I am extremely skeptical about such claims. One such alternative design was the THTR design, which was implemented in the Jülich AVR reactor. It was also claimed to be passively safe.

https://en.wikipedia.org/wiki/AVR_reactor

But there were incidents when the plant was basically out of control. Worse, the design is based on graphite spheres which contain the fuel. That is only safe as long as the spheres in the hot reactor do not come into contact with air, which will cause them to burn, or with water, which will form hydrogenium-oxygen mixtures. Burning graphite was both a main ingredient in the Windscale fire, and in the Chernobyl disaster. There were also important mechanical problems with the spheres. In retrospect, these claims for passive security were unwarranted and the plant was dangerous. With the experience from the AVR, one can also say, that the nuclear industry is not transparent at all about safety problems. Also, it is not only very hard to make such plants inherently safe, if this also very expensive. Unfortunately, this conflicts with the goal of every company, which is to make a profit which is as large as possible.