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For in-core reactor application, we have developed a new system in order to measure the thermal neutron flux from 107 n.cm-2.s-1 up to 1014 n.cm-2.s-1 at a temperature of 310°C. For this purpose, a new fission chamber with an external diameter of 3 mm has been developed. To obtain the wide range, the single detector operates continuously in the three modes, pulse counting, Campbelling or mean-square-voltage measurement and current. The new electronics system is built to work with this 3 modes simultaneously. Its design is based on massive use of digital technology and advanced digital signal processing. To transmit the signal from the fission chamber to the electronic cabinet, we have used a mineral coaxial cable with typical characteristics specially designed in order to operate in pulse mode and an external diameter of 1.4 mm to be introduced into the core of the reactor. Experiments were carried out in the ISIS and OSIRIS reactors, both experimental facilities available on the CEA Saclay site. These experiments have shown the capability of the system to obtain a linear measurement of the neutron flux from 106 n.cm-2.s -1 up to 2.1014 n.cm-2.s-1 at a temperature of 37°C. The next step, planed at the end of the year 2004, is to operate at the temperature of 310°C during 1000 hours.

This work deals with the final qualification of the IRINA in-core neutron flux measurement system in the MTR OSIRIS reactor. A specific irradiation device has been set up to validate the last changes in the complete system (electronic, transmitting cable and monitor). Experimental results shows the IRINA measurement system meet entirely the in-core reactor conditions requirements: a thermal neutron flux from 10 7 n.cm -2 .s -1 up to 10 14 n.cm -2 .s -1 and a temperature of 300°C during a minimum operating time of 1000 hours.

MARINE is a research preject conducted at CEA!Saclay research centre. It is a new concept of wide range neutron fluence rate monitoring system, The sensor gs a very common one, a well known fission ¢ hamber which has been used by nuclear industry fbr years. The innovation lies in the digital electronics that allows wide range operation on more than 12 decades, with tuneable compromise between response time and accuracy. After having been a demonstrator, MARINE has been industrialized, A CEA research reactor has been the first reactor to be equipped by this new instrument for its neutronic Instrumentation and Control. First divergence occurred on august 2002, After having recalled the basic principle of this instrument, we will give a report of the first divergence results, demonstrating all the benefits for the end user.