All 2 entries tagged Rsb

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

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) .

Jessica Marshall : 15 Jun 2023 13:32 |  Tags: Dense Materials Powder Metallurgy Rsb Sintering Success |  Comments (0) |  Close comments |  Report a problem

First irradiation studies of RSBs at the Dalton Facility

Writing about web page https://www.dalton.manchester.ac.uk/research/facilities/cumbria-facilities/

Last week was a first in the field of Radiation Dense Materials in that samples of Reactive Sintered Borides (RSBs) and cemented Tungsten Carbide (cWC) were irradiated for the first time by proton beam and gamma irradiation at the Dalton Cumbrian Facility in the Westlakes Science Park during some truly beautiful springtime weather.

Much work on simulating the radiation response and attenuating properties of a cWC, cWC-RSB and tungsten boride shielding concepts has occured during the 2010s onward [C.G. Windsor et al 2015 Nucl. Fusion 55 023014,C.G. Windsor et al 2018 Nucl. Fusion 58 076014], however, data on the radiation response of cWCs [Shielding materials in the compact spherical tokamak https://doi.org/10.1098/rsta.2017.0443] is very sparse due to their recent adoption as candidate shielding materials. No data on radiation response exists for RSBs due to their novelty so this will be the first time any practical data will be obtained from irradiated RSB materials.

The planned experimental work at DCF fell into two main topics: Proton irradiation and gamma irradiation. Each type of radiation would take place at two different intensities and at two different temperatures.

Proton radiation most closely resembles the conditions at or near the plasma-facing component of a tokamak reactor and hence was to take place at ambient and at 600^oC.

Gamma radiation will be significant at all parts of a tokamak reactor but particularly near the superconducting magnets. These irradiations were performed at -196^oC (77K) and at ambient. Each experiment consisted of three samples: cWC, RSB and W metal alloy with eight different irradiation conditions with a 9th sample set to sit in the gamma irradiator for long-term irradiation studies.

So....how did the work go and what happened over last week? Read on.

The gamma irradiation mostly went to plan. Low dose gamma irradiation was set to 30 kGy for both the 77K and ambient irradiation. High dose gamma radiation samples was set to 240 kGY for ambient and 90 kGY for 77k. The lower dose at 77K is a result of the different sample positioning due to the dewar and the requirement to change the N₂ the dewar every 5 kGy to prevent excessive ozone formation, which is an explosion hazard. All gamma irradiated samples except the long-term samples have been returned.

Proton irradiation was less straightforward. The high dose ambient proton irradiation was successful, with a steady state temperature of 125^oC and a total dose equivalent to 1.66 x 10¹⁸ protons. Subsequent proton irradiation attempts were unsuccesful, mostly due to the plasma failing the strike and therefore enable the proton beam to irradiate the samples. However, these sample will be irradiated this week and sent by post.

This is one of the many hazards of experimental work in that failure is always an option but nevertheless this work on completion will provide an important first step in realizing the cWC-RSB concept as practical radiation shielding materials whatever the damage or lack of is present on analysis.

This work would not be possible without the dedication of the staff and researchers at the DCF who make this possible.

Jessica Marshall : 30 Mar 2022 15:27 |  Tags: Dcf Gamma Radiation Irradiation Nnuf Proton Rsb Tungsten Carbide |  Comments (0) |  Close comments |  Report a problem