Teruo Furuta

Reaction behavior of zircaloy-4 in steam-hydrogen mixtures at high temperature

Abstract Examinations have been conducted in steam-hydrogen mixtures comprising various hydrogen volume fractions, at temperatures ranging from 1223 to 1373 K, to determine the reaction behavior at the inside surface of burst cladding during a LOCA transient. Oxides and ductility of reacted Zircaloy-4 tubes were examined to identify hydrogen absorption. The total weight gain varies with hydrogen volume fraction, and sharply decreases at a critical level of the hydrogen fraction, depending on temperature and steam flow rate. Dense and porous oxides form on the metal at hydrogen fractions below and above the critical level, respectively. Hydrogen absorption accompanying the appearance of porous oxide comprising monoclinic and tetragonal phases occurs above the critical level, and causes the reduction in ductility. The reaction in the mixture can well interpret the behaviour at the inside surface of burst cladding.

The influence of helium distribution and grain size on high-temperature embrittlement of stainless steel

Abstract In order to study the high-temperature embrittlement related to helium from the viewpoint of the distribution of helium and the grain size, helium ( 7.5 × 10 −6 atomic fraction) was injected into stainless steel treated in various ways, using a cyclotron. Helium retarded the tendency towards recrystallization of stainless steel, and the grain size of the specimen recrystallized after injection was clearly smaller. The high-temperature embrittlement related to helium in stainless steel was appreciable above 650°C, and could be classified in terms of the mean grain diameter and the distribution of helium.

The effect of cold working on creep rupture properties for helium-injected austenitic stainless steel

Abstract In order to study the effect of helium on the high temperature embrittlement of stainless steel, helium (7.5 × 10 −6 atomic fraction) was injected into cold-worked stainless steels by using a cyclotron. At 650°C, it appeared that the reduction in creep-rupture strength due to helium was larger as cold-working was increased, but a loss of rupture elongation was less for a particular degree of cold-working. The 10% cold-worked material showed particularly good creep-rupture properties in the presence of helium. The loss of ductility was more pronounced in the creep test than in the tensile test.

Effect of Burst Temperature on Coolant Channel Restriction in Multirods Burst Tests

In order to study the effect of burst temperature on the coolant flow channel restriction, burst tests of fuel bundles were performed. Each bundle consisted of 49 rods (7×7 rods), and bursts were conducted in flowing steam. Burst temperature was changed by changing the internal gas pressure in rods. After the burst, the ballooning behavior of each rod and the degree of coolant flow area restriction in the bundle were measured. Maximum swelling of rod occurs when the burst temperature is around α and α+β phase boundary, and this phenomenon is almost the same as that in single rod burst tests. Maximum coolant flow area restriction is also observed in this condition.

Improvement of Creep Properties in a Helium Injected Austenitic Stainless Steel

The effect of helium on creep properties was studied in AISI Type 316 austenitic steels after two kinds of treatment, namely, cold rolling and grain-boundary strengthening. Helium was injected into the specimens using a cyclotron, and the creep-rupture tests were performed at 650°C in air. In the cold-rolled specimens, the creep-rupture strengths increased with cold working. The loss of ductility due to the helium injection was minimum at about 10 percent of cold rolling. In the grain-boundary strengthened treatment, serrated grain boundaries were produced by the two step solution treatment. The specimens with serrated grain boundaries had good creep-rupture strength in both the presence or absence of helium. However, a specimen with extreme grain growth during the two step solution treatment had low creep ductility and severe helium embrittlement. A specimen which had serrated grain boundaries without extreme grain growth had excellent creep properties in both helium uninjected and injected cases.