Switching between PWR and BWR

[scurrilous]

I know there's old threads on this, just looking for some discussion.


Any thoughts from people that have licensed on both PWR and BWR?

[thenuttyneutron]

BWRs are simple compared to a PWR.  Changing power with a BWR can be fast simply by changing the recirculation flow through the core.  You will also find that the EOP are a flow chart.  You can't cook book it like you can a Westinghouse.

I talked to a RE that was licensed with me at a PWR about BWRs.  He is a RE/ Core Design manager now that first cut his teeth at a BWR.  He told me that the BWR has a better neutron economy.  It made sense because the voids keep the neutrons fast and more likely to get absorbed by U-238.  This will have beneficial affects later in core life.

[Bonds 25]

PWR's insert their CRB's upside down, have clean turbines, large containments and can't load follow...........not to mention constant boron addition and required concentration levels. You mention boron addition at a BWR (via SLC) and it signals "time to look for a new job"

BWR BWR BWR BWR !!!! A real Nuclear Power Plant.  Not a wimpy "the background on the frisker inside containment is over 100 cpm

[SloGlo]

....  Not a wimpy "the background on the frisker inside containment is over 100 cpm

sew you're saying that b.w.r.s make gobs of energy an p.w.r.s make jobs of energy?

[hamsamich]

Wow...didn't know you two were licensed on BWRs AND PWRs!!  Congrats.

[Bonds 25]

Sorry, I will refrain from spewing my "wimpy" PWR humor in the future.

I fantasize about being an RO sometimes, but then I remember how unbelievably awesome it is being an HP and protecting the public from the DEADLY effects of ionizing radiation.

Saving the public's lives (HP) >>>> Making DEADLY radiation (RO)

[MMM]

PWR's insert their CRB's upside down, have clean turbines, large containments and can't load follow...........not to mention constant boron addition and required concentration levels. You mention boron addition at a BWR (via SLC) and it signals "time to look for a new job"

BWR BWR BWR BWR !!!! A real Nuclear Power Plant.  Not a wimpy "the background on the frisker inside containment is over 100 cpm

Personally, I like being able to walk through the plant with a bottle of water on a hot day in my PWR, not having to go through several rad monitors every day, not having to worry about being contaminated if there's a packing leak. Spending all day inside an RCA for JPMs at a BWR sucked.

[Bonds 25]

Its just a joke, I have worked way more PWR's in my career, I just happened to land permanently at a BWR......and not because I decided due to the design. If I was at a PWR, I would be picking on the BWR's.


I love all Nuclear Plants equally.....well except Ice Condenser Plants, screw those guys 

[TVA]

Being the only person in the world has been a Shift Manager on a BWR and a PWR I can and will answer any questions you might have.
Looks like I am the only person in this thread who has operational experience.

1: PWR rarely add boron except post shutdown.

2: BWR are easy as hell to operate.

3: BWR have better fuel economy and actually around 60% of the fissions at EOC are from Pu 235.

4: From a license aspect I liked PWR better. Especially for remembering containment valve isolations and logic.

5: I found PWR EOP rules to be boring as hell. Love the BWR flow chart wild west feel.
On the other hand there is no prioritization with PWR procedures. That was nice.

6: All the physics and check valve testing on a PWR during startup SUCKED! Also pressurization sucked as one had to be very careful on the BFPL curves. Also having to due special evolutions set up for low pressure cooldown was a bit well it sucked.

7: Control rods on both types made sense. One thing I loved about PWRs was NO rod patterns also when one group of rods was at a certain position the others would start moving. Saying that... power dependent rod positions on a PWR sort of sucked. I liked the idea of once rods are in the core stays shutdown under all conditions. PWRs are a combination of boron and control rods.

8: Both have dose issues. Depends on where you are in the plant. On the average guys in a BWR are more dose concsious.

[TVA]

I licensed at an Ice Plant. Wow whoever came up with that idea was f@#$%^d in the head






Modified for language

[Bonds 25]

3: BWR have better fuel economy and actually around 60% of the fissions at EOC are from Pu 235.

You sure?

[hamsamich]

probably...all the U is gettin gone....while PU is still being produced...I don't know why it would be different in BWRs though.

[TVA]

3: BWR have better fuel economy and actually around 60% of the fissions at EOC are from Pu 235.

You sure?

Given I worked with Reactor Engineering on EOC start ups yes I am sure.
Its why BWR have EOC RPT/ARI

[Bonds 25]

I was under the impression it was Pu-239.....

[TVA]

probably...all the U is gettin gone....while PU is still being produced...I don't know why it would be different in BWRs though.

Voids keep neutrons at various energy states for longer. The core is a lot bigger. U238 absorbs the neutrons and ends up as PU239 and 240 ( a resonant absorber) . Transients at EOC are faster and nastier. It’s also why so many BWRs are on 2 year cycles. Bigger core, more PU239. Moderator coefficent can be slightly positive at certain times. PWR does the exact opposite.

[TVA]

I was under the impression it was Pu-239.....

You are correct. Just saw my typo!

[TVA]

Commercial PWR operate all rods out then dilute as the core ages. Eventually you get to the point where you have to add so much water to maintain power you put in a clean demin periodically to remove boron to maintain power. Eventually that stops working so you let power coast down. Iirc its about .75% a day. Once we got to around 75% power it was outage time

[Bonds 25]

You are correct. Just saw my typo!

 

[scurrilous]

I can and will answer any questions you might have.

No real questions, just curious what people had to say. I've heard people say it's hard to switch from PWR to BWR and vice versa, but personally I don't think it could be that bad... If you could license at one plant I'm sure you could do it at another, just a question of whether you want to go through class again.

[TVA]

Actually knowing what to study isn’t hard. Once you license the exam process is the same.
When I got my first license I studied too much.
An example is I would memorize power supplies to everything.
I came to realize what I call the Big Pump Little Pump theory. There are only about 10 big safety related pumps. Half will be off a big safety related power supply. Half from the other. A Train pumps will have a suffix A or C. Same with Busses
B Train are B and D.
On exams I would look for the A and match it with the Big Bus that had an A in it.
Little pumps same theory.
Works like a charm.

The theory was a bit different but only on the reactor side. Thermal limits for a BWR are more complicated and they change as the core ages. PWR Boron changes things too.

The major difference was Emergency Procedures. BWR use flow charts and rely on more decision making by the Operators and the CRS. Once you are done with something you leave it. If equipment gets restored you simply use it.

PWRs have a family of accidents and events.
So the EPs are a lot different.
First you enter a wide ranging procedure called E0. You do this for every scram. A BWR does not require entry on all scrams. Only if you meet certain conditions
Anyway you enter E0 and if you meet certain conditions you go to another EOP
You are only in ONE EOP at a time.
While doing this an individual is taking data for status trees. Each has it’s own color
Red: Priority 1. If you are in red you leave whatever procedure and go to the red procedure. Once done with a red you go back to the procedure you were in.
Orange: If you are in a procedure and an orange path comes up you enter it UNLESS you are already in a red path and have not entered it.
Once done you go back to the last procedure you were in.
Yellow: Yellow paths are optional.
However if you elect to enter a yellow path you leave whatever procedure you are in perform the yellow path and once complete you go back to the procedure you were in when you entered the yellow path.
Red and Orange paths have priorities too
Say you are in EO
You have a safety injection so you leave EO and enter E1 because thats what E0 tells you to do.
About 5 minutes later the STA tells you that you meet the conditions to enter say Red Path 3.
You leave E1 and enter Red Path 3.
You are midway through it and the STA says you meet the conditions for Red Path 1 which is the highest priority procedure.
You leave Red Path 3 and enter 1
When you are done with 1 you go back to 3 where you left off even if the conditions no longer exist.
Once done with 3 you go back to E1 wherever you left it.

The issue I had is the first 5 to 7 steps of each procedure is repetitive. You might have already done it in a previous procedure. You still do it anyway. The reasoning is you can enter a red path from virtually anywhere so you have to ensure the items get done. Even if you have done them you still do them anyway.
Coming from a BWR that was unusual for me and I had to break the BWR habits.

The way power changes in a PWR and BWR is totally different.
In a BWR you simply lowered core flow till around 68% power.
Then you put in certain control rods
Then flow
Then Rods
At about 20% power you scrammed the plant.
Going up same way

PWR: You raised or lowered turbine load.
When after temperature reached a certain point you either added pure water or boron OR you move control rods to a certain position.
20% power you scrammed if shutting down for an outage.

If something happened that required lowering power rapidly aka a runback BWR was simple. Recirc flow simply lowers and power and the turbine follow it.

PWR the turbine runs back. The reactor follows.
Control rods insert automatically to keep reactor temperature within a certain temperature range around Turbine First State Pressure aka TRef
Iirc at SQN it was within 1.5 degrees.
The issue is for any given power in a PWR rods must be above a given position to prove the reactor can be shutdown. A commercial PWR can literally reach 45 % power at the beginning of a cycle if the rods are in and there is no boron in the core.
So if you are in the proper temperature band and you get an alarm for rods too far in you have to add borated water at a certain rate to compensate. From the time you start until boron starts having an affect is around 5 or so minutes.
You know when it starts having some bite as you can hear the indicators click as the rods move out. It’s not a science. Takes a lot more time to address a run back on a PWR than a BWR.

What I described was for a Westinghouse 4 Loop Reactor.

[MMM]

No real questions, just curious what people had to say. I've heard people say it's hard to switch from PWR to BWR and vice versa, but personally I don't think it could be that bad... If you could license at one plant I'm sure you could do it at another, just a question of whether you want to go through class again.

The change in reactor theory can be difficult if you spent a lot of time on one. The emergency procedures seem to be pretty different. Personally, I prefer the BWR boards that are just a flow chart. If you made it through license class on one, you should be able to make it through on the other, you just have to relearn some things and unlearn others.

[TVA]

Unlearning was hard. The ATWS procedure on a BWR is the exact opposite as on a PWR.
PWR had full families of accidents that don’t exist in BWRs.
I loved both but probably love BWRs a bit more.
Currently SRO certified on a BWR 6.

[TVA]

Fossil plants are really cool on the heat source side.

[TVA]

Your question about going through class again.
It’s a young man’s sport. Last time I went through class I started at 43. Finished just as I turned 46.
It was getting irritating maybe because I had already licensed twice before.
Wouldnt do it now.
When I certified I did not go through class.
I was offered the chance to self study for the written and to take the simulator portion when ready. I asked if I had to be pretty or just prove I can operate the AOPs and the EPs. I was told just get through the later but not be a total moron about it. A month later I took the written and got a 100. I then watched a requal crew in the simulator, practiced twice so I knew how to manipulate the plant computer and give orders ( I had two excellent guys who were formerly licensed on the plant as my ROs) I then said bring it and did my scenario. Had a couple comments but overall did well.
Was asked if I would consider licensing.
I said for a million a year. They laughed, I didnt!

[Bonds 25]

Props to TVA for being one hell of a poster in this thread!! Great information, man. Its finally you are your best, cleansed of your worst.


Although it did take a dirty, low level (dumb) RP to point out that Pu-239 is the majority of core fission at the EOC for BWR's....and not Pu-235 or whatever "typo" you inserted. 

[TVA]

Props to TVA for being one hell of a poster in this thread!! Great information, man. Its finally you are your best, cleansed of your worst.


Although it did take a dirty, low level (dumb) RP to point out that Pu-239 is the majority of core fission at the EOC for BWR's....and not Pu-235 or whatever "typo" you inserted. 

I was like what is he talking about?
Then I noticed the what was in the color ree.


Btw I have never said anyone in this industry is dumb. That is far from the case!


Thank you!

[hiddencamper]

As others have said, BWR EOP/AOP are very different and grant a tremendous amount of operational authority to the unit supervisor.

The EOPs are built around stabilizing your critical safety parameters but do not diagnose or correct the problem, it’s up to the operator to determine the problem, fix it, determine which things need immediate attention or are “causing” the event and focus on those.

An example is an ATWS with main steam isolated. You absolutely need to get power down by terminating feedwater injection, otherwise you’ll dump too much steam into the pool and exceed the heat capacity limit. You’ll be in the containment and rpv EOPs at the same time, and the only reason you’re in the containment EOP is because you’re dumping tons of steam into it. To stabilize containment you need to lower power. But I’ve seen cases where the unit supervisor will stop ATWS EOPs to take time to try and address containment, which makes the problem worse.

So it really takes a different type of mentality. The nrc seems to hate it. But I’m on the emergency procedure committee for BWR owners group and we do a hell of a lot of work to keep them highly functional.

Wait for next rev of EOPs, ATWS response gets crazy.

Aside from that, BWRs are a pain dealing with the rod sequence, and are finicky as hell at low power. They are easy to operate overall though. BWR = Better Water Reactor

[shehane]

A lot of good discussion here.  From an HP's point of view I preferred BWRs.  Complacency happened at the PWRs I worked because everything is clean and the bad stuff sneaks up on you.  At the BWRs you just knew you could find something bad anywhere you looked so you were more careful.  Just my opinion.  I would take a big nasty BWR any day.