I have been researching nuclear power plants for a while, I understand the basics. But I have a few questions

1. If a e scram is used (slamming the control rods down in to core) dose that kill ALL reactions? And how long after is cold shut down status  reached? In normal operation parameters

2. What are the pros and cons of the 2 main ytpes of Water cooled reactor (boil and pressure)?

Not sure if any one hear knows but Google has yet to satisfied.

Thanks

SCRAM does not immediately render the reactor safe - it just stops the fission chain reaction by absorbing neutrons. As they discovered at Fukushima, the core stays crazy hot for maybe 24 hours after SCRAM... in that case, loss of power to the plant meant the coolant boiled off and the core melted down.

I really like the CANDU reactor design. It is inherently safe, can run continuously for years, runs on un-enriched uranium, produces lower-level waste, and is overall a really elegant solution to the challenge of safe civil nuclear power generation. The downside of CANDU is the cost relative to PWR/BWR due to the cost of producing heavy water.

The candu tech is cool. Why harvest the tritium out of the heavy water in only some of them? Isn't tritium use in other applications and hard to come by?

The slr1 reactor incident has been my main focus for a while.  The water hammer affect described is just insane!

I thought there was a temperature rise at the scram, because the energy from the absorbed neutrons has to go somewhere.  The temperature doesn't start falling until a little later.

As a 30+ year nuke answers to your 2 simple questions could fill a book.

I have  worked at both PWR's and BWR's and that question alone is enough for a long discussion. BWR's for various reasons are frowned on and have either been phased out or are on their way out. My opinion is BWR's got a bad rap.

You need to find a  couple of nuke people (at least one from ops) and sit down at lunch for a good long interesting discussion.

There is still an enormous amount of heat still in the reactor and it is still generating heat after a unit is tripped.  The backup cooling systems have to run off of of site power and have generators or site that provide a backup for that.  

Cooling water has to flow in both PVR and BWR after a trip or it will melt as we have seen in Japan.

The new Westinghouse 1000 series PVR have a passive cooling system that uses a water deluge and convection along with condensation along the walls of the sealed containment structure to cool the reactor in the event that all the backups fail.  It is a VERY safe design and is the only design being built in the US at this time.  There are two reactors going in at the VCS plant in Chapin SC at this time and both of them are the 1000 series reactors.  

It can take weeks to trip and go completely cool.  There are a lot of variables that come into play.  

I don't work in the field but have a friend who does.  (EP at VCS)

Here is a quick and dirty summary. I was not in ops so it should be high level enough for normal people to understand, but dumb enough that an ops guy would jump my case.

The time to cold shutdown is dependent on many things, but mainly decay heat. Basically, it's when the coolant is maintained below boiling at atmospheric pressure. If a unit is near the end of its cycle, cold shutdown may be reached relatively quickly, but if a unit has to be taken down early in the cycle for some reason, it will take much longer. If all of the safety systems aren't working, it may take longer to cool. At Fukushima, the reactor cooling systems became inoperable, which allowed the coolant to boil off, causing core meltdown.

PWRs generally have more parts that operate at higher pressures, but the secondary side (steam) is not irradiated. This reduces dose and makes things on the secondary side easier to work on. They do require steam generators which are extremely expensive...an error in design of replacement SGs permanently shutdown San Onofre due to the prohibitive costs to fix the error. PWRs also use boron to control reactivity, a system that can be a pain in the ass to maintain. Ps usually have more generating capacity.

BWRs usually have fewer parts, but the steam is produced in the reactor and is irradiated. This results in more dose and things are a pain to replace/maintain/etc due to contamination (crapped up). Bs do not use boron except as a last resort...as in permanent shutdown. Bs usually have less generating capacity.

The general concept for each type is the same. Keep the core covered by keeping your safety systems operable. US plants do this by "defense in depth". Basically, each safety system has more than one "train" so if one goes down, you have another one or more as backup. Some systems are redundant. The plant is designed in such a way that in a design basis event (accident) the systems initiate in a controlled manner at certain set points to maintain core integrity. The Senior Reactor Operators and their crews know every detail of the units and how they operate. The must go through rigorous training to become licensed and ongoing training every 6, 9, ? (don't remember) weeks to maintain their license.

That's based on my limited experience at the fleet level of a utility having both Ps and Bs. But I've escaped that world.

TMR
Triple Modular Redundancy
As just a start.

Once you take a reactor critical for the first time there will be decay heat produced. The amount of decay heat depends on how fuel you have used. So after the first shut down decay heat will be small but grows over time.

SCRAM does not kill all reactions. It kills enough to keep the amount of reactions below the self sustaining level. One of the pluses of a pressurized water setup is as the water temp goes up it moderates less neutrons, you moderated neutrons for fission. Same theory with boiling water as the water boils off you get less moderated neutrons


Wiki explains the difference pretty well  PWR and BWR

Not a nuclear guy by any stretch but I imagine its because of the proliferation concerns of tritium.

Low energy electrons are so useful.


Around 5 KeV electrons are less than on old CRT generated.

It does have some odd uses though.
Neutron initiators for fusion.
Since the idiots are mostly working on fission technology it is not as important.

The relatively short half life makes it impossible to 'keep it around' for very long.
For research you need a ready source and equipment to separate and concentrate it.

Tag/Bump, nuclear stuff fascinates the hell out of me.

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Neutron sources are pretty much COTS, though, right?

 


Very good summary. If anyone wants operational details, I have senior reactor operator licenses on both BWRs and PWRs. I'm currently the ops superintendent at a Westinghouse 3 loop PWR.


 

 

Nothing like in the US. They used an RBMK graphite moderated reactor. They aren't inherently safe like US plants.

We have used graphite moderated recotrs in weapons programs.

The last of them was shut down long ago.

We never used them commercially to generate power.