I find this resource very useful - Japan Travel Update (As of 2 October) - JNTO Singapore Office
According to Japan tourism board:
Does a visit to Japan impede pregnancy or affect reproduction function? No. Risks of permanent infertility must only be considered if a person is exposed to very high levels of radiation (3,500~6,000 mSv per year for testis, versus 2,500~6,000 mSv per year for ovaries). A person is unlikely to be exposed to the radiation level exceeding 20 mSv per year even if he/she spends an entire year in Japan, unless he/she enters the access-restricted areas mentioned above.