Good points James,
The ice condenser versions had slipped my mind. The discussion also reminds me of the partial vacuum containment systems in the US (Surrey 1 &2 and 2 others as I recall), which I remember included a spray to take the building back to sub-atmospheric pressure relatively slowly after an overpressure incident. Are you familiar with the containment of the three nuclear plants in Ontario which include a large vacuum reservoir shared with 4 and 8 reactors and include a water spray pressure suppression system? Some very ingenious systems have been designed and placed in service.
Duane Pendergast wrote:
I’m adding a bit to Jerry’s response to your lack of dousing question.
“OTOH, most contemporary NPP designs have dousing reservoirs below the dome
roof, which the EPR doesn't have.... any idea why ?”
A containment system without a dousing pressure suppression system will require a substantially more pressure resistant building for a typical design basis loss of coolant event. A strong building will be more resistant to some off design basis events such as the ones that occurred at Three Mile Island and Chernobyl. Avoiding pressure suppression in the design thus subtly enhances the capability of the containment system to contain a broader selection of events – possibly at an increase of cost.
Actually, I don’t think most contemporary designs include pressure suppression, but I’ve been out of the business for a few years and haven’t looked into containment issues, so maybe changes have taken place.
Three Mile Island containment had no pressure suppression system intended to cope with a loss of coolant. It did contain an event which released hydrogen into containment that then rapidly burned raising internal pressure quickly to about 60 psi I recall. If it had been designed with pressure suppression for the design basis LOCA, the consequences of the oddball off-design event at TMI might not have been so benign. Chernobyl provides another even more complex story which would involve a lot of semantics with respect to the definition of containment so I’ll spare you.
My guess is that something like 30-40% of reactors world-wide have a pressure suppression containment with BWRs and VVERs and some RBMKs tending to have pressure suppression and PWRs tending not to (although there are few PWRs with pressure suppression from melting ice. The design tradeoff is the additional complexity and cost of a pressure suppression pool (and the benefits of having a large supply of water and a heat sink available) vs. the cost of a large enough containment to provide the same pressure reduction by simple expansion. The tradeoff is not an open and shut choice. GE and several of its utility customers had a multi-year research and refitting program to resolve some technical issues related to suppression pools followed by a multi-year litigation to decide who paid.
Pacific Northwest National Laboratory
These comments are mine and have not been reviewed and/or approved by my management or by the U.S. Department of Energy.