Safety Injection during Main Steam Line Break

[Hiddencamper]

Doing some more checkup.

MTC is the change in reactivity for a change in degree temperature.

I'm pretty sure it becomes less negative as you progress from beginning to end of cycle.

The SLOPE of the MTC curve also becomes larger towards EOC (Slope is what determines the overall reactivity effect due to a change in temperature).

See this image for what I'm talking about.

https://drive.google.com/file/d/0B-HOaUJyFtPhNkhaZVJIaGF3UmM/edit?usp=sharing

I guess I'm not completely understanding how this works in PWRs. A "More Negative" MTC would make me think that MSLB at EOC is LESS severe. Or is it MORE severe because there is more reactivity worth bound up in the MTC? I would think that your MTC would have LESS worth at end of cycle, because you are in a region with warmer/hotter water already...sorry lot of thoughts/questions

Sorry if I'm making this confusing.

 

[QuantumPion]

Doing some more checkup.

MTC is the change in reactivity for a change in degree temperature.

I'm pretty sure it becomes less negative as you progress from beginning to end of cycle.

The SLOPE of the MTC curve also becomes larger towards EOC (Slope is what determines the overall reactivity effect due to a change in temperature).

See this image for what I'm talking about.

https://drive.google.com/file/d/0B-HOaUJyFtPhNkhaZVJIaGF3UmM/edit?usp=sharing

I guess I'm not completely understanding how this works in PWRs. A "More Negative" MTC would make me think that MSLB at EOC is LESS severe. Or is it MORE severe because there is more reactivity worth bound up in the MTC?

Sorry if I'm making this confusing.

If you have a large negative MTC, then a small increase in power causes a large decrease in reactivity (good for normal operation). However, this also means a small decrease in coolant temperature causes a large increase in reactivity (bad for main steam line break - where you have a large, rapid decrease in temperature causing a very large increase in reactivity and power).

 

[Hiddencamper]

If you have a large negative MTC, then a small increase in power causes a large decrease in reactivity (good for normal operation). However, this also means a small decrease in coolant temperature causes a large increase in reactivity (bad for main steam line break - where you have a large, rapid decrease in temperature causing a very large increase in reactivity and power).

Ok, I think we are thinking the same thing.

More or less, the change in reactivity due to a change in moderator temperature at EOC will be more severe than at beginning of cycle.

With regards to the absolute magnitude/value of reactivity tied up in moderator temperature, I've been taught that the absolute value of reactivity due to temperature is less negative towards EOC. However that's really outside the scope of the question. The NRC fundamentals PWR question bank, used for the PWR licensed operator exam, says the same thing with regards to absolute value of reactivity.

Our crazy BWRs, depending on fuel design, can actually become overmoderated below 300 degrees F and have positive MTC. This happens when you go to long cycle + power uprate + new fuel designs.

Edit: Jim's post is great stuff. That makes a lot of sense.

 

[jim hardy]

PWR has competing temperature effects in moderator.
Water expands with temperature,separating the molecules which lessens its effectiveness at slowing down neutrons. That gives it a healthy negative temperature coefficient.
When boron is added to the water, the boron atoms also separate with temperature making them less apt to absorb neutrons. That effect is opposite , making the overall moderator temperature coefficient less negative at beginning of life when there's maximum boron..

Steam break cools the reactor
so the worry is that with a large negative temperature coefficient it'll return to power , though at lower than normal operating temperature , and continue feeding steam into containment if that's where the break is. That's why SI trips feeedwater pumps too.



From a Westinghouse AP1000 description:

The moderator temperature (density) coefficient is defined as the change in reactivity per degree change in the moderator temperature. Generally, the effects of the changes in moderator density and the temperature are considered together.
The soluble boron used in the reactor as a means of reactivity control also has an effect on the
moderator density coefficient, since the soluble boron density and the water density are decreased when the coolant temperature rises.
A decrease in the soluble boron density introduces a positive component in the moderator coefficient. If the concentration of soluble boron is large enough, the net value of the coefficient may be positive.
The initial core hot boron concentration is sufficiently low that the moderator temperature
coefficient is negative at operating temperatures with the burnable absorber loading specified.
Discrete or integral fuel burnable absorbers can be used in reload cores to confirm the moderator
temperature coefficient is negative over the range of power operation.
The effect of control rods is to make the moderator coefficient more negative, since the thermal neutron mean free path, and hence the volume affected by the control rods, increase with an increase in temperature.
With burnup, the moderator coefficient becomes more negative, primarily as a result of boric acid
dilution, but also to a significant extent from the effects of the buildup of plutonium and fission
products

http://www.nrc.gov/reactors/new-reactors/design-cert/ap1000/dcd/Tier 2/Chapter 4/4-3_r14.pdf

If you need some reading on the subject to put you to sleep, here's a study of steam breaks ...
https://www.oecd-nea.org/science/docs/2000/nsc-doc2000-21.pdf
I was going to quip "Rip Van Winkle must've written this", but after i got used to the awkward layout it became quite interesting...

One of the major concerns for the MSLB transient is the return to power and criticality in the latter half of the transient.
Because of this concern, the MSLB scenario is based on assumptions that conservatively maximise the consequences for a return to power. These assumptions, along with a detailed description of the reference problem, can be found in the following paragraphs...
...
...
The initial steady state problem places the reactor at 650 effective full power days (EFPD), end of cycle (EOC), with a boron concentration of 5 ppm, average core exposure of 24.58 GWD/MT, and equilibrium Xe and Sm concentrations. The initial operating conditions are as follows: the initial RCS pressure is 2 170 psia (the normal operating value), the initial pressuriser liquid level is set to 220 temperature compensated inches (a typical HFP level) and the initial cold leg temperature is at the normal value of 557 °F, which compensates for instrument error. Table 2.1 gives a detailed description of the initial steady state conditions for this transient...

page 53 of 136 has graphs of power vs time for various simulated steamline breaks. Looks like a return to ~ ten or twenty percent power after about a minute.

 

[mudweez0009]

I'm still a little confused. So from you guys' debates, I got that it is more severe at EOL. Maybe it comes down to me not having a full grasp on MTC.

My understanding of reactivity:

• I get that reactivity is based on Keff, and that if Keff>1 then the value of reactivity is positive, and if Keff <1 then the value of reactivity is negative.

• Reactivity is affected by temperature, among other things.

• The amount of reactivity change per degree change in moderator temperature is the moderator temperature coefficient.

• (From Jim's post): If moderator temp increases (which is just water flowing through the core?), then the water expands, causing it to not slow down neutrons, meaning more neutrons escape rather than being captured for further fission. So this why Jim said it gives a negative temp coefficient, because if less neutrons are being fissioned, then the reactivity value based on Keff decreases.

• I found a graph relating MTC to moderator temp, showing that MTC decreases as moderator temp increases. Below the graph it says that at moderator temp of room temperature, MTC is about -5 to -10 pcm/K and decreases down to about -25 pcm/K at operating temperature. Then at EOC, it can increase back up, even to being slightly positive.

I'm not sure from what I know how a reactivity decrease (from moderator temp increase) affects MTC any more at EOL than BOL, or vice versa.

I get that MTC is a function of reactivity, as it depends on reactivity change in the equation, but from that, can it be clarified what it means to discuss both reactivity AND MTC in terms of "positive" and "negative"? I feel it should be said in terms of "Less positive or more negative" OR "more positive or less negative"...

 

[QuantumPion]

I'm still a little confused. So from you guys' debates, I got that it is more severe at EOL. Maybe it comes down to me not having a full grasp on MTC.

My understanding of reactivity:

• I get that reactivity is based on Keff, and that if Keff>1 then the value of reactivity is positive, and if Keff <1 then the value of reactivity is negative.

• Reactivity is affected by temperature, among other things.

• The amount of reactivity change per degree change in moderator temperature is the moderator temperature coefficient.

• (From Jim's post): If moderator temp increases (which is just water flowing through the core?), then the water expands, causing it to not slow down neutrons, meaning more neutrons escape rather than being captured for further fission. So this why Jim said it gives a negative temp coefficient, because if less neutrons are being fissioned, then the reactivity value based on Keff decreases.

• I found a graph relating MTC to moderator temp, showing that MTC decreases as moderator temp increases. Below the graph it says that at moderator temp of room temperature, MTC is about -5 to -10 pcm/K and decreases down to about -25 pcm/K at operating temperature. Then at EOC, it can increase back up, even to being slightly positive.

I'm not sure from what I know how a reactivity decrease (from moderator temp increase) affects MTC any more at EOL than BOL, or vice versa.

I get that MTC is a function of reactivity, as it depends on reactivity change in the equation, but from that, can it be clarified what it means to discuss both reactivity AND MTC in terms of "positive" and "negative"? I feel it should be said in terms of "Less positive or more negative" OR "more positive or less negative"...

Reactivity is usually expressed in units of pcm (percent mille). So a reactivity of 10 pcm means k-effective is 1.00010 (i.e. the neutron flux increases by a factor of 1.00010 per neutron generation). MTC is expressed in units of pcm per degree F, e.g. -1 pcm/F would mean if moderator temperature decreases by 1 F than reactivity will increase by 1 pcm. Does this help?

Note that a change in reactivity does not affect MTC directly. Only changes in temperature or fuel composition do. Reactivity is simply the rate of change of the neutron population.

 

[jim hardy]

Then at EOC, it can increase back up, even to being slightly positive.

can you post link to that graph?

Starting at page 77 of this document (linked earlier) are graphs , and from a pretty credible source..
http://www.nrc.gov/reactors/new-reactors/design-cert/ap1000/dcd/Tier 2/Chapter 4/4-3_r14.pdf

Figure 4.3.24 on page 81 of 89 shows it going more negative as the cycle progresses (BOC is no burnup left side of chart, EOC is on right)
MWD/MTU is acronym for "Megawatt Days per Metric Ton of Uranium", a strange unit that's convenient for reactor engineer types.

I get that MTC is a function of reactivity, as it depends on reactivity change in the equation,but from that, can it be clarified what it means to discuss both reactivity AND MTC in terms of "positive" and "negative"?

ahhh here's why i was disappointed that teacher didn't do some reactivity calculations.

Keff is calculated as a product of probabilities.

Pages 9 to 16 of 65 here are a good rundown http://www.cedengineering.com/upload/reactor%20nuclear%20parameters.pdf


basically K = ε X p X f X η

where:
ε is a number very near 1.0 that represents probability of a fission being thermal not fast(fast fission factor)
p is a number near .95 to 1.0 that represents probability of a neutron not getting absorbed in a non-fission capture in the fuel (resonance escape probability) ie probability that if it gets absorbed by fuel it'll cause a fission
f is a number somewhat less than 1 representing probability that a thermal neutron is absorbed in the fuel instead of something else like a control rod(thermal utilization factor),
η is a number representing the number of neutrons produced per fission, and runs a little more than 2. It varies from ~2 to 2.5 depending on fuel isotopes.

When the result of that four term product is exactly 1, you are exactly critical.
So i guess i told a white lie up above - it's a product of three probabilities and a constant for isotoope.

Poison like boron or rods affects f
ε and p change with burnup
moderator temperature affects how far a neutron must travel to get slowed down, hence it affects f and probably p (perhaps a genuine nuclear type can help me here?)
AND temperature affects how much boron is in the core which is definitely f.

A lot to absorb i know

but your curiosity is invigorating to an old guy like me who loves this stuff. Secondhand Lion, you know...

Keep up the good work !

 

[mudweez0009]

Okay, thanks guys.

can you post link to that graph?

http://www.energy.kth.se/courses/4A1627/Material2005/PhysicsPart/02%20Reactivity%20Rev%200.pdf

Pages 27 and 28

 

[Astronuc]

Okay, thanks guys.



http://www.energy.kth.se/courses/4A1627/Material2005/PhysicsPart/02%20Reactivity%20Rev%200.pdf

Pages 27 and 28

The example is for a BWR rather than a PWR. The curve shows MTC as a function of moderator (coolant) temperature, and in a BWR, the coolant does not use soluble boron as is the case in a PWR. Also, BWRs operate at lower coolant temperature (Tsat ~ 286) and at shutdown, the temperature decreases to ~100 C or less when the head is removed. However, at shutdown in a BWR, all the control rods are in the core at shutdown.

For a PWR, the soluble boron is mostly gone, and one can use feedwater temperature reduction to add some reactivity to the core to extend the cycle during coastdown. Also, at EOC, there is a fair amount of Pu-239/-241 built up in high burnup fuel, and the burnable poison in the fresh fuel (feed batch, which becomes once-burned at EOC) is depleted.

MTC will also depend on the enrichment and use of burnable poison, which are somewhat affected by core design, e.g., batch size and cycle length/exposure. I've seem some plants on 24 month cycles have issues with + MTC, however, I can't remember if it was BOC, MOC or EOC, and it might have been during a transition cycle.

The pdf that Jim cites states, "if a reactor is over-moderated, it will have a positive MTC." It could, but not necessarily so. IIRC, use of enriched (in B-10) boron is one method of reducing MTC.

 

[jim hardy]

Thanks Astro for the insight.

MTC will also depend on the enrichment and use of burnable poison, which are somewhat affected by core design, e.g., batch size and cycle length/exposure.

So the designer can tweak core design to somewhat bend MTC where he wants it... makes perfect sense..
I could accept that accumulation of Pu as cycle progresses might change η, and depletion of U235 might affect ε
but that's something i'd ask a reactor engineer about rather than pretend i know .

thanks again.

 

[mudweez0009]

Okay this is going to be another random question, but this is evidently the trend of this course..
I actually created a new thread for this topic for my specific questions, but it doesn't seem to be attracting anyone. I figured while I have a few people's attention, I may as well post it here, even though it is off our current topic.
I will admit upfront that these are directly from my homework. From this thread, I hope I have proven I am genuinely trying to learn the material and not just ask for answers. But I need help, and can't find any equations anywhere (yes, we got calc problems.. and yes, weren't given reference material).

The thread link: (https://www.physicsforums.com/showthread.php?t=747913#taglist)

You can go there if you choose, or we can continue it here, as this conversation has definitely evolved throughout its life anyway. If you choose to stay here, here is my post in the linked thread..

I am having issues with some problems relating to a plant theoretically shut down on natural circulation, and calculating the core ΔT and natural circulation flow rate.. Can anyone provide some equations or theory I could use to assist me? I'm not familiar with this material and have spent hours searching Google and cannot find much.

Problem 1:
Givens:
Initial Decay heat = 2.5% rated thermal power.
Initial Core ΔT = 14 deg F
Final Decay Heat = 1% rated thermal power
Find: Final Core ΔT.

Problem 2:
Givens:
Initial natural circulation flow rate = 3.5% full power flow rate.
Initial Core ΔT = 15 deg F
Final Core ΔT = 8 deg F
Find: Final natural circulation flow rate

 

[QuantumPion]

Homework questions should be posted in the homework help forum, they have specific guidelines about showing your work and such.

That being said, I'd need more information about what topics you've been covering in this course specifically in order to know where to start.

 

[mudweez0009]

Homework questions should be posted in the homework help forum, they have specific guidelines about showing your work and such.

That being said, I'd need more information about what topics you've been covering in this course specifically in order to know where to start.

I made my account right when I started this thread, so I'm unfamiliar of the rules. Thanks for the heads up.

That said, we literally are covering big picture theory on how the plant systems are integrated.. The course is taught once a week. We spent a day for each the steam generator, turbine, CVCS system, electric stuff (totally lost me), cooling water/condensor, etc. For this specific class, we were talking about natural circulation. We then get assigned very specific homework such as this, and most of us, especially us non-nuclear engineers, don't know how to do it. I would love to show you the slides from the course to prove how useless they are.

--------
edit: The template for homework requires "useful equations" and "an attempt at solving the problem".. Kind of hard to do when I don't know any equations. :grumpy:

 

[jim hardy]

wow that's sketchy.

It's a mechanical engineering problem, not a nuclear one.
It assumes a-priori knowledge about the system.my approach would be:
(and a genuine mechanical engineer might well have a better one)
in natural circulation the driving force for flow is the difference in density between:
water in the hotleg going up to the steam generator
and water in coldleg returning from it.

And teacher didnt give that height.

so driving head is Δ $\rho$ g h

with height unknown.

%power divided by ΔT should be pretty linear with flow, it's just moving heat,and flow should be in proportion to √driving head (bernoulli)
is density of subcooled water fairly linear with temperature over the small range of ΔT ? (Teacher didn't give us pressure...)
If so then ratio flow/√ΔT = constant should be reasonable approximation.Bounce that around the ME circle in your class and see if anythiing comes of it.
Maybe try those equations in homework thread too.

In range of .01 to .1, just how nonlinear is √ function? Not very, as i recall
i'd run trial calcs on both flow/ΔT and flow/√ΔT ...

 

[QuantumPion]

Yeah my confusion is similar. Natural circulation is a complicated process dependent on many variables. My thoughts of approaching it was based on a simple energy balance. But they don't tell you the temperature so there is insufficient information to determine anything. My only guess is that it is a super oversimplified proportion problem.

 

[jim hardy]

see recent post in your homework thread

old jim

 

[FermiAged]

Jim Hardy - Did you used to work for FPL,specifically at Turkey Point? If so, I we worked together on the Turkey Point / St. Lucie Simulators.

 

[jim hardy]

Well -- Nuclear Power is a small world...

check your PM inbasket

old jim

 

[mudweez0009]

Speaking of Turkey Point, I was reading about that the other day, and how its ultimate heat sink is an elaborate canal system, miles and miles long (and I think I estimated about 10 square miles off of Google Maps)... And I thought to myself, "why in a hot, humid climate like the southern tip of Florida, would the heat sink be canal systems".. I imagine they need to be that long due to how hot it is, that heat removal is so inefficient. It seems so obvious to me, and I feel like cooling towers would have been much more appropriate and MUCH less environmentally invasive. What was the reasoning behind the canals?! It was bothering me.

On another note, getting back to natural circulation. I found the equations to use in the above post and solved the problems without issue, and posted the equations in the homework thread (for anyone else that may stumble upon this thread some day). As for another inquiry:

Does natural circulation ALWAYS happen in a power plant, or does it only happen when the plant loses all power? And I guess from an operator's standpoint, when the plant loses all power (normal and emergency), what kinds of things are monitored (alarms, gauges, etc.) to make sure that its working and the plant is becoming stable again?

 

[jim hardy]

What was the reasoning behind the canals?! It was bothering me.

Nobody had built a salt water cooling tower at the time, around 1969.

There was concern about salt spray drifting downwind and ruining the potato fields. A surprising fraction of the country's winter potatoes comes from those fields . Hurricane Donna in 1960 had put so much salt onto them it was a decade before the ones within a few miles of the bay recovered.

Also the dewpoint in S Florida runs so high there was concern over just how well they'd work in summer months, when air conditioning load strains the electric grid down there. . When temperature and humidity are both 100 your sweat just doesn't evaporate.

Actually they built a small test tower and concluded they were glad they'd opted for the canals. They cool a lot by emitting radiant heat.

images courtesy of http://lew-cabintalk.blogspot.com/2012_02_01_archive.html

Crocodiles moved right into the canals and are doing very well. An eighteen footer used to hang out on our intake. Most days you can hear them grunting adjacent the employee parking lot.
I figure they're another level of security.

FOR A SPECIES that, as recently as last year, was listed as endangered, the American crocodile is surprisingly easy to find--as long as you can get past the armed guards. More than one-fifth of the crocodile's U.S. population, about 400 juveniles and adults, lives at Florida Power and Light's (FPL) Turkey Point nuclear power facility in Homestead, Florida.

http://www.nwf.org/news-and-magazin...hives/2008/why-is-this-crocodile-smiling.aspx

 

[jim hardy]

Does natural circulation ALWAYS happen in a power plant, or does it only happen when the plant loses all power? And I guess from an operator's standpoint, when the plant loses all power (normal and emergency), what kinds of things are monitored (alarms, gauges, etc.) to make sure that its working and the plant is becoming stable again?

In a PWR it's only when power is lost to the pumps. Usually that's during a grid blackout.
The main pumps are too large to be powered by the emergency diesels - 3,000 hp diesels won't start 7000 hp pumps.

The geniuses who designed the plants (ahem - Rickover) realized that natural circulation, being natural, is pretty hard to mess up. So he placed the reactor below the steam generator to make a thermosyphon where gravity does your pumping for you. Navy plant i am told can go to some low power on natural circulation enabling the submarine to move very slow and quiet, no mechanical noise from those big pumps. Maybe somebody who knows for sure could elucidate. The premise for natural circulation is :

during a blackout
IF
you've got liquid water (term is subcooled, ie below saturation temperature) in the reactor;
and you have water in the steam generator that you can boil away,,
THEN
heat will move from the core to the steam generator by natural circulation.

The three necessary elements are primary inventory, primary subcooling, and secondary inventory.
So the operators watch reactor pressure and temperature to make sure the water there is subcooled,
they watch pressurizer level to make sure they're maintaining inventory,
they watch steam generator level to make sure there's inventory there as well,
and they watch steam generator pressure because so long as it's at saturation pressure for primary temperature, that confirms decay heat is being moved successfully.

At TMI the trouble was they let the primary system get down to saturation pressure and steam filled the top of the primary side pipes, blocking flow. They lost both primary inventory and subcooling.

After TMI, one midnight shift we pulled our reactor pressure gage and wrote adjacent each cardinal point on its scale the corresponding saturation temperature. That way we could directly verify subcooling without having to memorize the steam tables or remember where we left them.

Our operators used to quip: " It's only water. And we'll keep it that way."

hope above helps.

old jim

 

[FermiAged]

Turkey Point was REQUIRED to construct the canals to reduce the amount of warm water releassed to Biscayne Bay. Cooling towers are expensive! A benefit of the canals is that they serve as habitat for the only remaining American Crocodiles.

The driving head from temperature (density) difference is always there but it is small relative to that provided by the Reactor Cooling Pumps. In the NuScale design, it IS the only driving force and offers a simpler design at the cost of reduced power density.

Following loss of forced circulation, core Delta T will initially rise until the density differences leads to sufficient flow to maintain a heat balance. Peak Delta T will approach full power Delta T. When decay heat (in PWRs, loss of RCPs will trip the plant), Delta T will remain stable and steadily decrease.

Natural circulation flows will be a small fraction of that provided by pumps, about 2-3%. Usually, this flow is too small to be seen on flow or Delta P instruments. So nat circ is monitored by differences between cold and hot leg temperatures and Core Exit Thermocouples. It is important to maintain secondary side heat sink, so steam generator levels and pressures will also be monitored. A Steam Bypass System does this automatically but needs to be monitored.

If the RCS is overcooled by excessive steam flow out the steam generators (malfunctioning Steam Bypass or zealous operator), pressurizer level will also be watched to look for formation of steam voids in the the RCS (these can form at the top of the SG tubes or the Reactor Vessel Head.

I provided a derivation of the nat circ relations on the other thread.

 

[mudweez0009]

Thank you all for clearing that up. Makes sense. I figured since its dealing with saturation temp/pressure that monitoring temperature and pressure would be dead giveaways.

 

[jim hardy]

Turkey Point was REQUIRED to construct the canals to reduce the amount of warm water releassed to Biscayne Bay.

That is so.

The two fossil units there were built in early sixties. They drew cooling water from the bay and discharged it back into the bay a couple miles south. A small "bald spot" appeared on the bay bottom at the discharge point, it is unclear whether that was from the heat or just the velocity. I can attest that in winter the fishing was fabulous right at the plant's warm water side, the fish and manatees loved the warmth. But in summer they headed for cooler water. One winter day a sailfish had got lost and showed up in our intake - i never heard of one in inland waters but there he was, a small guy four or five feet long.

Environmentalists didn't like the idea of a nuclear plant at all and seized on the warm water and shallow Biscayne Bay issue. We add about fifteen degrees to the water and in summertime the shallow parts of the bay get up 90 degrees F, maybe a few degrees more.

Anyhow the utility was told they couldn't dump that much warm water into the bay.
So they had to provide for cooling some other way.
Their first plan was to dilute the cooling water to reduce its exit temperature. They bought five huge pumps, like twelve feet in diameter, and had them delivered to the site. That would have lowered the temperature but increased the flow rate, the figure i remember is 2200 cubic feet per second which is a decent sized river.

The environmentalists did further studies of the bay and objected to circulating that much water over the fragile "Turtle Grass" that grows there. They may have been right on that one. It's a staple in manatee diet.

So the utility had to do something quick and they were skittish about building cooling towers that might not work.

Well - some corporate entity owned a few tens of thousands of acres of bayfront just South of the plant and had plans to put an oil refinery there. Seadade i think it was.
Wouldn't THAT have made the environmentalists happy - dredging a channel clear across the bay !
So the utility was able to get that property for their cooling canals.
And that's how the canals came about.

The crocodiles were not forseen. They are great PR , but are becoming so numerous they're spreading. We had a huge one cruising our neighborhood in the Keys. Think for a minute about crocodiles in your kids' swimming hole... If you read early history of Miami , Miami Beach was an awful place where people went mostly to hunt crocodiles. I recommend "Commodore's Story" by Ralph Munro, an early Miami pioneer .

The last time i visited South Biscayne Bay it was looking great. Plenty of grass on the bottom and lots of wildlife. It's now a marine sanctuary of some sort and fishing is not allowed,
but when a huge city springs up adjacent a natural paradise you are faced with choices -you either let the people wreck the place or you put in rules that some folks are going to regard as Draconian.
Google "Columbus Day Regatta" . It happens just across the bay from the plant.
http://www.floridayacht.com/events/columbus-day-regatta/img/aerial.jpg
old jim

 

[mudweez0009]

That is very interesting Jim, and Fermi! I heard about the habitat it had formed, which generates pros and cons, but we won't get into those! I can't even imagine a 12 foot diameter pump. That would have been very impressive to see.

Anyway, back to hammering you guys with questions..

what are the concerns if HPSI and charging is lost? I was reading about these:
http://www.nrc.gov/reading-rm/doc-collections/gen-comm/info-notices/1988/in88023s5.html

I imagine you would lose the abilility to inject boron, lose seal water injection flow to the RCPs, wouldn't be able to maintain pressurizer level and prevent make-up to the RCS, resulting in fuel damage, etc. Are these all reasonable consequences?

 

[FermiAged]

For a Large Break LOCA the RCS would depressurize to the point where Accumulators discharge (about 600 psia) and ultimately where Low Pressure Safety Injection can take place (about 300 psia). Both of these systems would replenish inventory and provide boron.

For a Small Break LOCA, HPSI and charging are more important as the RCS pressure will level off above Accumulators and LPSI. This is Functional Recovery territory. I would first try heat removal with the SGs while sending someone to vent/start the HPSI pumps. If that is insufficient, the RCS would have to be depressurized using pressurizer relief valves. The idea would be to get the RCS pressure low enough for Accumulators/LPSI.

You are talking about losing 2 or 3 HPSI pumps and 2 or 3 Charging Pumps. Its hard to believe that the pump that had the most recent surveillance would be gas bound.

Can I ask what your background is? You sound like an engineering student.

 

[mudweez0009]

For a Large Break LOCA the RCS would depressurize to the point where Accumulators discharge (about 600 psia) and ultimately where Low Pressure Safety Injection can take place (about 300 psia). Both of these systems would replenish inventory and provide boron.

For a Small Break LOCA, HPSI and charging are more important as the RCS pressure will level off above Accumulators and LPSI. This is Functional Recovery territory. I would first try heat removal with the SGs while sending someone to vent/start the HPSI pumps. If that is insufficient, the RCS would have to be depressurized using pressurizer relief valves. The idea would be to get the RCS pressure low enough for Accumulators/LPSI.

You are talking about losing 2 or 3 HPSI pumps and 2 or 3 Charging Pumps. Its hard to believe that the pump that had the most recent surveillance would be gas bound.

Can I ask what your background is? You sound like an engineering student.

So basically, for small break LOCA, loss of HPSI/charging is more severe because the RCS pressure doesn't drop enough to allow other remedial operations to initiate?

What about my guesses of losing boron injection and RCP seal injection? It seems from your description that you only lose boron injection on a small-break? Are either of these major concerns that could result in further damage, or are they minor compared to pressure concerns?

And yes, I am an engineering student. I am currently halfway through grad school, on my way to a masters degree in mechanical engineering. Just took a nuclear engineering course out of curiosity and now realized that one course can't even cover the BIG picture items that I would like to know. I really am trying to learn the components of the plant and how they interact. (If situation A happens, what happens to B, C, and D) type of stuff..

 

[mudweez0009]

For a Large Break LOCA the RCS would depressurize to the point where Accumulators discharge (about 600 psia) and ultimately where Low Pressure Safety Injection can take place (about 300 psia). Both of these systems would replenish inventory and provide boron.

For a Small Break LOCA, HPSI and charging are more important as the RCS pressure will level off above Accumulators and LPSI. This is Functional Recovery territory. I would first try heat removal with the SGs while sending someone to vent/start the HPSI pumps. If that is insufficient, the RCS would have to be depressurized using pressurizer relief valves. The idea would be to get the RCS pressure low enough for Accumulators/LPSI.

Also, do accumulators deliver boron when there is a loss of all power?

 

[FermiAged]

Yes. They are essentially tanks of borated water driven by a charge of nitrogen (at a typical pressure of about 650 psia). They discharge to the RCS through check valves (like a door that only swings one way) that are closed or opened by the differential pressure across the valve. Under normal operating conditions the RCS pressure of 2250 psia keeps them closed. When RCS pressure falls below 650 psia, the valves open and the tanks discharge based upon the RCS pressure and level in the tank (which determines the elevation head and N2 pressure).

The accumulators (a Westinghouse term - CE designed plants call them Safety Injection Tanks - I don't know what B&W calls them) require no electrical power to function. Because there is no pump that requires time for power source alignment, start signal and start up, the accumulators can be the first source of safety injection in some accidents.

 

[mudweez0009]

That is what I figured. Thanks for confirming!

 

[jim hardy]

RCP seal cooling used to be PWR's Achilles heel.
Westinghouse came up with an improved one that's passive, but it was after I'd retired so I never saw one.. That would seem to be be a comfort.

http://www.westinghousenuclear.com/Products_&_Services/docs/flysheets/NS-FS-0106.pdf

We added some fittings (I think back in the 90's) whereby one could connect a portable diesel driven pump to cool the seals should the unthinkable happen.