Information Notice 1998-40, Design Deficiencies Can Lead to Reduced ECCS Pump Net Positive Suction Head During Design-Basis Accidents

Design Deficiencies Can Lead to Reduced ECCS Pump Net Positive Suction Head During Design-Basis Accidents
	ML031040547
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:	10/26/1998
From:	Roe J; Office of Nuclear Reactor Regulation
To:	;
References
	IN-98-040, NUDOCS 9810210103
	Download: ML031040547 (9)
	v • d • e

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555-0001

October 26, 1998

NRC INFORMATION NOTICE 98-40: DESIGN DEFICIENCIES CAN LEAD TO

REDUCED ECCS PUMP NET POSITIVE

SUCTION HEAD DURING DESIGN-BASIS

ACCIDENTS

Addressees

All holders of operating licenses for nuclear power reactors, except those licensees who have

permanently ceased operations and have certified that fuel has been permanently removed

from the vessel.

Purpose

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

addressees to the fact that Incorrect level instrument setpoints or other control deficiencies can

render emergency core cooling system (ECCS) pumps inoperable during certain design-basis

accidents. 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

Oconee Nuclear Station

In late 1997, during a self-assessment audit of the high pressure injection (HPI) and low

pressure Injection (LPI) systems, the licensee noted that the design drawing for the borated

water storage tank (BWST) did not have a zero reference point. Subsequently, the licensee's

engineering staff determined that an elevation difference between the level transmitters and the

Instrument taps for the BWSTs of all three Oconee units had resulted in up to an 18-inch non- conservative error between Indicated and actual BWST level. The difference was caused by a

failure to compensate for instrument tap height when calibrating the BWST level Instruments.

At plant construction, the magnitude of the error was approximately 4 Inches, but the error

increased to approximately 18 inches following modifications In 1989 that replaced the BWST

level transmitters. In addition, on February 19, 1998, the licensee's engineering staff

determined that the emergency operating procedures (EOPS) did not adequately account for

uncertainty in the reactor building emergency sump (RBES) wide-range level instruments, IB

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IN 98-40

October 26, 1998 which could have resulted In the Instruments reading up to 18 inches lower than the actual

level. The RBES level instrument uncertainties were caused by inadequate design analysis.

This was discussed In Inspection Report 50 50-269, 270, 287/98-12 and Licensee Event Report

(LER) 50-269/98-04, Revision 1.

St. Lucie Nuclear Plant

During the Unit 1 steam generator replacement outage in 1997, the licensee replaced the

engineered safety features actuation system (ESFAS) bistables. A system engineer later

determined that the ESFAS recirculation actuation setpoint (RAS) bistable setpoint for the

Refueling Water Tank (RWT) level was Incorrect. An Investigation of the discrepancy found

that, during a setpoint calculation enhancement effort In 1993, a new calculation was created, which changed the span of the RWT level measurement and indication Instrumentation loop.

This calculation produced a new setpoint for the RWT level by revising the measurement span

to indicate the actual tank level bottom as "0 feet'. Previously, the measurement span indicated

0 at the 1-foot level where the RWT level instrument tap is located. The new setpoint

information was not incorporated Into the procedure used to calibrate the ESFAS bistables, resulting in a RAS setpoint of 3 feet from the tank bottom instead of 4 feet required by

Technical Specifications. This was discussed In Inspection Report 50-335, 389/97-16 and LER

50-335197-11.

H.B. Robinson Nuclear Plant

Between April 7 and May 23, 1997, NRC conducted a design Inspection at Robinson and raised

several Refueling Water Storage Tank (RWST) instrumentation related Issues that Impacted

ECCS components. Plant Emergency Operating Procedures (EOPs) directed all ECCS pumps, except one safety injection (SI) pump and one containment spray (CS) pump, to be stopped

when the RWST level reached 27 percent The remaining SI and CS pumps were directed to

be stopped when the RWST level reached 9 percent. The plant evaluated and modified the

number of SI pumps starting following a LOCA. The modification resulted in two (as opposed to

three) SI pumps starting following a LOCA. With two SI pumps getting a start signal, and

assuming a single active failure of one SI pump, the NPSH requirement for the running SI pump

was higher, and this higher NPSH requirement was not considered in the modification. A

calculation to determine the level at which vortexing became a concern had not been performed

prior to the modification. The licensee regained the margin by reducing instrument

uncertainties and by raising the water level In the RWST.

The NRC design team also found that the containment sump level setpolnts utilized channel

uncertainty for normal environmental conditions rather than the adverse conditions that could

exist in the containment after an accident. This had the potential for adversely affecting

residual heat removal (RHR) pumps In the recirculation mode of operation. These Items were

discussed in Inspection Report 50-261/97-201 and LER 50-261/97-08.

Discussion

In the Oconee Nuclear Station's Final Safety Analysis Report (Sections 6.2 and 6.3), the

licensee states that during certain loss-of-coolant accidents, reactor operators must be capable

of manually providing a flowpath from either the BWST or the RBES to the HPI, LPI and reactor

IN 98-40

October 26, 1998 building spray (RBS) pumps. The errors described above created a conflict between the

BWST and RBES levels specified in the EOPs and the BWST and RBES levels Indicated in the

control room. As a result, during certain design-basis accident scenarios, Including small-break

LOCAs, the level errors could have delayed swapover initiation. This could have caused

vortexing in the BWST or reduced NPSH to the ECCS pumps, or both.

The design basis of the St. Lucie facility requires that during certain LOCAs, ECCS subsystems

must be capable of automatically transferring suction to the containment sump on receipt of a

RAS. Because of the incorrect trip setpoint of the RWT level instrument bistables, automatic

transfer of the ECCS pumps' suction source from the RWT to the containment sump, under

certain conditions, would cause an open-channel flow condition. Without operator intervention

to initiate manual transfer to the containment sump before the open-channel condition, damage

to the ECCS pumps could occur as a result of air entrainment.

At H.B. Robinson, the cause of the reduction in SI pump NPSH was a failure to adequately

assess the impact of single SI pump operation on system flow and NPSH during a 1988 modification. Inadequate NPSH to ECCS pumps could have led to the inoperability of critical

,

safety-related systems and loss of core cooling under some design-basis LOCA conditions.

The preceding examples demonstrate the importance of thorough assessment and analysis for

any modification involving safety-related level instrumentation or ECCS pump operating

conditions. Information Notice 98-22, "Deficiencies Identified During NRC Design Inspections,"

dated June 17, 1998, also described ECCS swapover analysis errors at D.C. Cook, H.B.

Robinson, Three Mile Island, Wolf Creek, and Ginna.

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.

W. Roe, Acting Director

(Deision of Reactor Program Management

'ffice of Nuclear Reactor Regulation

Technical contact: B. Desal, RH

D. Lanyl, RII

(803) 383-4571

(561) 464-7822 E-mail: bbdinrcgov, E-mail: dri@nrc.gov

D. Billings, RlI

N. Fields, NRR

(864) 882-6927

(301) 415-1173 i

E-mall: debl@nrc.gov

E-mail: enf@nrc.gov

Attachment: List of Recently Issued NRC Information Notices

js

t/1>STO

<2-

',Attachment i

IN 98-40

October 26, 1998 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information

Date of

Notice No.

Subject

Issuance

Issued to

98-39 Summary of Fitness-for-Duty

10/26/98

All holders of oDerating licenses

Program Performance Reports for

Calendar Years 1996 and 1997

for nuclear power reactors

98-38

98-37

98-36

98-35

98-34 Metal-Clad Circuit Breaker

Maintenance Issued Identified

By NRC Inspections

Eligibility of Operator License

Applicants

Inadequate or Poorly Controlled

Non-Safety-Related Maintenance

Activities Unnecessarily Challenged

Safety Systems

Threat Assessments and

Consideration of Heightened

Physical Protection Measures

NRC Configuration Control

Errors

10/15/98

10/01/98

9118/98

9/4/98

8128198

All holders of operating licenses

for nuclear power reactors.

All holders of operating licenses

for nuclear power reactors, except those who have

permanently ceased operations

and have certified that fuel has

been permanently removed from

the reactor vessel.

All holders of operating licenses

for nuclear power reactors

All U.S. NRC fuel cycle facilities

power and non-power reactor

licensees (Safeguard issues, not

for public disclosure.)

All holders of Operating licenses

for nuclear power reactors, except

for those who have ceased

operations and have certified that

fuel has been permanently

removed from the reactor vessel

OL = Operating License

CP = Construction Permit

IN 98-40

October26, 1998 building spray (RBS) pumps. The errors described above created a conflict between the

BWST and RBES levels specified in the EOPs and the BWST and RBES levels indicated in the

control room. As a result, during certain design-basis accident scenarios, including small-break

LOCAs, the level errors could have delayed the initiation swapover initiation. This could have

caused vortexing in the BWST or reduced NPSH to the ECCS pumps, or both.

The design basis of the St. Lucie facility requires that during certain LOCAs, ECCS subsystems

must be capable of automatically transferring suction to the containment sump on receipt of a

RAS. Because of the incorrect trip setpoint of the RWT level instrument bistables, automatic

transfer of the ECCS pumps' suction source from the RWT to the containment sump under

certain conditions would cause an open channel flow condition. Without operator intervention

to initiate manual transfer to the containment sump before the open channel condition, damage

to the ECCS pumps could occur as a result of air entrainment.

At H.B. Robinson, the cause of the reduction in Si pump NPSH was a failure to adequately

assess the impact of single Si pump operation on system flow and NPSH during a 1988 modification. Inadequate NPSH to ECCS pumps could have led to the inoperability of critical

safety-related systems and loss of core cooling under some design-basis LOCA conditions.

The preceding examples demonstrate the importance of thorough assessment and analysis for

any modification involving safety-related level instrumentation or ECCS pump operating

conditions.

Information Notice 98-22, "Deficiencies Identified During NRC Design Inspections," dated June

17, 1998, also described ECCS swapover analysis errors at D.C. Cook, H.B. Robinson, Three Mile Island, Wolf Creek, and Ginna.

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.

0 i

/S

'Id b

Jacl W.R

Acing Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contact: B. Desai, RII

D. Lanyi, RHI

(803) 383-4571 E-mail dri@nrc.gov

E-mail: bbd@nrc.gov

(561) 464-7822 D. Billings, RHI

N. Fields, NRR

(864) 882-6927

(301) 415-1173 E-mail: debl@nrc.gov

E-mail: enf@nrc.gov

Attachment: List of Recently Issued NRC Information Notices

DOCUMENT NAME: S:\\DRPMSEC\\98-40.IN

See previous concurrence

To receive a copy of this document, indicate in the box C=Copy wlo attachment/enclosure E=Copy with lttachmentlenciosure N = No copy

OFFICE

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DATE

10/08/98

1017/8/98

10116/98

10/20/98 l 10k;_8 "

l 10/21/98 l I

OFFICIAL RECORD COPY

IN 98-40

October 26, 1998 bul ing spray (RBS) pumps. The errors described above created a conflict between the

BWS

nd RBES levels specified in the EOPs and the BWST and RBES levels indicated in the

control rhom. As a result, during certain design-basis accident scenarios, including small-break

LOCAs, t

level errors could have delayed the initiation swapover initiation. This could have

caused vort ing in the BWST or reduced NPSH to the ECCS pumps, or both.

The design bas of the St. Lucie facility requires that during certain LOCAs, ECCS subsystems

must be capable

automatically transferring suction to the containment sump on receipt of a

RAS. Because of

e incorrect trip setpoint of the RWT level instrument bistables, automatic

transfer of the ECCSumps' suction source from the RWT to the containment sump under

certain conditions woul

cause an open channel flow condition. Without operator intervention

to initiate manual transfe o the containment sump before the open channel condition, damage

to the ECCS pumps could

ur as a result of air entrainment.

At H.B. Robinson, the cause o

e reduction in Si pump NPSH was a failure to adequately

assess the impact of single Si pu

operation on system flow and NPSH during a 1988 modification. Inadequate NPSH to CCS pumps could have led to the inoperability of critical

safety-related systems and loss of cor cooling under some design-basis LOCA conditions.

The preceding examples demonstrate th

importance of thorough assessment and analysis for

any modification involving safety-related le I instrumentation or ECCS pump operating

conditions.

Information Notice 98-22, 'Deficiencies Identified uring NRC Design Inspections," dated June

17, 1998, also described ECCS swapover analysis

ors at D.C. Cook, H.B. Robinson, Three Mile Island, Wolf Creek, and Ginna.

This information notice requires no specific action or wtitte response. If you have any

questions about the information in this notice, please conta one of the technical contacts listed

below or the appropriate Office of Nuclear Reactor Regulation NRR) project manager.

Jack W. Roe, Acting irector

Division of Reactor Pr

am Management

Office of Nuclear Reacto egulation

Technical contact: B. Desai, RII

D. Lanyi, RI\\

(803) 383-4571 E-mail drl@nrc.

v

E-mail: bbd@nrc.gov

(561) 464-7822 D. Billings, RII

N. Fields, NRR

(864) 882-6927

(301) 415-1173 E-mail: debl@nrc.gov

E-mail: enf@nrc.gov

Attachment: List of Recently Issued NRC Information Notices

DOCUMENT NAME: S:\\DRPM_SEC\\98-40.lN

See previous concurrence

To receive a copy of this document, Indicate In the box C=Copy wlo attachment/enclosure E=Copy with attachment/enclosure N = No copy

OFFICE

PECB

I

RH (TchjContacts

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C:PECB

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DATE

10/08 /98

1017/8/98

10/16/98

10/20/98

10/21/98

/ /98

OFFICIAL RECORD COPY

IN 98-xx

October xx, 1998 building spray (RBS) pumps. The errors described above created a conflict between the