1 Advantages of combining gamma scanning techniques and 3D dose simulation in dose optimisation problems. F.Vermeersch IDPBW, Nuclear Studies Occupational Exposure Management at NPPs Espace de la Tête d’Or Congress Centre March

2 Content Dose prognoses and optimization for operations in complex environments 3D dose simulation tool Site characterization Traditional measurements Using gamma scanning equipment combined with 3D dose simulation tools. Example on site Conclusion

3 Geometry of the installation Source distribution and strength Shielding configuration, fixed or mobile Work organization Dose optimization in complex environments Application of ALARA in nuclear installations is complex. We need to evaluate the dose for the different activities and environments. Dose is influenced by: In an operating plant: Plans and technical information are generally available and well documented There is a return of experience from previous tasks (maintenance, repair) A good set of dose and dose rate measurements is available. There is a living knowledge on technical and dose information

4 Optimization in changing work environments ALARA in changing installations is even more complex Changing geometry's Changing source distributions and strengths Changing shield distributions Changing work groups And sometimes there is a lack in geometrical and radiological information

5 What do we need for a good ALARA study ? Compare different scenario’s involving the following information: Type of work or techniques used Work duration Number of workers Work force distribution Shielding requirements and shielding method applied Evaluate activities with a direct impact on sources (chemical cleaning). Develop work simulation tool allowing the dose assessment of a work scenario in a 3D environment Evaluate methods or actions that can lead to a dose reduction or dose optimization for a given job description. Predict the dose for a given job description. Lets make a simulation of the described job.

6 3D dose modeling and planning tool Based on: 3D model including material, geometry and sources Point-kernel dose calculation, with build- up correction Allows: Dose assessment for tasks, trajectories and scenarios Individual and collective dose assessment Source strength calculation from measured dose rate sets. Source Sensitivity Analysis VISIPLAN 3D ALARA planning tool

7 Dose analysis Analysis of individual trajectories Analysis of scenarios Evaluation of individual and collective dose

8 However before calculations can start a model needs to be build Geometry and materials CAD, technical data, paper plans Survey Source model Technical data radiological measurements

9 Radiological Characterization of a site. Site history Dose rate measurements (4) at different locations in the work area Spectral Analysis on samples (sweeps, fluids, resins,….) Traditional Disadvantage: can be dose intensive source geometry and distribution is difficult to assess

10 Source inference based on dose measurements Dose measurement Source model Source strength calculation by fitting calculated dose rate sets to measured dose rate sets Dose calculation Spectral information

11 Detecting source locations, geometry and composition. Gammacam M31 AIL Systems Inc. CartoGam RadScan Gamma camera’s External spectral detector needed Gamma scanners Internal spectral capability EDR scanner A methodology needs to be developed to interpret the measurements

12 To show the viability of an integrated approach to minimise occupational exposure through the combination of different technologies including gamma scanning, geometrical scanning, human motion simulation tools and a radio-geometrical modelling tool. Virtual Reality in Maintenance Outage and Repair VRIMOR

13 Integrated approach

14 Gamma Scanner EDR scanner from CIEMAT

15 Measured and derived quantities for source strength analysis Instrument Dose Rate Effective Dose Instrument Dose Response function µ Relationship between dose and instrument read out.

16 Methodology of source modeling using gamma scanning Source geometry and location  Through interpretation of scans taken from different positions. Source composition  Interpretation of the spectra  Analysis of site history Source strength  Source strength determination by fitting a calculated scan to a measured scan based on the response function of the scanner, the source spectra and the 3D information of source and materials in the model.

17 Application in a Nuclear Power Plant Almaraz NPP

18 Geometric Information LFM VISIPLAN 3D ALARA planning tool Geometry interface

19 Scan position 1 Scan position 2 Gamma scan taken from two locations

20 Application on site Gamma Scans Two scans from different positions

21 Technical and materials information 1-It is a pipe of the drainage system. its function is to collect the drainage from upper plants 2- It is a 6 inches pipe: DA-x G. Made of stainless steal. External Diameter: 168,3 mm. Wall thickness: 7,11mm. It is shielded with lead of 3 cm thickness. 3- This pipe contains leaks, drains, and any other thing coming from the floor. 4- The tanks are filled with pressurized air. The thickness is indicated in the picture.

22 Scan position 1 Scan position 2 Drain pipe shielded with lead Position of a hot spot confirmed in the two scans Part of it is not shielded Gamma scan taken from two locations

23 Source Model

24 Source model and source strength fitting. Scan 1 Scan 2 Derived source model simulating the drainage system. A B C

25 Modeling Results Comparison with dose measurements.

26 Dose plot based on the fitted sources Main dose contribution is not caused by the hotspot. The main contribution is due the contaminated drainage lines.

27 Conclusion A reduction of the dose uptake during the characterization of the site to determine the location and the geometry of the sources the determination of the source strength through the use of the sensitivity curve of the gamma scanner and the 3D radio-geometrical model. A more realistic or reliable radio-geometrical model to make dose assessment for work scenarios The combined use of 3D dose simulation and gamma scanning enables:

28 Trajectory Simulation HeSPI (UPM) ERGODose (NNC ) Trajectory calculation VISIPLAN (SCKCEN) (planning) Detailed Trajectory Simulation