Understating the risks is just as irresponsible as overstating it.
There is no explicit by-line on this article, but the video contains an interview with BBC reporter Chris Hogg in Tokyo that repeats that a half life of 8 days means “that after 8 days the risk will have dissipated”.
The reporter is WRONG. Twice, because that is also not what the officials said. His ignorance of basic physics, in this case a topic I always teach in a college general education class, led him to misinterpret what was actually said by a government spokesman and hence mislead the public.