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In context with new cask designs and their approval procedure, the experimental testing of impact limiters under drop test conditions becomes more and more important in order to assess the damage mechanics behaviour and safety margins for validation reasons. In recent years, various designs of impact limiters have been tested by the Federal Institute for Materials Research and Testing within specific component testing and particularly with regard to type B package design approval procedures. The paper focuses on the experimental realisation of impact limiter tests and presents implemented measurement techniques to determine the amount of deformation and to explain the impact behaviour by means of photogrammetric metrology and three-dimensional fringe projection method, high speed motion analysis and adjusted deceleration measurements.
In context with new cask designs and their approval procedure the experimental testing of impact limiters under drop test conditions becomes more and more important in order to assess the damage mechanics behavior and safety margins for validation reasons.
In recent years various designs of impact limiters have been tested by the Federal Institute for Materials Research and Testing (BAM) within specific component testing and particularly with regard to type B package design approval procedures.
The paper focuses on the experimental realization of impact limiter tests and presents implemented measurement techniques to determine the amount of deformation and to explain the impact behavior by means of photogrammetric metrology and 3-d fringe projection method, high-speed motion analysis and adjusted deceleration measurements.
Packages for the transport of radioactive material are often equipped with impact limiters consisting of wood, encapsulated by Steel sheets. These impact limiters shall ensure the transport cask meets the IAEA safety requirements. After damage caused by the mechanical tests the package has to withstand a severe fire scenario. According to the regulations 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.
Due to results of the French institute IRSN it was shown that after the fire test an additional energy supply from a pre-damaged impact limiter should be taken into account. The combustion or smouldering of wood was of interest.
BAM started a first test phase to examine the issue of combustion for such kind of package components. The goal was to understand the phenomena under the consideration of relevant regulatory boundary conditions. Several metal buckets were filled with wood and equipped with thermocouples. The test specimens have been prepared with different damage arrangements to take the influence of the mechanical tests into account. This paper shows the experimental Setup and the conduction of the tests. The first test shows that pre-damaged metal encapsulations can lead to smouldering of the wood and with this to a Supplement energy release after the end of the 30 minute fire. The consequence could be, to consider additional thermal loads of wood filled impact limiters to filled the IAEA regulations, if the conditions of the tests are transferable to the safety analysis of the package design.
Fire Influence to Wood Filled Impact Limiters - Implications for the Package Design Safety Case
(2023)
Impact limiters with wooden components are widely used in the design of packages for transportation of radioactive material. In most designs, the wood is encapsulated with steel sheets. Impact limiters mainly determine the mechanical and thermal behaviour of the package in accident conditions of transport in accordance with the IAEA Regulations.
In context with research and development for package design approval competence, the thermal behaviour of heavy-weight packages was investigated at BAM with an artificially pre-damaged generic impact limiter design. Within this first investigation, the pre-damaged impact limiter with a diameter of 2.3 meters was mounted on a water tank simulating the thermal capacity of a cask during the fire test. The water tank is part of a water circulating system built of several components such as pump, heater, cooler, sliding valve, flow meter, thermocouples and control unit in order to measure the heat flux.
Furthermore, the investigations focus on the effects this additional heat generation would have on the cask and especially on the lid-closure system with the gasket.
The results of these experiments could find consideration in the safety case of the transport packages of radioactive material using wood filled impact limiters.
Packages for the transport of radioactive material shall meet the mechanical and thermal test requirements of the International Atomic Energy Agency (IAEA) regulations for package design approval. Besides mechanical testing, the Federal Institute for Materials Research and Testing (BAM) performs thermal tests in accordance with the IAEA regulations. The thermal test includes a 30-minute 800°C fully engulfing fire.
BAM continuously performs various thermal experiments for the investigation of the thermal response of packages with respect to the IAEA fire. The purpose of this paper is to give an overview of the already performed, ongoing and future physical tests and experiments of BAM in the field of thermal investigations. These research and development works shall support our competencies for the authority package design assessment.
BAM operates a propane gas fire test facility. To be able to carry out comparative investigations and validity between the propane fire and the in detail prescribed pool fire test in the regulations, BAM carries out various calorimetric tests and investigates the boundary conditions of the fire with the help of fire reference packages. At the same time, we are conducting various fire scenarios with wood-filled impact limiters. Large-scale fire tests of impact limiters are carried out on a full scale as well as on a small scale. Influencing variables are investigated in particular by means of geometric changes and the consideration of artificial damages, in particular holes. In addition to propane fire as a heat source, thermal scenarios are also investigated with hydrogen as heat source and an infrared radiator system to ignite test specimens. For these numerous test arrangements, the transferability to existing and newly developed transport package designs is essential and fruitful within the review of design approvals, especially for Dual Purpose casks with a long-lasting operation time.
Packages for the transport of spent nuclear fuel are designed to endure severe accidents. To obtain approval, these transport packages must adhere to the specification-based criteria of the international transport regulations SSR-6 of the International Atomic Energy Agency (IAEA). To ensure compliance with these requirements, specific mechanical and thermal tests need to be addressed with respect to the package type. Typically, SSR-6 prescribes a mechanical test followed by a thermal fire test as part of different testing scenarios. To approve the latter test of the sequence, BAM performs calorimeter tests in advance with so-called fire reference packages for characterizing the actual fire and its impact on the package to be tested. Packages are designed with different geometry sizes depending on their purpose. For previous tests, the implemented test setups in the fire test stand were sufficiently dimensioned and could cover all requirements in this respect. However, to cover additional testing needs in the future, BAM is expanding the test setup for the purpose of testing significantly larger packages.
In previous test setups one ring burner for propane surrounding the test specimen was sufficient. The limiting size in this configuration was the design height of the transport package to be tested. According to the thermal test of the IAEA-Regulations [1], a 30-minute fully engulfing 800°C pool fire or an equally severe fire, e.g., propane gas fire, must be applied to the transport package. Possible adjustments such as nozzle cross-section and propane mass flow can be adjusted to a certain extent. Further modifications, to cover significantly higher and larger packages all-around with a fully engulfing fire, must be accomplished with an additional, second burner ring. Both burner rings had the same dimensions and were mounted on top of each other at different heights to create a significantly larger volume of fire that completely engulfs the package including its impact limiter.
To meet the IAEA regulatory boundary conditions, the enhanced fire test stand with the second burner ring is tested with a large fire reference package and will then be used for real-size transport packages after all parameters are successfully met. This fire reference package represents the external geometry of a generic transport cask for radioactive material and is equipped with numerous temperature sensors to record temperature curves at the interior wall surfaces.
Packages for the transport of radioactive material are designed to en-dure severe accidents. Packages for the transportation of radioactive material must demonstrate that the package can withstand certain prescribed tests from the IAEA Regulations [1]. In addition to mechanical tests, a thermal test in form of a fire test must be carried out. As packages to be tested at BAM are signifi-cantly larger than previous package designs, BAM has expanded an existing fire test stand. A modular concept is chosen, which means that the arrangement of the burner nozzles can be adapted to the test specimen. The dimensions of the burner rings, the type, the orientation and the number of burner nozzles can be varied depending on the test specimen. In addition, various pumps can be used to set the corresponding mass flow. With the help of a calorimeter test, the fire test stand can be qualified for a specific size of packages regarding the boundary conditions of the IAEA Regulations [1]. Due to the typically wood filled impact limiters in German package designs, a fire test is necessary, as experiments have shown that possible openings that occurred during a mechanical test contributed to the igni-tion of the wood filled impact limiters within the prescribed 30 minutes of the IAEA Regulations [1]. From a series of experiments, two experiments are pre-sented to show the possibilities to obtain different temperatures and temperature rates in the test specimen. In addition to sensor data, the heat flux into the package is calculated to verify that the IAEA boundary conditions are satisfied. In addition to the temperature data, other data such as wind speed and wind direction are also recorded to explain subsequent effects in the measurement data in a comprehen-sible manner.
Packages for the transport of radioactive material are often equipped with impact limiters consisting of wood, encapsulated by steel sheets. These impact limiters shall ensure the transport cask meets the mechanical and thermal IAEA regulatory test requirements. After damage caused by the mechanical tests the package has to withstand a severe fire scenario. According to the regulations during and following the thermal test, the specimen shall not be artificially cooled and any combustion of materials of the package shall be permitted to proceed naturally.
Corresponding to results of the French institute IRSN combustion and smouldering of wood inside the impact limiter occurred during and after the fire test. An additional energy supply from a pre-damaged impact limiter to the cask could be the consequence for the safety assessment of the containment.
BAM started a first test phase to examine the issue of combustion for such kind of package components. The goal was to understand the phenomena under the consideration of relevant regulatory boundary conditions. Several metal buckets were filled with wood and equipped with thermocouples. The test specimens have been prepared with different damage arrangements to take the influence of the mechanical tests into account. This paper shows the experimental setup and the conduction of the tests. The first test shows that pre-damaged metal encapsulations can lead to smouldering of the wood and with this to a supplement energy release after the end of the 30 minute fire. BAM is in the preparation process for a second test phase. A thermal test will take place with a wood filled test specimen weighing about 2Mg.
Packages for the transport of radioactive material are often equipped with impact limiters consisting of wood, encapsulated by steel sheets. These impact limiters shall ensure that transport casks meet the IAEA safety requirements. After damage caused by the mechanical tests the package has to withstand a severe fire scenario. It is required that the mechanical tests have to produce maximum damage, taking into account the thermal test. Furthermore, any damage, which would give rise to increased radiation or loss of containment or affect the confinement system after the thermal test, should be considered. Concerning the thermal test, 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. Different works from the French Institute for Radiological Protection and Nuclear Safety (IRSN) and BAM show that additional energy supply from a pre-damaged impact limiter to the cask could occur caused by smoldering of the wood. This effect should be considered within the safety assessment of the package. A heat wave from the fire could overlap with the additional energy from the impact limiter in the sealing system. In 2015 BAM conducted small scale
fire tests with wood filled metal drums showing continuing combustion processes during the cooling down phase. As not much is known about smoldering processes in wood filled impact limiters, it is highly complex to define pre-damage of impact limiters, which are conservative, regarding the most damaging energy flow from the impact limiter to the containment system in dependence of time. More research has to be done to develop models to examine the effects of smoldering impact limiters on the containment of packages for the assessment. The process of smoldering is described with regard to the requirements in the thermal safety assessment. Parameters influencing the smoldering process are identified. BAM operates test facilities to examine the issue of mechanical damage, combustion and heat transfer of packages for transport of radioactive material. A thermal test will take place with a wood filled test specimen with a diameter of about 2.3 meters. The aim is to understand the phenomena of smoldering under the consideration of relevant regulatory boundary conditions.