gordana dodig-crnkovic department of computer science and engineering mälardalen university 2003
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PROFESSIONAL ETHICS IN SCIENCE AND ENGINEERING CD5590 LECTURE 12. Gordana Dodig-Crnkovic Department of Computer Science and Engineering Mälardalen University 2003. CASE STUDY. RISKS IN TECHNOLOGY AND SCIENCE PRECAUTIONARY PRINCIPLE. The ABB Atom Criticality Safety Handbook. - PowerPoint PPT PresentationTRANSCRIPT
Gordana Dodig-Crnkovic
Department of Computer Science and Engineering
Mälardalen University2003
PROFESSIONAL ETHICS IN SCIENCE AND ENGINEERING
CD5590 LECTURE 12
RISKS IN TECHNOLOGY AND SCIENCE
PRECAUTIONARY PRINCIPLE
CASE STUDY
Gordana Dodig-Crnkovic
ABB Atom AB, 1999
Nuclear Fuel Division, Dept. BCD
SE-721 73 Västerås, Sweden
E-mail: [email protected]
The ABB Atom Criticality Safety Handbook
1 Introduction
2 Organization of Work for CSE
3 CSE Step by Step: Order Form-Check Lists-Evaluation Report-Implementation
4 Modeling Methods and Calculation Tools used for CSE
(4.1 CSE Methods; 4.2 Precautionary Principle; 4.3 Benchmarks and Validation)
5 CSE for Fuel Fabrication Plant
6 CSE for Transports
7 CSE for Fuel Storage
8 Standards, Handbooks and Standard Literature
9 Common Material Compositions
10 Most Important Physical Factors affecting Criticality Safety
11 Reflection and Interaction
12 Criticality Safe Parameters for Isolated Systems
(12.1 Isolated Homogeneous Systems; 12.2 Pipes;
12.3 Cylinders and Slabs with Different Reflector and Absorber Materials; 12.4 Heterogeneous Systems)
13 A short Review of Criticality Accidents
14 Glossary of Terms in Nuclear Criticality Safety
15 Handbook administration
CSH-A Table of Contents
Criticality Safety Handbook Mission
•Strengthen the company's criticality safety culture
•Set standards for making criticality safety analyses
•Document organization, routines, and methods in the field of criticality safety
•Standardize and document analysis procedures, methods, and acceptance criteria
•Provide general guidance in matters of NCS principles and practices at ABB Atom.
•Serve as a reference source in the broadening and strengthening of the safety culture in the
organization
The Regulatory Basis
In assessing the criticality safety at ABB Atom we apply the methodology outlined in SKIFS 1998:1 as well as ANSI/ANS Standards, and ISO 1709.
Safety in SKIFS 1998:1 is described in terms of “defense in depth”, which means that physical barriers against e.g. inadvertent criticality must exist.
Barriers are also necessary for the mitigation of the consequences of a possible criticality event in systems in which criticality is judged as a scenario not too far-fetched.
1 Prevention of Failures and Abnormal Operationby robust design and high quality in construction, operation and maintenance
2 Control of Abnormal Operation, Detection of Failures
by permanent surveillance, periodic testing, protection systems, understanding of abnormal behaviour in safety reports
3 Control of Accidents within the Design Basis
by engineered safety features and accident procedures, bounding incident and accident cases within categories with maximal radiological consequences
4 Control of severe plant conditions
by prevention of accident progression and mitigation of accident consequences
5 Mitigation of consequences of significant off-site radiological releasesby elaboration of an emergency response plan
THE CONCEPT OF DEFENSE IN DEPTH
5
Normal Condition
1
2
3
4
4
1
2
3
5
Severe Accident
Design Basis Accident
Abnormal Operation
Abnormal Operation
Design Basis Accident
Severe Accident
The CSE-Piece of Nuclear Safety Puzzle
SAFETY & SAFEGUARDSDepartment
SÄK Safety CommitteeCriticality Safety Group, KSG
SKI(Swedish Nuclear Power Inspectorate)
SKI’s independent reviewer
Safety Advisory Board (BERNS)
Nuclear Fuel Factory
Workshops (Production)
Fuel Storage(Nuclear Power Stations)
CSE-responsible groupTransports
Criticality Safety Group: KSG
•Enables direct communication between CSE, workshops- and operative safety personnel
•Improves long-term planning of CSE
ABB Atom Fuel Division’s Safety Committee: SÄK
• Criticality Safety• Radiation Protection• Fire-fighting• Conventional Safety• Environmental protection
Order Form and Checklist
A request for a criticality safety analysis requires filling in of an order form with the necessary characterization of the system/process in question.
To assure that all relevant scenarios and types of possible problems are taken into account, we have a Checklist for Systems Containing Uranium.
The Checklist consists of a number of questions, which must be answered with yes/no or a description, and a responsible person must sign each of them. Complete Request for CSE includes both a filled-in order form and a signed Checklist.
The precautionary principle described in CSH-A as applied to CSE means that the risk of an inadvertent criticality must not be underestimated under any circumstances!
(The Precautionary Principle in Maastricht treaty states that the absence of certainty given our current scientific knowledge, should not delay the use of measures preventing a risk of large and irreversible damages to the environment, at an acceptable cost.)
Modeling Methods and Calculation Tools used for CSE
The Precautionary Principle
Criticality safe: Risk landscape
keff defines only one single point!
Analyzing safety against criticality is like exploring a risk landscape, which can have a very detailed structure.
Our aim is to identify relevant regions of significant risk. (Risk = Probability x Consequence).
Judgement of what can be considered as likely/unlikely or possible/impossible is made in accordance with existing experience and our best knowledge. Corresponding PRA is used to support the choice of proper scenarios.
What does it mean criticality safe?
0.84
0.86
0.88
0.9
0.92
0.94
0.96
0.98
1
1.02
0 2 4 6 8 10 12 14
parameter
keff
k1 k2 säker gräns kritisk
Säkerhetsmarginal
Säkerhets-marginal
keff as a rule is a function of several parameters. It is of great
importance to understand its behavior with different parameter
variations. It is the slope of keff-curve that indicates how fast one is
approaching safety-relevant limits.
keff < 0.95 is an common definition.
keff < 0.98 can be accepted for accidental
scenarios, under the condition that PRA
(probabilistic risk analysis) can confirm
extremely low expected frequency for that
type of events.
keff
CSE
BENCHMARK AND VALIDATION OF ANALYSIS METHODS
PHOENIX / KENO CodesCriticality Benchmark Study
for Homogeneous systems with Low Moderator Concentrations, BRP 96-064
Experiment number and type keff ±
89-group 42-group NITAWL 3, 100 cans 1.023 ± 0.003 1.051 ± 0.0024, 100 cans 1.020 ± 0.002 1.052 ± 0.002 1.021 ± 0.01038 cans 1.011 ± 0.003 1.041 ± 0.00278 cans 1.026 ± 0.002 1.055 ± 0.002 80 cans 1.024 ± 0.003 1.058 ± 0.002
cyls.zrefl
0,65
0,7
0,75
0,8
0,85
0,9
0,95
1
1,05
1,1
15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
diam (cm)
kef
f +
3
cyl.zrefl.c50
cyl.zrefl.w30
cyl.zrefl.bfp.c50
cyl.zrefl.bfp.w30
cyl.zrefl.pvc.c50
cyl.zrefl.pvc.w30
limit
Critical and Safe Parameters 5% enriched 235 U systems
An infinite cylinder with different types of absorbers and
reflectors
c50 = 50 cm concrete reflector; w30 = 30 cm water reflector bfp.c50 = 0,64 cm BFP (absorber) and 50 cm concrete reflector bfp.w30=0,64 cm BFP and 30 cm water reflector pvc.c50 = 1,0 cm PVC (absorber) and 50 cm concrete reflector pvc.w30 = 1,0 cm PVC and 50 cm concrete reflector
CSE FOR SYSTEMS/PROCESSES OF ABB ATOM FUEL FABRICATION PLANT
This kind of CSE is the most challenging one in terms of modeling.
”You can make your model more complex and more faithful to reality, or you can make it simpler and easier to handle. Only the most naive scientist believes that the perfect model is the one that perfectly represents reality. Such a model would have the same drawbacks as a map as large and detailed as the city it represents, a map depicting every park, every street, every building, (…), and every map.”
James Gleick, CHAOS
CSE FOR TRANSPORTS OF FISSILE MATERIAL
The interpretation of IAEA Safety Standards in terms of mandatory scenarios against which transport containers must be checked is an issue of current interest.
Geometry changes because of postulated accident conditions (expansion of fuel rod pitch, fissile material distribution, moderation conditions etc.) are crucial. Work on defining acceptance criteria is now in progress in Europe.
CSE FOR FUEL STORAGE
Off-normal condition scenarios for fuel storage systems, especially for fuel pools require investigation. Boundary conditions such as maximum water temperature and void must be defined.
If the burnup credit is applied, uncertainties in material compositions must be addressed. Uncertainties of other types such as changes in fuel element moderation conditions (even local ones), alteration of fuel rod pitch as well as variation in fuel element distance (earthquake scenarios), etc must be taken into account.