How Japan lost calculated nuclear risk

[jpak]

http://www.reuters.com/article/2011/03/29/japa-nuclear-risks-idUSL3E7ET2D120110329

<snip>

VENTS AND GAUGES

Although U.S. nuclear plant operators were required to install "hardened" vent systems in the 1980s after the Three Mile Island incident, Japan's Nuclear Safety Commission rejected the need to require such systems in 1992, saying that should be left to the plant operators to decide.

A nuclear power plant's vent represents one of the last resorts for operators struggling to keep a reactor from pressure that could to blow the building that houses it apart and spread radiation, which is what happened at Chernobyl 25 years ago. A hardened vent in a U.S. plant is designed to behave like the barrel on a rifle, strong enough to withstand an explosive force from within.

The U.S. Nuclear Regulatory Commission concluded in the late 1980s that the General Electric designed Mark I reactors, like those used at Fukushima, required safety modifications.

The risks they flagged, and that Tokyo did not heed, would come back to haunt Japan in the Fukushima crisis.

<much more>

[PoliticAverse]

1. Not as much the decision to ignore the arguments that a tsunami could overwhelm their sea walls...

and that the backup generators and their fuel supply should be located
in a more secure location.

[kristopher]

3. I don't know... (post to RC and Q about Chernobyl)

Perhaps if we throw one more into the mix a similar thread will emerge...




http://www.nrc.gov/reactors/operating/ops-experience/vessel-head-degradation/images.html

Davis Besse: Incident history

Over the years of its operation, the plant has experienced several incidents, none of which have resulted in exposure to dangerous levels of radiation.


On September 24, 1977, the reactor, running at only 9% power, shut down because of a disruption in the feedwater system.<4> This caused the relief valve for the pressurizer to stick open. As of 2005, the NRC considers this to be the fourth highest ranked safety incident.<5>

Loss of feedwater event
On June 9, 1985, the main feedwater pumps, used to supply water to the reactor steam generators, shut down. A control room operator then attempted to start the auxiliary (emergency) feedwater pumps. These pumps both tripped on overspeed conditions because of operator error. This incident was originally classified an "unusual event" (the lowest classification the NRC uses) but it was later determined that it should have been classified a "site area emergency".<6>

Tornado
On June 24, 1998 the station was struck by an F2 tornado.<7> The plant's switchyard was damaged and access to external power was disabled. The plant's reactor automatically shut down at 8:43 pm and an alert (the next to lowest of four levels of severity) was declared at 9:18 pm. The plant's emergency diesel generators powered critical facility safety systems until external power could be restored.<8><9>


Erosion of the 6-inch-thick (150 mm) carbon steel reactor head, caused by a persistent leak of borated water.



Reactor head hole

In March 2002, plant staff discovered that the boric acid that serves as the reactor coolant had leaked from cracked control rod drive mechanisms directly above the reactor and eaten through more than six inches<10> of the carbon steel reactor pressure vessel head over an area roughly the size of a football (see photo). This significant reactor head wastage left only 3/8 inch of stainless steel cladding holding back the high-pressure (~2500 psi) reactor coolant. A breach would have resulted in a loss-of-coolant accident, in which superheated, superpressurized reactor coolant could have jetted into the reactor's containment building and resulted in emergency safety procedures to protect from core damage or meltdown. Because of the location of the reactor head damage, such a jet of reactor coolant may have damaged adjacent control rod drive mechanisms, hampering or preventing reactor shut-down. As part of the system reviews following the accident, significant safety issues were identified with other critical plant components, including the following: (1) the containment sump that allows the reactor coolant to be reclaimed and reinjected into the reactor; (2) the high pressure injection pumps that would reinject such reclaimed reactor coolant; (3) the emergency diesel generator system; (4) the containment air coolers that would remove heat from the containment building; (5) reactor coolant isolation valves; and (6) the plant's electrical distribution system.<11> Under certain scenarios, a reactor rupture would have resulted in core meltdown and/or breach of containment and release of radioactive material. The resulting corrective operational and system reviews and engineering changes took two years. Repairs and upgrades cost $600 million, and the Davis-Besse reactor was restarted in March 2004.<12> The U.S. Justice Department investigated and penalized the owner of the plant over safety and reporting violations related to the incident. The NRC determined that this incident was the fifth most dangerous nuclear incident in the United States since 1979.<3>

Criminal prosecutions
On January 20, 2006, the owner of Davis-Besse, FirstEnergy Corporation of Akron, Ohio, acknowledged a series of safety violations by former workers, and entered into a deferred prosecution agreement with the U.S. Department of Justice. The deferred prosecution agreement relates to the March 2002 incident (see above). The deferment granted by the NRC were based on letters from Davis-Besse engineers stating that previous inspections were adequate. However, those inspections were not as thorough as the company suggested, and as proved by the material deficiency discovered later. In any case, because FirstEnergy cooperated with investigators on the matter, they were able to avoid more serious penalties. Therefore, the company agreed to pay fines of $23.7 million, with an additional $4.3 million to be contributed to various groups, including the National Park Service, the U.S. Fish and Wildlife Service, Habitat for Humanity, and the University of Toledo as well as to pay some costs related to the federal investigation.
Two former employees and one former contractor were indicted for statements made in multiple documents and one videotape, over several years, for hiding evidence that the reactor pressure vessel was being corroded by boric acid. The maximum penalty for the three is 25 years in prison. The indictment mentions that other employees also provided false information to inspectors, but does not name them.<13><14>

2008 discovery tritium leak
The NRC and Ohio EPA were notified of a tritium leak accidentally discovered during an unrelated fire inspection on October 22, 2008. Preliminary indications suggest radioactive water did not infiltrate groundwater outside plant boundaries<15>

2009 unintentional discharge of firearm
In November 2009, a plant security officer was using the restroom and his firearm discharged while in the holster. The officer sustained a non life threatening wound to his calf. No cause was found for the discharge.<16>

2010 Replacement reactor head problems
After the 2002 incident, Davis-Besse purchased a used replacement head from a mothballed reactor in Midland, Michigan. Davis-Besse operators replaced the original cracked reactor head before restarting in 2004. On March 12, 2010, during a scheduled refueling outage, ultrasonic examinations performed on the control rod drive mechanism nozzles penetrating the reactor vessel closure head identified that two of the nozzles inspected did not meet acceptance criteria. FirstEnergy investigators subsequently found new cracks in 24 of 69 nozzles, including one serious enough to leak boric acid. Root cause analysis is currently underway by the Department of Energy, First Energy, and the NRC to determine the cause of the premature failures.<17> <18> Crack indications required repair prior to returning the vessel head to service. Control rod drive nozzles were repaired using techniques proven at other nuclear facilities. The plant resumed operation in 2010. The existing reactor vessel head is scheduled for replacement in 2011.<19>


Future

The facility's original nuclear operating license expires on April 22, 2017. On August 11, 2006 FirstEnergy Nuclear Operating Company (FENOC) submitted a letter of intent (Adams Accession No. ML062290261).<20> The submission date for the application is August 10, 2010. This initiates a long process that results in an application approval or revocation. Public hearings<21> are a vital part of any application review and information on this process can be found on the U.S. Nuclear Regulatory Commission (NRC) website at NRC.gov. <4>. The site map contains many valuable links <22>
http://en.wikipedia.org/wiki/Davis-Besse_Nuclear_Power_Station#cite_note-21


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That is a sketch of the facts. Below, the is the 28 page policy analysys by the Union of Concerned Scientists puts them into a meaningful framework built around the relationship between the industry and its regulators.

Davis-Besse: One Year Later
Nearly one year ago, on March 6, 2002, workers repairing a cracked control rod drive mechanism (CRDM) nozzle at the Davis-Besse Nuclear Power Station in Ohio discovered a football-sized cavity in the reactor vessel head.1 Their finding is linked to two other discoveries 15 years earlier. On March 13, 1987, workers at Turkey Point Unit 4 in Florida discovered that a small leak of borated water had corroded the reactor vessel head. Their revelation prompted the Nuclear Regulatory Commission (NRC) to require all owners of pressurized water reactors,2including Davis-Besse, to take specific measures to protect plant equipment from boric acid corrosion. On March 24, 1987, the NRC learned that control room operators at the Peach Bottom Atomic Power Station in Pennsylvania had been discovered sleeping while on duty. That revelation prompted the NRC to issue an order on March 31st requiring Peach Bottom Unit 3 to be immediately shut down.3

The three findings spanning 15 years are intertwined. Turkey Point demonstrated that a small amount of boric acid leaking onto the reactor vessel head corrodes carbon steel at a high rate. Had the FirstEnergy Nuclear Operating Company, the owner of Davis-Besse, remembered Turkey Point’s lesson, the serious damage at Davis-Besse would have been averted. Peach Bottom demonstrated that a pervasive safety culture problem creates unacceptable conditions for operating a nuclear power plant. Had NRC remembered either Turkey Point’s or Peach Bottom’s lesson, they would have issued the order they drafted to shut down Davis-Besse. It would have been the first shut down order issued by the agency since the Peach Bottom order. But both FirstEnergy and the NRC forgot the past and relived the wrong event from March 1987 by having yet another reactor vessel head damaged by boric acid corrosion.

Many individuals, from both within and outside the NRC, have accused the agency’s move towards risk- informed decision-making as the reason for its failure to issue the order to shut down Davis-Besse. On the contrary, the NRC’s handling of circumferential cracking of control rod drive mechanism (CRDM) nozzles as reported by the Oconee nuclear plant in February 2001 was a successful demonstration of proper application of risk-informed decision-making with the sole and significant exception of its mistake in not issuing the shut down order for Davis-Besse. But even that mistake, as bad as it was, does not impugn the risk-informed decision-making process for the simple reason that the NRC deviated from that process. Had the NRC adhered to its risk-informed decision-making process, it would have issued the shut down order for Davis-Besse and capped off a stellar example of how this process can and should be used.

In February 2001, the NRC learned of a new aging mechanism, the circumferential cracking of stainless steel CRDM nozzles based on inspection results from Oconee. The NRC properly reacted to this finding by revisiting the nuclear industry’s inspection regime for CRDM nozzles. It determined that the existing inspection regime did not provide adequate assurance that circumferential cracks would be identified and repaired. The NRC did not require all plant owners to immediately address this inspection shortfall, which would have imposed an unnecessary regulatory burden on those plants with low susceptibility for the problem. Nor did the NRC allow all plant owners to address the shortfall at their next regularly scheduled refueling outage, which would have imposed an unnecessary challenge to safety margins at those plants with high susceptibility. Instead, the NRC applied risk-informed decision-making by issuing Bulletin 2001-01 in August 2001 to all owners of pressurized water reactors. This Bulletin required the high susceptible reactors to resolve the inspection shortfall by December 2001, the medium susceptible reactors to resolve the inspection shortfall at their next regularly scheduled outage, and merely collected information from the low susceptible reactors.

Only two reactors with high susceptibility for circumferential cracking of CRDM nozzles did not conform to the inspection requirements...

At this point, the NRC abandoned its risk-informed decision-making process.....

http://www.ucsusa.org/assets/documents/nuclear_power/davis-besse_retrospective_030303db.pdf

[RC]

2. What does Chernobyl have to do with what happened in Japan?

Besides nothing that is?

[Nihil]

7. Exactly as much as Davis-Besse has to do with it ...

... but that doesn't stop people spamming the thread with their
usual dribbles of paste buffer faeces ...

:shrug:

[Statistical]

4. Strange as much as the NRC is continually bashed as corrupt.

They mandated the installation of a safety upgrade in the US, a mandate that was never required in Japan.

Even worse this particular component could have improved the situation Japan is now facing.

"First, U.S. researchers concluded that a loss of power at one of the nuclear plants would be one of the "dominant contributors" to the most severe accidents. Flooding of the reactor building would worsen the risks. The NRC also required U.S. plants to install "hard pipe" after concluding the sheet-metal ducts used in Japan could make things much worse.

"Venting via a sheet metal duct system could result in a reactor building hydrogen burn," researchers said in a report published in November 2008."

What if everything bad had happened up to the hydrogen explosion. What if instead of a hydrogen explosion destroying secondary containment, fuel ponds, and internal systems that hydrogen had been vented safely to outside via hardened vent. No doubt the situation would still be critical in Japan but they would have had many more options available.

[CRH]

5. They also designed the plant around a 7.0 magnitude quake, ...

when four decades earlier they had an 8.0 quake. Why would anyone design a plant to specifications 10 times less than the region had recently experienced?

Then investors with obvious political connections, saddle the public with any excessive liability. Whoever the original investors and planners, they should all be hunted down and bankrupted along with anyone who inherited ill gotten gains.

[kristopher]

6. Do you think regulatory perfection is possible?

I don't. Corruption, graft, vanity, cronyism, anger, hate, vindictiveness, shortcuts, penny-pinching, bad judgement, blind spots and well intentioned mistakes are part and parcel of every single system of co-opertive behavior the earth has ever produced.

Pointing to obvious human flaws that exist everywhere as the "problem" is really little more than scapegoating (see post 3 above). The real question is how do we incorporate this inevitability into use of a technology where the worst case consequences of failure are so dire?

Where in our cost/benefit calculations do we account for the long term negative ramification to an entire nation?

We have alternatives that are far superior for carbon reduction.

http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=439x626150