No. 1 and 3 were to be eventually closed due to a 1995 agreement Ukraine made with the EU. Ukraine agreed to close the remaining units in exchange for EU assistance in modernizing the shelter over reactor No. 4 and improving the energy sector of the country, including the completion of two new nuclear reactors, Khmelnitski 2 and Rovno 4. Reactor No. 1 was shut down in 1996 with No. 3 following in 2000. Computer systems SKALA (Russian: СКАЛА, система контроля аппарата Ленинградской Атомной; sistema kontrolya apparata Leningradskoj Atomnoj, “Control system of the devices of the Leningrad Nuclear Power Plant”) was the process computer for the RBMK nuclear reactor at the Chernobyl nuclear power plant prior to October 1995. Dating back to the 1960s, it used magnetic-core memory, magnetic tape data storage, and punched tape for loading software. SKALA monitored and recorded reactor conditions and control board inputs. It was wired to accept 7200 analog signals and 6500 digital signals. The system continuously monitored the plant and displayed this information to operators. Additionally, a program called PRIZMA (Russian: ПРИЗМА, программа измерения мощности аппарата; programma izmereniya moshchnosti apparata, “Device power measurement program”) processed plant conditions and made recommendations to guide plant operators. This program took 5 to 10 minutes to run, and could not directly control the reactor. Known accidents and incidents 1982 reactor #1 partial meltdown On 9 September 1982, a partial core meltdown occurred in reactor No. 1 due to a faulty cooling valve remaining closed following maintenance. Once the reactor came online, the uranium in the tank overheated and ruptured. The extent of the damage was comparatively minor, and no one was killed during the accident. However, due to the negligence of the operators, the accident was not noticed until several hours later, resulting in significant release of radiation in the form of fragments of uranium oxide and several other radioactive isotopes escaping with steam from the reactor via the ventilation stack. The accident was not made public until several years later, despite cleanups taking place in and around the power station and Pripyat. The reactor was repaired and put back into operation after eight months. 1984 reactor #3 and #4 incident According to KGB documents, declassified in Ukraine on 26 April 2021, serious incidents occurred in the third and fourth reactors in 1984. According to the same documents, the central government in Moscow knew as early as