Combustion Engineering, Inc.

Lawrence V Corsetti

William J Bryan

Satya R Pati

Zeses E Karoutas

Stephen C Hatfield

Patrick A Perrotti

Paul F Joffre

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.

Use of shape memory alloys in fuel pellet holddown springs

A burnable-absorber-containing zirconium alloy is described for application to the inside surface of cladding tubes for light water nuclear reactors. The alloy comprises naturally occurring erbium in a range from a measurable amount up to about 20 wt. % or isotopically purified erbium-167 in a range from a measurable amount up to about 5 wt. %; tin in a range from a measurable amount up to about 0.5 wt. %; iron in a range from a measurable amount up to about 0.2 wt. %; chromium in a range from a measurable amount up to about 0.1 wt. %; niobium in a range from a measurable amount up to about 0.1 wt. %; silicon in a range from about 50 to about 120 parts per million ('ppm'); oxygen in a range from a measurable amount up to about 800 ppm; and the balance zirconium. Such an alloy provides an effective absorber material for reactor control, while providing adequate mechanical properties and corrosion resistance for the intended application.

Zirconium alloy absorber layer

A burnable absorber controls axial power peaking or moderator temperature coefficient while additional elements are added to improve strength and/or corrosion resistance in a zirconium alloy containing erbium in a range of from about 0.05 to 2 wt. % selected from the group consisting of a naturally occurring distribution of isotopically enriched erbium-167 and a combination thereof; in a range of from a measurable amount up to 1.4% tin; from 0.2 to 0.5 wt. % iron; from 0.07 to 0.25 wt. % chromium; in a range of from a measurable amount up to 0.6 wt. % niobium; in a range of from a measurable amount up to 0.5 wt. % vanadium; 50-120 ppm silicon; 1000-2200 ppm oxygen and a balance of zirconium. Alternatively, the erbium can be replaced by gadolinium in a range of from about 0.05 to 6 wt. % selected from the group consisting of a naturally occurring distribution of gadolinium isotopes, isotopically enriched gadolinium-157 and a combination thereof.

Corrosion resistant zirconium alloy absorber material

A corrosion resistant metallic coating (60) of zirconium nitride is applied to the cladding tube (40) of a nuclear fuel rod (20). The zirconium nitride is reactively deposited on a zirconium-alloy cladding tube by a cathodic arc plasma deposition process. The zirconium nitride coating provides superior wear test results and enhances the corrosion resistance of the cladding tube.

Method for applying corrosion resistant metallic coating of zirconium

Integral vanes 4 with optimized size, shape and bend angles maximize coolant mixing and fuel rod 12 heat transfer downstream. Recessed weld nuggets 5 with no vane cutout are optimized for size, strength and corrosion resistance. Staggered arches 20',22' and springs 20,22 minimize turbulence and reduce grid pressure drop and promote coolant mixing. Crowned arches 20',22' and springs 20,22 decrease scoring of fuel rods 12 and are sized to minimize turbulence and pressure drop. Minimum cutouts in unslotted section of grid strip 46,46' give 15-20% strength increase. Intermediate weld and tapered end slots 48 give 15% strength increase. Ribbed and round dimple stiffeners 38,39 on outer strips increase buckling resistance, reduce handling damage and spreads accidental loading. Outer strips 32 are optimized for strength, handling, turbulence generation and pressure drop. They also divert enough flow to interior of fuel assembly to match thermal power distribution and eliminate fuel rod corrosion concerns.

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Granby, CT, United States of America

Lawrence V Corsetti