A TakagieSugeno fuzzy power-distribution method for a prototypical advanced reactor considering pump degradation

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A TakagieSugeno fuzzy power-distribution method for a prototypical advanced reactor considering pump degradation. This paper proposes a TakagieSugeno (TeS) fuzzy logic-based power distribution system. Two TeS fuzzy power distribution controllers have been designed and tested. Simulation shows that the devised TeS fuzzy controllers provide improved performance over traditional controls during daily load-following operation under different levels of pump degradation.
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Nuclear Engineering and Technology
journal homepage: www.elsevier.com/locate/net
Invited Article
A TakagieSugeno fuzzy power-distribution method for a prototypical
advanced reactor considering pump degradation
Yue Yuan a, Jamie Coble b, *
a Institute of Nuclear and New Energy Technology, Tsinghua University, Collaborative Innovation Center of Advanced Nuclear Energy Technology, Key
Laboratory of Advanced Reactor Engineering and Safety of Ministry of Education, Qinghua Yuan, Beijing, 100084, China
b Department of Nuclear Engineering, University of Tennessee, Knoxville, 210 Pasqua Engineering Building, Knoxville, TN, 37996, USA
a r t i c l e
i n f o
a b s t r a c t
Article history:
Advanced reactor designs often feature longer operating cycles between refueling and new concepts of
Received 20 June 2017
Accepted 20 June 2017
Available online 24 June 2017
operation beyond traditional baseload electricity production. Owing to this increased complexity,
traditional proportionaleintegral control may not be sufcient across all potential operating regimes. The
prototypical advanced reactor (PAR) design features two independent reactor modules, each connected
Advanced Reactors
Fuzzy Control
Multimodular Operation
Power Distribution
to a single dedicated steam generator that feeds a common balance of plant for electricity generation and
process heat applications. In the current research, the PAR is expected to operate in a load-following
manner to produce electricity to meet grid demand over a 24-hour period. Over the operational life-
time of the PAR system, primary and intermediate sodium pumps are expected to degrade in perfor-
mance. The independent operation of the two reactor modules in the PAR may allow the system to
continue operating under degraded pump performance by shifting the power production between
reactor modules in order to meet overall load demands. This paper proposes a TakagieSugeno (TeS)
fuzzy logic-based power distribution system. Two TeS fuzzy power distribution controllers have been
designed and tested. Simulation shows that the devised TeS fuzzy controllers provide improved per-
formance over traditional controls during daily load-following operation under different levels of pump
© 2017 Korean Nuclear Society, Published by Elsevier Korea LLC. This is an open access article under the
1. Introduction
cycles, some as long as 40 years [1], introduce furthercomplications
as the evolving condition of key components and systems may
Advanced small modular reactors (AdvSMRs) can potentially
affect the plant's operation.
complement the current eet of large, baseload light water reactors
Primary and intermediate sodium pumps are key components in
and replace fossil fuel-based energy production to support safe,
the reactor coolant system, which ensure that heat is removed from
carbon-neutral energy. AdvSMRs support new concepts of opera-
the core and transferred to the energy-producing balance of plant
tion, such as load following and power peaking, as renewable en-
system. These pumps may degrade during long-term normal plant
ergy sources more deeply penetrate the energy grid. These new
operation, which has a negative effect on the performance of the
concepts of operation will precipitate new research in system dy-
reactor power block. As pump degradation is detected and moni-
namics and control. The control system, the function of which is to
regulate the output power and temperatures of the reactor system
this will negatively impact the economics and availability of the
during operation, is of great importance to the realization of the
system. Alternatively, the distribution of power production across
economic goals and the improvement of performance. Liquid metal
independent reactor modules could be adjusted to compensate for
reactors (LMRs) present additional control challenges not seen in
degraded condition in one module, thereby extending the operating
the current eet of baseload light water reactors, including addi-
period of the overall system while meeting reactor power demands.
tional feedback effects and large time delays due to thermal inertia
In order to improve the economic competitiveness of advanced re-
of sodium coolant. Long-term control over planned operating
actors, it is important to take pump degradation into consideration
when designing control system for the reactor block.
* Corresponding author.
E-mail address: jamie@utk.edu (J. Coble).
The condition and performance of pumps is not directly
measured during operation, and the available ow from pumps is
1738-5733/© 2017 Korean Nuclear Society, Published by Elsevier Korea LLC. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/
Y. Yuan, J. Coble / Nuclear Engineering and Technology 49 (2017) 905e913
usually unknown. Traditional control strategies may be challenged
20 MWe power for a total reactor block output of 40 MWe. The
in controlling the system in the face of these uncertainties. Previous
intermediate heat exchangers and steam generators are also based
work has investigated the use of model predictive control for
on those at Experimental Breeder Reactor-II [13], whereas the
control of LMRs under normal conditions [2]. That work focused on
balance of plant model is adapted from [14].
a single large-scale reactor operating under normal load-following
The PAR design adopts the multimodular concept, which means
conditions with no equipment degradation. The proposed model
that each unit can be operated independently with different power
predictive control approach could potentially be extended, but it
output as desired. The multimodular operation supports greater
would likely require models of the degradation of key equipment
availability of the overall system by providing some level of
and systems as well as a model of the overall nuclear power system.
redundancy in heat production. Smaller reactor cores are expected
Fuzzycontrol offers a straightforward strategy that does not require
to be more responsive to fast changes in demand as expected with
explicit modeling of the reactor system or the equipment condition.
power-peaking modules to accommodate intermittent renewable
The TakagieSugeno (TeS) fuzzy control method studied in this
production, although this is not the focus of the current work. Of
work is a powerful tool in the control of complex systems, espe-
particular interest in the current work is the possibility of using the
cially those with uncertainty [3].
exibility of multimodular plants to compensate for potentially
Fuzzy theories have been studied for application in nuclear
degrading equipment in one module. The overall control strategy of
systems in many aspects, including the control of U-tube steam
the PAR is described in the following subsection, including both
generators [4,5], the control of nuclear reactor power [6,7], and
local control in each module and global control (e.g., power dis-
water level control of a steam generator [8]. Work by Na and
tribution) in the full power block.
Upadhyaya [9] investigated fuzzy control for power distribution
across the core of a single pressurized water reactor. Luan et al. [10]
2.2. Control targets of the control system
demonstrated a TeS-based fuzzy controller for load following
control of reactor. This paper goes beyond the prior work by
For multimodular power blocks, power distribution between
applying fuzzy methods for high level power distribution control
the modules needs to be considered in the design of control
under uncertain equipment condition and performance.
strategy, on the condition that the total output power of the
This paper presents the results of applying a TeS-based fuzzy
modules matches the demanded load prole.
power distribution controller to the prototypical advanced reactor
Moreover, to provide a steady environment to the reactor cores,
(PAR) model. The following section introduces the PAR design and
it is reasonable to choose keeping the inlet and outlet sodium
temperatures constant during daily operation as a control target for
naleintegralederivative (PID)-based control of the PAR under
the control system [15].
normal conditions, as developed by Liu [11], is also described. The
For the proposed concept of operation, the control targets of the
performance of this control strategy is demonstrated under normal
control system can be summarized as follows:
and degraded conditions. Section 3 introduces the proposed TeS
controller for power distribution across the two reactor modules in
1. The total power of the reactor power block meets the demanded
the PAR and presents the results of two proposed TeS controllers,
one giving preference to maintaining key temperatures in the pri-
2. The temperature of the inlet sodium in each reactor core is
mary system and the other giving preference to meeting power
constant (371.5 C)
demands. Finally, Section 4 draws conclusions from the current
3. The temperature of the outlet sodium in each reactor core is
work and suggests approaches for the integration of the power
constant (472.7 C)
distribution controller in a larger supervisory control strategy.
The available actuators to meet these control targets include
2. PAR design
external reactivity (control rod motion) in each reactor module,
primary sodium ow rate in each reactor module, and secondary
sodium ow rate in each reactor module. In this control scheme,
evaluation of online monitoring, enhanced risk assessment, and op-
demand is evenly divided across the two power modules to provide
erationsand maintenanceplanningforthegeneralclassofAdvSMRs.
the total load. For speed of simulation, the feedwater temperature
The PARdesignincludesmany featuresofAdvSMRs,suchasnonlight
and ow rate to the steam generators follow a program set by the
water coolant, multimodular operation, deliberately small power
overall power block power and the power produced byeach reactor
output, and advanced concepts of operation. The PAR design is
module, respectively.
intended to support load following, cogeneration and process heat
applications, and so-called passive safety features. The PAR is not
2.3. Control strategy under normal conditions
intended to represent any specic AdvSMR design currently being
developed; instead, it is a platform for testing online monitoring and
One means of operating the PAR power block would be to evenly
controls strategies that may be necessary to support the future
split production of the demanded load between the two modules.
development and deployment of any in the class of AdvSMRs.
This strategy is reasonable when the two modules both operate
under normal conditions. Traditional PID controllers can then be
2.1. Description of the PAR design
used in the control of power-level and temperatures of each
module. This approach to system control was studied by Liu [11]; a
A schematic diagram of PAR is shown in Fig. 1 [12]. The PAR
full discussion of the proposed control scheme is given there, along
power block includes two independent, pool-type LMR cores, each
with the relevant PID gains. Using primary and intermediate so-
with an integral intermediate heat exchanger and a dedicated
dium pumps to control the outlet and inlet sodium temperatures,
steam generator located outside the primary containment. Steam
respectively, and external reactivity to control the power produc-
from the two modules is mixed in a steam header and sent to a
tion, the control strategy for a single module is shown in Fig. 2.
common balance of plant. A simulation model of the PAR design
Under normal conditions, when no equipment degradation is
was previously developed in MATLAB-Simulink [11]. The two LMRs
affecting module performance, the two reactor modules are oper-
are based on Experimental Breeder Reactor-II [13], each providing
ated independently, but their operation is identical.