Here is a patent from 1978 showing how to reduce CYA in water using sodium hypochlorite.
US Patent 4,075,094 - Sodium Hypochlorite Treatment fro Removal of Cyanurate Compounds from Aqueouss Waste Streams, Ronald H. Carlson, FMC Corp., Feb 21, 1978.
On a weight basis, this reaction requires a ratio of 259.5 parts by weight of sodium hypochlorite to 100 parts by weight of cyanuric acid. At least 90 percent of the cyanuric acid nitrogen is oxidized to nitrogen gas, the balance being oxidized mostly to nitrates. The reaction of sodium hypochlorite with cyanuric acid proceeds most rapidly at pH 9.0 to 10 and increases in rate 2-3 times for every 10.degree. increase in temperature. The effect of the initial concentration of cyanuric acid and sodium hypochlorite on the reaction rate will be discussed below. The residence time for destruction of 95 percent of the cyanuric acid present in the waste stream can range from more than 200 hours to less than 5 minutes depending upon the reaction conditions.