The DIstributed Sensing for COrium Monitoring and Safety (DISCOMS) project considers the use of optical fiber sensing cables embedded into the concrete floor under the reactor vessel for remote monitoring of a severe nuclear accident. This article focuses on the selection and testing of single-mode optical fibers with limited radiation-induced attenuation (RIA). To simulate the normal operation period of the reactor, followed by a severe accident, several gamma and mixed (neutron–gamma) irradiations were performed, thanks to the Atomic Energy Commission (CEA) Saclay facilities, POSÉÏDON irradiator and ISIS reactor, up to a gamma cumulative dose of about 2 MGy and fast neutrons fluence ( ${E} \,\, >1$ MeV) of $6\times 10^{15}$ n/cm2. In comparison with the first gamma test on standalone fibers, a significant increase of the RIA at 1550 nm appeared during the second test on fibers encapsulated in sensing cables. Molecular hydrogen generated by the cable compound radiolysis induced an increase of the hydroxyl (OH) attenuation broad spectral peak centered at 1380 nm. The radiation-induced OH growth mechanism is confirmed by the comparison of the extended absorption spectral responses of the standalone and encapsulated fibers. A third gamma irradiation run permitted to measure the radiolytic hydrogen production yield of some compounds of a dedicated temperature cable sample. The efficiency of a carbon-coating layer over the silica cladding, acting as a barrier against hydrogen diffusion into the optical fiber core, was successfully tested under gamma irradiation as well as in a final test under neutron irradiation.

中文翻译：

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核电厂发生严重事故时用于监测钐的光纤和光缆的辐照试验

用于 COrium 监测和安全的分布式传感 (DISCOMS) 项目考虑使用嵌入反应堆容器下方混凝土地板中的光纤传感电缆对严重核事故进行远程监测。本文重点介绍具有有限辐射诱导衰减 (RIA) 的单模光纤的选择和测试。为了模拟反应堆的正常运行期，随后发生严重事故，在原子能委员会 (CEA) 萨克雷设施、POSÉÏDON 辐照器和 ISIS 反应堆的帮助下，进行了多次伽马和混合（中子-伽马）辐照，最高可达γ 累积剂量约为 2 MGy，快中子注量 (${E} \,\, >1$ MeV) 为 $6\times 10^{15}$ n/cm2。与对独立光纤的首次伽马测试相比，在对封装在传感电缆中的光纤进行第二次测试期间，1550 nm 处的 RIA 显着增加。由电缆化合物辐射分解产生的分子氢引起以 1380 nm 为中心的羟基 (OH) 衰减宽光谱峰的增加。通过比较独立和封装光纤的扩展吸收光谱响应，证实了辐射诱导的 OH 生长机制。第三次伽马辐照运行允许测量专用温度电缆样品的某些化合物的辐射分解氢产率。二氧化硅包层上的碳涂层作为阻止氢扩散到光纤纤芯的屏障的效率在伽马辐射下以及在中子辐射下的最终测试中都得到了成功测试。