The Loss of Fluid Tests (LOFT) were an early attempt to scope the response of real nuclear fuel to conditions under a loss-of-coolant accident, funded by USNRC. The facility was built at Idaho National Laboratory, and was essentially a scale-model of a commercial PWR. (Power/volume scaling was used between the LOFT model, with a 50MWth core, and a commercial plant of 3000MWth).
The original intention (1963–1975) was to study only one or two major (large break) LOCA, since these had been the main concern of US rule-making hearings in the late 1960s and early 1970s. These rules had focussed around a rather stylised large-break accident, and a set of criteria (e.g. for extent of fuel-clad oxidation) set out in Appendix K of 10CFR50 (Code of Federal Regulations). Following the accident at Three Mile Island, detailed modelling of much smaller LOCA became of equal concern.
38 LOFT tests were eventually performed and their scope was broadened to study a wide spectrum of breach sizes. These tests were used to help validate a series of computer codes (such as RELAP-4, RELAP-5 and TRAC) then being developed to calculate the thermal-hydraulics of LOCA.