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Transmutation of All German Transuranium under Nuclear Phase Out Conditions - Is This Feasible from Neutronic Point of View?

Merk B, Litskevich D - PLoS ONE (2015)

Bottom Line: A basic insight for the optimization of the time duration of the deep burn phase is given.Further on, a detailed balance of different isotopic inventories is given to allow a deeper understanding of the processes during transmutation in the molten salt fast reactor.The effect of modeling and simulation is investigated based on three different modeling strategies and two different code versions.

View Article: PubMed Central - PubMed

Affiliation: Institute of Resource Ecology, Helmholtz-Zentrum Dresden - Rossendorf, Dresden, Germany.

ABSTRACT
The German government has decided for the nuclear phase out, but a decision on a strategy for the management of the highly radioactive waste is not defined yet. Partitioning and Transmutation (P&T) could be considered as a technological option for the management of highly radioactive waste, therefore a wide study has been conducted. In the study group objectives for P&T and the boundary conditions of the phase out have been discussed. The fulfillment of the given objectives is analyzed from neutronics point of view using simulations of a molten salt reactor with fast neutron spectrum. It is shown that the efficient transmutation of all existing transuranium isotopes would be possible from neutronic point of view in a time frame of about 60 years. For this task three reactors of a mostly new technology would have to be developed and a twofold life cycle consisting of a transmuter operation and a deep burn phase would be required. A basic insight for the optimization of the time duration of the deep burn phase is given. Further on, a detailed balance of different isotopic inventories is given to allow a deeper understanding of the processes during transmutation in the molten salt fast reactor. The effect of modeling and simulation is investigated based on three different modeling strategies and two different code versions.

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Related in: MedlinePlus

Description of the calculation cycle for the simulation of a MSR.
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pone.0145652.g004: Description of the calculation cycle for the simulation of a MSR.

Mentions: The HELIOS code is an industrial standard software which performs the neutron transport calculation, the burn up calculation, and if requested the cross section preparation in defined calculation areas. Originally, the HELIOS code has been written for the simulation of solid structured fuel assemblies. The possibility of online refueling and online reprocessing is not foreseen. To deal with these special features of molten salt reactors a PYTHON script has been developed, which is based on the special features of the HELIOS package. All input data, which is constant during the whole reactor operation, is stored in a so-called expert input. The changing material configuration is given in the user input which is written new in every cycle using the PYTHON script. Within each cycle 5 burnup steps are calculated in each HELIOS run. Both inputs are merged in the pre-processor AURORA, which creates the updated input for the HELIOS run for the determination of the neutron flux distribution and the burnup of the materials. The results are finally evaluated for each cycle in the post-processor ZENITH. Here it is decided which isotopes will be fed back into the next user input which is created with the help of the PYTHON script (see Fig 4). Theoretically, it is possible to simulate a molten salt reactor precisely by using small time steps in this calculation loop. In a real MSR two different time scales for the salt cleanup can be observed, due to the different extraction methods for the fission products. There are the helium bubbling for the gaseous and the volatile fission products with a comparably short acting time and the online salt cleanup for the dissolved fission products with a significantly longer acting time. A new strategy has been developed. It is characterized by the use of a reduced burnup per cycle (5 GWd/tHM using five burnup steps in HELIOS). It is coinciding with a full removal of the gaseous and the volatile fission products. At the end of the cycle, only a partial removal of the dissolved fission products are removed (16.6%, and 15% for the lanthanides). This methodology leads to a full clean up time of ~450 days, as it has been defined in the EVOL benchmark description. The recovery of the U-233 and Pa-233 from the fertile salt in the blanket will be performed in a real MSFR with a process which is very comparable to the salt cleanup process. The speed of processing has to be determined in the design of the blanket size and configuration. The process is modeled by withdrawing both materials at the end of each cycle from the isotopic configuration of the blanket salt. The amount of U-233 which can be harvested from the blanket depends strongly on the dimension and the composition of the blanket. This optimization has to be performed in conjunction with the decision how long the deep burn phase should last. However, it has to be accepted that there is a physical limit for the amount of U-233 which is determined by the available amount of neutrons for the breeding process.


Transmutation of All German Transuranium under Nuclear Phase Out Conditions - Is This Feasible from Neutronic Point of View?

Merk B, Litskevich D - PLoS ONE (2015)

Description of the calculation cycle for the simulation of a MSR.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4696651&req=5

pone.0145652.g004: Description of the calculation cycle for the simulation of a MSR.
Mentions: The HELIOS code is an industrial standard software which performs the neutron transport calculation, the burn up calculation, and if requested the cross section preparation in defined calculation areas. Originally, the HELIOS code has been written for the simulation of solid structured fuel assemblies. The possibility of online refueling and online reprocessing is not foreseen. To deal with these special features of molten salt reactors a PYTHON script has been developed, which is based on the special features of the HELIOS package. All input data, which is constant during the whole reactor operation, is stored in a so-called expert input. The changing material configuration is given in the user input which is written new in every cycle using the PYTHON script. Within each cycle 5 burnup steps are calculated in each HELIOS run. Both inputs are merged in the pre-processor AURORA, which creates the updated input for the HELIOS run for the determination of the neutron flux distribution and the burnup of the materials. The results are finally evaluated for each cycle in the post-processor ZENITH. Here it is decided which isotopes will be fed back into the next user input which is created with the help of the PYTHON script (see Fig 4). Theoretically, it is possible to simulate a molten salt reactor precisely by using small time steps in this calculation loop. In a real MSR two different time scales for the salt cleanup can be observed, due to the different extraction methods for the fission products. There are the helium bubbling for the gaseous and the volatile fission products with a comparably short acting time and the online salt cleanup for the dissolved fission products with a significantly longer acting time. A new strategy has been developed. It is characterized by the use of a reduced burnup per cycle (5 GWd/tHM using five burnup steps in HELIOS). It is coinciding with a full removal of the gaseous and the volatile fission products. At the end of the cycle, only a partial removal of the dissolved fission products are removed (16.6%, and 15% for the lanthanides). This methodology leads to a full clean up time of ~450 days, as it has been defined in the EVOL benchmark description. The recovery of the U-233 and Pa-233 from the fertile salt in the blanket will be performed in a real MSFR with a process which is very comparable to the salt cleanup process. The speed of processing has to be determined in the design of the blanket size and configuration. The process is modeled by withdrawing both materials at the end of each cycle from the isotopic configuration of the blanket salt. The amount of U-233 which can be harvested from the blanket depends strongly on the dimension and the composition of the blanket. This optimization has to be performed in conjunction with the decision how long the deep burn phase should last. However, it has to be accepted that there is a physical limit for the amount of U-233 which is determined by the available amount of neutrons for the breeding process.

Bottom Line: A basic insight for the optimization of the time duration of the deep burn phase is given.Further on, a detailed balance of different isotopic inventories is given to allow a deeper understanding of the processes during transmutation in the molten salt fast reactor.The effect of modeling and simulation is investigated based on three different modeling strategies and two different code versions.

View Article: PubMed Central - PubMed

Affiliation: Institute of Resource Ecology, Helmholtz-Zentrum Dresden - Rossendorf, Dresden, Germany.

ABSTRACT
The German government has decided for the nuclear phase out, but a decision on a strategy for the management of the highly radioactive waste is not defined yet. Partitioning and Transmutation (P&T) could be considered as a technological option for the management of highly radioactive waste, therefore a wide study has been conducted. In the study group objectives for P&T and the boundary conditions of the phase out have been discussed. The fulfillment of the given objectives is analyzed from neutronics point of view using simulations of a molten salt reactor with fast neutron spectrum. It is shown that the efficient transmutation of all existing transuranium isotopes would be possible from neutronic point of view in a time frame of about 60 years. For this task three reactors of a mostly new technology would have to be developed and a twofold life cycle consisting of a transmuter operation and a deep burn phase would be required. A basic insight for the optimization of the time duration of the deep burn phase is given. Further on, a detailed balance of different isotopic inventories is given to allow a deeper understanding of the processes during transmutation in the molten salt fast reactor. The effect of modeling and simulation is investigated based on three different modeling strategies and two different code versions.

Show MeSH
Related in: MedlinePlus