Project Subjects
Transport and Storage for Recyclable Nuclear Fuel
Background and Objective
Japanʼs basic policy has been to reprocess spent fuel (recyclable nuclear fuel) and to effectively utilize
collected plutonium and uranium, etc. Under this basic policy, various efforts should be made as far as reasonably
practicable considering some delays in the schedule of the Rokkasho reprocessing plant and the improvement of
the plant capacity factor in future.
In this project, to support nuclear power generation with excellent stability and ﬂexible nuclear fuel cycle,
we accomplish the early realization of the economical and reliable storage technologies with a large capacity forrecyclable nuclear fuel. Furthermore, we propose the safe and rational transport technologies considering thefuture demand (three times increase as much as now transported) of the shipments of the radioactive materials
due to the full operation of the nuclear fuel cycle.

Main results
1. Development of the economical concrete cask storage technologies
For early realization of the austenitic stainless steel canister for the concrete cask storage technology, it isvery important to establish a method to prevent penetration through the canister wall thickness due to the stresscorrosion cracking (SCC) in salty environments. Therefore, from improvements from the materials and environmental aspects, we proposed the practical solutions for the reduction of welding residual stress of the metal
canister and sea salt particles in the cooling natural air [N09]. The salt particle collection device with a low ﬂow
resistance for the air inlet of the storage building was proposed. In order to get more assurance of this device, wehave started the ﬁeld test at a coastal site (Fig.1). Furthermore, with the test device simulating the inlet air ductconﬁguration of the concrete cask, we obtained the chloride deposition velocity on the heated stainless steel test
specimens installed in wind tunnels in the test house near the sea (Fig.2).
2. Development of the next generation storage system with a large capacity
As a vault storage technology with a large capacity has an economical advantage, under the cooperative
research agreement with CEA and EDF, a large reinforced concrete vault structure was heated to around 80°
Cwhich could correspond to the evaluation of the thermal cracking and matrix transition, and improvement in thedesign temperature of 65°
C currently applied to the nuclear building. We measured the thermo-hydro-mechanicalbehavior of such a structure over time (Fig.3).
3. Long-term integrity of the conﬁnement of the transport cask of fresh MOX fuelTo propose the practical inspection period related to the conﬁnement of the transport cask of fresh MOX
fuel, we performed the heating-acceleration aging test using several types of erastomer gasket. As a result, theirintegrities for the long term usage (f years) under 70°
C were demonstrated [N09002].
4. Radiological impact assessment at the release from a hypothetically submerged transport package of fresh MOX fuelUsing an ocean general circulation model applied to the projection of global warming, we evaluatedconcentrations of radioactive materials at the release from sea bottoms due to the hypothetical submergence ofthe transport package of fresh MOX fuel. We conﬁrmed the estimated dose equivalents for the public were quite
smaller than the ICRP recommendation (1mSv/year) (Fig.4) [V09041].
Other reports

14[L09001]

Nuclear Technology
10000

2

Q: Deposition of Salt (mg/m as Cl)
t: Time (h)2Deposition of Salt（mg/m as Cl）

Air Inlet
1000

3（11 mg/m as Cl）
Laboratory Test

Q = 5.07 t

101
Field Test

0.1

（2 μg/m3 as Cl）
0.01
1.E+00NaturalVentilation
Concrete Cask

Salt Particles

CanisterWater

Fig.1 The salt particle collection device
The device is installed at the inlet and composed ofmultiple trays ﬁlled with water.

Q = 0.0892 t

100

1.E+01

Heatedspecimens(5pieces perunit)

1.E+02

1.E+03
1.E+04Time（h）

Laboratory Test
Field Test

1.E+05

1.E+06

1.E+07

Field wind tunnel(5 units)

Fig. 2 Comparison of accumulated salt amountproﬁle between laboratory test and ﬁeldtest
The relationship between laboratory test and ﬁeld test (4kmaway from the coast) related to the chloride deposition
velocity was obtained.

Vault Structure[unit/m3]Surrounding
Soil
Heater: 100kW

Temperature Distribution
Inside Ceiling
Inner Surfaceof CeilingFig. 3 Temperature proﬁle in the vault and relative humidity evolution inside concrete
A large reinforced concrete vault structure has been heated
to 80°
C during two years, and the relative humidity evolution proﬁle inside concrete (thickness 55cm) was obtained.

Fig. 4 Distributions of the radionuclides concentrations of radioactive materials at therelease from a hypothetically submergedtransport package of fresh MOX fuelUsing an ocean circulation model, the concentrations ofradioactive materials at the release from sea bottoms forcoastal areas were estimated. The monthly mean tracer
concentration (unit/m3) in the ocean surface layer (0-100mdepth) was acquired from the simulation by the seasonalchanged ﬂow ﬁeld. We conﬁrmed that the patterns of seasonal change were same after second simulated years fromthe simulation for three years. X shows the release point oftracer in January of ﬁrst simulated year. ▽shows the maximum concentration in November of third simulated year.

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