1. 5  Development of Solution Fuel Behavior Observation System in TRACY under Supercritical Conditions
 


Fig. 1-10 Diagram of the solution behavior observation system


This picture, (80KB)

Fig. 1-11 Behavior of nuclear power and voids when fissile solution was fed into core tank at 58 l/min to simulate conditions of reactivity addition at JCO criticality accident


Radiolytic gases are generated with a rapid increase in power when a system using fissile solution, as in a reprocessing facility or in a nuclear fuel treatment facility, becomes supercritical. The radiolytic gases grow into voids; and the voids rise to the surface of the fissile solution. Power is governed greatly by the behavior of the voids. To understand the phenomena of supercriticality, it is necessary to make a computational model based on the real behavior of the voids and the fissile solution. Therefore, the solution fuel observation system was developed to observe real-time behavior of voids and fissile solutions in TRACY.
Figure 1-10 is a diagram of the solution fuel observation system. The radiation-resistant optical fiberscope is introduced into the TRACY core tank from the top. It can observe about one-forth of the fissile solution surface. Images from the optical fiberscope are fed to the radiation-resistant video camera and are recorded real time by the video recorder.
Figure 1-11 shows the video images captured by the system with the power produced in the supercriticality experiment simulating the JCO criticality accident. When the reactivity exceeds criticality, the rapid increase in power swiftly increases the temperature of the fissile solution and radiolytic voids are generated. These voids create negative reactivity, which reduces the net reactivity and reduces the power. As the radiolytic voids move to and reach the fissile solution surface, negative reactivity diminishes, reactivity again increases, and the power again increases. This leads to a power oscillation that continues until the reactivity added to the system is compensated for by the negative reactivity resulting from the temperature increase of the fissile solution. The torus-shaped cluster of voids rising to the fissile solution surface was clearly observed
2 or 3 seconds after the first power peak appeared. These images of the behavior of the fissile solution and radiolytic voids are unique and invaluable for the development and improvement of computational kinetic models; these models will be far better than models based on power and pressure data alone.



Reference
K. Ogawa et al., Development of Solution Behavior Observation System under Criticality Accident Conditions in TRACY, J. Nucl. Sci. Technol., 37(12), 1088 (2000).

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Persistent Quest - Research Activities 2001
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