Perspectives on PSA

George Apostolakis
Head, Nuclear Risk Research Center, Japan
Former USNRC Commissioner
apostola@mit.edu
PSA 2015
Sun Valley, Idaho
April 26-30, 2015
2015

11

Back to PSA 2013
• Frustration over slow progress Too many people focus on the P of PRA. It’s the accident
scenarios that provide the most benefit
 Use of quality PRAs could have helped to prioritize theNRC’s Fukushima recommendations in a more holisticmanner PRAs have shown that the plant risk profile is plantspecific. Yet, in our regulations, we don’t always accountfor this insight• Industry’s frustration
 Expensive NFPA 805 applications and NRC review out ofcontrol

20152

A Setback: Requiring Plant-Specific PRAs
• COMGA14-0002 / COMWDM14-0002
 Operating reactor licensees should submit summary
plant-specific PRA information delineating the dominantrisk contributors
 The required PRA summaries should be available within
ten years of the issuance of the SRM associated with thismemorandum• Commission disapproved (August 1, 2014)• NRC Staff (SECY-13-0132; December 6, 2014)
“It is unlikely that the safety benefits of plant-specificassessments would meet the “substantial increase in overallprotection” threshold in the backfit rule (10 CFR 50.109)”
20153

A Hope: Risk Prioritization Initiative• COMGEA-12-0001 / COMWDM-12-0002


2015

Enhance safety by applying probabilistic risk
assessment to determine the risk significance of current
and emerging reactor issues in an integrated mannerand on a plant-specific basis.
An additional benefit would be that licensees would beincentivized to develop high-quality PRAs that would
support enhanced safety now and into the future.

4

Risk Prioritization Initiative• Option 2 (voluntary)
 Establish pilot of an NRC expert panel to characterize
and prioritize regulatory actions using risk insights
 Scheduling would be based on existing processes
augmented with risk information
 Staff recommends approval• Option 3 (voluntary) Prospective rules/orders that allow for licensees tosubmit plant-specific implementation schedules using arisk-informed prioritization process Staff recommends pilot

2015

5

ACRS Letter, March 11, 2015
1. We endorse the staff's recommendations to implement Option 2
and to proceed with a trial application of Option 3.
2. The staff should explicitly include risk information as an input
to decisions and priorities for proposed regulatory actions
regardless of the Commission's decisions about specific options
or approaches presented in this SECY paper.
3. A challenging aspect of the proposed risk-informed
prioritization process involves the methods by which risk
information and other metrics will be used to develop consistentmeasures of the significance of issues that affect plant safety,
security, emergency preparedness, radiation protection, andequipment reliability. If the Commission endorses a prioritization
process, the staff should expedite development of regulatory
guidance for its use and reviews.
20156More Hope: Risk-Management Regulatory Framework (NUREG-2150)
MissionEnsure adequate protection of public healthand safety, promote the common defense andsecurity, and protect the environment

Objective

Manage the risks from the use of byproduct, source andspecial nuclear materials through appropriate performancebased regulatory controls and oversight

Risk Management Goal

Provide risk-informed and performance-based defense-in-depth protectionsto: Ensure appropriate barriers, controls, and personnel to prevent, contain,and mitigate exposure to radioactive material according to the hazard
present, the relevant scenarios, and the associated uncertainties; and Ensure that the risks resulting from the failure of some or all of theestablished barriers and controls, including human errors, aremaintained acceptably low

Decisionmaking Process

Use a disciplined process to achieve the risk management goal:
Identify issue

Identify
Options

Analyze

Monitor

Implement
Decision

Deliberate

Figure ES-1 Proposed Risk Management Regulatory Framework
20157

Power Reactor Option 2 – Voluntary
Alternative Risk-Informed Licensing Basis• Maintain existing generic regulatory structure• Rule would allow licensees with quality PRAs toapply for approval of a licensing basis supporting aperformance-based, risk-informed alternative tocertain deterministic regulations of low-safetysignificance• Licensees would search for and mitigate plantspecific risk vulnerabilities
NRC Staff presentation to ACRS subcommittee, 2/20/15
2015

8

Multi-unit Issues• U.S.A.
 Currently at most 3 units Vogtle will have 4
 Adjacent sites: Salem 1&2 and Hope Creek (3 total); Nine
Mile Point 1&2 and FitzPatrick (3 total)• Canada Pickering: 6
 Darlington: 4
 Bruce Power: 8• Japan Kashiwazaki-Kariwa: 72015

9

Current Situation• General Design Criterion 5: Structures, systems, andcomponents important to safety shall not be shared among
nuclear power units unless it can be shown that such sharing
will not significantly impair their ability to perform their safetyfunctions, including, in the event of an accident in one unit, anorderly shutdown and cooldown of the remaining units.

• U.S. Safety Goals are applied to single units.
• PRAs, with few exceptions, are performed for singleunits.

2015

10

CNSC Workshop
November 17-20, 2014
• MUPSA Infrastructure Lack of experience and guidance for performing MUPSA• Selection of Initiating Events
 Most external events involve multi-unit challenges• Accident Sequence Modeling Need to account for multi-unit dependencies including
functional, human, and spatial dependencies
 Need to consider the timing of releases from differentunits• Site Based Risk Metrics
 Need for additional risk metrics beyond CDF and LERF tofully express the risk profile of a multi-unit site

201511CNSC Workshop (continued)• Accident Progression and Source term
Characterization
 Need to define new release categories that adequately
describe the releases from multi-unit accidents. This
includes release magnitudes, energies, and timing fromreactor units, spent fuel storage, and other radiologicalsources• Evaluation of Radiological Consequences Includes consideration of different points of release fromthe plant, possible differences in time of release, andrelease energies for plume rise considerations.

• Site-Based Safety Goals
 Need to define multi-unit site based acceptance criteria
for evaluating the integrated risks from a multi-unit sitePSA
201512