[en] In a fuel assembly, one water rod of a very large diameter is disposed at the center and an upper tie plate is disposed at the upper portion thereof. The water rod comprises an upper water rod and a lower water rod. The upper tie plate integrated type neutron absorber has a rod like shape having an outer diameter that can be inserted into the water rod, and comprises a neutron absorbers made of boron or the like and an upper tie plate. A spent fuel assembly after burning is removed by pulling up the upper tie plate and the upper water rod integrally. Subsequently, the upper tie plate integrated type neutron absorber is inserted and secured in the lower water rod of spent fuel assembly. With such procedures, critical safety of the spent fuel assembly storage system can be improved easily. Accordingly, storage and transportation efficiencies for the spent fuel assembly can be improved and neutron exposure can be reduced. (I.N.)

[en] A blade of a control rod for a BWR type reactor is formed into a box-like shape. A hollow box-like blade is constituted by putting a water gap between a support spacer and a (n, γ) reaction-type neutron absorber containing a hafnium metal, and water permeable holes are formed to the upper portion. Reactor water is boiled by γ heat generation of neutron absorber in the water gap during reactor operation. The water permeable hole is determined to such a size as keeping steams in the blade but releasing them so as not to increase the inner pressure. Reactor water intrudes into the blade through the water permeable holes during stoppage of the reactor. With such a constitution, a reactivity worth is automatically reduced during reactor operation, and the reactivity worth is automatically increased upon stoppage of the reactor. Accordingly, a blade history effect can be moderated with no disadvantage for the critical safety. (I.N.)

[en] In a method of evaluating a service life of control rods in a BWR type reactor, a not-irradiated control rod is used as a standard control rod, and a calibration curve is determined based on a measured value for a neutron transmission rate, a burning dependent transmission rate and burning dependent reactivity of the not-irradiated control rods. Reactivity of an irradiated control rod is evaluated based on the measured value for the neutron transmission rate and the calibration curve, to determine the extent of the depletion of the evaluation value of the reactivity from the reactivity upon no-irradiation, thereby evaluating the degree of the nuclear service life of the irradiated control rods approaching to a limited predetermined value. Even for a control rod using neutron absorbers of complicate nuclear property different from a B₄C control rod comprising only ¹⁰B, the nuclear service life can be evaluated by measurement and analysis. (N.H.)

[en] We conducted cyber security risk assessment for the Rokkasho Reprocessing Plant using attack scenario-based approach. Assessment performed last year showed an underestimate of risk from internal threats in some attack scenarios such as malware infection and log alteration, because checklists used to evaluate attack possibilities, which were provided by the risk assessment package, mainly assumed external threats. In order to consider contribution from internal threats, we modified some criteria for checklists. We reevaluated the assessment with the modified criteria this year, and confirmed that internal threats were appropriately taken into account. (author)

[en] We conducted a feasibility study on intrusion detection systems as a cyber-security measure for an industrial control systems network. Intrusion detection systems can detect network connections of malicious terminals and network communication by malicious programs such as computer viruses. We made a comparison with three detection methods and three detection algorithms on control systems availability, detecting functions, ease of deployment and operability. We selected the port mirroring method with machine learning algorithm through the comparison. We introduced an intrusion detection system with the selected method / algorithm on a trial basis to the actual control systems network and verified the functionality. (author)