"cold shutdown" that doesn't require coolant circulation?

Hiddencamper

I appreciate the link. As I said, the VVER in this case has a shield building. Also, they are a 72 hour plant that uses a pool of water, similar to the AP1000.

nikkkom

Before Fuku, nuclear industry was assuring us mere mortals that nuclear power is safe.

If back then I would merely suggest that maybe Japanese NPPs are not that safe I would be laughed at and ridiculed here by the people like you.

Do you realize how severe a hit the public trust in your industry took on 11 March 2011? You (collectively) proved to be incompetent to run your power plants safely, and arrogantly lying about it.

If you feel offended by the above, consider that I still think nuclear power generation makes sense and should not be abolished. Many people are far less forgiving. Here's a sample of the Fukushima jokes from the Internet:

> I've just ordered an empty cardboard box from Fukushima. It was the cheapest microwave I could find.

> I really enjoyed my holiday to Fukushima. But, ever since I got back, I've had this strange pain in my flippers.

> An old woman stands in the market with a "Fukushima mushrooms for sale" sign. A man goes up to her and asks, "Hey, what are you doing? Who's going to buy Fukushima mushrooms?" And she tells him, "Why, lots of people. Some for their boss, others for their mother-in-law..."

> Old grandpa calls his grandson 8 year old little Hoshi to him to tell him something sad about the family. "You know kid this will be hard for you to preceive but you must know that your parents were born in Fukushima." The kid shakes his head in disbelief. Then grandpa continues. "I have another sad thing to tell you too... You were also born in Fukushima." The kid shakes his other head.

nikkkom

I read it. I'd LOL if it wouldn't be so sad.

"4.3.4 Roles and Responsibilities
...
Control room crews did not include an individual dedicated to maintaining an independent view of critical safety functions and advising control room management on courses of action to ensure core cooling, inventory control, and containment pressure control were maintained and optimized. In some countries, operating crews include an individual with engineering expertise and training in accident sequences and accident management to provide additional defense-in-depth if an event were to occur. The need for such a “shift technical advisor” was one of the lessons learned from the Three Mile Island Nuclear Station accident."

"4.6 Knowledge and Skills
...
While it is not clear that the isolation condenser could have been placed in operation following the station blackout and loss of DC electrical power, uncertainty over the operating status of the system contributed to priority-setting and decision-making that were not based on accurate plant status. (Note that operator training on a vendor’s control room simulator that differed in certain significant ways from the actual control console was one of the contributing factors to the 1979 accident at Three Mile Island Nuclear Station.)"

^^^^ Emphasis mine.

Lesson to learn for dummies: USE FRACKING "LESSONS LEARNED" FROM PREVIOUS ACCIDENTS!

rmattila

I don't see how the existence of the outer containment is relevant for the feasibility of the steam-air heat exchangers, as they are in any case located outside the containment:



No water needs to be added other than for compensating leaks - the decay heat is dumped directly into air with a closed-loop natural circulation from the SGs.

a.ua.

These funny stories (anecdote in Russian) have 26 years of history
They come up in the Soviet Union after Chernobyl.
There were a lot of funny stories about his underwear made ​​of lead and a broken rubber band.
Japan badly taught history. Fukushima-received.

Hiddencamper

So when my explosion hits the air cooled heat exchanger and it fails catastrophically I'll make sure that everyone knew you said it would be ok.

Also with regard to the lessons learned, you bolded the very things that I've been pointing out to people. Japan did not incorporate lessons learned, the US already learned those lessons and incorporated it. And we also incorporated lessons learned from Fukushima. There's not a lot of public evidence about this because it all is coordinated through INPO, which is confidential, but the orders we get from INPO are just as mandatory as the ones we get from the NRC.

rmattila

From the protection point of view, the heat exchangers are equivalent to main steam lines, which also contain clean water and can be broken in case of external hazards. In those situations, SBO need not be considered and the emergency feedwater may be credited. The SBO device is not the only way to cool the reactor.

Please recheck your quotes - I have not said anything regarding lessons learned. Just been trying to point out the ideas regarding SBO that are currently being discussed internationally especially after the Forsmark incident in 2006, which pointed out the possibility of failures propagating through the electric grid in an unexpectedly widespread manner.

HowlerMonkey

Who cares about explosions, missiles, or earthquakes?

Let's start small with simply having no power for........forever with nothing else damaged.

Astronuc

One then has to go with natural convection, hopefully with an intact primary system, or if the primary system fails, e.g., it suffers a LOCA, then containment must be such to allow heat transfer to the environment without failure, or at least with minimal containment breach. In the latter situation, the internal pressure must be controlled via condensation of the steam from the coolant, assuming an LWR. Then the coolant catch/collection system would have to be above the core to ensure it can be returned to the core.

Then there needs to be piping to return collected coolant back to the RPV. One would then need a valve system that is closed during normal operation, and opens only during an accident event.

Otherwise, there is an existing decay heat removal system.

Cold shutdown of an operating reactor core requires coolant circulation in order to remove the decay heat. There has to be some heat removal, otherwise the fuel would heat up to melting temperature, but in an LWR, the cladding would corrode rapidly well below melting temperature.

Decay heat can be somewhat mitigated by operating a reactor at low power density with fuel to low burnup (as is planned in at least one SMR design, and to some extent in a CANDU), but then there is an economic penalty.

etudiant

Very interesting information.
It strongly suggests that CANDU designs are inherently safer.
How large is the 'economic penalty' you indicate?
Could the safety differential justify that difference?

nikkkom

More frequent fuel reloading and more voluminous waste. Something like x3 more waste by mass, but which is about x3 less radioactive.

gmax137

I'm not so sure about that. The decay heat level in the first hours following the reactor shutdown/trip are barely affected by the burnup (for any reasonable burnup). And, I think that the most risk occurs during those early hours, because it seems that the likelihood of core melt is much less at longer times, when decay heat is lower and more operator action (including aid from offsite) is possible.

In other words, lower burnup reduces the decay heat in the long term (days after trip), but that isn't where the big problems are.

rmattila

Burnup does indeed not have a big effect, but power density wrt total heat capacity in the core does. CANDU, RBMK and AGR are good in this respect but have other, less favourable characteristics in other fields.

etudiant

The greater volume of spent fuel is clearly an economic issue.
Is the more frequent refuelling of the CANDU also an issue if the reactor can be refuelled during ongoing normal operations?

Astronuc

CANDU units can do on-line refueling, so they can maintain high capacity factors. The burnups have been in the range of 1-1.5% FIMA, but may now be higher. The enrichments are lower, so the utility does not have to purchase more uranium ore as compared to LWRs using higher enrichment, which partially offsets the increased volume of spent fuel.

mheslep

Just curious: that's due only to the tritium atoms in the water? Not another source?

Hiddencamper

While the fuel in BWRs (and PWRs) is solid, all solid material has some miniscule amounts of diffusion. As such, some fission products get into the primary coolant, such as Iodine, Cesium, Xenon, and even Boron from the control rods. During normal operation, there are chemistry samples done, and the specific activity of all of these fission products are looked at, as the ratio of the different fission product decay chains is a sign of whether or not the fuel has failed (Cracked) or if it is just simple diffusion of fission products through the cladding material.

Tritium comes not just from hydrogen absorbing neutrons, but also from the boron in the control rods. The B-10 can absorb a neutron and then undergo double alpha decay, leaving behind a tritium atom. Any boron in primary coolant, or any tritium/boron that leaches out of the rods will also increase tritium inventory in the primary coolant.

In all reactors, when the reactor is online, the main source of radiation in the primary coolant loop is N-16. N-16 is a very short lived isotope (several seconds), and is virtually completely gone within a few minutes after shutdown. When the reactor is offline, cobalt-60 (which comes from stellite material in valve seats as well as on control rod blade rollers used for preventing the blades from rubbing the fuel material), Co-60 is the main gamma emitter when the reactor is offline, usually in the form of hot particles which get trapped in the reactor coolant system.


tl;dr most of the fission products and decay chains make it into primary coolant, not just tritium.

Additionally, primary coolant in both BWRs and PWRs is radioactive. PWRs have more tritium because they use Boron as a chemical shim, while the only tritium in BWR coolant is that from neutron capture and leeching. BWRs do not have a secondary coolant loop, but PWRs do, and their secondary loop also has radioactive products in it. PWRs have drastically less, as only things which leech through the steam generator tubes or pass through tube leaks generally get into secondary coolant. Additionally, reclaimed rad-waste water (which is reprocessed for reactor or secondary use) may contain slight amounts of fission products which werent removed in the rad waste system. Secondary cooling loops have rather large levels of tritium however (compared to BWRs) as well, because tritium does not get removed in the normal rad waste process, as it chemically looks the same as normal water, and rad waste processing is primarily chemical/resin/ion exchange based.