April 2, 2018
Kyushu Electric Power Company Inc.

Genkai Nuclear Power Station Unit 3:
Checking status of the small steam leak from the air vent pipe of the deaerator
Kyushu Electric Power Company confirmed a small steam leak from the air vent pipe of thesecondary system of Genkai Nuclear Power Plant Unit 3, which is PWR type and rated
electric output 1.18 million, around 19 o'clock on March 30. Genkai Nuclear Power Plant
Unit 3 was under periodical inspection, resumed power generation on March 25 this year,and adjusted operation with 75% electricity output at that time.
Since the small steam leak was confirmed, it was decided that the load would be dropped
from the electric output of 75% to stop power generation as soon as it becomes ready andinspections will be conducted as a precaution.
There is no radiation influence on the environment by this event.
(as already reported on March 30)[New information as of April 2]
The examination of the air vent pipe revealed there was a dent in the surface of the pipe andalso a penetrating hole in the dent. In addition, there were observed inside the heat insulatordiscoloration and adhered substance like rust. Since the affected pipe is located outside thebuilding, it is assumed that rainfall had come through a gap in the exterior panel, wetted theinsulator and caused the surface of the pipe to partly erode until it got penetrated.
As countermeasures, rainproof treatment shall be strengthened along with replacing theaffected pipe, exterior panel and insulator. Likewise, reinforcement of waterproofing andreplacement of the pipe, exterior panel and insulator will be implemented in terms of otherfifteen air vent pipes than the affected pipe.
Attachment:
Genkai Nuclear Power Station Unit 3: Checking status of the small steam leak from the air
vent pipe of the deaerator

(Attachment)
April 2, 2018
Kyushu Electric Power Company Inc.
(As of 10:00am)

Genkai Nuclear Power Station Unit 3
Checking status of the small steam leak from the air vent pipe of the deaerator
1.

Date and time of the event
Around 19:00, March 30, 2018

2.

Place of the event
Genkai Nuclear Power Station Unit 3

3.

How the problem was detected and handled
Genkai Unit 3 restarted power generation on March 25, 2018. It was in the controlled
operation with 75% output when the small steam was detected around 19:00, March 30,
from the air vent pipe of the deaerator in the secondary system.
Therefore the power was decreased so that the generator got off the grid, which madepossible inspection of the air vent pipe of the deaerator.
No radioactive impact to the environment due to this even is confirmed.
(See appendices for details)(Event history)
March 25

14:29

Synchronizing to the Grid

March 2600:35

35% output

March 27

17:00

50% output

March 30

19:00

75% output

March 30

around 19:00

Small steam leak was detected

March 31

01:00

Start decreasing output

March 31

06:02

Generator off the grid

March 31

09:00

Start preparation for self-inspection

April 1

14:20

Start of self-inspection

4.

Check results

Since a small steam leak was found from the 5th air ventilation pipe (hereinafter referred toas "the affected pipe") of the 3B deaerator, check of all the air ventilation pipes (total of 16 ineach of the 3 A and 3 B deaerator) was carried out as follows.
(1) Check of insulation material of air ventilation pipes (including exterior plate)a.

Exterior plate
Condition check on the exterior panels of all the air ventilation pipes of the3A and 3B deaerators was carried out.
The results are as follows.
[The affected pipe]
Significant rust was observed on a part of the lower surface of the exterior
panel of the pipe.
[Other air ventilation pipes]
No significant rust was found on the exterior board of the other air ventilation
pipe.

b.

Thermal insulation material
Condition check on thermal insulation materials of all ventilation pipes of 3Aand 3B deaerator was carried out. The results are as follows.
[The affected pipe]
Adhered substances such as discoloration and rust were found in the heatinsulation material, which contacts the pipe partly.
[Other air ventilation pipes]
No adhered matter such as discoloration or rust was found for the heatinsulation material of the air ventilation pipe other than the affected pipe.
(Appendix – 4, 5)(2) Check of air ventilation pipesa.

Observation check
Condition check on all ventilation pipes of deaerators 3A and 3B was carriedout. The results are as follows.
[The affected pipe]
A clear indent was found in the horizontally running part of the affected pipe.
The indent was on the upper side of the pipe and one penetrating hole(length approx. 13 mm × width approx. 6 mm) was found in it.
The pipe in the vicinity of the penetrating hole was indented in the direction

from the outside to the inside of the pipe.
No clear indent was found in other areas of the affected pipe.
[Other air ventilation pipes]
No clear indent was found in the air ventilation pipes other than the affectedpipe.
b.

Inner check
After detaching the affected pipe, a fiber scope was inserted inside andcheck of inner surface of the pipe was carried out. As a result, thepenetrating hole was found on the upper side of the pipe runninghorizontally.
The inner check revealed there was no clear denting in the direction from theinside to the outside of the pipe.
(Appendix – 4, 6)

5.

Estimated cause

The affected pipe is located at the top of a deaerator installed outdoors.
Therefore, seams are filled by caulking or the like so that rainwater does not enter inside theexterior panel.
Confirming the situation of the exterior panel and pipe, it is considered that rainwater
intruded from the gap of the exterior board, the heat insulation material absorbed water andbecame a wet state, causing the erosion of external parts, which progressed and became
penetrating hole.
6.

Counter measure

Replacement of the affected pipe, insulation material and exterior plate in which thepenetrating hole was found will be conducted.
In addition, with respect to 15 air ventilation pipes other than the affected pipe, the heatinsulation material and the exterior board will be replaced with new ones. At the same time,
all the air ventilation pipes will be replaced as precaution.

Appendices1.

System diagram (omitted)

2.

Schematic of the deaerator (omitted)

3.

Specification of the deaerator

4.

Photographed locations of the heat insulator (incl. the exterior panel) and the air ventpipe

5.

Visuals of the heat insulator (incl. the exterior panel) and pipes

6.

Visuals of the air vent pipe

Appendix – 3

Deaerator Main Spec
1.Main Spec
Main Material

Main Item
Name

Deaerator

Water Storage TankNameType

Horizontal Spray Tray

Horizontal Cylindrical Tray

Shell

NumberHeadMaximum Pressure

Tray

Deaerator

Water Storage
Tank

Maximum Temperature
Volume of WaterStorage Capacity(NWL)
Bore Size
Shell Thickness
Head Thickness
Full Length

2.Ventilation Pipe Spec
Name

Deaerator Air Ventilation Pipe

Outer Size
Thickness
Material

The blank cell contains commercially confidential
information which cannot be disclosed

Appendix – 4

Photographed locations of the heat insulator (incl. the exterior
panel) and the air vent pipe
Circled numbers show photographed
locations of the affected 5th Air Ventilation
Pipe of the 3B Deaerator.
Photos are included in the Appendix 5 and 6.

HeaderLeak point
Deaerator※Photos of ⑥ and ⑦ were taken at 3rd Air Ventilation Pipeof 3A Deaerator for comparison with an undamaged pipe

Deaerator 3B
Air Ventilation Pipes

Deaerator 3A

AirDeaerator 3B
Leak point(5th Air Ventilation Pipe )Water Storage Tank

Appendix – 5 (1/2)

Visuals of the heat insulator (incl. the exterior panel) and pipes○ Near the Leak Point (5th Air Ventilation Pipe of the Deaerator 3B)

Photo ①

Appendix – 5 (2/2)

Visuals of the heat insulator (incl. the exterior panel) and pipes○ Outside Observation Condition of Thermal Insulation Material(5th Air Ventilation Pipe of the Deaerator 3B)

Photo ②○ Inside Observation Condition of Thermal Insulation Material(5th Air Ventilation Pipe of the Deaerator 3B)

Photo ③

Appendix – 6 (1/3)

Visuals of the air vent pipe (Outside)○ Leak Pipe(5th Air Ventilation Pipe of the Deaerator 3B)

Photo ④
○ Leak Point (5th Air Ventilation Pipe of the Deaerator 3B)

Photo ⑤

Appendix – 6 (2/3)

Visuals of the air vent pipe (Outside)○ Other Leak-Free Pipe (3rd Air Ventilation Pipe of the Deaerator 3A)

Photo ⑥

Photo ⑦

Appendix – 6 (3/3)

Visuals of the air vent pipe (Inside)○ Inside Observation Condition of Leak Pipe(5th Air Ventilation Pipe of the Deaerator 3B)

Photo ⑧