Reliability, Availability, Maintainability And Inspectability Research Articles

Failure mode and reliability study for dynamic confinement and conditioning of the IFMIF-DONES radiological areas

The reference engineering design of the IFMIF-DONES nuclear Heating, Ventilation, and Air Conditioning system (HVAC) has been analyzed in terms of potential failure modes and consequences as well as life-cycle reliability and availability. The HVAC system performs the safety function of preventing lithium fire and uncontrolled releases of radioactive materials from the radiological areas. The results of the Reliability, Availability, Maintainability and Inspectability (RAMI) analysis are of high practical importance for future activities on the system optimization and safety demonstration. This paper proposes a unified approach to the Failure Mode and Effects Analysis (FMEA) that can be applied to the plant systems evaluation in terms of the failure frequency, severity, and detectability. The reliability and availability calculation has been performed for two sets of data, the U.S. NRC collection representing the industry standards of fission power plants, and the fusion-specific data gathered from several sources and integrated by Monte Carlo-based method. Inherent availability of above 99.4% has been reached for the HVAC system based on the fusion-specific data. The use of reliability data from the commercial fission plants increased the system availability to nearly 99.8%, thus indicating the potential for allocation of higher availability requirements to the HVAC functions.

Preliminary RAMI analysis of CRAFT cryogenic system

The Comprehensive Research Facility for Fusion Technology (CRAFT) is a large scientific device in China's 13th Five-Year Plan. The RAMI (reliability, availability, maintainability, and inspectability) analysis method is used to control the technical risk of the CRAFT cryogenic system, which can better guarantee the stable operation of the CRAFT system. Functional breakdown is performed first to understand the functions of the CRAFT cryogenic system, and then IDEFØ diagram is used to describe the hierarchical structure and relationship between each function in the cryogenic system.A preliminary RAMI analysis of 200W@4.5 K helium refrigerator system with the main function of DF1 was carried out. Failure mode, effect and criticality analysis was used to identify and evaluate the failure mode of 200 W helium refrigerator. A criticality chart of the failure mode was drawn based on the evaluation results. For the failure modes with medium and high risks in the initial criticality chart, there was no high risk after risk mitigation measures were taken.The logical basis of the reliability block diagram was obtained from the structural relationship between each function described in the IDEF0 diagram. Based on these logical structures, a reliability block diagram composed of components that implement basic functions was drawn. Input reliability data to calculate the reliability and inherent availability of the main function DF1.The results of Reliability block diagram analysis showed that the inherent availability can be greatly improved after taking improvement measures such as preparing spare parts to reduce the mean time to repair. Reliability was also greatly improved when measures such as regular inspection and maintenance were taken to reduce the failure rate.

RAMI analysis of the helium refrigeration system of HL-2M tokamak

The 500 W@4.5 K helium refrigeration system operated in HL-2M Tokamak is the first domestically made cryogenic system independently designed and manufactured in China. It is expected to cool down HL-2M cryousers for the first time around June 2021. In the requirement document of helium refrigeration system, the mean time between failures (MTTF) should be at least 8000 hours, and the inherent availability of the subsystem should be 60%. This paper presents the RAMI (Reliability, Availability, Maintainability and Inspectability) analysis of the failure modes of the HL-2M helium refrigeration system as well as the corresponding effects and criticality to guide the design of the components and the preparation for operation and maintenance. The description of the risk mitigation actions regarding the design, testing, maintenance and operation in order to reach the expected targets of enhancing the reliability and availability of the refrigeration system.

RAMI analysis for the ITER In-Vessel Coils System

The ITER project is the largest international collaboration in the scientific field ever set up. It forms the heart of a unique collaborative agreement to build the first experimental nuclear fusion device designed to prove the scientific and technological feasibility of sustained fusion power generation. Among hundreds of systems, the In-Vessel Coils System plays a crucial role in ITER: ensuring and maintaining stable plasma operations. ITER has an ambitious inherent availability target for plasma production. To be able to achieve this objective, the potential technical risk that may affect the machine operation, was assessed by means of RAMI (Reliability, Availability, Maintainability and Inspectability) approach. The RAMI analysis for the IVC system was performed on the system design, following the Staged Approach Configuration adopted by ITER for Construction and Operation phases. A functional breakdown was prepared, resulting in the system being divided into 3 main functions described using the IDEFØ method. A qualitative analysis was performed applying the Failure Modes, Effects and Critical Analysis technique in order to identify the potential effects due to different anomalies of the IVC components. Criticality chart highlights the distribution of the Failure Modes across three risk zones with regard to their probability of occurrence and the impact on the availability. In relation to the operation of the IVC System, the analysis identified 32 risks, none of whom were classified as major. To estimate the reliability and availability of IVC system and to assess the compliance to the requirements, a quantitative analysis was performed using the Reliability Block Diagrams Analysis. The inherent availability of the IVC system during DT phase was calculated over the 20 years of ITER lifetime. The availability of the ITER IVC system results to be compliant with the inherent availability requirement for DT phase.

RAMI analysis of the collective Thomson scattering system front-end – Part1 – Failure modes effects and criticality analysis

ITER is a tokamak nuclear fusion reactor intended to demonstrate the feasibility of nuclear fusion as a carbon-free energy source. In order to control potential technical risks, ITER subsystems are assessed through Reliability, Availability, Maintainability and Inspectability (RAMI) analysis, which includes Failure Modes Effects and Criticality Analysis (FMECA).This paper deals with the FMECA of the front-end components of the Collective Thomson Scattering (CTS) diagnostic, which involves a top-down functional breakdown of the system, identification of critical components and potential failure modes, their effects and consequences for the system. Furthermore, the FMECA methodology allows for the analysis of possible mitigation actions, which may reduce failure mode risk levels.The FMECA was performed in two stages, one concerning the failure modes of the CTS itself, and one concerning the failure modes, which may interrupt ITER operations. Results indicate that there are no failure modes that pose a significant risk to ITER operations. However, mitigation actions were required in order to reduce the risk levels of failure modes, which may compromise CTS diagnostics availability.This article covers the first half of the RAMI analysis of the CTS diagnostic, the FMECA.

Approach in improving reliability of DEMO

Reliability, Availability, Maintainability and Inspectability (RAMI) are key elements in the engineering development of the Demonstration Power Plant (DEMO) reactor. RAMI assessments play an important role during all design cycle phases by focusing on different aspects depending on the development stage. In fact, system functions, related requirements and deriving constraints are the main objective of RAMI assessment during pre-conceptual and conceptual design phases, when getting insight on the rationale of the plant. The identification of potential failure mechanisms, needs of design updates to remove such mechanisms or mitigate related consequences, become the main goal of analysis as design details increase during subsequent plant development phases. Some of the RAMI analyses performed in the 2019 for different DEMO systems and breeding blanket configurations are here presented. Results in terms of expected annual frequency of failures of components, of specific failure events and reliability/availability parameters are reported together with indications about criticality and suggestions for designers to improve reliability and availability of the systems and of the reactor. The study is based on Failure Mode and Effect Analysis (FMEA) and Reliability Block Diagram (RBD) analysis methodologies.

RAMI evaluation of the beam source for the DEMO neutral beam injectors

Abstract DEMO is a first-of-a-kind DEMOnstration fusion power plant [1] , [2] and is intended to follow the ITER experimental reactor. The main goal of DEMO will be to demonstrate the possibility to produce electric energy for the grid from the fusion reaction early in the second half of the century. The injection of high energy neutral (1 MeV) particle beams is one of the main tools to heat the plasma up to fusion conditions, control the plasma burn phase and ramp the plasma down. Within the EUROfusion Framework a conceptual design of the Neutral Beam Injector (NBI) for the DEMO fusion reactor is currently being developed. Thereby, Reliability, Availability, Maintainability and Inspectability (RAMI) have to be taken into consideration for the conceptual design of the DEMO NBI, together with the exploitation of the currently available return of experience from the ITER NBIs. Comparing the failure risk of two different source concepts due to the considered failure modes has allowed for further design developments aiming at exploiting the advantages of the modular approach while minimizing its drawbacks.

Experimental demonstration of a laser proton accelerator with accurate beam control through image-relaying transport

A compact laser plasma accelerator (CLAPA) that can stably produce and transport proton ions with different energies less than 10 MeV, $l1%$ energy spread, several to tens of pC charge, is demonstrated. The high current proton beam with continuous energy spectrum and a large divergence angle is generated by using a high contrast laser and micron thickness targets, which later is collected, analyzed and refocused by an image-relaying beam line using a combination of quadrupole and bending electromagnets. It eliminates the inherent defects of the laser-driven beams, realizes precise manipulation of the proton beams with reliability, availability, maintainability and inspectability (RAMI), and takes the first step towards applications of this new generation of accelerator. With the development of high-rep rate Petawatt (PW) laser technology, we can now envision a new generation of accelerator for many applications in the near future soon.

Preliminary RAMI assessment for HCPB and HCLL ITER test blanket module ancillary systems

A RAMI (Reliability, Availability, Maintainability and Inspectability) assessment performed on the ITER Test Blanket Module (TBM) ancillary systems is presented. The assessment is aimed at evaluating design that may jeopardize the achievement of the overall 75% availability requirements for the TBM plant breakdown structure. The ancillary systems of the European Test Blanket Modules to be operated in ITER that have been analyzed in this assessment are the helium cooling systems (HCSs) of both the Helium Cooled Lithium Lead (HCLL) and Helium Cooled Pebble Bed (HCPB), the lithium-lead loop of the HCLL TBM and the Tritium Extraction System (TES) of the HCPB TBM. RAMI performance was assessed by means of reliability block diagrams (RBDs) over a foreseen mission of 20 years, with operating cycles reflecting ITER schedule. In particular, a set of events leading to unavailability of the systems was initially defined by means of a failure mode and effect analysis. Then RBDs were implemented according to reliability-wise integration of the components included in such systems. Different RBDs were defined depending on the component being judged to impact normal operation or start-up operation mode. Systems analysis was performed exploiting a modular approach in order to elicit the relative contribution to overall availability so to support possible design improvement by highlighting critical sub-systems. In particular the unavailability of cooling, tritium extraction and trapping functions were assessed separately for HCLL and HCPB concepts. Finally the integrated impact of all ancillary systems on overall tokamak operational availability was estimated and the assessed systems, considering the current preliminary level of design development, appear able to meet the expected performance.

RAMI: The main challenge of fusion nuclear technologies

RAMI (Reliability, Availability, Maintainability and Inspectability) is one of the most severe challenges of Fusion Technologies, and it is probably the engineering branch where the fusion community is the least competent. This paper summarizes the RAMI statistics in existing fusion machines, the RAMI approaches adopted in ITER and in DEMO, and the expected availability targets in these two machines. The paper then discusses these approaches and targets and recommends adopting a Reliability Growth program for future fusion devices.

RAMI analysis for EAST upper full tungsten divertor water cooling system

EAST (Experimental Advanced Superconducting Tokamak) device is a D-shaped full superconducting tokamak with actively water cooled plasma facing components. As the EAST project technical risk control and possible failure mitigation approach, RAMI (Reliability, Availability, Maintainability and Inspectability) analysis was required for the upper full tungsten divertor water cooling system, which insures the system to cool the PFCs with high efficient and safety without leakage. At the same time the cooling water could be at suitable pressure, temperature and velocity, water parameters of cooling circuit also could be monitored. A functional breakdown was prepared and all functions are described using the IDEFØ (Integration DEfinition Function – language Ø) method. FMECA (Failure Mode, Effects and Criticality Analysis) was performed to the system initial risk. There are 31 risks for the initial state, including 7 major risks. No major risk remains after taking into account all the actions. RBDs (Reliability Block Diagrams) were prepared to calculate the reliability and availability of each function. The initial availability of upper divertor cooling water system was 93.63%, after optimization the expected availability was 98.56% over 11,520h. It was assessed that the upper full tungsten divertor water cooling system RAMI analysis results meet the EAST project requirement during this design phase and the results will be qualified further when the system design is updated.

Conceptual design of the DEMO neutral beam injectors: main developments and R&D achievements

The objectives of the nuclear fusion power plant DEMO, to be built after the ITER experimental reactor, are usually understood to lie somewhere between those of ITER and a ‘first of a kind’ commercial plant. Hence, in DEMO the issues related to efficiency and RAMI (reliability, availability, maintainability and inspectability) are among the most important drivers for the design, as the cost of the electricity produced by this power plant will strongly depend on these aspects. In the framework of the EUROfusion Work Package Heating and Current Drive within the Power Plant Physics and Development activities, a conceptual design of the neutral beam injector (NBI) for the DEMO fusion reactor has been developed by Consorzio RFX in collaboration with other European research institutes. In order to improve efficiency and RAMI aspects, several innovative solutions have been introduced in comparison to the ITER NBI, mainly regarding the beam source, neutralizer and vacuum pumping systems.

RAMI assessment for IFMIF lithium facility

A RAMI (reliability, availability, maintainability and inspectability) assessment performed on the IFMIF (International Fusion Materials Irradiation Facility) Lithium Facility (LF) is presented. Given the high availability requirements for the IFMIF plant, a target requirement of 94% availability has been attributed to the LF and its feasibility verified for the proposed system design. The LF performance for the foreseen operation mission has been investigated by the mean of failure mode, effect and criticality analysis (FMECA) and reliability block diagrams (RBDs). The first assessment performed on the base of the present design did not satisfy the above target requirement. Then, possible optimizations in design solutions and maintenance policy have been investigated. The RBD analysis shows that with some improvements the LF could be able to comply with the availability target requested, as the obtained mean availability for 10 years of simulation is of 93.4% and the inherent availability more than 99%. The reliability to operate the LF without failure during the yearly scheduled operation time is about 64%. Most critical components in terms of impact on LF reliability and availability, are: (i) the Li loop Target Section (back plate) and electro-magnetic pumps for the main loop, (ii) the getter beds of the hydrogen hot trap and the electromagnetic pump for the impurity control system.

RAMI Analysis of HCCB TBS for ITER

ITER is the first worldwide international experimental nuclear fusion facility, which aims to prove the physics and technological basis for future fusion power plants. As main stages of ITER technical risk control, the reliability, availability, maintainability and inspectability (RAMI) approach should be applied to all ITER components during their design phase to reduce potential technical risks. Test blanket modules play a key role in ITER. Helium cooled ceramic breeder (HCCB) TBM is one of TBM concepts which were proposed by China. HCCB TBM and its ancillary system are called HCCB test blanket system (TBS). The RAMI analysis was performed on the conceptual design of the ITER HCCB TBS in this paper. A functional breakdown was prepared in a bottom-up approach, resulting in the system being divided into 3 main functions, 1 support function, 14 sub-functions and 50 basic functions. These functions were described using the IDEF0 method. Reliability block diagrams were prepared to estimate the reliability and availability of each function under the stipulated operating conditions. The inherent availability of the HCCB TBS expected after implementation of mitigation actions was calculated to be 94.69 % over 2 years. A failure modes, effects and criticality analysis was performed with criticality charts highlighting the risk level of the different failure modes with regard to their probability of occurrence and their effects on the availability.

Preliminary RAMI analysis of WCLL blanket and breeder systems

DEMO will be a prototype fusion reactor designed to prove the capability to produce electrical power in a commercially acceptable way. One of the key factors in that endeavor is the achievement of certain level of plant availability. Therefore, RAMI (Reliability, Availability, Maintainability and Inspectability) will be a key element in the engineering development of DEMO.Some studies have been started so as to develop the tools and models to assess different design alternatives from RAMI point of view. The main objective of these studies is to be able to evaluate the influence of different parameters on DEMO availability and to focus the critical parts that should be further researched and improved in order to develop a high-availability oriented DEMO design.A preliminary RAMI analysis of the Water Cooled Lithium-Lead (WCLL) blanket and breeder concept for DEMO has been developed. The amounts of single elements that may fail (e.g. more than 180,000 C-shaped tubes) and the mean down time associated to failures inside the vacuum vessel (around 3 months) have been highlighted as the critical parameters influencing the system availability. On the other hand, the necessary developments of tools/models to better represent the system performance have been identified and proposed for future work.

RAMI approach as guidance for optimizing the design of the WEST machine protection system using IR thermography measurements

The WEST project (Tungsten (W) Environment in Steady State Tokamak) is targeted at minimizing risks in support of the ITER divertor strategy. Part of the machine protection system will be based on Short Wave InfraRed (SWIR) thermography diagnostic which consists in monitoring and controlling in real time the power load on the plasma facing components through the surface temperature measurements. The inherent availability objective of such a machine protection diagnostic is essential for WEST operation. A functional analysis of the IR system from highest level main functions down to basic operational functions has been developed. The availability of the initial design has been assessed by making a RAMI (Reliability, Availability Maintainability and Inspectability) analysis. Despite mitigation actions to reduce the frequency of potential failures and their time to repair, the availability required by the project could not be reached. With the aim of achieving the availability target, a recommendation was made to consider an alternative design. This paper presents a RAMI analysis of the IR thermography diagnostic whose results have led to modifying the design of antennas protection system to a more available system as required by the WEST project.

RAMI analysis for DEMO HCPB blanket concept cooling system

A preliminary RAMI (reliability, availability, maintainability and inspectability) assessment for the HCPB (helium cooled pebble bed) blanket cooling system based on currently available design for DEMO fusion power plant is presented. The following sub-systems were considered in the analysis: blanket modules, primary cooling loop including pipework and steam generators lines, pressure control system (PCS), coolant purification system (CPS) and secondary cooling system. For PCS and CPS systems an extrapolation from ITER Test Blanket Module corresponding systems was used as reference design in the analysis. Helium cooled pebble bed (HCPB) system reliability block diagrams (RBD) models were implemented taking into account: system reliability-wise configuration, operating schedule currently foreseen for DEMO, maintenance schedule and plant evolution schedule as well as failure and corrective maintenance models. A simulation of plant activity was then performed on implemented RBDs to estimate plant availability performance on a mission time of 30 calendar years. The resulting availability performance was finally compared to availability goals previously proposed for DEMO plant by a panel of experts. The study suggests that inherent availability goals proposed for DEMO PHTS system and Tokamak auxiliaries are potentially achievable for the primary loop of the HCPB concept cooling system, but not for the secondary loop. A sensitivity analysis is also presented to explore results dependency on key estimated parameters and analysis assumptions.

RAMI analysis of the ITER Central Safety System

ITER is the first worldwide international project aiming to design a facility to produce nuclear fusion energy. The technical requirements of its plant systems have been established in the ITER Project Baseline. In the project, the Reliability, Availability, Maintainability and Inspectability (RAMI) approach has been adopted for technical risk control to help aid the design of the components in preparation for operation and maintenance. A RAMI analysis was performed on the conceptual design of the ITER Central Safety System (CSS). A functional breakdown was prepared in a bottom-up approach, resulting in the system being divided into 2 main functions and 20 sub-functions. These functions were described using the IDEF0 method. Reliability block diagrams were prepared to estimate the reliability and availability of each function under the stipulated operating conditions. Initial and expected scenarios were analyzed to define risk-mitigation actions. The inherent availability of the ITER CSS expected after implementation of mitigation actions was calculated to be 99.80% over 2 years, which is the typical interval of the scheduled maintenance cycles. This is consistent with the project required value of 99.9±0.1%. A Failure Modes, Effects and Criticality Analysis was performed with criticality charts highlighting the risk level of the different failure modes with regard to their probability of occurrence and their effects on the availability of the plasma operation. This analysis defined when risk mitigation actions were required in terms of design, testing, operation procedures and/or maintenance to reduce the risk levels and increase the availability of the main functions.

Hardware availability calculations and results of the IFMIF accelerator facility

Hardware availability calculations have been done individually for each system of the deuteron accelerators of the International Fusion Materials Irradiation Facility (IFMIF). The principal goal of these analyses is to estimate the availability of the systems, compare it with the challenging IFMIF requirements and find new paths to improve availability performances.Major unavailability contributors are highlighted and possible design changes are proposed in order to achieve the hardware availability requirements established for each system. In this paper, such possible improvements are implemented in fault tree models and the availability results are evaluated.The parallel activity on the design and construction of the linear IFMIF prototype accelerator (LIPAc) provides detailed design information for the RAMI (reliability, availability, maintainability and inspectability) analyses and allows finding out the improvements that the final accelerator could have. Because of the R&D behavior of the LIPAc, RAMI improvements could be the major differences between the prototype and the IFMIF accelerator design.

Availability Requirement for ITER Plasma Parameter Measurements

The diagnostics are critical systems for the operation and research program of ITER, as they are used to protect the components, to control the plasma discharge, to understand the behaviour of the plasma and to measure its performance. Representing more than 50 subsystems, they add an extra level of complexity and technical challenge to the project. In order to ensure that the overall ITER machine will be able to reach its ambitious availability objective, a Reliability, Availability, Maintainability and Inspectability (RAMI) approach has been defined and applied to the diagnostics as well as all the other ITER core systems.The purpose of this study is to estimate the inherent availability of the measurements groups used for machine protection and basic control in order to ensure that the ITER machine reaches its inherent availability objectives.