[en] Since the operator's mission in NPPs is increasingly defined by cognitive tasks such as monitoring, diagnosis and planning, the focus of human error analysis should also move from external actions to internal decision-making processes. While more elaborate analysis of cognitive aspects of human errors will help understand their causes and derive effective countermeasures, a lack of framework and an arbitrary resolution of description may hamper the effectiveness of such analysis. This paper presents new model-based schemes of event description and error classification as well as an interactive computerized support system. The schemes and the support system were produced in an effort to develop an improved version of HPES. The use of a decision-making model enables the analyst to document cognitive aspects of human performance explicitly and in a proper resolution. The stage-specific terms used in the proposed schemes make the task of characterizing human errors easier and confident for field analysts. The support system was designed to help the analyst achieve a contextually well-integrated analysis throughout the different parts of HPES

[en] Dry storage of spent fuel rods is being considered as an alternative to the interim storage method until a final decision on their final disposal is made. Most studies on the integrity of spent fuel rods in dry storage have focused on cladding creep, which is known to be the most likely failure mechanism, and reorientation of hydrides to secure their retrievability after dry storage. Little attention has been paid to delayed hydride cracking (DHC) because this phenomenon will not occur due to limited stresses and slow diffusion of hydrogen at low temperatures below 200 .deg. C. However, Simpson and Ells reported a failure of unirradiated Zr-2.5Nb fuel rods after their long-term storage at room temperature, the cause of which was recognized to be DHC. Therefore, it is clear that in contrast to what is believed to be that no DHC occurs in the spent fuel rods in dry storage, they would fail as long as stress raisers such as surface flaws or the weld region are present inside the cladding tube. Especially, high burnup fuel rods may have incipient cracks on the inside cladding surface due to an interaction of the fuel and the cladding during reactor operation

[en] Delayed hydride cracking (DHC) velocity of Zr- 2.5Nb pressure tubes is one of the material testing items for pressure tube surveillance to be examined regularly. Thus, it is required to establish a model to accurately predict the DHC velocity with operating conditions. According to our new DHC model called Kim's model, the DHC velocity is governed by the supersaturated hydrogen concentration above the heating solvus or the terminal solid solubility for dissolution of hydrogen (TSSD) or ΔC at the test temperature. However, by arguing that the DHC velocity increased with increasing hydrogen concentration dissolved in the bulk, not the ΔC, Shek pointed out that Kim's model is invalid. The aim of this work is to show the validity of Kim's model by checking if the DHC velocity of the Zr-2.5Nb tube is governed either by total hydrogen concentration dissolved in the bulk as suggested by Shek or by the ΔC as shown in Kim's DHC model

[en] Austenitic stainless steels used for PWR core internal components degrade in the environment of radiation and high temperature water during their long-term service. As they suffer from intergranular cracking at the neutron fluence over the critical value, this degradation mechanism termed irradiation assisted stress corrosion cracking (IASCC) is one of the hot issues in light water reactor (LWR) industry to aim at pursuing license renewal of commercial reactors. Much attention has been paid to an understanding of the IASCC mechanism, which is yet to be achieved. IASCC appears to be very similar to intergranular stress corrosion cracking (IGSCC) in view of intergranular cracking but the former differs from the latter because the former can occur even without corrosion. Consequently, intergranular cracking of IASCC should be taken into account from mechanistic view points. The aim of this study is to analyze the IASCC susceptibility of austenitic stainless steels in view of material compositions and the environment, and hence to guide research directions to take in order to elucidate the IASCC mechanism

[en] The dipole cutoff behavior for the proton form factor has been and still is one of the major issues in high-energy physics. It is shown that this dipole behavior comes from the coherence between the Lorentz contraction of the proton size and the decreasing wavelength of the incoming photon signal. The contraction rates are the same for both cases. This form of coherence is studied also in the momentum–energy space. The coherence effect in this space can be explained in terms of two overlapping wave functions. (paper)

[en] We investigated the biodistribution, radiolocalization, and radioimmunotherapeutic potential of ¹³¹I-labeled Nd2 in athymic nude mice bearing human pancreatic carcinoma xenografts. ¹³¹I-Nd2 was accumulated at high levels in the tumor, in contrast to blood, liver, spleen, and other normal organs. The tumor was clearly delineated in scintigraphs. The volumes of tumors of mice injected with 7.4 MBq of ¹³¹I-Nd2 were 80% less than those of tumors before injection of radiolabeled Nd2. Fibrous or vacuolar degeneration was seen in histological sections of tumors of 7-week-treated mice. The growth of tumors in mice treated with misonidazole, a hypoxic cell radiosensitizer, and then injected twice with 3.7 MBq of ¹³¹I-Nd2 was suppressed over 7 weeks. Neither leucocytopenia nor thrombocytopenia was severe after injection of radiolabeled Nd2. Thus ¹³¹I-labeled Nd2 may have clinical application in the radioimmunotherapy of pancreatic cancer. (author)

[en] Research highlights: → This study shows first that temperature and yield stress dependences of crack growth rate in zirconium alloys can analytically be understood not by the Dutton-Puls model but by Kim's new DHC model. → It is demonstrated that the driving force for DHC is ΔC, not the stress gradient, which is the core of Kim's DHC model. → The Dutton-Puls model reveals the invalidity of Puls' claim that the crack tip solubility would increase to the cooling solvus. - Abstract: This work was prompted by the publication of Puls's recent papers claiming that the Dutton-Puls model is valid enough to explain the stress and temperature dependences of the crack growth rate (CGR) in zirconium alloys. The first version of the Dutton-Puls model shows that the CGR has positive dependences on the concentration difference ΔC, hydrogen diffusivity D_H, and the yield strength, and a negative dependence on the applied stress intensity factor K_I, which is one of its critical defects. Thus, the Dutton-Puls model claiming that the temperature dependence of CGR is determined by D_HC_H turns out to be incorrect. Given that ΔC is independent of the stress, it is evident that the driving force for DHC is ΔC, not the stress gradient, corroborating the validity of Kim's model. Furthermore, the predicted activation energy for CGR in a cold-worked Zr-2.5Nb tube disagrees with the measured one for the Zr-2.5Nb tube, showing that the Dutton-Puls model is too defective to explain the temperature dependence of CGR. It is demonstrated that the revised Dutton-Puls model also cannot explain the yield stress dependence of CGR.

[en] The aim of this work is a second reply to Puls's comments on the author's first reply to the paper published in J. Nucl. Mater. 393 (2009) 350-367. The Dutton-Puls model indicates that the CGR is governed not by the stress gradient but by the ΔC that results from a decrease in the crack tip solubility due to the stress when compared to the bulk solubility, demonstrating that Puls's defense of the Dutton-Puls model is inconsistent and invalid. Given the fact that DHC involves three consecutive processes such as nucleation, growth and cracking of hydrides at the crack tip, Puls's claim that DHC is simply a diffusion-controlled process and the CGR is governed solely by the rate of hydride growth is incorrect, yielding many of the unsolved issues related to DHC. It is confirmed that Kim's criticism that the Dutton-Puls model for the crack growth rate (CGR) is established based on a faulty thermodynamic basis is correct.

[en] Crack growth rates (CGR's) were determined under sustained and cyclic loads using 17 mm compact tension and cantilever beam specimens taken from Zr-2.5Nb tubes with 6 to 100 ppm H. Under sustained loads, the CGR of the Zr-2.5Nb tubes increased with increasing supersaturation of hydrogen, ΔC and leveled off above 20 to 25 ppm H of the ΔC. Under cyclic loads with 1 cycle/min, the CGR at 250 deg. C decreased with decreasing R. In contrast, striation spacing, corresponding to the critical hydride length, decreased with decreasing R, indicating easier cracking of the hydrides under cyclic loads. It is demonstrated that the governing factor for the CGR under the decreased ΔC and cyclic loads is the hydride nucleation rate which becomes slower than the rates of growth and cracking of hydrides. (authors)

[en] Crack growth rates (CGR's) were determined under sustained and cyclic loads using 17 mm compact tension and cantilever beam specimens taken from Zr-2.5Nb tubes charged to 6-100 ppm H. The cyclic load effect on the CGR was investigated at 250 deg. C where load ratios, R were varied from 0.13 to 1 with a constant K_max. Under sustained loads, the CGR of the Zr-2.5Nb tube increased with supersaturation of hydrogen, ΔC and leveled off above 20-35 ppm H of the ΔC. Under cyclic loads with 1 cycle/min, the CGR at 250 deg. C decreased with decreasing R: 3.2 x 10^-8 m/s at R = 1 and 4.8 x 10^-9 m/s at R = 0.13. The striation spacing, corresponding to the critical hydride length, decreased with decreasing R, indicating easier cracking of the hydrides under cyclic loads. The decreased CGR under cyclic loads and its dependence on the ΔC are discussed using Kim's delayed hydride cracking model.