Superman IV: The Quest For Peace

Superman saves a spaceship of cosmonauts whose ship was thrown off course by debris, then visits his home-town of Smallville as Clark. Now that his adoptive parents have died, Clark has inherited their now-unattended farm. In an empty barn, he uncovers the capsule that brought him to Earth, and removes a luminescent green Kryptonian energy module. A recording left by his mother Lara states that its power can be used only once. Unwilling to sell the farm to a mall developer, Superman returns to Metropolis, where he stops a runaway Subway Train after the conductor collapses at the Controls.
After returning to the Daily Planet, Clark learns that the newspaper went bankrupt and has been taken over by David Warfield, a tabloid tycoon who fires Perry White and hires his own daughter Lacy as the new editor. Lacy takes a liking to Clark and tries to seduce him. Clark agrees to go on a date with her. Following the news that the United States and the Soviet Union may engage in nuclear war, Clark is conflicted about how much Superman should intervene. After receiving a letter from a concerned schoolboy, Superman travels to the Fortress of Solitude to seek advice from the spirits of his Kryptonian ancestors. They recommend that he let Earth solve its own problems, or seek new worlds where war has been outlawed. After asking for advice from Lois Lane, Superman attends a meeting of the United Nations, announcing to the assembly that he will rid the planet of nuclear weapons. Various nations fire their nuclear warheads into space, which are collected by Superman into a giant net and then thrown into the sun.
Meanwhile, young Lenny Luthor breaks his uncle Lex Luthor out of prison. Returning to Metropolis, Lex and Lenny steal a strand of Superman's hair from a museum, and create a genetic matrix which Lex attaches to a U.S. nuclear missile. After the missile is test launched, Superman intercepts it and throws it into the sun. A glowing ball of energy is discharged, which develops into a superhuman. This "Nuclear Man" makes his way back to Earth to find his 'father' Lex, who establishes that while his creation is powerful, he will deactivate without solar light. A vicious battle ensues between Lex's creation and Superman. While saving the Statue of Liberty from falling onto New York, Superman is infected with radiation sickness by a scratch from Nuclear Man's radioactive claws. Nuclear Man kicks Superman into the distance with such strength that his cape is torn away.
To Lois' disgust, the Daily Planet (which has been reformatted as a tabloid newspaper) publishes the headline "Superman Dead?" Lois indicates a desire to quit and seizes Superman's recovered cape for herself. Lacy is also upset and reveals to Lois that she cares for Clark. Lois ventures to Clark's apartment where she proclaims her love for Superman. Felled by radiation sickness, Clark staggers to his terrace where he retrieves the Kryptonian energy module and attempts to heal himself. Having developed a crush on Lacy, Nuclear Man threatens mayhem if she is not brought to him. The newly restored Superman agrees to take him to her to prevent anyone else from being hurt. Superman lures Nuclear Man into an elevator car, trapping him inside and then depositing it on the far side of the moon. As the sun rises, Nuclear Man breaks free due to a crack in the elevator doors and Superman is again forced to defend himself. At the end of the battle, it appears as though Superman has been defeated, and he is driven into the moon's surface by his opponent.
Nuclear Man forces his way into the Daily Planet and abducts Lacy, carrying her into outer space. Superman frees himself from the moon's surface and pushes it out of its orbit, casting Earth into an eclipse, nullifying Nuclear Man's powers and leaving Lacy helpless in space. Superman rescues Lacy and returns her to earth, then recovers Nuclear Man and deposits him into the core of a nuclear power plant, destroying him. What had been Nuclear Man becomes electrical power for the entire electrical grid. Perry White secures a loan to buy a controlling interest in the newspaper, making David Warfield a minority shareholder and protecting the paper from any further takeovers. In a press conference, Superman declares only partial victory in his campaign, saying, "There will be peace when the people of the world want it so badly that their governments will have no choice but to give it to them". Superman also recaptures the fleeing Luthors. He places Lenny in Boys Town, telling the priest that Lenny has been under a bad influence, and returns Lex to prison.

Question: What kind of sickness is Clark suffering from?
Answer: Radiation