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Occasional Topics > CN1 - JP1 - CN2 - JP2 - CN3 - JP3 - JP4-JP5(1)
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Japan Column
 
July 22th, 2011
Measures for Tsunami Striking Nuclear Power Station in Japan
Special Article: The Great Tohoku Earthquake (1)
 
 

1. Outline of Tsunami Occurred in Fukushima

The tsunami caused by the Great Tohoku Earthquake occurred on March 11, 2011. The principal cause of the accident at Fukushima Nuclear Power Station No. 1 was a loss of all of safety functions by the tsunami beyond the anticipation.
The possibility of a failure of cooling apparatus caused by earthquake movement seems low when considering the facts that the maximum acceleration by the earthquake was in the same level in value as the one measured at the station according to the observation data, and comparing with circumstances of the disaster at Onagawa Nuclear Power Station. It is presumed that the sea water pump and the emergency diesel generator lost its functions, which developed into a loss of all of AC power. Investigation on tsunami that hit the Fukushima Nuclear Power Station No.1 was carried out (no effect of crustal movement is considered), and the results are described as itemized in the below;

(1) inundation height: was O.P. about 14-15m (inundation depth is about 4-5m) from the sea level at the area of the main building ,

(2) inundation area: was extended over sea side area (land height O.P. about +4m) and all areas of the main building,

(3) run-up height: was O.P. about +14.5m estimated from marks left on slanted area, or road.

As viewing in the above, a 15m high tsunami that hit Fukushima Nuclear Power Station, which height exceeded 9.5 m over 5.9m of an evaluation value examined by Japan Society of Civil Engineering at the power station. This outline is based on information provided by Nuclear and Industry Safety Agency.

2.About Implementation of Emergency Safety Measures for All Other Nuclear Power Stations Considering Relevancy to the Disaster at Fukushima Nuclear Power Station

2.1 Instructions Given by the Nuclear and Industry Safety Agency

On March 30th, 2011, the agency gave all operators an instruction, “About Implementation of Emergency Safety Measures for All Other Nuclear Power Stations Considering Relevancy to the Disaster at Fukushima Nuclear Power Station” . The contents of the instruction are shown as follows:
“While continuing to cope with the accident occurred recently at Fukushima Nuclear Power Station No.1, the drastic measures are worked out as getting the whole picture of the accident as well as a mechanism of the tsunami occurred to understand and clarifying how it happened. Based on information known for the failure of cooling functions due to a loss of all AC powers at Fukushima Nuclear power station, the agent requested operators, which include many other nuclear power stations currently in operation as well as ones scheduled to be in operation, to plan now for the emergency safety measures as stated in the code 2.2 from, and also to quickly report a status of the implementation for which report will be examined strictly by inspection.”

2.2 The Contents and Implementation of Emergency Safety Measures

The tsunami owing to a great earthquake caused the accident at Fukushima Nuclear Power Station, which brought serious outcomes as described in the below;

(1) was unable to secure the emergency power as loss of outer power occurred,

(2) lost the sea water facility or its functions to release heat into sea from the core after its shutdown,

(3) was unable to mobilize supply of cooling water when stopped cooling for the spent fuel pool or normal water supply from the facility,

It is conceivable that those were direct causes to magnify the accident which brought further into either the nuclear disaster, or a larger scale of the disaster. For these reasons, all operators except Fukushima Nuclear Power Station No. 1 and No.2 were called for reinforcement of safety measures, which are described as follows;

a. Demand on the Regulations
Even in case of emergency of a loss of all three functions ( all AC power sources, sea water cooling, and cooling spent fuel pool), actions to recover cooling functions are to be taken while preventing damage of the core and spent fuel, and controlling release of radioactive materials.

b. Specific Items on Demand
These items on demand are presented as follow:

1) carrying out an emergency inspection; to inspect equipment and facilities for handling of emergency,

2) inspection on the plan for response to emergency and on drill implementation; to inspect the plan on assumption of the loss of all AC power sources and functions of sea water cooling and cooling spent fuel pool,

3) securing of electric powers; to mobilize and secure alternative electric power when the emergency electric power is not secured due to loss of electric power in the facility,

4) securing of a heat removable system as last measures in emergency; to prepare flexible recovery measures for the heat removable system on assumption a loss of a sea water facility or its functions,

(5) securing of cooling spent fuel pool in emergency; to implement flexible measures to provide cooling water in the case that cooling spent fuel pool or normal water supply stops, and

(6) implementation of measures needed for now concerning about structures of each site.

Operators of all nuclear power stations were requested to immediately take in the emergency measures mentioned in the above , and also requested to submit a status report of implementation of these emergency safety measures (including the future plan) to Nuclear and Industry Safety Agent. Once the agent receives the status report and an application for its permission for the safe code that is taken in the safety measures, they approve the permission after examining the adequacy. In the same time, the safety inspection makes sure the implementation status for each power station.

2.3 Criteria for the Examination of Confirmation on Implementation Status of Emergency Safety Measures

It is announced officially that the confirmation is made by verifying each item in the measures to see that it is appropriately implemented based on criteria of the examination, of which items are described in the below:

(1) implementation of the emergency inspection; to maintain equipment appropriately, that is that equipment units, and parts and materials needed in emergency are in good condition and are ready for use,

(2) inspection of the plan for emergency measures and implementation of the drills;

- to maintain systematically the manual of emergency measures, and to make the relevant people familiar with the manual and to get the people trained,
- to show clearly their duties and the person in authority in the procedural manual to respond to the emergency before fuel damage occurs, and
- to have the manual that reflects items that was improved as results of the drills, and to have PDCA in cycling to make the continuous improvement.

(3) securing emergency electric power

- to have the power-supply car with enough capacity and the connecting cable that is long enough to connect, and also to hold equipment and materials in storage on the ground that is high enough, and
- to make sure through the drill exercise the total time necessary to move the car to the site and to connect the cable.

(4) securing the heat removable system as last step for emergency

- to secure the pump that has enough flow rate and discharge pressure, to have the temporary hose that is long enough, to secure multiple water sources which have abundant water, and to keep and install the equipment and materials on the ground that is high enough for fear that a tsunami hits them,
- to secure the monitoring instruments for water level, temperature and pressure in the reactor, and to secure driving sources of equipment which composes the cooling system, and
- to properly incorporate in the procedure manual the instruction and the authority to operate a reactor container vent and to pour sea water into the reactor.

(5) securing cooling spent fuel pool for emergency

- to secure the pump that has enough flow rate, the temporary hose that is long enough, multiple water sources that have abundant of water, and to hold the equipment and materials on the ground that is high enough not to be affected by tsunami,
- to secure the monitoring instruments for water level and temperature in the spent fuel pool , and to secure driving sources for equipment which composes a system to maintain water level,
- to properly incorporate in the procedure manual the instruction and the authority to operate to pour sea water into the spent fuel pool.

(6) implementation of necessary measures for now to deal with issues on structures of each site.

- to have a plan to install additional emergency power generator(s) as earliest possible on the ground that is high enough not to be affected by tsunami. Nevertheless, to have a plan to install the alternative of a large-capacity generator as earliest as possible while emergency power generator(s) are not installed yet.
- to formulate a plan to secure reserve electric motors for sea water pump and alternative sea water pumps (underwater pump, mobile pump) which are necessary for recovery of residual heat removal system installed in the building in order to bring into a cold shutdown quickly,
- to have a plan, concerning about much higher tsunami, to reinforce the building flood protection, to install or reinforces coast levee, and to install as earliest as possible flood barriers to the surrounding areas of buildings and equipment installed outside the building .

3. Implementation Details of Emergency Safety Measures for All Nuclear Power Stations that Reflects the Fukushima Accident

3.1 Outlines

All operators handled appropriately the emergency safety measures for their own nuclear power station, of which results were reported to Nuclear and Industry Safety Agent. The nuclear safety inspector examined the application for permission of the safe code change due to the measures and reports of their implementation status of the emergency safety measures submitted by operators. The inspector checked those on site to see a status of the deployment of power-supply car(s), and equipment and materials for pump car(s) as well as preparedness for the manual to handle emergency and implementation of the drills to respond to emergency. Results of these examination were disclosed to public.
The protective measures are noted as follows: as for the short-term measures, there are the measures to take for a loss of all AC power sources, and to take for building flood, whereas there are the mid-long term measures to enhance safety reliability by speeding up cold shutdown and also to take protective measures for tsunami attack. The following sections show a summary of what was confirmed about implementation of the emergency safety measures.

3.2 Measures for a Loss of All AC Powers

It was confirmed that even in case of a loss of all three functions which are all AC power sources, sea water cooling, and cooling spent fuel pool , the core is kept under the control of cooling by pouring water, which prevents damages of the core and spent fuel as well as the emission of a large amount of radioactive materials, and brings into cold shutdown at the end. The confirmed details are as follows:
(1) To Make an Emergency Plan
- confirmed that the emergency plan is formulated based on the safety code and the procedure manual,
- confirmed that the emergency plan in case of a loss of all AC powers includes the following items; 1)to have evaluation of analysis on a proper amount of water that is required to take out decay heat and to cool down the core, 2) to have a procedure manual to properly describe both water and electric power supply that are provided by water pump cars and power-supply car(s), and are carried out within a timeframe, 3) to be able to keep the reactor in a hot shutdown without a fuel damage by taking these measures,
- confirmed to install receiving inlets for water and power in multiple places of the building and also to provide multiple passages for power-supply car(s) and water pump car(s) to access in advance,
- confirmed to be able to bring into a cool shutdown by keeping the reactor cooling consistently for a long time (for PWR) or by installing temporary pump(s) or restoring sea water pump(s) (for BWR and PWR),
- confirmed that the safety code and the procedure manual clearly lay down authority for a chief of the nuclear power station to fend against the crisis and to make a decision of how to handle reactor container vent(s) and to pour water and sea water as well, which makes quick response to the emergency.
(2) To Secure Power Sources in Emergency
- confirmed that the power supply capacity is sufficient enough for monitoring of the central control room, measurement instrument operation, and valve unit operation, and also confirmed fuel used for the power-supply car to be effectively secured as well as improvements made to move storages to a higher ground and to move the reserve equipment and parts to a place closer to the site as well.
- drills confirmed that it can be done to transport, install and connect power- supply car(s) and cable(s) within the timeframe that the electric power must be restored, which timeframe is within 8 hours for BWR and 5 hours for PWR. The drills also showed that it took 3 hours for each nuclear power station of Tepco Kashiwazaki Kariha and Tokai, and about 130 min. at most for Kyushu Electric Power which has PWR. By the same token, it was 4 hours for Monjyu.
-there were cases in the drills that it took more time to transport, install and connect power-supply car(s) and cable(s). Accordingly it was confirmed to undertake the guidance to improve the way of the cable installation and to continuously take in shortening the time required.
(3) To Secure a Heat Removal System in Emergency
- confirmed that the pump car has enough capacity to supply water for taking out decay heat , and confirmed the setup that a fuel supply for a pump car is properly done,
- the drills confirmed that it can be done to transport, install and connect pump car(s) and hose(s) within the timeframe that the pump car must be ready to pure water, which timeframe must be at least within 8 hours for BWR and within 5 hours for PWR though, it was at most 4 hours for BWR at TohokuTotsu and 3 hours for HokkaidoHaku ,
- there were cases in the drills that it took more time to transport, install and connect pump car(s) and hose(s). Accordingly it is confirmed to undertake the guidance to improve the way of the transportation of hoses and to continuously take in shortening the time required.
- confirmed to secure multiple water tanks that can supply enough water, and to install the facility that takes in and supplies seawater in case of seawater use,
- confirmed to have the procedures and the setup that can make venting quickly and securely by learning from the drill to construct a vent line that is necessary to vent (BWR),
- confirmed the setup cable of venting from either the central control room or from the site in case that an air driven valve is used as venting valve, including securing a substitute for the driving source of a nitrogen cylinder
(4) Equipment Inspection and Drill implementation
- confirmed with people concerned in attendance that the equipment inspection plan is made and the inspection is implemented as well,
- confirmed that the comprehensive drill is implemented including a field drill using real equipment like a power- supply car and a pump car, a drill using a simulator for the operation and the step to operate an equipment, a drill to handle the case that loses simultaneously all functions of (全号機?) in the nuclear power station,
- confirmed with the people in attendance that issues raised from the drills and the related information are shared with parties concerned, and that leads them to make improvements in the situation.
(5) Safety Code Change
It is confirmed that the safety code or the procedure manual stipulates a plan for emergency measures which includes staff deployment, implementation of drills, deployment of equipment and materials, and periodical evaluation of these setups.

3.3 Flood Protection Measures for Buildings

The operators are to take the flood protection measures taking account of a 15m high tsunami (maximum) exceeded 9.5m which height is evaluated by the local office of Japan Society of Civil Engineers. A table 1 shows a summary of information which exhibits evaluation of tsunami and flood protection measures by nuclear power station . The flood protection measures are required to have no impact of tsunami for the equipment used for the case of a loss of all AC powers. The following items are confirmed:
- confirmed with people concerned in attendance that flood protection measures for the reactor building satisfy the requirement to protect the equipment used for the case of a loss of all AC power from the building flood even though going through a tsunami in the same magnitude as that of Fukushima Nuclear Power Station No.1 ,
- confirmed that the short term measures at all nuclear power stations is completed early,
- confirmed that flood protection measures for equipment used for the case of a loss of all AC powers is completed by those actions .

3.4 Actions to Improve Reliability by Expediting Cold Shutdown

It is demanded to have an effective action plan to reinforce emergency electric powers and also to improve reliability of the measures for a loss of all AC powers so that it makes possible to take into cold shutdown in several days. The following items are confirmed:
(1) Securing Reserve Seawater Pump(s) with Electric Motor
- confirmed the plan that can bring in about one yea reserve electric motor (s) for seawater pump and alternative seawater pump(s) which are used for parts of the residual heat removal,
(2) Installation of Air-Cooled Emergency Generator
- confirmed the plan that installs air-cooling emergency generator(s) in one to two years to provides essential amount of electricity used for each reactor.

3.5 Protective Actions for Tsunami

It is demanded to have an effective plan to make further improvement on reliability of emergency safety measures by maintaining reinforced water-tightness, coast levee, and flood barrier in good condition for fear that a tsunami impacts important equipment on a reactor safety.
(1) Installation of a Coast Levee and a Levee Surrounding the Building , and Adopting Water-Tightness Surrounding the Building.
The following items are confirmed:
- confirmed a plan to materialize enforced water-tightness surrounding the building in two to three years,
- confirmed a plan to construct flood barrier(s) or coast levee(s) in two to three years, taking account of 15 m high tsunami and the like

4. Concluding Remarks

It was concluded that emergency safety measures reported by each operator is properly implemented. From this time on, they must follow the safety inspection to make sure of a progress on the implementation of prevention measures for building flood as well as a progress on the mid-to-long term protection measures that is scheduled to implement, which includes securing reserve electric motor (s) for seawater pump, installation of air-cooling emergency generator(s) and protective actions for tsunami. Furthermore, I trust that they must undertake constant reliability improvement on emergency safety measures even though they continue to make unyielding efforts toward necessary improvements.

It was concluded that emergency safety measures reported by each operator is properly implemented. From this time on, they must follow the safety inspection to make sure of a progress on the implementation of prevention measures for building flood as well as a progress on the mid-to-long term protection measures that is scheduled to implement, which includes securing reserve electric motor (s) for seawater pump, installation of air-cooling emergency generator(s) and protective actions for tsunami. Furthermore, I trust that they must undertake constant reliability improvement on emergency safety measures even though they continue to make unyielding efforts toward necessary improvements.
Measures for Tsunami Striking Nuclear Power Station in Japan-Special Article: The Great Tohoku Earthquake (1)-