Title: Risk Informed InService InspectionResults of Studies on Nuclear Power Plants and Heavy Water Plants
1Risk Informed In-Service Inspection-Results of
Studies on Nuclear Power Plants and Heavy Water
Plants
- Santhosh
- Reactor Safety Division, BARC
- Mumbai, India.
2Overview of Presentation
- Introduction
- RI-ISI Methodology
- Case Study 1 Heavy Water Plants
- Case Study 2 Indian PHWRs
- Conclusions
3Risk Analysis in PublicPolicy Decision
- Most of the public policy decisions that are made
involve the allocation of resources. - Available resources, whether natural or human,
are finite. Therefore, resource allocation
involves certain trade-offs. - The outcome of many ,if not most, public policy
decisions is uncertain.
4Risk Analysis in PublicPolicy Decision
- The best way to deal with such uncertainties is
the risk analysis. - Determining or estimating the probability of
various outcomes gives a more complete picture
than focusing only on the most likely (or the
desired) outcome. - The cost of resources allocated can be compared
to the benefits to inform decisions.
5Risk Assessment in Industry
6(No Transcript)
7 RI-ISI Methodology
8RISK INFORMED IN-SERVICE INSPECTION
- CONSEQUENCE
- HEALTH
- DAMAGE
- TOXIC
- ECONOMIC
- LIKELIHOOD FREQUENCY
- SERVICE DATA ANALYSIS
- STRUCTURAL RELIABILITY ANALYSIS
- REMAINING LIFE MODELS
- EXPERT JUDGEMENT
- RISK MATRIX
- DEFINES THE INSPECTION CATEGORY,
- METHOD, FREQUENCY AND SCOPE OF INSPECTION
LIKELIHOOD FREQUENCY
RISK
INSPECTION
9Advantages of RI-ISI
- Decision making based on the risk criteria and
deterministic information - Better focus on allocating resources to high
safety significant components. - In- Service Inspection based on failure modes of
components and associated risk
10Guides for RI-ISI
- NUREG 1661- RI-ISI for Nuclear Power Plants by US
Nuclear Regulatory Commission - API 581- Base Resource Document Mainly used by
Chemical, Oil Petrochemical Industries - ASME RBI Guidelines Vol. 3- for Fossil Fuel
Plants - EPRI- Risk Based Maintenance Guidelines
- Risk based Inspection MAintenance Procedures
(RIMAP) Workbook
11Case Study 1RI-ISI of Heavy Water Plant
12Scope and Objective
- Apply RI-ISI for components connecting the
CT1-HT1 towers, and compare with the existing ISI
plan - To demonstrate the reduction in inspection
achieved through adopting RI-ISI without
compromising the plant safety - To ensure that the inspection will be focused on
more safety significant components
13Schematic Diagram of HWP
14Steps Involved
- Scope boundary of the study
- Data collection on piping and equipment
- Finding the inventory in each component (mass of
H2S in liquid gas) - Evaluate the failure probability consequence
- Establish the categories for failure probability,
consequence risk - Conduct a risk impact analysis
-
15Piping Failure Analysis Structural Reliability
- Material properties for failure analysis
- Possible damage mechanisms
- Past inspection history for degradation rate
- ASME B31G-Failure Pressure Model for estimating
the remaining strength of a corroded pipeline - Limit state function is formulated for estimating
the pipeline failure probability - COMREL tool for computing the failure probability
16Equipment Failure Analysis Bayesian Updation
Technique
- Plant specific failure incidences were collected
for various equipment from SRUORs - Analyzed the failure incidences for identifying
the exact failure mode - Updated the generic information with the plant
specific data using Bayesian technique - Developed software for data base management and
reliability analysis
17DAMAGE
- Chemical
- Quantity
- State
- Economic loss
18Consequence Category Specified in API 581
19Damage - Piping
20Damage - Equipment
21Health - Piping
22Health - Equipment
23Consequence Matrix
24Consequence Category- Equipment
25RISK MATRIX
26Risk Category - Equipment
27Risk Impact Analysis
CURRENT INSERVICE INSPECTION (ISI) PROGRAMME HAS
THREE INSPECTION CLASSES, VIZ. A, B C A
CARRYING H2S AND NON-ISOLATABLE B CARRYING H2S
AND ISOLATABLE C UTILITY FLUIDS Consequence is
considered in an implicit manner, but failure
potential are not considered
28Risk Impact Analysis
29Risk Impact Analysis-Results
30 Case Study 2RI-ISI of Nuclear Power Plants
31Current PHWR ISI Programme
- Currently In-Service Inspection is based on CAN
standards - CAN/CSA-N 785.4-94 - Inspection categories are defined as a function
of fatigue usage factor, stress ratio and size of
failure (RE) - Fatigue usage factor is determined as per the
rules given in ASME Boiler and Pressure Vessel
Code
32INSPECTION CATEGORY FOR MEDIUM FAILURE SIZE
INSPECTION CATEGORY FOR LARGE FAILURE SIZE
Scope, frequency methods of inspection in
categories A, B, C1 C2 are decided by expert
group formed by utility
33RI-ISI for NPPs International Scenario
34Importance Measure in RI-ISI
- ASME-WOG SUGGESTED RRW RAW IN ISI PRIORITISION
35ASME-WOG on Indian PHWR
- Applied ASME-WOG ranking scheme on process and
safety systems of Kaiga Generating Station using
KGS PSA results - RAW and RRW have been evaluated for initiating
events considering the frequencies as 1/year and
0/year respectively
36SYSTEM PRIORITISATION - ASME/WOG
37Application on Indian PHWRs
- RI-ISI was applied on piping segments connecting
the Primary Heat Transport System Shutdown
Cooling System - Leak and rupture frequencies for piping segments
were evaluated using Thomas model - Possible degradation mechanisms were considered
38Application on Indian PHWRs
- Consequence is quantified using Conditional Core
Damage Probability - EPRI Risk matrix was applied for risk
categorization - Risk impact analysis was carried out comparing
with the current ISI programme
39PHT of Indian PHWRs
40Component Failure Frequency
- STATISTICAL METHODS PAST EXPERIENCE
- DEGRADATION MECHANSIMS
- THOMAS MODEL WELDS, DIAMETER, LENGTH,THICKNESS,
DESIGN, AGE, ETC - MECHANISTIC MODELS - BY UNDERTSANDING THE
PREVALENT PHENOMENA IN THE COMPONENT
41Classification of Degradation Mechanisms
42Possible Degradation Mechanisms in Indian PHWRs
Atmospheric Corrosion
Boiler
Erosion Corrosion
SCC, CF
Turbine
Generator
Calandria
Condenser
SCC, Pitting, etc
Hydriding,
43Risk Matrix
44ISI CATEGORIES FOR COMPONENTS IN PHT
45ISI CATEGORIES FOR COMPONENTS IN SDCS
46Code for Inspection Methods
- Visual examination 1
- Dimensional examination 2
- Surface examination 3A (LPT, MPT, ET)
- Volumetric examination 3B (UT,RT,ET)
- Integrative examination - 4
47RESULTS
48Suggested Inspection Method
49Conclusions
- RI-ISI was applied to HWPs and Indian PHWRs and
demonstrated its advantages over the current ISI
programme - Reduction in quantum of inspection which in turn
improves the plant down time and cost - RI-ISI provides a basis of quantification for the
inspection programme - RI-ISI focuses inspections on most significant
areas, where - Degradation mechanisms are present
- Consequence of potential failure are greater
- Overall plant safety improvement is possible
50Thank you for your attention