International audienceThe Total Ionizing Dose (TID) hardness of digital color Camera-on-a-Chip (CoC) building blocks is explored in the Multi-MGy range using 60Co gamma-ray irradiations. The performances of the following CoC subcomponents are studied: radiation hardened (RH) pixel and photodiode designs, RH readout chain, Color Filter Arrays (CFA) and column RH Analog-to-Digital Converters (ADC). Several radiation hardness improvements are reported (on the readout chain and on dark current). CFAs and ADCs degradations appear to be very weak at the maximum TID of 6 MGy(SiO2), 600 Mrad. In the end, this study demonstrates the feasibility of a MGy rad-hard CMOS color digital camera-on-a-chip, illustrated by a color image captured after 6 MGy(SiO2) with no obvious degradation. An original dark current reduction mechanism in irradiated CMOS Image Sensors is also reported and discussed

Vulnerability of Optical Frequency Domain Reflectometry (OFDR) based sensors to high γ-ray doses (up to 10 MGy) is evaluated with a specific issue of a radiation-hardened temperature and strain monitoring system for nuclear industry. For this, we characterize the main radiation effects that are expected to degrade the sensor performances in such applicative domain: the radiation-induced attenuation (RIA), the possible evolution with the dose of the Rayleigh scattering phenomenon as well as its dependence on temperature and strain. This preliminary investigation is done after the irradiation and for five different optical fiber types covering the range from radiation-hardened fibers to highly radiation sensitive ones. Our results show that at these high dose levels the scattering mechanism at the basis of the used technique for the monitoring is unaffected (changes below 5%), authorizing acceptable precision on the temperature or strain measurements. RIA has to be considered as it limits the sensing range. From our vulnerability study, the OFDR sensors appear as promising candidates for nuclear industry even at doses as high as 10 MGy.

We studied the responses of fiber-based temperature and strain sensors related to optical frequency domain reflectometry (OFDR) and exposed to high γ-ray doses up to 10 MGy. Three different commercial fiber classes are used to investigate the evolution of OFDR parameters with dose, thermal treatment and fiber core/cladding composition. We find that the fiber coating is affected by both thermal and radiation treatments and this modification results in an evolution of the internal stress distribution inside the fiber that influences its temperature and strain Rayleigh coefficients. These two environmental parameters introduce a relative error up to 5% on temperature and strain measures. This uncertainty can be reduced down to 0.5% if a prethermal treatment at 80 °C and/or a preirradiation up to 3 MGy are performed before insertion of the fiber in the harsh environment of interest. These preliminary results demonstrate that OFDR fiber-based distributed sensors look as promising devices to be integrated in radiation environments with associated large ionizing doses

Abstract-Total Ionizing Dose (TID) effects are studied on a radiation hardened by design (RHBD) 256x256-pixel CMOS image sensor (CIS) demonstrator developed for ITER remote handling by using X and γ-rays irradiations. The (color) imaging capabilities of the RHBD CIS are demonstrated up to 10 MGy(SiO2), 1 Grad(SiO2), validating the radiation hardness of most of the designed integrated circuit. No significant sensitivity (i.e. responsivity and color filter transmittance) or readout noise degradation is observed. The proposed readout chain architecture allows achieving a maximum output voltage swing larger than 1 V at 10 MGy(SiO2). The influence of several pixel layout (the gate oxide thickness, the gate overlap distance and the use of an in-pixel P+ ring) and manufacturing process parameters (photodiode doping profile, process variation) on the radiation induced dark current increase is studied. The nature of the dark current draining mechanism used to cancel most of the radiation induced degradation is also discussed and clarified.

TCAD simulations are conducted on a 4T PPD pixel, on a conventional gated photodiode, and finally on a radiation hardened pixel. Simulations consist in demonstrating that it is possible to reduce the dark current due to interface states brought by the adjacent gate, by means of a sharing mechanism between the photodiode and the drain. The sharing mechanism is activated and controlled by polarizing the adjacent gate at a positive off voltage, and consequently the dark current is reduced and not compensated. The drawback of the dark current reduction is a reduction of the full well capacity of the photodiode, which is not a problem when the pixel saturation is limited by the readout chain. Some measurement performed on pixel arrays confirm the TCAD results.

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We study the performance of Optical Frequency Domain Reflectometry (OFDR) distributed temperature sensors using radiation resistant single-mode optical fibers. In situ experiments under 10 keV X-rays exposure up to 1 MGy(rm SiO-2) were carried out with an original setup that allows to investigate combined temperature and radiation effects on the sensors within a temperature range from 30circrm C to 250circrm C. Obtained results demonstrate that optical fiber sensors based on Rayleigh technique are almost unaffected by radiation up to the explored doses. We show that a pre-thermal treatment stabilize the sensor performance increasing the accuracy on temperature measurement from sim 5circrm C down to sim 0.5circrm C by reducing the packaging-related errors (such as ones related to coating modification) that could be introduced during the measurement. These results are very promising for the future integration of Rayleigh based sensors in nuclear facilities

We present an innovative architecture of a Rayleigh-based optical fibre sensor for the monitoring of water level and temperature inside storage nuclear fuel pools. This sensor, able to withstand the harsh constraints encountered under accidental conditions such as those pointed-out during the Fukushima-Daiichi event (temperature up to 100 °C and radiation dose level up to ~20 kGy), exploits the Optical Frequency Domain Reflectometry technique to remotely monitor a radiation resistant silica-based optical fibre i.e. its sensing probe. We validate the efficiency and the robustness of water level measurements, which are extrapolated from the temperature profile along the fibre length, in a dedicated test bench allowing the simulation of the environmental operating and accidental conditions. The conceived prototype ensures an easy, practical and no invasive integration into existing nuclear facilities. The obtained results represent a significant breakthrough and comfort the ability of the developed system to overcome both operating and accidental constraints providing the distributed profiles of the water level (0–to–5 m) and temperature (20–to–100 °C) with a resolution that in accidental condition is better than 3 cm and of ~0.5 °C respectively. These new sensors will be able, as safeguards, to contribute and reinforce the safety in existing and future nuclear power plants.