Yesterday I was digging around for more information about ionizing radiation and I discovered that NASA technically limits astronauts' exposure to 100 millisieverts a year to avoid central nervous system effects. In practice, astronauts often receive more exposure than allowed, particularly during solar minimums.
What is important though is that NASA acknowledges that ionizing radiation in excess of 100 millisieverts causes central nervous system damage in ADULTS:
Sieffert, Alyssa. Megan. (2014). ASTRONAUT HEALTH & SAFETY REGULATIONS: IONIZING RADIATION. Scitech Lawyer, 10(4), 20-22. Retrieved November 23, 2015 from http://login.ezproxy1.lib.asu.edu/login?url=http://search.proquest.com/docview/1681907395?accountid=4485
Currently, based on NCRP recommendations, NASA limits career exposure to amounts that cause a three percent (3%) risk of exposure-induced death (REID). However, setting forth such guidelines is complicated because exposure to ionizing radiation affects individuals of varying ages and genders differently. Health standards for astronauts in all stages of flight are established by NASA's Office of the Chief Health and Medical Officer (CHMO), including standards for radiation exposure....
....Currently, based on NCRP recommendations, NASA limits career exposure to amounts that cause a three percent (3%) risk of exposure-induced death (REID).25 However, setting forth such guidelines is complicated because exposure to ionizing radiation affects individuals of varying ages and genders differently. For example, a 35-year-old males REID due to cancer reaches 3 percent upon 720 mSv exposure.26 In contrast, a 35-year-old female reaches the REID due to cancer threshold upon 550 mSv exposure...
...Additional dose limitations to prevent noncancer effects are also set forth by NASA, and to avoid noncancer effects in astronauts' central nervous systems, exposure must be limited to 100 mSv per year...
Majia here: While I am extremely concerned about all people in Japan's exposure to Fukushima radiation (especially kids'), workers at the site face the greatest exposure risk, especially since TEPCO has raised their exposure standard to 250 millisieverts. Here is an excerpt from my recent work on Fukushima:
Workers at the site face direct challenges to their health. In December of 2012, The Asahi Shimbun reported that TEPCO found 178 workers whose thyroid glands evidenced exposure levels exceeding 100 millisieverts.[i]
One hundred and sixty-three workers were calculated to have had thyroid doses exceeding 200 millisieverts. The highest dose recorded was 11,800 millisieverts, although two workers were found with exposure levels over 10,000 millisieverts.
In July of 2015, Japan raised the allowable exposure levels for plant workers to 250 millisieverts, doubling the previously established 100 millisievert a year exposure.[ii]
The maximum annual exposure rate was also raised for people who are working in contaminated areas, including government officials and bus drivers, to 100 millisieverts a year.[iii]
Long term consequences for these workers is unclear, but human rights advocates see them as vulnerable to harm and economic exploitation.[iv] Plant workers are particularly vulnerable to harm and exploitation because they are not TEPCO’s direct employees, but rather are hired by subcontracting companies. The subcontractors are the agents responsible for the workers’ safety and for monitoring their health.[v] Workers interviewed by the Japanese media have described ubiquitous lack of safety features at the plant, including adequate protection for incoming workers.[vi]
[i] Y. Oiwa (1 December 2012) ‘High Thyroid Radiation Doses in 178 Fukushima Workers’, The Asahi Shimbun, http://ajw.asahi.com/article/0311disaster/life_and_death/AJ201212010050, date accessed 7 December 2012.
[ii] Hiromi Kumia, “Nuclear watchdog proposes raising maximum radiation dose to 250 millisieverts,” The Asahi Shimbun (July 31, 2015) http://ajw.asahi.com/article/0311disaster/fukushima/AJ201507310057.
[iii] Gov't to raise maximum annual radiation exposure ahead of restart of nuclear reactors,” The Mainichi (june 30, 2015),
[iv] M. Aoki and T. Tada (9 December 2012) ‘Worker Wants New Government to Secure Safety at Fukushima Plant’, The Asahi Shimbun, http://ajw.asahi.com/article/0311disaster/fukushima/AJ201212090052, date accessed 10 December 2012.
[v] Working Conditions at Fukushima Daiichi, NHK (Jul. 16, 2014) http://www3.nhk.or.jp/nhkworld/english/news/nuclearwatch/20140716.html
[vi] “Researchers to study long-term effects of radiation on Fukushima workers,” The Mainichi (March 14, 2015), http://mainichi.jp/english/english/features/news/20150314p2a00m0na011000c.html