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Loss of Cooling Function Accident at Rokkesho Reprocessing Plant – High Level Radioactive Liquid Waste at Risk

July 31, 2022
On July 2, a serious accident of loss of cooling function occurred at the Rokkasho Reprocessing Plant. As a result, cooling of high-level radioactive liquid waste (2.6 m3) stored in “Feed solution tank B” in the preliminary stage of crow solidification was interrupted for eight hours. This liquid waste is dangerous because it generates heat for a long period of time, and if the cooling function is lost, the liquid waste is expected to boil and evaporate in 24 hours and cause a hydrogen explosion in 280 hours.

Tanks of dangerous high-level radioactive liquid waste

The cause was an accidental closing of a dividing valve. The valve in question is located near the coils that cool the high-level radioactive liquid waste. When the cooling function of the internal loop is lost, the emergency response is to connect hoses from outside to inject cooling water and close this partition valve. Loss of cooling function is assumed to be caused by a major earthquake or aircraft collision, and the work will be carried out in a great hurry.

Locked with metal chains and padlocks

The dividing valve in question
Locked with a metal chain and padlock

According to the press conference materials of the nuclear fuel company, the valve was closed by mistake, so a metal chain was wrapped around the valve and padlocked so that it could not be closed easily. However, where will the master key of the padlock be kept at the site where many things may have fallen down in a major earthquake? What will you do if you cannot find the key? Where will you find the cutter to cut the metal chain when the padlock does not open?

I must say that metal chains and padlocks are the worst possible response to a minute-by-minute cooling function restoration operation. According to NFI, similar locks and additional work will be implemented at 539 locations in the vitrification building by the end of July, and at 2,500 locations throughout the plant by the end of the year. The cooling function is placed in a very dangerous situation. It is only a matter of using paper-based seals that can be cut by hand.

Those who thought of metal chains and padlocks are those who do not know what to expect in a serious accident. Furthermore, it is a “countermeasure that was done in a rush. A calm Phase 3 response is necessary to deal with a serious accident. JNFL’s post-accident response is completely in Phase 4, making a series of mistakes and “digging its own grave. JNFL should quickly move to Phase 3 and reset the metal chain and padlock measures.


Confusion at the site due to multiple drawings?

Although JNFL attributes the cause of the accident to human error in misidentifying the dividing valve, it is possible that the piping drawings and the actual piping were different. The reason to suspect this is the 2019 and 2020 applications.
This is because the hose connections and shut-off valves have been renumbered, some numbers have disappeared from the drawings, some new connections have been added, and there are two connections with the same number that cannot be distinguished.
For safety reasons, changing the numbers is not a good idea. If it were to be changed, it would require a lot of corrective work and would be a source of human error.

2019 Application Form
2020 Application form

Pick up the numbers on the 2019 and 2020 drawings in order: numbers 1-8 are the same, but number 9 in 2019 is gone and number 10 is number 9 in 2020; number 12 has two locations in 2019 and both are number 11 in 2020; number 13 in 2019 is 2020. In 2019, there are two locations with number 12, and in 2020 both are number 11; number 13 in 2019 is replaced by number 12 in 2020; numbers 15, 16, and 25 in 2019 are gone and number 14 is created where it was not in 2019.

Comparison of 2019 and 2020 numbers

KDDI’s major communications outage was a “mix-up in the operations manual. The operator who was doing maintenance on the router was working according to the manual. The work was not too difficult. But the reason for the mistake was that the manual they were referring to was an older version.”
At the reprocessing plant where the loss of cooling function accident occurred, the drawings and on-site confirmation are also urgently needed.

Also, which department at NFI approved the safety measures for the construction of System A that caused the accident? We do not even know if the Regulatory Commission approved them. I am shocked at the unbelievable response to the construction of a very dangerous facility.

The reprocessing process is a very dangerous and complicated process that must be carried out steadily, but JNFL has repeatedly responded to incidents of this magnitude in a panicked and erroneous manner. It has become clear that JNFL’s attitude toward safety is problematic and that they have not accumulated any experience. As a business operator, I cannot entrust JNFL with reprocessing.

<Reference.
Drawings for 2019 and 2020
2020/4/28 examination material pdf000309774
https://www.nsr.go.jp/disclosure/law_new/REP/180000013.html
2019/3/8 examination material pdf000264093
https://www.nsr.go.jp/disclosure/law_new/REP/180000009.html

Material on evaporation and drying

Examination Meeting on the Conformity of Nuclear Fuel Facilities, etc. to New Regulation Criteria
https://www.nsr.go.jp/activity/regulation/tekigousei/nuclear_facilities/index.html

FY 2015 Review Meeting on Conformity of Nuclear Fuel Facilities, etc. to New Regulation Criteria
https://warp.da.ndl.go.jp/info:ndljp/pid/11275007/www.nsr.go.jp/disclosure/committee/yuushikisya/tekigousei/nuclear_facilities/ h27fy/index.html
Handout for the 65th Meeting June 29, 2015
 Document 2

https://warp.da.ndl.go.jp/info:ndljp/pid/11275007/www.nsr.go.jp/data/000112379.pdf

89th Session December 21, 2015 (2015)
https://warp.da.ndl.go.jp/info:ndljp/pid/11275007/www.nsr.go.jp/disclosure/committee/yuushikisya/tekigousei/nuclear_facilities/ 00000060.html
Handout 2(1)
https://warp.da.ndl.go.jp/info:ndljp/pid/11275007/www.nsr.go.jp/data/000134166.pdf

Source: https://note.com/otake_susumu/n/nb6cb13e56279?fbclid=IwAR1bDyUEdnh5tjxhfok17Q5_Fbv0pME3eA_OwP94dMxkNpC9UvRxSgrZw2w

August 4, 2022 - Posted by | Japan | , , ,

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