Construction of the HTTR In-Core Components

摘要

The reactor internals of HTTR consist of graphite and metallic core support structures and shielding blocks and are designed to support core elements and to shield neutron fluence. They also have functions to restrict by-pass flow for ensuring the core cooling performance and to maintain the temperature of metallic core support structures within their design limits.rnThe detailed design of the HTTR core support structure was approved by the government through safety review, 1990-1991. Machining of all graphite components, which consist of about 150 large blocks, was finished in September 1994 successfully. Machining and fabricating of the metallic components were also finished in September.rnPrior to their installation in the reactor pressure vessel (RPV), the assembly test of actual reactor internals was performed at the works to confirm above mentioned functions. The assembly test was conducted by examining fabricating precision of each component and alignment of piled-up structures, measuring circumferential coolant velocity profile in the passage between the RPV and reactor internals as well as under the core support plates with respect to structural integrity, and measuring by-pass f low rate through gaps between graphi te components which may degrade core performance. The another purpose of the assembly test was to confirm the installation procedure of those components.rnAll components were assembled at the works according to the planned procedure, and the tests were executed while assembl ing. As a result of the tests, measured level difference and gap width between reactor internals were negligible from core thermal and hydraulic performance point of view. Coolant flows uniformly in circumferential direction at any axial level in the RPV. By-pass flow rate was found to be suppressed sufficiently and far less than the design limit.rnThe assembly test was also conducted for the core restraint mechanism(CRM). The CRM is placed periphery of every layer of permanent reflector blocks(PRBs) to push them inward for restricting by-pass flow between PRBs. Binding force of the CRM should be set so as to keep stresses in PRBs and CRM within their stress limit duringrnnot only normal operation but also transient condition. The peripheral distribution of binding force was measured to confirm that binding force was well adjusted at designed value and distributed uniformly.rnAfter completion of the assembly test at the works, all components were disassembled and government inspection of those components was carried out. Installation of the reactor internals in the RPV was started at the construction site of HTTR in April 1995. Installation was proceeded with the procedure confirmed at the works. And in the installation process, main items of the assembly test at the works were conducted to investigate the reproducibility of assembling. The test results were equivalent and reproducibility was confirmed.rnThe installation was successfully completed in September 1995 and government inspection1 was also finished in September.