New reactor head arrives at Davis Besse nuclear power plant

[kristopher]

They are finally preparing to repair the gaping hole in Davis Besse's head.



Press release from plant owner:

New reactor head arrives at Davis Besse nuclear power plant

Akron, Ohio, November 29, 2010 — FirstEnergy Nuclear Operating Co., a unit of FirstEnergy Corp., announced that the new reactor head for the Davis-Besse Nuclear Power Station in Oak Harbor, Ohio, has been off-loaded at the Port of Cleveland and will be transported by truck to the plant next week.

Final work on the reactor head was completed in France, including the installation of control rod drive mechanism nozzles made of material less susceptible to cracking under high temperatures and pressures.

The head measures nearly 17 feet in diameter, is eight-feet tall and weighs more than 82 tons. A comprehensive pre-service inspection was conducted by FENOC personnel before the head was shipped from Antwerp, Belgium, on November 5.

The new reactor head will be placed in a specially constructed building at Davis-Besse where new control rod drive mechanisms and other components will be fitted before installation takes place in the fall of 2011.

FirstEnergy is a diversified energy company headquartered in Akron, Ohio. Its FENOC subsidiary also operates the Beaver Valley Power Station in Shippingport, Pennsylvania, and the Perry Nuclear Power Plant in Perry, Ohio.

What they'd rather not discuss:

The reactor core at the Davis-Besse nuclear plant sits within a metal pot designed to withstand pressures up to 2,500 pounds per square inch. The pot -- called the reactor vessel -- has carbon steel walls nearly six inches thick to provide the necessary strength. Because the water cooling the reactor contains boric acid that is highly corrosive to carbon steel, the entire inner surface of the reactor vessel is covered with 3/16-inch thick stainless steel.

But water routinely leaked onto the reactor vessel's outer surface. Because the outer surface lacked a protective stainless steel coating, boric acid ate its way through the carbon steel wall until it reached the backside of the inner liner. High pressure inside the reactor vessel pushed the stainless steel outward into the cavity formed by the boric acid. The stainless steel bent but did not break. Cooling water remained inside the reactor vessel not because of thick carbon steel but due to a thin layer of stainless steel. The plant's owner ignored numerous warning signs spanning many years to create the reactor with a hole in its head.

Workers repairing one of five cracked control rod drive mechanism (CRDM) nozzles at Davis-Besse discovered extensive damage to the reactor vessel head. The reactor vessel head is the dome-shaped upper portion of the carbon steel vessel housing the reactor core. It can be removed when the plant is shut down to allow spent nuclear fuel to be replaced with fresh fuel. The CRDM nozzles connect motors mounted on a platform above the reactor vessel head to control rods within the reactor vessel. Operators withdraw control rods from the reactor core to startup the plant and insert them to shut down the reactor.

The workers found a large hole in the reactor vessel head next to CRDM nozzle #3. The hole was about six inches deep, five inches long, and seven inches wide. The hole extended to within 1-1/2 inches of the adjacent CRDM nozzle #11. The stainless steel liner welded to the inner surface of the reactor vessel head for protection against boric acid was at the bottom of the hole. This liner was approximately 3/16-inch thick and had bulged outward about 1/8-inch due to the high pressure (over one ton per square inch) inside the reactor vessel.

What could have happened?

A loss-of-coolant accident (LOCA) occurs if the stainless steel liner fails or CRDM nozzle #3 is ejected. The water cooling the reactor core quickly empties through the hole into the containment building. The containment building is made of reinforced concrete designed to withstand the pressure surge from the flow through the break.

To compensate for the reactor water exiting through the hole, water inside the pressurizer (PZR) and the cold leg accumulators flows into the reactor vessel. This initial makeup is supplemented by water from the Refueling Water Storage Tank (RWST) delivered to the reactor vessel by the high, intermediate, and low pressure injection pumps. The makeup water re-fills the reactor vessel and overflows out the hole in the reactor vessel head. Approximately 30 to 45 minutes later, the RWST empties. Operators close valves between the pumps and the RWST and open valves between the low pressure injection (RHR) pumps and the containment sump. Water pouring from the broken reactor vessel head drains to the containment sump where the RHR pumps recycle it to the reactor vessel. A cooling water system supplies water to the RHR heat exchanger shown to the left of the RHR pump to remove heat generated by the reactor core.
On paper, that's how the safety systems would have functioned to protect the public. But the following examples suggest that things might not have gone by the book:

-The Three Mile Island nuclear plant experienced a loss of coolant accident in March 1979. Emergency
pumps automatically started to replace the water flowing out the leak. Operators turned off the pumps
because instruments falsely indicated too much water in the reactor vessel. Within two hours, the reactor
core overheated and melted, triggering the evacuation of nearly 150,000 people.

-At the Callaway nuclear plant in 2001, workers encountered problems while testing one of the emergency
pumps. Investigation revealed that a foam-like bladder inside the RWST was flaking apart. Water carried
chunks of debris to the pump where it blocked flow. The debris would have disabled all the emergency
pumps during an accident.

-At the Haddam Neck nuclear plant in 1996, the NRC discovered the piping carrying water from the RWST
to the reactor vessel was too small. It was long enough but it was not wide enough to carry enough water
during an accident to re-fill the reactor vessel in time to prevent meltdown. The plant operated for nearly 30
years with this undetected vulnerability.

-At several US and foreign nuclear power plants, including the Limerick nuclear plant 8 years ago, the force
of water/steam entering the containment building during a loss of coolant accident has blown insulation off
piping and equipment. The water carried that insulation and other debris into the containment sump. The
debris clogged the piping going to the emergency pumps much like hair clogs a bathtub drain. According to
a recent government report, 46 percent of US nuclear plants are very likely to experience blockage in the
containment sumps in event of a hole the size found at Davis-Besse opens up. For slightly larger holes, the
chances of failure increase to 82 percent.<1>

Thus, events at Davis-Besse may have gone by the book had the stainless steel failed it would have become the subject of many books on the worst loss of coolant accident in US history...
UCS -- Aging Nuclear Plants -- Davis-Besse: The Reactor with a Hole in its Head

http://www.ucsusa.org/assets/documents/nuclear_power/acfnx8tzc.pdf







Scapegoating of Davis Besse by NRC
http://www.ucsusa.org/news/press_release/federal-agency-scapegoating-0141.html

Retrospective
http://www.ucsusa.org/nuclear_power/nuclear_power_risk/safety/davis-besse-retrospective.html

[madokie]

1. I'm hoping we stay lucky

There was a lot of luck there at Davis-Beese whether anyone wants to admit it or not.

[kristopher]

2. Yes, a huge amount of luck.

If you haven't done so, I recommend reading this:
Scapegoating of Davis Besse by NRC
http://www.ucsusa.org/news/press_release/federal-agency-scapegoating-0141.html

It is a detailed accounting of the supposed oversight performed by the NRC.

“Work performed without deviations.” Andrew Siemaszko wrote these words on Work Order No. 00-
001846-000 and signed his name on April 25, 2000. Nearly five years later, the Nuclear Regulatory Commission (NRC) cited these four words in its Order banning Siemaszko from working in the nuclear industry. The NRC’s Order stated that Siemaszko’s four words misled the agency into believing the reactor vessel head at the Davis-Besse nuclear plant in Ohio had been completely cleaned during the refueling outage in April 2000 and inspected to show no signs of damage. As this rebuttal will clearly prove, the facts indisputably show that contrary to the NRC’s baseless charge, Andrew Siemaszko did not falsify this work order and an associated condition report. The NRC was as wrong in its April 21, 2005, Order against Siemaszko as it was in its November 28, 2001, decision to shelf the Order it had drafted to require Davis-Besse to be shut down for a safety inspection and allow the reactor to continue operating.

The NRC seems to have recurring judgment lapses when it comes to Davis-Besse. The NRC’s April 2005 sanction against Andrew Siemaszko is baseless, unfair, and deplorable. It is a regulatory travesty. But don’t rely on our analysis. Follow the paper trail – the path not taken by the NRC – and see for yourself the terrible injustice perpetrated against Andrew Siemaszko. ...

The final page is one of the strongest statements I've ever seen come out of the UCS and it's implications bear directly on our ability to trust those who manage the risks of using nuclear power for electricity.

NRC picture of damage:


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

[madokie]

3. And they want us to allow more of these being built

Stupidest thing I've ever seen man do is embrace nuclear energy for our power needs.

That one was close, hopefully it's opened the eyes of the NRC to take a more forceful approach in inspecting our reactors. I wouldn't bet on it though.

The potential of killing a lot of people quickly and contaminating a large area is way too high for me to ever get comfortable with using nuclear for producing our electrical energy.

[GliderGuider]

4. It sounds to me like this was a management issue as much as an engineering issue.

This should prompt improvements in construction, testing, inspection, maintenance, reporting and oversight.

Yes, it was close, but it didn't happen. Effective engineering and management practices are predicated on implementing lessons learned. This was a hard lesson, I hope it's learned well by all stakeholders.

At this time nuclear power is still less dangerous to civilization than carbon, and more useful than renewables.

[Kolesar]

5. Multiply the probablity of "error" by 10,000

http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=115x263653

I put "error" in quotes because misfeasance is a bigger problem.

[GliderGuider]

6. What's the probability of another Besse-Davis?

Before you start multiplying unknown quantities by big scary numbers you need to know what the little number is.

Also, if we were to build 10,000 nukes there is no chance they would be Gen III. The new Gen IV designs are much, much safer, so that needs to be taken into account.

Regardless, we aren't going to be building 10,000 nukes or 6 million wind turbines. We will be building coal plants... So you can stop worrying about teh nuculars.

[madokie]

7. Where are these gen 4 reactors being used?

We were told that the gen 3 was safe so what makes you think we'll buy this one hook line and sinker like you suggest?
just curious you know, just curious...

[joshcryer]

9. No where. The nuclear industry and the fossil fuel industry doesn't want them.

They change the way we do business with energy.

[Kolesar]

8. "Before you start multiplying unknown quantities by big scary numbers you need to know what the litt

Do you ever leave this place?