Nuclear Reactor Cooling System

Questions and Answers

What is the design pressure that satisfies the commitment for the RNS?

800 psig

1000 psig

900 psig (correct)

1100 psig

During which operations does the RNS provide LTOP for the RCS?

Only during refueling operations

During refueling, startup, and shutdown operations (correct)

Only during startup and shutdown operations

Only during normal operation

What is the purpose of the IRWST Gravity Injection to RCS Hot-Leg thru RNS Suction function?

To reduce the RCS pressure

To provide makeup to the RCS hot leg during cold shutdown and refueling conditions (correct)

To increase the RCS temperature

To bypass the RNS during emergency situations

What is the benefit of using the RNS to cool the RCS following an MSLB?

It prevents continued secondary coolant steaming Signup and view all the answers

At what temperature does the release of airborne radionuclides cease after an MSLB?

Below boiling conditions Signup and view all the answers

What is the role of the RNS in plant recovery following an accident?

It provides closed-loop heat removal Signup and view all the answers

What is the primary purpose of the RNS system?

To remove decay heat from the RCS during normal operation Signup and view all the answers

Which of the following is a safety-related function of the RNS system?

CTMT Isolation Signup and view all the answers

Which valve is NOT part of the RCS pressure boundary isolation function?

RNS-V080 IRWST Suct Vent Signup and view all the answers

What is the purpose of the flow path available via the test connection in the discharge CTMT penetration?

To provide a flow path for the long-term CTMT-inventory makeup/ultimate removal Signup and view all the answers

What is the design consideration for the RNS piping and components outside containment?

To minimize the probability of containment bypass Signup and view all the answers

What is the function provided by the 2 parallel paths, each containing 2 MOVs in series in the RNS pump suction piping?

RCS pressure boundary isolation Signup and view all the answers

Which of the following is NOT a non-safety related function of the RNS system?

CTMT inventory makeup/ultimate removal Signup and view all the answers

What is the operating pressure of the RCS that the RNS piping and components are designed to withstand?

2235 psig Signup and view all the answers

Study Notes

Purpose and Functions

The Reactor Natural circulation System (RNS) is an active, non-safety decay heat removal system.
It is used under normal conditions when the Steam Generator System (SGS) and Main Steam System (MSS) are ineffective.
During accident conditions, it supplements the Passive Exothermic System (PXS).
RNS provides cooling to the Reactor Coolant System (RCS) at reduced temperature and pressure conditions after shutdown.
It also cools the In-containment Refueling Water Storage Tank (IRWST) during normal plant conditions.

CTMT Isolation

RNS provides CTMT isolation for the RNS piping that penetrates the Containment Thermal Treatment Module (CTMT) barrier.
Outside CTMT, valves RNS-V011, RNS-V012, and RNS-V022 provide isolation.
Inside CTMT, valves RNS-V002A/B, RNS-V013, RNS-V020, RNS-V021, RNS-V023, and RNS-V061 provide isolation.

RCS Pressure Boundary Isolation

RNS provides a RCS boundary at the RNS suction and discharge interface with the RCS.
This function is provided by two parallel paths, each containing two Motor-Operated Valves (MOV) in series in the RNS pump suction piping and two parallel paths each containing a stop-check valve and a check valve in series in the pump discharge piping.
RCS pressure boundary valves include RNS-V001A/B, RNS-V002A/B, RNS-V015A/B, and RNS-V017A/B.

CTMT Inventory M/U

RNS provides a flow path for long-term CTMT-inventory makeup/removal in case of design-basis leakage from CTMT after a Loss-of-Coolant Accident (LOCA).
This flow path is available via the test connection in the discharge CTMT penetration, which is normally locked-closed and plug-capped.

Interfacing System LOCA

The RNS piping and components are designed to have an ultimate rupture strength not less than the RCS operating pressure (2235 psig), with a design pressure of 900 psig.

LTOP and IRWST Gravity Injection

RNS provides Low-Temperature Overpressure Protection (LTOP) for the RCS during refueling, startup, and shutdown operations.
It also provides an alternate gravity-injection path through RNS-V023 to provide makeup to the RCS hot leg during cold shutdown and refueling conditions.

RCS Cooldown and Shutdown/Post-Accident Heat Removal

Following a Main Steam Line Break (MSLB), RNS can be used to reduce the RCS temperature below boiling conditions within 72 hours after reactor shutdown.
It provides closed-loop heat removal from the core and the RCS during shutdown operations to achieve plant recovery following successful mitigation of an accident.