biological shield

noun

1. a protective shield impervious to radiation, esp the thick concrete wall surrounding the core of a nuclear reactor

Example Sentences

One of the central challenges is pouring the concrete – 3m tonnes in total – needed to build not only the massive foundations but also the vast biological shield around the reactor, which reduces the radiation to levels safe for humans.

From The Guardian

The more people who are vaccinated, the stronger the effect of herd immunity, which acts as a biological shield against communicable diseases for entire populations.

From Time