Subject: TEPCO Earthquake Information Update on May 24: Alternative Circulation Cooling System for Unit 2 Spent Fuel Pool
TEPCO submitted a report on the installment of alternative cooling and filtering system of Spent Fuel Pool of Unit 2 for its effectiveness on stable cooling of spent fuel in the spent fuel pool and safety to NISA on May 21st.
TEPCO Washington Office: 202-457-0790
Kenji Matsuo, Director and General Manager
Ikuo Nishimura, Deputy General Manager,
Alternative Circulation Cooling System of Unit 2 Spent Fuel Pool
At Unit 2, Fukushima Daiichi Nuclear Power Station (“Unit 2”), both external and in-house electricity supply were lost due to Tohoku-Chihou-Taiheiyou-Oki Earthquake. As such, the function of Spent Fuel Pool Cooling and Filtering (Clean up) System (“FPC”) was lost.
As a temporary measure, we connected the fire fighting hose to FPC and are supplying freshwater to account for the vaporized water in the Spent Fuel Pool from time to time.
In order to maintain the level of water in the Spent Fuel Pool and ensure that fuels are submerged, we decided to install a temporary pump and heat exchanger system (“Circulating Cooling System”) to remove the decay heat continuously and lower the volume of vaporization of water in the Spent Fuel Pool.
The system is comprised of (i) a system that circulates water in the Spent Fuel Pool through the heat exchanger (“Primary System”) and (ii) a system that releases heat from the Primary System to ambient air by a cooling tower (“Secondary System”).
- Primary System: comprised of a pump, a heat changer, piping, valves, I&C equipments.
- Secondary System: comprised of a pump, a cooling tower, a surge tank, valves, I&C equipments. Heat from the Primary System is transferred to the Secondary System by the heat exchanger and released to the ambient air by the cooling tower.
[Design feature and measures to achieve safe operation]
1. Equipment Soundness
a. Structural strength and seismic safety
The system is designed to have either equaling or surpassing seismic resistance as in general industrial equipment.
It is not likely the primary system would be damaged. Even so, we could use a stand by fire engine in the site to supply water into the pool and maintain the fuel under water.
For corrosion prevention, we will inject deoxidazed fresh water with hydrazine.
2. Leakage Prevention Measures
- Install drain catcher under the heat exchanger unit.
- Install alarms and interlocks to cope with leakage due to pipe break.
3. Radiation Protection
- To reduce field work duration, pump and heat exchanger are modularized.
- Install shield at surrounding part.
- Remotely monitor dose from TSC building (anti-seismic important building).
- We plan to start operation in the end of May.
- For Unit 1 and 3, we plan to start operation in the end of June and for Unit 4, in the middle of July.
5. Specification of Major Component
2 Trains (1 Train Stand-by)
Heat Transfer Area
(1.17MW/Unit) – Decay Heat 0.6MW as of April 30
Primary 1.0MPa, Secondary 0.5MPa
Primary 100℃, Secondary 100℃
Approx. 650mm x 820mm x 1850mm
Approx. 2150mm x 3570mm x 3415mm
6. Other information
- Vender: Toshiba
- Performance: Once started operation, pool water temperature will decrease from 70-80 C to 65 C in 1.5 days. Then temperature will be about 41 C after 1 month.
- System Life: Considering consumables like mechanical seals, we think the system would be available for one year (per train). Since we install two trains, we will be able to operate about two years. Because the system is scalable, we could add necessary components later based on needs.
- TEPCO English website
- METI(Ministry of Economy Trade and Industry)
- NISA(Nuclear and Industrial Safety Agency) http://www.nisa.
- JAIF(Japan Atomic Industrial Forum Inc.)
- FEPC(The Federation of Electric Power Companies of Japan)