It is not the lake water that is corroding the pipe...it is inexpensive and inappropriate metal used for the pipe at initial construction. They need to replace all the pipes.

Wolf Creek Assures NRC It's Fixing Water Issues

Officials from Wolf Creek, the only nuclear power plant in Kansas, updated the Nuclear Regulatory Commission Thursday on their efforts to solve persistent problems with the water supply that cools safety equipment at the plant. As Kansas Public Radio's Bryan Thompson reports, the NRC has been aware of the problems for the last five years.
 The essential service water system brings water into the plant from Coffey County Lake—not to cool the reactor itself, but to cool equipment needed to shut down the reactor in an emergency. The lake water has caused corrosion in the pipes, and when the pumps kick on, the surge in water pressure has blown small holes in the pipes. The NRC was looking for assurances that the company is finally on a path to resolve the problem. Wolf Creek site vice president Cleve Reasoner said he’s confident, but not certain.
“We have good confidence in our logic, and we’re seeing positive numbers, but the reality is until you’ve got the material in hand or the confirmation is signed, there is risk," says Reasoner. "Don’t know how to give you a percentage confidence number, but it’s not 100%.”

Wolf Creek officials emphasized that the plant is under new management, and has a new, hands-on approach to addressing engineering problems. The company has already replaced nearly four miles of underground pipe. The repairs are scheduled to be finished next spring, at a cost of more than $28 million.