Solution : https://service.sap.com/sap/support/notes/216881 (SAP Service marketplace login required)
Key words : 
dbwr additional key words psaptemp, ~ftp/general/3rdparty/oracle/hp_ux64/8, ~ftp/general/3rdparty/oracle/compaq_tru64/8, oracle data dictionary table fet$, high disk access rate, symptom database shutdown takes, oracle database takes, oracle bug fix, large cpu time, hp/ux 11 64 bit
Related Notes : 
       
| 659946 | FAQ: Temporary tablespaces | 
| 432377 | ODMA modifies Storage settings for Temporary TS | 
| 416772 | General tablespace types, temporary tablespace parameters | 
| 189198 | CREATE/DROP TABLE takes a while(HP-UX 11.0 64bit) | 
| 183842 | Shutdown (immediate) takes a very long time | 
| 183791 | Locking on temporary tablespace of Oracle |