Licensing Branch IV |
| To: | |
| Lingam S, 301-415-1564 | |
| References | |
| Download: ML21243A543 (9) | |
Text
Request for Partial Exemption from 10 CFR 50.62(c)(1)
Risk-Informed Process for Evaluations (RIPE)
Pre-Submittal Meeting Palo Verde Nuclear Generating Station (PVNGS)
September 1, 2021
2
- Introduction
- Issue Description
- Design Features
- RIPE Screening Results
- Risk Insights
- Schedule Agenda
3 10 CFR 50.12 partial exemption from 10 CFR 50.62(c)(1) using RIPE process to remove the Diverse Auxiliary Feedwater Actuation System (DAFAS) from the PVNGS licensing basis must have equipment from sensor output to final actuation device, that is diverse from the reactor trip system, to automatically initiate the auxiliary (or emergency) feedwater system and initiate a turbine trip under conditions indicative of an ATWS Diverse turbine trip and diverse scram system are unaffected by this request DAFAS not credited in UFSAR Chapter 6 and 15 safety analyses DAFAS is a Modicon Programmable Logic Controller (PLC 984-685) based system Obsolete and not supported by the vendor DAFAS is a unique, proprietary design Spare parts are not readily available Maintenance requires significant engineering resources to reverse engineer components Frequent fiber optic communication problems affecting system availability Issue Description
4 Reactor Protection System (RPS) 4 channels with 15 Trip parameters Core Protection Calculator, Steam Generator (SG) Low Level, and High Pressurizer Pressure Trips provide sufficient protection from an ATWS event Engineered Safety Features Actuation System (ESFAS)
Provides AFAS-1 and AFAS-2 on receipt of Low SG level signal Supplementary Protection System (SPS) 4-channel safety related Diverse Scram System Trips on high pressurizer pressure Opens Reactor Trip Circuit Breakers and Motor Generator set load output contactors Exceeds 10 CFR 50.62 requirements Diverse Turbine Trip Trip on control element drive mechanism power bus undervoltage (SPS trip interrupts power to this bus)
Design Features
5 Applicable guidance documents:
NEI 21-01, Industry Guidance to Support Implementation of NRCs Risk-Informed Process for Evaluations, April 2021 NRC Guidelines for Characterizing the Safety Impact of Issues, June 2021 TSG-DORL-2021 NRR Temporary Staff Guidance, Risk-Informed Process for Evaluations, January 2021 PVNGS has implemented Risk-Informed Completion Times
[ML19085A525] and 10 CFR 50.69 [ML18243A280]
APS qualifies to use the RIPE process Issue screened in as adverse, but minimal impact on safety RIPE Screening Results
6 Risk Insights A plant specific risk assessment was conducted
- DAFAS function is to actuate Auxiliary Feedwater if ESFAS fails
- ESFAS Auxiliary Feedwater Actuation Signal is a two out-of-four channel actuation system
- DAFAS determined to have minimal benefit ensuring Auxiliary Feedwater actuated
- Bounding surrogates used for the relative change in risk
- No risk management actions are required to offset the risk
7 The PRA model used reflected the following:
Fully compliant internal events, flooding, fire and seismic PRA models All Other External Hazards listed in RG 1.200, Revision 3, screened out Addressed all NRC license conditions from the 10 CFR 50.69 and RICT License Amendments No open finding level Facts and Observations (F&Os)
No newly developed methods No additional key assumptions or sources of uncertainty PRA model fully compliant with NRC RG 1.200, Revision 3 Risk Insights
8 Risk Insights Therefore, removing DAFAS from the licensing basis is not risk-significant and has a minimal impact on safety.
Case CDF LERF PVNGS Baseline 5.5x10-5/year 9.5x10-6/year PVNGS DAFAS Sensitivity 5.5x10-5/year 9.5x10-6/year Increase in Risk between Baseline & DAFAS Sensitivity 3.2x10-9/year 5.9x10-11/year NEI 21-01 Acceptance Guideline 1.0x10-7/year 1.0x10-8/year NRC RG 1.174 Acceptance Guideline 1.0x10-4/year 1.0x10-5/year
9 Completed a challenge board with NEI on June 24, 2021 Pre-submittal meeting on September 1, 2021 Integrated Decision-Making Panel planned for September NRC requested to observe Planned submittal early October 2021 Discuss NRC approval schedule Schedule