The new generation internal beam dump of the Super Proton Synchrotron (SPS) at CERN will have to dissipate approximately 270 kW of thermal power, deposited by the primary proton beam. For this purpose, it is essential that the cooling system features a very efficient heat evacuation. Diffusion bonding assisted by hot isostatic pressing (HIP) was identified as a promising method of joining the cooling circuits and the materials of the dumps core in order to maximize the heat transfer efficiency. This paper presents the investigation of HIP assisted diffusion bonding between two CuCr1Zr blanks enclosing SS 316L tubes and the realization of a real size prototype of one of the dump’s cooling plates, as well as the assessments of its cooling performance under the dump’s most critical operational scenarios. Energy-dispersive x-ray spectroscopy, microstructural analyses, measurements of thermal conductivity, and mechanical strength were performed to characterize the HIP diffusion bonded interfaces (CuCr1Zr-CuCr1Zr and CuCr1Zr-SS 316L). A test bench allowed to assess the cooling performance of the real size prototype. At the bonded interface, the presence of typical diffusional phenomena was observed. Moreover, measured tensile strength and thermal conductivity were at least equivalent to the lowest ones of the materials assembled and comparable to its bulk properties, meaning that a good bonding quality was achieved. Finally, the real size prototype was successfully tested with an ad hoc thermal test bench and with the highest operational thermal power expected in the new generation SPS internal beam dump. These results demonstrated the possibility to use HIP as a manufacturing technique for the cooling plates of the new generation SPS internal beam dump, but they also open up the way for further investigations on its exploitability to improve the cooling performance of any future high intensity beam intercepting device or in general devices requiring very efficient heat evacuation systems.

The Beam Dump Facility (BDF), currently in the study phase, is a proposed general-purpose fixed target facility at CERN. Initially will host the Search for Hidden Particles (SHiP) experiment, intended to investigate the origin of dark matter and other weakly interacting particles. The BDF particle production target is located at the core of the facility and is employed to fully absorb the high intensity (400 GeV/c) Super Proton Synchrotron (SPS) beam. To validate the design of the production target, a downscaled prototype was tested with beam at CERN in 2018 in the North Area primary area in a dedicated test at 35 kW average beam power. This contribution details the BDF prototype target operation, fully remote removal intervention and foreseen post-irradiation examination plans.

As part of the effort to move forward the Fluoride salt-cooled High-temperature Reactor (FHR) technology, the Advanced High Temperature Reactor (AHTR) is being developed at Oak Ridge National Laboratory (ORNL) and several other institutions. Due to its plank fuel design and inherently low heavy metal loading, which challenges fuel utilization, online refueling is considered as an option for improving the economic viability of this reactor. This work presents the thermal hydraulic modeling of the online refueling for the AHTR. Analyses at the single channel and fuel assembly level have been performed in order to develop a model of the reactor. The reactor modeling has been integrated with CFD studies for characterizing the steady state conditions and the refueling transient. The simulations of the transient have been complemented by the analysis of the stability of the refueling operation. This work demonstrates the viability of online refueling from a thermal hydraulic standpoint and develops a modeling approach for this type of operational transient.

The Beam Dump Facility (BDF) is a proposed general-purpose facility at CERN, dedicated to fixed target and beam dump experiments, currently being developed in the context of the Physics Beyond Colliders program. The design of the facility will allow to host different types of experiments, of which SHiP is planned to be the initial one. The core of the facility is a high-density target/dump absorbing the full intensity of the SPS beam and generating a cascade of particles that are detected downstream the target complex. The target and its shielding blocks are positioned inside a vessel, which is planned to be passivized with helium, in order to reduce the activation of the gas surrounding the target and to extend the operational life of materials and equipment. The passivation system that will be in charge of purifying and circulating the helium is a critical component for the operation of the facility. Fluid dynamics simulations have been performed to study the circulation of the helium through the vessel. A detailed design of the helium passivation system and its main components has been developed.

The beam dump facility (BDF) project is a proposed general-purpose facility at CERN, dedicated to beam dump and fixed target experiments. In its initial phase, the facility is foreseen to be exploited by the Search for Hidden Particles Experiment. Physics requirements call for a pulsed 400 GeV/c proton beam as well as the highest possible number of protons on target each year of operation (4.0 x 10(19)/year), in order to search for feebly interacting particles. The target/dump assembly lies at the heart of the facility, with the aim of safely absorbing the full high intensity Super Proton Synchrotron beam, while maximizing the production of charmed and beauty mesons. High-Z materials are required for the target/dump, in order to have the shortest possible absorber and reduce muon background for the downstream experiment. The design of the production target is one of the most challenging aspects of the facility design, due to the high energy and power density deposition that are reached during operation, and the resulting thermomechanical loads. The nature of the beam pulse induces very high temperature excursions between pulses (up to 100 degrees C), leading to considerable thermally induced stresses and long-term fatigue considerations. The high average power deposited on target (305 kW) creates a challenge for heat removal. During the BDF facility comprehensive design study, launched by CERN in 2016, extensive studies have been carried out in order to define and assess the target assembly design. These studies are described in the present contribution, which details the proposed design of the BDF production target, as well as the material selection process and the optimization of the target configuration and beam dilution. One of the specific challenges and novelty of this work is the need to consider new target materials, such as a molybdenum alloy as core absorbing material and Ta2.5W as cladding. Thermostructural and fluid dynamics calculations have been performed to evaluate the reliability of the target and its cooling system under beam operation. In the framework of the target comprehensive design, a preliminary mechanical design of the full target assembly has also been carried out, assessing the feasibility of the whole target system.

The proposed Beam Dump Facility (BDF) is foreseen to be located at the North Area of the SPS. It is designed to be able to serve both beam dump like and fixed target experiments. The SPS and the new facility would offer unique possibilities to enter a new era of exploration at the intensity frontier. Possible options include searches for very weakly interacting particles predicted by Hidden Sector models, and flavour physics measurements. In the first instance, exploitation of the facility, in beam dump mode, is envisaged to be for the Search for Hidden Particle (SHiP) experiment. Following the first evaluation of the BDF in 2014-2016, CERN management launched a Comprehensive Design Study over three years for the facility. The BDF study team has since executed an in-depth feasibility study of proton delivery to target, the target complex, and the underground experimental area, including prototyping of key sub-systems and evaluations of the radiological aspects and safety. A first iteration of detailed integration and civil engineering studies have been performed in order to produce a realistic schedule and cost. This document gives a detailed overview of the proposed facility together with the results of the studies, and draws up a possible road map for a three-year Technical Design Report phase, followed by a 5 to 6 year construction phase.

The beam dump facility (BDF) is a project for a new facility at CERN dedicated to high intensity beam dump and fixed target experiments. Currently in its design phase, the first aim of the facility is to search for light dark matter and hidden sector models with the Search for Hidden Particles (SHIP) experiment. At the core of the facility sits a dense target/dump, whose function is to absorb safely the 400 GeV/c Super Proton Synchrotron (SPS) beam and to maximize the production of charm and beauty mesons. An average power of 300 kW will be deposited on the target, which will be subjected to unprecedented conditions in terms of temperature, structural loads and irradiation. In order to provide a representative validation of the target design, a prototype target has been designed, manufactured, and tested under the SPS fixed-target proton beam during 2018, up to an average beam power of 50 kW, corresponding to 350 kJ per pulse. The present contribution details the target prototype design and experimental setup, as well as a first evaluation of the measurements performed during beam irradiation. The analysis of the collected data suggests that a representative reproduction of the operational conditions of the beam dump facility target was achieved during the prototype tests, which will be complemented by a postirradiation examination campaign during 2020.

Several academic and commercial organizations around the world are developing the Fluoride salt-cooled High-temperature Reactor (FHR) technology, due to its safety features and potential to generate high temperature energy for electricity and process heat applications. The Advanced High Temperature Reactor (AHTR) being considered in this study is a FHR design developed at Oak Ridge National Laboratory (ORNL). It is based on the use of graphite as moderator, FLiBe as coolant, and hexagonal fuel elements with fuel plates (or "planks") composed of TRISO particles embedded in a carbonaceous matrix. The AHTR reference design is based on traditional batch refueling approach, which requires to shut down the reactor and replace/reshuffle a certain amount of fuel assemblies in the core at a specific frequency. Several options have been evaluated in the design process, in order to maximize the cycle length and optimize the use of fuel. However, the relatively short cycle and poor fuel utilization are intrinsic features of this family of reactors, due to the low heavy metal loading in the core and insufficient moderation, which are competing aspects in terms of core volume fraction. Since the fuel is expected to be more expensive than the fuel of light water reactors (LWR), this issue might challenge the economic viability of the AHTR. In order to eliminate or ameliorate this issue, a novel approach to refueling has been developed and proposed, consisting of continuous on-power refueling, or on-line refueling, in which the refueling procedure is performed at full power or partially reduced power (the reactor is not shut down) and a single assembly is removed for each refueling operation. A systematic neutronic and thermal-hydraulic analysis approach has been developed and performed to assess the viability and safety of the refueling operations, followed by the evaluation of the core design requirements and a quantification of the economic advantages resulting from the implementation of this procedure.

The Beam Dump Facility (BDF) Project, currently in its design phase, is a proposed general-purpose fixed target facility at CERN, dedicated to the Search for Hidden Particles (SHiP) experiment in its initial phase. At the core of the installation resides the target/dump assembly, whose aim is to fully absorb the high intensity 400 GeV/c Super Proton Synchrotron (SPS) beam and produce charmed mesons. In addition to high thermo-mechanical loads, the most challenging aspects of the proposed installation lie in the high energy and power density deposition that are reached during operation. In order to validate the design of the BDF target, a scaled prototype is going to be tested during 2018 in the North Area at CERN, upstream the existing beryllium primary targets. The prototype testing under representative beam scenarios will allow having an insight of the material response in an unprecedented regime. Online monitoring and an extensive Post Irradiation Experimental (PIE) campaign are foreseen. The current contribution will detail the design of the BDF target/dump core as well as the design and construction of the prototype target assembly. THE BEAM DUMP FACILITY TARGET The Beam Dump Facility (BDF) [1], currently in its design phase, is a fixed-target facility proposed to be situated at the North Area of the SPS. This general purpose facility is aimed at the Search for Hidden Particles (SHiP) experiment [2] in the first instance. The BDF target sits at the core of the installation with a double function: on one side, it must absorb safely and reliably the full SPS primary beam. On the other side, its design has been optimized from a physics perspective point of view (in terms of geometry, material, gaps, etc.) to maximize the production of charmed mesons. It can be considered as a beam dump/absorber, since it will contain most of the cascade generated by the interaction with the primary beam. The high power deposited is one of the main challenges of the BDF target design, with 320 kW of average power deposited and 2.56 MW over the 1-second slowly extracted spill. Such high beam power expected on target requires beam dilution [3], as well as a large beam spot diameter, in order to avoid target failure. The dilution pattern generated by the upstream magnets and the beam size have been optimized taking into account the aperture restrictions from the extrac∗ edmundo.lopez.sola@cern.ch tion line magnets and the mechanical performance of the target. As a result, the SPS primary beam will be diluted in 4 turns over a 50 mm radius circle for each 1-second pulse, with a beam spot size of 8 mm 1σ. Target Design and Material Selection The materials sought for the BDF final target are high-Z materials with a short nuclear interaction length, in order to increase the re-absorption of pions and kaons produced in the intra-nuclear cascade process. The proposed target design currently consists of several collinear cylinders of TZM ((0.08%)titanium-(0.05%)zirconium-molybdenum alloy) and pure tungsten (W), cladded with pure Ta or a Wcontaining Ta-alloy, with a diameter of 250 mm and different thicknesses, for a total effective target length of around 1.3 m (see Figure 1). For the first part of the target core, TZM is chosen because of its higher strength, better creep resistance and higher recrystallization temperature compared to pure molybdenum [4]. For the second part of the target, pure W is selected, since it fulfills the physics requirements (high density and short interaction length) and has proven a good performance under irradiation [5]. The proposed target cylinders have variable lengths, which have been iteratively adjusted to have the most uniform possible energy deposition in each of the blocks. The optimization of the blocks’ length aims at minimizing the level of temperatures and stresses reached in the target materials. Figure 1: Layout of the Beam Dump Facility target core. Given the high energy deposited and the high temperatures reached during operation (above 180◦C in the cladding and core materials of several target blocks after the beam impact), the target requires active water cooling. The cooling water will flow through a 5 mm gap foreseen between the different blocks with high (roughly 4 m/s) velocity, in order to provide an effective heat transfer coefficient (HTC) between the cooling medium and the blocks. However, the 9th International Particle Accelerator Conference IPAC2018, Vancouver, BC, Canada JACoW Publishing ISBN: 978-3-95450-184-7 doi:10.18429/JACoW-IPAC2018-WEPMG002 WEPMG002 2604 Co nt en tf ro m th is w or k m ay be us ed un de rt he te rm so ft he CC BY 3. 0 lic en ce (© 20 18 ). A ny di str ib ut io n of th is w or k m us tm ai nt ai n at tri bu tio n to th e au th or (s ), tit le of th e w or k, pu bl ish er ,a nd D O I. 07 Accelerator Technology T20 Targetry high-speed water in contact with the pure W and TZM blocks could induce undesired corrosion-erosion effects. Therefore, all the target core blocks will be cladded via diffusion bonding achieved by means of Hot Isostatic Pressing (HIP) with Ta or Ta-alloy [6] [7], due to their high corrosion resistance, and its convenience as high-Z material with short interaction length. The preliminary structural calculations performed on the BDF final target assuming pure Ta as cladding material led to the conclusion that the maximum stresses expected in the tantalum cladding may be critical for the target operation. The simulations performed have shown that the Tantalum cladding of some of the target blocks can reach a maximum Von Mises stress of 110 MPa, leading to an unacceptable safety margin with respect to the yield strength of tantalum at high temperatures, which is assumed to be around 100 MPa at 150◦C [8]. Plastic deformation of the cladding material is an undesired effect, taking into account that the core materials are expected to work always in the elastic regime. The cyclic plastic deformation of the cladding during a long period could lead to premature fracture of the tantalum layer, and/or to detachment of the cladding with respect to the base refractory metal, reducing or blocking the heat dissipation through the cladding material. A tantalum-tungsten alloy with 2.5% content in pure W (Ta2.5W) has been considered as alternative cladding material, this alloy having a much higher strength at high temperatures than pure Ta [9]. Ta2.5W has similar thermo-physical properties to pure Ta, a good corrosion-erosion resistance as well, and is expected to present the same diffusion bonding compatibility with W and TZM as pure Ta. BDF TARGET PROTOTYPE Due to the unprecedented conditions to which the BDF target materials will be exposed in terms of temperature, stress and radiation levels, it has been proposed to test a prototype of the BDF target under proton beam. A dedicated experiment will be executed in the CERN North Area Primary Target zone during 2018 [10], in particular upstream the existing T6 beryllium target. The unknown reliability of the intermetallic bonded surfaces when exposed to the beam impact is one of the main motivations for this test. The prototype core is foreseen to be impacted by 10 pulses, and it has been designed to achieve a meaningful reproduction of the level of temperatures and stresses reached in the BDF final target [11]. Target Prototype Operation The target prototype will be tested in the CERN’s North Area under a non-diluted primary proton beam but using the same cycle configuration as of the BDF final target (i.e. spill length of 1 second and repetition rate of 7.2 seconds). Consequently, the required beam intensity to reach representative temperatures and stresses with respect to the final target is lower and expected to be in the range of 3-4·10 p+/cycle. Table 1 shows a comparison between the BDF final target beam and the target prototype beam parameters. The experimental setup foreseen in the North Area for the prototype testing is justified by the need of a slow extracted beam to reproduce the final BDF target operational conditions, which could not be achieved under the fast extracted beam of other dedicated experimental facilities at CERN such as HiRadMat [12]. The prototype assembly has been installed on a motorized table with horizontal translation motion which will align the target replica with the beam axis during the dedicated beam time for the test, and will remove it from the beam trajectory during normal SPS operation. Table 1: BDF Final Target and Target Replica Beam Parameters Comparison Baseline BDF final Target characteristics target prototype Proton Momentum [GeV/c] 400 400 Beam intensity [p+/cycle] 4·10 3-4·10 Beam dilution 4 circular No sweeps/s Expected r.m.s spot 8/8 3/3 size (H/V) [mm] Cycle length [s] 7.2 7.2 Spill duration [s] 1 1 Average beam power 320 20 on target [kW] Average beam power 2.5 0.14 during spill [MW] Target Prototype Design and Construction The target replica consists on a reduced scale prototype composed of 80 mm diameter cylinders and the same thickness distribution as the BDF final target, as shown in Figure 2. Tantalum and Ta2.5W are used as cladding materials in order to evaluate the performance of both materials during operation. The prototype assembly includes two concentric stainless steel tanks: the outer tank ensures the leak-tightness of the assembly, compatible with an operational pressure of 22 bar, provides an interface for the electrical and water connections, and encloses the inner stainless steel tank. The target blocks are sitting on the inner tank lower shell, only constrained in the Z-direction by 2 pins that allow free-body expansion of the blocks within 50 μm, but ensure a gap of 5 mm between the blocks, necessary for the water cooling. The target prototype cooling system design intends to replicate the most critical characteristics of the cooling system foreseen for the final BDF target: high pressure, 5 mm channels and high water speed between

The objective of this work is to simulate the Liquid Salt Test Loop (LSTL) using the TRACE system code. The LSTL is an experimental facility built at Oak Ridge National Laboratory to test the thermal hydraulic behavior of a circulating FLiNaK liquid salt. A literature review of the experimental work and the heat transfer and friction correlations for pebble beds was performed to identify the correlations that can be used to simulate the flow of FLiNaK through a pebble bed. The selected correlations were implemented in the TRACE source code and tested using 1-D pipe components. The modified version of TRACE was then used to develop models for each component in the loop. Each component was tested separately to assess its correct physical behavior. The components were integrated into a comprehensive loop model, including the main loop and the air cooling system. The model was used to compute the steady state conditions of the loop, in particular calculation of the pressure distribution and other global operational parameters. The loop-filling transient was analyzed, along with other specific transient conditions such as the pump trip and the loop behavior under natural circulation conditions. The TRACE model was used to help characterize loop thermal hydraulic behavior and to help interpret results from loop shakedown testing. (C) 2017 Elsevier Ltd. All rights reserved.

The Advanced High Temperature Reactor (AHTR) is one of the most promising advanced designs, since it allows low pressure operation, implements passive safety with large safety margins, and heats the coolant to high temperatures resulting in high plant efficiency. The currently considered fuel design employs fuel plates made of TRISO particles dispersed in a graphite matrix, so the fuel density and consequently heavy metal loading is relatively low; several options for improving the fuel utilization and cycle length are under evaluation, among which there are variations of the fuel assembly design and online refueling. The fuel assembly of the AHTR uses fuel plates enclosed into a hexagonal graphite box, and it is cooled by Flibe, which flows through thin rectangular channels located between fuel plates. This innovative fuel assembly design requires optimization from the thermal and neutronic standpoints. The work developed recently aims to provide a better understanding of the flow in the channels and the 3D temperature distribution within the assembly. In particular, the following features are being evaluated: power removal by the inter-assembly flow, flow distribution for the intra-assembly channels, effects of the thin internal channels on the 2D temperature distribution of the assembly, maximum fuel temperature. This work will provide indications how to improve the overall design of the assembly, regarding the flow distribution and the geometry of the system. The ultimate aim is to provide a model of the assembly, as simple as possible while providing adequate results, which will be integrated in a full core model for the evaluation of the operating conditions and transients, particularly the online refueling.

The Advanced High Temperature Reactor (AHTR) is a fluoride-cooled and graphite-moderated reactor concept designed by Oak Ridge National Laboratory (Holcomb et al., 2011). The modeling and optimization of the heat removal system and the core structure is required, in order to obtain an adequate heavy metal loading and to provide effective cooling capability. The single channel MATLAB model provides a simple tool to evaluate the steady state conditions for the coolant and the fuel plate and the effects of the power distribution; sensitivity studies on the main design parameters of the fuel element are performed. A RELAP5-3D single channel model is developed for the validation and comparison with the MATLAB model; this model is the starting point for the development of a full core model, enabling the study of transients. A one-third fuel assembly model is then analyzed, consisting of six fuel plates and modeling the heat conduction of graphite through RELAP5-3D conduction enclosures. Since the assembly model is not suitable for the implementation in a full core model with the same level of detail, several simplifications have been evaluated, involving the modeling of the plate through a single heat structure and the modeling of different plates through a single plate. A SCALE model of the fuel assembly was developed for the evaluation of the reactivity feedback and the power distribution in the core. The results from the neutronic evaluations and the assembly model were implemented in a full core model, involving the core, the main reactor structures, the cooling system and the safety system (DRACS). The RELAP5-3D core model was used for the evaluation of the steady state conditions and the effects of a loss of forced cooling accident (LOFC). (C) 2013 Published by Elsevier Ltd.