1. FLEX SUPPORT GUIDELINE TO ISOLATE THE SI ACCUMULATORS
FSG -10
FLEX SUPPORT GUIDELINE TO ISOLATE THE SI ACCUMULATORS
30”
Hello to everybody. This is my first presentation in this forum, and I will talk about ASVAD, a new element which is our simple answer to a serious problem, the nitrogen injection, but before I should start with some short words about myself, and about the presentation itself.
THE IMPORTANCE TO AVOID THE NITROGEN INJECTION TO RCS AND THE SERIOUS DRAWBACKS OF THIS GUIDE TO ACCOMPLISH THIS TASK
by Arnaldo Laborda Rami
CEO of

2. ABOUT THE PRESENTATION
Introduction.
The FSG-10 guide.
The Issues implementing the FSG-10.
The best alternative: The ASVAD safety valve.
Benefits using ASVAD.
Conclusions.
Questions & Answers.
3:09”
I have only twenty minutes to show this presentation, so I’ll try to go faster across the slides. Fortunately this forum is a forum of experts, and I’m sure you don’t need deep explanations to understand the topic. Knowing my limited English skills, I tried to do a self-explanatory presentation, because my spoken words could not be at the level that you deserve. And this document will remain in your mind during more time than my words.
The presentation has six parts. This introduction is the first. At the second part we will know the behavior of the plant in front to a ELAP scenario, and we will focus on the accident evolution and their problems.
During the third part I will talk about the new element ASVAD designed to cope with the nitrogen issue. Fourth part is to describe the ASVAD benefits. And Finally the fifth and sixth part are reserved for the conclusions and the question time. Possibly it will not be enough time to give answers, so could be a good idea to note all your questions and answer it later face to face or by . After the presentation there is a short handout with the main idea of the presentation. You could take it freely.

3. WHY ATTEND THIS PRESENTATION?
After this presentation, we will understand:
The effects of the nitrogen injection to RCS.
The FSG-10 guide.
Their weakness to isolate the accumulators.
The ASVAD alternative and its benefits.
03:50”
Why attend this presentation?... To get answers to these questions: first to understand the Nitrogen Injection Issue. To know what ASVAD is and how it works. And finally To discover their benefits and how it can help us during the ELAP accident.

4. INTRODUCTION 1
During the ELAP accident, it could be a moment when the safety accumulators have to be isolated or vented, to preclude the nitrogen injection to RCS. The PWROG wrote the FSG-10 as a guide to know how to perform this operation.
But this work can have important issues that can challenge their success. This presentation discusses this, and the ASVAD alternative.
ASVAD is a new safety valve specifically designed to automatically perform all the FSG-10 work.
5:00”
Now is time to give a short introduction… and to explain why a simple maintenance engineer like me is doing this kind of presentation. The presence of non-condensable gas into the reactor cooling pipes is not a new topic. There are a lot of studies which talk a lot and deeply about this matter (by example the NEI nine-ten from USA), but from an understanding perspective. I never have noticed that any study that has confronted the issue from a “how-to avoid” perspective (or at least about the nitrogen from the safety accumulators). I do this way, and I have designed the ASVAD valve trying to avoid this nitrogen injection issue.

5. The issue: The nitrogen injection to RCS
During the RCS depressurization after an ELAP accident.
The Containment building is contaminated by the radioactive steam.
During the accident, the AFW turbine can sustain the injection to SG’s to evacuate the heat of the core.
The nitrogen reaches the top of SG’s tubes. Now, the “natural circulation” is stopped. M
Water
The nitrogen comes to the upper part of reactor vessel displacing the water…
The reflux cooling mode begins… but is a less efficient mode and is also disturbed by the nitrogen.
When the water ends, the nitrogen from accumulators enters into the RCS …
Without enough steam to spin the AFW turbine, the injection to SG’s stops.
12:00”
Despite the primary pressure are low now, the leak still continue, and when all the water of accumulators ends, then the nitrogen starts to get into the system. First it goes to the reactor downcomer and the vessel head. But soon it goes to the higher part of the SG tubes. At this point, the nitrogen stops the natural circulation disturbing the refrigeration of the core. Now the reflux mode begins. This interruption of the natural circulation diminishes the amount of the steam in the secondary side, and auxiliary turbine can’t pump more water to SG. I must to note that despite in this slide, there is only one accumulator, this effect is simultaneous in all of the accumulators in the system (it can be three or four accumulators injecting their nitrogen to the reactor)
The RCS “natural circulation” transfers the excess of heat from the core.
If the FLEX Equipment can’t be able to maintain the RCS pressure above the nitrogen pressure, then…
The RCP seals are leaking.

6. THE FSG-10 2
Purpose:
Provides actions to isolate or vent the accumulators to prevent RCS nitrogen injection.
Entry conditions:
Is entered from ECA-0 during a station blackout (SBO or ELAP) to allow SGs to be further depressurized for long-term cooling.
From FSG-8 or FSG-9.
From other plant specific procedures.
06:00”
Now is time to describe the problem… the effects OF NITROGEN INJECTION DURING A ELAP SCENARIO. ELAP is the acronym of Extended Loss of Alternate Current Power.

7. The FSG-10 in Brief Determine when isolation is required.
Determine if isolation valves can be powered from FLEX equipment.
Deploy FLEX equipment to Re-energize Accumulator Discharge Isolation Valves.
Close the Isolation Valve.
Verify the closure of the valve.
Repeat the actions 3, 4 & 5 to each valve.
If not achieved try to vent accumulators.
End of the procedure.
06:00”
Now is time to describe the problem… the effects OF NITROGEN INJECTION DURING A ELAP SCENARIO. ELAP is the acronym of Extended Loss of Alternate Current Power.

8. 3 THE FSG-10 STEPS: STEP 1: Determine when isolation is needed.
If SGs will be depressurized below 290 psig, isolation MUST BE DONE.
Issues: Operators must be watchful with the SGs or RCS pressure evolution. If available, the WR accumulator level will be the best info to be used. The correct moment is just before the accumulator gets empty of water. But this moment is difficult to be know without the proper instrumentation.
06:00”
Now is time to describe the problem… the effects OF NITROGEN INJECTION DURING A ELAP SCENARIO. ELAP is the acronym of Extended Loss of Alternate Current Power.

9. THE FSG-10 STEPS:
STEP 2: Determine if isolation valves can be powered from FLEX equipment.
If not, accumulator venting should be tried. Go to step 7 (plan B).
Issues: A FLEX source of AC power is needed to isolate these valves. Depending of the valve electrical circuitry situation, a heavy and long cable is needed to feed these circuits.
06:00”
Now is time to describe the problem… the effects OF NITROGEN INJECTION DURING A ELAP SCENARIO. ELAP is the acronym of Extended Loss of Alternate Current Power.

10. THE FSG-10 STEPS: STEP 3: Deploy FLEX equipment to Re-energize.
Deploy a cable from the FLEX to the Valve control cabinet. Connect it and energize the circuits. If not achieved, go to Step 7.
Issues: Deploying a heavy and long cable across dark and closed rooms can be very challenging. Correct phase order must be followed. This task can take a lot of time and operator efforts until the connection is ready.
06:00”
Now is time to describe the problem… the effects OF NITROGEN INJECTION DURING A ELAP SCENARIO. ELAP is the acronym of Extended Loss of Alternate Current Power.

11. THE FSG-10 STEPS: STEP 4: Close the Isolation Valve.
Issues: To be able to close the valve, many elements must work properly to achieve it: FLEX generator, electrical circuits and protections, the cabling, the AC motor, torque limiters, limit switches, gears, the valve itself....
If only one element fail, all the operation fails.
In this situation the containment ambient is is harsh, challenging all these elements.
06:00”
Now is time to describe the problem… the effects OF NITROGEN INJECTION DURING A ELAP SCENARIO. ELAP is the acronym of Extended Loss of Alternate Current Power.

12. THE FSG-10 STEPS: STEP 5: Verify the closure of the Valve.
If not achieved, go to Step 7.
Issues: Could be difficult to verify the closure of the valve. The simple indication of the limit switches can not guarantee the full closure. No instrumentation signals can determine it. If the valve remains not fully closed, it will be a slow, but continuous- nitrogen injection to RCS.
06:00”
Now is time to describe the problem… the effects OF NITROGEN INJECTION DURING A ELAP SCENARIO. ELAP is the acronym of Extended Loss of Alternate Current Power.

13. THE FSG-10 STEPS:
STEP 6: Repeat steps 3 to 5 to all the remaining isolation valves.
If achieved, go to Step 8. If not, to Step 7.
Issues: All of these maneuvers must be done AT THE SAME time (in parallel) over all the accumulators. All the accumulator are seeing the same RCS pressure and will be empty of water approx. at the same time. If not, it will be nitrogen injection from the last isolated accumulators.
06:00”
Now is time to describe the problem… the effects OF NITROGEN INJECTION DURING A ELAP SCENARIO. ELAP is the acronym of Extended Loss of Alternate Current Power.

14. THE FSG-10 STEPS:
STEP 7 (plan B):Verify available the motive force for Accumulator Vent Isolation Valves (AVIV).
If not available, go to Step 8.
Issues: If no AC power available, compressed air is less probable to be available. Fully operative pipes must be available also. These valves needs both electric power and air to operate. It is even more challenging to recover these valves than the isolation valves.
06:00”
Now is time to describe the problem… the effects OF NITROGEN INJECTION DURING A ELAP SCENARIO. ELAP is the acronym of Extended Loss of Alternate Current Power.

15. You have burn your options, but the accident still continues!!….
THE FSG-10 STEPS:
You have burn your options, but the accident still continues!!….
And with nitrogen inside…
STEP 8: End of the procedure. No further actions can be taken.
If achieved, good work...you’re lucky heroes!
If not, do not blame yourself. It’s really very difficult to achieve it. Ask your managers why they did not implement the ASVAD safety valve to avoid the nitrogen injection issue.
06:00”
Now is time to describe the problem… the effects OF NITROGEN INJECTION DURING A ELAP SCENARIO. ELAP is the acronym of Extended Loss of Alternate Current Power.

16. THE SIMPLE SOLUTION TO THE NITROGEN INJECTION ISSUE
THE ASVAD 4
THE SIMPLE SOLUTION TO THE NITROGEN INJECTION ISSUE
Automatic
Safety
Valve for
Accumulator
Depressurization
16:30”
OK, we know the nitrogen injection issue and their effects, It’s time to proceed with the third part of the presentation, to know what ASVAD is. ASVAD is the acronym of Automatic Safety Valve for Accumulator Depressurization.

17. HOW ASVAD IS INSTALLED? STANDARD INSTALLATION Accumulator Vessel.
Safety Relief Valve.
Outlet Isolation Valve.
Non-return Valve.
Inlet/Vent Valve.
Manual Isolation Valve.
The ASVAD Valve.
NITROGEN
ASVAD
EXAUST
NITROGEN
18:00”
This valve is installed in the nitrogen side of the accumulators system. This is a simple diagram of the standard accumulators…there are (…..) …. And finally the ASVAD element is installed here.
BORATED WATER M T
RCS

18. HOW ASVAD WORKS?
The ASVAD operating principle is the balance of forces. At normal pressure, there is a force upwards that overcomes the spring force. This force keeps the shut-off plug closed. This is the normal operating position.
During the water injection, the nitrogen expands, and the pressure in the accumulator drops until a certain value is reached. Now, the force of the opening spring is enough to move the shut-off plug off its seat, opening the path from the pressure chamber to the outlet exhaust ports.
Once this happens, the pressure drops quickly in the bottom pressure chamber, and the shut-off plug reaches its full opened state.
This provides an open path to exhaust all the residual nitrogen in the accumulator.
22:00”
Now we will know how ASVAD valve works. Their principle of work is the balance between the force done by the nitrogen pressure in the chamber with the force done by a spring. At normal pressure, their force are greater than the spring force, and the valve remain closed and stable.
When accumulator injection starts, the nitrogen expands and their pressure drops as the water out from the accumulator. When this pressure drops under certain level (the level when the accumulator become empty of water) these pressure is not enough to overcome the spring force, and suddenly the shut-off element open and discharge the residual nitrogen to the atmosphere. Now, It will be remain opened permanently.
This is the main function of the valve… to open and exhaust the nitrogen just at the moment when water ends (or at least near this point).

19. 5 ADVANTAGES OF ASVAD. It does ALL THE WORK of FSG-10 guide.
NO EXTERNAL ENERGY is needed.
NO OPERATOR assistance is required.
Performs its function at the CORRECT MOMENT and over all the accumulators.
ASVAD senses the accumulator internal pressure and decides when the accumulator should be vented.
Once actuated, it vent COMPLETELY the accumulator. No further delayed nitrogen injections are possible.
Their action can be verified by the available instruments (accumulator or containment pressure & temperature).
Operators can FORGET ABOUT Nitrogen Injection Issue, and focus on performing other mitigation tasks.
28:17”
I’m sure that now, most of the audience will guess what are the benefits using this new Element ASVAD. The most important one is that the ASVAD valve doesn’t need ANY external energy to work. It will work despite the ELAP accident. Second benefit is that doesn’t require any human assistance to work, and it will do their action at the correct moment (or to be precise, near this moment). This way the operator will not be burdened with the nitrogen injection issue and they can be focused into other recuperation tasks.
Secondary benefits of the ASVAD valve is that from their simplicity of design. Their installation in the existent systems could be very easy, just adding a isolation valve and few foot of pipe at the “clean side” of accumulators. The rest of benefits are self-explanatory… but I will give a brief explanation of it…

20. MORE ADVANTAGES OF ASVAD.
HIGH RELIABILITY due its robust and simple design.
HARD ENOUGH to bear the post-Loca environment.
EASY TO BE INSTALLED in the accumulator system.
EASY TO BE LICENSED. Not adding a new failure mode to the system.
INTRINSICALLY SAFE. No EMC. No software. Ciber-attack proof 
EASY TO BE QUALFIED. It only need a nuclear class 2 qualification.
EASY TO BE OPERATED. It can be remotely actuated if needed.
EASY TO BE MAINTAINED. No wear in the valve. Easy to be disassembled. Few spares needed.
EASY TO BE TESTED. It just need a functional and a leak test.
EASY TO BE ADJUSTED. To the desired pressure actuation.
HIGH QUALIFIED LIFE. No further investment$ required.
28:17”
I’m sure that now, most of the audience will guess what are the benefits using this new Element ASVAD. The most important one is that the ASVAD valve doesn’t need ANY external energy to work. It will work despite the ELAP accident. Second benefit is that doesn’t require any human assistance to work, and it will do their action at the correct moment (or to be precise, near this moment). This way the operator will not be burdened with the nitrogen injection issue and they can be focused into other recuperation tasks.
Secondary benefits of the ASVAD valve is that from their simplicity of design. Their installation in the existent systems could be very easy, just adding a isolation valve and few foot of pipe at the “clean side” of accumulators. The rest of benefits are self-explanatory… but I will give a brief explanation of it…

21. Why not take advantage of ASVAD to wipe this threat?6
CONCLUSION.
Why not take advantage of ASVAD to wipe this threat?
Now, we know enough about:
The ELAP Nitrogen Injection Issue and its risks.
The FSG-10 Guide and their problems.
The ASVAD safety valve, and how it operates.
The ASVAD advantages & benefits.
29:35”
We talked about the Nitrogen Injection Issue and their risks, about ASVAD and how it works, and their advantages… Now is time to give my final conclusions, but I’m sure that everybody in the auditorium has their own conclusion about ASVAD , and I hope your conclusion are the same like mine… ASVAD is a good Solution to avoid these risks and to enhance the safety of the plant in front to these accidents.
ASVAD is THE BEST SOLUTION to avoid the Nitrogen Injection to RCS. It can help very much to cope with the ELAP accident.

22. More info at www.asvad-nuclear.com7
QUESTIONS?
30:30”
Now is YOUR time to make questions. There is not enough time to answer properly and possibly my English skills could be not enough to do it fluently. Anyway I’ll be pleased to answer all the questions across my address. This address was at the beginning of this presentation. And is easy to remember… ASVAD at ono dot com.
Now is YOUR time to ask...
More info at