Information Notice 1996-05, Partial Bypass of Shutdown Cooling Flow from Reactor Vessel

Partial Bypass of Shutdown Cooling Flow from Reactor Vessel

ML031210502
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, Three Mile Island, 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, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	01/18/1996
From:	Crutchfield D Office of Nuclear Reactor Regulation
To:
References
IN-96-005, NUDOCS 9601110058
Download: ML031210502 (9)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 January 18, 1996 NRC INFORMATION NOTICE 96-05: PARTIAL BYPASS OF SHUTDOWN COOLING FLOW FROM

THE REACTOR VESSEL

Addressees

All holders of operating licenses or construction permits for boiling water

reactors.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information

notice to alert addressees to potential problems associated with monitoring

reactor coolant temperature while operating in the shutdown cooling mode of

the residual heat removal system. 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 are not NRC requirements; therefore, no specific

action or written response is required.

Description of Circumstances

On July 8-9, 1995, partial bypass of shutdown cooling flow from the reactor

vessel occurred at the Hope Creek Nuclear Station. With residual heat removal

pump B running, the recirculation pump discharge valves for both A and B

recirculation loops were .,roedd to prevent thermal binding (Figure 1, which

for clarity shows only recirculation and residual heat removal loops B).

However, the A discharge valve still became thermally bound. To prevent the B

discharge valve from thermally binding, the licensee partially opened the B

discharge valve. Because recirculation pump discharge valve B was open, some

of the shutdown cooling flow bypassed the reactor vessel and went through

recirculation loop B. This reduced shutdown cooling flow through the core and

increased core temperature until boiling occurred and the reactor vessel

started to pressurize. Plant operators were unaware of the heatup because the

bypass flow caused indicated water temperature, measured at the inlet to the

residual heat removal heat exchanger, to be less than the unmeasured reactor

vessel exit water temperature at the recirculation outlet nozzle. The

temperature of water exiting the reactor vessel is normally lower than the

core exit temperature at the top of the active fuel due to internal bypass

flows. The reduced shutdown cooling flow exacerbated this condition. Two

transitions from cold to hot shutdown occurred without being recognized by the

operating crew. The event was terminated when the licensee closed

recirculation pump discharge valve B and restarted residual heat removal

pump B.

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IN 96-05 January 18, 1996 Discussion

To prevent thermal binding during plant cooldowns, Hope Creek operating

procedures specified that the recirculation pump discharge valves be

alternately opened and closed. When the recirculation pump discharge valve is

stroked open and then closed in a short time, the effect on shutdown cooling

is negligible. During this event, however, plant operators deviated from the

operating procedure and left the recirculation pump discharge valve partially

open. As a result, part of the shutdown cooling flow was diverted away from

the reactor vessel, significantly reducing core flow. After this event, the

licensee decided not to stroke the recirculation pump discharge valves and

removed this step from the operating procedures.

The reactor vessel level during shutdown operation is important in maintaining

cold shutdown conditions. Hope Creek operating procedures specified that

reactor vessel water level be maintained about 4.6 m [15 ft] above the top of

the active fuel, a level corresponding to the water spillover elevation in the

steam separators. The significant flow reduction through the core allowed the

coolant in the core region to heat up and the reactor vessel to pressurize.

The licensee later determined that reactor vessel level should be maintained

above the elevation of the steam separator spillover point to ensure adequate

core cooling during shutdown conditions. Maintaining this level would allow

natural circulation within the reactor vessel if the shutdown cooling system

was not available. The licensee revised the operating procedures to specify

that reactor vessel water level be maintained above the bottom of the

predryers on the steam separators, about 6.1 m [20 ft] above the top of the

active fuel, during cold shutdown operation.

Valid core outlet temperature information was not available during most of

this event. During the event, the residual heat removal system pumps were

stopped some of the time for surveillance testing of the residual heat removal

system valves. During such times. measurements were not available to indicate

the temperature of water exiting from the reactor vessel, normally taken as

the temperature of water at the residual heat exchanger. At other times, the

bypass flow through the open recirculation pump discharge valve caused the

measured water temperature to be lower than the temperature of water exiting

the reactor vessel. Finally, significant bypass flow via inactive jet pumps

inside the reactor vessel meant that the temperatue of water exiting the

reactor vessel was not representative of the temperature of water exiting the

core. (The last is true even during normal shutdown operation unless all jet

pumps are active.) Other temperature indications, such as the reactor vessel

metal and reactor water cleanup system inlet temperature, do not represent

water temperature exiting the core. As a consequence, water in the core

apparently reached saturation temperature faster than anticipated when the

residual heat removal system pumps were stopped because the core was initially

hotter than shown by available instrumentation. At times when a residual heat

removal pump was running, the jet pump bypass flows led to a temperature

indication lower than the core exit temperature. Both situations led to

unanticipated and initially unrecognized pressurization.

IN 96-05 January 18, 1996 The licensee revised operating procedures to provide additional guidance for

monitoring reactor vessel pressure and vessel metal temperature when the

shutdown cooling system is not in service. This guidance includes considering

pressurization of the reactor vessel as a transition to the hot shutdown

condition.

Related Generic Communication

Information Notice 93-45, "Degradation of Shutdown Cooling System

Performance," June 16, 1993 This information notice requires no specific action or written response. If

you have any questions about the information in this notice, please contact

one of the technical contacts listed below or the appropriate Office of

Nuclear Reactor Regulation (NRR) project manager.

-ennis M. Cru c ele Director

Division of Reactor rogram Management

Office of Nuclear Reactor Regulation

Technical contacts: Robert Summers, Region I

(609) 935-5373 Internet:rjs@nrc.gov

Scott Morris, Region I

(609) 935-5373 Internet:saml@nrc.gov

C. Vernon Hodge, NRR

(301) 415-1861 Internet:cvh~nrc.gov

Attachments:

1. Figure 1. Hope Creek Shutdown Cooling System with Open

Recirculation Pump Discharge Valve

2. List of Recently Issued NRC Information Notices

9'VL

Attachment 1

. my JN 96-05 January 18, 1996 RHR Pump

Shutdown Cooling System

(1 of 2 Loops)

Figure 1 Hope Creek Shutdown Cooling System wtth Open Recirculation Pump Discharge Valve

Attachment 2 IN 96-05 January 18, 1996 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

96-04 Incident Reporting Require- All radiography licensees

ments for Radiography and manufacturers of radio- Licensees graphy equipment

96-03 Main Steam Safety Valve 01/05/96 All holders of OLs or CPs

Setpoint Variation as a for nuclear power reactors

Result of Thermal Effects

96-02 Inoperability of Power- 01/05/96 All holders of OLs or CPs

Operated Relief Valves for PWRs

Masked by Downstream

Indications During Testing

96-01 Potential for High Post- 01/03/96 All holders of OLs or CPs

Accident Closed-Cycle for PWRs

Cooling Water Temperatures

to Disable Equipment

Important to Safety

95-58 10 CFR 34.20; Final 12/18/95 Industrial Radiography

Effective Date Licensees

95-57 Risk Impact Study Regarding 12/18/95 All holders of OLs or CPs

Maintenance uurinsy Low-Power for nuclear power reactors.

Operation and Shutdown

95-56 Shielding Deficiency in 12/11/95 All holders of OLs or CPs

Spent Fuel Transfer Canal for nuclear power reactors.

at a Boiling-Water Reactor

OL = Operating License

CP = Construction Permit

IN 96-05 January 18, 1996 The licensee revised operating procedures to provide additional guidance for

monitoring reactor vessel pressure and vessel metal temperature when the

shutdown cooling system is not in service. This guidance includes considering

pressurization of the reactor vessel as a transition to the hot shutdown

condition.

Related Generic Communication

Information Notice 93-45, "Degradation of Shutdown Cooling System

Performance," June 16, 1993 This information notice requires no specific action or written response. If

you have any questions about the information in this notice, please contact

one of the technical contacts listed below or the appropriate Office of

Nuclear Reactor Regulation (NRR) project manager.

original signed by

Dennis M. Crutchfield, Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Robert Summers, Region I

(609) 935-5373 Internet:rjs@nrc.gov

Scott Morris, Region I

(609) 935-5373 Internet:samlnrc.gov

C. Vernon Hodge, NRR

(301) 415-1861 Internet:cvh@nrc.gov

Attachments:

1. Figure 1. Hope Creek Shutdown Cooling System with Open

Recirculation Pump Discharge Valve

2. List of Recently Issued NRC Information Notices

DOCUMENT NAME: 96-05.IN

• See Previous Concurrence Tech Editor Reviewed 11/14/95 To receive a copy of this document, Indicate In the box: 'C" - Copy without enclosures _No

E" - Copy with enclosures copy -

OFFICE PECB/DRPM I D:DSSA I C:PECB/DRPM I D:D M -I

NAME CVHodge* JTWiggins* AEChaffee* DM eld

DATE 11/20/95 12/11/95 12/14/95 01/ y/96 OFFICIAL RECORD COPY

This document was made available to the Hope Creek project manager 112095, the Hope Creek

resident inspector, the document control desk, and the public document room 112095.

IN 95-XX

December xx, 1995 The licensee revised operating procedures to provide additional guidance for

monitoring reactor vessel pressure and vessel metal temperature when the

shutdown cooling system is not in service. This guidance includes considering

any future pressurization of the reactor vessel as a transition to the hot

shutdown condition.

Related Generic Communication

Information Notice 93-45, "Degradation of Shutdown Cooling System

Performance," June 16, 1993 This information notice requires no specific action or written response. If

you have any questions about the information in this notice, please contact

one of the technical contacts listed below or the appropriate Office of

Nuclear Reactor Regulation (NRR) project manager.

Dennis M. Crutchfield, Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Robert Summers, Region I

(609) 935-5373 Scott Morris, Region I

(609) 935-5373 Vern Hodge, NRR

(301) 415-1861 Attachments:

1. Figure 1. Hope Creek Shutdown Cooling System with Open

Recirculation Pump Discharge Valve

2. List of Recently Issued NRC Information Notices

DOCUMENT NAME: G:\VERN\HOPBYPAS.INF

• See Previous Concurrence

l*PECB/DRPM *REGI/D:DRS *D:DSSA l C:P[ BDRPM D:DRPM

CVHodge JTWiggins GMHolahan AEANffee DMCrutchfield

12/20/95 11/20/95 112/11/95 I1J/A4/95\ JS 11/ /95 .M4494 This dncument was made available to the Hope Creek project manager 112(095, the

Hope Creek resident inspector, the document control desk, and the public

document room 112095.

Information Notice 95-XX The licensee revised operating procedures to provide additional guidance for

monitoring reactor vessel pressure and vessel metal temperature when the

shutdown cooling system is not in service. This guidance includes considering

any future pressurization of the reactor vessel as a transition to the hot

shutdown condition.

Related Generic Communication

Information Notice 93-45, "Degradation of Shutdown Cooling System

Performance,' June 16, 1993 This information notice requires no specific action or written response. If

you have any questions about the information in this notice, please contact

one of the technical contacts listed below or the appropriate Office of

Nuclear Reactor Regulation (NRR) project manager.

Dennis M. Crutchfield, Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Robert Summers, Region I

(609) 935-5373 Scott Morris, Region I

(609) 935-5373 Vern Hodge, NRR

(301) 415-1861 Attachments: 1. Figure 1. Hope Creek Shutdown Cooling System with Open

Recirculation Pump Discharge Valve

2. List of Recently Issued NRC Information Notices

• See Previous Concurrence xA\

_*PECB/DRP *REGI/D:DRS *D:DSSA C.PECB/DRPM D:DRPM

CVHodge JTWiggins GMHolahan AEChaffee DMCrutchfield

12/12/95 -11/20/95 112/11/95 11/ /95 11/ /95 This document was made available to the Hope Creek project manager 112C195, the

Hope Creek resident inspector, the document control desk, and the public

document room 112095.

doc: g:\vern\hopbypas.inf

/

Information Notice 95-XX The licensee revised operating procedures to provide additional guidance for

monitoring reactor vessel pressure and vessel metal temperature when the

shutdown cooling system is not in service. This guidance includes considering

any future pressurization of the reactor vessel as a transition to the hot

shutdown condition.

Related Generic Communications

1. Generic Letter 95-07, Pressure Locking and Thermal Binding of Safety- Related Power-Operated Gate Valves," August 17, 1995

2. Information Notice 93-45, Degradation of Shutdown Cooling System

Performance, June 16, 1993 This information notice requires no specific action or written response. If

you have any questions about the information in this notice, please contact

one of the technical contacts listed below or the appropriate Office of

Nuclear Reactor Regulation (NRR) project manager.

Dennis M. Crutchfield, Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Robert Summers, Region I

(609) 935-5373 Scott Morris, Region I

(609) 935-5373 Vern Hodge, NRR

(301) 415-1861 Attachments: 1. Figure 1. Hope Creek Shutdown Cooling System with Open

Recirculation Pump Discharge Valve

2. List of Recently Issued NRC Information Notices

• See Previous Concurrence

PECB/DRPIAfRE% /D-DRS lD:DSSA \ C:PECB/DRPM [D:DRPM

CVHodge JTWiggins GMHolahan / AEChaffee DMCrutchfield

11a/95 11/0/95 95 j

11/ /95 11/ /95 This document was made available to the Hope Creek project manager 112095, the

Hope Creek resident inspector, the document control desk, and the public

document room 112095.

doc: g:\vern\hopbypas.inf