On March 2, 2012, we confirmed that in the Unit 5 of Kashiwazaki Kariwa nuclear power station (boiling-water reactor, rated output is 1,100MW), which had been under a regular inspection, an air isolation dumper (valve) of the two emergency air ventilation systems in the main control room*1 was unable to close due to safety treatment in the regular inspection and did not temporarily satisfy a restriction for operation*2, when works related to the radiated fuel (hereinafter called "radiated fuel work") were conducted in the reactor buildings in February 2012, whereas a safety regulation for reactor facilities of Kashiwazaki Kariwa nuclear power station provides that both of the two emergency air ventilation systems in the main control room must be workable.
Concerning this case, on March 16, 2012 Tepco received a warning from Nuclear and Industrial Safety Agency (NISA) of Ministry of Economy, Trade and Industry. Furthermore, Tepco received an instruction document*3 which instructed Tepco to investigate the direct cause of the safety regulation breach and the fundamental cause derived from the organizational structure, and to report the countermeasures to NISA.
(previously announced in the period until March 16, 2012)
Today we announce that we reported the result of the investigation and the countermeasures to NISA.
As a result of the investigation for the direct cause of the safety regulation breach, it was found that the related persons in our company had not sufficiently understand the restriction for operation regarding the air intake dumper of the emergency air ventilation systems in the main control room.
Therefore, we assumed that in the development of the regular inspection process, the timings of the dumper inspection and the radiated fuel work were not right and no one was aware that the status of the emergency air ventilation systems in the main control room was not appropriate even when applying for radiated fuel work, and thus the radiated fuel work was conducted though the dumper was unable to close.
We will invite the attention of the related persons in our company to this case and promptly amend a guideline drawn up in our company for appropriate understanding of the safety regulation and thus improve the related persons' understanding.
Furthermore, in order to draw up inspection plans complying with the safety regulations etc., we will strengthen a rule for checking with a department in charge of confirmation of the safety regulation compliance when we draw up progress schedules of the regular inspections. We will improve other workflows, for instance, we will amend a check sheet for prior check when applying for radiated fuel work.
Although we have worked through work improvements in Kashiwazaki Kariwa nuclear power station so far, we suppose that standardization of work and checking systems are not necessarily sufficient as a result of the investigation for the fundamental cause derived from the organizational structure. We will improve the business quality through reform of the work process and continuous work restructuring.
END
○Attachment
The investigation result for the safety regulation breach regarding the operation of the emergency air ventilation systems in the main control room in the Unit 5 of Kashiwazaki Kariwa nuclear power station.(PDF 33.4KB)
The direct causes, the root cause from our organizational structures and the preventive measures for the safety regulation breach regarding the operation of the emergency air ventilation systems in the main control room in the Unit 5 of Kashiwazaki Kariwa nuclear power station.(PDF 1.53MB)
*The aforementioned attachments are only available in Japanese.
We apologize for any inconvenience this may cause.
*1 Emergency air ventilation systems in the main control room
Air conditioning equipment installed separately in order to operate and take measures in the main control room without the workers exposed to excessive radiation at accidents. There are 2 systems of these and only one system can provide 100% capacity.
*2 Restriction for operation
Safety regulations provide a "restriction for operation" with regard to reactor operation and in this case it provides that when workers work on radiated fuel, both of the 2 systems of emergency air ventilation systems in the main control room (2 fans, 1 filter unit and necessary dumpers (valves) and duct) shall be workable.
*3 Instruction document
"Violation of safety regulations for the operation of emergency air ventilation syststems in the main control room of Unit 5 of Kashiwazaki Kariwa nuclear power station (instruction)"
(March 15, 2012, NISA, No.3)
*We have provided a Japanese press release version of the instruction document received from NISA. However, at this time we have reserved the right to provide an English version due to potential misunderstandings that may arise from an inaccurate rendering of the original Japanese text. We may provide the English translation that NISA releases in our press releases. However, in principle we would advise you to visit the NISA website for timely and accurate information.
