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Cladding

Cladding is the thin walled metal tube that composes the outside of a fuel rod. It's purpose is to prevent corrosion of the fuel by the coolant & release of fission contents into the coolant. Although ZirconiumZirconiumZirconium is a metal used in reactor cladding Zirconium has excellent heat transfer properties and allows for efficient heat transfer. However, it has a negative reaction called Zircaloy hydriding, where zirconium and hydrogen combine for form zirconium hydride, embrittling reactor cladding and resulting in perforations. alloy is common, aluminum and stainless steel is also used.

Cladding Types

Zirconium alloy has been used for so long due to it's properties being very good for nuclear reactors.

  • New research suggests that there is an alternative - SiGA cladding. This cladding is made from silicon carbide-- silicon and carbon in a crystalline format. It is able to survive very high temperatures but is brittle.
  • They plan on solving this by incorporating the fiber into its cladding, reinforcing the material metaphorically like repair into concrete.

Zirconium Cladding Safety Issue

The issue with using zirconium alloy is that upon contact with STEAM (which may occur during a large scale LOCALOCALoss of Cooling Accident - inside of Nuclear Reactors, this is the official term for if there is a loss of coolant used to cool the reactor. \#stub), it reacts to form the highly flammable hydrogen gas. Hydrogen RecombinersHydrogen Recombinersactually called this Passive autocatalytic recombiner (Wikipedia) but this is a word jumble Most popular company that makes these is Framatone - which is a nuclear reactor based company. Hydrogen Recombiners are nifty devices that are integral to BWRs (and really most reactors). In the event of the zirconium alloy cladding on fuel rods mixing with the water, hydrogen is created, and this gas can lead to devastating explosions (Fukushima Reactor) Recombiners have plates/pellets coated with pla can be used to manage this, however.

This reaction is accelerated at high temperatures. (This also occurs in heavy water reactors such as the CANDU reactor.)

This reaction is the direct cause of the Three Mile Island Nuclear Incident. This was also the cause of the Fukushima ReactorFukushima ReactorThe purpose of this page is to inform people of what happened at Fukushima and the reactor incident, and to give information about the plant itself. (present tense will be used throughout this) Fukushima Reactor Fukushima Daiichi NPP is plant that hosts 6 BWR reactors, using Light Water. This resulted in Fukushima being capable of delivering a combined power of 4.7 GWe (4700 MWe). Units 1, 2, and 6 were made by GE, 3 & 5 by Tobisha, and 4 by Hitachi. All 6 reactors were designed by GE. Unit 3-- where when the generators went out, hydrogen gas was vented into the reactor maintenance halls, and it reached a high enough concentration to explode. This reaction was also occured during chernobyl - where steam from the reactor escaped.

Furthermore, during a possible LOCA, Hydrogen EmbrittlementHydrogen EmbrittlementAs defined by a few research articles, hydrogen embrittlement is the polymerization of hydrogen dissolved in steel (or other items) into hydrogen molecules, causing stress concentrations that exceed the strength limitations of the steel, resulting in tiny cracks in said steel. once embrittlement has occurred, it cannot be reversed. This phenomenon can lead to hydrogen leaking, and deterioration to the performance of steel materials. However, it is not only limited to steel: iron, nickel, titani can occur, where 5-20% of the released hdyrogen gas diffuses into the cladding forming zirconium hydrides. This process also weakens the rods cladding due to the lower ductility, forming blisters and cracks.

Why is zirconium alloy cladding used?

It is mainly used due to its high strength and low neutron absorption. IT can be subjected to a high strain rate and harsh conditions regardless of other means.

Furthermore, it is exceptionally resistant to corrosion and high temperatures, and it absorbs minimal neutrons produced by nuclear fission

Zirconium in general is also used by the chemical industry, and in the medical industry as it is called zirconia and used for dental and surgical implants due to its biocompatibility and durability.