the Fukushima I nuclear accidents. After venting the hydrogen in the maintenance hall of those three reactors, the mixture of hydrogen with atmospheric oxygen exploded, severely damaging the installations and at least one of the containment buildings. Zirconium is a constituent of the uranium zirconium hydride (UZrH) nuclear fuel used in TRIGA reactors. Space and aeronautic industries Materials fabricated from zirconium metal and ZrO2 are used in space vehicles where resistance to heat is needed. High temperature parts such as combustors, blades, and vanes in jet engines and stationary gas turbines are increasingly being protected by thin ceramic layers, usually composed of a mixture of zirconia and yttria. Medical uses Zirconium-bearing compounds are used in many biomedical applications, including dental implants and crowns, knee and hip replacements, middle-ear ossicular chain reconstruction, and other restorative and prosthetic devices. Zirconium binds urea, a property that has been utilized extensively to the benefit of patients with chronic kidney disease. For example, zirconium is a primary component of the sorbent column dependent dialysate regeneration and recirculation system known as the REDY system, which was first introduced in 1973. More than 2,000,000 dialysis treatments have been performed using the sorbent column in the REDY system. Although the REDY system was superseded in the 1990s by less expensive alternatives, new sorbent-based dialysis systems are being evaluated and approved by the U.S. Food and Drug Administration (FDA). Renal Solutions developed the DIALISORB technology, a portable, low water dialysis system. Also, developmental versions of a Wearable Artificial Kidney have incorporated sorbent-based technologies. Sodium zirconium cyclosilicate is used by mouth in the treatment of hyperkalemia. It is a selective sorbent designed to trap potassium ions in preference to other ions throughout the gastrointestinal tract. A mixture of monomeric and polymeric Zr4+ and Al3+ complexes with hydroxide, chloride and glycine, called Aluminium zirconium tetrachlorohydrex gly or AZG, is used in a preparation as an antiperspirant in many deodorant products. It is selected for its ability to obstruct pores in the skin and prevent sweat from leaving the body. Defunct applications Zirconium carbonate (3ZrO2·CO2·H2O) was used in lotions to treat poison ivy but was discontinued because it occasionally caused skin reactions. Safety Although zirconium has no known biological role, the human body contains, on average, 250 milligrams of zirconium, and daily intake is approximately 4.15 milligrams (3.5 milligrams from food and 0.65 milligrams from water), depending on dietary habits. Zirconium is