Interview at nuclear station 2

[ScottyUK]

I've landed an interview at a British AGR nuclear power station. I'm from a CCGT background so I'm familiar with the standard electrical plant and control systems which exist within a power generation environment. I'm much less clued up on the nuclear side of things, other than having a rudimentary understanding of how the different reactor types work. Does anyone know of any good reference material on the 'Net? I'm more than happy to buy texts etc, but I'd like to get a bit more clued up prior to Monday's interview and on-line is probably the quickest way to do this.

Thanks in advance.



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If we learn from our mistakes,
I'm getting a great education!

 

[itsmoked]

mc5w: The reason I asked "what isotope" is because I can't recall any Hydrogen Isotope that decays in minutes, only Tritium's 12 years.

Thanks mc5w.

 

[ScottyUK]

Guys,

I promised an update when I got it:

I'm through to the last round, which is a morning on the simulator desk. The interview was ok, technically it was not especially challenging, although it was mainly process-based rather than electrical. The key question was 'draw a block diagram of a nuclear plant and explain the key functions of the blocks'. Thanks to those who posted the helpful links earlier.

The job has changed - or maybe the original advert maybe wasn't as clear as it could have been - and the position is actually the engineer running the reactor-turbine-generator module. I'm not 100% whether I want to let go all my 'proper' engineering and go over to Operations. I've been on the project and maintenance engineering side for a long time, and I'll miss it if I give it up. On the other hand I have a chance to learn a whole lot and the company would be investing a lot of money in training me. In a few years I would have gained a lot of additional experience and this would probably open up some opportunities that would not otherwise present themselves.

Anyone working in a similar position at a nuke station? How is the job? I can obviously ask my colleagues in Ops at our site, but our industry is quite different from nuclear generation in many ways.



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If we learn from our mistakes,
I'm getting a great education!

 

[Barryng]

At least in a PWR (I do not know BWRs), H2 is intentionally added to act as an oxygen scavenger for corrosion control. The concentration is required to be >35cc/kg during power operations and must be reduced to <5cc/kg to open up the reactor coolant system when shutdown. This is the major source of H2 during normal ops but there is also a much lesser contribution from electrolysis of water.

During accident conditions, water will react with the zirconium that is extensively used in the construction of the core. The fuel pellets are contained in metal tubes (called cladding) made of a zirconium alloy. This alloy reacts with water if the temperature gets sufficiently high. This reaction is very exothermic and is therefore self sustaining. It also releases large amounts of hydrogen. This is the major source of hydrogen released under accident conditions and was mostly the source of the hydrogen explosion experienced at TMI.

Heavy water was mentioned above. Canada uses heavey water because it allows them to use natural uranium instead of the slightly enriched (<4.5%) uranium required in a light water reactor. The trade off is the high cost of heavy water vs. the high cost of enriching fuel. In terms of the reactivity balance in the core, light water is a better moderator (ability to slow down neutrons to ambient kinetic energy levels) but heavy water absorbs less neutrons (bad for neutron efficiency). At least at the operational level, any contribution to the net core reactivity from the minimal amount of deuterium that may be present is not even thought about.

I also have to address the TMI comment above. The TMI event was clearly a training issue. The operatoring crew responded in a manner that was completely consistent with their training both from past experience in the nuclear navy and plant hot license training. They were dealing with an accident that they had no training for either in theory or in practice (a pressurizer steam space LOCA). However, many of its major symptoms mimicked a very different event (a LOCA anywhere but the pressurizer). In their minds they had a valid concerns for terminating safety injection although they were obviously wrong. Interestingly, securing safety injection did not start the core damage sequence. Core damage only began when they later shut down the Reactor Coolant Pumps. There were certainly many other contributing factors but bottom line was inadequate training specifically in terms of thermodynamics theory and simulator training. Hot license training programs now typically include about three weeks of thermo vs. about one day prior to TMI. We all now have plant specific simulators which were mostly non-existant back then.

 

[Barryng]

ScottyUK, I am a EE by education but I have also worked in almost every area associated with these plants. Over a lot of years, aside from engineering, I was a QC supervisor, STA(Shift Technical Advisor - post TMI requiremnt in US)) and went through an 18 month Hot License class (Senior Reactor Operator). I was also an Ops training instructor and have spent all to many humiliating hours as a student on the simulator (even though I enjoyed it all). I also have considerable experience as a simulator instructer/evaluator. I am currently in Electrical Maintenance. I spent almost 10 years in the Ops end of the business and enjoyed the experience. I was never a board operator because that is a bargaining unit position (surprisingly) and I am in an exempt status. I have always enjoyed being a student so Ops always had the extra advantage, to me, of having to attend a week of requal training (class + simulator) every six weeks. I do have to comment that most everyone else did not like the training and the associated written and simulator exams. I did have some oppurtunity to operate the real plant during my license training. It was a memorable experience for me, for example, to start up and control a three million horsepower reactor and one million horsepower turbine-generator.

The experience of the control room operators is typically very different from mine as my operations experience has always been from a different perspective. In the US anyone who operates a control that effects reactivity must either be licensed or in license training. Most, but not all, plants extend this requirement to the turbine controls. Almost all the people I know that are licensed only remain licensed because of the exceptionally good compensation that goes with these positions. Todays control room enviroment is very structured. Nothing is done without a procedure in hand and numerous people looking over ones shoulder. Three way communications, peer checks, verbatim procedural compliance, etc. are strictly enforced. It is not uncommon for operators (including supervision) to incurr discipline (days off without pay) for errors including administrative issues. Idle conversation is very limited and the administrative workload is almost overwhelming. At least in the plants that I have had experience with, the work hours are long due to the never ending battle to maintain a sufficiently large qualified staff (attrition is very high). The continuous requalification training and associated exams does cause much anxiety among many people. I do not know what the culture is like in the UK, but it is a very tough job in the US. One has to really admire the abilities of those that do this everyday for years.

One last comment. Interestingly, it appears that those with four year engineering degrees frequently have a harder time in license programs than those without degrees. I am not sure why, but an engineering degree does not predispose someone for an easy experience. I will never forget how humbled I felt at the end of the second day of my hot license class.

 

[itsmoked]

Thank you Barryng for that clear detailed response and the very interesting administrative view of the "inside".

 

[mc5w]

itsmoked,

You got the decay backwards. Free neutrons turn into light hydrogen atoms over time. This is the reason why cosmic radiation does not rain neutrons upon us. If free neutrons did not run into hydrogen atoms then the uranium in the earth's crust would make us glow really good and have 3 eyeballs. The half life for the reaction is 12 minutes. This is one of the sources of hydrogen gas in a reactor. The other source is metal corrosion.

 

[itsmoked]

I didn't get it backwards!! I didn't get it at all!

But I do now. (Sent me scrambling for to the books) Free neutrons bust into a proton, electron, and an anti-neutrino.
In 12 minutes as you said.

 

[mc5w]

Only half the free neutrons decay into hydrogen atoms in 12 minutes. In 2 hours the decayed fraction is even greater.

If you had something with a half life of 100,000 years it would take 2 million years for 99.9% of the atoms to decay. After throwing in the half life of daughter atoms and their radioactivity it could take extremely long times for some radioactive stuff to become innocuous.

One of the things that initiated the TMI accident is that a relief valve failed to close, which released reactor coolant as steam. There was no limit switch attached to the relief valve to tell the operators that it was stuck open. There was also no television camera in the containment building that would have made it obvious that something was leaking steam. The operators had no idea that a relief valve could stick open ( which I have seen on domestic hot water heaters ) and figured that the controls for the emergency cooling system were malfunctioning.

Therefore, some of the lack of training was that there was directive to the effect, " if the emergency cooling system turns on, send someone out to physically check for a leak. Do not assume that the controls are malfunctioning." The TMI accident could just have easily been initiated by a minor leak at a gasket. Some of it is that some people who troubleshoot stuff can only diagnose problems that they specifically encountered before on the job or in the classroom. These people when they encounter a new problem have a hard time figuring it out. There was no directive to go get somebody who is smarter when a strange problem comes up and there are quite a few people who will not consult somebody who is smarter or who has more knowledge. I know when I am stumped or when a problem is quite strange.

I have had some instances where the same breakdown would keep happening because of some persistent condition. For instance, I had a punch press where I had to pull out the lubricating oil tank, dump out all of the oil, scrape and wahs it, put in new oil and stick in new oil filters once per month. The culprit was that large amounts of dirt had accumulated in the hollow parts of the press when it was at another plant.

 

[electricpete]

Since we are retelling the TMI story, another item that contributed to the misdiagnosis was that the operators saw pressurizer level increasing and interpretted that the water being injected exceeded the water leaking out. This led them to shut off the safety injection. But in fact the pressurizer level increased because a steam bubble had formed in the reactor.

Today operators in the US receive much more training including thermal dynamics. There have been significant improvements in many areas including training and post-accident monitoring instrumentation.

To Scotty, my observation is that an engineer in operations at a nuke plant has a better opportunity to move up the ladder than an engineer in engineering. But you have to be prepared for a lifestyle change including shiftwork.


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[mc5w]

A minor loss of pressurization due to a small leak can cause an unwanted steam bubble in all kinds of things that are supposed to be filled with water. If you have had to purge air bubbles form any size domestic hot water heating system you know what kind of pain in a certain body part air bubbles or steam bubbles can be. Now multiply purging a domestic forced hot water or gravity hot water heating system by how big a nuclear plant is and you would think that a male elephant is doing unnatural acts to you.

Really, though, I did work a job as a corrugator maintenance technician/millwright in a paperboard box plant for about 10.5 months. Learned a lot about medium pressure steam systems and what can go wrong with them. One time I had to take apart a float valve steam trap that has a bypass tube ( about as big as the type of needle for stabbing drugs directly into the heart ) in order to find out why it stopped passing condensate. Because of the way that condensate piping was routed down and then back up the steam trap needed to pass a minimum constant flow through the bypass tube to keep air bubbles from stopping the trap from working. Th problem was a small piece of teflon gasket material from a rotary steam joint that we had fixed a few days earlier.

 

[itsmoked]

Bet you learned about *LOUD* machines there too!

 

[ScottyUK]

Last weekend I was invited to spend an hour being observed on the AGR simulator desk after getting through the interview stage. It was quite a change to what I'm used to: no DCS graphics, lots of individual instruments and manual switches. I believe the central computer is an old Ferranti Argus, which is virtually a museum piece by today's standards.

The lifestyle change is clearly something to think long and hard about. There are pluses and minuses, as with most things in life. Overall I think I will adapt pretty well. I think epete's observation about promotional prospects is true in the CCGT power industry too.

Barryng - thank you for taking the time to write your post. Well worth a star! I think there must be a lot of similarities in the way the US and UK industries are structured. Even during my brief simulator experience it was clear how tightly controlled everything is. Your remark about everything being done with the procedure in hand seems to be spot on.

In your opinion, is the high attrition rate of desk engineers because of the very formal, regimented environment or because the job is stressful on the workers? I'm mildly concerned that degree-qualified engineers have a tougher time than their unqualified peers! Any idea why that might be?



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If we learn from our mistakes,
I'm getting a great education!

 

[Barryng]

ScottyUK, the high attrition rate in operations is due to a combination of factors including but not limited to, a high unrelenting work load, long hours with high required overtime, stressful control room enviroment, stress due to ongoing testing (written & simulator) required to maintain qualifications & pay, and draconian punitive responses to even honest errors of judgement. The geographic area also sometimes significantly impacts the attrition rate. These factors vary in significance from plant to plant as each plant seems to have its own unique culture formed by a combination of the personalities managing/supervising it, the employees, and its history. I have seen two plants owned by the same utility with significantly different attrition rates. I know of plants that rarely conduct hot license classes because their ops attrition rate is almost zero and I know of other plants that have continuous overlapping hot license and non-license classes because of their never ending struggle to maintain suffcient control room and field staffing. I once left a plant because it was an unpleasant place to work and live. I found and entirley different experience at another plant owned by the same utility.

Before accepting employment you should try to informally talk with those that are already employed. Ask about the attrition rate and the amount of overtime and how much of it is forced. Ask about the work schedule. Some plants work eight hour shifts and some work twelve hour shifts. The twelve hour schedule has the benifit of many more full days off and even provides a full week off every six weeks or so. The downside is that the hours are long and if overtime is regularly required it quickly eats into the available days off. Some people love this schedule some hate it. You have to decide but need to do this before you accept the job. The world of classrooms, examinations, and constant evaulation are just part of the commercial nuclear world and exists everywhere. It never stressed me but I know of many others whos quality of life is adversley effected by the constant worry.

On the positive side, the pay and compensation is excellent. Not only are base salarlies high but there are sometimes significant monetary retention incentives associated with these jobs. I left a position once that included almost a 25% increase above my base salary with license/certification pay and geographical retention bonuses. Some of the retention bonuses are based on successfully passing annual requalification exams. It is not infrequent to see someone loose thousands of Dollars when they fail a written or simulator exam on the first attempt.

I am not at all familiar with the licensing process in the UK. However, in the US, ScottyUK, as a degreed engineer, I would expect you to enter an approximately 18 month or longer program that would license you as a SRO (Senior Reactor Operator) and for you to spend little or no time "on the board" (except during training). I would expect to see someone with both a four year engineering degree and an SRO to be part of the shift supervisory staff. A typical single unit control room has two board operators, two supervisors, and circa five or six non-licensed field operators.

A post TMI requirment is to have a four year degreed and properly trained engineer within ten minutes of the control room. This is called an STA (Shift Technical Adviser). The STA's purpose is to provide an INDEPENDENT (from the operating crew) oversight during accident conditions. I would guess that the UK has a simialr postion and it might be something you might want to consider. In my opinion the best STA's are clearly the full time STA's that have also been through a hot license class. Some plants use full time STA's where other plants make it a collateral position for their staff engineers.

ScottyUK, I hope this gives you some usefull insight and answers your question.

 

[ScottyUK]

Barry,

More excellent insight. Thanks for taking the time.



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If we learn from our mistakes,
I'm getting a great education!