Evaluation Study on Mod 9Cr-1Mo Steel Tube Integrities of Once-Through Type Steam Generator

Abstract

Mod.9Cr-1Mo steel is expected to be suitable tube material for FBR Demonstration Reactor Steam Generator (DFBR SG), which is a once-through type SG, due to its excellent property of strength particularly at elevated temperature. This R and D program has been performed to study the feasibility of application of Mod.9Cr-1Mo steel to that tube. This program is divided as follows: (1) 5000 hr. endurance tests during cycle thermal transients; (2) hydraulic stability test; (3) tube/tube-support year tests. For item (1) tests, three SG units were manufactured and subjected to 5000 hr. endurance tests during cyclic thermal transients (which simulate DFBR SG heat hystereses). These tests were performed according to our expectations and the whole operations went quite well. As the result of material testing after completion of the experiments, it was found that the parent material and weld joint of Mod.9Cr-1Mo steel had almost the strength of virgin material and didn't show much change of hardness. For item (2) test, hydraulic stability was noticed specially at high superheat temperature. Applicability of the evaluation method usually utilized to the prototype reactor plants was investigated, and it was concluded that it was applicable to DFBR SG too. For item (3) tests, tube/tube-support wear was investigated using SUS 304 steel and Inconel 718 steel as tube support. Inconel 718 steel tube support showed good wear characteristic. This study has been performed as a collaboration between the Japan Atomic Power Company (JAPC) and Power Reactor and Nuclear Fuel Development Corporation (PNC). The JAPC's study has-been performed as a part of joint research and development projects for DFBR under sponsorship of the nine Japanese electric power companies, Electric Power Development Co. and JAPC.