Noble gas ???

[dinutt]

  any experiences out there  or have ideas to help reduce our noble gas issues during Rx Head lift (ventilation etc.). ... known fuel leak..in planning stages now !! 1 year out.......

[grantime]

Ventilation can help.  But you will need a lot of air turnover.  If you have enough gas then you will be at risk of tripping your plants release monitors limits.  OPS sometimes has a dim view if you put them into the emergence release calculations

Depending on whether you are a BWR or PWR then perhaps OPS can help by venting gas off of RCS prior to opening systems.  In PWR venting the VCT repeatedly can get some out before you open up anything. Also several of these isotopes have fairly short half lives.  If the outage schedule can support it any delays on opening systems will help--I doubt that this is an option.

Keep in mind that Noble gasses may not be your only problem.  Iodine can come boiling out as well.  And just to add to the fun Iodine soaks into some metal parts and then get released latter.  Were you at Farley (mid to late 80's)the outage when we heated the RHR impeller and had iodine uptakes several weeks into an outage?

[wlrun3@aol.com]

  any experiences out there  or have ideas to help reduce our noble gas issues during Rx Head lift (ventilation etc.). ... known fuel leak..in planning stages now !! 1 year out.......

   ...ineffective RCA egress protocols will seriously impact outage schedule goals...

   ...prior planning ( supplies, procedures, well understood personnel and material flow paths ) and an informed concensus among all involved departments will effectively mitigate undisciplined budgetary compomise...

    ...contingency planning and adequate preparation will prevent a minor inconvenience from becoming an unsuccessful outage...

[dinutt]

  Gran,wr3 thanks for your input on my topic.no or I don't remember being at  Farley then.I think I started coming there in 90's I .understand too that Iodine can be another problem as well......thanks again for your input and ideas!!!!
Di

[Floydbob]

What levels of Xe-133 eq are we talking about in the RCS?  If levels are high enough, I would think that iodines would also be a problem.  Certainly venting the VCT a bunch prior to shut down would help but there are many factors to consider.

[Marvin]

Just a few little leakers or the whole pot leaking like a sieve?  It really makes a difference.  A few little leakers is (relatively) easy to manage, then there's the leaking like a sieve scenario.  If it's a whole bunch leaking, then you might have a problem.  If the whole pot is leaking, then I would get in touch with some of the experts at the plants who have faced that situation, like San Onofre in the 80's.  They can provide a much more detailed response than my memory can.  It's been over 20 years since I have played with noble gas and fuel fleas.

[retired nuke]

  any experiences out there  or have ideas to help reduce our noble gas issues during Rx Head lift (ventilation etc.). ... known fuel leak..in planning stages now !! 1 year out.......

Wow - running with leakers for a year...that's gonna be a fun outage.
The last leakers I dealt with we shut down and pulled them mid-cycle - there were 8 in the batch, and mgmt opted to make the problem go away.
Prior to that, I was at Palisades in the 90's - check with them, we had particles and pieces everywhere, but it was from an old bundle (outer ring position - not in the flux area) - no gas probs...
I also dealt with a leaky SRV at a plant - low level gas in the Ctmt - affected the RO2s - made them read 20 mR/hr all day - we ended up bagging them for use in ctmt until ventilation fixed that.

Good luck

[grantime]

Leaking fuel can be gift that keeps on giving.  Farley had water jetting in early 80's that badly damaged several bundles.  Managment decided to run entire cycle like that.  We were still finding loose pellets years later.  It took at least 10 years before noble gas levels wouldn't peg an RO-2 on some systems. 

[wlrun3@aol.com]

Leaking fuel can be gift that keeps on giving.  Farley had water jetting in early 80's that badly damaged several bundles.  Managment decided to run entire cycle like that.  We were still finding loose pellets years later.  It took at least 10 years before noble gas levels wouldn't peg an RO-2 on some systems. 

   ...is there a consistent ratio between Iodine and Noble Gas in the discussed fuel assembly integrity context...

   ...does the location of the assembly matter...

   ...does the age of the assembly matter...

   ...i was recently made aware, at an old combustion engineering reactor, of "source assemblies"...

   ...as it was explained to me, there were two of these among the roughly 200 total fuel assemblies...

   ...their purpose was to retain neutron emission capability and serve as startup sources following refuel...

   ...going into the outage it was known that one of these was one of four compromised fuel assemblies...

   ...those that had seen this before predicted, given the leaking "source assembly", that the outage would be exceptionally noble gas intensive...which it was...

   ...are source assemblies common to all PWR designs...

   ...do BWR designs have a similar arrangement...

   ...can noble gas/iodine outage conditions be predicted given core status...

   ...what is a "soft shutdown"...

   ...does the nature of the shutdown process affect noble gas/iodine outage conditions... 

   ...what operations evolution can cause noble gas/iodine to come out of solution during outage...

   ...can this be forseen and prepared for...

[dinutt]

Wilrun well said and correct !!  Grantime sounds like a gift you wish you never received  that's  incredible.and now??

Di

[wlrun3@aol.com]

Wilrun well said and correct !!  Grantime sounds like a gift you wish you never received  that's  incredible.and now??

Di

   ...thankyou for starting this thread...

   ...noble gas/iodine has always been a challenge for me (initial entry, Waterford, 1st refuel, 1986, plastics and iodine canisters)...

   ...i still don't understand it to my satisfaction...

   ...i was hoping that the operations department forum posters who have, in the past,  been so helpful would find this topic, and my previously posted questions, interesting, relevant and challenging...

[thenuttyneutron]

I think the biggest issue is the fighting between Ops, RP and the senior management.  Sometimes getting an outage completed "on time" does not work well with what RP wants.

I know my plant has some leakers from what we think are new assemblies installed during our last outage 7 months ago.  We now have some limits on how fast we can change reactor power for normal maneuvering.  Just hope you don't get a plant trip from 100% power because those will really get things stirred up.

Wlrun3:  Soft Shutdown is a term I learned about just recently.  It is basically where you shut down a reactor without just dropping the control rods in the core once you have lowered power.  Instead you drive them in with the control rod drive.  There are some important tidbits about this. 

At the PWR I work at, we have 3 types of control rods.  They are; Safety Rods, Regulating (reg) Rods and Axial Power Shaping Rods.  Using Control rods and boron allows us to control PWR reactors.  The Safety Rods must all be out 100% before you make the reactor critical.  There are limits on how high you can make your boron concentration due to reactivity coefficients.  The problem with too much boron is that it can make your moderator temperature coefficient positive which is a big NO NO (it can be slightly positive at the beginning of core life for a few hours during zero power physics testing).

A soft shutdown uses both boron control at certain concentrations (Reactor Engineers figure this out) and the Control Rod drive inserting the reg rods to shut the reactor down before you even start to move in your safety rods.  Once the reactor is shut down, you can then insert your safety rods.  It is a balance between boron and control rod worth depending on the time in the core life.

[ISFSI]

Sounds like your talking about a B&W Unit (APSR's).  With that Unit's specifications, a 'soft shutdown' may be permissible.

OTOH - a CE Unit has a Tech Spec that requires an all rods droipped scenario with an average time validation required to be performed on a refueling cycle basis.  This is usually done using a visicorder and co-ordinated by the Ops Dept with the I&C taking the measurements for Tech Spec satisfaction.

Can a degassing using the VCT on PWR's be useful in reducing the Noble Gas content of the RCS when shutdown?  One trade off would be the increased waste water to treat and release, but conversely the dose saved may prove beneficial.

YMMV

[RAD-GHOST]

There are a lot of different processes that can be utilized, but the primary deciding factor is.....

...SCHEDULE!

RG!    

[ISFSI]

Oops....forgot to metion...

If Ops decides to collapse the pressurizer bubble to the quench tank and vent this to containment - want to guess how long it'll be before the release permit is done and how long it'll take to get levels down?

Something else to consider - If the above scenario plays out, someone should be wary of the impact on the Control Room Ventilation envelope as well.  Auto activation of the radmonitors associated with the Control Room envelope are frowned upon by the NRC.  It used to be a Saftey Sytsem activation...reports, Eplan calls...etc...getting an Outage off on the wrong foot like that can be a real headache for the duration of the outage...BTDT

[wlrun3@aol.com]

Well, it's Friday night and I'm not real sleepy anyway, so here's an answer from an old memory.  I was a containment tech at a west coast PWR in the mid-80's when the whole pot was leaking, so bear in mind that my memory is skewed in that direction.  Of course, this is not an all inclusive list since my memory fails me, but it was interesting to assemble.  Bear in mind that the presence of high iodine levels in addition to xenon and krypton adds an additional layer of complexity.  To keep it simple, let's arrange things in DO's and DONT's.  First the DO's:

DO'S

DO 1.  Make sure everybody knows what to expect.  The folks sitting at the RCA egress will belly-ache anyway, but at least you can say "I told you so"

DO 2.  Make sure your techs know that noble gas can mask real contamination issues.  You don't want a bunch of people sitting around waiting to decay when they might have something else on them along with the noble gas (like a flea, which goes along with damaged fuel).

DO 3.  Make sure your protocols for getting through the monitors are firmly established and nobody's blowing things off when it comes to getting out (yes, everyone will be tempted to say let's get out of here, it's just noble gas anyway).

DO 4. Start a noble gas log that's easy to fill out and get some junior RP person involved in tracking and maintaining.

DO 5. Refresh everybodies memory on  what a fuel flea is and what to do if you start finding them (see 2 above).  You might dig out some old flea thumbrules.

DO 6.  Think about additional iodine charcoal units on your portable HEPA's.

DO 7.  Get everybody into company provided modesties, make arrangements for folks to sit around the exits while they are waiting to decay (chairs maybe) and make sure they have a place to use the restroom, drink water (some will be heat stressed), and change if that's what they are going to try to do to get out.

DO 8.  Think about the air during and after the head is pulled.  What iodine concentrations do you expect?  Do you have enough iodine respirator cartridges?  They are not any fun -- it's like breathing through a heavy straw.  Should you use supplied air in some instances?  Of course, it all depends on the iodine in the RCS.  We had to wear the darned things on the refuel deck for way too long.  Refuel deck people will start to alarm the PCM's due to iodine after a while, even with the cartridges.  You may have to rotate people to make sure they can get out to go home (I'm not talking about xenon or krypton here).

DO 9.  Identify where you can expect gas to show up in the aux building and plan on controlling it.  We had plenty of herculite and covered doors and openings when necessary to get the gas to stay in the room instead of going out into the hall.

DON'Ts (inventive ways to screw up an already bad gas situation)

DON'T 1.  Let some overzealous junior RP pre-load all the air sample heads with iodine cartridges, then leave them inside the can until it's time to use them.

DON'T 2.  Evacuate the RCS or CVCS system (You said PWR didn't you?) into the can until the appointed time through the appointed path.  You might even want to plan this.

DON'T 3.  Let anybody take an open air ion chamber (like an RO-20) into the can without a bag around it.  It will still get gassed up over time, but the bag will slow things down.  Take it out of the can, remove the batteries and dessicant and bake for an hour or two at about 120 degrees to get the gas back out.

NOTE:  There were times we had well over 300 MPC's of xenon and krypton in the can.  I don't know what that equates to in DAC, but if you are bored and have some old MPC tables............I don't remember the iodine levels, but they were high enough to create exposure problems.

Well, that's all I can think of right now.  It's getting late and my memory fails me anyway.  If you have any specific questions, I might be able to answer them.  Just have to jog my memory. 

In short, just hope the whole pots not leaking by the time the head is ready to lift.

Nice to see you are still out there -- I hope it goes well.

   ...that took a bit of effort...thankyou Marvin....

[wlrun3@aol.com]

Sounds like your talking about a B&W Unit (APSR's).  With that Unit's specifications, a 'soft shutdown' may be permissible.

OTOH - a CE Unit has a Tech Spec that requires an all rods droipped scenario with an average time validation required to be performed on a refueling cycle basis.  This is usually done using a visicorder and co-ordinated by the Ops Dept with the I&C taking the measurements for Tech Spec satisfaction.

Can a degassing using the VCT on PWR's be useful in reducing the Noble Gas content of the RCS when shutdown?  One trade off would be the increased waste water to treat and release, but conversely the dose saved may prove beneficial.

YMMV

   ...palisades last refuel outage...

   ...like the trade off mentioned, does the operations department's evolution options always consider exposure...

   ...does the radiation protection/alara department provide the estimates for exposure given evolution options considered or are the consequences understood well enough by operations personnel from extrapolation/experience to proceed without outside discussion...

   ...what is APSR...i'm familiar with OTSG in reference to B&W...

   ...i was unaware of the "permissibility" of a soft shutdown...how does it work..

   ...thankyou for taking the time to reply...much appreciated...

[ISFSI]

APSR = Axial Power Shaping Rod.  Permanently attached rod to drive motor configuration.  Not a possible to drop into the core.  Not credited for safe-shutdown.  Used primarily to control the flux distribution in the core for a more even power distribution/production.

In as far as RadPro involved in the evolutions like this...I would say it should be mandatory.  RadPro/Ops/Chem should all be on board to ensure that the best method for dealing with the scenario as it un-folds can be addressed by the respective specialists.

[wlrun3@aol.com]

I think the biggest issue is the fighting between Ops, RP and the senior management.  Sometimes getting an outage completed "on time" does not work well with what RP wants.

I know my plant has some leakers from what we think are new assemblies installed during our last outage 7 months ago.  We now have some limits on how fast we can change reactor power for normal maneuvering.  Just hope you don't get a plant trip from 100% power because those will really get things stirred up.

Wlrun3:  Soft Shutdown is a term I learned about just recently.  It is basically where you shut down a reactor without just dropping the control rods in the core once you have lowered power.  Instead you drive them in with the control rod drive.  There are some important tidbits about this. 

At the PWR I work at, we have 3 types of control rods.  They are; Safety Rods, Regulating (reg) Rods and Axial Power Shaping Rods.  Using Control rods and boron allows us to control PWR reactors.  The Safety Rods must all be out 100% before you make the reactor critical.  There are limits on how high you can make your boron concentration due to reactivity coefficients.  The problem with too much boron is that it can make your moderator temperature coefficient positive which is a big NO NO (it can be slightly positive at the beginning of core life for a few hours during zero power physics testing).

A soft shutdown uses both boron control at certain concentrations (Reactor Engineers figure this out) and the Control Rod drive inserting the reg rods to shut the reactor down before you even start to move in your safety rods.  Once the reactor is shut down, you can then insert your safety rods.  It is a balance between boron and control rod worth depending on the time in the core life.

   ...it sounds like information available to the reactor engineering department allows them to predict noble gas/iodine air concentrations during outage...

   ...planned evolutional ventilation line ups must also be available...

   ...given the current industry learning curve status, with 90% plus availabilty factors, deviations from the plan must be rare...

   ...recent conspicuous reductions in exposure, industry wide, and increased and ongoing sensitivity to exposure control suggests that noble gas/iodine outage issues will become, as did so many other exposure challenges, a thing of the past...

   ...this topic...it's beginning to look like this will be driven, as was the notable recent source term reductions, by the operations, chemistry and reactor engineering departments...

   ...if i'm right, this would allow the radiation protection department, during outages, to avoid the embarrassing experience of being reactive after the fact and, instead, be prepared for well understood and anticipated performance expectations...

   ...are the outage delays presented by noble gas/iodine issues, in the more conspicuous cases, of such magnitude as to seriously impact outage success...

   ...or, given the options available to the operations department, is an outage noble gas/iodine issue secondary, understandably, when overall outage success is at stake...

[wlrun3@aol.com]

APSR = Axial Power Shaping Rod.  Permanently attached rod to drive motor configuration.  Not a possible to drop into the core.  Not credited for safe-shutdown.  Used primarily to control the flux distribution in the core for a more even power distribution/production.

In as far as RadPro involved in the evolutions like this...I would say it should be mandatory.  RadPro/Ops/Chem should all be on board to ensure that the best method for dealing with the scenario as it un-folds can be addressed by the respective specialists.

   ...i'm unfamiliar with operations department procedures but aren't there RP hold points, just like in the field, and aren't the procedures driven by the requirements of the various CFR's...

   ...i'm thinking the CFR that requires an alara program...

   ...thankyou, again, for the informative and knowledgeable replies on this topic...

[dinutt]

  wlrun3 /Marvin you guys are the best ! thanks for all this input  on my topic it has enlightened me to say the least and Marvin Ditto on the  effort!!!   I am am sure all depts will be engaged with this evolution, but exactly what RG says it will come down to" Schedule " as we all know in the industry..  Nutty Neutron you are so right !!! We still need to do the right thing !!alot of what you all are saying are great ideas and all the right questions  we should be asking and controls in place too.so with that I am going to  communicate to my management  all your input.  wlrun3 I agree it has been quite a learning experience for me as well with this topic...again thanks all ,post post!!!!!
Di

[wlrun3@aol.com]

wlrun3 /Marvin you guys are the best ! thanks for all this input  on my topic it has enlightened me to say the least and Marvin Ditto on the  effort!!!   I am am sure all depts will be engaged with this evolution, but exactly what RG says it will come down to" Schedule " as we all know in the industry..  Nutty Neutron you are so right !!! We still need to do the right thing !!alot of what you all are saying are great ideas and all the right questions  we should be asking and controls in place too.so with that I am going to  communicate to my management  all your input.  wlrun3 I agree it has been quite a learning experience for me as well with this topic...again thanks all ,post post!!!!!
Di

   Di...

   ...i'm curious...which of the three designs in florida, lucy-combustion, turkey-westinghouse, crystal-B&W, is mosted noted for noble gas/iodine issues...

   ...are there designs that are known to be more of a problem, based not on fuel integrity, but on mechnical configuration...



 

[dinutt]

  wlrun3 tp-Westinghouse not sure on your design question it could  all  be in the mech end of the design.I don't have a clear answer for you sorry ..I am sure there are alot of folks out here that may have some good in sight on your question and if you have some ideas out there share with us on this and your thoughts.......
Di

[wlrun3@aol.com]

   ..."A soft shutdown uses both boron control at certain concentrations (Reactor Engineers figure this out) and the Control Rod drive inserting the reg rods to shut the reactor down before you even start to move in your safety rods.  Once the reactor is shut down, you can then insert your safety rods.  It is a balance between boron and control rod worth depending on the time in the core life"...

   ...how helpful is a soft shutdown in reducing outage dose...

   ...is it costly in terms of outage hours sacrificed to achieve it...

   ...what impact does soft shutdown have on our forum topic...noble gas...

    ...by the way, best response to a technical forum topic question i've seen in a while...nice job...




   

[thenuttyneutron]

   ..."A soft shutdown uses both boron control at certain concentrations (Reactor Engineers figure this out) and the Control Rod drive inserting the reg rods to shut the reactor down before you even start to move in your safety rods.  Once the reactor is shut down, you can then insert your safety rods.  It is a balance between boron and control rod worth depending on the time in the core life"...

   ...how helpful is a soft shutdown in reducing outage dose...

   ...is it costly in terms of outage hours sacrificed to achieve it...

   ...what impact does soft shutdown have on our forum topic...noble gas...

    ...by the way, best response to a technical forum topic question i've seen in a while...nice job...




   

I was just answering a question about what soft shutdowns are.  Doing a soft shutdown can reduce dose a lot at my plant. 

*abbreviation*: Control Rod Drive Mechanism = CRDM

The reasons for this are the way the control rod drive assemblies are designed at my plant.  The safety and req CRDMs are latched to a lead screw.  This lead screw is connected to the tops of the actual control rods with a bayonet lug.  These lead screws are long and allow the CRDM to insert and withdraw the CRs.  The actual CRDM grapples this lead screw and moves it up and down by just rotating around it.  The way it does this is almost too hard for me to describe with words.  I could better explain it with a drawing.

Above where the CRDM grapples to the control rod assembly lead screw is a ball check valve.  This allows water to flow up into the upper portions of the CRD mechanism (CRDM) when the rods are dropped in the core during a reactor trip.  During a reactor trip, the CRDMs are deenergized which causes the control rod lead screws to detach from the CRDM and drop in the core.  Softshut down does not do this and the rods are driven in with the CRDM rather than using gravity.


Ok, enough tech stuff on how the CRDM is designed.  When the reactor is tripped, it stirs up lots of crud.  This crud can then accumulate in the areas above the ball check valve. There is a lot of work done on the control rod drives mechanisms during an outage.  These workers can get lots of dose just because of tripping the reactor and getting that crud up there.

The actual shutdown time that is requires vs. a reactor trip going into an outage is not that much.  These reactors are already taken to a lower power prior to the planned trip.  The extra time to do the soft shutdown is not a big issue.

There is a lot of tech stuff in here.  I am trying to edit this with a better description of how these are made.  Keep the questions coming and I will try to answer them to the best of my ability.