FSG -10FLEX SUPPORT GUIDELINE TO

ISOLATE THE SI ACCUMULATORS

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 www.asvad-nuclear.com

ABOUT THE PRESENTATION

1. Introduction.

2. The FSG-10 guide.

3. The Issues implementing the FSG-10.

4. The best alternative: The ASVAD safety valve.

5. Benefits using ASVAD.

6. Conclusions.

7. Questions & Answers.

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.

WHY ATTEND THIS PRESENTATION?

INTRODUCTION

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.

1

M

The issue: The nitrogen injection to RCS

During the RCS depressurization after an ELAP accident.

The RCP seals are leaking.

Water

Without enough steam to spin the AFW turbine, the injection to SG’s stops.

The nitrogen comes to the upper part of

reactor vessel displacing the

water…

When the water ends, the nitrogen from

accumulators enters into the RCS …

The reflux cooling mode begins… but is a less

efficient mode and is also disturbed by the nitrogen.

The nitrogen reaches the top of SG’s tubes.

Now, the “natural circulation” is stopped.

If the FLEX Equipment can’t be able to maintain the RCS pressure above the nitrogen

pressure, then…

The RCS “natural circulation” transfers

the excess of heat from the core.

During the accident, the AFW turbine can sustain the injection to SG’s to evacuate the heat of the

core.

The Containment building is

contaminated by the radioactive steam.

THE FSG-10

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.

2

The FSG-10 in Brief

1. Determine when isolation is required.

2. Determine if isolation valves can be powered from FLEX equipment.

3. Deploy FLEX equipment to Re-energize Accumulator Discharge Isolation Valves.

4. Close the Isolation Valve.

5. Verify the closure of the valve.

6. Repeat the actions 3, 4 & 5 to each valve.

7. If not achieved try to vent accumulators.

8. End of the procedure.

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.

3

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.

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.

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.

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.

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.

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.

THE FSG-10 STEPS:

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.

You have burn your options, but the accident

still continues!!….

And with nitrogen inside…

THE ASVAD

THE SIMPLE SOLUTION TO THE NITROGEN INJECTION ISSUE

AutomaticSafetyValve forAccumulatorDepressurization

4

HOW ASVAD IS INSTALLED?

RCS

M

NITROGEN

NITROGEN

T

ASVAD

BORATED WATER

EXAUST

STANDARD INSTALLATION

Accumulator Vessel.Safety Relief Valve.Outlet Isolation Valve.Non-return Valve.Inlet/Vent Valve.Manual Isolation Valve.The ASVAD Valve.

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.

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.

5

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.

CONCLUSION.

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.

ASVAD is THE BEST SOLUTION to avoid the

Nitrogen Injection to RCS. It can help very much to

cope with the ELAP accident.

6Why not take advantage of ASVAD to wipe this

threat?

QUESTIONS?

More info at www.asvad-nuclear.comNow is YOUR time to ask...

7