1. Chapter 7 Thermal-hydraulic Issues in RIR
I. What is RIR ?
II. History of Nuclear Safety Regulation
III. Appendix K in Deterministic Safety Analysis
IV. Option 3 RIR
V. Thermal-hydraulics research for Option 3 RIR

2. I. Introduction of Risk-Informed-Regulation
1. Definition of Risk
Risk = Consequence X Frequency
Measure of Risk
Population(Social) Risk
Individual Risk
Safety Goal
Upper Bound Goal
Lower Bound Goal
Lower Bound Goal for NPP (NRC)
Individual Risk ; 원전으로 인한 추가적 위험 배제
Social Risk ; 타 발전원 보다 덜 위험, 다른 사회적 위험도
에 상당한 추가적 위험 불허

3. Recognitive Risk Real Risk vs Recognitive Risk
Factors of Recognitive Risk
Ignorance or uninformation
Biased knowledge for conse-quence and frequence
No role to control
Mass panic
Mode of Transportation
Year
Deaths
Passenger miles in millions
Deaths/billion passenger miles [km]
British Deaths/billion passenger (km)
Bus 43
244,600
0.176[0.11]
0.4
Air Carrier
321
1,357,874
0.236[0.15]
0.3
Rail (Amtrak) 18
10,608
1.697[1.05]
1.0
Passenger car & Motorcycle
1998
41,471
1,754,174
23.6[14.6]
4.0

4. 2. RIR: Risk Informed Regulation
Current Regulation
deterministic regulation
Prescriptive regulation
Future Regulation
RIPBR(Risk Informed Performance Based Regulation)
Purpose of RIR
Enhance Safety Decisions
Efficiently Use NRC Resources
Reduce Unnecessary Industry Burden
Improve Public Confidence
결정론적사고해석(EM) 과 확률론적 사고해석(PSA)

5. Risk Triplet
1. What can go wrong? --- Accident Scenarios (LOCA, Transient)
2. How likely is it? --- Frequency, Probability, Uncertainty
3. What are the consequences? --- Core Damage, Radioactive Release, Cancer, Fatality
Risk analysis is a method to systematically describe the above triplet in order to understand the consequence, sensitivity and mutual effect between systems due to the risk.

6. II. History of Nuclear Safety Regulation
Before 1957
- Probability calculation for radiation source and consequence during postulated
accidents
- WASH-2 (AEC, 1950) ; Exclusive area radius
- WASH-740(AEC, 1957) ; Windscale reactor accident
Consider occurrence and consequence of accidents in large nuclear plant
2. SL-1 사고 ; 3 person dead
- possibility of power excursion
- need of containment
3. Concept of maximum credible accidents(DBA)
- safety features to prevent the accidents which may result in the core melt
- containment, “isolated castle” to prevent the leak of radioactive materials
- LOCA as DBA and target of regulation (AEC/NRC)
Defense in Depth
Multitiple Barriers and Multiple Levels of Protection
DBA and ESF(Engineered Safety Features)
ECCS, containment, etc
Deterministic Safety Analysis

7. 5. PSA (Probabilistic Safety Analysis) 6. RIR or RIPBR
4. Severe Accident
(1) WASH-1400 (1975) ; Reactor Safety Study(RSS)
- Adopt of PSA
(2) TMI accident(1979.3)
- Severe Fuel Damage(SFD)
- radiation source term
- recognize the importance of PRA
(3) Chernobyl accident (1986)
  Beyond DBA ; NRC safety goal
5. PSA (Probabilistic Safety
Analysis)
6. RIR or RIPBR
(1) Existing NPP
(3) Future reactors
Integrated decision in RIR

8. PSA 수행 절차

9. History of Nuclear Regulation

10. III. Appendix K in Deterministic Safety Analysis
Produce significant margin for PCT calculation
Too conservative but old fashioned
Still doctrinaire faith even recent pile of research report with huge budget

11. Doctrinaire Faith Faith for 2200 oF Old fashion
1966 – 1967 study
; Zr embrittle and rupture temp.
(1370 oC ) << M.T. (1820 oC )
1971 AEC policy statement
; 2200 oF (AEC1971)
AEC public rulemaking hearing
(1972.1~’73.12, Report of 22,000pp )
1974 Jan. 4 “Acceptance Criterion for ECCS” ( 2200 oF or 1204 oC )
Findings on 1204 oC Criterion after 1973 hearing
Old fashion
 Uchida & Tagami Correlation for
P/T Anlaysis in Containment
Design
O Preformance data ; 1965
O Dimension
Chamber (cylinder); H 90cm
test plate ; 14 x 30 cm
O Pressure condition ; 1 ~ 3 atm

12. IV. Options for Risk Informing 10 CFR 50
OPTION 1. Make No Change to Current Part 50
Obsolete Now
OPTION 2. Make Changes to the Scope of SSCs Covered by Those Sections of Part 50 Requiring Special Treatment
South Texas Project Initiative for Graded Quality Assurance Granted in 2001 – Provided Basis for Option 2 Development
SSC (Structure, System, and Component) Categorization Using Risk Insights as Part of the Integrated Decision Making Process
RG Issued in January 2006 for Trial Use
OPTION 3. Risk-Informed, Performance-Based Revision to 10 CFR Part 50
Selective Implementation
Overall Part 50 Revision Process Currently Ongoing
To become an Entirely New Part – 10 CFR Part 53
Refer to SECY , “Options for Risk-Informed Revisions to 10 CFR Part 50 – Domestic Licensing of Production and Utilization Facilities,” December 23, 1998.