Nuclear Electric Power Safety Operation and Control Aspects J. Brian Knowles

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Nuclear Electric Power Safety Operation and Control Aspects J. Brian Knowles

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Contents

Preface ix
Glossary xiii
Principal Nomenclature xv
1. Energy Sources, Grid Compatibility, Economics, and the
Environment 1
1.1 Background, 1
1.2 Geothermal Energy, 3
1.3 Hydroelectricity, 5
1.4 Solar Energy, 7
1.5 Tidal Energy, 8
1.6 Wind Energy, 13
1.7 Fossil-Fired Power Generation, 17
1.8 Nuclear Generation and Reactor Choice, 20
1.9 A Prologue, 30
2. Adequacy of Linear Models and Nuclear Reactor Dynamics 34
2.1 Linear Models, Stability, and Nyquist Theorems, 34
2.2 Mathematical Descriptions of a Neutron Population, 44
2.3 A Point Model of Reactor Kinetics, 45
2.4 Temperature and Other Operational
Feedback Effects, 49
2.5 Reactor Control, its Stable Period and
Re-equilibrium, 51
3. Some Power Station and Grid Control Problems 56
3.1 Steam Drum Water-Level Control, 56
3.2 Flow Stability in Parallel Boiling Channels, 59
3.3 Grid Power Systems and Frequency Control, 63
3.4 Grid Disconnection for a Nuclear Station with
Functioning “Scram”, 71
4. Some Aspects of Nuclear Accidents and Their Mitigation 79
4.1 Reactor Accident Classification by Probabilities, 79
4.2 Hazards from an Atmospheric Release of Fission
Products, 82
4.3 Mathematical Risk, Event Trees, and Human Attitudes, 84
4.4 The Farmer-Beattie Siting Criterion, 87
4.5 Examples of Potential Severe Accidents in Fast Reactors
and PWRs with their Consequences, 93
5. Molten Fuel Coolant Interactions: Analyses and
Experiments 101
5.1 A History and a Mixing Analysis, 101
5.2 Coarse Mixtures and Contact Modes in Severe Nuclear
Accidents, 105
5.3 Some Physics of a Vapor Film and its Interface, 110
5.4 Heat Transfer from Contiguous Melt, 115
5.5 Mass Transfer at a Liquid–Vapor Interface and the
Condensation Coefficient, 121
5.6 Kinetics, Heat Diffusion, a Triggering Simulation,
and Reactor Safety, 124
5.7 Melt Fragmentation, Heat Transfer, Debris Sizes, and
MFCI Yield, 131
5.8 Features of the Bubex Code and an MFTF
Simulation, 140
6. Primary Containment Integrity and Impact Studies 148
6.1 Primary Containment Integrity, 148
6.2 The Pi-Theorem, Scale Models, and Replicas, 155
6.3 Experimental Impact Facilities, 160
6.4 Computational Techniques and an Aircraft Impact, 165
7. Natural Circulation, Passive Safety Systems, and
Debris-Bed Cooling 173
7.1 Natural Convection in Nuclear Plants, 173
7.2 Passive Safety Systems for Water Reactors, 179
7.3 Core Debris-Bed Cooling in Water Reactors, 181
7.4 An Epilogue, 186
References 192
Index 207

Preface

If the industries and lifestyles of economically developed nations are
to be preserved, then their aging, high-capacity power stations will soon
need replacing. Those industrialized nations with intentions to lower
their carbon emissions are proposing nuclear and renewable energy
sources to fill the gap. As well as UK nuclear plant proposals, China
plans an impressive 40% new-build capacity, with India, Brazil, and
South Korea also having construction policies. Even with centuries of
coal and shale-gas reserves, the United States has recently granted a
construction license for a pressurizedwater reactor (PWR) near Augusta,
Georgia. Nuclear power is again on the global agenda.
Initially renewable sources, especially wind, were greeted with
enthusiastic public support because of their perceived potential to
decelerate global climate change. Now however, the media and an
often vociferous public are challenging the green credentials of all
renewables as well as their ability to provide reliable electricity
supplies. Experienced engineering assessments are first given herein
for the commercial use of geothermal, hydro, solar, tidal and wind
power sources in terms of costs per installed MW, capacity factors,
hectares per installedMWand their other environmental impacts. These
factors, and a frequent lack of compatibility with national power
demands, militate against these power sources making reliable major
contributions in some well-developed economies. Though recent global
discoveries of significant shale and conventional gas deposits suggest
prolonging the UK investment in reliable and high thermal efficiency
combined cycle gas turbine (CCGT) plants, ratified emission targets
would be contravened and there are also political uncertainties.
Accordingly, a nuclear component is argued as necessary in the
UK Grid system. Reactor physics, reliability and civil engineering
costs reveal that water reactors are the most cost-effective. By virtue of
higher linear fuel ratings and the emergency cooling option provided by
separate steam generators, PWRs are globally more widely favored.
Power station and grid operations require the control of a number of
system variables, but this cannot be engineered directly from their full
nonlinear dynamics. A linearization technique is briefly described and
then applied to successfully establish the stability of reactor power,
steam drum-water level, flow in boiling reactor channels and of a Grid
network as a whole. The reduction of these multivariable problems to
single input-single output (SISO) analyses illustrates the importance of
specific engineering insight, which is further confirmed by the subsequently
presented nonlinear control strategy for a station blackout
accident.
Public apprehensions over nuclear power arise from a perceived
concomitant production of weapons material, the long-term storage of
waste and its operational safety. Reactor physics and economics are
shown herein to completely separate the activities of nuclear power and
weapons. Because fission products from a natural fission reactor some
1800 million years ago are still incarcerated in local igneous rock strata,
the additional barriers now proposed appear more than sufficient for
safe and secure long-term storage. Spokespersons for various nonnuclear
organizations frequently seek to reassure us with “Lessons have
been learned”: yet the same misadventures still reoccur. Readers find
here that the global nuclear industry has indeed learned and reacted
constructively to the Three Mile Island and Chernobyl incidents with
the provision of safety enhancements and operational legislation. With
regard to legislation, the number of cancers induced by highly unlikely
releases of fission products over a nuclear plant’s lifetime must be
demonstrably less than the natural incidence by orders of magnitude.
Also the most exposed person must not be exposed to an unreasonable
radiological hazard. Furthermore, a prerequisite for operation is a
hierarchical management structure based on professional expertise,
plant experience and mandatory simulator training. Finally, a wellconceived
local evacuation plan must pre-exist and the aggregate
probability of all fuel-melting incidents must be typically less than 1
in 10 million operating years.
Faulty plant siting is argued as the reason for fuel melting at
Fukushima and not the nuclear technology itself. If these reactors
like others had been built on the sheltered West Coast, their emergency
power supplies would not have been swamped by the tsunami and
safe neutronic shut-downs after the Richter-scale 9 quake would have
been sustained.
To quantify the expectation of thyroid cancers from fission product
releases, international research following TMI-2 switched from intact
plant performance to the phenomenology and consequences of fuel
melting (i.e., Severe Accidents) after the unlikely failure of the multiple
emergency core cooling systems. This book examines in detail the
physics, likelihood and plant consequences of thermally driven explosive
interactions between molten core debris and reactor coolant
(MFCIs). Because such events or disintegrating plant items, or an
aircraft crash are potential threats to a reactor vessel and its containment
building, the described ”replica scale” experiments and finite element
calculations were undertaken at Winfrith. Finally, the operation and
simulation of containment sprays in preventing an over-pressurization
are outlined in relation to the TOSQAN experiments.
This book has been written with two objectives in mind. The first is to
show that the safety of nuclear power plants has been thoroughly
researched, so that the computed numbers of induced cancers from
plant operations are indeed orders of magnitude less than the natural
statistical incidence, and still far less than deaths from road traffic
accidents or tobacco smoking. With secure waste storage also assured,
voiced opposition to nuclear power on health grounds appears
irrational. After 1993 the manpower in the UK nuclear industry
contracted markedly leaving a younger minority to focus on decommissioning
and waste classification. The presented information with
other material was then placed in the United Kingdom Atomic Energy
Authority (UKAEA) archives so it is now difficult to access. Accordingly
this compilation under one cover is the second objective. Its
value as part of a comprehensive series of texts remains as strong as
when originally conceived by the UKAEA. Specifically, an appreciation
helps foster a productive interface between diversely educated
new entrants and their experienced in situ industrial colleagues.
Though the author contributed to the original research work herein, it
was only as a member of various international teams. This friendly
collaboration with UKAEA, French, German and Russian colleagues
greatly enriched his life with humor and scientific understanding.
Gratitude is also extended to the Nuclear Decommissioning Authority
of the United Kingdom for their permission to reproduce, within this
book alone, copyrighted UKAEA research material. In addition thanks
are due to Alan Neilson, Paula Miller, and Professor DerekWilson, who
have particularly helped to “hatch” this book. Finally, please note that
the opinions expressed are the author’s own which might not concur
with those of the now-disbanded UKAEA or its successors in title.