Criticality Safety Study for the Disposal
of Damaged Fuels from Fukushima
Daiichi Reactors
Xudong Liu
Abstract This paper summarizes our previous works on neutronics analysis for the
disposal of damaged fuels from Fukushima Daiichi reactors. Three major stages
have been identified for the criticality safety assessment after disposal. In order to
evaluate the criticality safety for certain repository conditions and engineered
barriers designs, neutronics models have been defined for different stages, and
numerical results have been calculated by a Monte-Carlo code MCNP. For stages
when fissile nuclides in the damaged fuels remains in the vicinity of the engineered
barriers, the neutron multiplicity (k eff ) for a canister containing fuel debris surrounded by buffer was calculated over the leaching time. For the stage when fissile
nuclides originated from multiple packages deposit in far-field host rocks, the
critical masses for uranium depositions were studied for various rock types and
geometries. The methodology presented in the present paper could be further
improved and utilized to assist the repository system design and criticality safety
assessment in the future.
Keywords Criticality safety Á Geologic disposal Á Damaged fuels Á Fukushima
accident Á Radioactive waste management
1 Introduction
The accident at the Fukushima Daiichi Nuclear Power Station in March 2011
generated damaged fuel in three crippled reactors, containing nearly 250 metric tons
of uranium and plutonium along with fission products, minor actinides, and other
materials such as fuel cladding, assemblies, and in-core structural material [1]. The
damaged fuels will have to be disposed of in a deep geological repository. For a
prospective repository, a criticality safety assessment (CSA) should be performed to
ensure that the repository system including the engineered barriers and far-field
X. Liu (&)
Department of Nuclear Engineering, University of California, Berkeley, CA, USA
e-mail: xdliu@berkeley.edu
© The Author(s) 2017
J. Ahn et al. (eds.), Resilience: A New Paradigm of Nuclear Safety,
DOI 10.1007/978-3-319-58768-4_23
269
of Damaged Fuels from Fukushima
Daiichi Reactors
Xudong Liu
Abstract This paper summarizes our previous works on neutronics analysis for the
disposal of damaged fuels from Fukushima Daiichi reactors. Three major stages
have been identified for the criticality safety assessment after disposal. In order to
evaluate the criticality safety for certain repository conditions and engineered
barriers designs, neutronics models have been defined for different stages, and
numerical results have been calculated by a Monte-Carlo code MCNP. For stages
when fissile nuclides in the damaged fuels remains in the vicinity of the engineered
barriers, the neutron multiplicity (k eff ) for a canister containing fuel debris surrounded by buffer was calculated over the leaching time. For the stage when fissile
nuclides originated from multiple packages deposit in far-field host rocks, the
critical masses for uranium depositions were studied for various rock types and
geometries. The methodology presented in the present paper could be further
improved and utilized to assist the repository system design and criticality safety
assessment in the future.
Keywords Criticality safety Á Geologic disposal Á Damaged fuels Á Fukushima
accident Á Radioactive waste management
1 Introduction
The accident at the Fukushima Daiichi Nuclear Power Station in March 2011
generated damaged fuel in three crippled reactors, containing nearly 250 metric tons
of uranium and plutonium along with fission products, minor actinides, and other
materials such as fuel cladding, assemblies, and in-core structural material [1]. The
damaged fuels will have to be disposed of in a deep geological repository. For a
prospective repository, a criticality safety assessment (CSA) should be performed to
ensure that the repository system including the engineered barriers and far-field
X. Liu (&)
Department of Nuclear Engineering, University of California, Berkeley, CA, USA
e-mail: xdliu@berkeley.edu
© The Author(s) 2017
J. Ahn et al. (eds.), Resilience: A New Paradigm of Nuclear Safety,
DOI 10.1007/978-3-319-58768-4_23
269