Expected radiation exposure for the 30-minute work: 10 millisieverts per person.
The 4 workers (2 each for each reactor, I assume) will measure radiation levels, temperatures and humidity, water level, and take pictures.
The torus (Suppression Chamber) of Reactor 2 is considered to have sustained a damage on March 15, though TEPCO says it was not an explosion. TEPCO and NISA both agree that Reactor 2 has released the most radioactive materials, some of which though may have come from the dry vent.
From TEPCO's handout for the press in English, 3/13/2012:
Field Survey on the semi-basement floor of the reactor building
of Unit 2 and 3 at Fukushima Daiichi Nuclear Power Station
In order to grasp the leakage route (damaged part) of the reactor cooling water in the torus room*, the inflow part of the groundwater into the torus room and working circumstances in the torus room, we are planning to conduct survey in the torus room in the future. This time we are planning to conduct field survey of the semi-basement floor of Unit 2 and 3 which connects to the torus room as the preliminary survey. (The reactor building of Unit 1 is exempt from this survey because the water level of the accumulated water is higher than semi-basement floor.)
*Torus room: The room that holds large torus-shape suppression chamber which store water for Emergency Core Cooling System. It is located at the bottom of the Primary Containment Vessel and around it.
◎Survey contents (Plan)
・Measurement of air dose, dust density, temperature and humidity and taking pictures on the semi-basement floor of the reactor building
・Confirmation of opening and closing condition of gate of the torus room and measurement of door surface dose
・Confirmation of water level at stairway which connect to the basement floor of the reactor building and any obstacles
◎Working Organization (Plan)
・Survey date: March 14, 2012 12:00～12:30
・Worker: Four TEPCO staffs
・Expected dose: 10 mSv/person
・Place: Northeastern and northwestern corner on the semi-underground floor of the reactor building of Unit 2, northeastern corner on the semi-underground floor of the reactor building of Unit 3
The expected dose of 10 millisieverts is high. TEPCO is using own employees for works at high radiation locations. Probably many of the employees of the affiliate companies have already maxed out on the annual dosage limit and waiting for a reset on April 1.
The worker who tweets from Fuku I said in his tweet from yesterday that there are workers wearing tungsten vests on the operation floor of Reactor 3 building, removing the debris.
Carbon-based workers acting as robots.