MAIN ADVANTAGES

• It is ALL TIME AVAILABLE from the first moment. Always waiting for its moment to act.
  

• It FULLY AVOIDS the nitrogen injection problem.

• NO EXTERNAL POWER is needed. Uses its stored mechanical energy.
  

• NO OPERATOR assistance is required.

• It acts at the CORRECT MOMENT. It acts AUTOMATICALLY sensing the accumulator pressure.

• Once actuated, it COMPLETELY VENTS the accumulator. No further nitrogen injections are possible.

• It will SAVE ORGANIZATION EFFORTS, allowing them to focus on other recovering tasks.

• It ALLOWS TO DEPRESSURIZE THE RCS to lower levels. This WILL FACILITATE a lot the accident recovery.

• STABLE. It will remain fully closed until required. Will not disturb the normal operation.
  

• HIGH RELIABILITY due to its robust and simple design.

• HARD ENOUGH to bear the post-Loca environment. It’s pure Inox steel.
  

• EASY INSTALLATION in the accumulator system. Just need a connection.
  

• EASY LICENSING. Does not add a new failure mode. As any other element in the system.
  

• INTRINSICALLY SAFE. No EMC. No software. Cyber-attack proof. No need to deal with this aspects.
  

• QUALIFIED for nuclear use. It’s a nuclear class 2 valve.

• EASY OPERATION. It can be remotely actuated if needed.
  

• EASY MAINTENANCE. No wear. Few spare parts are needed. With minimal maintenance cost. “Install & Forget”.

• EASY TESTING. It can be functional and leak-tested. No need for complicated testing.
  

• EASY ADJUSTMENT to the desired pressure actuation. Just rotating the obturator.
  

• CHEAP. No expensive modification is needed. Easily affordable.
  

• HIGH QUALIFIED LIFE. No further investment$ will be required. “Buy once, use it Forever”.

Want more details?  Then, continue reading…

SO GOOD !

DETAILED ADVANTAGES

ASVAD will allow depressurizing the core cooling system to lower pressures. This will GREATLY FACILITATE the accident recovery.

• Once the nitrogen injection is completely avoided, the RCS can be depressurized to lower levels. This further depressurization will reduce the cooling leakage rate. This also will facilitate to injecting water at lower pressures, allowing the use of other alternative means (fire piping system, low-pressure pumps …). This can be one of the MAIN ADVANTAGES when installing the valve in the system. Never will be to worry about nitrogen, and the pressure in the RCS can be reduced at lower pressures allowing an easier accident recovery.
• Working at lower pressures will facilitate the emergency equipment operation in more relaxed conditions during the whole accident recovery (the fuel consumption will be lower, the hoses will be subject to lesser efforts, the flow rates will be lesser and will last longer, etc.).
• The further RCS depressurization will also mean that additional systems will be available for recovering the RCS level. A clear example of this is the fire piping system that could also be used in these circumstances. Even other lower-pressure pumps that were available could be used instead.
• It will save the organization’s efforts, allowing the operators to be focused on other recovery tasks. The valve fully avoids the accident complications due to nitrogen injection, unloading the organization from having to manage them.

ASVAD can do ALL THE FSG-10 WORK, automatically and with the highest probability of success.

• The ASVAD valve is permanently installed in the system, and then is available during the whole time to perform its safety function. It does not have inoperability periods.
• There is no need to take any decision about when to isolate or vent the accumulators. ASVAD will do for us sensing the internal pressure in the accumulator. When this pressure will be lower than the setpoint, ASVAD will open and vent the accumulator.
• Once started, it will remain open until the whole accumulator depressurization. It will do the work completely.
• ASVAD can guarantee the entire nitrogen removal, because it fully vents the accumulator. On the contrary, isolating the accumulator by closing the isolation valve cannot guarantee the full avoidance of the nitrogen threat. If the isolation is not perfect, sooner or later it will be nitrogen injection, despite they can be slower. And nothing more can be done to avoid it, than the full venting.
• After the ASVAD actuation, the fast accumulator depressurization can be seen by the pressure instrumentation (if available) despite they can be dis-calibrated by the influence of the harsh environment. It can be seen also in the containment pressure sensors as a little -but fast- rise of the pressure. Another sensor that can detect its actuation could be the containment temperature sensors, seeing the small temperature decrease done by the nitrogen expansion. If the isolation way is used, there is not a clear way to know if the isolation has been successful or not. ASVAD does not have this problem.
• When many elements are involved to do an actuation, the probabilities to fail increase (multiplying) with each new element added. ASVAD is only one element, and very simple. Then it has the highest success probabilities.
• Even if the selected point of their actuation is not the best, their actuation will be the best possible (better than FSG-10!). This point must be selected with the adequate safety margin, to guarantee that all the water will be injected (allowing some nitrogen injection), or on the contrary, to ensure that no nitrogen will be injected (allowing some volume of water loss). In both cases, the nitrogen injection will be limited or avoided. It will not be the whole nitrogen volume (all accumulators) getting inside the RCS pipes.

ASVAD is safe. It does not add any different failure mode to the accumulator system than other installed elements. There are only three ways of fail:

• Failed open. This failure can happen when the valve or its seal loses its mechanical integrity. It is a similar failure as the rest of the elements bearing the accumulator pressure. The result of this failure is the depressurization of the accumulator. This failure cannot be hidden because the pressure of the accumulator is always monitored and alarmed. Is the same way of failure when any other valve in the system fails open, or when a pipe connection fails, or a pipe breaks. Once discovered, it can be easily fixed by closing the manual isolation valve upstream. Other elements, such as the safety pressure relief valve, do not have this isolation possibility. ASVAD failures can be fixed without disturbing the accumulator operability.
• Failed closed. This failure could be due to the spring when it broke, or by the blockage of the shut-off element. It has the same (or less) failure possibilities as any other valve in the system. Could the most similar element can be the previously cited PORV. But in this case, and during normal operation, nothing happens because their default position is closed. It will be discovered when tested (similar to the PORV). If the valve fails, and the ELAP accident comes, then the valve could not open, but this situation is the same as today with no valve installed.
• Failed not fully closed. Or simply when the valve leaks nitrogen. This fail has similar consequences as the fail open, but its evolution will be slower, giving time to maintenance workers to fix it before it becomes a problem. 

We have to note that the ASVAD failure probability is extremely low, because it is a very simple valve with few components. And all its components are made of hard Stainless Steel.

Due to its design and construction, it is intrinsically immune to many of the postulated risks:

• Immune to the containment pressure. It even uses this pressure helping its own operation.
• Very robust against the temperature effects.
• Immune to Radiation.
• Immune to liquids or moisture.
• Immune to accelerations in the X and Y planes. Very robust in the Z plane.
• Immune to Electromagnetic fields. And it does not generate them either.
• Immune to corrosion and chemical attacks. Stainless steel F316.
• Immune to dust and dirt.
• Immune to cyber-attacks (obviously). Without software.
• Immune to electrical discharges or other electrical phenomena.
• Immune to fire and does not contribute as fire load.
• Very robust against projectiles due to its hard and rounded body.
• Does not include materials that can be easily radiologically activated.

ASVAD does not need any external energy to act.

• It is a full passive valve. Its energy is stored in the internal spring as mechanical energy. No electrical energy is needed to its operation.
  
• ASVAD uses a simple and physical principle: The accumulator pressure force versus the inner spring force.
• It will work passively despite the ELAP accident.

ASVAD does not need any human assistance to actuate.

• It is a full automatic valve. It will act ONLY when the accumulator become empty of water. The valve acts simply sensing the accumulator pressure…
• Acts at the correct moment: Not before, because the pressure will keep the valve closed. Not later, because the spring will surpass the pressure force and definitely will open the valve.
• It can be considered as an automatic pressure controller loop with adjustable setpoint capabilities.
• Anyway, even the manual mode operation is also available if desired.

ASVAD will significatively decrease the core damage probability.

• It will give a decrease in the CDF (Core Damage Frequency). By avoiding the nitrogen injection into the RCS, it also avoids its derived complications. The steam generators will not be disabled by the nitrogen, and will remain operative to cool the core.
• As the gas presence in the cooling pipes will be greatly diminished, its adverse effects in the cooling equipment (pumps) will be reduced. Then, the probabilities to suffer events as water hammer, cavitation or become air bound will be diminished.
• Therefore, the core damage probability will be surely reduced. The specific values of this CDF reduction must be calculated specifically by each particular case.

ASVAD can be even safer than other elements installed in the system, because by design, the pressure in the accumulator always tends to maintain the valve closed.

•  While in the accumulator is enough pressure, ASVAD will remain closed and static. It is unable to act until the pressure drops under the actuation level. This means that when ASVAD acts, the injection is in their final phase, there is no water in the accumulator, or at least there is not enough pressure to continue the injection. Then the valve only acts after the accumulator system gets inoperable.
• Its simple and robust design diminishes its failure probabilities. The valve is composed by less than 20 elements, and all these elements are also simple and statics. This simple and robust design, gives to the valve highest reliability.
• Its size and weight can be customized, but it will be small, because it doesn’t need to be bigger than 2” – 3” (the standard design is 1”). The only difference between sizes is its capacity to exhaust the gas in a shorter time. Its small size and weight also means that ASVAD is less sensible and less demanding to the seismic effects.

ASVAD can be easily installed in the accumulator system.

•  It only needs to be connected across a few foot of pipe and a manual isolation valve to one pre-existent penetration in the nitrogen side of the accumulator. It could be in parallel with the PORV. This isolation valve is only to allow doing maintenance without affecting the accumulator.
  
• The range of the system modification can be small or very small.
• Also the fixing elements required can be small, because their limited weight.
• If the remote option (manual operation) is installed, then it could also require a small installation of two electrovalves and their cabling.
• The connection to the system can also be customized to the final user-specific requirements.

The maintenance of ASVAD is easy. It is similar to the standard PORV maintenance.

•  It only needs a functional test to know if the actuation point remains into specifications, and a leak test to guarantee its good closure.
• If the setpoint actuation have to be adjusted, this is also easy to do (in some specified range).
• ASVAD can be easily disassembled into its components for a full inspection. No welding is required.
• The valve is fully static. Then there is no wear in any part of the valve.
• If the remote option (manual operation) is installed, then it can be tested –in some way- during normal operation (opened and closed).
• It only requires the replacement of some o-rings from time to time.
• If the manual isolation valve is installed (and closed), its maintenance can be done even online without disturbing the accumulator.

ASVAD is a robust valve. The quality of their material can guarantee a long life without corrosion or aging problems.

•  ASVAD is designed to work even during the standard LOCA accident. ASVAD is made of hard steel (AISI-316)
  
• Despite it could easily meet the ANSI nuclear class 1 if required; the ASVAD valve is designed to meet nuclear class 2. This valve is not a RCS pressure barrier. Then its requirements can be lower. In fact, it must meet the same specifications of the entire accumulator system.
• The ASVAD valve works installed in the nitrogen side of the accumulator. This side is the “clean” side of the accumulator. This means that this valve will not have boron deposition problems, despite their materials are compatible.
• The pressure chamber which bears the full pressure from the accumulator is relatively small. It can be even smaller if the safety floater option is not included.
• Due to its robustness and long life, the main investment will be only once. No further investments needed. Properly maintained, it can work until the closure of the plant. It can be enough to have only one or two full valve spares in the warehouse to be able to do online maintenance.