The urgent call to decarbonize our energy infrastructure, while simultaneously meeting growing energy demands, highlights the need for reliable and clean energy sources. Nuclear energy provides reliable, high-capacity baseload electricity while emitting zero greenhouse gases during operation. To adequately meet the energy needs of society and maintain economic viability, it is crucial to enhance the efficiency of nuclear power plant (NPP) operations. Upgrades to NPP operations require near-term Advanced technology Fuel (ATF), such as doped UO 2 , to increase the flexibility of plant operation without impacting safety margins. Small additions of metal oxide dopants are reported to increase grain size, thereby limiting fission gas release (FGR) and increasing pellet compliance to mitigate pellet-chemical interactions (PCI) and pellet-cladding mechanical interactions (PCMI). Prior to implementing doped UO 2 fuels into the reactor fleet, it is important to understand dopant effects on fracture behavior as it impacts fuel performance, such as thermal conductivity, and its tolerance to accident conditions. The availability of fracture data for irradiated and unirradiated UO 2 is limited, while only one study (N = 7, where N is the number of test samples) is available for unirradiated doped UO 2 . Hence, a knowledge-gap exists in the literature for fracture behavior of doped UO 2 fuel forms. The existing knowledge-gap in fuel fracture analysis partly stems from the inherent challenges in machining radiological materials into samples suitable for the traditional bend bar tests. Consequently, acquiring sufficient data to understand the stochastic fracture behavior of ceramic materials is difficult. The ball-on-ring (BOR) biaxial flexure test method utilizes simple right cylindrical geometries representative of commercial nuclear fuel, requires minimal surface preparation, and is tolerant of edge defects; these advantages reduce the time and cost of sample production. As a full understanding of the statistical fracture behavior for ATF concepts has not been established, this work aims to develop and establish the BOR test method to obtain statistical fracture data of undoped and doped UO 2 , providing insight into fracture behavior. Chapter two of this work presents a study performed to validate the BOR biaxial flexure technique using technical ceramics with well-known mechanical properties complemented with finite element analysis (FEA). Chapter three details a test case of CeO 2 and Ti-doped CeO 2 to obtain statistical fracture data. The CeO 2 material was selected as a surrogate for UO 2 to refine sample processing, characterization techniques, and the BOR test method for undoped and doped UO 2 . The research study performed on CeO 2 and Ti-doped CeO 2 was motivated by its use as an electrolyte material for intermediate temperature solid oxide fuel cells (IT-SOFCs). The Ti-CeO 2 samples were doped with 0.1 weight percent (wt%) TiO 2 and resulted in an increased characteristic strength (≈ 20%) and Weibull modulus compared to CeO 2 , making them a more robust option for IT-SOFCs. In the context of this collective study, it was intended to provide proof of concept for the BOR test method for the testing of UO 2 . Chapter four details the work to produce a benchmark dataset to establish the fracture behavior of undoped UO 2 using the BOR method. This work provides a robust dataset for a comparative analysis of the fracture behavior of doped UO 2 and future fracture studies of ATF concepts. Hertzian contact damage was observed for undoped UO 2 test batch 1 due to the small diameter loading ball (≈ 3 mm), which was no longer observed in test batch 2 with a larger loading ball (≈ 19 mm). The contact damage did not appear to influence fracture behavior as both datasets resulted in a characteristic strength and Weibull modulus that agrees with previously published transverse rupture strength (TRS) values for undoped UO 2 . In chapter five, the statistical fracture of doped UO 2 was acquired for UO 2 doped with TiO 2 or Cr 2 O 3 to investigate the effects of dopants on the fracture behavior of UO 2 . The interplay among grain size, dopant-induced defect structures, and pore size and distribution were explored. Both TiO 2 and Cr 2 O 3 doped UO 2 sample sets resulted in lattice contraction and a characteristic strength and Weibull modulus that were lower than expected based on density, pore size, and distribution. The increased grain size of TiO 2 doped UO 2 samples was expected to reduce the fracture strength, yet residual tensile stresses attributed to dopant incorporation in the UO 2 lattice had a greater impact on fracture behavior. Doped UO 2 samples resulted in a reduced fracture strength and with a larger scatter in TRS values. Collectively, the body of this work establishes a BOR test method for the rapid fabrication and mechanical testing of UO 2 and ATF concepts and presented a comparative analysis of fracture behavior for undoped and doped UO 2 fuels. The statistical fracture data presented in this study provide baseline data for enhanced fuel performance code predictions of fuel fracture behavior impacting phenomena during reactor operation. This work provides foundational analysis of fracture behavior to advance research on ATF concepts and assist in acceleration of fuel qualification for the current and future nuclear reactor fleets.
A Confirmation Rule is an algorithm run by network nodes to determine whether a block will remain permanently in the canonical chain. The only Confirmation Rule currently available in Ethereum's consensus protocol, Gasper, is FFG finalization. While it tolerates asynchronous network conditions, it is slow: in the best case, a transaction takes 13 to 19 minutes to confirm, depending on when it is submitted. We devise a Fast Confirmation Rule (FCR) for Gasper that, under synchrony and the assumptions stated in this paper, achieves a best-case confirmation time of 12 seconds, a single slot, providing an order-of-magnitude improvement over FFG finalization. The rule is complementary to finalization: users who trust synchrony obtain fast confirmations, while finalization remains available as a fallback that tolerates asynchrony. Gasper is an ebb-and-flow protocol: it combines LMD-GHOST, a fork-choice rule providing fast progress under synchrony, with FFG-Casper, a finality gadget providing finality under partial synchrony. The main technical difficulty is to reason jointly about these two components, so that a block confirmed by LMD-GHOST cannot be filtered out by FFG-Casper's rules. We prove that the rule satisfies both safety, confirmed blocks remain canonical, and monotonicity, a confirmed block remains confirmed at all future times.
Warhead verification systems proposed to date fundamentally rely on the use of information barriers to prevent the release of sensitive information. Measurements with information barriers significantly increase the complexity of inspection systems, make their certification and authentication difficult, and may reduce the overall confidence in the verifiability of future arms-control agreements. This article presents a concept for a new approach to nuclear warhead verification that minimizes the role of information barriers from the outset and envisions instead an inspection system that avoids the measurement of sensitive information, using a so-called zero-knowledge protocol. This is a protocol in which the data learned by one party (i.e., the inspector) allow him/her to verify that a statement is true (e.g., the inspected warhead is identical to an authenticated template), but does not reveal any additional information, e.g., does not leak any information that would help infer the design of the inspected warhead. There is a wide literature on zero knowledge proofs in the digital domain using cryptographic tools, and we draw on these ideas to achieve this in the physical domain. The proposed inspection system relies on active interrogation of a test object with 14-MeV neutrons, including both tomographic transmission measurements that are sensitive to warhead configuration, and scattering/fission measurements that are sensitive to material properties. The viability of the method is examined with MCNP Monte Carlo neutron transport calculations modeling the experimental setup.
The past decade has been a period of introspection in the radiological protection community. The International Commission on Radiological Protection (ICRP) has set out to produce a new set of recommendations; a draft document has been produced and made available on the ICRP web site. That draft has been widely reviewed and support for the proposed recommendations has been muted to say the least [1]. A subsequent draft is now being reviewed. As we wait for the final version it seems worthwhile to reaffirm the fundamental base for radiological protection as we practise it. The base is the set of three principles; justification, protection of the individual, and optimization of protection (the ALARA principle). Their importance seemed to be lost in the detail of the initial draft recommendations. I feel that without a clear statement of their primacy in the protection system we are in danger of the minutiae of the recommendations being applied in a far too arbitrary and restrictive way. There was a hint of this in the draft ICRP document on optimization that was available for review earlier this summer, in which it was argued that the so-called precautionary principle had been the driver for the evolution of the ICRP's thinking [2]. Some argue, correctly I believe, that this is not really a principle; it is more a poorly-defined and open-ended method of handling or reacting to uncertainties in our knowledge of risk. We see the precautionary principle rather loosely invoked in some risk management decisions as justifying arbitrary safety factors. `Applying the precautionary principle' sounds more substantial and scientific than just saying `to be on the safe side'. The influence of the principle is far more widespread though. The idea behind the precautionary principle originated in Germany in the 1960s but it was not until 1982 that it was endorsed internationally when the UN included it in the World Charter for Nature. It gained prominence in European treaties and was advocated by the UN Rio Declaration on Environment and Development in 1992. Initially the idea was that `uncertainty does not justify inaction'. The idea evolved and precaution began to take the place of science-based risk assessment and management. By the late 1990s the idea was that uncertainty also required shifting the burden and standard of proof [3]. The principle became `When an activity raises threats of harm to human health or the environment, precautionary measures should be taken even if some cause and effect relationships are not fully established scientifically. In this context, the proponent of an activity, rather than the public, should bear the burden of proof.' [4,5] In other words, uncertain risk requires forbidding the potentially risky activity until the proponent of the activity demonstrates that it poses no (or acceptable) risk. We are all aware of the impossibility of proving a zero but this wording may sound reasonable provided that the parenthetic `or acceptable' is the operative qualifier. For many though, it is not. Adams has described what he calls the {\it environmentalist paradigm}, in which possibility replaces probability as a criterion for protection regulation, and any agent harmful at high doses is considered harmful at exceedingly low doses [6]. Only zero risk is then acceptable when the precautionary principle is applied. This is a stultifying situation. Morris comments, in a broad-ranging critique, that the precautionary principle not only lacks any clear guidance on when and how it does apply, but perhaps more importantly it is devoid of any limitations of when it does apply [7]. Without such limitations, he notes, the precautionary principle will be a vacuum that can consume any and all products and technologies, since some risk and uncertainty is associated with every human activity. We could conclude that in radiological protection we would have no optimizing; no applying the ALARA principle. Radiation regulations based on the three fundamental ICRP principles have achieved an acceptable level of protection for decades. We should not abandon them to the arbitrariness of the precautionary principle when we have a sound basis for radiological protection in the clearly-enunciated principles of justification, individual dose limitation and optimization of protection. Radiological protection based on these principles includes elements of precaution. Why do we need a precautionary principle? This has been indirectly answered by asking: What if we were to apply the precautionary principle to itself? Its application carries the burden of untold risks and uncertainties. Thus, by its own definition, it should be abandoned [4]. This is not to argue that we should throw caution to the wind. The key is reasonableness. As Nilsson points out, though it is certainly better to be safe than sorry, it is important to distinguish unjustified precautionary action from justifiable precautionary action based on sound science and an appropriate assessment of the costs and benefits of taking action [8]. The precautionary principle fails to distinguish between the two, by elevating to the status of universal `principle' a notion that is only narrowly applicable. In Canada we are fortunate that we have sensible wording in the Federal Nuclear Safety and Control Act that provides the framework for many of the radiological protection regulations in Canada [9]. Part of its stated purpose is the limitation, to a reasonable level , of the risks to the health and safety of persons and the environment. The ICRP principle of dose limitation and the ALARA principle are coherent with this. Further, the Federal Government's Privy Council Office (PCO) has published guidance for its agencies on the application of precaution in science-based decision-making that reinforces the approach we have been taking in radiological protection and, in particular, emphasizes the importance of what is in essence the ALARA principle [10]. It notes that sound scientific information and its evaluation must be the basis for applying precaution. Peer review represents a concrete test for the practical application of precaution to decision making. A peer-review process can assess the soundness of the scientific evidence and its inherent credibility within the scientific community. Scientific advisors should give weight to peer-reviewed science and aim at sound and reasonable evidence on which to base their judgments. Moreover, the science function can be further supplemented by formal, structured and, where warranted, independent advisory processes that include widely recognized and credible individuals. I believe we can heartily subscribe to this. The guidance document lays out five principles that should guide the application of precautionary measures. They should be: Subject to reconsideration, on the basis of the evolution of science, technology and society's chosen level of protection. Proportional to the potential severity of the risk being addressed and to society's chosen level of protection. Non-discriminatory and consistent with measures taken in similar circumstances. Cost-effective, with the goal of generating an overall net benefit for society at least cost, and efficiency in the choice of measures. Finally, where more than one option reasonably meets the above characteristics, then the least trade-restrictive measure should be applied. We can see all three radiological protection principles reflected in this guidance. Particularly important is the emphasis on the link to scientific knowledge, rather than the whims of activist groups, together with the exhortation to assess the real and potential impacts of making a precautionary decision (whether to act or not to act), including social, economic and other relevant factors and risk-risk trade-offs. Apply the ALARA principle in other words. The guidance concludes with the expectation that Canadian agency officials will consider its guiding principles in decision-making and will work together in developing, in consultation with their stakeholders, guidance for the application of precaution in t
Waste Processors Management, Inc. (WMPI), along with its subcontractors Texaco Power & Gasification (now ChevronTexaco), SASOL Technology Ltd., and Nexant Inc. entered into a Cooperative Agreement DE-FC26-00NT40693 with the U. S. Department of Energy (DOE), National Energy Technology Laboratory (NETL) to assess the techno-economic viability of building an Early Entrance Co-Production Plant (EECP) in the United States to produce ultra clean Fischer-Tropsch (FT) transportation fuels with either power or steam as the major co-product. The EECP design includes recovery and gasification of low-cost coal waste (culm) from physical coal cleaning operations and will assess blends of the culm with coal or petroleum coke. The project has three phases. Phase I is the concept definition and engineering feasibility study to identify areas of technical, environmental and financial risk. Phase II is an experimental testing program designed to validate the coal waste mixture gasification performance. Phase III updates the original EECP design based on results from Phase II, to prepare a preliminary engineering design package and financial plan for obtaining private funding to build a 5,000 barrel per day (BPD) coal gasification/liquefaction plant next to an existing co-generation plant in Gilberton, Schuylkill County, Pennsylvania. The current report covers the period performance from July 1, 2003 through September 30, 2003. The DOE/WMPI Cooperative Agreement was modified on May 2003 to expand the project team to include Shell Global Solutions, U.S. and Uhde GmbH as the engineering contractor. The addition of Shell and Uhde strengthen both the technical capability and financing ability of the project. Uhde, as the prime EPC contractor, has the responsibility to develop a LSTK (lump sum turnkey) engineering design package for the EECP leading to the eventual detailed engineering, construction and operation of the proposed concept. Major technical activities during the reporting period include: (1) finalizing contractual agreements between DOE, Uhde and other technology providers, focusing on intellectual-property-right issues, (2) Uhde's preparation of a LSTK project execution plan and other project engineering procedural documents, and (3) Uhde's preliminary project technical concept assessment and trade-off evaluations.