Why is injecting seawater into a nuclear reactor equivalent to scrapping?

The reason why nuclear reactors will be scrapped after being injected with seawater is that using seawater as coolant will bring radioactive substances into the environment, and at the same time, seawater contains elements such as chlorine, which will combine with radioactive substances to form new harmful substances. In addition, the use of seawater as coolant may also lead to corrosion and salt deposition of nuclear power plant equipment, which may lead to nuclear leakage or other accidents.