The influence of burnup measuring error on the radioactive safety and fuel economy in pebble bed HTR

The pebble bed high temperature reactor uses a large number of fuel spheres to stack to form the core and operates in a non-stop refuelling mode. The burnup is measured after the fuel spheres passing through the core and reaching the bottom of the reactor. According to the measured value, it is determined whether the fuel spheres is reinjected into the core or discharged from the core. However, the measurement error of burnup depth is inevitable, which will cause the fuel spheres to be discharged from the core in advance without reaching the predetermined burnup, or the fuel spheres that reach the predetermined burnup to be injected into the core again, resulting in economic and safety problems respectively.

In order to study the influence of burnup measurement accuracy on the safety and economy of pebble bed high temperature reactor fuel spheres, this paper takes HTR-PM as the engineering background and carries out the following two aspects of work. 1)The discrete element model was used to simulate the core pebble flow motion, and the nuclides in all fuel spheres were calculated by coupling the nuclide stock software. 2) The measurement error of burnup index was analysed, and the proportion of fuel spheres that are unloaded in advance and excessively injected to the total number of fuel spheres at this error level was estimated, so as to characterize the economic and safety level of pebble bed high temperature reactor.

In this paper, the method framework of fuel measurement accuracy influence analysis was established, and specific indicators related to the safety and economy of reactor operation were proposed. The Discrete Element Model combined with nuclide inventory software, which coupled pebble flow motion and burnup calculation method, is beneficial to the analysis of core burnup distribution and the establishment of which is conducive to the analysis of the core burnup distribution and the establishment of the benchmark problem of the pebble bed HTR. (authors)