Publications

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The purpose of this report is to provide updates on the experimental components, methodology, and instrumentation under development for use in advanced studies of realistic drying operations conducted on surrogate spent nuclear fuel. Validation of the extent of water removal in a dry spent nuclear fuel storage system based on drying procedures used at nuclear power plants is needed to close existing technical gaps. Operational conditions leading to incomplete drying may have potential impacts on the fuel, cladding, and other components in the system. Water remaining in canisters upon completion of drying procedures can lead to cladding corrosion, embrittlement, and breaching, as well as fuel degradation. Additional information is needed on the drying process efficacy to help evaluate the potential impacts of water retention on extended longterm dry storage. A general lack of data suitable for model validation of commercial nuclear canister drying processes necessitates additional, well-designed investigations. Smaller-scale tests that incorporate relevant physics and well-controlled boundary conditions are essential to provide insight and guidance to the simulation of prototypic systems undergoing drying processes. This report describes the implementation of moisture monitoring equipment on a pressurized, submersible system employing a single waterproof, electrically heated spent fuel rod simulator as a demonstration of analytical capabilities during a drying process. A mass spectrometer with specially designed inlets was used to monitor moisture and other gases at 150 kPa to 800 kPa for a test simulating a forced helium dehydration procedure and below 1 torr for tests mimicking a vacuum drying process. The dew point data from the mass spectrometer was found to be in good agreement with a solid-state moisture probe. A distinct advantage of the mass spectrometer system was the capability to directly sample from the hightemperature (>200 °C) head space expected in a prototypic scale experiment where a solid-state moisture probe would suffer considerable loss of accuracy or fail altogether. The operational and analytical experiences gained from this test series are poised to support an expansion to assembly-scale tests at prototypic length. These assemblies are designed to feature prototypic assembly hardware, advanced diagnostics for in situ internal rod pressure monitoring, and failed fuel rod simulators with engineered cladding defects to challenge the drying system with waterlogged fuel.

Aging plants, efficiency goals, and safety needs are driving increased digitalization in nuclear power plants (NPP). Security has always been a key design consideration for NPP architectures, but increased digitalization and the emergence of malware such as Stuxnet, CRASHOVERRIDE, and TRITON that specifically target industrial control systems have heightened concerns about the susceptibility of NPPs to cyber attacks. The cyber security community has come to realize the impossibility of guaranteeing the security of these plants with 100% certainty, so demand for including resilience in NPP architectures is increasing. Whereas cyber security design features often focus on preventing access by cyber threats and ensuring confidentiality, integrity, and availability (CIA) of control systems, cyber resilience design features complement security features by limiting damage, enabling continued operations, and facilitating a rapid recovery from the attack in the event control systems are compromised. This paper introduces the REsilience VeRification UNit (RevRun) toolset, a software platform that was prototyped to support cyber resilience analysis of NPP architectures. Researchers at Sandia National Laboratories have recently developed models of NPP control and SCADA systems using the SCEPTRE platform. SCEPTRE integrates simulation, virtual hardware, software, and actual hardware to model the operation of cyber-physical systems. RevRun can be used to extract data from SCEPTRE experiments and to process that data to produce quantitative resilience metrics of the NPP architecture modeled in SCEPTRE. This paper details how RevRun calculates these metrics in a customizable, repeatable, and automated fashion that limits the burden placed upon the analyst. This paper describes RevRun's application and use in the context of a hypothetical attack on an NPP control system. The use case specifies the control system and a series of attacks and explores the resilience of the system to the attacks. The use case further shows how to configure RevRun to run experiments, how resilience metrics are calculated, and how the resilience metrics and RevRun tool can be used to conduct the related resilience analysis.

Digital Instrumentation and Control (I&C) systems in critical energy infrastructure, including nuclear power plants, raise cybersecurity concerns. Cyber-attack campaigns have targeted digital Programmable Logic Controllers (PLCs) used for monitoring and autonomous control. This paper describes the Nuclear Instrumentation and Control Simulation (NICSim) platform for emulating PLCs and investigating potential vulnerabilities of the I&C systems in nuclear power plants. It is being developed at the University of New Mexico's Institute for Space and Nuclear Power Studies (UNM-ISNPS), in collaboration with Sandia National Laboratories (SNL), with high fidelity emulytics and modeling capabilities of a physics-based, dynamic model of a PWR nuclear power plant. The NICSim platform would be linked to the SCEPTRE framework at SNL to emulate the response of the plant digital I&C systems during nominal operation and while under cyber-attack.

A programmable logic controller (PLC) emulation methodology can dramatically reduce the cost of high-fidelity operational technology (OT) network emulation without compromising specific functionality. A PLC emulation methodology is developed as part of an ongoing effort at the University of New Mexico's Institute for Space and Nuclear Power Studies (UNM-ISNPS) in collaboration with Sandia National Laboratories (SNL) to develop an emulyticTM platform to support cybersecurity analyses of the instrumentation and control (I&C) systems of pressurized water reactors (PWRs). This methodology identifies and characterizes key physical and digital signatures of interest. The obtained and displayed digital signatures include the network response, traffic, and software version, while the selected physical signatures include the actuation response time and sampling time. An extensive validation analysis is performed to characterize the signatures of the real, hardware-based PLC and the emulated PLC. These signatures are then compared to quantify differences and identify optimum settings for the emulation fidelity.