From: jgd@dixie.com (John De Armond) Newsgroups: sci.energy Subject: Re: AP Wire Story on Japan Reactor Keywords: Nuclear Power, ECCS Systems Message-ID: <s0hp3zn@dixie.com> Date: 9 Oct 92 04:11:15 GMT sxb@fermi.cray.com (Stephen Behling) writes: > Another point about ECCS actuation in BWRs...they do not run with borated >water (or the stuff would plate out on the fuel rods). The ECCS system is >borated, so if it does get accuated, the boron would have to be flushed out >before normal operation could be resumed. This could cause operators to >try other recovery techniques before ECCS is activated. [Note, I have no >knowledge about the actual plant technical specification and procedures >in this area.] Here's the rundown on the reactor protection system. GE came about as close to a standardized design as any so most plants adhere to this scheme. The borated water system you speak of is known as the Standby Liquid Control system and is the last ditch system that would be used only in extreme emergencies. As the inside joke used to go, when the SLC button is pushed it also drops a ticket to the local concrete vendor to start hauling in the concrete to fill in the reactor. The first system is called the HPSI (prounounced Hipsy) system. This consists of a pair of steam driven pumps located inside the secondary containment. The steam comes from the reactor. The pump takes suction from the torus (MkIII) or supression pool (MkIV) and injects the water on top of the core. Anything that actuates the ECCS also causes a containment isolation so the excess steam flows from the reactor to the torus/supression pool and forms a closed loop. The system is actuated when power is dropped to a fail-to-open valve on the steam line. The pump runs until the steam runs out. At that point the LPSI (Lipsy) system takes over. One pump is typically steam driven and the others are electric. They operate the same as the HPSI except they are higher volume, lower pressure pumps. If the LOCA is so severe that all reactor pressure is gone, the Core Spray system takes over cooling. This consists of several multi-thousand horsepower electric pumps that take suction from the torus/supression pool and pumps into a sparger header inside the reactor and over the core. All these systems can be reconfigured to take suction from the condensate system or the river. I've heard nothing more about the particulars of the incident in question. I still can't imagine what an operator could do that fits even some reasonable interpretation of the "facts". Since almost any SCRAM in a GE reactor causes containment isolation and thus activates the ECCS, the incident could have been as minor as a technician bouncing a reactor level transmitter. This is a common occurance because the trip setpoints are close to the operating points. A physical jar or even the act of valving one of the 4 transmitters out for calibration can jog the other three into generating a SCRAM. The way the reactor protection system works in a BWR is the "one out of two taken twice" concept. That is, there are 4 channels of reactor protection organized into two trains of redundant pairs. A single trip from each train causes a half-scram. Any trip on the other channel causes a full scram. So for example, a reactor water level transmitter can half-scram Train A and then something as innocuous as putting a channel of Train B in calibration mode (generates an automatic half-scram) would trip the reactor. Operators work REAL hard to minimize the state of half-scram :-) John -- John De Armond, WD4OQC |Interested in high performance mobility? Performance Engineering Magazine (TM) | Marietta, Ga |Interested in high tech and computers? jgd@dixie.com |Write me about PE Magazine Need Usenet public Access in Atlanta? Write Me for info on Dixie.com. Newsgroups: sci.energy From: jgd@dixie.com (John De Armond) Subject: Re: Another NUKE bites the dust ... Message-ID: <nbfp49f@dixie.com> Date: Tue, 06 Oct 92 08:59:25 GMT ems@michael.apple.com (E. Michael Smith) writes: >From the Oct 1 San Jose Murkey News, page 14A, dateline TOKYO (AP) >Quoted without permission: >*** BEGIN EXCERPTED QUOTE *** (elipsis ... denote deletions) >JAPANESE PLANT BARELY AVERTS CORE MELTDOWN >*** END QUOTED MATERIAL *** (thankfully) >There you have it. All the things that cause one pause about >a nuclear plant in the back yard. >One guy makes a mistake, and per the article, the plant is one system >away from a meltdown. Then the folks who are in charge don't bother >to tell the public for the better part of a day... >The article may be wrong, but that type of article is why the non-nukers >take a bit of a circumspect view of a nuke in every village ... Funny reaction, Mike. Based on what you've heard from us on the net, your instinct SHOULD have been to wonder just how inaccurate the news report was. Frankly I've not seen worse reporting since TMI. I really have no idea what happened. The "facts" presented fit nothing I know about a nuclear plant. Japan is a big fan of Westinghouse so it almost surely was a Big W unit. I'll call a friend at INPO tomorrow and see what I can find out. I don't even know where to start taking this one apart. Let's see. No way I know of for an operator to dummy in a false permissive. A technician could by manipulating wires, but only after clearing some access control points that are opened only under procedural control. Don't know what "plant's cooling pumps" are. Maybe the reactor coolant circulating pumps? Tripping these would cause a routine ECCS (Emergency Core Cooling System) activation. Nothing in the CVCC or makeup system, the only other systems communicating with the primary during normal operation, could do it. In the distorted media's sense of how things work, it MIGHT have been a secondary feedwater pump trip. Kinda seems likely now that I think of it. Some background. Assume a Westinghouse PWR. The concept of Defence in Depth dictates there be multiple heat sinks for the reactor. The NORMAL heat sink is the turbine and/or condenser. Heat flows through the primary system, boils water in the secondary system and steam carries heat out of the containment. If the turbine trips, steam is routed directly to the condenser in what is known as bypass mode. The turbine/condenser is also the ONLY NORMAL heat sink during shutdown. The normal shutdown mode is to trip the reactor (and because some obscurities from TMI Lessons Learned, also the turbine) and bypass steam to the condenser. The reactor coolant pumps (RCP)(devices that circulate coolant from the reactor to the steam generators) are left on. They input about 10 MWT in pumping loss and the reactor inputs another 100 MWt or so dropping rapidly to about 10 MWt 10 minutes after rod insertion. As the energy content in the primary drops, both the primary pressure and the steam pressure drop. At some predeterminad point the RCPs are stopped. When the primary pressure reaches about 400 psi (from a normal 2250 psi), the steam dump is secured and the Residual Heat Removal (RHR) system is activated. This takes the reactor to cold shutdown and continuously removes decay heat. The only part of the above chain that is considered safety-related is the RHR system. Feedwater is not, RCPs are not (though there's been talk about making RCPs safety-related.) If the main heatsink is gone (feedwater pumps off, condenser unavailable, etc), then the aux feedwater pumps, which are safety-related, start. Any of these pumps, typically 3 - two electric and one steam driven - can supply enough feedwater to remove shutdown heat. THe steam is simply dumped to the atmosphere (non-radioactive) via the atmospheric dumps. IF the feedwater pumps trip or something else causes loss of normal heatsink, (what I SUSPECT happened here), the pressure and temperature spike in the primary system will cause the Emergency Core Cooling System to activate. ECCS is fired on high or low pressurizer level, high rate of change of pressurizer level, low reactor coolant temperature, low primary pressure and a few other things I cannot remember. The first line of defence in the ECCS is the Safety Injection System (SIS). This consists of multiple redundant high pressure, high flow (hundreds of GPM) centrifugal pumps capable of pumping into the full reactor pressure head. Another pump, a high pressure positive displacement pump called the Charging Pump, is pressed into emergency service. This pump is run on high speed to deliver about 100 GPM and is capable of up to about 5000 psi service. The typical procedure is for the operator to determine what caused the ECCS actuation and then shut down those parts not needed. The Charging Pump can supply enough water for small break LOCAs (like TMI) while the SIS can supply enough flow to cool the reactor during the magical, mythical double-ended guillotine break. Both SIS and CP can be aligned to take suction from a number of sources. The normal source is the CVCC (chemical and volume control) storage tank that contains heated, borated water. When that is empty, suction is switched to the reactor building sump for recirculation mode. If that fails, the condensate storage tank, used to hold deionized water for the steam side, can be sourced. About 2 million gallons worth. If that fails, then the pumps can draw from river water. If the break/leak is large enough the SIS cannot maintain head, when the pressure drops to about 400 psi, the RHR system can be switched in for emergency mode. These pumps take suction from the same places in the same sequence. If the break is large enough that the pressure does drop, the next line of defence is the passive accumulator system. this constists of nothing more than a couple of 50,000 gallon tanks filled with borated water and pressurized to about 2000 psi under nitrogen. they are connected to but separated from the reactor system by checkvalves. When the pressure drops, the checkvalves open and the contents dump into the reactor. So far we have three layers of protection, the SIS, the accumulators and the RHR. I've not mentioned the Component Cooling System which has an emergency cooling mode. Couple more I can't recall the names of. My best guess is the operator did something to trip the feedwater pumps which caused a semi-routine ECCS activation. They determined what caused it and secured it. What we'd have called a "Green Book Event" at Sequoyah. (named because of the succession from white (normal), green (not normal), yellow (serious), and red (head for the hills)) Claiming the core was one system away from a meltdown is like saying that after someone pulls out in front of you and you use your brakes normally to slow down, you then say you were one brake application away from death. [Editorial mode on] Mike, I know you like to post ridiculous stuff just to stir shit. Is this one of those occasions? I hope you're not stupid enough to take seriously what you posted, as indicated in your trailer. Whatever, I've had enough. I've typed my last multipage treatise to try to counter this ignorance. It's futile. (Using "you" collectively now) You'll believe this kind of shit for the same reason you'll read and believe the National Enquirer. You want to find a Martian around every corner and a conspiracy under every rock. So be it. I'm going to leave it to you to get your nuclear info from the likes of Yackadamn. He's the arm-chair expert, after all. I don't care anymore. I've been out of the business for almost a decade and I've nothing to lose or gain either way. I make enough money and am crafty enough that I don't have to worry about energy costs. If there's any energy to be had, I'll have what I need. If you want to spend your time installing CFs and packing cracks and such because you can't afford your power rate, that's fine with me. We of the industry did our dead-level best to give you power that approached that ideal of being too cheap to meter. We have an unblemished safety record (yes, even TMI was a safety success of the first order) and yet you rejected it, perferring to fear things that don't EVEN go BUMP in the night. You get what you deserve. I once had a plant manager tell me "If the public wants us to burn cow shit at a dollar a KWH, we'll do it. No more fighting. I get paid the same regardless." My attitude exactly. AMF, John -- John De Armond, WD4OQC |Interested in high performance mobility? Performance Engineering Magazine (TM) | Marietta, Ga |Interested in high tech and computers? jgd@dixie.com |Write me about PE Magazine Need Usenet public Access in Atlanta? Write Me for info on Dixie.com. |