Commissioning and start-up of RA-8 critical assembly

The RA-8 critical assembly was designed as one of the experimental facilities for the CAREM Reactor Project. This paper describes the activities developed during the cold and hot commissioning, pointing out the difficulties and the solutions applied (some of them original ones). Moreover, this paper will show the main features of the newest nuclear installation of CNEA making a brief description of its characteristics. Among the special circumstances related to the commissioning that are described in the paper we can mention the following: 1. The facility shares the building with the Thermohydraulic Assay Laboratory (L.E.T.), another experimental facility of CAREM, and thus some shared systems have already been working for many years before this start up. Special procedures for these systems were designed to verify the proper functioning under the new requirements. 2. A new driving mechanism, based in hydraulic cylinders, was used to move the control rods. The criteria for acceptance and a validation of the procedure completeness have been carried out. 3. The implementation of a power measurement system based in neutron noise. 4. Measurement of Power Distribution using direct gamma counting from the fuel elements. 5. The commissioning was interrupted for a ten-month period because the personnel involved had to carry out the commissioning of the Egyptian Research Reactor 2. Also, the common activities during a commissioning are described, pointing out the major steps carried out and the results obtained. The following are examples of these activities: 1. Environmental dose survey (before fuel loading and during other stages). 2. Test of equipment and systems isolated from the rest of the plant. 3. Integrated system test (two or more systems working at the same time). 4. Start-up and power operation simulations before fuel loading. 5. Fuel loading strategy during the approximation to criticality by mass. 6. Modification of systems' components to improve the performance of the installation (e.g. hydraulic system pressure, control rod's length, nuclear instrumentation, core grid, etc). In the paper, the reasons to perform the modification and the results obtained are described. This paper shows how these particularities and other tasks made the RA-8 commissioning very hard and had required very high skills in the crew involved (CNEA-INVAP) to succeed. The lessons learned have been recorded and we hope they will be useful in the design stage of facilities of this kind or more complex. Finally, criticality was achieved on July 16, 1997 at 9:00 PM with a core configuration of 1300 rods (fuel elements), configuration very close to the calculated value of 1320. (author)