Helium Cooled Pebble Bed Test Research Articles

Preliminary Experimental Quantification of Helium Leakages from Flanged Connections at HCPB TBS Operative Conditions

The HCPB TBS (Helium-Cooled Pebble Bed Test Blanket System) is one of the two European TBSs that will be installed and tested in the ITER reactor. The use of flanged connections in the Helium Coolant System and the Tritium Extraction System of the HCPB TBS would make the remote maintenance operations easier and faster. Therefore, investigating the helium leakage from flanges becomes a fundamental step toward the control of the tritium activity in the Port Cell, as the helium flow will contain a variable but not negligible amount of tritium. The first set of experiments on helium leakages from flanged connections is described in this paper. The experiments were performed in a HeFUS3 facility, an eight-shaped helium loop designed to work at HCPB-TBS-relevant conditions. The facility can provide a helium mass flow rate in the range of 0.27–1.4 kg/s and can reach a pressure as high as 80 bar and a temperature up to 530 °C. Two types of gaskets were tested in this campaign: a spiral-wound gasket and an oval ring joint. The gasket/flange assemblies are described in detail in this paper, together with the test section that hosts them and the performed commissioning tests. The tests were carried out at 500 °C and 80 bar. In these conditions, the leak rate from the flange with the oval ring joint resulted in being, on average, 1.42·10−6 mbar∙L/s, while the leak rate from the flange with the spiral-wound gasket resulted in being, on average, 3.73·10−3 mbar∙L/s.

ASUSD nuclear data sensitivity and uncertainty program package: Validation on fusion and fission benchmark experiments

Nuclear data (ND) sensitivity and uncertainty (S/U) quantification in shielding applications is performed using deterministic and probabilistic approaches. In this paper the validation of the newly developed deterministic program package ASUSD (ADVANTG + SUSD3D) is presented. ASUSD was developed with the aim of automating the process of ND S/U while retaining the computational efficiency of the deterministic approach to ND S/U analysis. The paper includes a detailed description of each of the programs contained within ASUSD, the computational workflow and validation results.ASUSD was validated on two shielding benchmark experiments from the Shielding Integral Benchmark Archive and Database (SINBAD) - the fission relevant ASPIS Iron 88 experiment and the fusion relevant Frascati Neutron Generator (FNG) Helium Cooled Pebble Bed (HCPB) Test Blanket Module (TBM) mock-up experiment. The validation process was performed in two stages. Firstly, the Denovo discrete ordinates transport solver was validated as a standalone solver. Secondly, the ASUSD program package as a whole was validated as a ND S/U analysis tool. Both stages of the validation process yielded excellent results, with a maximum difference of 17% in final uncertainties due to ND between ASUSD and the stochastic ND S/U approach. Based on these results, ASUSD has proven to be a user friendly and computationally efficient tool for deterministic ND S/U analysis of shielding geometries.

Conceptual design of the enhanced coolant purification systems for the European HCLL and HCPB test blanket modules

The Coolant Purification Systems (CPSs) is one of the most relevant ancillary systems of European Helium Cooled Lead Lithium (HCLL) and Helium Cooled Pebble Bed (HCPB) Test Blanket Modules (TBMs) which are currently in the preliminary design phase in view of their installation and operation in ITER.The CPS implements mainly two functions: the extraction and concentration of the tritium permeated from the TBM modules into the primary cooling circuit and the chemistry control of helium primary coolant.During the HCLL and HCPB-TBSs (Test Blanket Systems) Conceptual Design Review (CDR) in 2015 it was recognized the need of reducing the tritium permeation into the Port Cell #16 of ITER. To achieve this and, then, to lower the tritium partial pressure in the Helium Cooling Systems in normal operation, the helium flow-rate treated by each CPS has been increased of almost one order of magnitude.In 2017, to satisfy the CDR outcomes and the new design requirements requested by Fusion for Energy (F4E, the European Domestic Agency for ITER), ENEA performed a preliminary design of the “enhanced” CPSs.This paper presents the current design of the “enhanced” CPSs, focusing on design requirements, assumptions, selection of technologies and preliminary components sizing.

Non-linear assessment of critical failure modes in the first wall of the European TBM

The assessment of the different components of the Helium Cooled Pebble Bed (HCPB) and Helium Cooled Lithium Lead (HCLL) Test Blanket Modules (TBMs) based on elastic FE analyses has been performed considering main failure modes and respective structural design criteria. This study has been carried out for the operation at full power and for the so-called Approach 2 cooling that is set up at reduced heat extraction capability for compliance with temperature targets to be relevant to DEMOnstration power plant blanket system. Consequently this situation is the worst condition in terms of cooling performance as a result it reveals that many locations in the First Wall (FW) become critical in the sense that certain criteria are not fulfilled, particularly those for immediate plastic flow localization, progressive deformation (ratcheting) and creep-fatigue interaction. Of course one can better reach code compliance by improving the cooling performance (so called Approach 1) but it will degrade the DEMO relevancy.The critical failure modes are re-assessed performing non-linear analysis using an elasto-viscoplatic model, particularly developed for RAFM steels such as the structural material EUROFER97 by Aktaa & Schmitt, and considering the appropriate design criteria of the inelastic route of RCC-MRx and SDC-IC. Despite the conservatism in these criteria, the results show all-clear signal with respect to immediate plastic flow localization and at least much smaller breaches of the limits with respect to the other failure modes. Reporting details and results of the non-linear failure assessments demonstrates their potential and capability in supporting specific and efficient improvements to the design of highly loaded components. The conservatism in the considered design criteria and ways for its reduction are discussed in addition.

Characterization of the cooling channels of First Wall Mock-up dedicated to the HCPB TBM qualification

The First Wall (FW) of the EU Helium Cooled Pebble Bed (HCPB) Test Blanket Module (TBM) faces the fusion plasma and experiences high heat fluxes; therefore its cooling channels design is a key R&D task for qualifying the HCPB TBM for the fusion reactors ITER and DEMO. Within the manufacturing and qualification activities performed in KIT for the HCPB TBM, a First Wall Mock-up (FWM) was designed and manufactured. The objective of this study is to characterize the hydrodynamic behaviour of the FWM cooling channels by investigating the coolant pressure drop for each channel. The FWM has a shape of rectangular prism (710mm×405mm×45mm) with 10 U-shaped cooling channels which have a square cross section (15mm×15mm) with rounded corners of 4mm radius. The FWM was integrated into a gas loop that has the relevant instruments and piping system for measuring and controlling the air (6bar abs.) flow parameters. This paper presents experimental measurements of the pressure drop across the FWM cooling channels. The present results support the qualification of the HCPB TBM mock-ups which will be tested in the Helium Loop Karlsruhe (HELOKA) facility with fusion-relevant heat flux and helium cooling.

Formation and accumulation of radiation-induced defects and radiolysis products in modified lithium orthosilicate pebbles with additions of titanium dioxide

Lithium orthosilicate (Li4SiO4) pebbles with 2.5 wt.% excess of silicon dioxide (SiO2) are the European Union's designated reference tritium breeding ceramics for the Helium Cooled Pebble Bed (HCPB) Test Blanket Module (TBM). However, the latest irradiation experiments showed that the reference Li4SiO4 pebbles may crack and form fragments under operation conditions as expected in the HCPB TBM. Therefore, it has been suggested to change the chemical composition of the reference Li4SiO4 pebbles and to add titanium dioxide (TiO2), to obtain lithium metatitanate (Li2TiO3) as a second phase. The aim of this research was to investigate the formation and accumulation of radiation-induced defects (RD) and radiolysis products (RP) in the modified Li4SiO4 pebbles with different contents of TiO2 for the first time, in order to estimate and compare radiation stability. The reference and the modified Li4SiO4 pebbles were irradiated with accelerated electrons (E = 5 MeV) up to 5000 MGy absorbed dose at 300–990 K in a dry argon atmosphere. By using electron spin resonance (ESR) spectroscopy it was determined that in the modified Li4SiO4 pebbles, several paramagnetic RD and RP are formed and accumulated, like, E' centres (SiO33−/TiO33−), HC2 centres (SiO43−/TiO3−) etc. On the basis of the obtained results, it is concluded that the modified Li4SiO4 pebbles with TiO2 additions have comparable radiation stability with the reference pebbles.

Feasibility study of a neutron activation system for EU test blanket systems

The Neutron Activation System (NAS) for the EU Helium Cooled Lithium Lead (HCLL) and Helium Cooled Pebble Bed (HCPB) Test Blanket Systems (TBSs) is an instrument that is proposed to determine the absolute neutron fluence and absolute neutron flux with information on the neutron spectrum in selected positions of the corresponding Test Blanket Modules (TBMs). In the NAS activation probes are exposed to the ITER neutron flux for periods ranging from several tens of seconds up to a full plasma pulse length, and the induced gamma activities are subsequently measured. The NAS is composed of a pneumatic transfer system and a counting station. The pneumatic transfer system includes irradiation ends in TBMs, transfer pipes, return gas pipes, a transfer station with a distributor (carousel), and a pressurized gas driving system, while the counting station consists of gamma ray detectors, signal processing electronic devices, and data analyzing software for neutron source strength evaluation. In this paper, a brief description on the proposed TBM NAS as well as the key components is presented, and the integration challenges of TBM NAS are outlined.

Creep fatigue assessment for EUROFER components

Creep-fatigue of test blanket module (TBM) components built from EUROFER is evaluated based on the elastic analysis approach in ASME Boiler Pressure Vessel Code (BPVC). The required allowable number of cycles design fatigue curve and stress-to-rupture curve to estimate the creep-fatigue damage are used from the literature. Local stress, strain and temperature inputs for the analysis of creep-fatigue damage are delivered by the finite element code ANSYS utilizing the Mechanical ANSYS Parametric Design Language (MAPDL). A developed external FORTRAN code used as a post processor is coupled with MAPDL. Influences of different pulse durations (hold-times) and irradiation on creep-fatigue damage for the preliminary design of the Helium Cooled Pebble Bed Test Blanket Module (HCPB-TBM) are discussed for the First Wall component of the TBM box.

Manufacturing pre-qualification of a Short Breeder Unit mockup (SHOBU) as part of the roadmap toward the out-of-pile validation of a full scale Helium Cooled Pebble Bed Breeder Unit

The key components of the Helium Cooled Pebble Bed Test Blanket Module (HCPB TBM) in ITER are the Breeder Units (BU). These are the responsible for the tritium breeding and part of the heat extraction in the HCPB TBM. After a detailed design and engineering phase performed during the last years in the Karlsruhe Institute of Technology (KIT), a reference model for the manufacturing of a HCPB BU mock-up has been obtained. The mid-term is the out-of-pile qualification of the thermal and thermo-mechanical performance of a full-scale HCPB BU mock-up in a dedicated helium loop. Several key manufacturing technologies have been developed for the fabrication of the HCPB BU. In order to pre-qualify these techniques, a Short Breeder Unit mock-up (SHOBU) is under construction and to be tested. This paper aims at describing the relevance of SHOBU with a full-scale HCPB BU, the constitutive parts of SHOBU, the manufacturing and joining technologies involved, the assembly sequence (taking into consideration functional steps like its filling with Li4SiO4 pebbles or its assembly in the HCPB TBM) and the welding procedures studied. The paper concludes with a description of the required pre-qualification tests performed to SHOBU, i.e. pressure and leak tightness tests, according to the standards.

ICONE23-1090 SINGLE STEP FABRICATION OF NANO-SIZED Li4SiO4 BREEDER BY MICROWAVE-INDUCED SOLUTION COMBUSTION SYNTHESIS

Li_4SiO_4 (lithium orthosilicate) is a promising ceramic tritium breeder for the future D-T fusion reactor, which is also considered as a candidate material for Helium Cooled Pebble Bed Test Blanket Module (HCPB TBM) of China. Simple and efficient microwave-induced solution combustion synthesis (MSCS) approach was adopted to prepare Li_4SiO_4 powder by using lithium nitrate and tetraethyl orthosilicate as raw materials. In MSCS, microwave power is a key factor, which controls the combustion mode, flame temperature, phase composition, and microstructure of the product. The synthesized Li_4SiO_4 particles are homogeneous distributed with an average crystalline size of 20 nm when the microwave power is 1100 W. The Li_4SiO_4 powder shows comparable sinterability to the conventional solid state reaction, which reaches 89.2% of theoretical density at 1173 K with a small grain size of 2 μm.

A generic data translation scheme for the coupling of high-fidelity fusion neutronics and CFD calculations

The design of fusion device components is achieved through iterative coupled neutronics and thermal hydraulics analyses. A translation scheme has been developed for transferring the nuclear heating data from Monte Carlo (MC) neutronic calculations to CFD simulations. It contains a generic data translation kernel which supports the high-fidelity data mapping of MC meshes on CFD meshes, and provides interfaces for processing the nuclear response data on the meshes for CFD codes. This translation scheme has been implemented in the open-source pre- and post-processing platform SALOME to extend its capabilities on data manipulations and visualizations. For verification purposes, a blanket test case based on the Helium Cooled Pebble Bed Test Blanket Module was investigated. The processing of the heating distribution data was validated through a so-called Inversion Check comparing the inverted heating field with the original MC tally distribution. The results of the verification have been discussed in detail, and the reliability of the data translation scheme is concluded.

Experimental layout and thermo-mechanical studies on a Thermo-mechanical Cycle Mock up (TCM) plate

In the frame of the activities of the EU Breeder Blanket Programme, the Karlsruhe Institute of Technology (KIT) is involved in several activities in support of the design and qualification of the Helium Cooled Pebble Bed Test Blanket Module (HCPB-TBM). During operation the TBM will be subjected to complex thermo-mechanical loads, especially the plasma facing parts, the so-called First Wall (FW). In the recent years significant effort was dedicated to the FE modeling of the TBM box as a complete assembly: detailed FE models (1 quarter) were developed and thermo-mechanical calculations were performed for the better description of the thermo-mechanical behavior of the HCPB-TBM box under nominal and accidental conditions. In parallel with the numerical studies the manufacturing process for the TBM-FW has progressed. Currently KIT has developed a manufacturing path that will allow the manufacturing of an FW plate, the so-called TCM (Thermo-mechanical Cycle Mock up), with an overall size of 710mm×484mm×30mm. The present paper presents the results of the numerical investigations of a mock up designed to qualify the manufacturing procedure of the TCM. For this the TCM will be subject to the same heat loads as the central part of a TBM-FW operating under TBM characteristic conditions (nominal surface heat flux of 500kW/m2 in pulsed regime). Based on the comparison with the numerical simulations of a full TBM box, a design of the test mock up including the support structure behind the TCM plate will be proposed with the aim of reproducing an equivalent level of stresses in the test object as in a TBM-FW.

Progress in the KIT approach for development of the HCPB TBM stiffening plate feasibility mock up fabrication

Sub-component manufacturing and assembly concepts for the fabrication of the Helium Cooled Pebble Bed Test Blanket Module have been developed since more than one decade in the KIT. In the present design the structure of the HCPB TBM can be sub-divided into three key components: (i) TBM box, (ii) stiffening plates and (iii) the breeder zone. The present fabrication and assembly routines is based on the assumption that each of the aforementioned sub-components can be assembled in parallel and independently before assembling the TBM. Therefore the procedures to fabricate these sub-components can be addressed in independent tasks. This paper shows the results of the KIT/industry collaboration with the final goal to develop a set of preliminary welding procedure specifications (pWPS) for the assembly of the HCPB TBM stiffening plate. Recently a promising set of draft pWPS could be identified in medium scale fabrication experiments. This paper recalls the results of qualification routines according to ISO 15614-11 (RCC-MR Edition 2007, RS 3570) in order to verify the parameters.

Set-up of a pre-test mock-up experiment in preparation for the HCPB Breeder Unit mock-up experimental campaign

The complexity of the experimental set-up for testing a full-scaled Breeder Unit (BU) mock-up for the European Helium Cooled Pebble Bed Test Blanket Module (HCPB-TBM) has motivated to build a pre-test mock-up experiment (PREMUX) consisting of a slice of the BU in the Li4SiO4 region. This pre-test aims at verifying the feasibility of the methods to be used for the subsequent testing of the full-scaled BU mock-up. Key parameters needed for the modeling of the breeder material is also to be determined by the Hot Wire Method (HWM). The modeling tools for the thermo-mechanics of the pebble beds and for the mock-up structure are to be calibrated and validated as well.This paper presents the setting-up of PREMUX in the L-STAR/LL facility at the Karlsruhe Institute of Technology. A key requirement of the experiments is to mimic the neutronic volumetric heating. A new heater concept is discussed and compared to several conventional heater configurations with respect to the estimated temperature distribution in the pebble beds. The design and integration of the thermocouple system in the heater matrix and pebble beds is also described, as well as other key aspects of the mock-up (dimensions, layout, cooling system, purge gas line, boundary conditions and integration in the test facility). The adequacy of these methods for the full-scaled BU mock-up is discussed and the next steps that follow PREMUX set-up are shown.

Two Different Medium-Scale First Wall Fabrication Experiments at KIT for ITER Helium-Cooled Pebble Bed Test Blanket Module

Subcomponent manufacturing and assembly concepts for the fabrication of the helium-cooled pebble bed test blanket module (TBM) for ITER have been developed over more than one decade at KIT, in particular the first wall (FW), which is a key element for the TBM fabrication. The design of this subcomponent foresees the manufacturing of a large U-bended plate of EUROFER with built-in channels for helium cooling. Manufacturing technologies developed at KIT are based on diffusion welding of two half-plates as the most promising option. This paper deals with the manufacturing of two medium-scale TBM FW mock ups according to two different industrial processes: a uni-axial diffusion welding process realized in a mechanic press at high temperature and a hot isostatic pressing process applied to a canned assembly at relatively low pressure.The qualification of the welds produced is described, and the results are compared to previous small- and medium-size scale experiments. The results of the recent FW fabrication mock ups are presented with regard to material data (e.g., ultimate strength, ductile-brittle transition temperature) and TBM-relevant parameters (e.g., deformation of cooling channels). The paper concludes with an overview of the strategy to evolve from 1/8th-scale experiments to TBM-relevant dimensions.

Thermo-mechanical analyses and assessment with respect to the design codes and standards of the HCPB-TBM Breeder Unit

The Helium Cooled Pebble Bed-Test Blanket Module (HCPB-TBM) is one of the two breeding blanket concepts currently under development in Europe. Key component of the HCPB-TBM, the Breeder Unit (BU), has entered the detailed engineering design phase. After establishing a base design, thermal and thermo-mechanical analyses have been performed under typical ITER operational conditions: the results are presented and discussed in this paper.A full scaled finite element model of the base design of the HCPB-TBM BU has been built to run thermal analyses of the beryllium and Li4SO4 pebble beds and thermo-mechanical analyses of the BU structure, both in steady state and in a typical transient regime during a pulse of the ITER D–T phase. The temperatures reached in the Li4SO4 and beryllium pebble beds in the BU base design are 930.8°C and 712.9°C, respectively, which are above the recommended values of 920°C for Li4SO4 and 650°C for the beryllium pebbles. The maximum temperature in the structural steel is 548.4°C, which remains under the design limit defined for the TBM studies (550°C). In order to decrease the temperature in the hot spots identified in the pebble beds, a reduction of the Li4SO4 and beryllium bed volumes has been adopted. As for the structural material, the thermo-mechanical analyses have been assessed with respect the RCC-MR design code (completed for irradiation damages with ITER SDC-IC). The results reveal some problematic points in the base design, concentrated in the coolant inlet and outlet pipes and in the connection region of the BU cooling plates with the BU backplate. Submodeling technique has been used to improve the design in these regions. An increase in the thickness of the coolant inlet and outlet pipes and a redesign of the BU backplate have led to a fulfillment of the codes and standards. The design modifications of pebble bed region and structural material have been implemented in the final design of the BU that is presently used as reference for the design and test of a BU mockup in KIT.

Non-linear failure analysis of HCPB Test Blanket Module

For the European Helium Cooled Pebble Bed Test Blanket Module (HCPB-TBM) the reduced activation ferritic martensitic (RAFM) steel EUROFER 97 is selected as a structural material. During operation the TBM will be subjected to complex thermo-mechanical loadings which yield at certain positions of the structure to stresses beyond the design limits of the structural material. Preliminary structural analyses of the TBM have shown critical behavior in several key points of the structure. An improved design has been proposed and in order to identify and assess the problematic positions in the improved version of the TBM a non-linear failure analysis is performed, for which a coupled deformation damage model developed at KIT for RAFM steels and recently implemented in the finite element code ABAQUS is used. The thermal loads in the form of non-homogeneous temperature fields distributions are obtained from a thermal analysis performed using the finite element code ANSYS on the same structure. Importing the temperature fields into the finite element code ABAQUS and applying the remaining loads – coolant internal pressure and structural boundary conditions – non-linear simulations are conducted taking into account the ITER-typical cyclic nature of the loading. The simulation results are evaluated and discussed considering ratcheting and damage at most critical highly loaded areas of the structure.

The fundamental role of fluid dynamic analyses in the design of the solid EU Test Blanket Module

In the frame of the activities of the European Test Blanket Module Consortium of Associates, the Helium Cooled Pebble Bed Test Blanket Module (HCPB TBM), the so-called solid TBM, is developed in Karlsruhe Institute of Technology (KIT). In the EU experimental strategy, a series of 4 different HCPB TBMs will be connected to the dedicated equatorial port n.16 during the ITER lifetime. The ITER TBM program has to provide DEMO relevant experimental data for the main functions of the blanket modules of a future fusion reactor.The preliminary thermo-mechanical design assessment of the TBM box (based on transient, steady state and accidental analyses) has been presented. All along the design assessment phase the fluid dynamic analyses play a fundamental role for the TBM sub-components, the Breeder Units (BUs) and the manifolds (MF) stages. This paper highlights the methodology implemented for the Computational Fluid Dynamic (CFD) analyses in the TBM design life cycle, and presents the results and the impact on the overall performance evaluation of the HCPB TBM. The following models are presented in detail: the CFD model of the TBM First Wall and its application to a reduced scale First Wall, the 3D CFD model of the BUs, and the thermo fluid dynamic modelling of the manifold systems.

Fluid dynamic and thermal analyses of a HCPB TBM Breeder Unit mock-up

In the frame of the WP08 EFDA Goal Oriented Training Program (GOTP) EUROBREED [1], the Working Package 1 is aimed at the design and procurement of a prototype of a Helium Cooled Pebble Bed Test Blanket Module Breeder Unit (HCPB TBM BU) and its testing in a dedicated experiment in a medium scale (<50 g/s) helium loop. This paper presents the design and analyses studies of the helium coolant fluid dynamics and of the thermal field in a HCPB TBM BU. After several design iterations, the helium coolant mass flow distribution has been improved between 3% and 7%. The analysis of the thermal field of the improved design has been performed. Considering steady state conditions with a heat flux deposed on the first wall equal to 500 kW/m 2 and a neutron wall load of 0.78 MW/m 2, the maximum temperature reached in the BU is 560.9 °C, about 2% above the maximum design temperature of the structural material (550 °C). As this maximum temperature is localized in a zone where there are not foreseen high stresses and the assumption for the analyses is conservative, the design presented for the Cooling Plates is considered as the reference for the production of the full scale BU mock-up.

KIT induced activities to support fabrication, assembly and qualification of technology for the HCPB-TBM

Fabrication concepts for the Helium Cooled Pebble Bed Test Blanket Module have been developed for more than one decade in the KIT (the former Forschungszentrum Karlsruhe). In accordance to the progressing design verification, key technology of fabrication and assembly need to be transferred from experimental scale to industrial application in relevant dimensions taking into account the requirements for qualification of processes. This paper describes fabrication development activities of the KIT recently started or planned to be performed in the near future. Several developments described in this paper are a continuation of activities done in the framework of EFDA/F4E contracts. Others will continue KIT (FZK) self financed developments. The general scope is to identify development needs and to minimize the risk in transfer and scale up of process parameters, already developed for small- and lab-scale fabrication Mock Ups, to bigger dimensions. This will provide the link between the present status (the experimental stage of welding) and the planned mid-term future activities, to define preliminary Welding Procedure Specifications (pWPS) for Mock Ups in TBM relevant size in collaboration with industry by prototypical Mock Ups.