<p> The use of high flux research reactors, such as the High Flux Isotope Reactor (HFIR), to produce a wide variety of both industrial and medical isotopes has been well documented and proven to be economically feasible. However, due to the lack of access to these high flux facilities by most countries, isotope production methods utilizing reactors with low to moderate flux levels are needed, especially for short lived medical isotopes whose production must be relatively close to the location where they will be administered. In recent years medical isotopes that can both be used for treatment and diagnostic uses have become of great interest. One of the most popular of these theragnostic radionuclides is lutetium-177. Production of high-grade Lu-177 can be achieved in both high and low flux reactors through two different production methods. The current work looks to determine the feasibility of producing Lu-177 via the indirect route, using the relatively low flux of PUR-1. This will be accomplished through the use of high-fidelity models and simulations to predict the resulting production rates of the desired products. The results of these models and simulations will then be compared to the results obtained from the experimental irradiation of various samples of ytterbium oxide in PUR-1. Many studies have successfully produced Lu-177 using moderate and high flux reactors and several papers have studied the predicted production rate for low to moderate flux reactors by using the reported thermal flux of various research reactors and the reported cross-section values for ytterbium. A Monte Carlo based model of PUR-1 will be developed to determine the radiative capture reaction rates for the ytterbium targets across all neutron energies. This model in conjunction with a simplified MATLAB model, to solve the series of partial differential equations describing the production and decay of each product isotope, will be used to predict isotope production rates and will be compared to experimentally obtained results. </p>

Nuclear systems heavily depend on Instrumentation and Control (I&C) entities for their protection, monitoring and control processes, all of which play an important role for their safety and security. The obsolescence of analog I&C systems, along with the increased costs for their maintenance, has rendered the adoption of digital control systems inevitable. Digitization offers numerous advantages to systems, ranging from precision in measurements to reduction in equipment and costs. However, it also comes with a number of challenges, most of which are related to increased failure risk, either from human or control systems error, and vulnerability to attacks, which can be a major threat to non-proliferation. These characteristics point to the category of Cyber Physical Systems (CPSs), namely collections of computational components that receive physical inputs from sensors, and are connected to feedback loops in order to adapt to new circumstances. The ever growing use of CPSs may increase the risk for cyber attacks, that threaten a system’s integrity and security. Plenty of research has been conducted on this topic. The focus of this work is to implement an architecture that can protect the system under review, namely Purdue University Reactor Number One (PUR-1), from these types of attacks. The reactor is physically modelled, through the use of point kinetics equations and reactivity calculations. Controllers existing in the plant are modelled and tuned for the purpose of controlling the reactor’s power. Mitigation of the cyber attacks is later examined through fault tolerance. One of the main ways to achieve fault tolerance in systems of this type is through redundant components, the so-called replicas. Replicas are later used in a process of voting, in order to detect failures. According to the Byzantine Fault Tolerance (BFT) protocol, which is the most popular protocol for this purpose, a maximum number of t faults can be tolerated by the system, when there are in total 3t+1 replicas in the system architecture. Redundancy, however, is not capable to keep a system safe by itself under all circumstances. For this purpose, software diversity is explored. According to this, software in the controllers gets diversified into distinct variants. Different software variants execute instructions, and other variants are expected to execute other actions. In the case where some tampered inputs crash (or deactivate) one of the variants, other variants take control and the system is tolerant against failures. Lastly, CPS inertia is exploited along with rollback recovery methods for the rebooting of the system after a failure. The actual algorithm for the system studied in this work uses three redundant controllers and performs as follows; the error term from the subtraction of the output from the setpoint is fed as input to the first two controllers, as well as to the delay queue connected to the third controller. The outputs of the first two controllers are compared, and then there are two cases of operation. In the case of a good message in the input, the variants in the controllers do not crash, thus the signal from the top two controllers reaches the plant. In the case of a bad message, at least one of the two controllers crashes, because at least one of the code variants fails due to the diversity. This automatically triggers the comparator, which sends a signal so that the output of the isolated controller is used and propagates towards the plant. After implementing a Graphical User Interface (GUI), which acts as a simulator and visualizes the system’s state, it is shown that PUR-1 is able to overcome bad messages regarding scram or control rod positions, when the protection architecture is activated. More specifically, when a bad message for scram is sent, the reactor manages to not drop its power level and continues to adjust the rod positions in order to achieve a specific power setpoint. Moreover, in the case of a bad message for the control rod positions, which means that the system is running open loop and thus is uncontrolled, the reactor manages to recover the rod positions and power level after some seconds. Conversely, when the protection system is deactivated, it is shown that bad messages regarding scram or rod positions are able to affect the reactor's state. In the case of the scram bad message, the reactor power drops immediately, while in the case of the rod position bad message, the power level changes uncontrollably.

<p>Modern reactors promise enhanced capabilities not previously possible including integration with the smart grid, remote monitoring, reduced operation and maintenance costs, and more efficient operation. . Modern reactors are designed for installation to remote areas and integration to the electric smart grid, which would require the need for secure undisturbed remote control and the implementation of two-way communications and advanced digital technologies. However, two-way communications between the reactor facility, the enterprise network and the grid would require continuous operation data transmission. This would necessitate a deep understanding of cybersecurity and the development of a robust cybersecurity management plan in all reactor communication networks. Currently, there is a limited number of testbeds, mostly virtual, to perform cybersecurity research and investigate and demonstrate cybersecurity implementations in a nuclear environment. To fill this gap, the goal of this thesis is the development of a real-time cyber-physical testbed with real operational and information technology data to allow for cybersecurity research in a representative nuclear environment. In this thesis, a prototypic cyber-physical testbed was designed, built, tested, and installed in PUR-1. The cyber-physical testbed consists of an Auxiliary Moderator Displacement Rod (AMDR) that experimentally simulates a regulating rod, several sensors, and digital controllers mirroring Purdue University Reactor One (PUR-1) operation. The cyber-physical testbed is monitored and controlled remotely from the Remote Monitoring and Simulation Station (RMSS), located in another building with no line of sight to the reactor room. The design, construction and testing of the cyber-physical testbed are presented along with its capabilities and limitations. The cyber-physical testbed network architecture enables the performance of simulated cyberattacks including false data injection and denial of service. Utilizing the RMSS setup, collected information from the cyber-physical testbed is compared with real-time operational PUR-1 data in order to evaluate system response under simulated cyber events. Furthermore, a physics-based model is developed and benchmarked to simulate physical phenomena in PUR-1 reactor pool and provide information about reactor parameters that cannot be collected from reactor instrumentation system.</p>