The EDR Gamma Scanner José M. Pérez* , O. Vela, E. de Burgos CIEMAT Dept. of Fusion and Particle Physics Madrid Work supported in part by the European Commission under the VRIMOR project, RTD Contract nº FIKS-CT-2000-00114.

Summary Presentation of the gamma scanner developed at CIEMAT Introduction Description of the equipment. Characterization Tests Integration with dose assessment CAD tools

Introduction Gamma scanner as imaging tool. In the range 100-1500 keV, a gamma scanner is conceptually the simplest option. Disadvantages vs gamma camera: The need of rotating mechanical systems represents a serious operational disadvantage: Complexity in operation (mobile parts) Weight and volume of the mechanical support Advantages: The simplicity of its position sensing technique, has intrinsic advantages, such as high contrast (source-to-background discrimination capability) (*) complete absence of imaging artifacts and crosstalk spectroscopic capability at low cost. relative high efficiency

Description of the equipment Mobile Head Scanner body Support

Hardware. Gamma Scanner

Hardware. Gamma Scanner Particular features Aim: minimize the connection complexity An on board computer control the total system. The computer works in slave mode commanded by a master PC connected via a RJ45 cable in a two-computers network.

Software Developed in Labwindows (National Instruments). Three basic operations have been implemented: Selection of the scenario to scan Scanning process Data process and visualization. A standard format for sharing spectrometric information with VISIPLAN (SCK·CEN) implemented. A header with scanning parameters and detector position Data relating relative coordinates of each scanned position and spectrometric information acquired in this position Spectra are provided in ANSI energy bands format (25 energy channels from 0.0 to 15.0 MeV). Several graphical modes have been implemented for visualizing the results Scanned areas in the image can be colored according with radiometric information such as total count rate, presence of determined isotopes or count rate in a previously defined energy band. The images of scanned areas become active. All the gathered radiometric information is available by clicking on the desired scanned area.

Scanner Directional Response Characterization Basic idea: to know the detector response for a radiation field with negligible background and a single point source located at different azimuthal  and zenithal  angles relative to detector z axis. Two levels were selected: 1. The range [–6,+6] degrees, both horizontal and vertical, would be scanned with 0.5º angular step 2. A larger angular step, 10º, would be used for the range [–80º,+260º] horizontal, [–45º,+80º] vertical, 10.0º step. Two isotopes considered: 137Cs and 60Co. Results integrated by SCK in VISIPLAN

Scanner Directional Response Characterization Color display for the [–6º,+6º] , 0.5º step scans. (Spectra correspond to the position represented in a red dot).

Scanner Directional Response Characterization Count rate obtained for a source positioned sequentially in the range [–6º,+6º] horizontal, same vertical, 0.5º step. 60Co 137Cs

Scanner Directional Response Characterization Count rate obtained for a 60Co source positioned sequentially in the range [–80º ,+260º] horizontal, [–45º,+80º] vertical, 10.0º step. (Results for fine scan in [-6,+6] included in green) 60Co 137Cs

Tests in a Controlled Facility Experimental Scenario: Two point sources: 137Cs, 1.55E12 Bq, located in a collimated irradiator. A second 137Cs source with weaker activity (5.22E8 Bq) hidden in a portion of pipe and positioned in the opposite corner of the field of view

Tests in a Controlled Facility

Tests in an Industrial Scenario Tests with the gamma scanner in Almaraz Nuclear Power Plant were performed. Scanner was transported to EA facility ground -5 by the Health Physics Department of the Plant making use of a crane and a mobile platform. Working conditions at this level of the EA building was severe relating temperature and humidity. Conditions were even worse at EA51 (environmental temperature close to 40º C and higher humidity). Background radiation levels were  5 mR/h at EA51 and ten times lower at EA ground -5 close to EA51 entrance.

Scanning at Almaraz NPP Hand measurements performed with GM ratemeters previously to the scan revealed that the dose rate in contact in the filter area was only ten times higher than the background level. At the moment of the measurements, relevant activity concentrations were not found, showing values similar to other parts of the pipes. The radiological situation of the facility EA51 at the date of scanning was not optimum for a remote survey. Differences < 10% in counting rate

Scanning at Almaraz NPP Other measurements were performed at this facility out of the EA51 The corridor at EA ground 5 near the entrance to EA51 presented a lower background level. Contact dose rate at elbow: 0.6-0.8 mSv/h Background dose rate at Detector position: ~5 uSv/h In contact to the pipe shielding, far away the elbow: 10-20 uSv/h

Scanning at Almaraz NPP The scan was repeated from other positions and different conditions, confirming the presence of the hot spot

Integration with VISIPLAN Example of EDR-VISIPLAN integration Modeling of EA5 - Almaraz NPP facility Radiological survey: EDR 3D Dose model: VISIPLAN (Geometrical model: laser scan)

Integration with VISIPLAN VISIPLAN simplified model: Cylinders in red: radioactive pipes. Cylinders in blue: conventional volumes (shielding) An agreement within 20 to 30 % was found between data estimated by VISIPLAN and measurements at different locations in the site.

Conclusions EDR : a pre-industrial fully operative gamma scanner prototype has been presented The hardware has been designed to be operated in hostile scenarios at large distances from the control computer via an Ethernet link. The detection capability has been characterized by studying in detail its directional response for two representative energies (660 keV and 1100-1300 keV). Characterized in an experimental laboratory with two point sources and tested in an industrial facility (NPP). Future actions Characterization of its sensitivity in scenarios with large continuous sources and high background level. Application in decommissioning