Inherent Safety Features Research Articles

Neutronics design study of an advanced lead-cooled modular nuclear reactor (ALMANAR)

A design of an advanced small modular reactor with long-life core is being studied in this paper. The core is designed to produce 45 MWth power with a lifetime of 20 years without refuelling. In order to achieve a compact design and have a good neutron economy, lead is considered as the coolant due to its excellent neutronics and thermo-physical properties. However, the lead coolant speed in the core is limited to 2 m/s to minimise the corrosion and erosion of the structural materials. On the other hand, U15N is used as the fuel which reflects excellent thermophysical properties and compatibility with lead. In this study, the neutronics properties of the core including the reactivity evolution during its lifetime, the control rod worth, and the fuel and coolant reactivity feedbacks are evaluated. It was found that ALMANAR could achieve a long-life core of about 22 effective full power years with very excellent inherent safety features. Monte Carlo Serpent code is used to perform the calculations in conjunction with the latest nuclear data library ENDF/B-VIII.0.

Estratégias de gerenciamento de reatividade para um reator nuclear de água pressurizada integral

In the last 15 years, there has been a growing interest in the small modular nuclear reactors (SMR) and their applications. SMRs offer numerous benefits, including inherent safety features. SMRs are under development for all main reactor lines, but an important role for its outstanding safety features will be played by the so-called integral pressurized water nuclear reactors (iPWR). To achieve high proliferation resistance, extended fuel cycles for iPWR have been proposed. Obtaining such a large cycle length, using low fuel enrichment, without shuffle, and with a relatively small core size is a challenge for the neutronic design of the reactor core. In this work, a full-core neutronic computational model based in Serpent code was developed, it permitted to simulate the performance of the proposed reactor core configurations. Different variants of use of integral burnable absorbents in 48-months fuel cycle were studied, and the reactivity worth of the control rod groups was estimated. A fuel cycle extended of more than 1400 EFPDs is reached, and a minimal reactivity penalty was obtained.

Design and experiments on an inflatable link robot with a built-in vision sensor

Soft robots and manipulators with inflatable links possess inherent safety characteristics that make them a very interesting choice for tasks requiring human-robot interaction. However, they may face important challenges in their performance due to low structural stiffness. Accurate positioning of the end effector may prove a difficult task due to limitations in gravity compensation, or due to the occurrence of oscillations during motion, especially in the absence of precise information about the payload that is being manipulated. In this paper a novel approach to the design and control of a robot with an inflatable link is proposed, where the link assumes the triple role of compliant structural element, touch sensor, and active mechanism to adjust the performance of vibration control algorithms. For this, a vision sensor is placed inside the link to provide information about the structural deformation. The sensor is used to measure the tip displacement, and also to detect contact of the link surface with the surrounding environment. The concept was implemented on a two-joint rigid manipulator with a single inflatable link. Experiments on vibration control and contact detection of the inflatable link are reported where the control system was able to significantly reduce tip oscillations, including when a payload was added to the tip. The robot was also able to make binary detection of contact between the inflatable link and the user, and change its operation mode accordingly.

A graphical inherent safety assessment technique for preliminary design stage

User-friendly plants are needed for equipment failure to not seriously affect its safety, productivity, or efficiency. Safer and user-friendly plants can be designed through the implementation of hazard prevention strategies during the design phase, which is known as the concept of inherent safety. The Graphical Inherent Safety Assessment Technique (GISAT) for preliminary engineering design stage is presented in this paper. GISAT incorporates information obtainable from the process flow diagram (PFD) in the assessment of inherent safety features of a process. This technique evaluates three inherent safety parameters, namely flammability, explosiveness, and toxicity. GISAT also utilises accident statistics in the construction of its graphical rating as the hazard level indicator for chemical process equipment assigned under five groups—reactor, heat transfer equipment, separation equipment, storage tank, and other equipment. In this technique, quantity of the chemicals involved in an equipment represents the weightage of the assessment that is used to identify the root-cause of hazards in each equipment. Hydrodealkylation process of toluene (HDA) to produce benzene is used as a case study to demonstrate the application of GISAT. The results indicate that heat transfer equipment E102 as safer in terms of flammability compared to other equipment while all equipment were found to be safer in term of explosiveness. Separation equipment V102, heat transfer equipment E102, and recycle gas compressor C101 were found to be safer in terms of toxicity. Meanwhile, heat transfer equipment E101, E102, and E103 as well as gas compressor C101 are regarded as safer in terms of fire, explosion, and toxic release combination type of accident as represented by the GISAT Total Score. After the level of hazard in each equipment have been identified, hazard prevention strategies can be applied to equipment with higher level of hazard for hazard reduction.

Passive decay heat removal system design for the integral inherent safety light water reactor (I2S-LWR)

The Integral, Inherently Safe Light Water Reactor (I2S-LWR) is an innovative Pressurized Water Reactor (PWR) concept being developed by a multi-institutional team led by Georgia Tech and in collaboration with Westinghouse, under the Department of Energy’s Nuclear Energy University Programs Integrated Research Projects (DOE NEUP IRP). The University of Michigan leads the design of the thermal-hydraulic and passive safety systems, in collaboration with Westinghouse and Bringham Young University. The I2S-LWR features an integral primary system configuration and is more conducive to the implementation of inherent safety features by eliminating potential accidents. In this paper, a novel passive Decay Heat Removal System (DHRS), is presented, consisting of a primary loop, an intermediate loop and a cooling tower loop. This passive system is designed to remove the I2S-LWR decay heat in the case of emergency heat removal transients, without the need for external power or operator action. The proposed DHR uses atmosphere as ultimate heat sink, to achieve indefinite decay heat removal. In this paper, firstly, the design of primary and secondary DHRS heat exchangers is optimized. Then the DHR heat removal characteristics are studied using the best-estimate thermal hydraulic code RELAP5. In addition, CFD simulations have been performed in order to investigate the DRHS helical coil primary heat exchanger performance with different coil pipe arrangements, and optimize its design. The performance of the proposed DHRS concept is investigated in case of a Station Black-Out (SBO) scenario. Operation of two, three and four DHRS trains is studied respectively. The results show that three out of four DHRS trains are sufficient to indefinitely remove the core decay heat successfully during a SBO, and keep the reactor in a safe state without the need of any other auxiliary active system.

Sensor Reduction of Variable Stiffness Actuated Robots Using Moving Horizon Estimation

Variable stiffness actuated (VSA) robots are expected to play an important role in physical human–robot interaction, thanks to their inherent safety features. These systems can control the position and stiffness concurrently by incorporating two or more actuators for each joint. Unfortunately, the need for extra sensors to measure the state of these actuators decreases the reliability of these systems. In this paper, we present a sensor reduction scheme for VSA robots. Specifically, we utilize moving horizon estimation (MHE) to estimate the unmeasured states of the system. Due to its ability to handle constraints, MHE is chosen as the estimation algorithm. The estimated states are then used by a nonlinear model predictive controller to implement a closed-loop control system. In order to show the efficacy of our framework, we conducted extensive simulation and real-world experiments with a reaction wheel augmented VSA system. The objective of these experiments was to compare the control performance of the sensor reduced system (from four encoders to two encoders) with the system using the full set of states for control. The results of these experiments show the feasibility of the MHE-based sensor reduction. Sensor reduction might increase the reliability of VSA robots and might facilitate their earlier introduction to the industrial environments.

Investigative Study of Neutronic Safety Parameters of HPR and EPR Using the MCNP Code

As part of technology assessment of proposed commercial nuclear power reactor technologies for Ghana’s Nuclear Power Programme, the neutronic safety parameters of the European Pressurized Reactor (EPR) and High Temperature Pressurized Reactor (HPR) reactor technologies are theoretically analyzed and compared. The MCNP neutronic code was employed as a computational tool to analyze the reactivity temperature coefficients, moderator void coefficient, criticality, and neutron behavior at various operating conditions. The HPR, which is still under construction and under theoretical safety analysis, showed good inherent safety features comparable to the already existing EPR technology.

Coupling simulation of neutron kinetics core model with CFD of IPWR steam line break accident

Abstract In this paper, development of coupled codes using two-group neutron diffusion kinetics code and computational fluid dynamics (CFD) solver Fluent has been introduced. Way of coupling, time step control algorithm and spatial mesh overlays have been summarized in detail which are basic components and challenges of the coupling methodologies. The implement and verification of coupled code have been modeled on integral pressurized water reactor (IPWR) IP200 with hexagonal fuel assembly in the core and once-through steam generators. The steam line break core transient was analyzed in coupled code simulation of a core boundary conditions derived from system code simulation results. The results presented transient three-dimensional distribution of the key operation parameters such as reactor power and coolant temperature, also demonstrated the inherent safety features of IP200. The current work will bring about the ability to explore multi-scale and multi-dimensional safety transient evaluations and give more precise neutronics/thermal-hydraulics mapping.

Radiological environmental impact analysis of a 2-MW thorium molten salt reactor during an accident

The thorium molten salt reactor–liquid fuel (TMSR-LF1) has inherent safety features. The accident occurrence possibility and their consequences are much lower for the TMSR-LF1 than that of traditional reactors. Based on accident analysis, the maximum credible accident and the radioactive source terms of the TMSR-LF1 were first estimated. Then, the total effective dose of the maximum credible accident was calculated. Based on calculations, the cover gas flow rate can significantly affect the radiation consequences of the maximum credible accident when it changes from 0 to 10 L/min. If no cover gas is flowing, a site-area emergency would be required within the range of 50–73 m from the reactor. In the case of cover gas flow, only an abnormal notification and an alert two emergency class would be required within the range of 50 m.

Fully ceramic microencapsulated fuel in prismatic high-temperature gas-cooled reactors: Design basis accidents and fuel cycle cost

Fully ceramic microencapsulated (FCM) fuel may enhance the already strong inherent reactor safety characteristics of a conventional High-Temperature Gas-Cooled Reactor (HTGR). FCM fuel uses an SiC matrix that exhibits higher stability under irradiation with limited swelling relative to a conventional graphite matrix. Additionally, the SiC matrix is expected to exhibit improved mechanical performance relative to graphite. The feasibility of FCM-fueled HTGRs has been explored in a previous study (Lu et al., 2018), and three FCM fuel concepts were identified to be able to maintain the cycle length of the reference conventional General Atomics 350 MWt prismatic modular HTGR.In this work, the previous investigation of the reactor core safety characteristics of HTGRs fueled by these three FCM fuels was significantly extended to detailed thermal hydraulics and neutronics analysis of normal operation and design basis accident scenarios. We found that these FCM-fueled cores would have a maximum fuel temperature ∼20–40 K higher than that of the reference HTGR core at the beginning of cycle (BOC) and ∼30–60 K higher at the end of cycle (EOC) during normal operating conditions. Pressurized (P-) and depressurized (D-) loss of forced cooling (LOFC) accidents as well as the control rod withdrawal accident were explored. The FCM-fueled cores would at most have a maximum fuel temperature ∼30–50 K higher than that of the reference core in a P-LOFC accident, ∼10–30 K in a D-LOFC accident and ∼30–50 K in a rod withdrawal accident. The conclusion of the study is that FCM fuel has a small impact on the reactor performance and safety characteristics during normal operation and design basis accident conditions within the existing and generic 350 MWt prismatic modular HTGR design we considered.Additionally, a fuel cycle cost comparison was also performed in the current study. We found that the FCM fuels may be up to 40%–74% more expensive than the conventional fuel. Further analysis of the economics of FCM fuel are needed, because the uncertainties in the assumptions for this study are high.

In-pin fuel motion dynamics for beginning-of-life core in fast breeder reactors

Melting of nuclear fuel can occur during any unexpected accident where there is rise in power. Specifically, in the unprotected transient overpower accident (hereafter UTOPA), fuel melts and flows axially inside the fuel pin. A previous study of this phenomenon, known as in-pin fuel motion, in a medium-sized fast reactor with an equilibrium core concluded that it basically enhances the inherent safety features. The objective of the present study is to confirm whether such an enhancement also occurs for the beginning of life core (hereafter BOL) and to quantify the differences. Therefore, this article reports the best estimate and conservative UTOPA analyses for both BOL and equilibrium cores. A fuel mass relocation analysis of both cores shows that due to the absence of fission gas perturbations upon melting, the axial relocation of molten fuel is least in the BOL core. This leads to a smaller relocation feedback in the BOL core for the same amount of melting. Results show that while the molten fuel relocation feedback does act as an inherent feedback for the BOL core, it is unable to prevent extensive fuel melting, especially under the conservative UTOPA analyses. On the contrary, such an extensive amount of melting is altogether avoided in the equilibrium core due to greater relocation feedback for lesser amount of melting. A thermodynamic analysis of molten fuel during UTOPA is carried out and it is found that there is a greater possibility of vapourization of molten fuel in the BOL core as compared to the equilibrium core.

Effect of reactor operator intervention during unprotected LOFA in a typical MTR

Abstract The main objective for reactor engineering and inherent safety features is to keep the nuclear fuel in a thermally safe condition with enough safety margins during all operational states (normal-abnormal and accidental states). In this work, an accident analysis of the unprotected loss of flow transient in a typical material test reactor is presented. The effect of reactor operator intervention during the accident in case of manually triggering the shutdown system at different flow coast down ratios is studied. Flow trip scenarios are compared for flow trip ratios of 14, 15, 20, 30, 40, 50 and 60 %. The calculations were performed with the nuclear reactor analysis code PARET. The reactor stability region is described in terms of initial reactor power, core inlet temperature, and power peaking factor.

Improvements in methodology to determine feedback reactivity coefficients

The reactivity of a nuclear reactor is the most important safety and operating parameter. Due to short reactor period, the Light Water Reactor (LWR) designs require the compensations of rapid unfavorable reactivity increases. The increase in fuel or moderator temperature leads to compensate the reactivity jumps as inherent safety characteristics. The safe and reliable reactor operation requires the accurate assessment of these reactivity changes. This paper highlights the improvements in the methodology to determine the feedback reactivity changes in IAEA MTR benchmark. This method incorporates the reactivity effects of fuel temperature in moderator regions and vice versa. For this purpose, a detailed 3D model of the IAEA 10 MW MTR benchmark reactor is developed employing OpenMC computer code. OpenMC is a probabilistic computer code for neutronic calculations. This work uses temperature-dependent JEFF 3.2 cross-sectional library. The model is validated against the reference results of eigenvalues for control rods (inserted and in fully withdrawn position), control rod reactivity worth, averaged thermal flux in the central flux trap, and power fraction for each fuel element at beginning of life. The validated model is applied to simulate the feedback reactivity coefficients against the conventional reference results. In order to improve the methodology, the effect of the moderator temperature and void on fuel is incorporated to obtain a more realistic value of the fuel temperature coefficient. Similarly, the moderator temperature coefficient and void coefficient are improved by incorporating the coupling effects of fuel temperature on moderator. This methodology can be applied to improve the LWR designs.

Characterization of bispecific antibodies that drive synthetic agonistic receptor - transduced T cells to mediate specific and conditional therapy in human pancreatic cancer models

Adoptive T cell therapy, namely chimeric antigen receptor (CAR) T cell therapy has been a groundbreaking and effective treatment of relapsed or refractory haematological malignancies. Still, many patients do not respond or relapse with treatment-resistant disease. Additionally, toxicities such as cytokine release syndrome remain problematic. Cancer heterogeneity, beyond cancer types and inter-patient differences, is present within every individual patient. This heterogeneity, especially in the context of solid tumors, has meant that targeted immunotherapies have fared relatively poorly, creating a need for a modular platform with a capacity to target multiple antigens simultaneously and/or sequentially. Likewise, treatment-related toxicities have limited the therapeutic efficacy and breadth of patient selection. To tackle these caveats through a modular and controllable approach, we equipped T cells with synthetic agonistic receptors (SARs) that are only activated when a tumor-associated antigen and a cross-linking bispecific antibody (BiAb) specific for both SAR T cell and tumor cell are also present. The SAR itself is constituted of an inert extracellular domain in the form of EGFRvIII, that is fused to the T cell activating domains CD28 and CD3ζ. The BiAb employed is a trivalent CrossMab, with two binding arms (2 x Fab) for the tumor-associated antigen (mesothelin), and one binding arm for the SAR receptor (EGFRvIII). We showed that BiAb triggering of the SAR is conditional upon the binding of the second BiAb specificity. What is particularly advantageous with this approach is that T cell activation may only occur when the BiAb is present and in proximity to the antibody-targeted tumor cell. This conditional T cell activation is an inherent safety feature of the platform, whereby if unwanted levels of T cell activation are observed, depletion of the BiAb from the system could result in the reversal of said activation, thus managing the potential toxicity. This work was able to determine the validity and efficacy of the approach. Through the generation of several human pancreatic cancer models, and extensive in vitro and in vivo testing, the platform could be characterized. Its translational relevance and significance as a next-generation adoptive T cell therapy with the potential to plug some gaping pitfalls of current ACT approaches were also shown.

Fuel cladding damage assessment based on reactivity insertion accidents for a 10 MWth LBE cooled fast reactor

Fuel cladding integrity affects the safety and economy of nuclear reactors, especially in accident condition. In this paper, based on the reactivity insertion accident (RIA) analysis, the fuel cladding damage has been analyzed for a 10 MWth LBE cooled fast reactor developed by Institute of Nuclear Energy Safety and Technology (INEST) using RELAP5. Simulation was carried out for control rod withdrawal accident with a reactivity insertion rate of 50.19 pcm/s for 4 s, both for scram and without scram. During the control rod withdrawal accident without scram, the highest cladding temperature was 714 °C, which was below the temperature limit of cladding integrity. It is concluded that the RIA will not cause reactor safety violation due to the reactor’s inherent safety feature.

Leveraging real-time and multitasking Ada capabilities to small microcontrollers

Small embedded microcontrollers typically operate for years without further programmer intervention, so that shipping software free of errors becomes paramount. The Ada programming language includes many safety characteristics (e.g., strong typing or contract-based programming) that help to largely reduce the number of errors introduced by programmers. However, Ada is barely used in microcontrollers with tight memory constraints due to the overhead introduced at run-time. The tasking semantics included in the language represent one major source of this overhead. In this paper we present a new Ada run-time environment that includes a new scheduling policy based on the one-shot task model that simplifies the implementation of the Ada tasking primitives and allows stack sharing techniques to be applied. Consequently, the proposed approach allows using the inherent safety characteristics of the Ada language along with a set of tasking constructs more suitable for small memory devices. Despite its simplicity, the tasking primitives have an equivalent, if not superior, expressiveness to the typical tasking constructs provided by the operating systems targeted to small microcontrollers. An implementation based on a small kernel, a modified run-time system and an automatic code transformation tool have been developed in the context of this work. Initial tests provide promising results, showing the tasking constructs are functionally correct and the proposed run-time features a small memory footprint.

The Emerging Role of InVitro-Transcribed mRNA in Adoptive T Cell Immunotherapy.

Adoptive Tcell therapy is a form of cellular therapy that utilizes human immune cells, often empowered by the expression of recombinant proteins, to attack selected targets present on tumor or infected cells. Tcell-based immunotherapy has been progressing over the past several decades, and reached a milestone with the recent US Food and Drug Administration (FDA) approval of chimeric antigen receptor Tcell therapy for relapsed and refractory leukemia and lymphoma. Although most studies have used viral vectors, a growing number of researchers have come to appreciate invitro-transcribed (IVT) mRNA for the development, testing, and application of Tcell-based immunotherapeutics. IVT mRNA offers inherent safety features, highly efficient recombinant protein translation, and the ability to control pharmacokinetic properties of the therapy. In this review, we discuss the history of IVT mRNA in adoptive Tcell therapy, from tumor-infiltrating lymphocytes and Tcell receptor-based therapies to chimeric antigen receptor therapy and gene-editing techniques, as well as prior and ongoing clinical trials.

Dynamical modeling and simulation analysis of a nuclear desalination plant based on the MED-TVC process

Nuclear fission reaction is a clean energy source that can provide thermal power to desalination processes for producing potable water. Due to the inherent safety features of the integral pressurized water reactor (iPWRs) and economic competitiveness of the multi-effect-desalination and thermal-vapor-compression (MED-TVC) process, it is reasonable to interconnect the iPWR with MED-TVC process to develop nuclear desalination plants (NDPs). Dynamic modeling is important for both the design and optimization of the control systems for nuclear desalination plants. In this paper, based on the balance of mass, momentum, energy and salt, a lumped-parameter dynamic model for the NDP composed of an iPWR named NHR-200II and the MED-TVC process is given for the plant control design, which is further deployed as a program on Matlab/Simulink platform. For the modeling verification, the steady points of some key process variables are shown with comparison to the design data, and the open-loop responses under the stepping of both the input seawater flowrate and TVC throat cross-section area are given, which not only show accuracy of this model but also illustrate the coupling between the nuclear steam supply system (NSSS) and MED-TVC modules. Then, a plant control strategy of the NDP based upon NHR-200II reactor and MED-TVC module is newly proposed. Based on the dynamic model, the control verification is finally performed, and the closed-loop responses in the cases of both power maneuvering and MED-TVC module bypassing show the feasibility and satisfactory performance of this control design.

SPARK-LS: A novel design of a compact liquid chloride salt cooled fast reactor based on tube-in-duct fuel concept

A novel design of a compact liquid chloride salt cooled fast reactor (SPARK-LS) was proposed in the present study as a distributed energy resource for easy transportation and convenient deployment in diverse applications, such as electricity generation and district heating. The SPARK-LS reactor with rated power of 40 MWth can operate for 10 effective full power years without refueling. An innovative tube-in-duct fuel concept with coolant inside the tubes and fuel outside was adopted to achieve higher fuel volume fraction and lower pressure drop when compared with traditional pin-type fuel. Neutronics and thermal-hydraulics design and preliminary safety analysis were accomplished to obtain an optimized core design by using the advanced reactor design and analysis code system SARAX. Titanium was adopted as the reflector material due to its low density, good corrosion resistance, large strength-to-density ratio and decreased albedo with the neutron spectrum hardening. The optimized core design featured with compact volume and light weight was proved to satisfy the design constraints of peak coolant temperature, peak fuel centerline temperature and coolant pressure drop. The negative coolant density reactivity coefficient in the full core was ensured during the whole core lifetime thanks to the compact core design and the adoption of the titanium reflector. Based on the quasi-static reactivity balance method, five anticipated transients without scram were analyzed to confirm the inherent safety feature of SPARK-LS. It was shown that passive shutdown could be achieved safely for all the transients and the residual decay heat after the shutdown could be removed automatically by the natural circulation of coolant.

In situ formed polymer gel electrolytes for lithium batteries with inherent thermal shutdown safety features

An in situ formed poly(vinylene carbonate)–lithium iodide gel electrolyte enables stable cycling of lithium metal and a thermal shutdown function.