Evaluation Procedures for Irradiation Effects and Sodium Environmental Effects for the Structural Design of Japanese Fast Breeder Reactors

Abstract

In the structural design of fast breeder reactors, irradiation effects and sodium environmental effects on structural materials have to be taken into account. In this paper, firstly, an evaluation procedure for irradiation effects on the mechanical properties of 316FR (FBR Grade 316 stainless steel), which is a newly developed stainless steel for the Japanese demonstration fast breeder reactor, is proposed. The procedure gives a limit of accumulated fast neutron fluence E>0.1 MeV as a function of temperature, so that the minimum tensile fracture elongation of 10 percent, which is the threshold for material to stay ductile, is maintained. Furthermore, the procedure determined a creep life reduction factor and a creep rate increase factor as a function of accumulated thermal neutron fluence E<0.4 eV, within the limitation of the accumulated fast neutron fluence, to account for the creep life reduction and the increase of creep rate due to irradiation. Secondly, an evaluation procedure for sodium environmental effects on the integrity of 316FR and modified 9Cr-1Mo steel was proposed. It gave a corrosion allowance as a function of temperature, oxygen content, and service time, based on corrosion tests. It determined that no correction factors that correspond to sodium environment on design allowable stresses, etc., are needed, because no adverse effects of sodium on the mechanical properties of 316FR and modified 9Cr-1Mo steel were to be expected in the service conditions of FBRs. Both the procedures have been incorporated into the Japanese Elevated Temperature Structural Design Guide for Demonstration Fast Breeder Reactor.

Code qualification of structural materials for AFCI advanced recycling reactors.

“…Furukawa et al (1998) reported tensile data on 316FR pre-exposed to sodium, and creep, fatigue, and creep-fatigue results on 316FR in flowing sodium. It was found that tensile properties of 316FR were not affected by sodium exposure at 500-550°C for 5000 h. Creep rupture tests conducted at 550-600°C in September 15, 2008 60 flowing sodium at the oxygen level of 1 ppm showed that creep rupture strength in sodium was slightly lower than that in air with predominant surface grain boundary cracking when the rupture time was between 1000 and 10,000 h; at the lower stress level and longer rupture time, sodium exposure had no influence on the creep rupture strength of 316FR, as shown in Figure 4.59 (Asayama et al 2001). …”

“…316LN-IG has higher allowable stresses than typical 316LN due to an optimal combination of the alloying elements such as carbon, nitrogen, nickel, chromium, manganese and molybdenum, with a tight specification of their allowable composition range. A comprehensive database has been established on 316LN-IG, including heat-to-heat variations, the effect of product size, fracture toughness, effects of neutron irradiation, etc., and the data can be found in the ITER Materials Properties Handbook ( The chemical compositions of 316LN, 316LN-IG, and 316FR stainless steels are given in Table 4-11 (Asayama 2001, Tavassoli 1995, Brinkman 2001. Significant data base of tensile, creep, fatigue and creep-fatigue properties of 316FR and 316LN base metal and weld metal can be found in the RCC-MR, ITER MPH and open literature.…”

“…Studies on the effects of sodium exposure have been done primarily on 316FR by the Japanese fast reactor program (Asayama et al 2001). They discussed the material degradation issues in sodium environment and the evaluation procedures to account for the sodium effects.…”

“…The emphasis of the 316LN-IG research was placed on the lower irradiation temperature behavior due to the low operating temperature (≤300°C) of 316LN-IG in the ITER components (Tavassoli 1995). Limited data of neutron-irradiated Japanese 316FR can be found in the open literature (Miyaji et al 1999, Asayama et al 2001). Tavassoli (1995) summarized the irradiation effects on tensile properties of 316LN-IG.…”

“…Similar effects of neutron irradiation on tensile properties were observed in the weld metal. Since the yield stress and the ultimate tensile strength are not degraded by neutron irradiation, no design factors are necessary (Asayama et al 2001).…”