asahi.com : Control rod stuck at nuclear plant –
THE ASAHI SHIMBUN
A control rod at the Kashiwazaki-Kariwa Nuclear Power Plant in Niigata Prefecture remains stuck, raising concerns that the July 16 earthquake may have distorted the shape of a key area in the reactor, officials said Thursday.
Operations at the Tokyo Electric Power Co. (TEPCO) plant have been suspended since the 6.8 magnitude temblor hit, causing a fire and considerable damage to the facilities.
The new finding about the control rod, a crucial component in a reactor’s operations, is likely to further delay a resumption of plant operations.
Since the rod is still in the fuel, and is being kept in place with support devices, there are no immediate safety concerns, company officials said.
TEPCO officials said that all 205 control rods at the No. 7 reactor were automatically inserted into the fuel to stop nuclear reactions right after the earthquake hit.
In an emergency at the reactor, pressure is applied from the bottom of the reactor so that the 4-meter-long rods are inserted into the fuel assembly.
The rods are made of material that absorbs neutrons, which are crucial in starting nuclear fission.
Checks are continuing on how the plant’s facilities were affected by the earthquake.
At the No. 7 reactor, the lid of the pressure vessel was removed to transfer the fuel to a pool adjacent to the reactor.
Since Oct. 11, control rods have been raised from the fuel for checks.
The No. 7 reactor is the first at the plant to have its lid removed since the earthquake.
On Thursday, workers found that one of the rods could not be moved. So far, 106 rods have been extracted, according to TEPCO.
Company officials said that one reason could be that devices intended to prevent the rod from slipping remained intact.
Another possibility is that the temblor distorted the shape of the facility, preventing the rod from moving.
Checking the exact cause is likely to take time since water that fills the reactor must be drained before an inspection of its interior.(IHT/Asahi: October 19,2007)