Chernobyl disaster other undamaged reactors at the power station, with No. 3 continuing to produce electricity up into 2000. The accident motivated safety upgrades on all remaining Soviet-designed reactors in the RBMK (Chernobyl No. 4) family, of which eleven continued to power electric grids . The disaster began during a systems test on 26 April 1986 at reactor 4 of the Chernobyl plant near Pripyat and in proximity to the administrative border with Belarus and the Dnieper River. There was a sudden and unexpected power surge. When operators attempted an emergency shutdown, a much larger spike in power output occurred. This second
Chernobyl disaster phase" and would not dissolve for 800–1000 years. Guidelines for levels of radioiodine in drinking water were temporarily raised to 3,700 Bq/L, allowing most water to be reported as safe, and a year after the accident it was announced that even the water of the Chernobyl plant's cooling pond was within acceptable norms. Despite this, two months after the disaster the Kiev water supply was abruptly switched from the Dnieper to the Desna River. Meanwhile, massive silt traps were constructed, along with an enormous 30m-deep underground barrier to prevent groundwater from the destroyed reactor entering the Pripyat River. Bio-accumulation of