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PostPosted: Nov 26, 2009 7:46 am 

Joined: Jun 17, 2009 9:51 am
Posts: 63
This is good news. I reviewed the Westinghouse presentation. It looks like the money shot is the slide on page 10.

I wonder if the Chinese will be using these changes? I suspect that Westinghouse is humoring the NRC and there is no real problem with the design as is.

However, there will probably be a lot of things that the Chinese and Westinghouse will want to tweak as they get more construction experience on the AP1000.

PostPosted: Nov 27, 2009 12:26 pm 

Joined: Dec 31, 2008 12:09 am
Posts: 236
Location: Berkeley, CA
More information from NEI Overview. One must admire Westinghouse. They are innovative and are fully committed to investing the resources and doing the work needed to be successful. Furthermore, they recognize the importance of the public having confidence in the safety of their reactors, and by being proactive to upgrade the design with the changes described below, they sustain confidence in the safety of the AP-1000. My expectation is that the cost impact of these changes is quite small, since it mainly involves a bit more steel (thicker plates, more tie bars, more reinforcing at the wall-to-roof joint), that do not impact the actual site assembly and construction time.

It will be interesting to learn if these design changes are being implemented on the new units in China. Because Westinghouse has stated that they are committed to maximizing the degree of standardization of AP-1000's worldwide, I would guess that they are going to (I'm pretty sure that they had not yet started the construction of the shield building on the units in construction), since this is a pretty simple set of changes to make if the shield building modules have not been fabricated yet.


Westinghouse Meets with NRC on AP1000 Shield Building Design

Nov. 19, 2009—Westinghouse is dealing with the technical issues the NRC raised
with the shield building design of its AP1000 reactor, an executive told the NRC

“We are confident we can address and resolve all technical comments on the shield
building,” said Bruce Bevilacqua, vice president, engineering, at Westinghouse.
The NRC noted the progress Westinghouse had made with the technical issues described
in an NRC press release in October (see Nuclear Energy Overview, Oct. 22).
“Westinghouse appears to have taken our concerns seriously,” said Laura Dudes,
deputy director, engineering division, at the NRC. “They have acknowledged the need
for modifications to enhance the shield building design.”

In October, the NRC said Westinghouse “has not demonstrated that certain structural
components of the revised AP1000 shield building can withstand design basis
loads.” The NRC added that “progress on the shield building review will require the
company to provide modifications to the design, as well as testing that demonstrates
the building will perform its intended safety function under design basis loads.”
This week’s meeting was the first step in a “technical dialogue” designed to resolve
these issues.

“Today’s discussion is a good first step to introduce the new design features for the
shield wall and begin a technical dialogue on engineering methods, analysis and testing,”
Dudes said. “However, the resolution of these issues will require a comprehensive
technical submittal from Westinghouse demonstrating how the new design addresses
both accident conditions and aircraft impact. It will also require … an in?depth
technical review by the NRC.”

The shield building protects the containment and provides structural support to the
containment cooling water supply. It is made of steel and concrete in what is known as
a steel composite design that is about 73 feet high and about three feet thick.

Bevilacqua said that the primary functions of the shield building were to provide passive
cooling and radiation shielding but that it also had to protect against “tornadoes,
seismic events and, of course, aircraft impact.”
“We are very much focused on making this an integrated structure that provides all
of its functions structurally,” said Bevilacqua.

In response to the NRC letter, Westinghouse has “actively and aggressively” done a
revaluation of the shield building, including soliciting the advice of outside experts
from the Shaw Group, Purdue University and other organizations, Bevilacqua said.

Some of the design enhancements Westinghouse have made include:

• adding shear-reinforcing tie bars so that the shield building acts as a single unit
• increasing the thickness of the steel?concrete composite plate that surrounds the
building to protect against buckling
• improving the connection between the base of the building and the reinforced
concrete roof.

Westinghouse is also conducting a series of 12 tests to ensure the building design is

Bevilacqua said that Westinghouse would go through a detailed technical review of
the shield building design in a proprietary meeting with the NRC conducted after the
public meeting.

“We are focused on demonstrating that the AP1000 shield building design is safe,
robust and meets regulatory requirements,” Bevilacqua said.
Enhancements to the shield building will be addressed in a revised integrated AP1000
shield building report from Westinghouse to be submitted to the NRC in January.
Westinghouse expects to receive approval of all design amendments to support the
first AP1000s coming online in the U.S. in the 2016 timeframe.
The slides for the public presentation given by Westinghouse along with more
information on the AP1000 design can be found here. << Thaddeus Swanek,

PostPosted: Nov 27, 2009 12:37 pm 

Joined: Jan 24, 2007 2:24 pm
Posts: 437
Location: Montreal, Quebec CANADA
I'm getting a little sick of the way this is being covered in the press, what with claims of massive design flaws, and safety issues blown out of proportion. The European news outlets have been the worst. The nuclear industry is in desperate need of better spin control and more situationally aware PR people.

PostPosted: Nov 29, 2009 2:20 am 

Joined: Dec 31, 2008 12:09 am
Posts: 236
Location: Berkeley, CA
DV82XL wrote:
I'm getting a little sick of the way this is being covered in the press, what with claims of massive design flaws, and safety issues blown out of proportion. The European news outlets have been the worst. The nuclear industry is in desperate need of better spin control and more situationally aware PR people.

Westinghouse did blunder in letting the shield-building issue blow up. But they have responded effectively. The important point is that they have retained the elements of the shield building that make it affordable to build (factory prefabrication and modular assembly), while proactively addressing the NRC's concerns. This is exactly the same response that you would see today from any major manufacturer of automobiles, pharmaceuticals, or packaged foods. Sustaining public confidence in product safety is vital for any business that wants to sell products today.

The AP-1000 will be substantially less expensive for Westinghouse to construct than EPRs and ABWRs, so the AP-1000 will remain a high-margin product for Westinghouse until the other vendors eventually bring competitive reactor designs into the market. Once the other vendors bring competitive ALWRs to the market, then none of the reactor vendors will make high margins on ALWR sales and they'll need to look for something better (AHTR and LFTR sound good).

From the perspective of the press and public perception, with Westinghouse's rapid and effective reaction I do not expect any significant problems with public confidence in the longer term. The more important thing is that as more AP-1000's enter into construction, the claims that nuclear power plants take too long to build and are too expensive will ring increasingly hollow. Vogtle is still on track to have new nuclear electricity on the grid in 2016. Sounds good to me.

PostPosted: Jan 06, 2012 12:57 pm 
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Joined: Oct 06, 2010 9:12 pm
Posts: 136
Location: Cleveland, OH
I see that the AP1000 finally got its approval: Now if we can only build some in the USA.

PostPosted: Jan 06, 2012 6:29 pm 

Joined: Nov 01, 2011 2:15 am
Posts: 73
Well, can you get the fresh water into the coolant loop just by gravity power alone when the system may be over-pressure and venting hydrogen gas? What do the experts say?

T. Wang

PostPosted: Jan 06, 2012 7:28 pm 

Joined: Jul 28, 2008 10:44 pm
Posts: 3072
I'm not an expert especially on Ap1000 BUT from the diagrams I've seen it works differently.

The coolant inside evaporates and then condenses on the ceiling inside the containment. The outside of the containment is not under pressure and gets cooled by water on the outside that then evaporates.

No need for the emergency cooling water to overcome a large pressure.


PostPosted: Jan 06, 2012 11:40 pm 

Joined: Apr 24, 2008 4:54 am
Posts: 491
Location: Columbia, SC
There are pressurized water tanks to get you through the first few hours (when decay heat is highest) and to let you depressurize the primary, then the above applies.

PostPosted: Jan 07, 2012 9:50 am 

Joined: Jul 14, 2008 3:12 pm
Posts: 5058
The AP1000 first tries to cool down in closed loop mode under pressure, using a natural circulation heat exchanger. This heat exchanger is just a rack of tubes sitting in a big pool of water. That water, which is a seperate pool (not radioactive) then heats up and boils at atmospheric pressure. The steam then rises and condenses on the containment walls and top, which is very large, made of highly conductive metal, and on the other side there is the outside air drawn in by passive chimney effect.

If the closed loop cooling does not work (eg due to a pipe break) the reactor will depressurize and use the core makeup tanks during this phase to keep the core covered. In this case the steam pressure going in the containment is larger due to the primary loop break, but the containment is designed for this, and passive cooling on the containment by steam condensing is also achieved in this case. The steam that is condensed flows back by gravity to the core.

There wouldn't be much hydrogen in any case because the core is always covered. However there are passive hydrogen recombiners that recombine the hydrogen to water before any large explosive mixture could form, should any hydrogen evolve.

PostPosted: Jan 08, 2012 6:26 am 

Joined: Jun 05, 2011 6:59 pm
Posts: 1337
Location: NoOPWA
Doesn't this all seem a bit ridiculous when compared to a molten salt dump?

DRJ : Engineer - NAVSEA : (Retired)

PostPosted: Jan 08, 2012 8:34 am 

Joined: Jul 14, 2008 3:12 pm
Posts: 5058
KitemanSA wrote:
Doesn't this all seem a bit ridiculous when compared to a molten salt dump?

A little bit, yes. But there's more to it. The molten salt dump is at least 20 years away in terms of a licensed large commercial reactor. The AP1000 is licensed now. USA has lots of dirty coal burners. These are much more ridiculous than any nuclear powerplant. Any nuclear plant we can build now can displace one or two of those dirt burners. The dirt burners store their waste in the environment, belching it right into our lungs. Considering that, everyone talking about nuclear waste problems is more than a little ridiculous.

The AP1000s will make lots of good plutonium for the molten salt reactor to use as startup material. Good synergy.

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