Utsunomiya stresses that "FDNPP decommissioning, and specifically fuel debris removal must be planned so that the extensive fission reactions do not occur. Gareth Law, a co-author from the University of Helsinki emphasized that this "is a tiny fraction of the reactor's overall boron inventory, and this may mean that essentially all of the control rod boron remains inside the reactors." The team hopes that this should prevent excessive fission reactions in the fuel debris. From this, they have been able to estimate the total amount of boron released from the FDNPP reactors was likely very small: 0.024-62 g. In the study the team also combined their new data with past knowledge on CsMP emissions. Dr Utsunomiya states that the presence of boron in the CsMPs "provides direct evidence of volatilization of the control rods, indicating that they were severely damaged during the meltdowns."Īmple boron likely remains in the reactors, but more research is needed The team's new results on boron-11/boron-10 isotopic ratios (~4.2) clearly indicate that most of the boron inside the CsMPs is derived from the FDNPP control rods and not from other sources (e.g., boron from the seawater that was used to cool the reactors).
![inside nuclear reactor meltdown inside nuclear reactor meltdown](https://media.sciencephoto.com/image/t1700394/800wm/T1700394-Nuclear_reactor_core_during_charging.jpg)
These microscopic particles were then emitted into the environment, and the particles hold vital clues about the extent and types of meltdown processes. CsMPs formed inside FDNPP reactor units 2 and/or 3 during the meltdowns. Using electron microscopy and secondary ion mass spectrometry (SIMS), the team has been able to report the first-ever measurements of boron and lithium chemistry from radioactive Cs-rich microparticles (CsMPs). Satoshi Utsunomiya and graduate student Kazuki Fueda of Kyushu University led the study. The study was an international effort involving scientists from Japan, Finland, France, and the USA. However, work just published in the Journal of Hazardous Materials now provides vital evidence that indicates that most of the control rod boron remains in at least two of the damaged FDNPP reactors (Units 2 and/or 3). Study shows direct evidence of volatilization of control rods during the accident.ĭespite the importance of this topic, the state and stability of the FDNPP control rod material has remained unknown until now. Many important questions remain: was boron from the control rods lost at high temperature during the meltdown? If so, does enough boron remain in the fuel debris to limit successive fission reactions within this material? These questions must be answered to support safe decommissioning. Currently, the fuel debris material from each reactor is cooled and stable however, careful assessment of these materials, including not only their inventories of radioactive elements but as well their boron content, a neutron absorber, is needed to ascertain if successive fission reactions and associated neutron flux could occur in the fuel debris during its removal. Fuel temperatures soon became high enough (>2000 ☌) to cause reactor meltdowns. On March 11th 2011, the control rods were inserted into the FDNPP reactors to stop the fission reactions immediately after the earthquake, but the later tsunami destroyed the reactor cooling systems. If so, it may limit fission events within the fuel debris. This was used as the control rod material in the FDNPP reactors, and it may now remain within the fuel debris. One of the materials in nuclear reactors that can lower the number of neutrons interacting with uranium-235 is boron carbide (B 4C).