Thesis Abstracts 2002
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Application Of Advanced Polymer Composites To Spent Nuclear Fuel Disposal Containers
By: Sergeant Ian Miedema, MEng (Nuclear/Eng.)
Supervisors: Dr. Hugues W. Bonin and Dr. Van Tam Bui
Abstract
Spent fuel disposal is one of the hottest topics in nuclear news, getting considerable amount of media coverage around the world. Canada as well as many other countries with nuclear electric generation plants have therefore been pushed to develop policy on this issue. One of the proposed and most widely supported strategies is to dispose of this by-product permanently in deep underground vaults. Through the use of engineered barriers including vault seals, vault composition, backfill and sophisticated containers, this radioactive material is isolated from the natural environment and the biosphere in particular. According to a design developed by Atomic Energy of Canada Limited, the seclusion must be maintained for approximately 500 years, which is a representative length of time it takes for the radioactive elements to decay to natural background levels.
The purpose of the current study is to determine the feasibility of using PEEK, an advanced polymer, and continuous carbon fibre in a consolidated composite as the principal disposal container component. Feasibility was determined by simulating the ultimate radioactive environment to which the containers will be exposed, and evaluating the mechanical and chemical changes induced by the ionizing radiation. The irradiation of the test specimens was completed by exposure to the mixed radiation field produced by the SLOWPOKE-2 nuclear reactor at various temperatures (20 C - 75 C) to a variety of doses.
The results show that this material is resistant to mixed fields of ionizing radiation up to and including 1 MGy at temperatures from 20 C to 75 C. Mechanically, the composite and virgin polymer samples are barely affected, rarely deviating beyond one standard deviation of the properties of unirradiated samples. Molecularly, crosslinking between adjacent polymer chains in the amorphous region is the primary observed phenomenon as a consequence of the radiation treatments. This effect is diminished with the application of heat during irradiation. Slight changes in crystallinity are also noted through molecular rearrangement, beginning with slight increases at lower doses, then minor decreases are noted with larger doses over 100 kGy. The presentation and discussion of the results lead to an examination of the implication of these findings for the design of a container fabricated with PEEK-graphite fibres composite material.
