SINGAPORE, June 9 (Reuters) - The viscosity spread between physical 180-cst and 380-cst cargoes rebounded on Monday to a two-session high, as soft bunker demand pressured the 380-cst market.     The viscosity spread, or the price difference between 180-cst and 380-cst cargoes, stood at $12.05 a tonne, up 19 cents a tonne from Friday, Reuters data showed.  
  FO180-SIN
    
  FO380-SIN
       Traders said there was some market intention to widen the viscosity spread, and given that the 180-cst market is smaller with fewer outlets where cargoes can move to, another way to pry apart the viscosity spread was to pressure the 380-cst market.     "There seems to be a viscosity spread play I think," said a Singapore-based trader, adding that Mercuria was aggressive in its offers for the 380-cst cargoes during Monday's cash trading.     The Swiss-based trader sold two 20,000-tonne parcels at discounts ranging $0.24-$1.00 a tonne to Singapore spot quotes, Reuters calculations showed.     Marine fuel traders said recent requirements for bunker fuel had been sparse.     In other market news, a South Korean nuclear power plant shut down a 950-megawatt Hanul No. 1 reactor on Monday, due to a control rod problem, the state-run nuclear reactor operator Korea Hydro and Nuclear Power Co Ltd said.      This outage puts the number of South Korean reactors offline at five out of a total of 23.  
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       The short-term impact is expected to be limited, traders said.     "Not such a big impact I think. Now, the electricity demand and supply balance is quite stable," said a South Korea-based fuel oil trader.      However, other traders said electricity supply could be tightened if the shutdown persists.     "If there are nuclear shut downs during the summer season, there could be enormous demand from the fuel oil-fired power plants," said another South Korea-based trader.                      *CASH TRADES - Two 380-cst trades.     Hin Leong bought from Mercuria 20,000 tonnes for June 27-July 1 at a discount of $1 to Singapore spot quotes.     PetroChina bought from Mercuria 20,000 tonnes for loading over June 29-July 3 at $594 a tonne.          *TENDER NEWS     India's Bharat Petroleum Corp Ltd has sold around 75,000 tonnes of 380-cst to Gulf Petrochem at an undisclosed price. About 35,000 tonnes will load from Mumbai over June 28-30 and the remaining will be loaded from Kochi over July 4-6.     Indian Oil Corp is offering around 30,000 tonnes of 380-cst for July 1-3 loading from Chennai, and 30,000 tonnes of ex-Kandla 380-cst loading over June 28-30. The ex-Chennai tender will close on June 12, with validity until the next day, and the other tender will close June 11, also valid till the next day.       FUEL OIL                                                                              CASH ($/T)          ASIA CLOSE       Change   % Change   Prev       RIC                                                           Close        Cargo - 180cst               606.58    -2.24      -0.37     608.82   
  FO180-SIN
    Diff - 180cst                  2.75    -0.69     -20.06       3.44   
  FO180-SIN-DIF
    Cargo - 380cst               594.53    -2.43      -0.41     596.96   
  FO380-SIN
    Diff - 380cst                  0.27    -1.32     -83.02       1.59   
  FO380-SIN-DIF
    Bunker (Ex-wharf)-           597.00    -3.00      -0.50     600.00   
  BK380-B-SIN
    380cst                                                                Bunker (Ex-wharf)              2.47    -0.57     -18.75       3.04                    Premium                                                                                                                                                     For a list of derivatives prices, including margins,                                  please double click the RICs below.                                   Brent M1             
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                                                        180cst M1            
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                                                      180cst M1/M2         
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                                                      180cst M2            
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                                                      Visco M1             
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                                                      Visco M2             
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                                                      380cst M1            
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                                                      380cst M1/M2         
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                                                      380cst M2            
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                                                      Cracks 180-Dubai     
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                                                      M1                                                                    Cracks 180-Dubai     
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                                                      M2                                                                    East-West M1         
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                                                         East-West M2         
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                                                         Barges M1            
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                                                       Barges M1/M2         
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                                                      Barges M2            
  HFOFARAAMc2
                                                       Crack Barges-Brent   
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                                                      M1                                                                    Crack Barges-Brent   
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                                                      M2                                                                      (Reporting by Jane Xie; Editing by Anupama Dwivedi)  ((jane.xie@thomsonreuters.com)(+65 6870 3495)(Reuters Messaging: jane.xie.thomsonreuters.com@reuters.net))  Keywords: MARKETS ASIA/FUELOIL