Radioactive water accumulating in Japan’s crippled Fukushima plant may start overflowing from service trenches in five days, potentially increasing the contamination from the worst nuclear crisis since Chernobyl.

Tokyo Electric Power Co. has been manually pumping water into overheating reactors after cooling systems broke down and much of that has overflowed into basements and trenches. The water is rising at a rate that means it will overflow as early as June 6, Bloomberg calculations from the company’s data show.

‘There is still a risk of radioactive water leaking into the sea,