Talk:Boiling water reactor safety systems

Deletion?

Why is this article flagged for deletion? —Preceding unsigned comment added by 195.228.35.219 (talk) 23:41, 14 March 2011 (UTC)

Why indeed? I found this article very useful as I was trying to learn a bit about BWR's in general, and Fukushima in particular. If this article would be deleted, I would hope that the majority of the information would be retained in the main BWR article. The diagram of the reactor core, showing the steam/water flow, was far more useful to me in finding an understanding of the thing than anything in the main BWR article, and I would suggest its inclusion there in any case. My only complaint (about both the main BWR article and this one) would be the use of jargon...there are places where the text is too dense for me to follow it, particularly with all the acronyms. I'd suggest trying to simplify it a bit, with the needs of the general reader (eg, encyclopedia user)in mind. All in all, a very helpful article. I hope you guys keep up the work! Cmichael (talk) 04:11, 15 March 2011 (UTC)

Introduction

Looks like an excellent article. Added the reference header than you missed. May I suggest that you add a introduction. Keep up the good work. Bjmullan (talk) 21:48, 28 February 2011 (UTC)

Looks like extremely amusing article now. —Preceding unsigned comment added by 178.37.148.163 (talk) 13:05, 13 March 2011 (UTC)

Yes; perhaps it could evolve into a description of how the safety systems at the Fukushima I Nuclear Power Plant were unable to prevent core damage following the 2011 Sendai earthquake and tsunami.— Wdfarmer (talk) 07:48, 14 March 2011 (UTC)

Whoever wrote it was sure optimistic and proven dead wrong .. —Preceding unsigned comment added by 173.230.187.166 (talk) 03:05, 16 March 2011 (UTC)

Should perhaps also mention situations that can cause hydrogen generation, and if/how the safety systems are designed to prevent and cope with this, (why they didn't work we can cover at Fukushima I Nuclear Power Plant ?) Rod57 (talk) 16:09, 14 March 2011 (UTC)

doi:10.1016/0029-5493(84)90263-2 could probably used as source for hydrogen... I only have access to the abstract, though (WP:REX?). 88.148.249.186 (talk) 18:13, 14 March 2011 (UTC)

ECCS is designed to limit hydrogren generation to <1% of the maximum theoretical hydrogren generation during postulated accident conditions. This is one of the three acceptance criteria for ECCS (<2200 degrees F in the fuel, < 17% oxidation of the cladding, <1% maximum hydrogren generation). In Mark 1 and Mark 2 containments, the containment is inerted to prevent hydrogren explosions. Some plant designs have hydrogren recombiners or igniters in their secondary containment should a leak from primary occur. Mark 3 containments contain hydrogen igniters and recombiners. — Preceding unsigned comment added by Hiddencamper (talk • contribs) 02:42, 28 February 2012 (UTC)

Additional questions

Good article, lots of rare Information. I really needed to know this! But I have some further questions, mostly about the rest of the water loops of the varous systems. At the moment my questions are regarding to the old desings, not ESBWR or ADWR:

• Where is the Main Steam Isulation Valve? Is it at the point where the steampipe passes through the RPV or the Containment? I think, the MSIV is closed at the beginning of a SCRAM to really seal the Containment?

• If I understand correctly, the needed power for the RCIC comes directly from the reactor. Like in the graphic there must be a small steam turbine. To make this work, there has to be a heatexchanger after the turbine where the steam is condensed. Can you say something about that? Where goes this heat? If the system should work permantently this heat must be transportet out of the reactor building. How? This would be a lot of heat if the reactor should be cooled only by RCIC in a controled fast shutdown...

• From where comes the fresh water for the RCIC? I assume to some fraction it is the condensed steam from the RCIC-Turbine. If RCIC is a closed cycle theare as to be a large heatexcanger/condensor. How exactly does this part of the system look like?

• Te Torus/Suppression Pools are only a heat buffer. First, this buffer works quite well, but it gets hotter and after some time water in the Torus starts to boil. Te buffer is saturated. So if HPCS and LPCS should work for a longer period of time there must be a system to really remove heat from the reactor. How? Is there some kind of heatexchanger to coll the water after it is taken from the Torus an before it is injected into the RPV? (More or less same question as for the RCIC)

• In the graphic are mostly shown ways to get water into the RPV but the main idea ist to get heat aut of it and so all water injected to the core also has to leave it after a while. How does that happen? Only by the RCIC and the ADS? So if the HPCS is activated, also the ADS activates, because it is not possible only to add water to the RPV?

Well, this are a lot of questions but you have already given so much detailed information about his complicated topic that I am confident you can answer them! Best regards an much thanks! Schmidti --129.206.196.61 (talk) 19:10, 14 March 2011 (UTC)

1. MSIVs are located on the main steam lines on both sides of containment. That makes 8 total MSIVs (2 per steam line). This is based on BWR4 info, but I believe it is the same for the other designs. MSIVs do not close automatically on a Scram. Turbine stop valves close on a Scram to protect the turbine, but normally the MSIVs remain open. This allows steam to be dumped to the condenser through the bypass valves which is the easiest place to put the decay heat until the core is no longer boiling. MSIVs will close on low reactor water level to keep as much water in the core as possible.

2. RCIC is powered using reactor steam, which is diverted from the main steam lines into the RCIC turbine which turns the RCIC pump, and then the steam is dumped into the suppression pool below the reactor. The suppression pool acts as the condenser. The heat added to the suppression pool is removed using the Residual Heat Removal system which uses heat exchangers to remove the heat in the suppression pool and transport it out to the ultimate heatsink. The ultimate heatsink varies from plant-to-plant, but in a plant with cooling towers, it is usually a large body of water where water can be pumped and air-cooled.

3. RCIC has 2 sources of water: the Condensate Storage Tank, which is a large tank of fresh water, and the suppression pool. The CST is usually used first because it is cool and clean. If more than the CST is needed, water in the suppression pool (where the steam from the RCIC turbine is dumped) is used. This is a fully closed cycle (reactor water boils, steam turns the RCIC turbine, turbine steam is dumped in the suppression pool, suppression pool water is pumped through the RCIC pumps, water is pumped in the pressure vessel, water boils again) This system heats up fairly quickly, and the suppression pool must be cooled by the RHR system (basically pumps and heat exchangers). While RCIC and HPCI are steam-driven and require no AC power, the RHR system is AC powered and cannot operate during a loss of all off-site power and all the diesel generators (this is what caused the overheating at Fukishima, since they had no way to cool the suppression pool).

4. I pretty much covered this above. RHR pumps suppression pool water through heat exchangers which are cooled using the Emergency Service Water system, which then pumps the heat out to the ultimate heat exchanger. There are esentially 3 loops: the RCIC/HPCI core to turbine to suppression pool to core loop, the RHR suppression pool to heat exchanger to suppression pool loop, and the ESW heat exchanger to ultimate heat sink to heat exchanger loop.

5. Pressure in the core is regulated using pressure relief valves. ADS is for dropping reactor pressure to levels low enough to allow the low pressure emergency systems to inject water. The only outside source of water is the CST. Otehrwise it is all the same water in the vessel and suppression pool, so there is not overabundance of water. In the case where seawater is being manually injected into the vessel, normally the water in the suppression pool would rise, but the amount of water needed to be injected wouldn't need to be that much. At Fukishima, there is so much water being added to the vessel because the water is leaking into the basement of the reactor building. Polypmaster (talk) 07:39, 17 July 2011 (UTC)

Definition of reactor period

Article mentions but does not define or explain "reactor period" (as does SCRAM). It's not mentioned in BWR. What is it ? ...
Found definitions at Reactor period[1] "Reactor period is defined as that amount of time, normally in seconds, required for neutron flux (power) to change by a factor of e, or 2.718."
It seems to be a calculated property of the reactor (at that time) being its expected response to a hypothetical transient. Rod57 (talk) 09:57, 20 March 2011 (UTC)

Until we have reactor period I've put the definition in <ref></ref> for mouse-over. - Rod57 (talk) 15:36, 7 February 2021 (UTC)

RCIC

the RCIC section is wrong, on a GE BWR mark 1 or 3 the RCIC requires battery power as well to operate and shuts down when the suppression pool boils.--71.178.199.89 (talk) 01:32, 10 April 2011 (UTC)

---RCIC can run in a "Black start" mode when there is no DC power available. Control is only through a manual start up and setting of the throttle valve. This is unreliable as the turbine can still trip offline, and flow cannot be reliably controlled. Additionally, if there is core damage you will be filling the room with fission products which make it difficult to enter to restart if it trips during a black start. — Preceding unsigned comment added by Hiddencamper (talk • contribs) 02:37, 28 February 2012 (UTC)

Noting the BWR types that have the ECCS systems listed.

The ABWR and ESBWR are mentioned repeatedly as to which ECCS systems they have, but other BWR types are not listed. Specifically: BWR3s have an IC, do not have RCIC, have HPCI, LPCI, ADS. BWR4s have RCIC, no IC, HPCI, LPCI, ADS, Core Spray. BWR5/6 have RCIC, HPCS, LPCS, LPCI, ADS. I am not positive about which 5 or 6 has which ECCS system. That is basically correct though. Polypmaster (talk) 07:45, 17 July 2011 (UTC)

Oldest model of BWR in service

In the section "The safety systems in action: the Design Basis Accident":

"The description of this accident is applicable for the BWR/4, which is the oldest model of BWR in common service."

Fukushima I Unit 1 was a BWR/3, so this cannot have been right prior to the Fukushima accident. I removed the last clause, but does anyone have reliable information about what the oldest model in service now is? It might in fact now be a BWR/4 because of the loss of Fukushima I Unit 1, but that would need a citation. --David-Sarah Hopwood ⚥ (talk) 01:58, 3 March 2012 (UTC)

Update: according to List of BWRs, there are several BWR/2 reactors still in operation. I don't know to what extent they have been retrofitted with later safety features. --David-Sarah Hopwood ⚥ (talk) 22:09, 7 July 2012 (UTC)

Flavor text

There is a LOT of flavor text in this article with little or no cited/sourced fact. Industry professionals can overall agree that the majority of content in this article is correct, but the use of flavor text such as "massive" to describe the injection rate of LPCI make this article feel like it is not high-quality. Additionally there are many items which are specific to a particular plant or version of the BWR. — Preceding unsigned comment added by 50.40.124.56 (talk) 00:21, 30 May 2012 (UTC)

Notable Activations?

I find this un-necessary for this section. Firstly, the only ECCS system which actually activated during Fukushima was HPCI at unit 3, and only for a short time due to the total loss of DC power. The other 3 Fukushima units had lost their ECCS capability, which is why the accident happened in the first place, because they DIDNT activate. It doesn't make much sense to have this section in the article as it adds no real value. It should probably be moved to a Fukushima dedicated article. — Preceding unsigned comment added by 50.40.124.56 (talk) 04:50, 7 July 2012 (UTC)

Fukushima was certainly a notable activation of BWR reactor safety systems. Notice the title of the article; it is about BWR "safety systems" in general, not just the ECCS. And since the ECCS did activate at unit 3, I don't see your point. The title of that section could perhaps be made more relevant to its content, though.

On the other hand, "General Electric defended the design of the reactor, stating that the station blackout caused by the 2011 Tōhoku earthquake and tsunami was a "beyond-design-basis" event which led to Fukushima I nuclear accidents." is biased, because it implies that the cause of an accident being beyond-DBA is a valid defence of the reactor design. Arguably it's the opposite; the fact that a beyond-DBA situation happened means that the DBA was not realistically severe enough (similar tsunamis happen in that region on average every 100 years or so). The degree to which the DBA is a realistic model for the worst conceivable accident scenario is certainly relevant to a discussion of BWR safety systems -- it's relevant in general for all BWRs, and shouldn't be restricted to articles on Fukushima. --David-Sarah Hopwood ⚥ (talk) 22:07, 7 July 2012 (UTC)

It's not biased. The reason it is "Beyond DBA" is because DBA only assumes single failure criteria plus any failures from the accident initiator. DBA does NOT account for environmental factors like tsunami, earthquake, flooding, tornado, etc, as those are to be precluded from affecting the plant in the plant's original design. In the case of Fukushima, the plant was not properly analyzed for tsunami and flooding, and they even knew this. They failed to account for hydrodynamic forces from the tsunami, which led to them under-designing floodproofing features. It wasnt a "100 year tsunami" failure, it was a total failure to take into account the proper model for tsunami forces. DBA should probably be in a separate article, as it is not limited to just BWRs. As for "notable activations", safety systems actuate many times per week in nuclear power plants, I see no reason why Fukushima, where most systems actually did NOT actuate (because if they did they would have prevented the accident), as a reason for calling it a notable activation. The selection and spectra of DBAs is very correct, GEs statement is also correct, and I feel that there is a general misunderstanding of what design basis actually means for nuclear power plants, and understandibly so as nuclear engineers spend weeks in training on DBAs and design features of the plant, and what the actual meaning is.

None of the Fukushima 1-3 units has totally lost the ECCS-capability. RCIC and/or HPCI did work at units 2 and 3 even for some days and removed decay heat there considerably. At unit 1, there was the IC in function during aproximatly one hour, and since the decay heat moves in a strongly degressive manner away, there was even there a quite considerable decay heat remove. Unit 4 was not in service at the time of the earthquake/tsunami. --62.202.223.37 (talk) 08:55, 23 July 2012 (UTC)

RCIC and IC are not ECCS systems, however they are important to safety cooling systems (and in some cases safety related systems). HPCI is an ECCS system, and would have been the only ECCS system to activate in the case of unit 3. — Preceding unsigned comment added by 198.29.191.149 (talk) 19:11, 22 August 2012 (UTC)

A diagram of Mark II containment would be helpful

A diagram of Mark II containment would be helpful (to compare with mark I) - or an inline reference to a source with such a diagram. - Rod57 (talk) 15:27, 7 February 2021 (UTC)