# In Situ Neutron Radiography Investigations of Hydrogen Related Processes in Zirconium Alloys
## 2 Experimental Requirements  
In situ neutron radiography investigations of hydrogen-related processes occurring at temperatures between 250 and 1400 \({}^{\circ}\)C combine the requirements of laboratory reaction furnaces:  
* Well-controlled temperature protocol and homogeneous temperature fields;
* Well-defined and changeable gas atmosphere and nonreactive furnace structures and sample holders with the general needs of neutron radiography;
* High transmission by less material in the beam;
* The material of the sample environment in the beam should be distributed homogeneously to have as few as possible additional structures in the images;
* Short distance between sample and detector to increase the spatial resolution even at lower L/D;
* No overheating of the detector system by the in situ furnace;
* Low-activation materials, long-term activated components should be easily replaceable.  
Particularly, internal structures of the sample environment can change their position by thermal expansion, changing of sample's weight, or deformation. Such effects make referencing difficult or impossible. Even position changes smaller than the pixel size become visible. For instance, it is very difficult to reference a high-temperature image by using an image taken at room temperature. If possible, the reference image should be taken under the same conditions as the images to be referenced.  
In addition to high-temperature chambers available at the neutron source sites, some user-dedicated devices exist [11; 14]. In the following, the INRRO (in situ neutron radiography reaction oven) furnace of KIT [15] is introduced. Figure 3 gives a scheme of this high-temperature chamber. In Figure 4, pictures of the furnace mounted at ANTARES and a radiograph of the empty furnace are shown. The furnace can be applied for experiments between room temperature and 1500 \({}^{\circ}\)C. The INRRO consists of a water-cooled double-walled steel container with non-water-cooled flanges at opposite sides as beam windows. Inside the container is a ZrO\({}_{2}\) fiber thermal insulation and the furnace tube made of Al\({}_{2}\)O\({}_{3}\) heated by a niobium wire. Argon purges this part of the furnace. Thermocouples are installed between the heating wires and the furnace tube. The electric power is controlled on the basis of one of the thermocouples by an Eurotherm controller. The composition of the gas flowing through the furnace tube is defined by a Bronkhorst system consisting of two gas flow controllers (one for argon, the other one for an additional gas, such as H\({}_{2}\), O\({}_{2}\), or N\({}_{2}\),), a mass flow controller for water, and an evaporator and mixer (CEM). The sample can be mounted on a sample holder rod in an airlock. This allows keeping the furnace at temperature and moving the sample in and out of the furnace without longsome heat-up or cool-down.  
Figure 3: Scheme of the INRRO (in situ neutron radiography reaction oven) furnace of KIT.  
Another example is a special sample holder for in situ tensile tests at a defined temperature in the range of room temperature to 450 \({}^{\circ}\)C to study the hydrogen redistribution in stressed and precracked pressure tube samples constructed by CNEA, Buenos Aires, Argentina (see Figure 5). This sample holder can be mounted at a load machine and heat a sample to the test temperature. The first in situ tests with this sample holder were already performed at ANTARES, FRM II. The data analysis is still in progress, and the results are not yet published.