Daughter Catherine Sigmon told the New York Times her father died Jan. 7 of congestive heart failure and complications from a fall.
Among his accomplishments after serving in World War II, he established the Reactor Shielding Group at the Brookhaven National Laboratory, in Upton, N.Y., in 1945, the Times said.
In the early 1970s, he was director of reactor safety research at the Atomic Energy Commission and maintained that position in the successor organization, the Nuclear Regulatory Commission.
He was among the experts Congress asked for testimony in 1981 when the Israeli air force destroyed a small nuclear reactor being built by Iraqi leader Saddam Hussein. In 1983, New York Gov. Mario Cuomo named him to a commission to study the safety of the Shoreham nuclear reactor facility being built on Long Island Sound.
Kouts is survived by his wife, two daughters, three stepsons, a sister, a half-sister, and nine grandchildren.