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- Radioactive material (6)
- Transport packages (6)
- Safety assessment (5)
- Leakage rate (4)
- Spent fuel assessment (4)
- Spent fuel (3)
- Ageing (2)
- Finite element methods (2)
- Gas generation (2)
- High burn-up (2)
Organisationseinheit der BAM
The mechanical and thermal loadings associated with the routine, normal and accident conditions of transport can have a significant effect on the leak tightness of the sealing system of transport casks for spent fuel and high radioactive waste.
Applicants are requested by BAM to provide test programmes for verification of design leakage rates of the sealing system under the possible loads.
Two test series initiated to clarify the dependency of the standard leakage rate on dynamic lid displacement as well as the dependency of the useful elastic recovery ru of a metallic seal on temperature and time, are outlined in this paper as examples of present investigations:
Sliding tests simulating a lid displacement possible by a horizontal drop of the cask are carried out at the controlled drop test facility of BAM with test flange pairs equipped with metallic Helicoflex seals.
For specification of covering values for the useful elastic recovery ru GNS has started a very comprehensive test programme with overall 70 metallic seals installed in test flanges which are stored for a period of one year at three different temperatures up to 150°C.
This paper gives an overview about the current approach of BAM in the assessment of cask tightness and informs about the status of the running test series.
Verification of activity release compliance with regulatory limits within spent fuel transport casks
(2010)
Requirements and test programs for sealed radioactive sources are specified in international standards for safety in transport and in use.
Sealed sources which are approved as special form radioactive material according to the Transport Regulations, IAEA Safety Standards TS-R-1, must be able to withstand mechanical (9 m drop, percussion and bending) and thermal (800°C heat) tests without loss of radioactive content.
The International Standard ISO 2919 provides a set of tests which classifies the sources for their safety in use. Performance tests specified in this standard are temperature (high and low), external pressure, impact, vibration and puncture tests. Each test can be applied at different levels of intensity depending on typical usage.
As a criterion of pass or fail, leakage testing has to be done after each test.
The poster gives an overview of BAM s comprehensive test equipment and experience in testing sealed radioactive sources.
BAM, as the competent authority for approval of special form radioactive material, attaches great importance to a detailed audit of the required quality assurance programmes for design, manufacture, testing, documentation, use, maintenance and inspection. Applicants have to submit, together with their application documentation, information on general arrangements for quality assurance, as well as on quality assurance in production and in operation. Fields where BAM has often found deficiencies are leak test methods, weld seam quality and the safety level after use.
Packages for the transport of spent nuclear fuel shall meet the International Atomic Energy Agency regulations to ensure safety under different transport conditions. The physical state of spent fuel and the fuel rod cladding as well as the geometric configuration of fuel assemblies are important inputs for the evaluation of package capabilities under these conditions. Generally, the mechanical behavior of high burn-up spent fuel assemblies under transport conditions shall be analyzed with regard to the assumptions which are used in the containment and criticality safety analysis. Considering the complexity of the interactions between the fuel rods as well as between the fuel assemblies, basket, and cask containment, the exact mechanical analysis of such phenomena is nearly impossible. The gaps in Information concerning the material properties of cladding and pellet behavior, especially for the high burn-up fuel, make the analysis more complicated additionally. As a result, enveloping analytical approaches are usually used by BAM within the safety assessment of packages approved for transport of spent nuclear fuel.
To justify the safety margins of such approaches additional analyses are necessary. In this paper, numerical simulations of a spent fuel assembly Segment are presented. The segment modeled represents the part of a generalized BWR fuel assembly between two spacers.
Dynamic and quasi-static finite element calculations are performed to simulate the spent fuel behavior under regulatory defined accident conditions of transport. Beam elements are used for the modeling of the fuel rods representing the compound consisting of claddings and fuel pellets. The dynamic load applied is gathered from an experimental drop test with a spent fuel cask performed at BAM. A hot cell bending test performed at JRC Karlsruhe is the basis for obtaining the material behavior of the fuel rods. The material properties are determined by simulating the test setup of JRC and optimizing the results to fit the experimental load deflection curve. The simulations of the fuel assembly segment are used to get a better understanding about the loads on fuel rods under accident conditions of transport.
Transport packages for spent fuel have to meet the International Atomic Energy Agency requirements for different transport conditions. Physical state of spent fuel and fuel rod cladding as well as geometric configuration of fuel assemblies are important inputs for the evaluation of package capabilities under these conditions. In this paper, the mechanical behaviour of high burn-up spent fuel assemblies under transport conditions is analysed with regard to assumptions to be used in the activity release and criticality safety analysis. In particular the different failure modes of the fuel rods (fine cracks or complete breakage), which can cause release of gas, volatiles, fuel particles or fragments have to be properly considered in these assumptions. In view of the complexity of interactions between the fuel rods as well as between fuel assemblies, basket, and cask containment, the exact mechanical analysis of such phenomena is nearly impossible. The gaps in information concerning the material properties of cladding and pellets, especially for the high burn-up fuel, make the analysis more complicated additionally. In this context some practical approaches based on experiences of BAM Federal Institute for Material Research and Testing within safety assessment of packages for transport of spent fuel are discussed.