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Mitigation of Beyond-Design-Basis-Events, NuScale FSAR Chapter 20, PM-0619-65964, Revision 0
	ML19169A166
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Site:	NuScale
Issue date:	06/14/2019
From:	; NuScale
To:	; Office of New Reactors
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"Mitigation of Beyond-Design-Basis-Events, NuScale FSAR Chapter 20," PM-0619-65964, Revision 0.

NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360-0500 Fax 541.207.3928 www.nuscalepower.com

NuScale Nonproprietary Mitigation of Beyond-Design-Basis Events NuScale FSAR Chapter 20 Nadja Joergen sen Licensing Specialist Elizabeth English Licensing Specialist Chris Maxwell Senior Reactor Operator June 17, 2019 PM-0619-65964 Revision: O Copyright 2019 by NuScale Power, LLC.

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Objective of MBDBE Rule

Establish coping capabilities to prevent damage to fuel in any NPM and the SFP, and to maintain containment function by using plant and mitigating equipment during an extended loss of AC power (ELAP) concurrent with a loss of normal access to the normal heat sink (LUHS).

Key safety functions (core cooling, containment, spent fuel pool cooling) are established and maintained indefinitely, or until sufficient site functional capabilities can be maintained without the need for mitigation strategies.

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Indefinite Coping

" ... indefinitely, or until sufficient site functional capabilities can be maintained without the need for mitigation strategies"

- Means to plan for obtaining sufficient resources to maintain the three key safety functions until an alternate means of removing heat is established

- Allows new reactors to "establish different approaches from those of operating reactors" including using only "installed plant equipment for both the initial and long-term response"

"Alternate means of removing heat" may be provided by installed plant equipment.

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Indefinite Coping

NuScale considers a minimum coping period of 14 days using only installed plant equipment to be sufficient time to establish "alternate means of removing heat."

- In the Fukushima Daiichi accident, without pre-planning or a hardened pool makeup connection, and with limited access to off-site resources, personnel began

adding water to the Unit 4 SFP with fire and concrete pump trucks after 9 days; and

injecting water via the fuel pool cooling system at 14 days.

Beyond minimum installed equipment coping period, the continued use of installed plant equipment, ad hoc resources, and equipment repairs can be used to continue coping indefinitely.

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NuScale Coping Capability 5

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NuScale Power Plant Design

The NuScale Power Plant was designed to provide coping during an ELAP concurrent with a LUHS without:

- AC or DC electrical power

- Inventory addition

- Supplemental equipment

- Off-site resources

- Operator action (monitoring)

Extended coping duration is provided by the automatic response of installed plant equipment alone.

This strategy permits plant staff to focus on addressing the initiating event and restoring normal functional capabilities.

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Baseline Coping Capability Criteria, Conditions, and Assumptions

1. Plant equipme nt that is designed to be robust with respect to design basis external events is assumed to be fully available.

2. Plant equipme nt that is not robust is assumed to be unavailable.

3. Procedures and equipment relied upon should ensure that satisfactory performance of necessary fuel cooling and containment functions are maintained.

4. The fuel in the modules is required to remain covered at all times.

5. The fuel in the SFP is required to remain covered at all times.

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Boundary Conditions

1. Beyond-design-basis external event occurs impacting all modules at the site.

2. All modules on-site initially operating at power, unless site has procedural direction to shut down due to the impending event.

3. Each module is successfully shut down when required (i.e., all rods inserted, no anticipated transient without scram).

4. On-site staff is at site administrative minimum shift staffing, levels.

5. No independent, concurrent events, e.g., no active security threat.

6. All personnel on-site are available to support site response.

7. Spent fuel. in dry storage is outside the scope of the event.

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NuScale Power Plant Response Plant response without operator action or off-site resources!

ECCS initiation SFP level-UHS level - Top of fuel

Reactor trip 45'

DHRS UHS begins initiation to boil and UHS level-

Containment level lowers Weir bottom isolation 24 5 30 50: 4 5 I

hours days days days1 months months Installed plant safety systems

Passive core cooling I I

Passive containment heat removal I I

Passive spent fuel heat removal .1 I "1

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Core Cooling

Reactor coolant system inventory is preserved by containment isolation.

DHRS passively removes decay heat for the first 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months .

The ECCS cools the core for the remainder of an ELAP.

Modules are partially immersed in the reactor pool, which is part of the UHS.

Passive heat removal to the UHS maintains core cooling for more than 50 days without pool inventory makeup or operator action.

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Containment

Containment isolation valves (CIVs) and the CNV provide

, passive containment function. Without operator action or electrical power, the safety-related CIVs close to isolate the CNV.

Heat removal to the UHS passively controls temperature and pressure to ensure containment integrity. Peak pressure and temperature conditions for the CNV occur early in the event when the ECCS valves open and do not challenge containment integrity.

Containment cooling is maintained for more than 50 days without pool inventory makeup or operator action.

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Spent Fuel Pool Cooling

The Spent Fuel Pool is part of the UHS.

The Spent Fuel Pool is partially separated from the Refuel and Reactor Pools by the Weir Wall.

Sp~nt Fuel Pool Refuel Pool Reactor Pool Ultimate ~eat Sink

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Spent Fuel Pool Cooling

The SFP, as part of the UHS, communicates with the refueling pool and reactor pool above the SFP weir wall.

As such, the pools respond as a single volume during an ELAP until UHS level lowers below the opening in the weir wall.

The UHS inventory maintains passive cooling of the spent fuel in the SFP for more than 150 days following initiation of an ELAP without pool inventory makeup or operator action.

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Monitoring

No operator action is required to establish or maintain the required safety functions for more than 50 days following the onset of an ELAP. Therefore, no instrumentation is necessary to support operator actions.

However, instrumentation and DC electrical power are provided to allow the Control Room Operators to observe the response of installed plant equipment and verify the conditions necessary for indefinite coping have been established.

Indications remain available for a minimum of 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months .

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Conclusion

NuScale Power Plant Mitigation Strategy

- Rely on the automatic response of permanently installed, safety-related plant equipment to establish and maintain the three key safety functions and provide extended coping capabilities of greater than 14 days.

The NuScale Power Plant mitigation strategy does not require:

- AC or DC electrical power

- Inventory addition

- Off-site resources

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Portland Office Richland Office 6650 SW Redwood Lane, 1933 Jadwin Ave., Suite 130 Suite 210 Richland, WA 99354 Portland, OR 97224 541. 360. 0500 971.371.1592 Arlington Office Corvallis Office 2300 Clarendon Blvd., Suite 1110 1100 NE Circle Blvd., Suite 200 Arlington, VA 22201 Corvallis, OR 97330 541. 360. 0500 London Office 1st Floor Portland House Rockville Office Bressenden Place 11333 Woodglen Ave., Suite 205 London SW1 E 5BH Rockville, MO 20852 United Kingdom 301. 770.0472 +44 (0) 2079 321700 Charlotte Office 2815 Coliseum Centre Drive, Suite 230 Charlotte, NC 28217 980. 349. 4804 http://wwwnuscalepower. com

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NuScale Power Plant Response

NuScale Power Module response within the first minute of the loss of all AC power and without operator action:

- Reactor trip

- Decay Heat Removal System initiation

- Containment isolation

ECCS automatically initiates after 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months .

With the reactor shutdown and passive decay heat removal established, safe shutdown conditions are established.

Decay heat passively transferred to the UHS.

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NuScale Powe r Plant Response

After more than 5 days, the UHS begins to boil and SFP level begins to lower.

With UHS level greater than or equal to 45', core cooling and the containm ent function are maintained. It requires more than 50 days for UHS level to lower to this point.

Without any addition of inventory, Spent Fuel Pool level would:

- Fall below the UHS weir after more than 4 months.

- Reach the top of spent fuel after more than 5 months.

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NuScale Power Plant Response 80 70

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ML19169A166

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