Another issue is that graphite core. As I detailed previously with regard to the HTGR (part 6.4.3) it’s a potential fire hazard. Thus we would need to put the MSR within a containment dome of sorts. Again, as with the HTGR, this dome need not be built to the same exacting standards of a LWR dome as we are merely trying to contain a graphite fire, not an out of control reactor. We would need an effective on plant fire control team and some form of fire detection and suppression system, within the containment dome and all the necessary gear that this entails. Again, I refer you the relevant section of the HTGR anaylsis, but needless to say such an arrangement would involve certain costs.
One solution would be to remove the graphite core and seperate the reactor into two layers (see here) with an outer breeding blanket feeding on the neutrons (that would otherwise be absorbed by the graphite) produced by the active core. While such an arrangement gets around the fire risk issue, it would be technically harder to build and complicate an already narrow material choice, give the higher neutron flux parts of the core would now be exposed to, as well as well as the generally more complex nature of such a core arrangement (i.e. harder to manufacture, assemble and maintain).
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