Patent Number: 
Section: claims

1. A system for intervention in an atmosphere of radioactive gas, notably tritium, where this system includes:a dynamic confinement device, including:a removable confinement barrier, able to surround an intervention zone, anda controlled air extraction device, able to keep intervention zone at a lower pressure than the exterior of this zone,and also including:a monitoring device, to monitor the radioactive gas concentration in the air of the intervention zone, anda detection and signalling device, to detect the exceedance of a predefined threshold by this concentration, and to signal the exceedance to the person or persons present in the intervention zone,in which the monitoring device includes a device for measuring the volume activity of the radioactive gas, andthe device for measuring the volume activity of the radioactive gas includes:an ionisation chamber, anda device to cause samples of the extracted air to flow in the ionisation chamber. 2. A system according to claim 1, in which the controlled air extraction device includes:a filtration device, to filter any dust in the air which is extracted from the intervention zone,an adjustment device, to adjust the flow rate of the air which is extracted, anda ventilation device. 3. A system according to claim 2, also including a device for measuring the flow rate of the air which is extracted. 4. A system according to claim 1, in which the device to cause the samples to flow in the ionisation chamber includes:a first device of the Venturi type to extract the samples, anda second device of the Venturi type to restore the extracted samples. 5. A system according to claim 4, in which the device to cause the samples to flow also includes:a turbine to increase the flow of the samples in the ionisation chamber, anda device to adjust the flow rate of the extracted samples. 6. A system according to claim 1, also including a device for measuring the air flow rate in the ionisation chamber to monitor continuously the validity of the measurement of the volume activity of the radioactive gas. 7. A system according to claim 1, in which the detection and signalling device includes means to determine the radioactive gas concentration over time.