Standard&Poor's today has affirmed its ratings on Wal-Mart Stores Inc. as follows: -- Senior secured debt at double-`A', -- Senior unsecured debt at double-`A', -- Bank loan rating at double-`A', -- Commercial paper at `A-1'-plus, and -- Corporate credit rating at double-`A'. The outlook is stable. About $10 billion of rated debt is affected. The ratings affirmation follows the company's announcement that it intends to repurchase $2 billion worth of its common stock over the next 12-18 months. Wal-Mart generated strong operating results in year-end Jan. 31, 1997, with total revenues rising by 12% and comparable store sales rising 4.6%. Although operating margins were basically flat, the solid top line growth and significantly improved working capital management pushed