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Ralphy Boy
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Platinum
Re: One siren you don't want to hear
Ralphy Boy   1/25/2012 6:06:03 PM
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Beth... When my daughter was 8 or 9 my ex moved to within a mile of the Forked River Plant here in Jersey. Once when I picked her up I was told that they had an evacuation drill at school that week.

She said that they didn't use the buses though... Instead they had the kids stand where they would have been seated had the buses been used. Why no buses you ask?... Because they were at one of the other schools.

So much for timely evacuation of the schools.

My daughter is now a mom of 5 and has moved about 30 miles south of the plant. She lives on a lagoon and though she doesn't have her own boat we agreed on the same thought as before the move... If the plant goes radically bad, jump in a boat and head south along the inland water way.

It may get crowded as she passes Atlantic City, but the land routes will all be bumper-to-bumper standing-still. Plus the wind here is rarely from the north.

We lived through Three Mile Island without a good plan. Mostly what I just stated but for that one the winds were not likely going to be in our favor.

 

Ralphy Boy
User Rank
Platinum
False Alarms
Ralphy Boy   1/25/2012 5:32:46 PM
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Not nearly as heart stopping but we had a weird machine fault a few years back. It involved a too short or fuzzy to be fully reported optical sensor interrupt.

The interrupt was so weak that it would not be captured by the computer, but it would stop the machine. The only way to get going again was to shut down completely and reboot (about a 5 minute process).

Normally the fault should have been reported at the operator screen and then cleared. But with no report, clearing the fault was not possible... and in fact it was unidentifiable.

The machine in question had around 200 sensors and safety interlocks, 5 robots each with its own controller (and their own independent cycle), and a main controller... any of which could have been causing the problem.

To make things worst the fault was pretty rare (couple times a day). We had to resort to having a bunch of people watching every moving part to see if the stoppage could be linked to a specific movement.

Eventually it was narrowed down to one of the material advance motions. It was then noted that one of the reflection sensors was occasionally flickering just enough to be seen. It would happen during the material's advance.

A new sensor was installed and the problem went away. I don't know if the fact that the sensor was about the farthest one from the main controller contributed to the fuzzyness of the signal or not... but there you go.

I've tracked down fuzzy faults on other machines, but on that machine almost everything was reported and could be easily identified so this was totally unexpected.  

Sometimes it's the rare, hard to reproduce glitches that give the really big headaches...

 

Az kid
User Rank
Iron
Possible fix for nuclear plant false alarms
Az kid   1/25/2012 4:34:37 PM
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It may be possible to have corrected the issue by putting battery backup on

the system or a UPS on the AC line to the unit.  When power is disrupted it

would continue to operate.  Fairly good sized electrolytic capacitors on the

power supply mains may also do the job. 

   Without having the actual schematic and equipment in hand we can't know

all the details to know for certain, but some type of power backup or power

holding device during short duration power loss should prevent the false trips. 

   I like the idea posted earlier of an inhibit pulse immediately following power

outages however brown outs and the characteristic signature of the outage may

create a situation where the inhibit pulse is not reliable either or create a situation

where the alarm does not sound when there is an emergency.  This was why I got

to thinking of some kind of power backup approach.

bdcst
User Rank
Platinum
Re: One siren you don't want to hear
bdcst   1/25/2012 4:06:22 PM
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Beth,  I guess you are lucky to be living near Seabrook.  Folks who live in VT near Vermont Yankee may tell a different story.  There have been numerous false siren alarms, some due to hardware issues and some due to human error!

And even when things are working correctly just think of the horror that might overtake a visitor to the area who is clueless about siren test schedules.  It happened to me once and I should know better!  My wife and I were out for a hike in a wilderness area in New Hampshire, across the Connecticut River from Vernon Vermont, home to Vermont Yankee.   We were several miles down a forest trail when the wail of distant sirens rang out and kept on ringing.  The duration seemed far longer than any tests I had heard in the past.  Images of a nuclear disaster and invisible radioactive plumes filling the air danced in my head.  We had no radios on us, either broadcast, 2-way or ham.  And cellular technology had not yet reached us.  And even if it had, who would want to schlep a bag phone on a day hike?  Needless to say, after the sirens refused to quit, we did.  We returned to the parking area at the head of the trail wondering what the heck was happening.  Turned out to be a test with malfunctioning sirens that would not shut off!  Whew!  We figured that was the scenario but there was that tinge of doubt that kept us retracing our steps at a good pace.

William K.
User Rank
Platinum
Plant triggers false alarms.
William K.   1/25/2012 4:03:05 PM
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I am totally amazed that a system would have been released for delivery without the power interruption recovery process carefully checked. False alarms from an emergency warning system are a very serious problem because they would quickly lose credibility. A simple fix would have been to add an inhibit alarm mode that was triggered for any power system interruption, and a change in operaation mode to assure that the two trigger tones would always be sent for much longer than the inhibit alarm timer.

In our area, prior to the change to digital coding for our weather warning sirens, all of the trigger tones had to be held for about 30 seconds, after which time the siren would be triggered. The design was such that any power-return transient conditions would be ended long before the 30 second time, and the system would not respond to shorter signals.

This also allowed for testing the system without triggering by sendind a short tone pair. Detection could be verified but no siren would be activated.

Beth Stackpole
User Rank
Blogger
Re: One siren you don't want to hear
Beth Stackpole   1/25/2012 10:44:48 AM
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Jenn: In the 18 years that I've lived near the Seabrook nuclear plant in New Hampshire, there have never been sirens going off without warning--thankfully. Every once and a while, they do a planned test of the sirens, but the community is given lots of notice so there is no panic.

Alex is right about the dangers to community if sirens were to sound without that kind of advanced notice--people in this area receive evacuation instructions and local schools make parents sign forms at the beginning of the year spotlighting the school's evacuation process and procedures. There's even a sign on a shingled barn out on the island near where I live that says "No evacuation possible." People are very aware of what could happen and I can't even imagine the pandemonium that would ensue with random siren alerts.

Jennifer Campbell
User Rank
Gold
Re: One siren you don't want to hear
Jennifer Campbell   1/25/2012 9:53:36 AM
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Going back to my journalism roots, I want to know how the people living around the plant reacted while all these false-alarm sirens were going off. Beth, what does your family do, if anything, when the sirens go off? You can never be too careful, right?

Alexander Wolfe
User Rank
Blogger
False positives versus false negatives
Alexander Wolfe   1/25/2012 9:44:43 AM
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The technical problem here resulted in a wide-area false positive siren. This is a bad thing, social and process design wise. I don't know what the standard or best practices are in nuclear plants, but one would think that setting off an emergency siren for the community would be a two-step process. There would be an internal siren or alarm, and then it would be vetted by a plant manager or safety coordinator to verify that there's an issue, classify its level of serious, and then determine whether a community siren needs to be triggered. It's not a minor issue to have a false-positive siren go off in a 10-mile area where the population is going to feel they need to evacuate the area.

Beth Stackpole
User Rank
Blogger
One siren you don't want to hear
Beth Stackpole   1/25/2012 6:50:25 AM
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As someone who lives in close proximity of a nuclear power plant, it had to be very disconcerting to the public to hear the sirens go off without any kind of fair warning that it was a test. Kudos to figuring out the reason for the false alarm trigger. It sounds like it was unlikely your detective work could lead to a more sustainable solution that would have prevented the replacement of the alarms.

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