The new automatic high efficiency gamma spectrometric measuring system was developed in close cooperation of SURO, Institute of Experimental and Applied Physics, Czech Technical University in Prague and NUVIA company. The equipment is intended for sensitive measurement in deep underground laboratories such as LSM Modane (“Zero dose environment“). The expected use are measurements of ultra-low radionuclide activities in aerosol filters from radiation monitoring networks worldwide, biological and environmental samples from past nuclear accidents to study remediation and mitigation methods in late phase of nuclear accident, in geological and environmental samples to study radionuclide migration from nuclear wastes depository in geological structures and transfer into environment etc.

We performed the pilot long-term measurements of air filters from monitoring stations in the Czech Republic in deep underground laboratory LSM Modane France. Due to the low radiation background, the detection level of nBq/m3 was reached. This level of sensitivity allows verifying atmospheric dispersion models of NPP release under a normal operation. The experimental setup consisted of the ultra-low background HPGe detector (ID: OBELIX; Ge volume of ~600 cm3) and a clean air supply provided by the anti-radon facility.

As the pilot experiment yield promising results we decided to construct a computer controlled sample changer, which would provide effective measurement time utilization and overall improvement of measurement logistics.The system (Fig 1) was developed by SURO and IEAP and constructed by NUVIA company.  

Basic parameters of this system are following:

• equipped with 2 HPGe high volume, ultra- low background detectors, low background Pb shielding (30 cm),
• storage capacity for 15 samples  (3L Marinelli),
• MDA is improved by using of radon free air and airtight box (4,4 m x 5,0 x 2,55 m) surrounding both HPGe detectors and temporary storage of samples for measurement.

Some applications:

1. Measurements of ultra-low radionuclide activity of aerosol filters from  radiation monitoring networksGoal: Sensitive methods for control of radionuclides effluents and for verification of atmospheric dispersion models under normal NPP operation or in case of radionuclide release or for retrospective analysis of hidden releases of radionuclide worldwide.
2. Measurements of ultra-low radionuclide activity of  biological and environmental samples with low residual activity from past nuclear accidents (Chernobyl, Fukushima, nuclear test) to study radionuclide transfer in environment
   Goal: New data for radionuclide transfer in environment and methods of remediation, the study of remediation and mitigation methods in late phase of nuclear accident.
3. Measurements of ultra-low radionuclide activity in geological and environmental samples to study radionuclide migration from nuclear wastes depository in geological structures and transfer into environment
   Goal: Research of new methods for radionuclide migration in geological structures and environment.