P. Lemoine

The Jules Horowitz Reactor (JHR) is a 100 MW multipurpose ma­terials testing reactor that was commissioned to replace another reactor, OSIRIS, which was built in the 1960s. JHR was initially designed to operate with a new high-density LEU fuel; however, because of difficulties in the development and qualification of this fuel, the reactor will begin operation with HEU fuel instead as described in the paragraphs to follow.

The JHR fuel elements consist of eight circular rings of curved fuel plates, each 1.37 mm thick (see Figure 4-1). The fuel elements have a 98 mm external diameter and a 600 mm active height. The nominal hydrau­lic gap (“coolant gap” in Figure 4-1) between the fuel plates is 1.95 mm; light water, which streams upward through the gap at a speed of 15 meters per second, is used for both cooling and moderating the core.

The core can contain 34 to 37 fuel elements and has up to 10 ex­perimental positions (see Figure 4-2). The designed neutron fluxes are 5.5 x 1014 fast neutrons per square centimeter per second (n/cm2-s) in the core and up to 4.5 x 1014 thermal n/cm2-s in the reflector.

fuel plate (1.37 mm thick.)

coolant gap (1.95 mm thick.)

stiffener

Aluminium filler or Hf control rod or Irradiation device (0 37 mm)

FIGURE 4-1 Schematic illustration of a JHR fuel element. The 1.37-mm-thick fuel plates form eight concentric rings, with coolant gaps of 1.95 mm between the plates. The center of the fuel element contains aluminum filler, a hafnium control rod, or an experimental position. SOURCE: Lemoine (2011).

The reactor was designed in 2002 using a reference fuel of high-density (8 grams uranium per cubic centimeter [gU/cm3]) UMo dispersion LEU fuel. Original plans had called for this fuel—in development under the RERTR program—to be qualified in 2006. In 2004, however, problems with the fuel’s irradiation behavior indicated that it would be unlikely to be avail­able in time for JHR’s completion. At the time of this symposium, UMo dispersion LEU fuel was still under development by the European initiative LEONIDAS, which is supported in part by the U. S. Department of Energy (DOE). Further optimization still needs to be done to qualify this fuel and demonstrate that it will be available at reasonable cost.

JHR still intends to use UMo dispersion LEU fuel when it becomes available. However, for the time being, JHR plans to use a neutronically equivalent uranium silicide (U3Si2) dispersion fuel enriched to 27 percent uranium-235. The higher enrichment of the silicide fuel is intended to bal­ance its lower density (4.8 gU/cm3) relative to UMo dispersion LEU fuel. The neutron-equivalent U3Si2 fuel is currently under qualification. Although this fuel has been used in other reactors, qualification for JHR is needed because its operating level is much higher than the operating levels of other reactors that use this fuel.