8P94

量研におけるIFMIF/EVEDA中性⼦原設計の現状

Current status of IFMIF/EVEDA neutron source designactivities at QST
落合謙太郎、小柳津誠、見城俊介、太田雅之、権セロム、佐藤聡

Kentaro Ochiai, Makoto Oyaidzu, Shunsuke Kenjo, Masayuki Ohta, Saerom Kwon and Satoshi Sato
量子科学技術研開発機構 六ヶ所研究所
National Institute for Quantum Science and Technology, Rokkasho Fusion InstituteIntroduction
The fusion neutron source (FNS) design activity has
been implemented as BA Phase II of theIFMIF/EVEDA project since 2021. As a result ofdiscussions between QST and F4E, it was determinedthat the FNS design studies related to the safety should
be prioritized, and the following items were decided toimplement by QST and F4E,i) Tritium migration estimation,ii) Erosion/deposition modelling in the lithium loop,iii) Accident analysis in Safety,iv) Study on the optimization of the Li-Oil Heat
Exchanger,v) Use of LIPAc as testing facility.
Tritium Migration Estimation
Huge amount of tritium are generated in the liquid Li
with Li(d,tx) and Li(n,tx) reactions and are trapped inhydrogen trap system. Certain amounts of tritium thatare not captured by the trapping device remains inliquid lithium and eventually permeates through thestructural material and vaporize into vacuum. The
purpose of this task is to evaluate the amount of tritium
leaking out and to review the specification
requirements for detritiation. From the evaluation
results, it was found that the amount of tritium as
hydrides in lithium in the vapor/mist trap is muchhigher than the others. The amount of tritium dissolvedin structural material in the EMP was largest amongwhole components of Lithium Facility, since it haslarge center-core in its structure.
Erosion/Deposition Modelling (EDM)
The issue of EDM is to study the dose fromradioactivity in lithium. In particular, the evaluation ofeffective dose rate is important data for maintenanceand replacement work related to the target system. The
dose rate due to the activated erosion products wereevaluated. The total source term in the F82H backplate has been estimated using by Monte Carlotransport code MCNP and inventory calculation code
FISPACT. The most conservative erosion/deposition

model was created, and the deposition amount wascalculated as 0.079 g. Based on the amount, the activity,
the contact γ-dose rate, and the dose rates around thepoint source as a function of the distance wereevaluated. These values were found to be much higher
than the hands-on criteria of 10 microSv/h.
Accident analysis in Safety
The activities consist of three issues: failure mode
analysis, safety control systems and the Material at
Risk (MAR). As part of MAR, we newly developed atritium diffusion code for tritium emitted from a fusion
neutron source facility and tested the code to validate
one. The code was developed based on the puff-Gaussmodel, which is capable of faithfully analyzing tritium
diffusion in unsteady field condition. This code enables
diffusion analysis using actual meteorological andtopographical data, which were not applied inconventional plume model analysis codes.
Li-Oil Heat Exchanger
The primary heat exchanger system HX1 for liquid
lithium target was redesigned. HX1 uses an oil heattransfer fluid for cooling lithium, and Therm-S900(Hydrogenated terphenyl: C18H22) has been
considered as a candidate material in IFMIF design
activity. Therm-S900 is not applicable to HX1 because
it is a toxic oil under Japanese regulations. Therefore,
QST has been considering alternative materials withless environmental impact. As a result of the study,
QST propose that dibenzyl toluene (C21H20), which
has lower toxicity, is one of the most promisingmaterials.
Use of LIPAc as testing facility
As for the item "Use of LIPAc as testing facility", weaim to obtain R&D data for designing an accelerator fora fusion neutron source in conjunction with the beam
operation of the prototype accelerator LIPAc being
developed at Rokkasho Fusion Institute. We will reflect
the data by LIPAc operation such as RAMI, activation,
neutonics to the FNS design.