In the aftermath of the Fukushima nuclear accident, many of the post-disaster responses undertaken by the Japanese government sparked vivid debates and criticisms from the civil society. These concern emergency responses such as the revision of public exposure dose limit, designation of evacuation zones, distribution of iodine tablets, and risk communication as well as mid and long-term policies including radiation dose monitoring, decontamination, waste management, return of evacuees, and health and food monitoring. Convinced that such public agitation derived from their lack of scientific knowledge, the authorities undertook a strategy to enhance their communication on radiological risk and its health effects. In this paper, we attempt to challenge the traditional notion of “risk communication” which considers that the concerned risks have been clearly defined by the scientific community and that the problem simply remains in communicating them “rightly” to the population. We argue, in contrary, that risks cannot be properly defined without understanding the “real” concern of the population – what they consider as risks - nor taking into account existing scientific controversies and uncertainties. In such a context, what we need is not so much of risk communication but rather participatory risk assessment where risks are debated by multiple stakeholders and actors including counter- or independent experts and third parties such as NPOs, and are defined collectively rather than decided single-handedly by policymakers – the authorities and their affiliated experts. The paper is drawn from the preliminary results of the SHINRAI (‘trust’ in Japanese) project led by the French Institute for Radiological Protection and Nuclear Safety (IRSN), in collaboration with Sciences Po Paris and Tokyo Institute of Technology (Tokyo Tech). This research examines the relation between science, expertise, trust and decisions in the aftermath of the Fukushima nuclear accident by conducting an extensive field interviews in the affected areas of the Fukushima prefecture.