Why? The kinds of UHPC being discussed in the article weren’t available even in the United States until the year 2000 but most of Iran’s nuclear facilities were built between 1974 and 2005. Even their primary enrichment facility in Fordow, which was struck with MOPs, was started no earlier than the mid-2000s as it was still unfinished in 2009.

Basically the majority of Iran’s facilities, even their major ones, are too old to have the kind of concrete being discussed in the article.