Back to 2007 listFailure to Carry out Procedures in Nitrogen Supply Pipe Replacement Work at Hamaoka Nuclear Power Station Reactors No. 3 and 4
February 28, 2007
Chubu Electric Power Co., Inc.
Chubu Electric is currently performing a survey to assess and examine whether there has been any data tampering, failure to perform necessary procedures or similar problems concerning its power generation equipment. The survey follows the Nuclear and Industrial Safety Agency's directive last November relating to inspections of power generation equipment.
This press release is to report that our survey has confirmed that necessary procedures were not carried out when replacing some nitrogen supply pipes(*1) at Hamaoka Nuclear Power Station Reactors No. 3 and 4 last year.
In this case, during the planning stage for replacing the pipe, the intention was to replace it with the same pipe material as that shown on the work plan prior to replacement, but instead a different material was used(*2). This means that procedures for submitting work plans required under the Electric Utility Law were not followed, and equipment was used without getting any pre-usage inspection.
Therefore this morning we have moved to stop using the replaced pipes that are in violation of the law and to isolate them from the rest of the system. After this, we will immediately execute the procedures for submitting work plans and replace the pipes with the same materials as those used previously by the end of April.
In the meantime, we believe the situation will not cause any safety-related problems, since we are using instrumentation compressed air systems, etc. that are completely separate from the nitrogen supply system in order to back up our supply of working gases.
This does present the possibility that the concentration of oxygen, which is contained in the working gases, could rise in the reactor containment vessel. We will therefore be collecting data every two hours to better monitor trends in relevant parameters, such as oxygen concentration, instrumentation compressed air pressure and so on. Operations will be shut down if there are any irregularities.
Chubu Electric will also be examining the cause of this incident and considering measures to prevent its recurrence. We will also continue our survey to assess and examine whether there has been any data tampering, failure to perform necessary procedures or similar problems.
At this point, we have not found any other cases of failure to perform procedures.
Chubu Electric is treating this failure to perform procedures as a serious situation. We will continue our effort to faithfully execute legal procedures by taking thoroughgoing measures to prevent recurrence.
(*1) Nitrogen supply pipes provide the working nitrogen gas to the main steam isolation valve and main steam release valve, which are located inside the containment vessel (where they replace gases with nitrogen gas during operation).
(*2) The pipe material is noted on the work plan. The pipe material noted on the work plan prior to replacement was STPL39 (for low-temperature service). During the replacement work last year, however, the piping in No. 3 was replaced with STPG370 (for pressure service) and that in No. 4 was replaced with STPT370 (for high-temperature service). These are all carbon steel pipes.
Attachment: Overview of Hamaoka Nuclear Power Station Reactors No. 3 and 4 Nitrogen Supply System
< Attachment >
Overview of Hamaoka Nuclear Power Station Reactors No. 3 and 4 Nitrogen Supply System
Attachment:
Overview of Hamaoka Nuclear Power Station Reactors No. 3 and 4 Nitrogen Supply System [PDF:79KB]
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