Nuclear Science and Engineering Research

4-13 Toward the Establishment of a Method for Treating MA Transmutation Fuels
ᴪ Development of the Technology for Pyrochemical Treatment of MA Nitride Fuel ᴪ(a)(b)

Molten salt electrolysis

Anode (Spent fuel) Cathode (Liquid Cd)+15−

N2 gasPu, MA

Molten salt

RE, AL, ALE

Anode residue:
Inert matrix, PGM, Mo

Pu-MA-Cd alloy

Renitridation
15

N2 gasPu: Plutonium
MA: Minor
actinides
RE: Rare earth
AL: Alkali metal
Mo: Molybdenum
ALE: Alkaline earth
PGM: Platinum group

Fig.4-28 Experimental apparatus for the study of
pyrochemical-treatment of MA nitride fuelExperiments using highly radioactive MAs such as Am havebeen conducted with the apparatus including the moltensalt electrorefiner (b) installed in the module for TRU hightemperature chemistry (TRU-HITEC) (a), which comprises hot
cells and a glove box with an inert gas atmosphere.
(c)

(d)

(e)

Distillation of Cd

Pu-MA-Cd alloy→ (Pu, MA)N

Fig.4-27 Outline of the pyrochemical treatment of MA
nitride fuelPu and MA in the spent MA nitride fuels are dissolved intomolten salt, separated from the FP elements, and recovered
into the Cd cathode by molten salt electrolysis. The recovered
Pu and MA are converted into nitrides to be used as fuels.

Fig.4-29 Am compounds and alloys obtained in our study
Molten salt electrolysis using a disk-shaped AmN sample(diameter: 4 mm, thickness: 1 mm) as an anode (c) has been
conducted to recover Am in a Cd cathode. From the Am–Cd
alloy obtained by molten salt electrolysis (d), an AmN powder
sample (e) was prepared.

Partitioning and transmutation (P&T) technology serves toseparate elements in high level radioactive wastes discharged
from reprocessing plants depending on their intended use andchemical character, and to transmute long-lived nuclides toshort-lived or stable ones. This technology aims at reducing theburden of high level waste and using repositories efﬁciently.
We have been conducting research and development of
the technology for transmuting highly radioactive longlived nuclides including minor actinides (MA: neptunium(Np), americium (Am), and curium (Cm)) using a dedicatedaccelerator-driven system (ADS). To transmute MA usingADS, neutrons produced by injection of an accelerated proton
beam to a metal target will be supplied successively to a
subcritical core to maintain ﬁssion chain reactions of MA andother elements in the core. The composition and chemical
form of the fuel pellets containing MA elements in the coreshould be appropriate for MA transmutation. Uranium-free
MA nitride has been selected as the first candidate for theMA transmutation fuel. Previous feasibility studies on thetransmutation system show that approximately 20% of theMAs in the fuel can be transmuted in one burning cycle ofapproximately two years. To increase the transmutation ratio,reprocessing of spent MA transmutation fuels and reuse of theMA elements existing in spent MA transmutation fuels arenecessary. Therefore, a method suitable for reprocessing MA

transmutation fuel should be developed.
We have been researching and developing spent MA
transmutation fuel reprocessing technology to recoverand reuse the MA in spent fuels. One of our concerns ispyrochemical treatment technology (Fig.4-27), which is basedon that developed to reprocess metal fuels for fast reactors.
This technology, in which molten salts and liquid metals areused as solvents, is suitable for treatment of MA transmutation
nitride fuels because solvents are resistant to radiation damage
and decay heat. Advantages such as the feasibility of recycling
the expensive and highly enriched 15N used in the nitride fuels
have also been pointed out. Conversely, one disadvantage isthe necessity of an inert gas atmosphere because the salts usedas solvents are hygroscopic.
Our experimental results with plutonium (Pu) and MA (Npand Am) samples at the lab-scale (Figs.4-28 and 4-29) indicatethat the elemental technologies are feasible. The similarity of thebehaviors of MA and Pu, which suggest that the technology has
advantages in terms of proliferation resistance in principle, havebeen certiﬁed. At present, our focus is on evaluating the detailed
behavior of the elements that are thought to exist in spent MA
transmutation fuels, including fission product elements andinert matrix elements such as zirconium (Zr) and titanium (Ti).
We also focus on the development of an engineering-scale
apparatus for nitride fuel treatment.

Reference
Hayashi, H. et al., Pyrochemical Treatment of Spent Nitride Fuels for MA Transmutation, Science China Chemistry, vol.57, issue 11, 2014, p.1427-1431.

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JAEA R&D Review 2016-17