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PostPosted: Feb 25, 2017 8:38 pm 
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I've been thinking about the effects of an Electro Magnetic Pulse and it's effects on all nuclear reactors, and it's effect on a reactor / Reactors in many forms. An EMP can come from the explosion of a Nuclear Arial bomb, OR From a Coronal Mass ejection (Sunspot) from the sun. This would destroy any Hi-Tech
Solid state device from a simple Fluke meter to large mainframe computers. Many systems to control a conventional reactor involve electronic digital meters as well as motor driven drives for valves or even control rods. ????? The best thing we have that will work is a Diesel engine, old technology, with a mechanical fuel pump, not the emissions approved computer controls used today. I.E. a 1980's VW Rabbit diesel engine and mechanical injection pump will run, but a late model with computer controlled injection may fail the computer control from the pulse. So if you lose all transistorized equipment in one pulse, how do you know what the reactor is doing and how do you shut it down? If your Diesel backup is running a generator to power your electric pumps, you may still have a BIG problem.

All Hail The Drain Tank and Molten Salt.

This is the only system that has some Solutions for this problem, if not most or even all. I think this could be a solution to lots of problems that haven't happened yet, but could.
Would Have
Could Have
Should Have.
Higher sea wall . . . Roof mounted Diesel engines. . . Electric switch gear not located in a Flooded basement. A diesel running some pumps directly, not by a Generator / motor pump.

I wish I could say I've got a lot of Engineering Degrees, and a bunch of Letters behind my name . . .
But I do get my hands dirty and rub elbows with other engineers now and then.

Do we now have something to sell the political "Nattering Nabobs of Negativity"?

Drain Tank, Molten Salt . . . . . I've scanned the site here with "Electro, Magnetic, Pulse" and found
nothing.

If I'm way off base, please let me know so I can delete this.

Steve


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PostPosted: Feb 26, 2017 10:35 am 
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EMP would likely be protected against by the reinforcing bars in most containment designs.
Indeed I have proposed a reactor with the equipment inclosed inside an array of meter thick cast iron blocks.

I have also been wondering about zinc-air batteries in place of emergency rated diesel generators.


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PostPosted: Feb 26, 2017 12:57 pm 
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Joined: Jul 14, 2008 3:12 pm
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Yes rebar cages would be like Faraday's cages, good protection. Similar for metal structures.

Power lines seem to be the main issue, them being like giant antenna's for the EMP. So the scenario is you lose the grid for a long time.

Reactor shutdown is usually fail-safe on loss of power (ie you need power to not shut down the reactor) but I'm not sure if this is true for all existing reactors.

What you really need is passive cooling to remove decay heat.


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PostPosted: Feb 26, 2017 3:49 pm 
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Joined: Nov 14, 2013 7:47 pm
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Location: Iowa, USA
This is how I see the problem, assuming a true "walk away safe" reactor design the loss of power from an EMP will mean that the reactor will not see any damage beyond the electronic monitoring and control systems. The reactor will be "safe" in that it will be very unlikely to release any radiation but now it's not producing any power. The primary goal, it would seem to me, is to restore monitoring systems quickly to verify the condition of the reactor and assess damage. The secondary goal is to get back online and producing power again quickly.

I first thought of how the US Navy builds their warships. First thing is redundancy, not only do these ships have two of everything but also the fancy GPS is backed up with charts and sextants. Another thing I've seen is that the ships use standard parts where they can, if a something breaks then it is removed and a spare put in its place. There's also the ability to route around damage. This ability to route around damaged parts relies somewhat on the redundancy but also in that there are places on the ship for wiring and piping to get plugged in and a temporary bypass put in place. Much of this is already done with nuclear reactors already so I don't see much that must be done to make it resistant to an EMP event.

Where I can see the greatest damage is in the turbine hall. If power is suddenly lost then that spinning turbine will see a surge and/or sudden drop in load, this is likely to damage the turbine. Assuming the turbine survives the initial EMP event a lengthy loss of power could be a problem. I recall that while a turbine cools it is kept spinning slowly so that as heat rises inside the top does not get too much hotter than the bottom. What can happen if the turbine is stopped while still hot is that a temperature difference builds, the heat expands the top while the cooler parts on the bottom contract, and now you have significant forces on the mechanics. This can destroy the turbines. I don't know how big of a problem this is as this may be a solved problem already.

I'll see this brought up every once in a while on how we are terribly unprepared for any kind of attack on the electrical grid. Things like spares and standardized parts are almost unheard of. People speculate that if the USA experienced an EMP event that large portions of the nation could be without electrical service for years.

The need to get a nuclear reactor back on line quickly seems rather moot if the electrical distribution center at the plant is all fried. If a reactor can go into a safe state after loss of power then the issue is just monitoring the reactor to make sure no radioactive material was inadvertently released, and to secure the site from people that might wander in or be intent on doing further damage.

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Disclaimer: I am an engineer but not a nuclear engineer, mechanical engineer, chemical engineer, or industrial engineer. My education included electrical, computer, and software engineering.


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PostPosted: Feb 26, 2017 5:41 pm 
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If the electrical systems are unavailable, you can't run the plant so the primary goal, for a Gen II/III reactor, is to assure reactor shutdown. Then immediately the next goal will become assuring sufficient cooling for shutdown (decay heat) of the reactor core. The third goal in priority would be to assess if the containment is ok. The "three C's" - control, cool, contain.

If the reactor is shut down and there is sufficient cooling, the third goal is not very important actually.

For most gen II/III reactors, meeting goal # 2 is going to be hard if they can't meet #1. (there must be a joke here somewhere but I'll let someone else make it).

For a Gen IV reactor, typically the design goal is to be inherently safe so shutdown or not is not the number one priority. The number one then is cooling. Then just need enough cooling for decay heat - more cooling doesn't do anything since the reactor would just make more power.


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PostPosted: Feb 26, 2017 6:55 pm 
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Location: Iowa, USA
Cyril R wrote:
If the electrical systems are unavailable, you can't run the plant so the primary goal, for a Gen II/III reactor, is to assure reactor shutdown.

I was assuming the question was on how to build future reactors to handle an EMP, not what would happen with currently operating reactors if they experienced an EMP. I see no reason to discuss both though.

Cyril R wrote:
For most gen II/III reactors, meeting goal # 2 is going to be hard if they can't meet #1. (there must be a joke here somewhere but I'll let someone else make it).

I'm sure that there is a joke there too but I'm not feeling creative enough to find one right now. Seriously though, what many people don't realize with the Fukushima meltdown is that the reactor itself survived the tsunami. This was not an EMP event but the result has many parallels. The control systems detected a seismic event of sufficient magnitude to trigger an emergency SCRAM, with the assumption that the backup electrical power would provide monitoring, control, and cooling. The primary cooling comes from the power provided by the reactor but with the reactor now shutdown there was not sufficient steam to drive the pumps. As I understand it the decay heat was sufficient for an hour or three to drive the pumps but once that was exhausted the pumps would stop and remaining decay heat would make temperatures rise again.

This is where my memory of the events get foggy. It was something like once steam pressure was lost it was impossible for the increasing heat to start driving the pumps again. They had restored some monitoring and control at this point by scavenging the parking lot for car batteries. Was this not enough to get the pumps running from the reactor power? Apparently so. At some point the heat in the core was sufficient to damage or overwhelm the control rods and fission restarted. This created a runaway heat problem.

In a Gen III+ or IV reactor there would be passive systems at several points in this series of events to prevent what happened at Fukushima. Primary among them is a system to remove heat without the need for electric power.

Cyril R wrote:
For a Gen IV reactor, typically the design goal is to be inherently safe so shutdown or not is not the number one priority. The number one then is cooling. Then just need enough cooling for decay heat - more cooling doesn't do anything since the reactor would just make more power.

I don't follow. I understand that while the reactor is operating there is an inherent property of drawing more heat from the system induces a feedback that more heat is produced. Once a Gen IV reactor has undergone SCRAM then does not all fission stop? If not then this is not "walk away safe". If so then increasing cooling would reduce temperatures more quickly, no?

Cyril R wrote:
The "three C's" - control, cool, contain.

For a Gen III+/IV reactor these should be automatic, no? Once SCRAM is initiated there should be no risk of containment loss, since we are assuming the only systems damaged were the electronics, or so I assume. I suppose one would want the ability to monitor the reactor and verify the reactor has not suffered damage beyond the electronics. Depending on the design and engineering compromises made some sort of control/cool/contain will need to be restored since even though the cooling is automatic it will be designed to last only so long before some sort of maintenance is needed. Therefore one can allow the system to operate without human intervention for the time that the passive systems can maintain themselves. That's not saying the people operating this reactor walk away for a vacation and come back after the passive systems become overwhelmed. What is does do is allow the operators to step back and approach cautiously with radiation monitoring equipment, bring in firefighting vehicles (trucks, boats, helicopters) and top off the cooling systems, or whatever the system requires.

If the passive cooling can last, for example, a week then this gives plenty of time to call in the National Guard with their military grade (EMP hardened) trucks and haul in whatever equipment is needed to restore control over the reactor.

This gets back to my earlier point of designing the system to handle an EMP gracefully through redundancy and backups. Presumably any reactor will have systems capable of withstanding radiation due to the nature of being within the vicinity of a nuclear reactor. Hardening everything against such an event would be exceedingly expensive and unnecessary given passive systems to control and contain the reactor. Presumably the most fragile systems are communications. After the event has passed I would assume that communications would be restored with spares brought on site, much like how a Navy ship would replace the damaged systems in a similar situation. Failing that bringing in more people as runners, setting up paper cups and strings, whatever, will have to do until proper repairs can be done.

I will say that if the concern is over how to address the risk of an EMP event with currently operating reactors then I have a rather simple answer. Start building new reactors with EMP hardened systems from the start. Trying to retrofit old reactors to handle this, assuming that they cannot already, would seem to me to be exceedingly expensive. This is especially true if speaking about the USA, we have a 40 year span where no new reactors were built. That means any existing reactors are far enough along in their operational lifespan that doing such upgrades would be better spent on building new.

That is, of course, just my opinion.

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Disclaimer: I am an engineer but not a nuclear engineer, mechanical engineer, chemical engineer, or industrial engineer. My education included electrical, computer, and software engineering.


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PostPosted: Feb 26, 2017 8:40 pm 
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Joined: Jul 14, 2008 3:12 pm
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Quote:
I was assuming the question was on how to build future reactors to handle an EMP, not what would happen with currently operating reactors if they experienced an EMP. I see no reason to discuss both though.


There's a fairly strong bifurcation even in modern reactors. There's the evolutionary path where failures can occur but you just keep adding more backups to deal with it, versus the passive approach where you eliminate the failure mode so you don't need additional backups. The two "camps" seem to dislike and even distrust each other to some extent.

Quote:
The primary cooling comes from the power provided by the reactor but with the reactor now shutdown there was not sufficient steam to drive the pumps.


The reactor is a heat source not a heat sink. So it does not provide cooling. It provides heating. When the Daiichi BWRs were shut down, there was continued heat generation from the decaying short-lived fission products and - actinides. Some of the BWRs were fitted with a steam driven turbine pump that indeed used steam from the reactor to run a cooling pump. Unfortunately the heat sink for this system is a relatively small pool of water in the containment. Not only is this a finite heat sink, it also serves as the heat sink for depressurizing the reactor. So they ended up saturating their heat sink with decay-heat-produced steam. As you know a turbine requires a heat sink, so when that ran out the turbine pump became inoperable. Normally there are electrically driven pumps and heat exchangers that remove heat from the heat sink, e.g. to the sea or cooling towers, but these were not available without power. So it became a case of "moving the problem from the core to somewhere else" until the "somewhere else" ran out. And then, both the "somewhere else" (containment) and the core were in trouble. An obvious design flaw - what is the point of a boot-strap cooling system if the heat sink is not equally boot-strapped?

Quote:
Quote:
It was something like once steam pressure was lost it was impossible for the increasing heat to start driving the pumps again.


Yes, if you depressurize the reactor the reactor the steam feed pressure drops, so the turbine pump could trip on low pressure. However, that is not very relevant if you have no heat sink since it will trip on high temperature/high pressure instead. Either way the system fails.

Quote:
I don't follow. I understand that while the reactor is operating there is an inherent property of drawing more heat from the system induces a feedback that more heat is produced. Once a Gen IV reactor has undergone SCRAM then does not all fission stop? If not then this is not "walk away safe". If so then increasing cooling would reduce temperatures more quickly, no?


A reactor with inherent safety will, if not shut down by rods or other devices, just produce whatever power the heat sink is drawing off it. However, there's a minimum - not reactor power, that can go down to milliwatts - the minimum is the decay heat power. This is not a chain reaction, but rather the opposite, a decaying rate of heat production by the fission products and to a lesser extent some of the short lived actinides. This decay heat is there whether or not the reactor is shut down. It was the bane of Fukushima. The problem is you can't shut this decay heat down, it's just there, at a known and predictable, declining rate. It's not that much power compared to the reactor, but nuclear reactors are closed-loop systems. Lose the heat sink and the decay heat just builds up if not removed.

Quote:
Once SCRAM is initiated there should be no risk of containment loss, since we are assuming the only systems damaged were the electronics, or so I assume.


This is not a given at all, see above. If the decay heat is not removed it will melt down the core eventually. This is what happened at Fukushima. A Gen IV reactor should be fitted with passive cooling so it will passively remove this decay heat to the outside environment. But engineering such systems is not a trivial matter and requires great attention in the design. Once properly designed and analyzed these systems become extremely reliable in operation.

Quote:
If the passive cooling can last, for example, a week then this gives plenty of time to call in the National Guard with their military grade (EMP hardened) trucks and haul in whatever equipment is needed to restore control over the reactor.


It is going to depend on the geographic scale of the EMP damage. If it is a small country or state then yes. If a larger area is affected you quickly run into capacity problems even in the military. Only so many EMP hardened equipment is available... so then it could take a long time for recovery. A week is pretty good though.

Quote:
Presumably any reactor will have systems capable of withstanding radiation due to the nature of being within the vicinity of a nuclear reactor.


Depends. The systems in containment are usually radiation-hard, especially systems close to the reactor. But if you're talking about electrical building and power supplies, I don't know. They are not intrinsically radiation-hard. If they are in reinforced concrete or metal buildings I expect them to be ok on account of conductive shielding provided by these buildings.

Quote:
Start building new reactors with EMP hardened systems from the start.


This is good advice. All the Gen III+ and Gen IV designs I've seen are intrinsically hardened by the nature of their systems design. However, I would like to know more details of what EMP hardened means. If it is just grounding with rebar and metal buildings then it will be easy. I suspect it may be more involved in some equipment instances.


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