Use of shape memory alloys in fuel pellet holddown springs

摘要

A composite holddown spring for applying an axial force to a fuel pellet stack in a nuclear reactor fuel rod. The composite holddown spring comprises a shape-memory alloy spring portion and a conventional metal spring portion. The shape-memory alloy spring portion has a two-way memory characteristic such that it contracts to a low temperature configuration at ambient temperatures wherein the axial force exerted by the shape-memory alloy spring portion is minimized and expands to a high temperature configuration at operating conditions wherein the axial force exerted by the shape-memory alloy spring portion is maximized. Somewhat conversely, the conventional metal spring portion weakens and contracts at operating temperature and strengthens and expands at atmospheric temperature.