UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS

Guest
2024-11-23 18:24
 HOME     CONFERENCES     SEARCH            LOGIN     NEW USER     IMAGES   


Conference: Bucharest University Faculty of Physics 2016 Meeting


Section: Optics, Spectroscopy, Plasma and Lasers


Title:
Fiber optical monitoring of concrete blocks for radioactive waste management


Authors:
D. SPOREA(1), A. STANCALIE(1), L. IONASCU(2), M. NICU(2)


Affiliation:
1)National Institute Laser, Plasma and Radiation Physics, 409 Atomiștilor St., Măgurele, RO-077125, Romania

2)Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, Magurele, Romania


E-mail
dan.sporea@inflpr.ro


Keywords:
radioactive waste, Fiber Bragg gratings sensors, Optical fiber sensors, Optical Backscatter Reflectometer


Abstract:
Optical fiber sensors are for a long time used to monitor strain, displacement or vibration induced in civil engineering structures such as dams, tunnels, bridges, or buildings. Fiber Bragg gratings sensors can be assembled into quasi-distributed sensing systems. Real distributed systems are based on scattering phenomena in optical fibers such as Rayleigh or Brillouin. The present paper focused on a new application of discrete optical fiber sensors applied in monitoring of radioactive waste conditioning by cementation. This process is of interest for ordinary and modified Portland cement as some reactive metals as aluminum and magnesium are not compatible with the pore solution alkalinity. The pH developed in Portland cement matrix exceeds the value 13.0 which is outside of aluminum passivation domain. The chemical reaction implies formation of aluminum oxo-hydroxides and gaseous hydrogen, the result being internal stress as a result of waste volume change and cracks of the conditioning matrix. Monitoring of temperature evolution and internal stress are of great importance to understand the chemistry of the binder and to establish the optimal process parameters mainly for big volumes. For temperature monitoring a setup including two thermocouples and one optical fiber temperature sensor was used. The data is collected automatically with a NI 9211, thermocouple differential analog input module, while the signal from FBG temperature compensating probe is recorded by a Micron Optics sm125 interrogator. One of the thermocouples was employed to monitor the ambient temperature, and the other one works in parallel with the optical fiber temperature probe for comparison. These are embedded into the concrete tested block. In this paper, we suggest a set up to monitor strain inside the concrete blocks based on a Draw Tower Grating. The chain of DTGs operates in connection with the Micron Optics interrogator or with Luna Innovation 4600 Optical Backscatter Reflectometer.


Acknowledgement:
The authors acknowledge the financial support of the Romanian Executive Agency for Higher Education, Research, Development and Innovation Funding (UEFISCDI), under Grant 8/2012, project “Sensor Systems for Secure Operation of Critical Installations”.