Taku Arai

Effects of Cold Work, Sensitization Treatment, and the Combination on Corrosion Behavior of Stainless Steels in Nitric Acid

Abstract Corrosion behavior of two stainless steels (SS) was investigated in nitric acid (HNO3) for the effect of cold work (CW), sensitization heat treatment (Sens.), and a combination (CW + Sens.). The corrosion rate of the solution-treated type 304 SS (UNS S30400) with extra-low carbon (type 304ELC SS [UNS S30403]) increased with time and reached constant values after 1,000 h of immersion. However, constant corrosion rates were obtained for 25% Cr-20% Ni-Nb (type 310Nb SS [UNS S31040]) from the initial stage of immersion. CW mitigated corrosion of the solution-treated SS. The effect of CW was different on the two types of SS, with the sensitization heat-treated type 304ELC SS showing higher corrosion rates and type 310Nb SS lower corrosion rates by CW. Corrosion resistance of type 310Nb SS was superior to type 304ELC SS after all treatments. Chromium concentration of the sensitization-treated type 304ELC SS was lower in the grain-boundary region than of the solution-treated one, although no chromium ca...

Applicability of Master Curve Method to Japanese Reactor Pressure Vessel Steels

The Master Curve method has been proposed and recognized worldwide as an alternative approach to evaluate fracture toughness of reactor pressure vessel (RPV) steels in brittle-to-ductile transition temperature range. This method theoretically provides the confidence levels of fracture toughness in consideration of the statistical distribution, which is an inherent property of fracture toughness. In this study, a series of fracture toughness tests was conducted for typical Japanese RPV steels, SFVQ1A and SQV2A, to identify the effects of test temperature, specimen size, and loading rate, and the applicability of the Master Curve method was experimentally validated. The differences in test temperature and specimen size did not affect master curves. In contrast, increasing loading rate significantly shifted master curves to higher temperatures. The lower bound curve based on the master curve could conservatively envelop all of the experimental fracture toughness data. The present rule, in which the lower limit of fracture toughness is indirectly determined by Charpy impact test results, can be too conservative, while the application of the Master Curve method may significantly reduce the conservativity of the allowable level of fracture toughness.Copyright

Effect of Neutron Irradiation on Stress Corrosion Cracking of Sensitized Type 304 Stainless Steel in High-Temperature Water

Abstract An in-core constant load test was carried out to examine the effect of pre-irradiation on the intergranular stress corrosion cracking (IGSCC) behavior of thermally sensitized Type 304 stainless steel ([SS] UNS S30400) in a simulated boiling water reactor (BWR) water environment. It was shown that, in constant load tests, preirradiated, thermally sensitized Type 304 SS had a lower IGSCC susceptibility, a larger time to failure, than unirradiated, thermally sensitized SS for a given stress level. An out-of-core constant load test and interrupt slow strain rate tensile (SSRT) tests also were carried out to discuss the in-core test result on unirradiated, thermally sensitized Type 304 SS, simulating radiation hardening by work hardening. The out-of-core tests, with surface observations, suggested that an increase in proof strength by neutron irradiation would be the main cause of the lower IGSCC susceptibility of the preirradiated Type 304 SS, since the increase in proof strength would prevent a form...

Recent Development of Code Case on Use of Ductile Cast Iron for Transport and Storage Cask for Spent Nuclear Fuel

Code Case N-670 “Use of Ductile Cast Iron Conforming to ASTM A874/A 874M-98 or JIS G5504-1992 for Transport Containments, Section III, Division 3” which permits use of ductile cast iron for transport containments of spent nuclear fuel was revised to the Code Case N-670-1, “Use of Ductile Cast Iron Conforming to ASTM A874/A 874M-98 or JIS G5504-2005 for Transport and Storage Containments, Section III, Division 3”. Items revised were as follows: (a) Scope was expanded to use for transport and storage, and changed to conform year edition of JIS G5504, (b) The elongation requirement was deleted form the code case to reflect the change of year edition of JIS G5504, (c) Temperature condition of −40 °C was clearly provided for fracture toughness test, (d) Design fatigue curve was re-established, (e) External pressure chart was re-established. Technical basis of the revised code case are described in this paper.Copyright

Fracture Toughness of Ductile Cast Iron and Applicability of Fracture Mechanics to DCI Casks

The JSME Cask Code, Rules for Construction of Metallic Casks, has a scope of using three types of casks fabricated by stainless steels, forged low alloy steels and ductile cast irons (DCI). On the other hand, the use of DCI for Cask material is not within the scope of the ASME Code, Section III, Division 3. In this paper, the fracture toughness of DCI for JSME cask code was compared with those of quenched and tempered low alloy steels. Furthermore, applicability of fracture mechanics to DCI casks is demonstrated by the results of fracture tests of reduced scale model casks. The results deny criticism arising from the fact that the DCI is not homogeneous material due to precipitation of spheroidal graphite particles for the application of the fracture mechanics.Copyright