[en] A two-dimensional code for analysis of sodium boiling in LMFBR fuel assemblies has been developed at ORNL. This code, THORAX, has been used to analyze tests in 19- and 61-pin electrically-heated, simulated LMFBR fuel assemblies in the THORS facility. THORAX has simulated well the transient growth of the two-dimensional boiling region and the resulting static flow instability leading to dryout. Extrapolation of results to a full size fuel pin bundle shows that two-dimensional effects are reduced but still significant. The code will be extended to include a loop model in support of forthcoming tests in the THORS-SHRS Assembly 1 loop, which will include two parallel 19-pin simulated driver bundles