Photo : A drone attempting to inspect the radiation level on the cover of primary containment vessel of Reactor 2 by Tepco
Following up this article : Tepco halted contaminated water processing as exhaust filters breached
Tepco announced most of the exhaust filters of ALPS (Advanced Liquid Processing System) were found to be breached on the 9th of September, 2021. Those filters were replaced as recently as two years ago.
ALPS is equipped with 25 exhaust filters, which process the radioactive gas from the byproduct slurry. According to Tepco, 24 of 25 filters were confirmed to be breached. These filters had been broken also two years ago, but Tepco did not report the fact in public. Tepco had continued operating ALPS without identifying the systematic problem that caused the filters to be damaged. Tepco commented that the company did not recognize it as a problem that time.
No abnormality in the environmental radiation level has been observed, according to Tepco.
https://www.tepco.co.jp/decommission/information/newsrelease/reference/pdf/2021/2h/rf_20210906_2.pdf
https://www.tepco.co.jp/decommission/information/newsrelease/reference/pdf/2021/2h/rf_20210909_2.pdf