Core Reactor

Fuel Assemblies

The Core has 61 Fuel Assemblies (FA) of hexagonal cross section, which provide CAREM-25 with a nominal thermal power of 100 MW. Its components are typical of the PWR fuel assemblies.

Each fuel element has 108 fuel rods of a 9 mm diameter and a 1,4 m active length.

The core is completed with 18 guide tubes for the control rods and 1 instrumentation tube.

The fuel is UO2 enriched at 1.8 and 3.4%. An 8% weight of Gd2O3 is used as burnable poison in specific fuel rods, in order to keep reactivity approximately constant along the fuel cycle.

The main features considered for the fuel design were the use of enriched uranium, the use of burnable poisons, the higher final burn-up (compared to PHWRs), the absorbing elements of cluster type and the required low pressure-loss of the assembly.

The design of the CAREM fuel element represents a technological challenge, since the Argentine experience in the manufacture of fuel elements was restricted to the elements of the Atucha and Candu stations and to fuels for research reactors.

The design conditions were established in agreement with standards ANSI/ANS-57.5 and ANS-51.1 and with the functional requirements for fuel elements gathered from standard ANSI/ANS-57.1 and the NUREG-800 report.

The safety limits of the dimensions and characteristics of the fuel rods were verified using the BACO (Fuel Rod Code) code developed by CNEA.

Absorbing elements

Absorbing elements (AE) are used for reactivity control during normal operation (Adjust and Control System), and to produce a sudden interruption of the nuclear chain reaction when required (Fast Extinction System).

AE consist of a cluster of rods linked by a mechanical element (namely "spider"), so the whole cluster moves as a single unit. Absorber rods fit into the guide tubes, at the 18 positions not occupied by fuel rods in the fuel element. The absorbing material is an Ag-In-Cd Alloy.

Boron injection is not used for reactivity control during normal operation.