Tornado Cuts Power to Surry Nuclear Plant (Virginia)

[jpak]

http://wydaily.com/local-news/6301-tornado-cuts-power-to-surry-nuclear-plant.html

The U.S. Nuclear Regulatory Commission staff is monitoring the situation at the Surry nuclear power plant after the site lost offsite power early Saturday evening due to a tornado affecting an electrical switchyard next to the plant.

The NRC is monitoring the event through the NRC resident inspectors at the site and in the Atlanta regional office. The plant is operated by Dominion.

The two units at the Surry plant automatically shut down after losing offsite power. Four of the plant’s diesel generators started to power the units’ emergency loads, an NRC spokesman said in a press release. Plant operators have partially restored offsite power to both plants, and safety systems have operated as needed.

<more>

[liberal N proud]

1. Nuclear power plant which generates electricity loses power?

:wtf:

They don't even generate their own power?

[RC]

2. When a nuclear power plant loses the load, there is no choice but to shut down

Simple physics. What to do with all that heat that suddenly has no place to go. When they shut down, then another power source needs to be available for the cooling operations and controls. That is the reason for the backup generators
In other words, you can't idle a nuclear power plant and still get usable power from it the way you can from, say a gas fired generator.
On the plus side you can get tremendous amount of power for a relative small foot print, compared gas, oil or coal generating the same amount of power.

[kristopher]

3. That sounds like a classic Rube Goldberg machine.

http://www.rubegoldberg.com/

[RC]

7. No kris, it's because you don't understand or refuse to understand why they do the things they do

on anything concerning nuclear. If you did understand, you'd see the automatic shutdown and emergency backups is really straight forward and fairly simple in concept - and in operation.
Rube Goldberg is far more complicated than anything nuclear.

[bananas]

9. kris has it right - these are Rube Goldberg devices

and you've demonstrated your own misunderstanding of them a number of times.

[Name removed]

22. Deleted message

Message removed by moderator. Click here to review the message board rules.

[bananas]

10. Reactors are required to shut down when a hurricane approaches to prevent a Fukushima

http://www.energypulse.net/centers/article/article_display.cfm?a_id=514

The Current State of US Nuclear Safety Regulations and Transmission Grid Reliability
10.22.03 Stephen Maloney, Principal, Devonrue LTD

<snip>

As plant operating experience developed through the 1970s, however, it became evident to most risk analysts that the potential for extended transmission grid unavailability coincident with the loss of the onsite emergency power supplies was sufficiently high to warrant additional measures. In the nuclear power industry, this scenario combining transmission grid unavailability (such as occurred in the 2K3 Blackout) with total loss of all onsite emergency power is referred to as a “Station Blackout.”

Depending on circumstances, the Station Blackout reactor accident scenario can be particularly dangerous to public health and safety. The reactor core can melt on time scales comparable to the TMI accident. Unlike the limited loss of cooling event at TMI, however, the core damage scenario in a Station Blackout can be particularly severe, including a so-called “early high energy release” comprising a particularly heavy “portfolio” of fission products dispersed far and wide within a few hours.

<snip>

On one hand, the hurricane threat was addressed in the Station Blackout rule. Specifically, the rule calls for early shutdown of nukes threatened by a hurricane track. We are now all familiar with the nukes prudently shutting down ahead of the hurricanes by the press reports on Fox and CNN at this time of year. This procedure alone substantially eliminated the risk from most long-duration power loss events known in the 1980s.

<snip>

Readers Comments

<snip>

Joseph Somsel 10.23.03
Having served with Mr. Maloney on the industry group that helped formulate and implement the improvements for station blackout, I can state that the man knows about which he speaks.

<snip>

[bananas]

11. Reactor containment buildings are not designed to contain a meltdown

- Reactor containment buildings are not designed to contain a meltdown,
and can rupture in a matter of hours.

- In 2002, the NRC's own inspector general concluded:
"NRC appears to have informally established an unreasonably high burden of requiring absolute proof of a safety problem, versus lack of a reasonable assurance of maintaining public health and safety."

See http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=115x280732

[PamW]

34. It shows an appalling ignorance of physics.

If you have a power plant that is generating a significant amount of
energy - and I don't care what type of power plant it is - if you lose
the load, you have to shut it down.

Where does the energy that you are generating go if you lose your load?

I have an analogy that even an anti-nuke might be able to understand.

Instead of electricity, suppose your product was water. You have a plant
that is pumping water from the ground, or a river, or a lake... whatever
and sending it into the municipal water supply.

Suppose something happens to your outlet piping - a boulder falls on your
output pipe and crushes it, or a landslide of earth falls into your open
aqueduct and blocks it. Your water plant has no way to get water to the
municipal water system.

What do you do? You shutdown the pumps!!! You can't keep pumping up more
water if you have no place to send it.

Besides the physics, nuclear power plants are required BY LAW to shutdown
in any event where the connection to the power grid is lost.

PamW

[Wilms]

4. I don't think it's correct to imply an unloaded generator can't be run.

But it is correct to say that when a nuke is shut down you still need the cooling system to work.

I read that two design philosophies for nukes are to have outside power used to run the cooling system, or use power from the plant to do it (and rely on b/u gens in case of shut down), with the former being considered safer.

If that's the case, it's not clear to me why there aren't transfer switches to allow a nuke cooler to run off of the plant in case of loss of outside power. So I'm not at all sure I understand the issue.

If anyone does, please post.

[kristopher]

6. A speculation

The safety issue is always bumping up against the cost issue. Both are extremely problematic for nuclear. They are already far more expensive than the alternatives, so there is generally a *strong* financial component to decisions involving redundant systems.

[Turbineguy]

12. Here's some info:

http://books.google.com/books?id=4ewKE8MZAZIC&pg=PA573&lpg=PA573&dq=nuclear+plant+buss+tie&source=bl&ots=xA_eR1QYy9&sig=tFPw_fNTlia2D7Zd6RkAl7RfV2c&hl=en&ei=KlWrTbeXBdHViAKU5-zvDA&sa=X&oi=book_result&ct=result&resnum=1&ved=0CBgQ6AEwAA#v=onepage&q&f=false

Basically the system is set up so that if one system fails, the other automatically pulls in. Breakers for one system are held from closing in this case by voltage from another system. In the case of the emergency diesel, a starting air valve is held closed by voltage from the other two sources. If voltage is lost the valve fails to stay closed and supplies air and starts the diesel.

The in-plant main generator supplies voltage to plant functions even if disconnected from the grid. If this generator should trip or lose voltage, grid power is then sent to the in-plant electrical system. If that fails, the emergency diesels start. Once voltage is up, they put themselves on line to the in-plant system for vital equipment (such as reactor cooling) within seconds. Diesels are kept hot by heaters so no warm-up time is needed. Starting air bottles are protected by check valves so that if air pressure from the compressor is lost, the bottle maintains sufficient starting air pressure.

These systems are very straightforward in operation but by nature complex. It's been my experience that things are designed to be as simple as can be.

http://www.nucleartourist.com/systems/diesel1.htm

In the case of reactor controls, the control rods cycle in, killing the chain reaction at high speed for a SCRAM. The Scram system is independent and automatic.

In the event of a failure, these systems function without human operator effort. In order to restore normal operation the human operator must move controls.

As for safety and cost, damaged equipment is expensive to fix (far greater than scheduled overhauls) and results in expensive and unscheduled down-time. Power plant maintenance systems are such that break-down maintenance is only allowed on equipment that is cheaper to replace than fix. Like perhaps the control room coffee maker. Loads of people (such as myself) make a good living keeping costs down by maintaining systems and machinery at 100% reliability.

[kristopher]

13. I'm referring to the cumulative effect of a particular "culture of safety"

A good case in point is the trouble Areva is having selling their GenIII product. It is substantially "safer" than its GenII predecessor but it is also substantially more expensive. So much so, in fact, that Areva announced last year it was turning back to the GenII designs in order to enhance its competitive profile in today's global market.

[Turbineguy]

16. That goes to the central problem with safety.

You don't know how safe things are until they are not.

A product that is touted as "safer" has to demonstrate that. If people are experiencing 100% safety from the Gen II, how can they determine what is safer? Remember the car seat belt and then airbag controversy? Many people had to die to prove seat belts and then airbags were safer than not.

Ironically, an older acquaintance of ours (a chemical engineer, no dummy) refused to wear a seat belt in any car. He died in a car crash (in 1990) at a fairly slow speed where wearing a seat belt would have allowed him to walk away.

[kristopher]

18. It is a discussion we do not need to have.

http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=115x288674

[Wilms]

15. WHAT!?! They don't perform routine maintenance on the control room coffee maker!?!

Do they have an on-site back-up? :D

Thanks. Help me understand how that's set up.

I don't know if you have an idea about how they did things at the Fukushima plant. Is it a generalized thing to run the plant from it's own power? I thought I read grid power somewhere else, but I suppose they're one and the same. Is that correct?

And if the grid line dropped, the plant would run off it's own power? And go to diesels if the reactor had to be shut?

Initial reports from Japan said there was no damage to the plant from the quake (which might have been a stretch) and that the tsunami swamping the diesels was the culprit (though I wonder if more than the diesels got soaked). But assuming those reports were correct, I've wondered if it feasible (at least theoretically) for a smaller turbine/generator to operate off the heat still be put out from a reactor while it's cooling, and thereby run the cooling pumps?

[Turbineguy]

17. I don't know about Fukushima.

Maybe one of the our in-house nuke wizards would.

But things seemed to be going fine until the diesels quit.

I doubt that decay heat which starts at 7% and drops rapidly would spin those generators for long. (That, by the way was the test that was being conducted that led to the Chernobyl disaster.) Big turbines, lots of gland sealing steam, high voltage excitation power requirements and then auxiliary steam pressure would drop quickly. Turbine feed pumps are very inefficient at low loads.

[Statistical]

28. Many US reactors of later design (built in late 70s or early 80s) do have

secondary turbines designed to use waste heat to provide redundant emergency power. NRC regulations still mandate use of isolated diesel generators and scam is any of 4 sources of primary power are lost.

While secondary turbines improves margin of safety a backup diesel generator is still requires because of the risk of interconnected systems. Damage to coolant flow systems in reactor could result in loss/destruction of secondary turbines also. This plant (surry) doesn't have secondary turbines.

[PamW]

38. I think you mean..

and scam is any of 4 sources of primary power are lost.
---------------------

I think you mean scram.

Lets not gratuitously give the anti-nuke any more verbal ammo...

PamW

[Turbineguy]

45. Thinking about it

it makes sense to run the plant auxiliaries from the grid as a primary means. The reliability of the grid as a whole is higher than any one individual plant. That means a SCRAM or main generator trip would not create a lights out emergency.

[Statistical]

27. It is called loss of redudancy.

In US nuclear plants have 4 sources of power.
1) Reactor itself
2) Grid intertie
3) On-site backup (diesel)
4) Off-site backup (diesel)

A reactor CAN operate at full power with only one of 4 sources of power. However it is OPERATING PROCEDURE than when any one of 4 sources of power is lost for the reactor to SCRAM. It is a precautionary measure.

The rational is that the level of protection has dropped. Say the odds of losing 4 of 4 sources of power is one in a billion. If one source of power is already gone the odds in losing 3 of 3 remaining sources of power may only be 1 in a million. From a statistical point of view the margin of safety has declined.

"If that's the case, it's not clear to me why there aren't transfer switches to allow a nuke cooler to run off of the plant in case of loss of outside power."
There are however operating procedures by the NRC mandated a full scram under a variety of abnormal conditions. Loss of any one of the 4 sources of power are one of the conditions that mandate an immediate scram. The scram kicked automatically. No human interaction requires. The reactor sensed loss of grid power, kicked on generators, and scrammed, alerting operators. The whole process takes 15-20 seconds tops.

[Wilms]

31. Thanks, Statistical. n/t

[Throckmorton]

42. Not a scram, an LCO action Statement

Our Tech Spec Limiting Condition for Operation reads: With two credit off-site source inoperable, restore the off-site source to operable status, or decrease operating Mode to Mode 3 (hot standby) within 72 hours. With Three off-site sources inoperable, restore one inoperable off-site source to operable status with 1 hour, or decrease operating Mode to Mode 3 (hot standby) within 6 hours. In our case, the loss of three off-site sources does not cause an LOP, but the LCO for loss of a third off-site source also requires that the site net generation immediately down power (rapid downpower) to less than 1590 Mw, as the transmission lines cannot handle the overload that is produced be both units remaining at full power.

There is good reason for not immediately tripping the units, as the combined short term loss of generation, may in and of itself cause a Loss of Grid type LOP, which means a prolonged period without off-site power (4 to 24 hours, but who knows how long it will really be, our last loss of grid LOP occurred in July of 1977). In the 2003 blackout, our station stayed on-line, as Eastern Connecticut and Rhode Island stayed up.

[PamW]

35. More bad physics...

I don't think it's correct to imply an unloaded generator can't be run.
--------------------------

If the generator is unloaded, that means there is no complete circuit. Hence,
there is no back EMF - the torque that it takes to turn the generator when it is
unloaded is insignificant compared to when it is loaded.

Since the generator is unloaded, the turbine is unloaded. What happens if the
turbine is unloaded - there is a mismatch in torques. If one were to keep the
same steam flow rate, the torque the turbine is generating is not matched by
an equivalent torque due to load.

It would be just like driving down the highway at high speed with your foot hammered
down on the throttle, and then shifting your car into neutral.

What happens to your car engine if you keep your foot to the floor when the transmission
has be shifted into neutral thus disconnecting the load from the engine?

PamW

[Wilms]

43. Thanks, Pam.

I appreciate efforts to correct mistakes. As you are well aware, I think it's best to not let errors--even my own--stand unchallenged and/or unacknowledged and thereby risk misleading others.

You?

:hi:

[bananas]

8. No, they are required to shut down by the NRC to prevent them from going Fukushima

[Throckmorton]

20. Correct

They are powered from the electrical grid, via the switchyard, and the Station Reserve Transformers (or some plants call them the start-up transformers.)

The reason that they cannot power themselves in an event of this nature is that the response time of the turbine control system just can't compensate for a load rejection of about 90%, which is what occurs when the connection to the grid is lost. Large fossil and hydro plants can't handle it either (but some smaller fossil plants(<200 Mw)are designed to cope with large load rejects by bypassing main steam to the condenser).

It is kind of like sliding your transmission into neutral while driving 65 mph on the highway. The turbine starts to over speed, and weighing several 100 tons, at doesn't handle that well. So the main stop valves go closed, in under 100 milliseconds, stopping steam flow to the turbine. Unlike the control valves, the stop valves have one function, to close as fast as physically possible to halt turbine over speed.

Incidentally, the accident at Chernobyl was as a result of an experiment where they were trying to use the main turbine as a power source post LOP-trip. While this experiment was not the root cause of the accident, at was what they were trying to accomplish when they allowed themselves to get all wrapped around the axel.

[Wilms]

23. Thanks for your post.

And now I'm further confused.

Above I wrote:

I read that two design philosophies for nukes are to have outside power used to run the cooling system, or use power from the plant to do it (and rely on b/u gens in case of shut down), with the former being considered safer.

I (thought I) read that a few weeks ago. No link. :( Something about off-station/on-station, perhaps. Any of that ring a bell? What did I misunderstand?


BTW: "...they allowed themselves to get all wrapped around the axel." Great quip.

[Throckmorton]

24. I am not aware of any US Nuclear Plant that stays on-line

after a loss of off-site power. They are just to large, not to mention the reactor physics that get in the way. Down-powering a reactor to under 15% power is not a simple thing, so even if the turbine controls could handle the load change, getting the reactor and main feed systems to respond as needed would be just a nightmare. Thats why the control rod drive system de-energized on a reactor trip (or SCRAM as it is sometimes called). This allows the reactor to go sub-critical, and stop making Fission Heat almost immediately.

In a PWR, the control rod grippers, essentially electromagnets, de-energize, and the rod fall into the core under gravity (takes about 2.7 seconds from full out to full in). In BWRs where the control rods go in from the bottom, they are driven in using stored air pressure. BTW, I hate BWR designs with control rods from the bottom (not all are designed that way, only most of the, I like having gravity as my friend, and not my enemy.

[Statistical]

29. Even if a US reactor COULD operate at minimum power NRC regulations prohibit it.

As you are aware but others reading might not be the reactor will trip automatically when any abnormal condition is detected. A whole host of conditions can lead to a reactor trip but loss power from any one of four sources is one condition that will lead to a trip.

Equipment senses loss of power or loss of connectivity to one of its primary sources
1) reactor main turbine
2) grid-intertie
3) diesel generator
4) off-site diesel generators

Technically with loss of grid a reactor COULD operate normally on diesel generators. The turbines could be disconnected and cooling system used to remove 100% of thermal output (turbine only removes about 30% of thermal output at peak load anyways). Alternatively reactors could be designed with a secondary turbine to provide station power and divert most of coolant around that secondary turbines (i.e. 980MW straight to cooling, 20MW to secondary turbine).

Still NRC regulations would prohibit that. Any loss of primary requires initiates an automatic trip.

[Throckmorton]

32. Id say it would go to licensed design basis,

if it were licensed to handle a full load reject, then it would be allowed.

I am not aware of any US plants so licensed, or any foreign one either for that matter.

Really just an academic argument anyway, as I cant imagine why you would want to run that way.

[PamW]

37. Actually there are some that can handle it....

Id say it would go to licensed design basis,

if it were licensed to handle a full load reject, then it would be allowed.
==============================

Actually, there are some that can handle it. There are a few nuclear power plants
that have "Full Turbine Bypass Capability".

That is, they have condensers that are sized to take the full power output of the
reactor. Typically the condenser is sized to handle just the waste heat which is about
60% of the full power.

But the few that have condensers that have 100% bypass capability, can open a turbine
bypass valve and dump the full steam flow directly into the condenser, and bypass the
turbine.

It's designed so that very short term repairs or adjustments can be made on the turbine
and or generator without taking the whole plant down.

PWRs that don't have that capacity would use atmospheric steam dump in lieu of full bypass.

PamW

[Throckmorton]

41. I don't see turbine repairs being done that way.

There are no isolation vaaves between the turbine and the condenser.
The ADV's are only good for about 20% rated power, often on main turbine trips the code safeties have to lift.
We decreased Tave a few years ago by 3 degrees F to reduce the likelyhood of lifting them.

BWR's can kill the jet pumps and shed a lot of power that way, about 40% as I recall.

[Yo_Mama]

33. And for good reason

Because now you would have a reactor in fission with no alternate power source. That just doesn't make sense.

[PamW]

36. The problem at Chernobyl was the Xenon Transient.

Incidentally, the accident at Chernobyl was as a result of an experiment where they were trying to use the main turbine as a power source post LOP-trip. While this experiment was not the root cause of the accident, at was what they were trying to accomplish when they allowed themselves to get all wrapped around the axel.
-------------------

The operators were conducting an experiment with the Chernobyl RBMK Unit 4. However, just
as they started the experiment and had reduced reactor power, the load controller in Kiev
called and requested that they remain online since they really needed the power. The load
controller in Kiev released the plant to go offline about 12 hours later.

When you either shutdown or lower the power greatly on a reactor, it goes through what is
called a Xenon Transient. One of the most common fission fragments is Iodine-135 which decays
quickly to Xenon-135. Xenon-135 is both radioactive with a few hour half-life, and it is also
destroyed by neutron absorption. When you shutdown the reactor, you stop the production of I-135,
but there still is the equilibrium concentration in the core, so the rate of decay of I-135 and
hence production of Xe-135 doesn't change much. However, when you shutdown the reactor, you shutdown
the destruction of Xe-135 by neutron absorption. Since the destruction rate was in equilibrium
with the production rate, the production rate of Xe-135 now exceeds the destruction rate and
the amount of Xe-135 increases. It will build up for several hours and then drop back to zero when
all the I-135 and Xe-135 have finally decayed.

What's so important about this temporary build-up of Xe-135? Xe-135 is THE world champion
neutron absorber - it is a poison to the reactor.

This buildup of Xenon was attempting to shut the RBMK down. The operators where taking excessive
actions to keep it going - like bypassing interlocks that restricted how far they could withdraw
control rods. Because of that, they put the reactor in unstable territory, and a power excursion
was the result of the instability.

The Chernobyl design was an unstable design to begin with, as detailed in these course notes from
a class at MIT:

http://ocw.mit.edu/courses/nuclear-engineering/22-05-neutron-science-and-reactor-physics-fall-2006/lecture-notes/lecture30.pdf

PamW

[Throckmorton]

40. Thanks,

I wasn't going to go into detail about why it happened, only that the experiment they were going to attempt was in support of an LOP scenario when the main turbine continued to supply bus voltage during coast-down.

Rule 1 from license school: We don't experiment with the reactor.
Rule 2 from license school: We don't troubleshoot with the reactor.

[Turbineguy]

46. Thanks

There was a write up in the Bulletin of the Atomic Scientists at the time but I don't have that issue anymore.

[grahamhgreen]

5. It's only a matter of time before our next nuclear disaster. Let's hope it's not multiple plants

at the same time from a terror attack.

[madokie]

14. Sure hope it isn't near me when it does

but I guess with nuclear it matters not if its right next door as they have the potential to irradiate the whole world. I guess the difference is that the further you're away the more chance you have to bend over and kiss your ass goodby. That last part is only for snark, :-) OK

add: Why don't they just admit that nuclear is not yet and probably never will be ready for the big time. Nothing about it is a positive. Just think about all the co2 produced from building the plant to start with to mining the ore to processing that ore into fuel. Just doesn't seem cost effective to me.

[PamW]

39. It doesn't have to mean a disaster....

It's only a matter of time before our next nuclear disaster.
-----------------------

In the 40 years since the Fukushima reactors were designed and the
50 years since the Chernobyl reactor was designed, there are now
nuclear reactor designs that are "inherently safe".

One such design is Argonne National Lab's Integral Fast Reactor or IFR.

As nuclear physicist Dr. Till explains in this interview with PBS's Frontline,
Argonne put the IFR through the Chernobyl scenario and it just shut itself down:

http://www.pbs.org/wgbh/pages/frontline/shows/reaction/interviews/till.html

"Q: And you in fact ran an experiment that was comparable to what happened at Chernobyl?

A: Yes, yes. Let me go on a little bit about that, because it is a rather dramatic characteristic. The Chernobyl accident happened in April 26 of 1986. Earlier that month, the first week in April, with our test reactor in Idaho, in fact the same reactor control room where we're now sitting, we performed a demonstration of that characteristic, where if you cut off the coolant from the reactor, what would happen? ....Again, the reactor just quietly shut itself down."


PamW

[Wilms]

44. IOW there are *designs* that are safer?

But all units in operation, not so much?

[Fledermaus]

19. What if we were in the middle of the next "Spanish Flu" pandemic and there was a loss of power?

Two natural disasters at one time. Use nuclear power all the time forever, and it will happen. sooner or later, the odds are always in the favor of the casino. In the long run, its a game you can't win.

[Throckmorton]

21. Then I will die

either of the flu, or my job.

[NickB79]

25. Alternate Headline: Nuclear power plant safeguard systems perform as designed. nt

[kristopher]

26. You mean "Chernobyl level radiation releases are fission industry success story" ?

Good luck with that one...

[NickB79]

30. So there's been a Chernobyl-level radiation release at Surry?

Try to stay on topic here, kris. We're talking about a different nuclear powerplant, one where the safety protocols worked just as designed.