Cold shutdown that doesn't require coolant circulation?

[rmattila]

I've never been quite able to understand the difference between the "differences in BWR:s" document and the information about the Oyster Creek & Dai-ichi #1 found on the net: the document talks about one 29000 gallon IC tank and 90 min capacity, whereas Fuku 1 and Oyster Creek apparently have two IC tanks and several hours of capacity.

 

[Hiddencamper]

I've never been quite able to understand the difference between the "differences in BWR:s" document and the information about the Oyster Creek & Dai-ichi #1 found on the net: the document talks about one 29000 gallon IC tank and 90 min capacity, whereas Fuku 1 and Oyster Creek apparently have two IC tanks and several hours of capacity.

I think I'll be able to find out oyster's actual IC capacity.

That differences document states a 20 minute IC capacity (which is in line with Dresden's IC). I do know that IC capacity of the shell itself in some plants (like dresden) is only about 20-30 minutes per IC (i found this chapter of their FSAR online), but it can be extended to several hours with water pumped in via a diesel driven or electric driven motor from a water tank sitting outside the plant which refills the IC.

part of the reason for the smaller time is the greater decay heat load. Dresden is a very high power plant for the core size, so it has much more decay heat to deal with.

I've read claims that Fuku #1 has a 6 hour IC capacity in the heat exchanger shell...I'm a little skeptical (because I know some BWRs have much smaller ICs)...and there could be a translation issue here, but I have no verified evidence that they don't have a 6 hour IC capacity. I doubt we will ever get Fukushima's specifics for its IC size (in the form of a design document), but Oyster's should be in chapter 5 or 6 of their FSAR (they have a different FSAR layout so I'm not positive which chapter), and that's semi-publicly available. I know someone at oyster so I'll see if I can get a rough number.

 

[rmattila]

I have very limited knowledge of the GE BWRs. I know that the only ASEA BWR with IC, Oskarshamn 1, has 6 hour shell side capacity and capability to gravity-fill from the SFP (see http://www.ensreg.eu/sites/default/files/Swedish national report EU stress tests 111230.pdf , page 160), but that the capacity in SBO is limited to 2 hours due to the battery capacity needed to keep the valves open.

EDIT: The Spanish 466 MWe Santa Maria de Garona NPP, which AFAIK is close to FK1/1, apparently only has 1 hour worth of water on the shell side: http://www.ensreg.eu/sites/default/files/Spain_Stress-Tests.pdf , p. 157.

 

[Astronuc]

This might also be of interest in understanding BWRs.

https://netfiles.uiuc.edu/mragheb/www/NPRE%20402%20ME%20405%20Nuclear%20Power%20Engineering/Boiling%20Water%20Reactors.pdf

Oyster Creek and Nine Mile Point 1 are BWR/2 units without jetpumps, but with direct cycle.


FYI - Passive Safety Systems and Natural Circulation in Water Cooled Nuclear Power Plants
IAEA TECDOC 1624 - http://www-pub.iaea.org/books/IAEAB...culation-in-Water-Cooled-Nuclear-Power-Plants

 

[Hiddencamper]

I've never been quite able to understand the difference between the "differences in BWR:s" document and the information about the Oyster Creek & Dai-ichi #1 found on the net: the document talks about one 29000 gallon IC tank and 90 min capacity, whereas Fuku 1 and Oyster Creek apparently have two IC tanks and several hours of capacity.

Thanks to a colleague at Oyster, I've seen copies of Oyster's safety analysis report and their operations training manuals. The IC at Oyster can operate for 45 minutes each without a makeup water supply. so 2 ICs in service is 90 minutes. It also takes about 100k gallons to actually do a full cool down on the oyster creek reactor. This "several hours capacity" is not correct. The IC is only sized for a little over 90 minutes w/out makeup.

 

[nikkkom]

You can't take any credit for a passive air cooler if it cannot withstand all of the environmental effects it could be faced with.

Interesting. Your position boils down to "we can't build an air-cooled heat exchanger which can withstand 9M earthquake, therefore let's not have it at all".

Since you have to run reactor coolant through it

Wrong.

if it is hit by a missile or an airplane (which US nuclear plants are required to be designed for now) it no longer will be a functional system, and in fact, can create a credible leak path for reactor coolant and fission product release.

You are criticizing something different from my proposal, because in my proposal reactor water does NOT go directly thru air cooler; but anyway:
I am 100.00% sure Fukushima refugees would take a small, TMI-like transient radiation leak instead of a massive Cs-134/137 plume and ensuing permanent evacuation any day, thank you very much!

 

[nikkkom]

What I was specifically referring to was the fact that you cannot bring a reactor to cold shutdown using IC alone.

In a SBO, your primary concern is not to bring reactor to cold shutdown. In a SBO, your goal is to not let it melt down. If IC would be able to stabilize RPV at 120C for days without any power, I am a happy camper.

 

[Hiddencamper]

Interesting. Your position boils down to "we can't build an air-cooled heat exchanger which can withstand 9M earthquake, therefore let's not have it at all".



Wrong.



You are criticizing something different from my proposal, because in my proposal reactor water does NOT go directly thru air cooler; but anyway:
I am 100.00% sure Fukushima refugees would take a small, TMI-like transient radiation leak instead of a massive Cs-134/137 plume and ensuing permanent evacuation any day, thank you very much!

Ok so are you talking about SBO or are you talking about design basis accidents?

In either case, why are you going to install something that isn't capable of functioning in ALL environmental and accident conditions. You can't even accredit it as safety. There is absolutely no purpose in nuclear to install a piece of equipment with a safety function if it cannot handle the design basis earthquake, floods, weather events (wind snow tornado), plus any effects from design basis accidents including jet impingment/pipe whip due to High energy line breaks, LOCA, LOOP, etc. So yes, if you cannot build a structure that can withstand all of that, then it is not worth it to built it at all in nuclear.

As for not having to run reactor coolant through it, I'm curious... how are you going to transfer heat from one loop to another? So you are going to use reactor natural circulation combined with gravity for a primary loop heat removal...but how are you going to get the secondary loop to do the same. It is a large challenge, but not an insurmountable one, but I have a feeling (based off of experience) that adding in another loop to a natural air cooled heat exchanger for LWRs is not going to be effective without AC electrical power or some other motive force.

 

[Hiddencamper]

In a SBO, your primary concern is not to bring reactor to cold shutdown. In a SBO, your goal is to not let it melt down. If IC would be able to stabilize RPV at 120C for days without any power, I am a happy camper.

There is still operational leakage even during SBO, so makeup is an issue as well (albiet a long term one). If you cannot bring the system to cold shutdown, it is very difficult to makeup to the vessel using external pumps, and is an issue we saw at Fukushima, when they couldn't get RPV and PCS pressures low enough to allow injection.

The IC on its own extracts too much heat from the reactor, a detailed analysis would need to be performed, but its possible it would cool the system down so rapidly that if would lose natural circulation for a period of time. You need motive force to somehow turn the IC "on" and "off". Additionally you still need motive force plus a makeup source to have the IC maintain the vessel in a hot standby condition, although that force does not necessarily need to be AC power.

 

[nikkkom]

Ok so are you talking about SBO or are you talking about design basis accidents?

SBO must be a design basis accident. Otherwise we will have more Fukushimas.

 

[nikkkom]

If you cannot bring the system to cold shutdown, it is very difficult to makeup to the vessel using external pumps, and is an issue we saw at Fukushima, when they couldn't get RPV and PCS pressures low enough to allow injection.

They couldn't bring RPVs to atmospheric pressure because some idiot decided that prolonged SBO "can't happen" and therefore accident planning and personnel training regime does not need to include instructions and drills for venting RPVs in SBO conditions.

This corporate/regulatory blunder has nothing to do with technical merits of ICs.

If anything, if IC maintains RPV internals at near 100 C and pressure just a tad above 1 atm, that makes injection easier, not harder.

 

[Hiddencamper]

SBO must be a design basis accident. Otherwise we will have more Fukushimas.

SBO can't be a design basis accident. Under plant design you can never have that many failures happen to put you in prolonged SBO. It wasn't a decision, its the fact that's how your design is of your facility. SBO is like any other extensive damage or severe accident, the fact that you got there in the first place meant that circumstances occurred which could not be prevented by design, and as such, you cannot plan for it like you would plan for any normal accident scenario.

Also, there are accident scenarios and procedures for venting the RPV, even in SBO conditions. The issues involved were due to the Japanese position to not vent until double the maximum containment design pressure. There were a lot of things that occurred as a result of this decision, such as not enough SRV accumulator pressure to actuate the SRVs in ADS or relief mode, failure of penetrations and seals in the PCV (and a potential breach in unit 2 PCV), etc.

 

[rmattila]

The term "design basis" is internationally a bit vague, since in some countries it refers to the original US definition, whereas in some countries additional more extensive conditions ("design extension conditions") and even severe accidents are in fact within the design basis. For example, the Finnish event classification is described in that post: https://www.physicsforums.com/showpost.php?p=3671859&postcount=566 and a SBO falls under the DEC B category, where systems are only required to withstand external conditions with frequency once per 1000 years, not once per 100 000 years as the DBC4 systems.

 

[rmattila]

As for not having to run reactor coolant through it, I'm curious... how are you going to transfer heat from one loop to another? So you are going to use reactor natural circulation combined with gravity for a primary loop heat removal...but how are you going to get the secondary loop to do the same. It is a large challenge, but not an insurmountable one, but I have a feeling (based off of experience) that adding in another loop to a natural air cooled heat exchanger for LWRs is not going to be effective without AC electrical power or some other motive force.

They're doing something like that at the Kudankulam VVER being built by Russia in India: http://www.frontlineonnet.com/fl2824/stories/20111202282403300.htm

http://www.frontlineonnet.com/fl2824/images/20111202282403305.jpg

 

[nikkkom]

SBO can't be a design basis accident. Under plant design you can never have that many failures happen to put you in prolonged SBO. It wasn't a decision, its the fact that's how your design is of your facility. SBO is like any other extensive damage or severe accident, the fact that you got there in the first place meant that circumstances occurred which could not be prevented by design, and as such, you cannot plan for it like you would plan for any normal accident scenario.

Also, there are accident scenarios and procedures for venting the RPV, even in SBO conditions.

Glad that you are sure there are.

From where I sit, empirical evidence (Fuku) says that those procedures are not known to people operating NPPs, and when SBO occurred, they had no idea what to do.

 

[Hiddencamper]

Glad that you are sure there are.

From where I sit, empirical evidence (Fuku) says that those procedures are not known to people operating NPPs, and when SBO occurred, they had no idea what to do.

Fukushima is a bad comparison to the rest of the world. Both plants I work at train on their SBO procedures, and it is well known how to handle the situation. If you read INPO's lessons learned, available here:http://www.nei.org/resourcesandstat...t-the-fukushima-daiichi-nuclear-power-station

you will see that it is very clear the Japanese deviated from several lessons learned by the US industry. And if you read the teleconference reports from the NRC website which were FOIAd from Fukushima, in the first one, it states very clearly that they were asking US plants (Exelon) to run simulator scenarios to figure out what was going on, and were asking GE for severe accident guidelines which are available at every US plant.

Japan really dropped the ball going into this, and the design of Daiichi didn't help it at all.

As for my comment about SBO, SBO is outside of design basis because it takes multiple accidents and failures, which is well beyond what you can realistically design for. To get to that point means something unpredictable happened, and as such, you need mitigation procedures, not blackout procedures.

 

[Hiddencamper]

They're doing something like that at the Kudankulam VVER being built by Russia in India: http://www.frontlineonnet.com/fl2824/stories/20111202282403300.htm

http://www.frontlineonnet.com/fl2824/images/20111202282403305.jpg

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]

Fukushima is a bad comparison to the rest of the world. Both plants I work at train on their SBO procedures, and it is well known how to handle the situation.

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]

If you read INPO's lessons learned, available here:http://www.nei.org/resourcesandstat...t-the-fukushima-daiichi-nuclear-power-station

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]

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.

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:

[PLAIN]http://www.frontlineonnet.com/fl2824/images/20111202282403306.jpg

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.]

Here's a sample of the Fukushima jokes from the Internet:

.

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]

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:

[PLAIN]http://www.frontlineonnet.com/fl2824/images/20111202282403306.jpg

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.

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]

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.

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.

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.

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]

Who cares about explosions, missiles, or earthquakes?

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

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]

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.

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]

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

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

 

[gmax137]

Very interesting information.
It strongly suggests that CANDU designs are inherently safer.
...

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]

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.

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]

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?

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]

True, BWR water is radioactive

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

 

[Hiddencamper]

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

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 weren't 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.

 

[mheslep]

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),

Interesting. Which comes about from dissolved N2 gas in the water, or some nitrate hanging about?

 

[Hiddencamper]

Interesting. Which comes about from dissolved N2 gas in the water, or some nitrate hanging about?

It is an (n,p) reaction:

O16 + n -> N16 + p

The oxygen is from the water in the reactor vessel.

See http://en.wikipedia.org/wiki/Nitrogen

N-16 is the reason we have a 3 foot thick concrete bioshield around BWR heater bays and turbines.