Information Notice 1988-74, Potentially Inadequate Performance of ECCS in PWRs During Recirculation Operation Following a LOCA

Potentially Inadequate Performance of ECCS in PWRs During Recirculation Operation Following a LOCA
	ML031150118
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, 05000000, Zimmer, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant, Crane
Issue date:	09/14/1988
From:	Rossi C; Office of Nuclear Reactor Regulation
To:	;
References
	IN-88-074, NUDOCS 8809080339
	Download: ML031150118 (8)
	v • d • e

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C.

20555

September 14, 1988

NRC INFORMATION NOTICE NO. 88-74:

POTENTIALLY INADEQUATE PERFORMANCE OF

ECCS IN PWRs DURING RECIRCULATION

OPERATION FOLLOWING A LOCA

Addressees

All holders of operating licenses or construction permits for Westinghouse

(W) and Babcock and Wilcox (B&W)-designed nuclear power reactors.

Purpose

This information notice is being provided to alert addressees to potential

problems that could result in inadequate performance of the emergency core

cooling system (ECCS) during the recirculation phase of operation following

a loss-of-coolant accident (LOCA).

It is expected that recipients will review

the information for applicability to their facilities and consider actions, as

appropriate, to avoid similar problems. However, suggestions contained in

this information notice do not constitute NRC requirements; therefore, no

specific action or written response is required.

Description of Circumstances

The NRC has received two licensee event reports on potential deficiencies in

performance of the ECCS during the recirculation phase of operation following.

a small-break LOCA. These events were reported by the licensees of the Oconee

and Turkey Point facilities after engineering analysis for each facility had

identified the potential problems.

Oconee Nuclear Station

During a technical review of nuclear safety-related mechanical calculations, the licensee discovered that the design analysis had not been adequately per- formed for the recirculation phase of operation following a small-break LOCA.

Subsequent engineering analysis indicated the following design deficiencies:

(1) Under certain small-break LOCA scenarios, when the borated water storage

tank (BWST) is depleted and the reactor coolant system (RCS) pressure

remains high (greater than the low-pressure injection (LPI) pump shut- off head), a piggyback-type operation is required to ensure core cooling.

This operation entails taking suction from the reactor building sump, through the LPI pumps, through the high-pressure injection (HPI) pumps,

880900339c

IN 88-74 September 14, 1988 and then to the RCS. However, because of (1) the high flow resistance

in the cross-connect piping between the HPI and LPI pumps, (2) the

potential for partially closed LPI discharge throttle valves, and (3)

the high flow rate downstream of the LPI pumps, there may not have been

adequate net positive suction head (NPSH) at the suction inlets of the

HPI pumps.

Inadequate NPSH would render the HPI system inoperable.

The

high flow rate would have occurred when the reactor building spray pumps

and HPI pumps take suction simultaneously from the LPI pump discharge.

The licensee has corrected the problem by revising the operating pro- cedures to provide guidance for maintaining adequate NPSH to the HPI

pumps operating in the piggyback mode.

The revised procedures provide

for (1) HPI flow limitations when the HPI and reactor building spray

pumps are piggybacked off the LPI pumps, (2) precautions on the use of

reactor building spray, and (3) precautions on the throttling of the

LPI discharge valves LP-12 and LP-14. (A simplified Oconee ECCS and

reactor building spray system are shown in Attachment 1.)

(2) A single failure of the "TD" ECCS switchgear during loss of offsite power

would have prevented the remote alignment of the LPI system to the HPI

system in the piggyback mode because (1) valves LP-9, LP-15, and LPI

pump B are powered by ECCS switchgear bus "TDV but their backup power

supplies are classified as load shed power supplies,'and (2) valves

LP-9.and LP-15 were in the normally closed position.

The licensee has corrected the problem by (1) changing valve LP-9 to a

normally open position so that it will not be required to operate when

the LPI system is being aligned with the HPI system in the piggyback mode

of operation, and (2) revising the emergency operating procedure to ensure

time is available for operators to locally, manually open valves LP-15 and

LP-16 (if the valves cannot be opened remotely) before LPI suction must be

swapped from the BWST to the reactor building sump.

Turkey Point Nuclear Station

As part of its ongoing design-basis reconstitution program, the licensee dis- covered a condition of potentially inadequate NPSH for the containment spray

and safety injection (SI) pumps during the recirculation mode of operation

following a LOCA.

Under these conditions, the low head residual heat removal

(RHR) pumps are providing flow to the containment spray pumps and the SI pumps.

A throttle valve in each RHR discharge line is normally throttled to 30 percent.

However, an analysis to support this valve throttling position had not been

performed. To resolve this discrepancy, the subject valves were locked in the

fully open, position until an engineering evaluation showed that the original

configuration (30 percent open) was acceptable.

IN 88-74 September 14, 1988 Discussion:

Following a small-break LOCA, the piggyback mode of operation may be required

(depending on the size and location of the break) to sustain injection flow

when the BWST (B&W plant) or refueling water storage tank (Westinghouse plant)

has been depleted and RCS pressure remains above the shutoff head of the low

head pumps.

As previously described, two mechanisms could prevent this in- tendeo piggyback mode from operating:

(1) insufficient MPSH at HPI (or SI)

pump suction inlets, or (2) inadequate operating procedures combined with

system design deficiencies for a loss-of-offsite-power condition. Although

the low head pumps provide relatively high discharge pressure, the intervening

cross-connect piping between the high head and low head systems and/or partially

closed low head pump discharge valves could result in excessive hydraulic

resistance and cause insufficient NPSH at the HPI (or SI) pump suction inlets.

Insufficient NPSH could also be caused by running multiple pumps off the dis- charge of a single pump that may increase the flow above the design flow rate

and consequently reduce the available pressure at the low head pump discharge.

These are safety concerns because of the reliance on HPI (or SI) for mitigating

small-break LOCAs, and in some cases, the piggyback-type operation is used for

hot leg recirculation even for large-break LOCAs.

There are no redundant systems to perform the function of the HPI (or SI) system

in the piggyback mode.

Although the reactor vessel high-point vents and the

power-operated relief valve(s) could be used to depressurize the RCS to low

head pump operating pressures, the related safety analysis had never been

performed -- thus, their effectiveness was not ensured.

No specific action or written response is required by this information notice.

If you have any questions about this matter, please contact one of the technical

contacts listed below or the Regional Administrator of the appropriate regional

office.

ar esI

E. ossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts: S. Israel, AEOD

(301) 492-4437

J. Thompson, NRR

(301) 492-1175 P. Wen, NRR

(301) 492-1172 Attachments:

1.

Figure 1, Simplified Oconee Emergency Core Cooling

and Reactor Building Spray Systems

2. List of Recently Issued NRC Information Notices

Figure 1 Simplified Oconee Emergency Core Cooling

and Reactor Building Spray Systems

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Attachment 2

IN 88-74

September 14, 1988 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information

Date of

Notice No.

Subject

Issuance

Issued to

88-73

88-72

88-71 Direction-Dependent Leak

Characteristics of

Containment Purge Valves

Inadequacies in the Design

of dc Motor-Operated Valves

Possible Environmental

Effect of the Reentry

of COSMOS 1900 and

Request for Collection

of Licensee Radioactivity

Measurements Attributed

to That Event

Check Vdlve Inservice

Testing Program

Deficiencies

Movable Contact Finger

Binding in HFA Relays

Manufactured by General

Electric (GE)

9/8/88

9/2/88

9/1/88

8/29/88

8/19/88

All holders of OLs

or CPs for nuclear

power reactors.

All holders of OLs

or CPs for nuclear

power reactors.

All holders of OLs

or CPs for nuclear

power reactors, fuel

cycle licensees, and Priority 1 material licensees.

All holders of OLs

or CPs for nuclear

power reactors.

All holders of OLs

or CPs for nuclear

power reactors.

88-70

88-69

88-48,

Supplement 1

Licensee Report of Defective

Refurbished Valves

8/24/88

All holders of OLs

or CPs for nuclear

power reactors.

88-68

88-67

88-66 Setpoint Testing of Pres- surizer Safety Valves with

Filled Loop Seals Using

Hydraulic Assist Devices

PWR Auxiliary Feedwater Pump

Turbine Overspeed Trip

Failure

Industrial Radiography

Inspection and Enforcement

8/22/88

All holders of OLs

or CPs for nuclear

power reactors.

All holders of OLs

or CPs for nuclear

power reactors.

All NRC industrial

radiography licensees.

OL = Operating License

CP = Construction Permit

IN 88-74 September 14, 1988 Discussion:

Following a small-break LOCA, the piggyback mode of operation may be required

(depending on the size and location of the break) to sustain injection flow

when the BWST (B&W plant) or refueling water storage tank (Westinghouse plant)

has been depleted and RCS pressure remains above the shutoff head of the low

head pumps. As previously described, two mechanisms could prevent this in- tended piggyback mode from operating:

(1) insufficient NPSH at HPI (or SI)