Work continued Wednesday to restore electricity to key equipment at the crippled nuclear reactors in the Fukushima No. 1 nuclear power plant, a day after electricity was restored to all six reactors via outside power sources.

In a foreboding sign, however, black smoke again spewed from the No. 3 reactor building at around 4:20 p.m., Tokyo Electric Power Co. said. Black smoke also rose Monday.

The smoke forced workers to evacuate but died down after about an hour and radiation levels in the unit mostly remained unchanged, Tepco said. However, it remained unclear when work would resume.

The main goal is to activate pumps in reactors 3 and 4 to circulate coolants in the reactors and spent-fuel pools that store used fuel rods.

Efforts so far have relied on seawater being manually sprayed or pumped from outside to cool the reactors.

Tepco said Wednesday it was checking to see whether the water pump in reactor No. 3 could inject fresh water into the reactor, and that after a test run it planned to begin activating the pumps Thursday.

While efforts to restore key equipment in reactors No. 1 and 2 were also under way, the tsunami that hit the plant March 11 appears to have damaged their water pumps, and high radiation levels around reactor No. 2 were stalling recovery attempts.

Reactors 5 and 6 had been connected to outside electrical sources as of Tuesday evening.

The Nuclear and Industrial Safety Agency said Wednesday electricity to power the various meters and gauges in reactors 1, 3 and 4 were restored early Wednesday, enabling certain measurements such as temperatures to be taken in the reactors.

The agency said that as of 10 a.m. Wednesday, the temperature of the pressure vessel of reactor No. 1 was approximately 390 degrees — an unusually high temperature — while the temperature of reactor 2 at 6 a.m. Wednesday hovered between 102 and 109 degrees and that of reactor 3 between 253 and 279 degrees.

The NISA said it has been injecting seawater since early Wednesday into reactor No. 1 to cope with the increasing temperature, adding it did not pose any immediate risks or danger.

The NISA also said it discovered that on March 18, an unusually high amount of radiation was found emanating from a building housing turbines located near reactor No. 2. Although the NISA said the radiation amount was approximately 500 millisieverts per hour, Tepco later denied that such a high level was detected, citing a miscommunication between the plant operator and the NISA.

The NISA said that while they were still unsure of the radiation’s immediate source, two workers who were in the building replacing pressure pump motors were exposed and further work halted.

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