Ohi No. 4 startup and modifications

KEPCO (Kansai Electric Power Company) intends to commence reactor startup at its Ohi No. 4 plant, located in Fukui Prefecture, Japan, on Wednesday July 18th, according to KEPCO's press release. The reactor is expected to achieve criticality on the 19th, and KEPCO expects to synchronize the generator with the grid on Saturday, July 21st and have the plant at full power by the 25th. At present, Ohi No. 3 continues to operate without fault and is indicating 101% rated power.

KEPCO has carried out a number of modifications and improvements to the Ohi No. 4 plant, which is a Mitsubishi 4-loop PWR plant presently rated at 3423 MWt and 1180 MWe net. The turbine generator has been upgraded, with integral one-piece forged turbine rotors being installed in the low pressure cylinders, new 'fully three dimensional' turbine blades of Mitsubishi's latest design and last stage blading of 54" size. These improvements are expected to increase power output by 3%-4% and will improve resistance to wear and corrosion. The blading also has Mitsubishi's latest ISB or Integrally Shrouded Blade design (which this author learned about at Mitsubishi's booth at the recent DD&R/ICAPP Exhibition concurrent with the ANS Annual Meeting.)

In the primary plant, shock damping has been improved by way of improved mountings for heavy equipment such as the main steam lines. Internally to the reactor plant, changes have been made in the seal welds on pressurizer primary connection and on relief valve lines, with Inconel 690 replacing the previous Inconel 600 weld material. KEPCO states that stress corrosion cracking in other plants was the driving force behind replacing these welded connections.

The plant has also received the latest model of digital control and indication equipment, considered necessary due to the obsolescence of the previously installed equipment (discontinued parts being the stated major problem.) According to KEPCO the entire control and indication as well as the protective logic are all new.

Eddy current inspection of the U-tubes in two steam generators (B loop and D loop) was conducted with no abnormalities found. Secondary plant pipe wall thickness measurements were made at 965 different locations as well.

It might go without saying, but during the shutdown the reactor was refuelled along normal lines with some new fuel inserted and some elements shuffled.

Finally, post-Fukushima special inspections included (but were not limited to) inspections of the spent fuel pool, its cooling system, and physical integrity as well as the ECCS or Emergency Core Cooling System including turbine-driven pumps.

Keep an eye on the APR Twitter feed (@atomicnews) for notifications of the startup of Ohi No. 4.

11:42 AM Eastern 7/17/2012
ATOMIC POWER REVIEW