In the assessment of radionuclide migration underground, the Ca/Si ratio of calcium silicate hydrate (C–S–H) gel formed as a secondary mineral is a key factor, because the sorption behavior of cationic nuclides such as cesium on the C–S–H gel depends on the Ca/Si ratio. In addition, this Ca/Si ratio of the C–S–H gel is changed by the formation of various compounds upon the reaction of Ca ions leaching from the C–S–H gel with coexisting anions. In this study, the effect of sulfate ions (up to 500 mM) on the sorption of Cs ions onto the C–S–H gel (Ca/Si ratios of 0.4, 0.8, 1.2 and 1.6) was examined and compared with that of carbonate ions. The obtained results show that the sorption ratio of Cs ions on the C–S–H gel slightly decreased with the increase in the concentration of sulfate ions under any Ca/Si ratio and that the effect of the copresence of sulfate ions on the decrease in the Ca/Si ratio of the C–S–H gel was extremely small compared with that of carbonate ions. That is, the C–S–H gel formed as a secondary mineral contributed to the retardation of the migration of Cs ions, even though the plume containing a high concentration of sulfate ions flowed around the repository.

 To analyze the radioactive wastes produced by the accident at the Fukushima Daiichi Nuclear Power Plant, we have been developing a laser absorption and emission spectroscopic system for sample screening. By the sputtering technique, neutral atomic vapor can be produced from a solid sample even if the chemical forms of the samples are complex. This system utilizes a DC glow-discharged hollow cathode atomic source that does not require an extensive chemical pretreatment. Although it is possible to perform emission spectroscopy for multi-element simultaneous analysis to clarify the elements of samples with this system, it takes much time to assign complex peaks of the samples. A program was developed for the rapid assignment of the emission spectra. We utilized a Czerny–Turner spectrometer, which has a low resolution power. The program written in Python could assign the large emission peaks because of the ease of signal discrimination.

 In the long-term energy supply and demand outlook, the energy mix has become a global trend, and nuclear power plants (NPPs) are required to maintain a certain power ratio over a long period in Japan. Under such circumstances and with the energy mix, the long-term operation (LTO) of existing NPPs is attracting attention. LTO requires proper management during the operation period of the NPP, including decommissioning; this is plant life management (PLM). In this study, we will take up PLM, which is an activity performed to realize LTO, give an overview of the current situation in Japan, and present performance indicators to measure its effectiveness. As a result, it becomes clear that a continuous improvement can be observed by adding a time axis to the form of knowledge that has been considered thus far. Furthermore, regarding the reduction in the number of accidental failures, which is the remaining issue related to physical deterioration, technical and organizational aspects will be discussed as countermeasures, and solutions will be presented along with a systematic diagram of knowledge management.

 We have developed a new pressure transmitter that reduces the signal drift effect for nuclear power plants. The drift is caused by hydrogen permeation and the radiolysis of silicone oil. The proposed method uses palladium, a hydrogen absorbing material, to suppress the drift due to hydrogen accumulation. The drift suppression and measurement performance of the pressure transmitter with Pd installed inside was evaluated. The experimental results in an environment equivalent to an actual plant operated for 10 years indicate that the amount of drift in the pressure transmitter with Pd was below the detection limit (＋0.01 kPa). The maximum error in the input/output characteristics was 0.16％, the error due to vibration was within ±0.1％, and the step response was 1.1 s or less. In the experiment of this research, it was confirmed that all relevant values were within those of the target performance.

 The purpose of this comment is to clarify the whole history of reactor and containment pressure change during the Fukushima meltdown accident. It is based on a new approach for film boiling, which is sustained after the Zr–H₂O reaction. As the reaction rate is proportional to the reactor or containment vessel pressure under film boiling, it increases rapidly and stops abruptly while sustaining film boiling. The containment vessel pressure change consists of three phases, namely, pressurization, holding a high pressure and depressurization. The containment vessel is pressurized with H₂ gas and steam produced by the Zr–H₂O reaction and depressurized by heat removal by heatsinks such as the containment vessel wall and inner concrete after the reaction stops. The high pressure between these pressure changes is sustained by balancing the amount of H₂ gas produced by the reaction and that of gas leaking from the gap of the top hat of the containment vessel. The amount of core decay heat is large, but the change of this is negligible. Thus, pressurization is calculated from the amounts of H₂ gas and steam produced by the Zr–H₂O reaction. The amount removed by the heatsink balances with that produced by the reaction during the high-pressure phase. Depressurization occurs after the reaction is over, so the reaction heat rate can be calculated from the heat removal rate of the heatsink, which is equal to the condensation rate during depressurization. The rate of gas leakage can be calculated from the reaction rate. It is very important that the reaction rate was slow owing to the insufficient steam supply, as the melted core in the Fukushima accident was covered with H₂ gas and steam at a pressure of 0.8 MPa or lower. This is different from the rate (at approximately 7 MPa) in the Three Mile Island accident, as the specific volume of steam at 0.8 MPa is ten times larger than that at 7 MPa. The calculation results based on this assumption show that almost all the Zr in each core of Units 1, 2 and 3 reacted with water. The location of a small penetration hole produced by the contact of the high-temperature H₂ gas with the suppression chamber wall, is estimated in Unit 2.