UPDATE 1-Taiwan's Formosa shuts desulphurizer on leakage

* Formosa likely to restart RDS in about week or less

* Term gasoline, diesel supplies not affected as of now

* One CDU in turnaround mode since end Nov (Adds comments, shutdown time)

SINGAPORE, Jan 3 (Reuters) - Taiwan's Formosa Petrochemical Corp has temporarily shut a desulphurizer unit at its 540,000 barrels per day (bpd) refinery in Mailiao after a leakage, with the downtime period expected to last between five and seven days, traders said on Tuesday.

They added that the shutdown had so far not affected runs at the refinery, which has shut one of its three crude distillation units (CDUs) since the end of November for maintenance.

One of two gasoline-making units were also in a turnaround mode and will resume operations in second-half January.

The residue desulphurizer unit (RDS) has around 80,000 bpd capacity. Formosa has another RDS of similar capacity which was destroyed by a fire in 2010 and has not been fully repaired since then.

"But considering that the recently affected RDS can be up and running in less than a week, the impact on its refining capacity should not be severely affected," said a trader.

The RDS is to remove sulphur from crude.

Following the fire in 2010 when one of the two RDS was destroyed, Formosa had to process sweet, rather than sour crude, as an alternative. (Reporting by Seng Li Peng and Jessica Jaganathan; Editing by Himani Sarkar)