Instrumentation&Control, I&C in the following, is implemented in every kind of power supplying industrial facility.

1. Introduction

Instrumentation&Control, I&C in the following, is implemented in every kind of power supplying industrial facility.

It follows that for the specificity and complexity of Nuclear Power Plants (NPPs) I&C must satisfy peculiar requirements related to safety, security, continuity of operation to assure high plant availability, radiation protection and monitoring, but also ergonomics and easiness of operability in order to reduce the risk of human errors.

It is worthy to note that all these aspects that makes peculiar the exercise of an NPP can be guaranteed only implementing a complex, computer-based I&C system. In fact without the I&C system the entire equipment that forms a NPP would be inoperable and no safe operation would be guaranteed also due to the complexity of the equipments, physical phenomena and processes involved: excluding the idea of placing an operator near each actuator that needs to be operated, another one near each gauge that needs to be read, and a group of people that performs calculation in order to instruct the “actuator operators”, main plant processes could not be controlled, or in the best situation, they should be conducted at a fixed state without any possibility of regulation and monitoring and therefore, the entire plant would be useless;

the EPR™ would be, for example, only a beautiful ensemble of components

.

I&C systems that perform I&C functions (control of a process) are implemented in the plant to allow an “harmonic”, functional and safe interaction of all components and systems.

This concept can be synthesized in the three roles of the I&C system identified by the IAEA in [1]:

̶ First of all it is the “eyes and ears” of the operator. If properly planned, designed, constructed and maintained, it provides accurate and appropriate information and

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permit judicious action during both normal and abnormal operation. It is therefore, with the human operator, vital for the safe and efficient operation of the plant.

̶ Secondly, under normal operating conditions it provides automatic control, both of the main plant and of many ancillary systems. This allows to relax the work-load of the operators.

̶ Thirdly, the I&C safety systems protect the plant from the consequences of any mistakes which the operator or the automatic control system may make. Moreover in abnormal condition I&C provides reliable and prompt mitigative actions.

At this point it is clear that to implement functional and effective I&C functions (carried on by an I&C system), a broad knowledge of phenomena, dynamics, processes and the their physics, equipments and their related features that characterize an NPP, as well as the plant operating requirements (either related to safety either related to economic operation), is required to the nuclear I&C engineer: he must be able to understand the nuclear thermal hydraulics phenomena, structural mechanics issues, neutronics, radiation protection issues, etc., in order to design the right I&C function and moreover he must be acquainted with the jargon of electronics and computer engineering in order to be able to cover the interface with I&C engineers in charge of practical (hardware and software) I&C implementation (Adapted from [1]).

This thesis work is in the context of the continuous innovation principle inspiring the EPR™

project and the enterprise in general.

Its main objective is the evaluation of the applicability of new software tools and calculation methodologies in the field of thermal hydraulic systems regulation and automation in order to make the satisfaction of constraints expressed in this chapter and in the EUR code more cost- effective and “straightforward”. More in detail its proposition is:

̶ to inspect the feasibility of modelling and simulation of present I&C functions on Matlab ^® /Simulink ^® software;

̶ to inspect the feasibility of thermal hydraulic system modelling on the same software

platform;

̶ to conduct a frequency domain validation/optimization based on the same software tool of some closed loop regulation and evaluate the performance of the software and the efficacy of the method in the design process of the regulation schemes.

The chosen process (together with its related I&C functions) for this validation and prototypical application of the Matlab ^® / Simulink ^® software concerns the sweeping of Reactor Coolant System (RCP) and the vacuum pulling and vacuum maintaining of the RCP.

RCP sweeping is performed before opening the RPV to perform refuelling. Primary circuit atmosphere is swept by nitrogen to eliminate FGs and hydrogen; after this first phase air sweeping is performed too. Nitrogen and air are provided by the SGN system and injected into the RCP. Gas is pulled out by the vacuum section of the NIVDS (in the following RPE).

When sweeping by nitrogen gas is routed to TEG while when sweeping by air gas is routed to EBA.

This process is performed by the aid of operational I&C which performs two closed loop regulations: pressure in the RCP and pressure at outlet of the vacuum section of RPE. It is on these loops that validation and/or optimization is going to be performed.

Vacuum pulling into of the RCP and vacuum maintaining into the RCP during its filling are performed after refuelling has taken place to avoid air bubbles accumulation into the primary circuit. There are no closed loop regulations in this process but only RCP pressure control by starting/stopping the vacuum pump. In this case the task is to find how often and how many times vacuum pump is called into operation and if requirements on RCP pressure are satisfied.

Validation and optimization rely on frequency analysis and stability margins methodology.

Since controllers involved in the closed loop control receive information only on the controlled variable of the loop (SISO system) and remaining variables acts as disturbances (see Figure 18), it is possible to perform frequency analysis and time domain tests on each loop independently providing each time required boundary conditions. Time domain analysis is required to take into account non linearities that are neglected in the frequency analysis.

Once a set of controller parameters is available, because it works well in this first phase, a time domain validation coupling the loops is performed.

Selected plant is the **** EPR ^™ .

Chapter 2 explains which the main innovations of the EPR™ reactor are.

Chapter 3 is about the operational states of the **** EPR ^™ and it provided to contextualize the processes that have been studied.

Chapter 4 describes the general I&C architecture of an EPR ^™ plant. Moreover a brief description of the I&C platform is provided since its characteristics influence the regulations to implement.

Chapter 5 is the starting point of the study: it presents the equipment involved, the processes to control and the I&C functions implemented to control the processes.

Chapter 6 follows the development of the study: it provides a brief description of the software tools used, it exposes the methodology followed to validate and, possibly, optimize the regulations. After, it presents the hypotheses and assumptions taken to model the system, both for the Thermal Hydraulic domain, both for the I&C domain.

Chapters 7 and 8 expose the resulting model and the results that have been possible to obtain.

Chapter 9 traces the conclusions of the work.

References

[1] IAEA STI/DOC/010/387: “Modern Instrumentation and control for Nuclear Power Plants;

a guidebook”; IAEA 1999