Boiler dynamics and control in nuclear power stations 2 : proceedings of the second international conference, Bournemouth, 23-25 October, 1979 : (also: BNES international conference on boiler dynamics)

435 Pages·1980·56.54 MB·English

by  Harding

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Pre ference
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The British Nuclear Energy Society, London, 1980
Conference sponsored by the British Nuclear Energy Society, the Institution of Electrical Engineers
and the Institution of Mechanical Engineers
Organized by the British Nuclear Energy Society
ORGANIZING COMMITTEE
M. H Butterfield (Chairman)
R. L. Carstairs
G B. Collins
G Duffett
A. Green
J. A. Hitchcock
R. Newnham
DrD. H. Rooney
M. Whitmarsh-Everiss
A. W. A. Willis
PR OD UCTION EDITOR
Bonny J. Harding
ISBN: 0 7277 0095 2
© The British Nuclear Energy Society, 1980
All rights including translation, reserved. Except for fair copying, no part of this publication may
be reproduced, stored in a retrieval system, or transmitted in any form or by any means electronic,
mechanical, photocopying, recording or otherwise, without the prior written permission of the
Managing Editor, Publications Division, Institution of Civil Engineers, PO Box 101, 26-34 Old
Street, London EC1P 1JH
The British Nuclear Energy Society as a body does not accept responsibility for the statements
made or the opinions expressed in the following pages
Published by the British Nuclear Energy Society, and produced and distributed by Thomas Telford
Ltd, 1-7 Great George Street, London SW1P3AA
Printed by Inprint of Luton (Designers and Printers) Ltd
Contents
Opening address. R. M. Southwood
Transients
1. U-tube steam generator modelling: application to level control and com­
parison with plant data. A. Gautier, J. F. Petetrot, A. Roulet, P. Ruiz and
G Zwingelstein 3
2. U-tube steam generator dynamics modelling and verification.
N. W. S Bruens 11
3. A grid disconnection trip strategy for a Benson system cycle in fast-reactor
power plant. J. B. Knowles and D. R. Farrier 21
4. Transient calculations of a 45 MW(th) steam generator model for sodium-
cooled fast breeder reactors. L. Chelli, G Papa and C. Salgo' 29
5. Development and verification of a space-dependent dynamic model of a
natural circulation steam generator. C. G Mewdell, W. C Harrison,
E. H. Hawley, R. S. Dumont and G H Green 35
Discussion on transients 47
Model validation
6. Peach Bottom II turbine trip test analysis. M S. Lu, H. S. Cheng,
C /. Hsu, D. /. Diamond, W. G Shier, M. M. Levine and F. Odar 51
7. Verification of a dynamics model of a sodium heated steam generator.
A. Izume and J. Kubota 61
8. Experimental simulation studies of PWR U-tube steam generators.
S. P Kalra, G Adams, R. B. Duffey, W. Lapson and R Lundberg 69
9. Transient two phase flow in a forced circulation Freon test rig.
H C. Simpson, D. H Rooney, T. M. S. Callander and K C. NG 11
10. Numerical simulation in unsteady-state running of the 45 MW scale
model SUPER-PHENIX steam generator. /. M Lecoeuvre, P. Hemmerich,
J. P. Fabregue and P. Lauret 87
11. Application of a two-dimensional boiler model to design and operational
problems in AGR and Magnox power stations. /. D. Balfour, T, Fallows,
C R. Gane, R. C. Hones, J. Lis, R. J. Preece and G M Gill 95
12. Hydrodynamic stability tests and analytical model development for
once-through sodium heated steam generator. /. Kubota, T. Tsuchiya,
T. Iwashita and K. Monta 105
13. Feed flow limit cycling in AGR boilers. C H. Green, P. Lightfoot,
R. Deam and B. Chojnowski 117
Discussion on model validation 125
Hydrodynamic stability
14. Flow instabilities in a once-through steam generator. H. Nariai,
M. Kobayashi, T. Matsuoka, Y. Ito and L Aya 131
15. Void-flow instability: prediction and verification of operating limits.
B. Vriesema and D. G H Latzko 139
16. Tube to tube excursive instability—sensitivities and transients.
M. Brown and M. W. Lay land
17. Prediction of dynamic stability limits of the 45 MW scale model of
SUPER PHENIX steam generator. /. Perrin and Ch. Simeon
18. Analysis of the hydrodynamic stability of natural circulation boilers.
/. Olive and J. P. Baby
19. Experimental determination of density-wave oscillations in full-scale
sodium-heated steam generators. J. Brasz and D. Van Essen
20. Steam generator stability at variable loads. P. A. Andreev, N. S. Alferov,
I. S. Kudriavtsev, P. M. Paramonov, B. L. Pascar, R. A. Rybin,
A. V. Sudakov, I. K Terentiev and E. D. Fedorovich
Discussion on hydrodynamic stability
Modelling and computational techniques
21. Improved calculation procedures for heat transfer and associated
pressure drop analysis. /. W. E. Campbell
22. A weighted residual approach to two-phase flow problems in nuclear
systems. U. Graf, P. Romstedt and W. Werner
23. Interactive simulation of nuclear power systems using a dedicated
minicomputer—computer graphics facility. C. Tye and A. O. Sezgen
24. Numerical comparison between a reference and simplified two-phase
flow models as applied to steam generator dynamics. J.-F. Dupont,
G Sarlos, D. M. Le Febve and P. Suter
25. AGR design and simulator reference dynamic total plant models.
P. Dulson
26. Simulation tools in CEA. A. Bonnemay, D. Delourme, P. Drusch,
Tran Tuc Vi and C. Samak
21. Dynamic modelling of nuclear steam generators. T. W. Kerlin,
E. M. Katz, J. Freels and J. Thakkar
28. BESBET II—A computer code for the simulation of severe transients in
LMFBR boilers. R. K. Thomasson
Discussion on modelling and computational techniques
Control systems
29. Dynamic analyses and control systems for steam generators in
LMFBRs. Y. Kohata, K Furuichi and Y. Sagayama
30. Control and operation of the SUPER PHENIX steam generators.
/. C. Schneider, G Skull, M. Hery and M. Debru
31. Application of multivariable frequency response methods to boiler
control system design. F. M. Hughes and G R Collins
32. Automatic control of steam generator levels in EDF PWR units.
C Miossec, J. Tassart and E. Irving
32 a. Towards efficient full automatic operation of the PWR steam generator
with water level adaptive control. E. Irving, C. Miossec and J. Tassart
Discussion on control systems
Codes
33. Gas cooled reactor plant once-through steam generator dynamics:
mathematical model and construction principles of steam generator automatic
control system. A. G Chernov, F. M. Kuts, L. A. Ostrovsky,
V. E. Pleshkov and I. G Polumordvinova 335
34. NUMEL—A computer aided design suite for the assessment of the
steady state, static-dynamic stability and transient responses of once-through
steam generators. P. Lightfoot, R. T. Deam, C. H. Green and J. Rea 347
35. DYMEL code for prediction of dynamic stability limits in boilers.
R. T. Deam 357
Discussion on codes 365
Data and steady state
36. Experimental advances on boiler heat transfer. M Cumo, G E. Farello
and G Palazzi 367
37. A technique for estimating steady state temperature variation
tube-to-tube within an AGR boiler from measurements external to the
pressure vessel. A. W. L. Morris 379
38. CROSSMIX: A mathematical model of a multi-pass cross-flow heat
exchanger with primary fluid mixing. T. Fallows, C. R. Gane, R. C Jones,
J. Lis and T. H. Massey 391
39. Prediction of steady, three-dimensional flow in pressurized-water steam
generators. G Hulme, P. Phelps, D. B. Spalding and D. G Tatchell 397
Discussion on data and steady state 407
Commissioning
40. Commissioning and subsequent development of boiler feedwater control
systems on the Prototype Fast Reactor. A. Bainbridge, J. Gray,
L. A. J. Lawrence and K T. C. McAffer 411
41. Commissioning of AGR boiler control systems. P. Warne 419
Discussion on commissioning 427
Closing address. /. Brown 429

Opening address
J. R. M. SOUTHWOOD, Nuclear Power Company Limited, Risley
The papers for this Conference cover a wide fining them to perform various feats of scienti­
range of topics, and reflect the increasing fic elegance can, however, be a dangerous dis­
understanding of the subject and its importance. traction. The temptation to concentrate on the
The behaviour and control of boilers affect the topic for its own sake must be resisted.
overall reactor plant performance directly. And Answers to three decimal places must be jud­
here I am using the word 'performance' in its ged against the difficulty of calibrating items
broadest sense - namely, how well it works. The such as thermocouples to better than plus or
boiler which does not have tube failures induced minus a few degrees.
by spurious transients, or which does not come One or two questions should be at the fore­
out of service due to a faulty control system, front of our minds in considering the approach
is the successful one. to modelling: How well do the modelling tech­
We have all become more aware of the import­ niques truly represent reactor conditions? How
ance of availability in achieving good overall sure are we that the available operational ex­
economics in plant operation. It is generally perience is reflected in the refining processes
true that the plant which has a good availability to improve the model? How relevant is the in­
will usually compete strongly with one which is formation obtained in using the model? Can
perhaps nominally more efficient but less rel­ that information be applied in practice, bearing
iable . in mind the engineering limits of control sys­
Our subject for this conference also has a tems and instrumentation systems? How relevant
very direct relevance to reactor safety. The is the scope of the model in relation to the
boiler or steam generator or heater exchanger actual characteristics of the plant, particular­
fulfils much more than its primary role of con­ ly under 'off-design' operation?
verting reactor heat to steam. Its response to Many of the difficulties encountered in heat
changes from the reactor, or from the demand for exchangers associated with reactors have been
steam, forms a vital link in the overall station linked to mundane design defects rather than
control scheme. shortcomings arising from fundamental technolog­
As the principal route for the removal of re­ ical problems.
actor heat, it plays a key role in the post trip Any modelling technique clearly has a limited
sequence. Its behaviour at this time can make a application if it disregards the most likely
great difference in the provisions considered reasons for shortcomings, and will only have
necessary to handle possible fault conditions. limited value if the conclusion from the study
The industry has had, in the recent past, some cannot be implemented in practical and economic
very striking examples of this around the world. engineering terms. For example, there will al­
Since the last conference in 1973, held in ways be difficulty in predicting the degree of
London, many more reactor-years of operation coolant missing in a gas-cooled reactor where a
have been accumulated, and a number of unpredic- large number of fuel channels are discharging
ted incidents have occurred during operation. gas, at varying temperatures, to the steam
It is disappointing, therefore, that there is generators. This lack of uniformity will prod­
not more operational information featured in the uce temperature scatter in the many parallel
papers presented. tube paths.
Difficulties have been experienced in commis­ Test rig work can, of course, help in validat­
sioning control equipment on site - in some ing models, particularly if the scale effect
cases, because the control system concept was can be minimized, but such results must be
weak, and in other cases, because the equipment treated with caution. We all know the anomalies
itself was inadequate. More information on which arise when comparing rig results with
such experiences would be very helpful. reactor measurements. What can be done in fut­
Perhaps this lack of balance in the papers can ure to improve the quality of such reactor
be remedied during the discussion periods. Any measurements and their relationship to rig work?
such contributions should give more opportunity Such difficulties and shortcomings should not
to compare actual performance with theoretical discourage the development of techniques which
predictions. are as versatile as possible. There is scope
Many of the papers concentrate on various as­ for improving the overall reactor performance by
pects of modelling. This is certainly an impor­ optimizing the performance of the steam gener­
tant topic and merits widespread discussion. ator in relation to the reactor characteristics.
The fascination of developing models and re­ There is also scope for improving output by
OPENING ADDRESS
finding ways of operating nearer constraint
boundaries set by material temperatures and
rates of change.
There is certainly scope for reducing the ex­
penditure necessary to protect against fault
conditions by understanding better the precise
behaviour of the plant when faults occur. Such
understanding can not only improve the plant in
terms of public safety but also in terms of the
economic protection of the investment in the
plant.
Finally, a very real contribution can be made
by the improvement of simulator models for op­
erator training. It is now widely recognized
that the general standards of plant operation
are just as important as the standards of plant
manufacture and installation. Improved operat­
ing standards will provide a large economic ben­
efit from the improvement in availability, in
addition to the confidence that, under fault
conditions, all the correct actions will be
taken.
The subject of this conference is undoubtedly
competing with reactor component design as one
of the more important features of nuclear power.
Your studies can do a great deal, not only to
contribute to more successful reactor operation
but also to establish public confidence in the
economics and safety of nuclear power.
1. U-tube steam generator modelling: application to level control
and comparison with plant data
A. GAUTIER, J. F. PETETROT, A. ROULET and P. RUIZ, Framatome and
G. ZWINGELSTEIN, Commissariat a VEnergie Atomique
A non linear multinode digital model of a recirculating U-tube steam generator is first described.
Comparison between the model and Fessenheim and Bugey tests results on power step and full load
rejection is given. These transients are of special interest because they provide information on
the boiler high frequency response and also insights into steam generator non linear behaviour.
An example of steam generator modelling as applied to control system design is then presented. This
example demonstrates major improvement of control loop performance at low load following implemen­
tation of a non linear gain which allows more efficient control of large perturbations. Results of
testing on the Bugey 4 plant are also indicated.
1. INTRODUCTION 2. STEAM GENERATOR MODELLING
Controlling the steam generator level in a large 2.1 Objectives
PWR plant is of major importance in order to
ensure sufficient cooling of the reactor, good A non linear model was developed with the triple
performance of the steam separators and dryers goal of :
and also to eliminate all risks of hydrodynamic
a) providing adequate simulation of all the
instability. As a result, a good control system
steam generator main parameters (with special
proves to be a determinant factor in overall
attention given to the water level) and this
plant availability.
for all kinds of small and large transients
such as load steps from any power level, full
Unfortunately, due to the presence of steam
load rejection and feedwater perturbations.
bubbles in the tube bundle, the steam generator
level is known to temporarily react in an adverse b) remaining as simple as possible and thus
manner to input variations : the level first using less computer time.
appears to increase under augmented steam flow
c) being fully validated by comparison with
and to drop under increased feedwater flow, the
actual plant test data.
opposite of what takes place in both cases over
longer periods. These effects, respectively known
2.2 Geometrical representation
as the swell and shrink phenomena, are signifi­
cantly greater at low load, which renders more
The U-tube steam generator is broken down into
hazardous the use of a high gain control loop at
5 main parts : the subcooled and boiling sections
reduced power level. Particular attention must
(which make up the heat transfer region) , the
therefore be paid to low load operation in the
riser (at the outlet of which separation of
control loop design process in order to develop
steam and liquid takes place in cyclone separa­
a system capable of satisfactorily controlling
tors) , the dome region in which steam is eva­
large transient while keeping a sufficient
cuated after going in the dryers) and finally
stability margin.
the downcomer region (where saturated liquid is
recirculated through the tube bundle after mixing
Designing the steam generator control system
with subcooled feedwater flow) .
thus requires a very good modelling of level
transients.
2.3 Main assumptions of the model
This paper first describes a steam generator
To develop a mathematical model for a complex
model which has been developed and validated in
system such as a steam generator, several simpli­
collaboration with the French Atomic Energy
fying assumptions have to be made. They are
Commission on the Fessenheim 1 and 2 and Bugey 2
reviewed hereunder.
to 5 nuclear plants. The paper then describes
how this model is currently in use to help fina­
Two phase flow
lize a substantial improvement to the current
control system whose preliminary testing on the
This is one of the most delicate points in
Bugey 5 plant has proven extremely promising.
steam generator modelling.
Details of the control loop modification and
plant testing are also given.
Homogeneous flow theory has been adopted, be­ Energy balance :
cause it provides the simplest technique for
analyzing two phase flows. Suitable average (2) (Pi hi S Z )
X fi
properties are determined and the mixture is
ZB dZB
treated as a pseudo-fluid that obeys the usual QB + Qi h! + f ^ + p
equations of single component flow. Is 'X 1 "d ' 4 ZT ' Hls "Is dt
This assumption has proven to be quite satis­ BOILING SECTION
factory considering the pressure range in the
Mass balance :
steam generator secondary side.
*g
Heat transfer (3) ^ CP S {Z - Z}) = QB - QT - S
2 2 T B 2
The heat exchanger calculation relies on the Energy balance :
classic assumptions of a one-dimensional flow
d
for both primary and secondary fluids. (4) -£ ({Z^ - ZJ p h S) - QB h - QT h
dt vl"T "BJ 2 2 2 lg 23
For the sake of simplification, the actual U-tube ZT - ZB
heat exchanger is replaced by a parallel flow ZT "1. S>hls ^ + S*<ZT " V f
heat exchanger. The length taken into account
on the primary side is the total length of the In the above equations, mass and energy balances
U-tube, whereas the length on the secondary side are derived in regions separated by a moving
is the height of the U-tube. All secondary fluid boundary, following the general scheme of refer­
is assumed to remain at saturation temperature. ence 1. The actual terms accounting for the boun­
dary movement can be derived using Leibnitz's
The global heat transfer coefficient is consi­
theorem. They have already been presented by E.
dered to be independent of primary and secondary
Taylor in a previous BNES conference on boiler
flows ; but its variation in accordance with
dynamics (references 2 and 3).
total heat flux is taken into account.
RISER
Energy and mass balances used for water
level calculation Mass balance
To determine the water level, it is necessary QT - Q2
<5> dt <>riser V >
to define a geometrical volume in which a mass riser
balance will lead to water level assessment. Energy balance :
For this purpose, geometrical boundaries are 3h3
arbitrarily defined : the upper limit is, of (6) at + ( 2 } p 9x
course, the water level itself ; the lower limit riser riser
is defined by the feedwater nozzle position.
DOME
In this volume perfect mixing of recirculating
Mass balance
and feedwater flox^s is assumed. The outgoing
flowrate is considered as the constant downcomer
flowrate. <7) dt (pvs W -X Q2 -
- Pressure drop WATER LEVEL
Mass balance
Analysis of pressure drops along the different
sections shows that they are due mostly to geo­
metrical changes. A simple homogeneous law is <8) dt ("is Sdn V Qal + (1 - X) Q2 QI
assumed.
Energy balance :
- Other assumptions
(9) dt v"(lPs. . Sd_n ZNM "hdj'
No heat transfer is considered between the tube
bundle region and the downcomer. Qal hal+ (1 ~X ) Q2 hls - hd1(Qal + {1"X} Q2)
The water is assumed to be separated from the DOWNCOMER
steam at the exit of the riser.
Energy balance :
The steam in the dome is assumed to remain satu­ q\ 3h
(10) ^ + 0
rated during any transient. The dome volume is 3t pd Sd 3x
taken to be constant.
MOMENTUM EQUATION
2.4 Main Equations
(11) a (Q2 + QB)2 + a QI2 + k (XQ2)2
Notations are explained at the end of the paper. x 2
N0N BOILING SECTION _2!f Q22
pd Sd p . S .
Mass balance : "riser riser
g(pd {Zd + z> - Z - p {z - Z }
(0 j£ (Pi S Z) - Qi - QB + p dZB N Pl fi 2 t fi
X B is Sl dt P . Z . )
riser riser