All entries for June 2023

June 15, 2023

The first ever RSB Big Sample and why it is so significant

A major step towards realization of Reacted Sintered Boride blocks for fusion applications

Establishing material properties of candidate materials for shielding is one part and manufacturing required materials with realistic dimensions for actual shielding is another. Till now the Radiation Dense Materials Group (RDMG) has worked extensively in reproducing Gen 1 RSBs in a lab based environment to produce Gen 2 RSBs.

This process also needs to be scalable. To test this we have attempted to make a much larger sample with a mass 20x greater than the standard samples. Successful densification of such samples is an important demonstration of how practical a sintering route is with respect to a specific material.

In general, most radiation shielding in a fusion reactor is in the form of tiles. These tiles are typically 20 - 30 mm thick with variable lateral sizes. Where materials made via powder metallurgy is concerned, the most important dimensional parameter is the part size.

This is defined as the diameter D of the largest sphere that can exist within a sintered part that is fully dense as shown in Figure 1:

Figure 1: Demonstration of part size of diameter D

The means that for a tile of dimensions 200 mm x 200 mm x 20 mm would require a part size D = 20 mm. Part sizes in most powder metal processes are seldom above 30 mm.

The real challenge comes when manufacturing lab based materials for practical applications. Thanks to Hyperion MT (Barcelona, Spain) for supplying sufficient milling media, we were able to manufacture decent size blocks of RSBs recently in the lab with the specification as given in Table 1.

Table 1: Specifications of RSB55_NFC regular* sample

Mass (g)

Diameter (mm)

Height (mm)

Density (g/cc)





Cross-sections show that the sample was defect free internally (figure 2c). Considering the fact that this sample was fabricated at one shot, the future of RSBs looks really bright in terms of industry scale fabrication. This is vital while aiming for better and bigger RSBs samples in near future. With further optimisation of the sample packing in sintering as well as the sintering run itself, the density and overall quality is expected to increase in the coming trials.

Figure 2: Various views for RSB55_NFC regular samples. a) To view b) Bottom view c) Cross-sectional view of as cut and polished sample

. A typical ITER identical monoblock tile geometry is shown in Fig. 3. In terms of geometry, the final aim is to fabricate RSBs with size and shape as used in ITER divertor. This aim looks more realistic now and this achievement is indeed a giant step towards this goal.

Figure 3: WEST plasma-facing unit (PFU) and the monoblock tile geometry. Monoblock tile geometry is identical to ITER.Source

Stay tuned for more interesting updates and insights from RDMG. Till then, keep researching, keep shielding!

*RSB55_NFC regular has about 30 at% Boron and NFC refers to no free carbon which means Carbon is added either in the form of Cr3C2 or WC. For more details, please check our latest publication (here) .

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