| Case Name |
Trouble hiding of Atomic Power Plant |
| Pictograph |
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| Date |
August 29, 2002 |
| Place |
Pref. Fukushima, Niigata |
| Location |
The first nuclear plant in Tokyo Electric Power Company Fukushima, the second
nuclear plant in Fukushima, and Kashiwazaki Kariwa nuclear plant |
| Machinery |
The structure of the core shroud is shown in figure 2. Many piling up the short cylinder, it welded the shroud long circle with tubular structure, it is supported vertically by shroud support. As for the shroud core (fuel assembly) At the time of function, and the accident which make the road where the chilled water which cools function and the core which are supported flows the core full it is it has the function of the divider in order to do with the water.
The structure of the reactor recycling type piping is shown in figure 3. As for reactor recycling type piping, high temperature inside reactor pressure container The pure water (the primary chilled water) through the purifier, with the piping which it circulates, it is connected to the condenser. |
| Overview |
Periodic inspections of nuclear power plants approximately once per year are required by law. The Tokyo Electric Power corporation from the latter half of the eighties to the nineties executed independent inspections while the fixed period inspecting at the Fukushima first nuclear power plant, the Fukushima second nuclear power plant, and the Kashiwazaki Kariwa nuclear power plant,. Although at that time cracking in the equipment was discovered, core shroud which is installed inside the reactor pressure container, the appraisal, repair, record and report to the country were inadequate.
After that, while cracking being discovered by also reactor recycling type piping at the nuclear power plant of the Tokyo Electric Power corporation, the Chubu Electric Power Co., Ltd. corporation and the Tohoku Electric Power Co., Inc. corporation, what cannot do report to the country was ascertained. In addition, at the nuclear power plant of the Japanese nuclear power generation corporation, while cracking of the shroud being discovered, what report to the country has not done after all was ascertained.
This way cracking was discovered by the equipment of many nuclear power plants, that without report to the country was left, or was repaired. When this cover-up was finally made known to the general public, a strong fear concerning the safety of nuclear power plants resulted.
In response to these incidents, the Electricity Enterprises Act was amended, the safety appraisal system for nuclear power plants was enforced, and the maintenance standard of the Japan Society of Mechanical Engineers was adopted. |
| Incident |
As a design * production standard of the phenomenon nuclear power plant, the notification which decides technical standard such as the structure regarding the atomic energy equipment for generation of electricity (the 501st number) it is. As for this notification not only as the technical standard in design and producing, as the technical standard after that in in-service inspection it was applied. Namely, efficiency when producing must be maintained either during service period, it is a request.
When producing welded products, weld defects occur often. If the defects can be detected with a non-destructive examination standard of design and production standard, then the defects can be repaired or exchanged. In principle, only the qualitative judgment of the presence of a defect is required. The most often used method of non-destructive examination the design and production standard is the radiation transmission test.
Weld defect it is not during service period as a policy, often crack such as fatigue and stress corrosion crack (the crack) causes. As for method of non-destructive examination radiograph is center unlike design and production standard. If non-destructive examination standard of design and production standard is applied to in-service inspection, if crack is detected, repairing or exchanging becomes principle. This difference of the method, radiation transmission test and radiograph furthermore is type of crack and the decision which does not depend on size.
Actually, as for crack occurring by way of the time when it is sufficient during service period it is the proper result, size of crack by after that appraising development, repair or you do not exchange it can allow the continuation of service of fixed period. But, this appraisal and allowance are not recognized as a policy, repairing or exchanging becomes principle.
At many nuclear power plants, while detecting the stress corrosion crack with the core shroud and reactor recycling type piping, the appraisal, repair, record and report to the country were inadequate. 2 at below are thought from the viewpoint of judgement of the technician who participates as the cause of that.
(1) Because application of non-destructive examination standard of design * production standard to in-service inspection lacks rational characteristic, this was ignored.
(2) Because as for measure to the stress corrosion crack the fact that it is considered sufficiently with the material and environment with policy, as for the stress corrosion crack is the supposition external affairs elephant of the design, the fact that the stress corrosion crack occurs was concealed. |
| Sequence |
As for economic industrial resource-saving energy agency atomic energy safety * preservation institute, on August 29th of 2002, to announce " the investigation and the like relates to the independent inspection work sheet of the enterprise in the nuclear power plant regarding illegitimately ", from 1986 age latter halves betting on the nineties at 3 nuclear power plants of the Tokyo Electric Power corporation, the GEII corporation (General Electric International Inc.) The ordering, in the independent inspection job which Tokyo Electric Power executes, the stress corrosion crack and that trillion Concerning discovery and repair job et cetera, the incident which has the doubt where illegitimate statement and the like was done was published. Opportunity of this case investigation the Ministry of International Trade and Industry (at that time in July of 2000), the declaration which was moved aside (information offer) is. After that, reaching up to September 20th, other than above-mentioned Tokyo Electric Power incident incident of the stress corrosion crack in reactor recycling type arranging pipe which report has not done at the nuclear power plant of Tokyo Electric Power, the Chubu Electric Power Co., Ltd. corporation and the Tohoku Electric Power Co., Inc. corporation, vis-a-vis the country became clear. In addition, on September 25th, incident of the stress corrosion crack of the core shroud which report has not done at the nuclear power plant of the Japanese nuclear power generation corporation, vis-a-vis the country became clear. Concerning these, on October 1st, the findings from of atomic energy safety and preservation institute (interim report) the oven you stopped. |
| Cause |
Judgement of the technician who participates is not true cause. As for problem that without check there is the organization which it passes. The guaranty of the safety which is due to the self-restriction of the enterprise from the guaranty of the safety with law system, in the present condition which is reforming to the guaranty of the safety which is due to self-restriction, runs out in execution of precise guarantee and risk management. Essential cause of the trouble hiding of the nuclear power plant is lack of quality guarantee system and risk management. |
| Response |
In order to examine recurrence preventive measure, comprehensive resource energy committee atomic energy safety and preservation sectional meeting atomic energy safe regulation laws examination sub-committee was installed. At 1st (September 13th) from 5th (October 31st) sub-committee, recurrence preventive measure (interim report) it collected. Concrete recurrence preventive measure is shown below.
** For the security activity of the enterprise guaranty
** In security being active of the enterprise establishment of the quality guarantee
** By the enterprise strengthening the match to the legal
** Clarification and transparency conversion of use of regulation
** Improvement of use of declaration
** Relates to slight phenomenon release and joint ownership conversion
** For safety regulation match to recovery
** System of safety regulation and inspection |
| Countermeasures |
Several of above-mentioned recurrence preventive measures have been executed already. It should feature, it means that the health appraisal system is enforced from October 1st of 2003.
The flow of the health appraisal system is shown in figure 4. It is the epoch-making system which requires periodic enterprise inspection and health appraisal with the amendment of Electricity Enterprises Act, Commercial Standard (the Japan Society of Mechanical Engineers standard) utilizes concretely.
** Periodic enterprise inspection
You located as " periodic enterprise inspection " the current independent inspection which is executed optionally by the enterprise, with respect to law. At the time of periodic enterprise inspecting, non-destructive test (radiographion) doing is required. As a concrete inspection method, maintenance standard 2002 year edition of the Japan Society of Mechanical Engineers is utilized.
** Health appraisal
At the time of periodic enterprise inspecting, when crack is detected to equipment, development is estimated concerning particular crack, appraising the health with respect to structure of equipment (health appraisal) is required. Object equipment of health appraisal is, the equipment which forms reactor pressure boundary (the class 1
equipment) the container and piping and the core shroud which belong (the core support structure). Furthermore, among the class 1 equipment, the SUS316 (L system) the recycling type piping and the like which uses the material was excluded, but it is the prospect that reliability of radiographion is guaranteed, is added to object equipment. Item of health appraisal, model of crack and appraisal unnecessary defect, is crack development appraisal and destruction appraisal, maintenance standard 2000 year edition of the Japan Society of Mechanical Engineers (identical contents to also maintenance standard 2002 year edition stipulation) utilize as a method. Destruction appraisal (the crack which is not allowed) judgement standard is stipulated, technical standard (the Ministerial ordinance which decides the technical standard of nuclear power generation equipment, " Ministerial ordinance 62"). As a concrete judgement standard, approved standard of destruction appraisal of maintenance standard 2000 year edition of the Japan Society of Mechanical Engineers is utilized.
** Appraisal result
Details of record item and report item to the country are decided. The result of health appraisal is the object of report, but appraisal unnecessary defect does not deal with of report.
** Enactment of related private regulation
Or more is amendment of law system, but separately from this Commercial Standard was enacted as a measure. Quality guarantee standard of electric technical regulation of the NEC Corporation association was taken a second look drastically as a measure to lack of the quality guarantee system which is essential cause, newly the JEAC4111-2003 " quality guarantee regulation for the safety in the nuclear power plant " was stipulated. This designates the ISO9001 as the base, quality the atomic energy states clearly the role of replacement and top management safely. Furthermore, technical guide of the defective size measurement in radiographion which becomes the base of health appraisal, electric technical guide JEAG4207-2004 of the NEC Corporation association to "the radiographi on guide in in-service inspection of the light water type nuclear power generation business equipment " it added stipulated. |
| Knowledge Comment |
Like whether above, at first glance, accident (trouble) it made standard of, it is visible. But, fact differs. Necessity of maintenance standard was recognized for a long time between the authorized personnel, from around 1993 started the job of standard compilation, was enacted in 2000 as the Japan Society of Mechanical Engineers standard. The fact that this is quoted to the technical standard of the country was established policy, but the trouble hiding of the nuclear power plant was detected immediately before the actualization. Namely, without maintenance standard application of design and production standard made trouble, trouble application of maintenance standard accelerated. Originally, as for standard before accident occurs, it is in order to prevent beforehand. But, if accident does not occur, the fact that it cannot cope is actuality. If the big damage is not experienced, every thing does not change, like the Japanese constitution in all fields you can think.
As for the method of coping with this, it is not other than utilizing the efficiency stipulated conversion and the Commercial Standard of law system. With only law system cannot guarantee safety. If it limits to the thing making, the enterprise makes standard with by its, protects standard with by its. This is kingcraft of the guaranty of safety. |
| Sequel |
In the future, maintenance standard of the Japan Society of Mechanical Engineers is acknowledged publicly by above, means to be applied to the maintenance of the nuclear power plant. Until here distance was not long, in addition even. Enactment of the ASME standard Secc.xi is 1972 years. At that time, our country dawn of research of fracture mechanics being period, was recognizing the importance of defective appraisal as an application of fracture mechanics, ASME standard was Bible of fracture mechanics application for the researcher.
Reaching up to 1988, the Secc xi corresponding study group was installed in the NEC Corporation association, started the investigation of ASME standard and the participation to ASMESecc.xi commission organizationally. Almost, simultaneously, in the Japanese Society for Non-destructive Inspection, the Japanese welding association and the Japanese high pressure American Institute of Technology et cetera, several commission in order to execute our national individual research with the introduction of maintenance standard to our country as a purpose, was installed, listed the result. Especially, the research commission the health appraisal during service period of nuclear power generation equipment of the Japanese high pressure American
Institute of Technology which is installed in 1991 regarding continued, after that, changing name $dm 3 years, presently contributed to the construction of the technical basis of maintenance standard largely. This way, opportunity of the maintenance standard decision in our country between the authorized personnel ripde.
And, reaching up to 1993, research committee such as the technical standard which relates to nuclear power generation equipment maintenance in generation of electricity equipment technical inspection association is installed, draws up maintenance standard original idea technical standard (notification) to with taking in the maintenance standard as a purpose, presently continues supplement and reform.
Reaching up to 1997, receiving the policy of application of efficiency stipulated conversion and Commercial Standard of technical standard of the country, equipment standard commission for generation of electricity was installed in the Japan Society of Mechanical Engineers. And, atomic energy ad hoc committee and the maintenance standard sub-panel listing aggregate power, it tackled standardization with above-mentioned maintenance standard original idea as a base, maintenance standard of unsolved question was born in 2000 as a 1st number of the Japan Society of Mechanical Engineers standard.
After that, in July of 2002, comprehensive resource energy committee reactor safety * preservation sectional meeting reactor safe sub-committee examined the maintenance standard of the Japan Society of Mechanical Engineers technically as the theme which it should tackle urgently destined for the efficiency stipulated conversion of technical standard and the application of Commercial Standard,, in order to be able to adopt the enterprise, proposed the fact that you service the system aspect. Furthermore, the study group regarding the ideal way of the synthesis resource energy committee reactor safety and preservation sectional meeting inspection which is installed in February of 2002 showed the directivity of the inspection system second look in the 7th commission of July of the same year, deliberated & acknowledged the service of above-mentioned maintenance standard.
The fact that the Tokyo Electric Power problem and the like is published is 2002 year 8 end of the month, service of maintenance standard having become established policy before the that has the necessity to clearly write. The criticism that has not shot the mark for dealing with the Tokyo Electric Power problem and the like, it introduced maintenance standard into mud rope system. |
| Scenario |
| Primary Scenario
|
Poor Value Perception, Difference in Culture, Difference of principle, Organizational Problems, Inflexible Management Structure, Information communication insufficiency, Misjudgment, Narrow Outlook, Standard defectiveness, Usage, Operation/Use, Core shroud, Usage, Maintenance/Repair, Inspection, Failure, Fracture/Damage, Stress corrosion crack, Loss to Organization, Social Loss, Confidence losing, Damage to Society, Change in Perception, Atomic energy infidelity
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| Number of Deaths |
0 |
| Number of Injuries |
0 |
| Multimedia Files |
Fig_2.Structure of a reactor core shroud
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Fig_3.Structure of a Primary Loop Recirculation System
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Fig_4.Integrity Evaluation System for Nuclear Power Plants
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| Field |
Material Science
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| Author |
KOBAYASHI, Hideo (Yokohama National University)
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