Realistic Bandwidth Estimation in the Theoretically Predicted Radionuclide Inventory of PWR-UO2 Spent Fuel Derived from Reactor Design and Operating Data

Nuclear energy for power generation produces heat-generating high- and intermediate level radioactive waste (HLWand ILW) for which a safe solution for the handling and disposal has tobe found. Currently, many European countries consider the final disposal of HLW and ILW indeep geological formations as the most preferable option. In Germany the main stream of HLW and ILW include spent fuel assemblies from nuclear power plants (NPPs), the vitrified waste and compacted metallic waste of the fuel assembly structural parts originate from reprocessing plants. An important task that occurs within the framework of the Product Quality Control(PQC) of nuclear waste is the assessment of the compliance of any reprocessed waste product inventory with the prescribed limits for each relevant radionuclide (RN). The PQC task is to verify the required quality and safety of nuclear waste prior to transportation to a German repository and to avert the disposal of non-conform waste packages. The verification is usually based on comparing the declared radionuclide inventory of the waste with the presumed or expected composition, which is estimated, based on the known history of the waste and its processing. The difficulty of such estimations for radioactive components from nuclear fuel assemblies is that reactor design parameters and operating histories can have a significant influence on the nuclide inventory of any individual fuel assembly. Thus, knowledge of these parameters is a key issue to determine the realistic concentration ranges, or bandwidths, of the radionuclide inventory. As soon as a governmental decision on the construction of a high-level waste repository will be made, comprehensive radionuclide inventories of the wastes assigned for the deposition will be required. The list of final repository relevant radionuclide is based on the safety assessmentfor this particular repository, thus it is likely to comprise more-or-less the same radionuclides that need to be declared for compacted metallic waste residual from the reprocessing of spentfuel assemblies. In Germany, the radionuclide declaration list for the disposal of used fuel assemblies is not yet specified. Although information of radionuclide composition of used nuclear fuel assemblies assigned to a specific repository would be provided by the nuclear industry. An estimation of the average radionuclide composition of the burnt-up fuel includingthe realistic inventory bandwidths for each of relevant radionuclides would be highly desirable before hand. This information is needed for the development of proof tools for the product quality control or safeguards, but also for the evaluation of various safety scenarios regarding the radionuclide mobility or contamination. [...

Determination and analysis of the uncertainty bandwidth of the nuclear inventory for assessment of radioactive waste

Waste packages often contain wastes forms of different types of spent fuels and of various operational history, whereas information about secondary reactor parameters may not be available. In this case the so-called characteristic fuel burn-up and cooling time are determined. These values are obtained from a correlations involving key-nuclides (easy-to-measure nuclides). Each correlation is associated with corresponding uncertainty bandwidth. The bandwidth strongly depends on secondary reactor parameters such as initial enrichment, temperature and density of the fuel and moderator, reactor‘s operational history. The purpose of our investigation is to understand the limitations of the scaling and correlations, to define and verify the range of validity, and to scrutinize the dependencies and propagation of uncertainties that affect the waste inventory declarations and their independent verification. This is accomplished by numerical assessment and simulation of the waste production processes using the widely accepted codes SCALE 6.0 and 6.1 to simulate the cooling time and burn-up of a spent fuel element

Evaluation and Parameter Analysis of Burn up Calculations for the Assessment of Radioactive Waste

The purpose of this work is to define and verify the range of validity and limitations of correlations used for nuclear waste characterization and to scrutinize the dependencies and propagation of uncertainties that affect the waste inventory declarations and their independent verification. This is accomplished by numerical assessment and simulation of waste production using well accepted codes SCALE 6.0 and 6.1 to simulate the cooling time and burn up of a spent fuel element. The simulations are benchmarked against spent fuel from the pressurized water reactor Obrigheim in Germany for which sufficiently precise experimental reference data are available

Determination of Bandwidths of PWR-UO2_{2} Spent Fuel Radionuclide Inventory Based on Real Operational History Data

An important requirement for the official approval of the safe final disposal of SNF is a comprehensive specification and declaration of the nuclear inventory in SNF by the waste supplier. In the verification process both the radionuclide (RN) activities and the associated uncertainties are required. Burn-up (BU) calculations based on typical and generic reactor operational parameters do not encompass any possible uncertainties observed in real reactor operations. At the same time, details of irradiation history are often missing, which complicates the assessment of declared RN inventories. Here, we present a set of burn-up calculations, in which the real operational histories of 339 published or anonymized PWR fuel assemblies (FA) are taken into account. These histories provide information about ranges of values of the associated secondary reactor parameters (SRP), which are useful for the 'SRP analysis'. Hence, we can calculate realistic variations in the spectrum of RN inventories. SCALE 6.1 with the ENDF/B-VII.0 library has been employed for the burn-up calculations. The results have been validated using experimental measurements from the online database SFCOMPO