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Damaged spent nuclear fuel (DSNF) can be loaded in German dual-purpose casks (DPC) for transport and interim storage. Encapsulations are needed to guarantee a safe handling and a tight closure, separated from the package enclosure. These encapsulations shall be durable and leak-tight for a long storage period, because they are usually not accessible within periodical inspections of the DPC. Due to the general design of DPCs for standard fuel assemblies, specific requirements have to be considered for the design of encapsulations for DSNF to ensure the loading in existing package designs. Especially the primary lid system of a DPC is designed for maximum loads due to the internal impact of the content during drop test conditions. The main difference of encapsulations for damaged spent nuclear fuel is that they have usually a much higher stiffness than standard fuel assemblies. Therefore the design of an internal shock absorber, e.g. at the head of an encapsulation is required to reduce mechanical loads to the primary lid system during impacts.
BAM as part of the German competent authority system is responsible for the safety assessment of the mechanical and thermal package design, the release of radioactive material and the quality assurance of package manufacturing and operation. Concerning the mechanical design of the encapsulation BAM was involved in the comprehensive assessment procedure during the package design approval process. An internal shock absorber was developed by the package designer with numerical analyses and experimental drop tests. Experimental drop tests are needed to cover limiting parameters regarding, e.g. temperature and wall thickness of the shock absorbing element to enable a detailed specification of the whole load-deformation behavior of the encapsulation shock absorber.
The paper gives an overview of the assessment work by BAM and points out the main findings which are relevant for an acceptable design of internal shock absorbers. The physical drop tests were planned on the basis of pre-investigations of the applicant concerning shape, dimension and material properties. In advance of the final drop tests the possible internal impact behavior had to be analyzed and the setup of the test facility had to be validated. The planning, performance and evaluation of the final drop tests were witnessed and assessed by BAM. In conclusion it could be approved that the German encapsulation system for damaged spent nuclear fuel with shock absorbing components can be handled similar to standard fuel assemblies in existing package designs.
Damaged spent nuclear fuel (DSNF) can be loaded in German dual-purpose casks (DPC) for transport and interim storage. Encapsulations are needed to guarantee a safe handling and a tight closure, separated from the package enclosure. These encapsulations shall be durable and leak-tight for a long storage period, because they are usually not accessible within periodical inspections of the DPC. Due to the general design of DPCs for standard fuel assemblies, specific requirements have to be considered for the design of encapsulations for DSNF to ensure the loading in existing package designs. Especially the primary lid system of a DPC is designed for maximum loads due to the internal impact of the content during drop test conditions. The main difference of encapsulations for damaged spent nuclear fuel is that they have usually a much higher stiffness than standard fuel assemblies. Therefore the design of an internal shock absorber, e.g. at the head of an encapsulation is required to reduce mechanical loads to the primary lid system during impacts.
BAM as part of the German competent authority system is responsible for the safety assessment of the mechanical and thermal package design, the release of radioactive material and the quality assurance of package manufacturing and operation. Concerning the mechanical design of the encapsulation BAM was involved in the comprehensive assessment procedure during the package design approval process. An internal shock absorber was developed by the package designer with numerical analyses and experimental drop tests. Experimental drop tests are needed to cover limiting parameters regarding, e.g. temperature and wall thickness of the shock absorbing element to enable a detailed specification of the whole load-deformation behavior of the encapsulation shock absorber.
The paper gives an overview of the assessment work by BAM and points out the main findings which are relevant for an acceptable design of internal shock absorbers. The physical drop tests were planned on the basis of pre-investigations of the applicant concerning shape, dimension and material properties. In advance of the final drop tests the possible internal impact behavior had to be analyzed and the setup of the test facility had to be validated. The planning, performance and evaluation of the final drop tests were witnessed and assessed by BAM. In conclusion it could be approved that the German encapsulation system for damaged spent nuclear fuel with shock absorbing components can be handled similar to standard fuel assemblies in existing package designs.
Assessment experience on packages loaded with damaged spent nuclear fuel for transport after storage
(2018)
In 2017 the first German package approval certificate was issued for a dual purpose cask (DPC) design with encapsulated damaged spent nuclear fuel. At the Bundesanstalt für Materialforschung und -prüfung (BAM) a comprehensive assessment procedure was carried out with respect to the mechanical and thermal design, the containment design and quality assurance for manufacturing and operation. Main objective of this procedure was to verify the Package Design Safety Report (PDSR) fulfils the requirements according to the IAEA regulations SSR-6.
Until now only standard spent nuclear fuel assemblies were designated for interim storage and transports. Due to nuclear phase out in Germany all other kinds of SNF in particular damaged fuel has to be packed. Therefore specific requirements have to be considered in accordance with international experiences written in IAEA technical reports. In Germany damaged spent nuclear fuel (DSNF) needs a tight encapsulation with special encapsulations and clearly defined properties.
Due to the limited amount of DSNF these encapsulations are designed for storage and transport in existing packages. From the assessment experience it has been seen, corresponding PDSR need an extensively expansion to cover the design of these encapsulations and their influences on the package. Then such well-defined encapsulations can be handled like standard fuel assemblies. The main difference to standard package components is, encapsulations with permanent closure achieve their specified condition not after manufacturing but only during operation after loading and closing.
Thus specific handling instruction and test procedures are necessary especially for welding, where BAM is able to survey the quality of this first part of operation.
The long-term sealing behavior of metal seals, assembled in the lid system of casks for transportation and storage of radioactive materials, has been investigated. For that purpose, phenomenological models describing the time- and temperature dependent behavior have been introduced by BAM since 2016, e.g. by using the time-temperature superposition principle. Results have shown that these models describe the relaxation behavior adequately and are suitable for extrapolations. In this work, the applicability of these models is checked by analyzing the necessary scope of tests, which must be carried out to get sufficient information about the long-term behavior of metal seals based on short-term tests.
Hydrogen Fire Testing
(2024)
In this presentation we present a new hydrogen-based test rig for an ongoing feasibility study of using hydrogen as an energy source for the thermal testing of transport packages containing radioactive materials. The test rig will be capable of combusting hydrogen for a wide range of different burner geometries, mass flows and if necessary hydrogen blends. As this type of fire test according to the IAEA boundary conditions does not yet exist, a large number of preliminary investigations, safety assessments and calculations must be carried out in order to develop a viable concept for hydrogen fires. In the first step of the feasibility study, the temperature, structure, and radiation of various hydrogen flames are surveyed. In future works, the results will make it possible to design burner frames that are suitable for fire reference tests in order to make comparisons with pool and propane fires used in assessment procedures today. In parallel comparative numerical simulations are conducted to model the thermal behaviour of hydrogen flames using the software package Ansys®. On the one hand, the numerical simulations support the experiments by providing an overview of numerous parameters and the measuring range; on the other hand, they will help with the design of the burner frame in future work. This paper gives an overview in the design and capabilities of the test rig. Furthermore, the results of the parameter studies show that burner geometry and mass flow provide a significant design margin for the thermal shape of the hydrogen flames. In addition, the results of the initial numerical calculations will be used to determine the necessary sensors, the positions, and their operating range. Only the optimal interaction allows a controlled system that permits user-defined hydrogen fires.
A new hydrogen-based test rig is being developed for a feasibility study on the use of hydrogen as an energy source for thermal testing in accordance with the IAEA SSR-6 guidelines for transport packages containing radioactive materials.
The test rig will be capable of combusting hydrogen for a wide range of different burner geometries, mass flows and if necessary hydrogen blends. As this type of fire test according to the IAEA boundary conditions (SSR-6 & SSG-26) does not yet exist, a large number of preliminary investigations, safety assessments and calculations must be carried out in order to develop a viable concept for hydrogen fires.
A new hydrogen-based test rig is being developed for a feasibility study on the use of hydrogen as an energy source for thermal testing in accordance with the IAEA SSR-6 guidelines for transport packages containing radioactive materials.
The test rig will be capable of combusting hydrogen for a wide range of different burner geometries, mass flows and if necessary hydrogen blends. As this type of fire test according to the IAEA boundary conditions (SSR-6 & SSG-26) does not yet exist, a large number of preliminary investigations, safety assessments and calculations must be carried out in order to develop a viable concept for hydrogen fires.
Investigation of the internal impact during a 9 m drop test of an accident-safe waste package
(2021)
The safety assessment of packages for the transport of radioactive material follows the IAEA regulations and guidance. The specified regulatory tests cover severe accidents and demonstrate the package containment system integrity. Special attention must be drawn to the behaviour of the content which could move inside the package due to unpreventable gaps caused by the loading procedure and the structure of the content. A possible internal impact of the content which occurs during the drop tests onto the lid system is investigated. The IAEA regulations SSR-6 and the Guidance SSG-26, revised recently, consider input from Germany and France related to the significance of internal gaps.
In the context of a waste package design assessment, a model was equipped with a representative content to conduct a drop test with an internal impact. The weight and kinetic impact of this content covered all possible real contents. The objective of the test was to maximize the load onto the lid system and to prove the mechanical integrity by complying with the required leak tightness. The test was conducted conservatively at a package temperature lower than -40 °C at the BAM Test Site Technical Safety.
This paper gives an overview of efforts to address internal gaps and their consequences, and the BAM efforts with the implementation of this topic into IAEA regulations and guidance material. The paper then focuses on the conduction of a drop test and investigation of internal component impact.
Packages for the transport of radioactive material are often equipped with impact limiters consisting of wood. Mostly this wood is encapsulated by steel sheets. The impact limiters are needed to ensure that the transport casks meet the IAEA safety requirements. According to the IAEA safety requirements a package has to withstand consecutively severe mechanical tests followed by a thermal test. The mechanical tests have to produce maximum damage concerning the thermal test. Following this, the impact limiters may have serious pre-damage when the thermal tests begins. The IAEA safety requirements state that during and following the fire test, the specimen shall not be artificially cooled and any combustion of materials of the package shall be permitted to proceed naturally.
Small scale fire tests with wood filled metal drums by BAM and works of the French Institute for Radiological Protection and Nuclear Safety (IRSN) showed that pre-damaged steel encapsulated wooden structures could start smoldering initiated by the thermal test. These processes supply additional energy to the cask which should be considered within the safety assessment of the package.
As not much is known about smoldering processes in encapsulated wooden structures with a reduced oxygen supply the need for a test was identified. To investigate the influence of a smoldering impact limiter concerning the amount of energy supplied to the cask in dependence of the time BAM conducted a large scale impact limiter thermal test. For that, a pre-damaged impact limiter with a diameter of 2,3 m was mounted on a water tank simulating a cask. A complex system of a regulated pump, a heater, a cooler, a slide valve, a flow meter and numerous thermocouples were installed and connected to a control unit to ensure all needed operating conditions.
After a pre-heating compared to typical SNF decay-heat, the 30 min lasting fire phase of the thermal test was started. After that, the expected and initiated smoldering began. The results of the large scale test are presented in this poster. Systematic small scale tests will follow to identify the influence of different parameters, e.g. moisture content and scale effects. The tests took place at BAM Test Site for Technical Safety (TTS) with its various possibilities for mechanical and thermal tests. The results of these tests will have direct influence in the safety assessment of transport cask for the transport of radioactive material.
Packages for the transport of radioactive material are often equipped with impact limiters consisting of wood. Mostly this wood is encapsulated by steel sheets. The impact limiters are needed to ensure that the transport casks meet the IAEA safety requirements. According to the IAEA safety requirements a package has to withstand consecutively severe mechanical tests followed by a thermal test. The mechanical tests have to produce maximum damage concerning the thermal test. Following this, the impact limiters may have serious pre-damage when the thermal tests begins. The IAEA safety requirements state that during and following the fire test, the specimen shall not be artificially cooled and any combustion of materials of the package shall be permitted to proceed naturally.
Small scale fire tests with wood filled metal drums by BAM and works of the French Institute for Radiological Protection and Nuclear Safety (IRSN) showed that pre-damaged steel encapsulated wooden structures could start smoldering initiated by the thermal test. These processes supply additional energy to the cask which should be considered within the safety assessment of the package.
As not much is known about smoldering processes in encapsulated wooden structures with a reduced oxygen supply the need for a test was identified. To investigate the influence of a smoldering impact limiter concerning the amount of energy supplied to the cask in dependence of the time BAM conducted a large scale impact limiter thermal test. For that, a pre-damaged impact limiter with a diameter of 2,3 m was mounted on a water tank simulating a cask. A complex system of a regulated pump, a heater, a cooler, a slide valve, a flow meter and numerous thermocouples were installed and connected to a control unit to ensure all needed operating conditions.
After a pre-heating compared to typical SNF decay-heat, the 30 min lasting fire phase of the thermal test was started. After that, the expected and initiated smoldering began. The results of the large scale test are presented in this poster. Systematic small scale tests will follow to identify the influence of different parameters, e.g. moisture content and scale effects. The tests took place at BAM Test Site for Technical Safety (TTS) with its various possibilities for mechanical and thermal tests. The results of these tests will have direct influence in the safety assessment of transport cask for the transport of radioactive material.