LWR (water cooled) reactors require high pressure to prevent water converting to steam. High-pressure containment building and systems are required. That includes a huge reinforced concrete building, to contain steam containing radioactive material; manual construction and size makes this one of the biggest expenses of building a LWR.
LFTRs are cooled by molten salt, so they operate at atmospheric pressure. LFTRs have no high pressure that could explode; high pressure containment is unnecessary.
Fukushima reactors had hydrogen explosions that damaged the buildings and reactors, and spewed radioactive material into the atmosphere. LFTRs have no steam or hydrogen.
There are a few sodium-cooled reactors in use. Sodium reacts violently to water. A broken pipe weld in a heat transfer unit heavily damaged the Monju Nuclear Power Plant. LFTRs have only chemically stable coolant.
The containment building for a LFTR would have radiation shielding, and would protect the reactor from external forces (depending on the site, might include car bombs, hurricanes, earthquake). But the huge expensive steam containment building of a LWR is not needed.