a running report on the Mihama-3 accident by Hosokawa Komei

Magpie News

a running report on the Mihama-3 accident by Hosokawa Komei

The reports posted below proceed from the most recent one. Scroll down to see older reports.

The content of this page was originally published as a MagpieNews mailing list message edited by Hosokawa Komei .

Contact Details
Dr K. Hosokawa
email: magpie@kyoto-seika.ac.jp
fax: +81-75-702-5213
snail mail: Dept of Environmental & Social Research,
Kyoto Seika University, 606-8588 Japan

Disclaimer: MagpieNews works in co-operation with CNIC for making a nuclear-free world. However, the editor of MagpieNews, and not the CNIC, is responsible for any mistake or error thay may be found in the text of MagpieNews.

12th report
4 September 2004
11th report
26 August 2004
10th report
24 August 2004
9th report
17 August 2004
8th report
16 August 2004
7th report
16 August 2004
6th report
14 August 2004
5th report
14 August 2004
4th report
12 August 2004
3rd report
10 August 2004
2nd report
10 August 2004
1st report
9 August 2004


MagpieNews #040904a1: Mihama Accident 12th report
150 Policemen raid the nuclear power station; unchecked weak points found out in many of the KEPCO reactors; FAC breakage had already occurred in PWRs and BWRs nationwide.
4 September 2004, Kyoto, Japan

Early this morning (September 4), a convoy of wagons carrying 150 officers from the Fukui Prefectural Police crossed the entrance bridge that connects the Mihama Nuclear Power Station and the outside world. The police are raiding the power station to confiscate the power plants’ safety inspection records and related documents and electonic files. The raid search may take a few days.

The police already sent engineers two days earlier (on Sep 2) to start physically cutting out the main pipe section that exploded in the August 9th accident at the power station’s reactor unit No.3. Two pieces of the carbon steel pipe (i.e. the very part of the burst and another unbroken section for comparison) will be confiscated and sent to the Japan Atomic Energy Research Institute (JAERI) in Tokai-mura, Ibaraki, east Japan, for close examinations.

After the fatal pipe burst at Mihama-3 PWR, the nuclear regulator NISA ordered all the utilities that run nuke reactors in Japan to review their inspection records to see whether any vulnerable part of the coolant piping of both nuclear and non-nuclear plants remained unchecked. Also NISA themselves had an urgent review of the past records of ‘incidents’ (which is a METI euphemism for troubles and accidents).

Results of these reviews have turned out awful in many ways.

NISA reported at a meeting of the Mihama-3 Accident Investigation Committee of METI, on August 19, that there had so far been 9 incidents of steam leaks and pipe breakage in nuclear power plants (not only PWRs but also BWRs) as well as 7 similar incidents in thermal power plants, fortunately all without casualties.

Japan Atomic Power Company (JAPCO) reported a ‘narrow escape’ story. In Tsuruga Unit 2 (PWR, 1,160MW, 15 years old), located not very far from Mihama in the same Fukui Province, the identical section of the secondary cooling pipe was not listed in the inspection checklist until 2001. The list was prepared by Mitsubishi Heavy Industry, the manufacturer of the Westinghouse model PWR (i.e. the same as the Mihama reactors). In 1999, Mitsubishi realized that carbon steel pipe wall thinning could proceed very much faster than they had calculated. So they say they have advised all the PWR operators (including KEPCO) of their concern. Fortunately in Tsuruga station, the operator (JAPCO) and Mitsubishi cross-checked the inspection handbook against the actual piping map, and they detected in December 2000 that a location downstream of an orifice in the condensate system of Tsuruga Unit 2 (i.e. the very same part of the pipe that were to explode in Mihama-3 in August 2004) was missing in the inspection list. The pipe in question in Tsuruga-2 has since been regularly tested with ultrasonic devices and, in September 2003, an excessive thinning was proved (the originally 12-mm thick pipe had been degraded to 7.2mm, i.e. only 2.2 years of safety life left against the state sanctioned limit of 6.4mm). The pipe is now to be replaced in December 2004 during scheduled outage. (This decision was taken before the Mihama-3 accident.)

Similar story is reported from Hokkaido Electric Power Company, which runs PWRs in its nuclear station in Tomari village, Hokkaido, northern Japan. In Tomari Unit 1 (PWR, 579MW, 15 years old), a similar fault in the checklist was detected in 1996. A section downstream of an orifice was missing in the list provided by Mitsubishi. The section in question was tested and wall thinning (10mm to 7.4mm) was confirmed. In 2000, the operator replaced the pipe with a new stainless steel one.

If KEPCO had followed the safety precaution such as actually taken in the Tsuruga-2 and Tomari-1 cases cited above, the Mihama-3 accident must have been avoided.

KEPCO revealed that there were 17 unchecked pipe sections in the 11 PWRs in Mihama, Takahama and Oh’i nuclear power stations, all in Wakasa District (Fukui Prefecture), north of Kyoto. These sections were all missing in the inspection handbooks prepared by Mitsubishi. One of the unchecked pipes in Mihama-3 had had its life expired 9 years ago without being inspected at all. Other uninspected pipes have been reported from Takahama-1, Takaham-2, Takahama-3, Oh’i-3 and Oh’i-4. (But even worse cases are reported from Mihama units, as described later.)

All these sections should have been checked if the company’s guideline (see MagpieNews #040817a: Mihama Accident Report No.9) were duly observed. Particularly serious cases in KEPCO include 4 unchecked locations in the main feedwater pipe (45mm in diameter) in Takahama Unit-3 reactor (between a valve downstream of the feedwater pump and the steam generators). In press conference, KEPCO refused to answer the question by a news reporter, ‘What if the feedwater pipe ruptures?’ The TMI operators would know the answer quite well.

Of the 17 unchecked pipe locations of concern mentioned above, KEPCO initially reported only six cases. Surprising even the pro-nuke METI officials, KEPCO claimed that the rest 11 cases are ‘virtually checked’ since the corresponding locations in their twin plant (i.e. another plant of the same model/design/age) had been checked and proved safe. This ghastly claim was naturally rejected as irrational by NISA, which ordered KEPCO to carry out actual thickness tests.

In Mihama’s Unit 2 reactor, an even more appalling practice of KEPCO has been disclosed. During the routine outage of the plant in September last year, KEPCO found at one section of the main feedwater pipe (i.e. the system which provides a SG with coolant in 80 times the atmospheric pressure) that the pipe wall was only 17.4mm thick (degraded from the original 21.4mm) whereas the minimal safe thickness required by the technical guideline was 17.4mm. The pipe should have been replaced immediately, but what KEPCO actually did was to apply an ad hoc discount to the guideline1 and restart the reactor in December 2003 with the old feedwater pipe. NISA investigators saw through the plot and ordered KEPCO to replace the pipe as soon as possible.

The above was revealed by NISA on August 27. Earlier on August 23, KEPCO stated in a press conference that the emergency inspection (conducted after the Mihama-3 accident) was completed at Mihama-2 and all the inspected pipe sections had no problem in thickness. NISA source says that similar practices of inadequate discounting of safety standard may be the case in several pipe sections in Mihama Units 1 and 3.

1: KEPCO here applied a thermal plant technical standard and unlawfully re-interpreted the mandatory thickness as 14.8mm. A shameless act of doctoring, obviously.

[sources: Kyodo News and Jiji Press; Mainichi, Yomiuri, and Sankei newspapers; NHK]

Key to acronyms:
NISA = Nuclear and Industrial Safety Agency (of METI)
METI = Ministry of Economy, Trade and Industry
KEPCO = Kansai Electric Power Company
JAPCO = Japan Atomic Power Company (a joint venture of 10 utilities)
FAC = flow-accelerated corrosion
PWR = pressurized water reactor
BWR = boiling water reactor

MagpieNews #040826: Mihama-3 Accident, 11th Report
Death toll turns to five
26 August 2004, Kyoto, Japan

One of the hospitalized workers who were severely injured in the August 9 accident at Mihama nuclear power station’s Unit-3 turbine building died yesterday (August 25). He had 89% of his body burned and was in critical condition in ICU at the Medical School Hospital of the University of Fukui. He had extensive skin transplantations in vain. The 30-year old subcontractor was survived by his wife and 3-month old baby daughter.

The toll of the Mihama-3 accident has turned to five.

As reported in the previous issues of MagpieNews, criminal investigation by the Fukui Police is on the way.

Fukui Labor Bureau (a Ministry of Health and Labor agency) and its district Labor Standards Inspection Office also decided earlier (on August 17) to file the case to prosecutors, accusing KEPCO, operator of the nuclear plant, of violating the industrial safety law by illegally forcing employees, mostly subcontractors, to work under dangerous conditions.

[sources: Kyodo News, Jiji Press, Japan Times, Yomiuri and Mainichi newspapers]

MagpieNews #040824a: Mihama-3 Accident, 10th Report
Another blast at a relatively new piping; Aging may not be the main factor of the Mihama-3 rupture
24 August 2004, Kyoto, Japan

In a shocking sequel to the Mihama-3 accident, there was an explosive breakage of a carbon steel pipe in the Unit-2 turbine building of Shinchi Power Station in Sohma City, Fukushima, east Japan.

On August 15, an originally 10.3mm-thick pipe (30cm in internal diameter) in the feedwater heater drain system ruptured at 66cm downstream of a valve where the pipe diameter is narrowed to 15cm internally. Highly pressured 200 Celcius steam burst out from a 9cm x 18cm hole on the pipe’s upper wall. It was lucky there was no casualty since nobody was in the turbine building at that moment. The broken part of the pipe wall was only 1.4mm thick. Cavitation and FAC (flow-accelerated corrosion) are suspect.

The Shinchi unit is a coal-fired thermal plant relatively young of age, 9 years old. But the rupture occurred in an extremely similar condition to that of the fatal pipe burst of August 9 at the 28-year old Mihama Unit-3 nuke plant. Engineers in the utilities are all stunned, because it is now probable that such corrosion thinning and rupture can occur at any time in any carbon steel piping where cavitation and FAC may be taking place.

It was not until August 17 that the operator of the Shinchi plant, Soma Kyodo Thermal Power, a JV of Tokyo and Tohoku Electric Power Companies, publicized that the accident had happened.

[sources: Mainichi, Kyodo, Japan Times, KEPCO, METI]

In the previous issue of MagpieNews (Mihama accident report No.9), KEPCO was illustrated as “the operators of the 12 nuclear reactors in Wakasa District. It should read “11 nuclear reactors.” (There are 15 reactors in Wakasa, of which eleven are run by KEPCO, two are run by JAPCO, the remaining two are the FBR Monju and ATR Fugen operated by the Government agency, JNC; Monju and Fugen are not running now.)

MagpieNews #040817a1: Mihama-3 accident, 9th report
Why all this happened? An analysis of corporate irresponsibility of the second-largest utility in the country.
17 August 2004, Kyoto, Japan

In the wake of the fatal burst at Mihama Nuclear Power Station (NPS)’s Unit-3 plant, the Ministry of Economy, Trade and Industry (METI) ordered all the power companies to re-check their checklists if there was any section of secondary cooling system remained unchecked.

Now, KEPCO (Mihama’s operator company) says, as an interim report to METI and Fukui Prefecture administration, that they have found that at least four sections of piping in their nuclear stations are not on the checklist (while they should be) and have never been inspected (while they should have been) since the start up of each reactor. The identified sections bear the same conditions as the ruptured Mihama-3 condensate pipe (i.e. made of carbon steel; located downstream of an orifice or a control valve where flow-accelerated corrosion is likely; etc).

These newly found sections are in by pass lines1, so there is no immediate danger to the operation of reactors2, says KEPCO. But the findings are of vital meaning that the utility has been operating the nuclear reactors with deficient checklists, which did cause the August 9 explosion that killed four local workers.

Not only the regulators (NISA, METI and NSC), but the utilities themselves have specific guidelines about which pipes to check first, how often to check, how to assess the degradation such as pipe wall thinning, and when to replace the degraded pipes. As for the secondary system, KEPCO has “Management Guideline for the Thickness of Secondary Coolant Piping” (1990), which is shared with other PWR operators (Shikoku, Kyushu and Hokkaido Power Companies and JAPCO). The guideline unequivocally specifies that carbon steel pipes in downstream of an orifice or a control valve, where FAC (flow-accelerated corrosion) is likely to occur, should be regularly tested.

The guideline also includes a formula to calculate the pipe wall thinning rate, so that the plant operators can anticipate the life (hardware durability) of carbon steel pipes. Now, it is revealed that, according to KEPCO’s own guideline formula, the pipe that exploded on Monday 9 was 13 years overdue (i.e. its life had lapsed 13 years ago!), and the other unchecked pipe that was identified yesterday is 9 years overdue. According to the formula, a 10mm carbon steel pipe in downstream of an orifice flowmeter is degraded, after 102,222 hours of PWR operation, to 4.7mm in thickness, which is the durability limit as sanctioned by NISA/METI. At the time of August 9 accident, Mihama-3 had been operating for a total of 186,000 hours and the broken pipe wall was only 0.6mm to 3.5mm thick.

KEPCO says they have not made the calculation because the pipes in question were not listed up. It’s now becoming very clear that the operator of the 11 nuclear reactors in Wakasa District (of Fukui Province), north of Kyoto, is doing the job in an unbelievably careless way.

Why all this happened is the focus of criminal investigation. Fukui Police has already started to investigate the Mihama-3 accident as a manslaughter case. KEPCO keeps its secretive corporate character, repeating that “we cannot talk much about what is under police investigation.”

MagpieNews sums up that the process is more or less like the following:

1) The accident in Surry-2 occurred in 1986.

2) The then Ministry of International Trade and Industry (MITI, currently METI), Tokyo, requested Japanese utilities to work out a new management guideline for the secondary cooling system of nuclear reactors.

3) KEPCO formulated a guideline in 1990, which mentioned above. (MITI/METI has not reviewed the details of the KEPCO guideline’s contents.)

4) KEPCO asked Mitsubishi Heavy Industry (manufacturer of the Mihama PWR) to collate this guideline with the actual piping map of the Mihama plant and prepare a checklist for routine inspections. Mitsubishi made a checklist of some 6,000 items of inspection. (KEPCO has not reviewed the Mitsubishi checklist seriously and has never checked it against its own management guideline.) Certain sections of the cooling system were missing in the Mitsubishi checklist; those sections include the location of the August 9 rupture and the newly identified locations mentioned above.

5) The inspection contract between KEPCO and Mitsubishi expired in 1996. The work was taken over by a KEPCO subsidiary, Nihon Arm Co., with the checklist unrevised. (Nihon Arm has not reviewed the Mitsubishi checklist against the KEPCO guideline; KEPCO has not asked Nihon Arm to do so.)

6) Mitsubishi engineers learned from US NRC documents and other expert reports that the pipe wall thinning downstream the orifice can proceed at a speed faster than they had previously assessed. In 1999 and in 2000, Mitsubishi advised Nihon Arm (and KEPCO) of the necessity of ultrasonic test in the condensate piping; Nihon Arm thought it was not urgent, without checking it against the guideline, and did not report the matter to KEPCO. KEPCO claims there was no advice either from Mitsubishi or Nihon Arm.

7) Nihon Arm realized, upon repeated notice from Mitsubishi in April 2003, that certain risky sections are missing in the checklist. Nihon Arm claims that they notified KEPCO; KEPCO denies it.

8) The periodic inspection of Mihama-3 in August 2003 was concluded without inspecting the pipe sections in question.

9) Nihon Arm added the sections in question onto the checklist and submit it to KEPCO. KEPCO claims that they had no explanation of the addition, let alone the reason of the addition. Nihon Arm says KEPCO must have received an e-mail message indicating that the added items were missing in the previous checklist. (The Mihama-3 accident would have been avoided if KEPCO and/or Nihon Arm had done the proper calculation of thinning rate of the sections newly added to the list.)

10) Periodic inspection of Mihama-3 was to commence on 14 August 2004, during which an ultrasonic test was going to be applied for the first time since commissioning of the plant to the condensate pipe which did not endure the last 5 days and ruptured on 9 August. Eleven workers were hit by the explosion, of which 4 were killed instantly and one is still unconscious in critical condition.

Simply if KEPCO had checked what its contractors were doing with the risky parts, the accident and the casualties would have been avoided. Dr Koide Hiroaki of Kyoto University Research Reactor Institute has this to say [Yomiuri Newspaper, 17 August 2004]: “The accident reveals the nature of corporate irresponsibility of KEPCO, who leaves imperative safety checks to its contractors and subcontractors and just keeps its hands off.”

At the moment, all the companies and the regulators are blaming each other. Well, Colombos of Fukui Police will be sorting out the matter, hopefully.

To wind up the brief, we have a couple of intriguing facts. First, before the accident, KEPCO had told the nuclear safety inspectors of the Fukui Prefecture that the August 2004 inspection of Mihama-3 would take 4 months rather than the normal 2 months. The explanation was “replacing of the piping may be necessary if some abnormalities are detected”. An insider suggests [Sankei Newspaper, 13 August] that the company was aware that an extensive replacement of the piping was necessary.

The other fact also indicates that KEPCO was aware of the structural problem with the orifice flowmeters. In the utility’s newest reactors, Oh’i-3 and -4 of which the construction started in 1987, they abandoned the orifice and adopted the flow nozzles, which is another kind of flowmeter with less FAC effect.

1: They are steam converter pipes in which steam heated to 200 Celcius and pressurized up to 20 runs to empower sea water desalting system and air conditioners in the turbine building
2: . The reactors in question are Takahama-1, Oh’i-3, Oh’i-4, and Mihama-3 (different section from that of August 9 accident). Of these, only Takahama-1 is running at the moment.

[sources: Kyodo, Yomiuri, Sankei, Mainichi, Asahi Broadcasting Corp., KEPCO, NSC, NISA/METI]

MagpieNews #040816b1: Mihama-3 accident, 8th report
Saltwater leak in the condenser may be another factor of the Mihama-3 cooling system breakage
16 August 2004, Kyoto, Japan

According to the previous “minor incident” record of the Mihama Unit-3 plant, which had the pipe rupture and the loss of secondary coolant accident last week, the unit had experienced saltwater leak in the condenser twice.

In Japanese PWRs, the secondary coolant, which is light freshwater/steam, is cooled down by the tertiary coolant, which is sea water. (Remember all the nuclear power plants in Japan stand by the sea.) Cold saltwater is taken in from the sea, made to run in 60,000 small tubes around the condenser, in which the sea water absorbs the heat of the turbine steam and then goes back out to the sea, this time as hot water. (The hot discharge bears not a small impact on the marine environment, but that’s another story now.)

In August 1993, in Mihama Unit-3 reactor system, salinity in the secondary coolant water was detected at downstream of the condenser. One of the condenser tubes had been damaged and the sea water leaked in. (The damaged tube was later plugged.)

In October 1998, again in Mihama-3, the mineral detector sounded. Sea water got in the condenser through of a hole in another tube. Ultrasonic test operators also found wall thinning in two other tubes. The degraded tubes were replaced.

Each time, the reactor was not shut down but had to lower its output to 50%. Demineralizer worked well so there was nothing wrong later, claims KEPCO.

It is, however, a basic of engineering that salinity accelerates corrosion, especially in carbon steels. Although KEPCO denies the possibility of the past saltwater leaks influencing in any way on the downstream pipe rupture of Monday 9, the scientific ground of the denial is not very clear. Even such information as how much saltwater got in the system has not been specified (although roughly estimated by kilograms, not by tons, at each time).

Mainichi newspaper’s report of this morning (16 August 2004) points out that the Surry Nuclear Power Station1 had also had accidental intake of sea water into the condensate system.

Salinity and corrosion in condenser tubes have been a sort of classic trouble in nuclear and conventional thermal power plants in Japan. KEPCO says they plan to replace the steel condenser tubes with titanium ones in order to avoid the problem.

1: See MagpieNews Mihama accident report No.3 and No.4 for the relevance of the 1986 Surry-2 accident to the Mihama-3 accident.

[source: Mainichi, CNIC, Kyodo]

MagpieNews #040816a1: Mihama-3 accident, 7th report
Was there really no radioactive leak? — and some other questions
16 August 2004, Kyoto, Japan

As the previous issue of MagpieNews referred to several nuclear stations in the Wakasa district, some readers requested a map to show the location of each. Well, CNIC has already provided us with a neat graphic.

For a list of nuclear reactors, jump to another webpage of CNIC:

There have been several comments and queries concerning the previous issues of MagpieNews on the Mihama accident.

The exchanges between Seok Kwanghoon of Green Korea, Seoul, and Hosokawa Komei, editor of MagpieNews, have already appeared on the No Nukes Asia mailing list, of which a part is reproduced [with some amendment] below.

[1] question from Seok:
Does the Japanese nuclear safety regulatory body monitor or regulate nuclear operaters’ activities in the secondary coolant system besides steam generators?

[reply from Hosokawa]
# The secondary system is rather disregarded or, to say the least, not paid serious attention to. Condensate system is not included in the obligatory check-up list, though most utilities include it in the so-called “voluntary inspection list” and report the results to the Nuclear and Industrial Safety Agency (of METI).

# In the case of Mihama-3, it’s been revealed that the condensate piping (and further downstream piping) was NOT on the check-up list prepared by the Mitsubishi Heavy Industry, manufacturer of the plant.

[2] question from Seok:
Is there any possibility that the rupture in condenser pipes can give any serious impacts on steam generators? Such as sudden decrease of atmosphere(pressure) in the pipes of steam generators to their simultaneous rupture or any coolant failure…

[reply from Hosokawa]
# Yes, there surely is. I briefly pointed it out in the Magpie 2nd Report (in the second para). The break occurred in the very mainstream of the coolant circulation. Sudden depression in the secondary system can make SG tube pinholes to crack.

# It is important to realize that the Mihama-3 accident is not just “steam leak” as reported in most newspapers, but definitely a LOCA(= loss of coolant accident)-type accident.

[comment by Seok on Hosokawa’s reply above]
# It’s quite helpful for us to understand the situation in Japan. Indeed, it should be recognized as literally LOCA. Media’s vocabulary “leak” must be originated from nuclear industry’s intention to hide the seriousness of the accident.


[3] further question from Seok:
Do you think most of carbon pipelines should be replaced with stainless steel ones? Or strict safety check can be enough?

[reply from Hosokawa]
# Basically, yes. It won’t be any final solution, however. The US Nuclear Regulatory Commission (NRC) warned the corrosion vulnerability of carbon steel not long after the Surry-2 accident in 1986 [for reference to the NRC generic letter in 1989, see MagpieNews Mihama Report No.4]. As a matter of fact, some other Japanese utilities (e.g. Shikoku Electric Power Co.), and even in some other KEPCO plants (namely, Takahama-3 and Oh’i1), they did replace the carbon steel piping in the secondary cooling system with chromium-rich steel (stainless) pipes.

# Since there seem to be many other factors that have eventually made the Mihama-3 rupture occur, change of piping material is no way an end of the story. But, yes, the careless use of carbon steel was one of the most crutial factors and replacement is “a must” any way. (It does cost, but “strict safety check” that can be regarded satisfactory would also cost quite a lot, given the number of sections in the piping which require periodic ultrasound tests.)


Other queries came from Berndt Frieboese of Berlin. With his kind permission, part of the exchange is shared with the readers below [Hosokawa’s replies have been corrected/amended]:

[4] question from Frieboese:
The ruptured pipe is the one that connects the condenser and the steam generator (SG), in which the secondary coolant runs. (MagpieNews text, Mihama Accident Report No.2)
As I understand PWR design, there should not be a direct pipe from the condensor to the steam generator. The secondary coolant circulation pump (aka feedwater pump) sits between the condenser and the steam generator, so there is a pipe from the condensor to the pump and a pipe from the pump to the steam generator.

[reply from Hosokawa]
# Yes, you are right. The rupture took place between the condenser and the feedwater pump. More precisely, it is downstream of the low-pressure feedwater heater and upstream of the deaerator.

[5] question from Frieboese:
In normal operation, these 2 pipes contain liquid water at a temperature well below 100 degrees C. In the pipe from the turbine to the condensor and from the condenser to the pump the pressure is very low, possibly below the normal atmospheric pressure of 1 kg/cm2, so there is no risk of this pipe exploding in normal operation.

[reply from Hosokawa]
# In the case of Mihama-3 PWR, the temperature and the pressure at the location in question is, at normal operation, 150 Celcius, 10 atm, flowing at 300t/min. KEPCO states that the temperature at the time of accident was 142 Celcius (= 287.60 F). The explosion was such that the flashed steam filled up the turbine/condenser building, which has 3 floors and total floor extention of 12,000m2, totally in only 2 minutes.

[6] question from Frieboese:
You also wrote:
The point of rupture is close to the condenser.
In MagpieNews040810a: Mihama-3 Accident, 2nd Report you wrote:
there is a narrowing of the main pipe (56cm to 34cm in diameter) just before the vapor gets to the ruptured area, and this design may have caused the mentioned problems worse. As I mentioned above, the pipe from the condensor is normally filled with liquid water, not with vapour or steam.

[reply from Hosokawa]
# Yes, you are right. The system is designed so. It is estimated that the hot, high-pressure water burst out and got evaporated almost immediately, filling the room with very hot steam. The four workers couldn’t escape the first attack of the steam. Autopsy tells that they inhaled the hot air and had their windpipe burned acutely and swollen, suffocating themselves to death. Their bodies had been already dehydrated when they were brought to the ambulances. The other workers, who survived but severely injured, were at some distance (20 meters or so) from the rupture and narrowly escaped the explosion. They got burned by the hot steam and also by the very hot water that had quickly covered the floor of the building by 15cm or so.

[7] commentary by Frieboese:
However, turbulence and possibly cavitation in the water might have increased the corrosion of the pipe.

[reply form Hosokawa]
# Yes, our best guess at this moment is that the orifice narrowing has been causing the turbulence and cavitation almost constantly, causing the pipe wall thinning immediately downstream of the narrowing (i.e. flow-accelerated corrosion). And the high pressure stress ended up in a ductile fracture.

[8] comment by Frieboese
Now Kansai Denki said that the steam contained no radioactivity, because it came from the secondary cooling system. However, I think that most PWR operators regard a certain amount of leakage through the steam generators, and thus a certain pollution of the secondary coolant, as acceptable. Since Mihama-3 uses old steam generators and the accident happened after several months of operation, I am sure that some radioactive substances must have escaped with the steam.

[reply from Hosokawa]
# After the 1991 Mihama Unit-2 accident, in which a degraded steam generator (SG) tube had a double-ended rupture, the SGs have been replaced with new ones both in Unit-2 and Unit-3. The three SGs in Unit-3 were replaced in 1996. So they are not very old. However, the new SGs have not been free from troubles: in August 2000, thinning in some tubes were detected and “a flat piece of metal” (according to KEPCO, believe or not!) was discovered inside a SG during routine dry-up inspection.

# Yes, you are quite right. Whether it was adequate or not to say “there was no leak of radioactivity” in the Mihama accident this time is yet to be found out. Independent lobbying groups, including those from CNIC and NNAF, are demanding that KEPCO and its regulator, Ministry of Economy, Trade and Industry (specifically its branch: Nuclear and Industrial Safety Agency, NISA) should disclose detailed plant data including the radioactive readings in the main steam pipe (i.e. from SG to condenser) before and after the accident.


[9] question from Frieboese:
The Mihama reactors were built by Mitsubshi, but in pictures the reactor buiding looks like a Westinghouse. Is the Mitsubishi reactor a copy of the Westinghouse? In this case, we could remind the public in Sweden that they have 3 reactors of the same design at the Ringhals plant.

[reply from Hosokawa]
# Yes, you got it right. Mitsubishi Heavy Industry is a licensee of the Westinghouse. The US-Japan linkage is roughly as follows.

# Eastern Japan (and Shimane in the west) is dominated by BWRs supplied by the Hitachi/Toshiba – General Electric cartel; whereas Western Japan (and Hokkaido in the north) is occupied by PWRs supplied by the Mitsubishi – Westinghouse cartel. Interestingly the first reactor in Japan (Tokai-1) was a UK Magnox model, but that was the only one. All the rest are US models.

# As to the immediate implication of the Mihama accident to the PWRs world-wide, I suggest you check the matter with the US Nuclear Regulatory Commission’s generic letter on the erosion/corrosion-induced pipe wall thinning (NRC Generic Letter 89-08, issued May 2, 1989).
[a PDF copy available from MagpieNews.]


Thank you very much, Kwanghoon and Berndt, for your valuable comments.

MagpieNews #040814b1: Mihama-3 accident, 6th report
Timeline of the Mihama-3 LOCA; malfunction of control valves recorded; essential information such as feedwater quantity yet to be disclosed
14 August 2004, Kyoto, Japan

The timeline of the Mihama Unit-3 accident, as far as made public by KEPCO (www.kepco.co.jp/pressre/2004/0809-4j.html in Japanese) and additional information reported in mass media, is as follows:

15:22 Seven fireboxes (alarms) in the all 3 floors of the Unit-3 turbine building started to ring.

15:23 Further more 16 fireboxes were also sounding. Direct current earthing alert in Loop A.

15:25 Turbine building already full of high-temperature steam.

15:26 Reactor operators begins to put the reactor output down manually.

15:28 Reactor trip signal. The loop A steam generator (SG) had shortage of water feed.’First Out Alarm’ activated. Emergency shutdown of the reactor.

15:30 Evacuation order broadcast in the turbine building (every 1 minute for some 10 minutes).

15:35 Hot shutdown stability confirmed.

15:45 Water level lowering in the deaerator.

15:58 Reactor cooling system (RCS) volation commenced.

16:05 Main steam isolated. (Turbine bypass valve switched to main steam relief valve.)

16:26 Main feedwater valve closed.

16:41 Turbine turning commenced.

16:55 Water level in all the three steam generators (SG) at about 33%, while auxiliary feedwater pumps were put on.

17:12 Turbine-powered auxiliary feedwater pump stopped; its outlet flow control valves (A, B, and C) were manually shut. [Later the operators tried to reopen these control valves to 60%, but the valves A and C did not responded. The cause of this malfunction is yet to be investigated.]

18:04 Heater 4, outlet valves (CW-016 A, B, and C) closed.

18:05 Heater 1, inlet valves (CW-015 A, B, and C) closed.

KEPCO stated that 800 tons of secondary coolant was lost but they refused to comment on how this quantity had been calculated or estimated. It has not been disclosed either how much water was fed in by the auxiliary feedwater pumps.

The probability of spreading of the failure in the second cooling system to a failure in the reactor core cooling (i.e. the Three Mile Island scenario) will definitely be one of the most important points of analytical debate on the Mihama-3 LOCA accident.

[source: KEPCO, NNAF, Asahi, Sankei]

MagpieNews #040814a1: Mihama-3 accident, 5th report
Plutonium burning (MOX) project suspended; restarting of FBR Monju also postponed; all KEPCO reactors (and possibly others) go under emergency inspection
14 August 2004, Kyoto, Japan

METI investigators who visited the Mihama Unit-2 nuclear plant yesterday (13 August) found that the thickness of the coolant pipe that burst in the Monday 9 accident had been reduced to only 0.6mm in two points of the rupture edge. KEPCO had stated that the thickness was 1.4mm, while the original wall thickness was 10mm.

Governor of Fukui Prefecture, Mr. Nishikawa Issei, requested in strong wording that KEPCO should shut down all the nuclear reactors for urgent inspection. Governor Nishikawa said he would reverse the approval he had given before the accident to the proposed MOX utilization (plutonium burning) in KEPCO’s Takahama Unit-3 and -4 reactors, which are located not far in the west of Mihama. He also suggested he would postpone his approval of the scheduled reboot of the fast-breeder reactor (FBR) Monju1, which stands very close to the Mihama nuclear power station.

KEPCO had just to take the Governor’s request and has decided to shut down all its 10 reactors, all in the Wakasa district of Fukui Prefecture (province). Already by the sunrise of Saturday 14th, three reactor units, Mihama-2, Takahama-2 and Oh’i (= Oi)-4, have been switched off. Two other reactors, Takahama-4 and Oh’i-3, had already been shut down for periodic inspection. The rest, Takahama-1 and -3, Oh’i-1 and -2, will also shut down in turn. During this emergency inspection, which will take 4 to 6 weeks at the shortest, ultrasonic test is to be conducted to find out pipe wall thinning in over 150 points in secondary coolant piping immediately downstream of an orifice and of an elbow. This is what KEPCO claims, but as already pointed out in previous issues of MagpieNews, there are many many more sections in which erosion/corrosion and thinning can occur. More thorough safety check is imperative.

KEPCO has already switched on LNG- and petro-thermal power stations in Osaka-Kobe areas in order to meet the hot summer demand for electricity in Kyoto-Osaka-Kobe megalopolis. It also plans to buy more megawatts than it regularly does from other utilities such as Tokyo Electric Power Co. (TEPCO) and Kyushu Electric Power.

Other utilities outside Kansai region are also receiving strong pressures from the local governments to carry out emergency check-up in nuclear and thermal power plants, which may have the same condenser piping defect.

In most overseas newspapers, TVs, radios, and net news, the Mihama nuclear power station is described as “350km west of Tokyo” or “200 miles west of Tokyo”. Well, you could say that, but more realistically, the plant is located 80km north of Kyoto and only 30km north of Lake Biwa, the largest freshwater mass in Japan and the source of drinking water for 14 million residents of the Kyoto-Osaka-Kobe megalopolis.

Therefore, possible radioactive release out of Monju, MOX-loaded reactors, or regular uranium-loaded reactors such as Mihama, would result in massive water contamination as well as in other serious influences on the economy and life in all over the wider Kansai.

1: Monju has been turned off since its 1995 accident. Monju is operated by the Government agency, Japan Nuclear Fuel Cycle Development Institute (JNC), not by KEPCO.

[sources: Mainichi, Kyodo, Yomiuri, KEPCO, METI, NNAF]

MagpieNews #040812a1: Mihama-3 accident, 4th report
70% of the coolant water lost; KEPCO had clear and precise warnings of the pipe rupture; most Japanese reactors need to shut down for emergency inspections
12 August 2004, Kyoto, Japan

Kansai Electric Power Co. (KEPCO), operator of the Mihama nuclear power plant that had the fatal accident on Monday 9th, confirmed that as much as 800 tons of coolant water had been lost through the breakage in the mainstream pipe of the Unit-3 reactor system. The utility is yet to disclose specific information concerning the impact at the moment of the accident of the loss of that much amount of coolant water to the reactor’s major cooling system, the steam-generator (SG). The nature as “LOCA” (loss-of-coolant accident, or Three-Mile-Island-type accident) of the Mihama-3 rupture is now evident, a serious accident scenario indeed. (800 tons = approx. 70% of the total secondary coolant.)

The size of the rupture (opening) is 38 to 57cm longitudinally (i.e. along the length of the pipe) x some 60cm latitudinally (roughly 1/3 around the pipe). Investigators sent by the Ministry of Economy, Trade and Industry (METI) found extensive oxidation on the pipe wall at and around the rupture opening; it is thus most likely that the erosion/corrosion process caused the pipe wall thinning that led to the rupture of the carbon steel pipe. In other words, the warning made by the US Nuclear Regulatory Commission (NRC) after analyzing the pipe rupture which occurred at Unit-2 plant of Surry Nuclear Station, Virginia1, has hit true, in a horribly coincidental way that the same number of people were killed in the two accidents.

It is also becoming clear that engineers of Mitsubishi Heavy Industry, manufacturer of the plant, had been well aware of the pipe wall thinning process downstream the orifice structure; they actually told KEPCO contractors to inspect the very point of the destruction in 1999, in 2000, and again in 2003, which advice KEPCO has not taken, apparently for economic reasons. The nature as an “artificial disaster” of the Mihama-3 accident is thus also evident.

As a matter of fact, in some other nuclear power plant, such as Tomari PWRs in Hokkaido, northern Japan, and Ikata PWRs in Shikoku, western Japan, the carbon steel pipes in the condensate area in question were replaced with stainless steel pipes; and unexpected degree of thinning were proven in the old pipes. This, however, does not mean that Mihama-3 was exceptional because there are so numerous pipe sections which bear structural conditions that may cause what NRC called “erosion/corrosion-induced pipe wall thinning” that every plant has hundreds or even thousands of “should-be-inspected but actually not-yet-inspected” pipe sections in the reactor cooling system.

1: NRC Generic Letter 89-08: Erosion/Corrosion-Induced Pipe Wall Thinning (issued May 2, 1989).

[sources: Asahi, NHK, Kyodo, Mainichi, KEPCO, METI, NNAF]

Magpie News #040810b3: Mihama-3 Accident, 3rd report
Police starts investigating the Mihama accident as a criminal case; KEPCO has apparently preferred cost saving to safety.
10 August 2004, Kyoto

Kansai Electric Power Co. (KEPCO) and other utilities which run the same type nuclear reactors will have to shut them all down in order to deal with the thinning of the coolant pipes.

It is now evident that the causing factors of the Mihama Unit-3 rupture accident, which occurred quite alarmingly in the Nagasaki Memorial Day, are in no way inherent in this particular plant, but rather common to all the pressurized-water reactors (PWRs) in Japan: (1) the use of carbon steel pipes in the condenser area rather than stainless ones; (2) the narrowing of the pipe (and thus disturbance of water/steam flow) with the installation of an orifice flowmeter at about 50cm upstream of the rupture; (3) lack of ultrasonic test; (4) aging of the plant; and (5) extremely similar accident had already taken place in a PWR at Surry Nuclear Power Station, Virginia, USA, in 1986, of which KEPCO was definitely aware.

It has also been revealed that KEPCO was well aware, in November 2003 at the latest, that thinning inside the condenser pipes was probable but the company has been putting off the specific inspection for cost-cutting reasons. Fukui Prefectural Police is now investigating the case as a criminal offence.

It is significant to point out here that the KEPCO once very clearly admitted in its press statement (24 April 2000) that an orifice structure had caused cavitation and pressure fluctuation inside a pipe of the Unit-2 reactor system of Mihama, which resulted in internal wall thinning and metal fatigue cracking of the pipe1. In the case of yesterday’s Mihama-3 accident, the orifice is at about 50cm upstream of the rupture.

Photos of the rupture can be viewed in the following URLs. (Disregard the Japanese texts that may come up as unreadable dingbats unless you have a Japanese font set in your computer.)

# [photo 1 (from Jiji Press): the main pipe; rupture is in the upper side in the center of the photo; the orifice is seen at the right-hand-side end of the photo]

## [photo 2 (from Mainichi Newspaper): the ruptured pipe seen from below; the broken insulater is hanging down.]

To have a look at what the narrowing by the orifice is like, try the following URL (again disregard the dingbats).

[sources: Kyodo, Jiji, Mainichi, KEPCO, METI, NoNukes Asia Forum.]

1: MagpieNews is indebted to Mr Yamazaki Hisataka, who reminded us of the relevance of the Mihama-2 incident of April 2000 in one of his expert postings to the NoNukes mailing list.

Magpie News #040810a2: Mihama-3 Accident, 2nd report
4 Killed in Mihama-3 condensate system rupture; 10mm-thick pipe had been thinned to 1.4mm while no inspection was carried out for 28 years
10 August 2004, Kyoto

What happened in the Unit-3 reactor at Mihama Nuke Power Plant is becoming clear. The main pipe in the condensate system has ruptured and 150-degree-Celcius water/steam gushed out onto the workers who were unlucky enough to be under the pipe. Eleven contract workers had severe burn and taken to the hospital. Four of them were dead on arrival. Two are in critical condition with 50-60% of burn all over the body. Five others are also in severely injured.

The ruptured pipe is the one that connects the condenser and the steam generator (SG), in which the secondary coolant runs. The point of rupture is close to the condenser. This means that the rupture took place in the very mainstream of the cooling system of the reactor. If the secondary coolant is lost or fails to run adequately, then the SG loses its heat-transfer function, causing the primary coolant overheated and the reactor core melt down. The Mihama Unit-3 has 3 loops of SG-condensate system, one of which has broken this time. In case two of the 3 loops should have been broken, it could have resulted in a meltdown accident.

It is most likely that the rupture was due to wall thinning of the carbon steel pipe, which is 56cm in diameter and 10mm thick. It was found that the actual thickness of the pipe was only 1.4 to 3.5mm at around the breakage. Two factors may be at work: i) aging of the plant — the main cooling system pipes suffer from high temperature and pressure so that the internal thinning, ductility and corrosion are constant problems; ii) there is a narrowing of the main pipe (56cm to 34cm in diameter) just before the steam gets to the ruptured area, and this design may have caused the mentioned problems worse.

Since the start up of the Mihama-3 in 1976, the operator company, KEPCO, has never conducted an ultrasonic test (UT) to the condenser pipe system in question. As a matter of fact, the unit was to go under annual inspection and overhaul from next week, during which UT was scheduled for the first time in 28 years. The victim workers were just carrying inspection machineries into the turbine building in which the condenser is housed.

Critics are demanding that the company should shut other reactors down immediately for emergency check up, because the conditions that resulted in the rupture in Mihama-3 are more or less the same in Mihama-1, Mihama-2 and several other reactors in the Wakasa region (western coast of the Fukui Province).

[sources: Kyodo, Asahi, KEPCO, NHK, NoNukes Asia Forum.]

[correction] In the first report (9 August 2004), MagpieNews referred to the casualties as ’employees’ (of KEPCO). Actually those killed and injured were not KEPCO employees, but workers of a contract company, Kiuchi Measuring, Inc. (= Kiuch)

Magpie News #040809a3: Mihama-3 Accident, 1st report [ver. 3]
Mihama-3 Nuke Station Accident
9 August 2004, Kyoto

There was an accident at the Unit-3 nuclear reactor (PWR, 826MW, 28 years old) of the Mihama Nuclear Power Station in Fukui Province, north of Kyoto, Japan.

At 15:28 local time [+900], the pressurized-water reactor system of the largest unit in the commercial power plant had a failure in its secondary coolant system; the reactor and the turbine was successively tripped.

High-temperature, high-pressure steam has erupted into the turbine room, killing four employees. Four others are reported to be in serious conditions. The toll may increase.

According to the operator company, Kansai Electric Power (KEPCO), the emergency back-up pumps are on so that the steam generator would not be overheated; the company says that there has been no radioactive release into the atmosphere. However, if it is an accident coming up with an uncontrolled pressure changes in the secondary coolant system, preventative pressure releases (i.e. letting the pressurized steam go out into atmosphere) may have taken place.

At the moment of the accident, the reactor was running at the normal thermal output of 2440MW. KEPCO’s emergency statement on the web makes no mention to possible causes of the accident, nor to the deaths of the employees.

[sources: Kyodo, Jiji, Asahi, Yomiuri, KEPCO statement, and the Ministry of Economics and Industry (METI) statement.]

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