Nuclear Safety or Risky Nuclear? - PowerPoint PPT Presentation

Loading...

PPT – Nuclear Safety or Risky Nuclear? PowerPoint presentation | free to download - id: 8098ef-YTMzY



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Nuclear Safety or Risky Nuclear?

Description:

Presented to: The Georgia Triangle Lifelong Learning Institute, January 21, 2011 Lecture 2 Nuclear Energy and Technology Dan Meneley, PhD, PEng – PowerPoint PPT presentation

Number of Views:137
Avg rating:3.0/5.0
Slides: 62
Provided by: danm139
Learn more at: http://www.cns-snc.ca
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Nuclear Safety or Risky Nuclear?


1
Nuclear SafetyorRisky Nuclear?
  • Presented to
  • The Georgia Triangle Lifelong Learning Institute,
    January 21, 2011Lecture 2 Nuclear Energy and
    Technology
  • Dan Meneley, PhD, PEng
  • Revised and presented to the Ottawa Branch of
    CNS, April 21, 2011

2
Outline of this Lecture
  • Why should we study nuclear reactor safety?
  • THE NEED FOR ENERGY
  • Some useful definitions
  • WHAT ARE WE TALKING ABOUT?
  • Risk and safety
  • UP FRONT ISSUES -- from the course outline
  • A bit of techie talk
  • THE NATURE OF THE BEAST
  • Experience and lessons from the past
  • Past performance Including the Daiichi disaster
  • The Present and Future
  • GUIDING PRINCIPLES

3
Energy Delivery
  • For the past 150 years we have lived on oil.
  • First oil well in North America was drilled in
    Ontario
  • Today we burn 1,000 barrels each second.
  • By 2100 CE we must have other energy sources in
    place
  • If we can wait 100 million years, there will be
    new oil formed
  • Coal can do the job for several centuries
  • But its environmental effects may be unmanageable
  • Uranium can do the job forever

THE NEED FOR ENERGY - 1
4
Why the big interest in this Topic?
  • The potential energy in heavy elements is
    immense
  • 1 kg (U) in CANDU produces about 180 MWh(th) 60
    MWh(e).
  • Typical 4 - person households electricity use
  • 1,000 kilowatt hours per month 12 megawatt
    hours per year
  • So, a mere 200 grams of uranium - 6 to 8 pellets
    - serves one household for an entire year.
  • If the same energy were obtained from fossil fuel
  • The fuel would be 30,000 times heavier
  • For example, about 6,000 kg of coal would be used
  • Carbon dioxide and massive quantities of ash
    would be produced
  • Yet we use less than 1 of uraniums potential
    energy
  • New technology is available that can use the
    remainder

?E ?mC2
THE NEED FOR ENERGY - 2
5
Consequences of energy deficiency
  • Changes in lifestyle
  • First, the poor people get poorer
  • Then, the rich people get poorer
  • Chaos, health degradation, and starvation follow
  • Energy wars?
  • We may already be involved in one of them
  • General collapse of modern civilization
  • Extreme, but possible

THE NEED FOR ENERGY - 3
6
Whats to Talk About?
  • Two sides of the story
  • The technical, hard science engineering side
  • The social, human understanding side

7
Whats to Talk About?
  • Two sides of the story
  • The technical, hard science engineering side
  • The social, human understanding side
  • All energy sources are important
  • But nuclear energy is uniquely capable of
    scaling up

8
Whats to Talk About?
  • Two sides of the story
  • The technical, hard science engineering side
  • The social, human understanding side
  • All energy sources are important
  • Nuclear energy is uniquely capable of scaling
    up
  • We (all of humanity) are in a fix
  • We are addicted to petroleum a limited resource
  • There are too many of us to sustain a low energy
    existence

9
Safety is a State of Mind
  • At the same time, I might feel perfectly safe and
    you might feel terribly threatened
  • Years ago, my brother was a military helicopter
    pilot. He could terrify me with maneuvers that
    were routine to him
  • Nuclear safety discussions take place at the
    border between technology and psychology
  • Risk is my topic today
  • Notionally, it is the inverse of safety
  • Objective risk is easier to discuss because it is
    usually expressed as the product of probability
    and consequence
  • Subjective risk is not often recognized, but is
    vitally important

10
Lets Talk Like Insurance Brokers
  • The insurer (we) is the society at large
  • You are the insured
  • We will compensate you for loss, should it
    occur
  • at a price
  • What price will we charge for this assurance?
  • a price calculated so that we show a profit, on
    average
  • How will we calculate the price?
  • by the average sum over all policy holders of the
    probability of loss times the promised
    compensation
  • Will you decide to pay the price?
  • that depends on what you expect to receive from
    us as the beneficiary, in both objective and
    subjective terms

11
Nuclear Risk vs Life Insurance
  • You are the beneficiary today
  • You also pay the premiums
  • Your risk of loss continues over the life of the
    power plants
  • We (society) promise you electricity for an eon
  • High reliability and reasonable cost, at low risk
  • Is this credible?
  • Your risk of loss is said to be insignificant
  • We also are members of this society
  • We think we know whereof we speak
  • Why should you believe us?

12
What is at Stake Here?
  • Energy, delivered reliably for many generations
  • The objective value of ample, economical energy
  • Avoided consequences of not having enough energy
  • Available alternatives can you get a better
    deal??

13
What is at Stake Here?
  • Energy, delivered reliably for many generations
  • The objective value of ample, economical energy
  • Avoided consequences of not having enough energy
  • Available alternatives Can you get a better
    deal?
  • better deal??
  • Objective and subjective risk
  • The real risk of personal harm NOT the average,
    but YOURS
  • The perception of being safe or unsafe, day by
    day

14
What is at Stake Here?
  • Energy, delivered reliably for many generations
  • The objective value of ample, economical energy
  • Avoided consequences of not having enough energy
  • Available alternatives can you get a better
    deal??
  • Actual and perceived risk
  • The real risk of personal harm NOT the average,
    but YOURS
  • A perception of being safe or unsafe, day by day
  • The key measure TRUST
  • How can you know? Whom can you trust?
  • Past performance, future expectations
  • Trust but verify as in international
    disarmament negotiations
  • Distrust, but value as we do all of our
    important institutions

15
Trust but Who should you trust?
  • Past performance
  • Trust the trustworthy
  • Engineering is a statutory profession with
    personal liability
  • Trust, but verify
  • Watchdogs are useful, even if theyre skilled
    professionals
  • The Canadian Nuclear Safety Commission is your
    watchdog
  • Who else has a deep interest in safety (low
    risk)?
  • Plant owners want to protect their investment
  • Customers want to avoid any radiation accidents
  • In our case, these are the same people

especially
16
Trust but Who should you trust (2)
  • Past performance
  • People working in many institutions are less than
    perfect
  • The frequency of institutional failure is seen to
    be large
  • Distrust, but value ref. Hugh Heclo On
    Thinking Institutionally
  • We cannot live without institutions in many forms
  • We need to watch them carefully, but respect them
    nonetheless

17
Alternatives A better deal?
  • Its a matter of scale
  • On a small scale, with few people, the job is
    quite easy
  • On a massive scale, with billions of people, the
    job is harder
  • We ask for solutions to serve billions of people
    for hundreds of years
  • A child now in diapers might find a brand new
    solution
  • Until then, nuclear fission energy is the only
    feasible answer.
  • Is this a credible statement?

18
Risk of Personal Harm - Actual
  • This can be calculated, albeit with uncertainty
  • Only the average risk can be quantified
  • Too many variables individual risk has a wide
    range of possibilities
  • Make conservative assumptions
  • Assume the most sensitive individual
  • For example, an infant
  • Assume maximum consequences
  • Ignore beneficial effects of low dose radiation,
    for example
  • Assume extreme failure conditions
  • Several unlikely events in sequence, conservative
    assumptions

19
But Are you still Feeling Unsafe?
  • Remember, you live in one of the richest, safest,
    best protected societies in all of history.
  • Canadian life expectancy at birth today is more
    than twice as long (gt80) as the poorest in
    Swaziland (lt40)
  • Swazilands life expectancy at birth today is
    about the same as was the US life expectancy at
    birth in 1850.

20
But Are you still Feeling Unsafe?
  • Remember, you live in one of the richest, safest,
    best protected societies in all of history.
  • Canadian life expectancy at birth today is more
    than twice as long (gt80) as the poorest in
    Swaziland (lt40)
  • Swazilands life expectancy at birth today is
    about the same as was the US life expectancy at
    birth in 1850.
  • Subjective risk is high for large events
  • Aircraft crash Actual less than 1 in 9 million
    per flight
  • Subjective risk is low for small events
  • Fatal car crash Actual about 1 in 5 thousand per
    year

Paul Slovic Elke U. Weber, Perception of Risk
Posed by Extreme Events, Proc. Conf. Risk
Management Strategies in an Uncertain World,
Apr. 2002
21
Is Nuclear energy dangerous?
  • Of course it is!!
  • A large amount of potential energy wrapped in a
    small package
  • Potential energy must be extracted at a
    controlled rate
  • The reaction products (the ashes of fission)
    must be managed
  • Dangerous, but manageable
  • Weve learned a lot over the past five decades
  • We know how to do this job
  • Are we perfect? No, but the residual risk is
    small
  • Less risky in the future
  • The technology is mature
  • Operational training and skill needs are clear
  • Worldwide institutional arrangements are in order

22
What are the risks?
  • The usual industrial risks
  • Mainly heavy objects, live steam, high voltage
  • Radiological risks
  • Digging uranium out of the ground and stimulating
    it to fission at a very high rate is a hazardous
    business
  • Under strict control, as we will see
  • Need to protect the plant, operating staff, and
    public
  • Sabotage risks
  • Hostile attack
  • Diversion of nuclear materials

23
What is being done to Reduce Risk?
  • Who is actually at risk?
  • The plant owner, in financial terms
  • Senior management, in terms of their careers
  • The plant operating staff, in physical terms
  • The local population, in lesser physical terms
  • The rest of us, almost entirely in financial
    terms
  • Who is doing what, to reduce risk?
  • The plant owners are training, testing, and
    retraining staff
  • The Canadian Nuclear Safety Commission is
    auditing operations
  • Atomic Energy of Canada is evolving new plant
    designs
  • Everyone is studying past operations for
    improvement ideas

24
Can terrorists make nuclear bombs?
  • First, can a reactor blow up like a nuclear bomb?
  • Absolutely not. (Too weak, too wet, too slow)
  • Terrorists who are they?
  • They are actually saboteurs -- why are we so
    afraid?
  • Are they working for a foreign government, or on
    their own?
  • Can they do it on their own?
  • Not unless we let them
  • Can they make a bomb from nuclear waste?
  • They can make an ordinary bomb a little more
    dangerous, but this is very difficult and
    dangerous mostly to themselves

25
Terrorists, continued
  • Diversion of nuclear material to hostile uses
  • This starts, most likely, as a financial
    transaction and may then become a tool for
    sabotage
  • This is a problem to be solved by cooperation
    between nations, not by nuclear plant designers
  • Attack on a nuclear facility by an armed group
  • To be a real threat, the group must have the
    active support of a national government and a
    powerful arsenal
  • Detection/detention is a job for the national
    police force
  • Crash of an aircraft into a nuclear station
  • Almost surely, the crash will cause shutdown of
    the reactor
  • A shut-down reactor is a pussy cat, not a tiger
    (Daiichi??)
  • Most of the people killed will have been
    passengers on the plane

26
Some Specifics of nuclear risk
  • The nature of the beast
  • Compare a coal plant and a nuclear plant . . .
  • Old reactor accidents
  • Louis Slotin, NRX, NRU, SL1, Windscale
  • Worlds largest power plant accident . . .
  • Chernobyl unit 4
  • Worlds 2nd largest power plant accident . . .
  • Three Mile Island unit 2
  • An accident that that didnt happen
  • Davis Besse pressurized water reactor

THE NATURE OF THE BEAST - 1
27
Is Nuclear safety different? -- Yes
HEAT ENERGY
FLY ASH
CARBON DIOXIDE
HEAT ENERGY
NEUTRONS
AIR
CONTROL
CONTROL
BOTTOM ASH
COAL
USED FUEL
URANIUM
THE NATURE OF THE BEAST - 2
28
The Neutron Chain Reaction
When the number of slow neutrons is
constant, the system is critical.
Leaked Neutrons
Delayed Neutrons appear after
Neutrons Slowing
10 seconds.
Down

Fast Neutrons slow down in about one
thousandth of a second
Delayed Neutrons
from Fission
Prompt
Neutrons
Neutrons
Diffusing
Leaked Neutrons
from
Fission
CONTROL THIS TO
"ASHES (Fission Products)
CONTROL HEAT
PRODUCTION
U235 FISSION
Captured
Neutrons
Slow Neutrons
HEAT
  • Some neutrons are captured in U238
  • and produce a useful fuel Pu239

THE NATURE OF THE BEAST - 3
29
Heat Balance the Key to control
  • A power reactor produces a lot of heat energy
  • A steam turbine uses almost all of this heat
  • The amount of heat added must equal the amount
    removed, at all times
  • If too much heat is added (or not enough heat is
    taken away), material temperatures rise water
    pressures increase
  • This is a dangerous combination

THE NATURE OF THE BEAST - 4
30
How fast can heat be released?
.07
Prompt Critical
.007
Reactivity (Dimensionless)
Prompt Neutron Lifetime 1 millisecond
.0007
Prompt Neutron Lifetime 0.01 millisecond
Normal Control Range
.00007
1
0.1
0.01
0.001
10
100
1000
10000
Time (T) Taken to Double the Reactor Power
(Seconds)
Power (t) Power (0) exp t/(T x 1.36)
THE NATURE OF THE BEAST - 5
31
Safe operating domain
THE NATURE OF THE BEAST - 6
32
Old Accidents
  • Louis Slotin (1945)
  • Re-Enactment of Slotin Experiment

33
National Research Experimental -- NRX
First Startup July 22, 1947 Accident 12 Dec
1952 Last Shutdown April 8, 1993
34
NRX Human Errors (1)
1. Control rod changes were made with the heavy water at a level that permitted the pile to go critical. It would have only required a short time to dump the heavy water to a safe level. This was a mistake in judgment as no instructions had ever been issued against such an operation.
2. It was realized by both the supervisor and the pile physicist that the operator in the basement was not thoroughly familiar with the pipes and valves. In such a critical hazardous experiment he should have been replaced. (Error in judgment).
3. Instructions were given over the telephone to change valve settings in a hazardous operation. Contrary to instructions all such valve changes were to be made on written instruction only.
4. The physicist had been instructed not to take charge of the control console. This instruction had come from his superintendent and in this case he did not take charge on the request of a supervisor. If he had been fully knowledgeable of the operation of the reactor he would not have made the mistake in buttons even though his instructions were wrong.
35
NRX Human Errors (2)
5. Free fall tests of the safety rods had never been practiced in the reactor. If this had been done it would have been found that the percentage of rod failures due to sticking was high. The clearance in these rods is so small that a bit of dust could cause them to hang up. Also there was some residual magnetism in the headgears that aided the rods in staying up. The reactor had always been operated under the assumption that the rods would fall in without the assistance of the accelerating air. This was never thoroughly tested and, in fact, was not true. (Error in judgment and design.)
6. The lights indicating the rods in the down position had not been functioning properly. As a result they were generally ignored. An error in design and judgment. It is interesting to note that these lights were being altered as time permitted with the intent that when alterations were complete the operation of the lights would be a requirement for reactor operation.
36
Windscale Production Reactors - UK
Built in the 1940s for Pu production. Loss of
control fire on Oct 11, 1957
37
National Research Universal - NRU
First startup Nov 11, 1957. Failure in
experimental channel May 24, 1958
38
SL-1 Stationary low power reactor 1
Major accident on Jan 3, 1961. Three operators
killed
US Army developed this concept for electricity
and heating at remote sites.
Operator
39
SL-1 Lessons Learned Prof. T.J. Thompson
  • (1) As far as possible, design, construction and
    operation should be the responsibility of a
    single organization.
  • (2) Responsibility for safety and all facets of
    reactor operation should be unequivocally defined
    -- ("a line organization should be used, not a
    committee").
  • (3) Safety review should be carried out by a
    single competent group external to the operating
    organization - reviews repeated by competing
    safety groups can "unduly harass the operating
    group and thereby reduce safety."
  • (4) The ultimate responsibility for operational
    safety must ultimately rest on the immediate
    operating team at the reactor - "in the final
    analysis the reactor shift supervisor and, in
    turn, the operator at the control console should
    have the authority to shut down the reactor if
    either believes it to be unsafe."

40
Three Mile Island-2 Final Reactor Configuration
March 28, 1979
Good design No overpower pulse Poor
operation Bad procedures Effective containment
41
Chernobyl Unit 4
April 26, 1986
42
Chernobyl Some Contributing Factors
  • The plant designer won a Lenin prize
  • Safety cautions from Kurchatov Inst. were ignored
  • Test procedure was mandated from Moscow
  • Effective command of the plant operation was
    turned over to the test team they were ignorant
  • Safety protective systems were disabled
  • Operation at low power continued in spite of ban
  • Test was continued in spite of serious operator
    errors

43
Davis-Besse Vessel Head Corrosion
Circa March 2002
An accident that did not happen
44
Another Accident that Didnt Happen
  • During the 1990s
  • Ontario fell out of love with nuclear energy
  • An open retirement package was offered to staff
  • More than 10,000 employees took the package and
    retired
  • About 4,000 skilled nuclear operations staff left
    the company
  • Nuclear Operations was placed under extreme
    stress
  • In 1997
  • Seven large nuclear units were shut down,
    voluntarily
  • Morale in the nuclear fleet hit rock bottom
  • Due to strong leadership within middle management
  • No serious consequences ensued

45
---- and One That Did Happen (??)tsunami
  • Design basis 5.2 to 5.7 metres
  • Measured wave 14 metres (TEPCO update)
  • Consequent multi-unit station blackout
  • Human errors
  • Insufficient grid protection from earthquake (??)
    jishin
  • Fossil units shut down, so the offsite grid
    collapsed
  • Insufficient protection of emergency power supply
  • Diesels in basement, fuel tanks at grade
  • Inter- unit electrical connections?
  • Failure to review promptly following Kobe event
    (1995)

46
Lessons Learned?
  • Human error dominated in all of these events
  • Machines are much too stupid to make mistakes
  • Humans also perform spectacular saves
  • Pickering pressure tube failure
  • Dislocation of OH nuclear operations in 1997 and
    beyond
  • Hudson River airline pilot landing in Hudson
    River
  • Chilean coal mine rescue
  • Studying others accidents is educational
  • It helps to avoid having to study ones own
    accidents
  • The practice builds care, caution and humility

47
What is Risk?
A thing of the Future
FUTURE
RISK LEVEL
PAST
UNCERTAINTY
0
48
Systems Design for Risk Reduction

Also known as Defence in Depth
Review
Maintain
Upgrade
Defence in Time
49
Risk and People -- To Err is Human
Uniquely

The human cycle of Performance
Institutional Factors?
50
A risk Management system
PEOPLE
AND
GOVERNMENT
SAFETY
SCIENTIFIC-
STANDARDS
TECHNICAL
AUTHORITY
COMMUNITY
OPERATING
ORGANIZATION
DESIGNER-
SAFETY
MANUFACTURER-
PERFORMANCE
CONSTRUCTOR
REGULATOR
INDUSTRY
REGULATORY
RESPONSIBILITY
RESPONSIBILITY
51
But What if Everything Goes Wrong?
  • Reactivity rises
  • Loss of control?
  • Safety shutdown fails?
  • ?Big energy release
  • High temperature
  • Steam Explosion
  • No Fuel Cooling?
  • Containment Rupture? Fuel Ejection Out of
    Reactor?
  • Widespread Distribution of Radioactive Fission
    Products?

.07
.007
Prompt Neutron Lifetime 1 millisecond
.0007
Prompt Neutron Lifetime 0.01 millisecond
.00007
1
0.1
0.01
0.001
10
100
1000
10000
52
Conclusion - Pickering A worst Accident
  • The important overall conclusions are as follows
  • The discharge of steam from a failed calandria
    vessel must consider the available physical heat
    transfer mechanisms and compartment volumes. This
    becomes the dominant discharge into containment
    volumes over and above the discharge from the
    initiating LOCA pipe rupture and determines the
    extent of over-pressurization of the containment
    envelope. Thus, containment integrity margins can
    be expected to be larger than in Pickering A for
    designs which have water filled reactor
    (calandria) vaults (Pickering B, CANDU-6) or
    shield tanks (Bruce A B, Darlington) which will
    further condense steam discharged from a failed
    calandria vessel, or for plants which have large
    multi-unit shared containment volumes (Bruce A
    B, Darlington). Since Pickering A has an
    acceptable margin it may be inferred that the
    margins for other CANDU plant will also be
    acceptable.
  • The original 1987 analysis was considered at the
    time by some, and to this date by others, to be
    speculative. This reassessment has demonstrated
    that the analysis was in fact robust and the
    conclusions remain significantly conservative and
    essentially unchanged by knowledge gained and
    discoveries made in the intervening years.
  • CANDU plants are capable of withstanding
    extremely unlikely events causing early core
    disruption without significant risk to the
    public.
  • Long term fuel cooling is required by all power
    reactors they must have an ultimate heat sink
  • Continuing electrical power supply is required
    by most water reactors

Prof. J.C. Luxat
53
Result another example
  • This reactor was vulnerable
  • Weak design
  • Poor operation
  • Bad management
  • After this accident
  • Design improved
  • Operating procedures changed
  • Better control systems installed
  • Management was changed
  • IAEA and WANO plant inspections were initiated

54
Yet Another example
Info. From Duane Arnold (BWR Mark 1)
54
55
Hiroshima, Then and Now
Daiichi did not produce such large health
consequences
56
Meltdown in a PWR
  • Concentrated fuel mass, small amount of hot, high
    pressure water around fuel
  • Poor maintenance practice
  • Operator misunderstanding
  • Management laxity
  • Poor procedures based on bad regulatory demands
  • Lucky outcome

57
THE SOLUTION Westinghouse AP 1000
Similar to BWR Mark I Primary Containment Concept
Depressurize
  • Water is added when Tcore exitgt 650 C
  • Steam is vented to containment
  • Ultimate heat sink --- conduction convection to
    atmosphere

58
ANOTHER SOLUTION - COOLING IN CANDU
Much more cool, low pressure water than either
PWR or BWR Filtered containment vent, passive
hydrogen-oxygen recombiners
CANDU 6 Dousing system
59
CANDU Power Supply reliability
  • Power setback and stepback capability
  • Unit continues to run on its own power supply
  • Duplicate service transformers unit station
  • Auto-transfer on loss of UST
  • Emergency supplies on site
  • Multi-unit sites (China, Korea, Romania,
    Ontario)
  • Inter-unit transfer bus
  • Grid feed-in logic (Ontario)
  • System recognizes station as potential power
    customer
  • Future modifications?
  • Ultimate heat sink?

60
Notional Risk Curves, and Trends
Disaster Range
Direct Experience Range
Risk Assessment Range
Utility economics performance requirements
Smart components and systems
Log Frequency
Regulatory Risk Acceptance Curve
Trends with increasing experience, knowledge, and
realistic consequence assessment
Log Consequence
Realistic accident modeling and consequence
assessment
61
Todays conclusions
  • What will tomorrow bring?
  • We dont know just wait, and the future will
    come
  • Oil and gas supplies will wane
  • The population of the earth will rise
  • Climate will change, in one way or the other
  • Nuclear fission energy will be available for all
  • Yes, someone might invent a better way, someday
  • But just in case they do not
  • There is plenty of uranium for many thousands of
    years
  • There is enough uranium available to supply ALL
    human energy needs for as long as we live on this
    earth
  • This technology can be safely managed, in the
    past
  • Will people reject the nuclear energy solution?
  • Doubtful but buildup might be delayed until time
    runs out
About PowerShow.com