With due caution because the main source is the Japanese government (whose credibility is below zero and may have reasons to let the shit hit the fan in order to dilute their own nuclear responsibility) I must mention that Tokyo (and Seoul?) accuse China of having suffered a radioactive accident at the experimental fast reactor (CEFR), located near Beijing.
China denies it.
The accident would have happened in October last year. Since early November radioactive iodine was detected over Europe and the exact cause was never pinpointed. I wonder if this may be it.
Main source: EneNews.