S. R. Shimjith

A Three-Time-Scale Approach for Design of Linear State Regulator for Spatial Control of Advanced Heavy Water Reactor

This paper introduces a technique for simultaneous decomposition of a non-autonomous singularly perturbed system into three subsystems namely “slow”, “fast 1” and “fast 2” respectively. Design of a composite controller in terms of the individual subsystem controllers is derived and the decomposition of the optimal control problem of the original high order system into three smaller order optimal control problems, with separate quadratic performance indexes extracted from the quadratic performance index of the original system, is discussed.

Design of Fast Output Sampling Controller for Three-Time-Scale Systems: Application to Spatial Control of Advanced Heavy Water Reactor

This paper introduces a formulation for design of Fast Output Sampling (FOS) controllers for three-time-scale systems. It is shown that the FOS control gain for a three-time-scale system can be obtained by combining the solutions of the three subsystem problems, obtained separately. Since three smaller order subsystem problems are to be solved in lieu of one high order problem, numerical ill-conditioning is completely avoided. Techniques for block-diagonalization and composite control of a three-time-scale system are also discussed. The proposed method is applied to the problem of spatial control of advanced heavy water reactor (AHWR). The model of AHWR is decomposed into three subsystems respectively named “slow,” “fast 1,” and “fast 2,” and separate subsystem control problems are cast from which an FOS controller for the original system is derived. Efficacy of the controller thus obtained is demonstrated through dynamic simulations. The controller thus designed employs only the output information to achieve arbitrary pole placement.

Coupled neutronics-thermal hydraulics model of Advanced Heavy Water Reactor for control system studies

A coupled neutronics-thermal hydraulics model of advanced heavy water reactor (AHWR) which can be used for control system studies, simulation etc. is presented in this paper. A nodal model is developed for core neutronics and a simple two-phase thermal hydraulics model is developed from first principles. Neutronics-thermal hydraulics coupling is achieved through the void reactivity feedback model. Selection of a suitable nodalization scheme through steady state analysis is discussed, and dynamic response of the model is also presented.

Dynamic Compensation of Vanadium Self Powered Neutron Detectors for Use in Reactor Control

The slow response characteristics of Vanadium SPNDs precludes their direct use for reactor protection and regulation applications. On the other hand, benefits offered by Vanadium SPNDs like better life span, simple response characteristics, easiness in handling the replaced SPNDs etc., make them desirable candidates for such applications. Therefore, a method to improve the response time of Vanadium SPNDs would enable them to be utilized for reactor control applications as well as to fulfill core monitoring and surveillance requirements. In this paper, two different dynamic compensators are designed for response improvement of Vanadium SPNDs using a mathematical model of the SPND derived from first principles. The model as well as the compensators are validated using the plant data collected from the 540 MWe PHWR units. It is established that the compensated Vanadium SPND signals are in very good agreement with the prompt Cobalt SPND signals. It is further demonstrated that the compensated Vanadium SPNDs can be used for computation of reactor bulk power as effectively as the Cobalt SPNDs. This puts forth the possibility of using Vanadium SPNDs in lieu of Cobalt SPNDs for reactor protection and regulation applications.

Kalman Filter-Based Dynamic Compensator for Vanadium Self Powered Neutron Detectors

Large nuclear reactors employ a wide variety of in-core detectors to determine the neutron flux distribution within the core. Among them Vanadium SPNDs are extensively used for flux mapping applications due to their accuracy. However, the slow response characteristics of Vanadium detectors precludes their direct use for reactor protection and regulation applications. Neverthless, by overcoming their inherent time delay, it is possible to use them in such applications. Moreover, benefits offered by Vanadium SPNDs like better life span, simple response characteristics, easiness in handling the replaced SPNDs etc., make them desirable candidates for such applications. Therefore, a method to improve the response time of Vanadium SPNDs would enable them to be utilized for reactor control applications as well as to fulfill core monitoring and surveillance requirements. In this paper, a Kalman filter-based compensator is proposed for online dynamic compensation of Vanadium SPND. Moreover, compensated flux obtained by Kalman filter is compared with the compensated flux obtained from existing dynamic compensators i.e. Direct Inversion and Tustin, and robustness of proposed algorithm is studied. The compensator is validated using the plant data collected from the 540 MWe PHWR units in India. It is established that the compensated Vanadium SPND signals are in very good agreement with the prompt Cobalt SPND signals. This puts the possibility of using Vanadium SPNDs in lieu of Cobalt SPNDs for reactor protection and regulation applications.

Investigation of Spatial Control Strategies for AHWR: A Comparative Study

Large nuclear reactors such as the Advanced Heavy Water Reactor (AHWR), are susceptible to xenon-induced spatial oscillations in which, though the core average power remains constant, the power distribution may be nonuniform as well as it might experience unstable oscillations. Such oscillations influence the operation and control philosophy and could also drive safety issues. Therefore, large nuclear reactors are equipped with spatial controllers which maintain the core power distribution close to desired distribution during all the facets of operation and following disturbances. In this paper, the case of AHWR has been considered, for which a number of different types of spatial controllers have been designed during the last decade. Some of these designs are based on output feedback while the others are based on state feedback. Also, both the conventional and modern control concepts, such as linear quadratic regulator theory, sliding mode control, multirate output feedback control and fuzzy control have been investigated. The designs of these different controllers for the AHWR have been carried out using a 90th order model, which is highly stiff. Hence, direct application of design methods suffers with numerical ill-conditioning. Singular perturbation and time-scale methods have been applied whereby the design problem for the original higher order system is decoupled into two or three subproblems, each of which is solved separately. Nonlinear simulations have been carried out to obtain the transient responses of the system with different types of controllers and their performances have been compared.

Comments on “Adaptive Fading Memory

In a recent paper (Tamboli, 2015), Tamboli, Duttagupta, and Roy have presented a comparative study of existing dynamic compensation algorithms based on Linear Matrix Inequality (LMI) based

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Filter Design for Compensation of Delayed Components in Self Powered Flux Detectors”

a priori filtering and Discrete time Algebric Riccati Equation (DARE) based Kalman filtering for delayed responding Self Powered Flux detectors (SPFD) with Vanadium and Platinum emitters. Moreover, authors have proposed an adaptive fading memory discrete time

Multipoint Kinetics Modeling of Large Nuclear Reactors

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