[en] A subcode has been developed which predicts failure (defined as loss of cladding integrity) of the zircaloy cladding of light water reactor fuel rods. This subcode, FRAIL (FRAP Integrity Limit), is linked to the FRAP-S and FRAP-T fuel rod codes producing a complete description of fuel rod behavior under both normal and off-normal operating conditions. These fuel codes supply information to FRAIL describing the state of the cladding during each timestep of operation. From this information, FRAIL predicts the percentage of failed fuel rods as a function of time. Although the primary purpose of the FRAIL subcode is the prediction of fuel rod failure during both normal and off-normal operating conditions, FRAIL also has the capability of calculating the average flow blockage as a function of time. This capability should prove to be useful in the evaluation of core hydraulic performance during a hypothetical off-normal transient. This report presents a description of FRAIL 3. The basic premises and general philosophy of the FRAIL subcode are presented in Section II. A complete description of one of the FRAIL models is included in Section III. Section IV presents a comparison between a FRAIL 3 prediction and Halden overpower data