Information Notice 1996-41, Effects of a Decrease in Feedwater Temperature on Nuclear Instrumentation

Effects of a Decrease in Feedwater Temperature on Nuclear Instrumentation

ML031060009
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:	07/26/1996
From:	Grimes B Office of Nuclear Reactor Regulation
To:
References
IN-96-041, NUDOCS 9607220160
Download: ML031060009 (10)

K) K) UNITED STATES NUCLEAR REGULATORY

COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555-0001 July 26, 1996 NRC INFORMATION

NOTICE 96-41: EFFECTS OF A DECREASE IN FEEDWATER

TEMPERATURE

Addressees

All holders of operating

licenses or construction

permits for pressurized

water reactors (PWRs).

Purpose

The U.S. Nuclear Regulatory

Commission (NRC) is issuing this information

notice to alert addressees

to the potential

for operation

above licensed power as a result of a decrease in feedwater

temperature

event affecting

nuclear instrumentation.

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 February 14, 1996, the licensee for the Comanche Peak Steam Electric Station was operating

Unit 2 at 95 percent rated thermal power near end-of-core life when a significant

reduction

in feedwater

temperature

occurred because of the loss of feedwater

heaters. This reduction, in turn, caused a reduction

in the reactor coolant system cold-leg temperatures.

The colder reactor coolant temperature, with a large negative moderator

temperature

coefficient, caused reactor power to increase to approximately

102 percent according

to ex-core nuclear instrumentation.

The nitrogen-16 (N-16)detection

system reached the overpower

turbine runback setpoint (109 percent)and initiated

a turbine runback. The N-16 detection

system measures N-16 activity in the primary coolant as a measure of the total power generation.

This system is a substitute

for the resistance

temperature

detector over-temperature

and over-power

reactor trip functions

used at other Westinghouse

PWRs. The plant stabil zed at an indicated

power of approximately

97 percent according

to the ex-core nuclear instrumentation.

After approximately

90 minutes, a second similar turbine runback occurred while restoring

balance-of-plant

equipment.

Following

this runback, reactor power was stabilized

at approximately

100 percent according

to nuclear instrumentation.

During the next 30 minutes, the reactor was operated at approximately

100 percent power as indicated

by nuclear instrumentation, with reactor coolant temperatures

below normal. The licensee noted that the N-16 9 6 0 7 2 2 0l 6 0 ujo i 7 9,oi4 (R ~IE ctG

IN 96-41 July 26, 1996 detection

system indicated

approximately

106 percent power and the computer-based plant calorimetric

system indicated

approximately

102 percent power.Subsequently, the reactor power was reduced to less than 100 percent by all indications.

Discussion

There are three aspects of this event which have generic implications.

First, with a loss of secondary

plant efficiency, programmed

T e can no longer reliably represent

core thermal power. Second, the venturi-based

input into the computer-based

calorimetric

system may not be accurate with cold feedwater.

And third, the final safety analysis report had not analyzed this transient

accurately.

Following

the second runback, operators

noted that reactor power indicated<100 percent according

to nuclear instrumentation.

Although the operators knew that cold feedwater

could cause an increase in the amount of neutron attenuation, they believed that the nuclear instrumentation

indicated conservatively (i.e., higher than actual) because they were maintaining

TA"e approximately

1.7 eC [3 OF] above T Ref. The licensee could not use the computer-based

calorimetric

until some time after the second turbine runback due to maintenance

activities.

Te , based on the main turbine impulse pressure, is programmed

as a functlon of turbine load and, for normal efficiency, is a good representation

of thermal power. When the unit lost the feedwater

heaters, the plant efficiency

decreased.

Because the main turbine electro-hydraulic

control system maintained

generator

output, core thermal power increased

to account for the loss of efficiency, and thus, TRef no longer accurately

represented

the core thermal power.The cold-leg temperature

is a more appropriate

indicator

of the accuracy of the nuclear instrumentation

than programmed

TY.e. As the cold-leg temperature

decreased, the amount of neutron attenuation

in the downcomer

area surrounding

the core increased

and hence affected the amount of neutrons reaching the detectors.

The licensee analysis showed that for every 0.6 C (1 OF] of cold-leg temperature

change, the nuclear instrumentation

was affected by 0.6 to 0.8 percent power. A review of the second transient

showed that the cold-leg temperature

was approximately

2.5 °C [4.5 OF] lower than when the detectors were last calibrated.

This corresponded

to a 3 to 4 percent error, which corresponded

to the difference

in the actual versus the indicated

power (104 percent actual versus 100 percent indicated).

During the review, the licensee noted that the computer-based

calorimetric

was 4 percent lower than the actual thermal power (N-16 power monitor).

The calorimetric

was based on feedwater

flow measured by venturis.

Although the calorimetric

calculation

used feedwater

temperature

as an input, temperatures

significantly

different

than the normal 227 OC [440 OF] introduced

errors into the calculation.

Finally, the actual events involved temperature

and power levels that exceeded those in the analysis of the Decrease in Feedwater

Temperature" event presented

in Chapter 15 of the licensee final safety analysis report. In that

IN 96-41 July 26, 1996 analysis, the inadvertent

opening of the low-pressure

heater bypass valve, coupled with the trip of the heater drain pumps, resulted in a feedwater temperature

drop of less than 19 'C (35 OF], and a corresponding

power increase of less than 10 percent. In the actual event, the feedwater temperature

dropped by approximately

111 °C (200 OF], and the licensee calculated

that reactor power would have increased

by approximately

35 percent without operator or protective

actions. The licensee determined

that although the initiating

events were the same, the Chapter 15 analysis did not account for the loss of extraction

steam to the high-pressure

heaters, which was the cause of the temperature

difference.

During the event, a level imbalance occurred between the two heater drain tanks, which resulted in the isolation of extraction

steam.The NRC staff review of analyses of feedwater

temperature

events at similar facilities

revealed that most of these analyses assumed similar initiating

events as the Comanche Peak analysis and had similar conclusions

concerning

the amount of feedwater

temperature

drop. The licensee has reanalyzed

the event to include a 119 OC [246 OF] feedwater

temperature

drop and concluded that all accident analysis parameters

remained within requirements.

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

project manager.Brian K. Grimes, Acting Director Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical

contacts:

Harry A. Freeman, RIV (817) 897-1500 E-mail: haf~nrc.gov

Chu-Yu Liang, NRR (301) 415-2878 E-mail: cylenrc.gov

Attachment:

List Of Recently Issued HRC Information

Notices A1h4 Stir A Je6tQ

K> KJ Attachment

IN 96-41 July 26, 1996 LIST OF RECENTLY ISSUED NRC INFORMATION

NOTICES Information

Date of Notice No. Subject Issuance Issued to 96-40 96-09, Supp. 1 96-39 96-38 Deficiencies

in Material Dedication

and Procure-ment Practices

and in Audits of Vendors Damage in Foreign Steam Generator

Internals Estimates

of Decay Heat Using ANS 5.1 Decay Heat Standard May Vary Signi-ficantly Results of Steam Generator Tube Examinations

Inaccurate

Reactor Water Level Indication

and Inad-vertent Draindown

During Shutdown Degradation

of Cooling Water Systems Due to Icing Failure of Safety Systems on Self-Shielded

Irradia-tors Because of Inadequate

Maintenance

and Training Hydrogen Gas Ignition during Closure Welding of a VSC-24 Multi-Assembly

Sealed Basket 07/25/96 07/10/96 07/05/96 06/21/96 06/18/96 06/12/96 06/11/96 05/31/96 All holders of OLs or CPs for nuclear power reactors All holders of OLs or CPs for pressurized-water

reactors All holders of OLs or CPs for nuclear power reactors All holders of OLs or CPs for pressurized

water reactors All pressurized

water reactor facilities

holding an operating

license or a construction

permit All holders of OLs or CPs for nuclear power reactors All U.S. Nuclear Regulatory

Commission

irradiator

licensees

and vendors All holders of OLs or CPs for nuclear power reactors 96-37 96-36 96-35 96-34 OL -Operating

License CP -Construction

Permit

• ~ -K> K IN 96-41 July 26, 1996 analysis, the inadvertent

opening of the low-pressure

heater bypass valve, coupled with the trip of the heater drain pumps, resulted in a feedwater temperature

drop of less than 19 *C [35 OF], and a corresponding

power increase of less than 10 percent. In the actual event, the feedwater temperature

dropped by approximately

111 *C [200 OF], and the licensee calculated

that reactor power would have increased

by approximately

35 percent without operator or protective

actions. The licensee determined

that although the initiating

events were the same, the Chapter 15 analysis did not account for the loss of extraction

steam to the high-pressure

heaters, which was the cause of the temperature

difference.

During the event, a level imbalance occurred between the two heater drain tanks, which resulted in the isolation of extraction

steam.The NRC staff review of analyses of feedwater

temperature

events at similar facilities

revealed that most of these analyses assumed similar initiating

events as the Comanche Peak analysis and had similar conclusions

concerning

the amount of feedwater

temperature

drop. The licensee has reanalyzed

the event to include a 119 *C [246 OF] feedwater

temperature

drop and concluded that all accident analysis parameters

remained within requirements.

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

project manager.Original signed by Brian K. Grimes Brian K. Grimes, Acting Director Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical

contacts:

Harry A. Freeman, RIV (817) 897-1500 E-mail: haf@nrc.gov

Chu-Yu Liang, NRR (301) 415-2878 E-mail: cyl~nrc.gov

Attachment:

List of Recently Issued NRC Information

Notices DOCUMENT NAME: G:\SSK2\INFONOT.C

P To receive a copy of this docunent, tndicate in the box CO~opy So attachment/enclosure

EsCopy with attachment/enctosure

N

• No cops OFFICE C BC:SRXB I BC:LPECB lI (A) DW M i NAME CYLiang* RJones* AChaffee*HAFreeman*

____ _DATE 16/ 3/96 16/21/96 17/08/96 17LI/96 I OFFILIAL MLLUM LWUF* See previous concurrence

Tech Editor reviewed & concurred

on 05/28/96

~1~1 -,K)IN 96-XX July XX, 1996 for the loss of extraction

steam to ti cause of the temperature

difference.

occurred between the two heater drain of extraction

steam.he high-pressure

heaters, which was the During the event, a level imbalance tanks, which resulted in the isolation The NRC staff review of analyses of feedwater

temperature

events at similar facilities

revealed that most of these analyses assumed similar initiating

events as the Comanche Peak analysis and had similar conclusions

concerning

the amount of feedwater

temperature

drop. The licensee has reanalyzed

the event to include a 119 'C [246 'F] feedwater

temperature

drop and concluded that all accident analysis parameters

remained within requirements.

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

project manager.Brian K. Grimes, Acting Director Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical

contacts: Harry A. Freeman, RIV (817) 897-1500 E-mail: haf~nrc.gov

Chu-Yu Liang, NRR (301) 415-2878 E-mail: cyl~nrc.gov

Attachment:

List of Recently Issued NRC Information

Notices DOCUMENT NAME: G:\SSK2\INFONOT.C

P To receive a copy of this document, indicate in the box CzAopy w/o attachment/enclosure

E-Copy with attachment/enclosure

N

• No OFFICE l kd BC: SRXB BC:PECB )D:DR NAME CYLiang* RJones* AChaffee*

BGrimes HAFreeman*

DATE 6/ 3/96 6/21/96 7/08/96 7/ /96 OFFICIAL RECORD COPY*See previous concurrence

IN 96-XX July XX, 1996 for the loss of extraction

steam to the high-pressure

heaters, which was the cause of the temperature

difference.

During the event, a level imbalance occurred between the two heater drain tanks, which resulted in the isolation of extraction

steam.The NRC staff review of analyses of feedwater

temperature

events at similar facilities

revealed that most of these analyses assumed similar initiating

events as the licensee analysis and had similar conclusions

concerning

the amount of feedwater

temperature

drop. The licensee has reanalyzed

the event pursuant to Section 50.59 of Title 10 of the Code of Federal Regulations

to include a 119 'c [246 OF] feedwater

temperature

drop and concluded

that all accident analysis parameters

remained within requirements.

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

project manager.Brian K. Grimes, Acting Director Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical

contacts:

Harry A. Freeman, RIV (817) 897-1500 E-mail: haftnrc.gov

Chu-Yu Liang, NRR (301) 415-2878 E-mail: cyl~nrc.gov

Attachment:

List of Recently Issued NRC Information

Notices DOCUMENT NAME: G:\SSK2\INFONOT.C

P To receive a copy of this document, indicate in the box C-Topy u/o attachment/enclosure

E=Copy with attachment/enclosure

N No copy OFFICE CONT:i kd l BC:SRXBLl

BC:iPECB lI (A)iD:iDRPM

I _NAME CYLiang* RJones* AChaffee*

BGrimes l _ HAFreeman*

DATE 6/ 3/96 6/21/96 7/08/96 7/ /96* See previous concurrence

OFFICIAL KLLUKV UV X!

IN 96-XX July XX, 1996 for the loss of extraction

steam to the high-pressure

heaters, which was the cause of the temperature

difference.

During the event, a level imbalance occurred between the two heater drain tanks, which resulted in the isolation of extraction

steam.The NRC staff review of analyses of feedwater

temperature

events at similar facilities

revealed that most of these analyses assumed similar initiating

events as the licensee analysis and had similar conclusions

concerning

the amount of feedwater

temperature

drop. The licensee has reanalyzed

the event pursuant to Section 50.59 of Title 10 of the Code of Federal Regulations

to include a 119 *C [246 *F] feedwater

temperature

drop and concluded

that all accident analysis parameters

remained within requirements.

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

project manager.Brian K. Grimes, Acting Director Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical

contacts:

Harry A. Freeman, RIV (817) 897-1500 Internet:haf@nrc.gov

Chu-Yu Liang, NRR (301) 415-2878 Internet:cyl

nrc.gov Attachment:

List of Recently Issued NRC Information

Notices DOCUMENT NAME: G:\SSK2\INFONOT.C

P To receive a copy of this document, Indicate in the box Conopy w/c attachment/enclosure

EnCopy with attachment/enclosure

N

• No OFFICE CONT: Ekd BC: SLB BC:PECB (A)D:DRPM NAME CYLiang* RJones* ACh)f BGrimes l ~~HAFreeman*tVt

DATE 6/ 3/96 6/21/96 7/7/96 7/ /96 OFFICIAL RECOR COPY* See previous concurrence

K-, /IN 96-XX June XX, 1996 for the loss of extraction

steam to ti cause of the temperature

difference.

occurred between the two heater drain of extraction

steam.he high-pressure

heaters, which was the During the event, a level imbalance tanks, which resulted in the isolation The NRC staff's review of analyses of feedwater

temperature

events at similar facilities

revealed that most of these analyses assumed similar initiating

events as the licensee's

analysis and had similar conclusions

concerning

the amount of feedwater

temperature

drop. The licensee has reanalyzed

the event pursuant to Section 50.59 of Title 10 of the Code of Federal Regulations

to include a 119 'C [246 OF] feedwater

temperature

drop and concluded

that all accident analysis parameters

remained within requirements.

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

project manager.Brian K. Grimes, Acting Director Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical

contacts: Harry A. Freeman, RIV (817) 897-1500 Internet:haffnrc.gov

Chu-Yu Liang, NRR (301) 415-2878 Internet:cyl@nrc.gov

Attachment:

List of Recently Issued NRC Information

Notices DOCUMENT NAME: G:\SSK2\INFONOT.CP

To receive a copy of this document, indicate in the box Ciropy w/dattachmeft1/enctosure

EnC OFFICE CONT:jkd _l BC: SRXB E C:PECB I _ A)D:DRPM I NAME CYLiang* RJones AChaffee BGrimes HAFreeman*

I- _DATE 6/ 3/96 6/2j /96 6/ /96 6/ /96 OFFICIAL RECORD COPY I oith attachment/enclosure

1

• No copy* See previous concurrence

IN 96-XX June XX, 1996 detection

system. The licensee believed that this system would probably not be significantly

affected by feedwater

temperatures

because of a different mass flow rate determination

method.Finally, the licensee's

final safety analysis report did not accurately

analyze this transient.

The actual events were similar to the analysis of the'Decrease

in Feedwater

Temperature

event presented

in Chapter 15. In that analysis, the inadvertent

opening of the low-pressure

heater bypass valve, coupled with the trip of the heater drain pumps, resulted in a feedwater temperature

drop of less than 35 OF, and a corresponding

power increase of less than 10 percent. In the actual event, the feedwater

temperature

dropped by approximately

200 OF, and the licensee calculated

that reactor power would have increased

by approximately

35 percent without operator or protective

actions. The licensee determined

that although the initiating

events were the same, the Chapter 15 analysis did not account for the loss of extraction

steam to the high-pressure

heaters, which was the cause of the temperature

difference.

During the event, a level imbalance

occurred between the two heater drain tanks, which resulted in the isolation

of extraction

steam.The NRC staff's review of analyses of feedwater

temperature

events at similar facilities

revealed that most of these analyses assumed similar initiating

events as the licensee's

analysis and had similar conclusions

concerning

the amount of feedwater

temperature

drop.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

project manager.Brian K. Grimes, Acting Director Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical

contacts:

Harry A. Freeman, RIV (817) 897-1500 Internet:haf@nrc.gov

Chu-Yu Liang, NRR (301) 415-2878 Internet:cyl

nrc.gov Attachment:

List of Recently Issued NRC Information

Notices DOCUMENT NAME: G:\SSK2\INFONOT.C

P To receive a copy of this docunent, indicate in the box Catopy w/o attachment/enclosure

E-C with attachment/enclosure

N

• No copy OFFICE lCONT:kd l BC:SRXB l BC:PECB l (A)D:DRPM NAME CYLiang 9 RJones AChaffee BGrimes HAFreema r _ _DATE /96 /96 6/ /96 6/ /96 OFFICIAL RECORD COPY