Passive Neutron Albedo Reactivity (PNAR) Prototype for Spent Nuclear Fuel Verification
Tupasela, Topi; Honkamaa, Tapani; Moring, Mikael; Turunen, Asko (2019-12-12)
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Tupasela, Topi
Honkamaa, Tapani
Moring, Mikael
Turunen, Asko
ESARDA
12.12.2019
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Tiivistelmä
The Finnish safeguards concept for encapsulation plant and geological repository includes verification
of all fuel items before encapsulation and disposal. The verification process is carried out according to
IAEA Group of Experts ASTOR (Application of Safeguards TO Repositories) recommendations. One
of the non-destructive assay (NDA) instruments featured in the concept is Passive Neutron Albedo
Reactivity (PNAR). The PNAR device will be used to verify the presence of fissile material in spent
nuclear fuel assemblies.
The PNAR instrument makes two relative neutron flux measurements. One in a neutron albedo
maximizing an one in a neutron albedo minimizing configuration. From the ratio of the two
measurements, a measure of the presence of fissile material can be calculated. The albedo
minimizing configuration is achieved by surrounding the fuel assembly with cadmium.
A prototype of the PNAR device is being built by STUK. The prototype is designed for underwater
measurements of BWR fuel used in Olkiluoto nuclear power plants. This article presents the final
design of the prototype device and presents the upcoming measurement plans with the detector. A
mock-up PNAR detector pod was assembled and tested under laboratory conditions to quantify the
detector signals and find potential sources of errors in the design.
of all fuel items before encapsulation and disposal. The verification process is carried out according to
IAEA Group of Experts ASTOR (Application of Safeguards TO Repositories) recommendations. One
of the non-destructive assay (NDA) instruments featured in the concept is Passive Neutron Albedo
Reactivity (PNAR). The PNAR device will be used to verify the presence of fissile material in spent
nuclear fuel assemblies.
The PNAR instrument makes two relative neutron flux measurements. One in a neutron albedo
maximizing an one in a neutron albedo minimizing configuration. From the ratio of the two
measurements, a measure of the presence of fissile material can be calculated. The albedo
minimizing configuration is achieved by surrounding the fuel assembly with cadmium.
A prototype of the PNAR device is being built by STUK. The prototype is designed for underwater
measurements of BWR fuel used in Olkiluoto nuclear power plants. This article presents the final
design of the prototype device and presents the upcoming measurement plans with the detector. A
mock-up PNAR detector pod was assembled and tested under laboratory conditions to quantify the
detector signals and find potential sources of errors in the design.