Prediction of fission product release during the LOFC experiments at the HTTR

Shi, D.*; Xhonneux, A.*; Ueta, Shohei   ; Verfondern, K.*; Allelein, H.-J.*

Demonstration tests were conducted using the High Temperature Engineering Test Reactor (HTTR) in Oarai, Japan, to confirm the safety of HTGR technologies and assure the expected physical phenomena to occur under given conditions. As part of the OECD directed LOFC (loss of forced cooling) project, a series of three tests at the HTTR has been planned with tripping of all gas circulators while deactivating all reactor reactivity control to disallow reactor scram due to abnormal reduction of primary coolant flow rate. The tests fall into anticipated transient without scram (ATWS) with occurrence of reactor recriticality. The paper will describe the Source Term Analysis Code System (STACY) newly developed at the Research Center Jlich and present the results of fission product behavior in the HTTR core under the LOFC test conditions. STACY encompasses the original verified and validated computer models for simulating fission product transport and release. For verification of the modernized and extended version, it was assured that results obtained with the original tools could be reproduced. One of the new features of STACY is its ability to also treat fuel compacts of (full) cylindrical or annular shape and a complete prismatic block reactor core, respectively, supposed sufficient input data be available. In the paper, calculations are based on time-dependent neutronics and fluid dynamics results obtained with the Serpent and MGT models.