SINGAPORE, March 13 (Reuters) - The 180-cst fuel oil cash differential turned positive on Thursday for the first time in more than a week, underpinned by demand for the lower viscosity fuel in April, trade sources said.     The 180-cst fuel oil cash differential was assessed at 33 cents a tonne to Singapore spot quotes on Thursday, up $1.33 a tonne from the day before, Reuters data showed.      "I'm a little optimistic on the 180-cst due to (Asia receiving) more high viscosity material," said a Singapore-based trader.     Of the 4.17 million tonnes of western fuel oil estimated for arrival in Asia, close to 2 million tonnes of it originate from the Americas and Caribbean, which export more viscous material.  
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       These cargoes, which is at least 700-centistoke, will need to be blended further into less viscous material that is suitable for cash trading in Asia, such as the 380-cst cargoes.     This tallies with the latest inventory data from Singapore trade agency IE Singapore. Shipments from the Americas made up a third of total imports, which rose 18 percent to a two-week high of 1.34 million tonnes in the week to March 12.     Exports, on the other hand fell almost 40 percent to a five-week low, as shipments to China and Malaysia more than halved to 104,600 tonnes and 57,000 tonnes, respectively. Exports to Taiwan were also absent after reaching 30,000 tonnes last week.     Overall, Singapore onshore fuel oil stocks rose 13.05 percent in the week to March 12 to a three week high of 19.478 million barrels (3.067 million tonnes).     Japan put two reactors on a shortlist for a final round of safety checks on Thursday, moving a step closer to reviving its nuclear industry, three years after the Fukushima disaster that led to the shutdown of all plants.  
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       Market sources, while skeptical of any restart in the near future, said premiums for low-sulphur fuel oil will slip should Japan operate its nuclear plants again, which will dent demand for the heavy distillate.     Since the Fukushima nuclear disaster in 2011, Japan has turned to coal, gas and oil to generate electricity.     Asia is also expected to be the dumping ground for excess fuel oil from Europe once new shipping fuel rules take effect from Jan. 15.     Vessels entering low sulphur zones around northwest Europe and North America have to switch from low sulphur fuel oil to gasoil as part of an effort to reduce marine pollution.  
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            *CASH DEALS: Two 380-cst trades, with BP buying both cargoes at $598 a tonne.     Unipec and Glencore each sold to the oil major 20,000 tonnes of 380-cst for April 1-5 and April 6-10 loading respectively.       *TENDER NEWS     Taiwan's Formosa sold 35,000-45,000 tonnes of pyrolysis fuel oil for March 24-26 loading from Mailiao to Petrobras at a premium of above $70 a tonne to Singapore spot quotes for 180-cst.     South Korean Western Power is seeking 45,000 tonnes of high sulphur fuel oil for April 16-20 arrival via a tender that will close on March 20.  
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            *MARKET NEWS     Singapore marine fuel sales fell to a year's low in February, in line with fewer vessel arrivals for bunker refuelling, also at a one-year low, according to data from the Maritime and Port Authority of Singapore (MPA).  
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         FUEL OIL                                                                           CASH ($/T)         ASIA CLOSE      Change   % Change   Prev       RIC                                                         Close        Cargo - 180cst             603.65     3.51       0.58     600.14   
  FO180-SIN
    Diff - 180cst                0.33     1.33    -133.00      -1.00   
  FO180-SIN-DIF
    Cargo - 380cst             597.74     1.17       0.20     596.57   
  FO380-SIN
    Diff - 380cst                2.45     0.23      10.36       2.22   
  FO380-SIN-DIF
    Bunker                     601.00     1.00       0.17     600.00   
  BK380-B-SIN
    (Ex-wharf)-                                                         380cst                                                              Bunker (Ex-wharf)            3.26    -0.17      -4.96       3.43                   Premium                                                                                                                                                For a list of derivatives prices, including margins, please                        double click the RICs below.                                        Brent M1            
  BRENTSGMc1
                                                      180cst M1           
  FO180SGSWMc1
                                                    180cst M1/M2        
  FO180SGSDMc1
                                                    180cst M2           
  FO180SGSWMc2
                                                    Visco M1            
  FOVISSGDFMc1
                                                    Visco M2            
  FOVISSGDFMc2
                                                    380cst M1           
  FO380SGSWMc1
                                                    380cst M1/M2        
  FO380SGSDMc1
                                                    380cst M2           
  FO380SGSWMc2
                                                    Cracks 180-Dubai    
  FO180SGCKMc1
                                                    M1                                                                  Cracks 180-Dubai    
  FO180SGCKMc2
                                                    M2                                                                  East-West M1        
  FOSGEWMc1
                                                       East-West M2        
  FOSGEWMc2
                                                       Barges M1           
  HFOFARAAMc1
                                                     Barges M1/M2        
  HFOFARAASMc1
                                                    Barges M2           
  HFOFARAAMc2
                                                     Crack               
  HFOFARAACMc1
                                                    Barges-Brent M1                                                     Crack               
  HFOFARAACMc2
                                                    Barges-Brent M2                                                        (Reporting by Jane Xie, editing by William Hardy)  ((jane.xie@thomsonreuters.com)(+65 6870 3495)(Reuters Messaging: jane.xie.thomsonreuters.com@reuters.net))  Keywords: MARKETS ASIA/FUELOIL