☆Ise-no-Kamikaze☆☆Move The Wind for The Justice☆: Fukushima Daiich　： Reactor cooling : TEPCO

2015年1月6日火曜日

Fukushima Daiich　： Reactor cooling : TEPCO

https://fdada.info/currentstatus/decommissioning-1

Reactor cooling

The cold shutdown condition will be maintained by cooling the reactor by water injection and measures to complement status monitoring will continue to be implemented.

Status of Progress Points

(1) Temperatures inside the reactors

Through continuous reactor cooling by water injection, the temperatures of the Reactor Pressure Vessel (RPV) bottom and the Primary Containment Vessel (PCV) gas phase have been maintained within the range of approx. 15 to 40℃ for the past month, though they vary depending on the unit and location of the thermometer.

(2) Release of radioactive materials from the Reactor Buildings

The density of radioactive materials newly released from Reactor Building Units 1-4 in the air measured at site boundaries was evaluated at approx.
1.3 x 10^-9 Bq/cm³ for both Cs-134 and -137. The radiation exposure dose due to the release of radioactive materials was 0.03 mSv/year (equivalent to approx. 1/70 of the annual radiation dose by natural radiation (annual average in Japan: approx. 2.1 mSv/year)) at the site boundaries.

(3) Partial observation of containment vessel interior

From the standpoint of supplementing the monitoring of reactor parameters, the interiors of the primary containment vessels of Units 1 and 2 were investigated to ascertain temperature, water level, dose and other conditions. Consideration is continuing to be given to conducting a similar interior investigation of Unit 3.
An alternate temperature gauge for the Unit 2 reactor pressure vessel has been installed and additional temperature gauges installed at Units 1 and 2.

(4) Improved reliability of circulating injection cooling

To address leaks from pressure hoses and other such issues related to piping along the reactor injection line, the hoses have been replaced with more reliable polyethylene pipe.
Appropriate backup facilities have been secured for the reactor coolant injection system (injection line pump: 3 systems; water source: 2 types; ensuring power sources from multiple buses, etc.). Even if the functionality of multiple systems involved in the injection of coolant into the reactor were to be lost simultaneously due to an accident, the injection of cooling water can be restarted using fire engines within three hours.

Investigation of Interior of Unit 1 PCV and Installation of Temperature and Water Level Gauges

The interior of the primary containment vessel was filmed with a camera, and the dose, water level and other conditions were investigated (10/9~13).
It was verified that the dose was a max. of approximately 11.1Sv/h, and the water level was approximately +2.8m above bottom of the containment vessel.
Additional temperature and water level gauges were installed (10/13). The temperature gauges have been used as the monitoring temperature gauges specified by safety regulations since 12/3.

Investigation of Interior of Unit 2 PCV and Installation of Temperature Gauge

The interior of the primary containment vessel was filmed with a camera, and the dose, water level and other conditions were investigated (1st :Jan 19; 2nd : May 26 - 27).
It was verified that the dose was a max. of approximately 73Sv/h, and the water level was approximately +60cm above bottom of the containment vessel.
An additional temperature gauge was installed (Sep 19). It has been used as the monitoring temperature gauge specified by safety regulations since Nov 6.
There are future plans to enhance monitoring function by permanently installing temperature and water gauges similar to those in Unit 1 (scheduled for end of February).

Installation of Alternate Temperature Gauge at Unit 2

Following the failure of the existing temperature gauge, an alternate temperature gauge (1 unit) was installed in addition to the temperature gauge already installed for monitoring (1 unit) (10/3).
Because both temperature gauges display almost the same temperature (approx. 43~46℃), it was confirmed that there were no problems with the installation. The gauge has been used as the monitoring temperature gauge specified by safety regulations (11/6).
As the thermometer installed at the Unit 2 RPV bottom after theearthquake had been broken, it was excluded from the monitoringthermometers (February 19).
On April 17, removal of the broken thermometer failed and was suspended. To facilitate removal, tests to check rust formation and fixing are underway (from May 12).
Some of the permanent supervisory instrumentation for PCV could not be installed in the planned locations due to interference with existing grating (August 13, 2013).
Reinstallation after resolving the twisted cables from May 20-22 was failed and these instruments were removed on May 27. New instruments will be installed in June.

Nitrogen Seal on Unit 1 Suppression Chamber (S/C)

Because it is assumed that gas from the time of the initial accident, which has a high hydrogen concentration, is remaining in the upper part of the S/C, nitrogen has been injected (10/23~early December) and (to 2%) the hydrogen concentration lowered sufficiently below the combustibility limit concentration※, which has further reduced risk of a hydrogen explosion.

Commencement of work to shorten the circulation loop

Regarding the work to shorten the circulation loop, the operation of which is scheduled for the end of FY2014, as the facility design was completed, the preparatory work will commence from June.

Reinstallation of supervisory instrumentation for Unit 2 PCV

Some of the supervisory instrumentation (thermometer and water-level gauge) for PCV could not be installed in the planned locations during the work in August 2013 due to interference with existing grating. Reinstallation after resolving the twisted cables from May 20-22 failed and these instruments were removed on May 27. New instruments will be installed in June.

Replacement of the thermometer at the bottom of Unit 2 RPV

Removal and replacement of the thermometer installed at the bottom of Unit 2 RPV, which was broken in February 2014, failed in April and the operation was suspended. The estimated cause was fixing or added friction due to rust having formed. To help remove the thermometer, tests to check rust formation and fixing are underway (from May 12).

Future Challenges and Direction of Responses

Maintenance of Monitoring Functions for Long-Term Stable In-Core Environment

An alternate temperature gauge (1 unit) has been installed to serve as the Unit 2 pressure vessel temperature gauge, and the insertion and installation of an additional temperature gauge through the TIP (traversing in-core probe) pipe is being studied in order to improve reliability.
At Units 1 and 3 also, alternate temperature gauges need to be installed prior to that in preparation for failure of a temperature gauge. Because the dose needs to be reduced in the vicinity of the installation location, possible sites for installation of the alternate temperature gauges are being narrowed down in FY 2012.

Addressing Risks in Event of Earthquake or Tsunami

With regard to earthquakes, it has been verified that there is sufficient seismic resistance to withstand an earthquake equivalent to the Tohoku-Chihou-Taiheiyo-Oki Earthquake (JMA seismic intensity scale 6+). Even if some of the equipment were to become unusable, appropriate backup equipment has been secured to be able to restart the injection of cooling water quickly.
With regard to tsunami countermeasures, a provisional seawall has already been installed in preparation for a tsunami striking due to aftershocks. To provide for a case where a tsunami surpassing assumptions were to hit, dedicated diesel generators have been deployed to ensure power as well as backup coolant injection pumps and cooling water injection pumps on high ground in order to maintain reactor cooling function. Also, power-generating vehicles have been deployed to prepare for any power interruptions.
In addition, fire engines have been deployed as alternative means for injecting cooling water should multiple backup systems become unusable.
Moreover, as new information is obtained, it will be thoroughly addressed, including responding to reviews regarding standard earthquake ground motion.

Avoiding Remote Risk of Hydrogen Explosion

To prevent any explosion of hydrogen generated from radiolysis of water inside the reactor pressure vessels at Units 1~3, nitrogen is continuing to be charged into the reactor pressure and containment vessels.
The hydrogen concentration inside the containment vessels of Units 1~3 is monitored and managed so that the concentration does not exceed the combustibility limit concentration (4%) by adjusting the amount of nitrogen charged.
Using a web camera, it is possible to monitor the pressure of injected nitrogen gas and the injected amount of nitrogen gas at the seismic-isolated building. In the event that unusual conditions are detected within these parameters or during an inspection, it will switch over to the standby facility. This includes valve manipulation or the switching over of the power supply.

Unit	Description	Category	Date of issue
Units 1-3	Commencement of the Reactor Water Injection at Units 1-3 of Which the Source is Condense Storage Tank (CST) at Fukushima Daiichi Nuclear Power Station	Document & photos	05 July 2013
Unit 1 & 2 & 3	Confirmation of Reactor Water Injection by the CST Reactor Water Injection System Line of Unit 2 at Fukushima Daiichi Nuclear Power Station	Document	04 July 2013
Unit 1 & 2 & 3	Reliability Improvement of the Feed Water System for Reactor Injection at Units 1-3 at Fukushima Daiichi Nuclear Power Station	Document	19 February 2013
Unit 3	Water Injection to the Reactor Utilizing the Reactor Water Injection Pump in the Turbine Building in the Case of Power Supply Suspension at Fukushima Daiichi Nuclear Power Station	Document	13 November 2012
Unit 1 & 2 & 3	The Reactor Pressure Vessel Temperature and the Amount of Water Injection to Reactor at Fukushima Daiichi Nuclear Power Station Unit 1 - 3 (Reference)	Document	13 September 2012
Unit 1 & 2 & 3	The Reactor Pressure Vessel Temperature and the Amount of Water Injection to Reactor at Fukushima Daiichi Nuclear Power Station Unit 1 - 3 (Reference)	Document	12 September 2012
Unit 1 & 2 & 3	Decrease in the Reactor Injection Amounts at Unit 1-3 at Fukushima Daiichi Nuclear Power Station (Follow-up Report)	Document & photos	11 September 2012
Unit 1 & 2 & 3	The Reactor Pressure Vessel Temperature and the Amount of Water Injection to Reactor at Fukushima Daiichi Nuclear Power Station Unit 1 - 3 (Reference)	Document	11 September 2012
Unit 1 & 2 & 3	The Reactor Pressure Vessel Temperature and the Amount of Water Injection to Reactor at Fukushima Daiichi Nuclear Power Station Unit 1 - 3 (Reference)	Document	10 September 2012
Unit 1 & 2 & 3	The Reactor Pressure Vessel Temperature and the Amount of Water Injection to Reactor at Fukushima Daiichi Nuclear Power Station Unit 1 - 3 (Reference)	Document	07 September 2012
Unit 1 & 2 & 3	The Reactor Pressure Vessel Temperature and the Amount of Water Injection to Reactor at Fukushima Daiichi Nuclear Power Station Unit 1 - 3 (Reference)	Document	06 September 2012
Unit 1 & 2 & 3	The Reactor Pressure Vessel Temperature and the Amount of Water Injection to Reactor at Fukushima Daiichi Nuclear Power Station Unit 1 - 3 (Reference)	Document	05 September 2012
Unit 1 & 2 & 3	The Reactor Pressure Vessel Temperature and the Amount of Water Injection to Reactor at Fukushima Daiichi Nuclear Power Station Unit 1 - 3 (Reference)	Document	04 September 2012
Unit 1 & 2 & 3	The Reactor Pressure Vessel Temperature and the Amount of Water Injection to Reactor at Fukushima Daiichi Nuclear Power Station Unit 1 - 3 (Reference)	Document	03 September 2012
Unit 1 & 2 & 3	Decrease in the Reactor Injection Water Amounts at Unit 1-3 of Fukushima Daiichi Nuclear Power Station	Document	03 September 2012
Unit 1 & 2 & 3	Fukushima Daiichi Nuclear Power Station Unit 1-3 RPV Temperatures and Reactor Injection Water Flow Rates (Reference)	Document	31 August 2012
Unit 1 & 2 & 3	Operational Commencement of the Refrigerators Installed by the Treatment Water Buffer Tank at Fukushima Daiichi Nuclear Power Station	Document & photos	17 July 2012
Unit 1 & 2 & 3	Change in the Water Injection Amounts at Fukushima Daiichi Nuclear Power Station towards Summer 2012	Document	25 May 2012
Unit 2	Results of Survey on Thermometer at Unit 2 Reactor, Fukushima Daiichi NPS	Document	03 March 2012
Unit 2	Fukushima Daiichi NPS Unit 2　The temperature of the lower part of the reactor pressure vessel (upper part of the bottom head／upper part of support skirt junction) (Reference)	Document	03 March 2012
Unit 1 & 2 & 3	Reactor Water Injection Line from the Reactor Water Injection Pump in the Turbine Building of Fukushima Daiichi NPS	Document	26 January 2012
Unit 1 to 3	Test Run of Reactor Injection Pump in the Turbine Building of Unit 1 to 3	Document	27 December 2011
Unit 1	Increase in the amount of water to the reactor of Unit 1 in Fukushima Daiichi Nuclear Power Station	Document	28 October 2011
n/a	Accumulated water treatment analysis result	Document	21 October 2011
Unit 2	Operation of Filling Water to Reactor Water Level Gauge in Unit 2 at Fukushima Daiichi Nuclear Power Station	Document	21 October 2011
n/a	Water injection practice at Fukushima Daiichi Nuclear Power Station	photos	12 October 2011
n/a	Reactor and Fuel Status in Case of a Reactor Water Injection System Malfunction	Document	01 October 2011
Unit 2 and Unit 3	Increase of water injection through the core spray system of Unit 2 and Unit 3 of Fukushima Daiichi Nuclear Power Station	Document	16 September 2011
Unit 2	Adjustment of the water injection amount after the addition of the injection line (reactor feed water system → reactor feed water system + Core Spray System) to the reactor of Unit 2, Fukushima Daiichi Nuclear Power Station	Document	14 September 2011
Units 1-3	Fukushima Daiichi Nuclear Power Plant Units 1-3 Additional installation of the Reactor coolant injection mini flow line	Document	11 September 2011
Unit 1-3	Water injection into the reactor of Fukushima Daiichi NPS Unit 1-3	Document	09 September 2011
Unit 3	Fukushima Daiichi Nuclear Power Station Monitoring Result Regarding Water Injection for the Reactor through Core Spray System of Unit 3 (air dose rate)	Document	03 September 2011
Unit 3	Flow Rate Adjustment after Addition of CS Line (FDW→FDW+CS)	Document & photos	31 August 2011
Unit2	Outline drawing of High Pressure Core Spray System Unit2 of Fukushima Daini Nuclear Power Station	Document	30 August 2011
Unit 3	Fukushima Daiichi Nuclear Power Station - Unit 3 Diversification of A Method of Water Injection to Nuclear Reactor by Adding Core Spray System Line	Document	23 August 2011
Unit 1-3	Schematic Drawing of the Reactor Water Injection System at Unit 1-3, Fukushima Daiichi Nuclear Power Station	Document	16 August 2011
Unit 1-4	System outline of circulating injection cooling	Document	01 July 2011
Unit 1-4	Outline of Circulation and Injection System of Cooling Water	Document	28 June 2011
Unit 5	Temperature of Reactor Water and Spent Fuel Pool, Unit 5 Fukushima Daiichi Nuclear Power Station	Document & photos	29 May 2011
Unit 1-3	Decay Heat of Fuel in Reactor(changes in a half year period after the earthquake)	Document	26 May 2011
Unit 3	Diagram of Water Injection to the Reactor Unit 3 of Fukushima Daiichi Nuclear Power Station	Document	08 May 2011