Three of the toroidal field (TF) coils of the JET Tokamak have develop
ed interturn faults. These faults have not been catastrophic and it ha
s been possible to continue operation and replace the faulty coils wit
h spares at the next pre-planned shutdown. The faults were found to be
due to water leaks. The coil coolant was changed from water to an ins
ulating fluid. All known faulty coils have been changed and latest mea
surements do not detect any faults on the installed coils.