Information Notice 2000-08, Inadequate Assessment of the Effect of Differential Temperatures on Safety-Related Pumps

Inadequate Assessment of the Effect of Differential Temperatures on Safety-Related Pumps

ML003712586
Person / Time
Issue date:	05/15/2000
From:	Marsh L Operational Experience and Non-Power Reactors Branch
To:
Petrone, C
References
TAC MA8653 IN-00-008
Download: ML003712586 (5)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555-0001 May 15, 2000

NRC INFORMATION NOTICE 2000-08: INADEQUATE ASSESSMENT OF THE EFFECT OF

DIFFERENTIAL TEMPERATURES ON SAFETY-

RELATED PUMPS

Addressees

All holders of operating licenses for nuclear power reactors.

Purpose

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

addressees of the potential for differential temperature conditions to affect the operability of

safety-related pumps. 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

The following describes two events that appear to have been caused by inadequate

engineering design assessment of the effect of differential temperatures on safety-related

pumps.

Arkansas Nuclear One, Unit 1 (ANO-1)

In 1992, the licensee for ANO-1 implemented a design change to replace the cast iron inboard

and outboard bearing housings on the low-pressure injection/decay heat removal (LPI/DHR)

pumps with stainless steel for improved service water corrosion resistance. The LPI/DHR

system is designed to remove decay heat from the core and sensible heat from the reactor

coolant system (RCS) during the last stages of a plant cooldown. It also provides a means of

automatically injecting borated water into the reactor vessel for cooling the core in the event of

a loss-of-coolant accident during power operation. During the September 1999 refueling

outage, the licensee implemented a design change to increase the viscosity of the lubricating oil

for the LPI/DHR pump bearings in order to reduce wear.

On February 5, 2000, ANO-1 began cooling down the plant in preparation for entering a

maintenance outage to install replacement parts on the D reactor coolant pump anti-rotation

device. When the RCS temperature had been reduced to 280-F and the pressure had been

reduced to 240 psig, the A LPI/DHR pump was placed in service for decay heat removal.

After 52 minutes, the licensee was forced to secure the A LPI/DHR pump when the inboard

bearing temperature reached approximately 160-F. The licensee then placed the B LPI/DHR

pump in service for DHR but stopped it after 16 minutes due to a high inboard bearing

temperature. The licensee tested both pumps by recirculating water from the borated water

storage tank and noted that the bearing temperatures remained stable at approximately 80-F.

During this test the pumped fluid, the borated water, was at ambient temperature. Upon

switching the B pump suction back to the RCS, the bearing temperature again rose to

approximately 160-F. In this instance the pumped fluid, the RCS water, was at a temperature

of approximately 250-F.

On February 6, 2000, the licensee changed the A LPI/DHR pump bearing oil back to the

original (lower viscosity) specification. When the A LPI/DHR pump was placed back in the

DHR mode of operation, the bearing temperature stabilized at 119-F. The licensee then

declared the LPI/DHR pump operable for the DHR mode only and proceeded to cool down the

plant. The licensee then changed the B LPI/DHR pump bearing oil back to original

specification. But, unlike the A pump, the B pump again had to be shut down due to high

bearing temperature. Inspection of the B pump following shutdown indicated that the inboard

bearing had to be replaced due to abnormal wear. Further details were provided by the

licensee in its Licensee Event Report (LER) 50-313/2000-002-00 dated March 6, 2000

(Accession No. ML003691450).

Beaver Valley Power Station, Unit 1

On February 8, 2000, the licensee for the Beaver Valley Power Station, Unit 1 (the licensee),

was performing a routine surveillance on the B river water pump. The pump tripped on over

current protection after approximately 3 seconds. A few hours later, startup of the C river

water pump was attempted and it also tripped after 3 seconds because of over current

protection.

The licensee determined that the over current trips were a result of pump binding. The cause

of the binding was thermal expansion of the pump shaft as a result of a temperature differential

between the river water (35 degrees F) and an elevated seal injection water temperature (70

degrees F). The river water pump seal water was being supplied by the non-safety related

filtered water system. At the time of the event, the filtered water system was in an abnormal

configuration that created the elevated water temperature. Further details on this event are

available in LER 50-334/2000-002-00 dated March 8, 2000 (Accession No. ML003692855),

LER 50-334/2000-002-01 dated April 27, 2000 (Accession No. ML003712023), and in NRC

Inspection Reports 05000334/2000-01 dated March 17, 2000 (Accession No. ML003693247),

and 05000334/2000-02 dated April 28, 2000 (Accession No. ML003709259).

Discussion

At ANO, the NRC performed a special inspection (report number 50-313/00-04; 50-368/00-04, Accession No. ML003708466) to follow up on the events which led to declaring both Unit 1 LPI/DHR pumps inoperable. The inspectors concluded that the failure to complete adequate

engineering evaluations for the replacement of the cast iron bearing housing with a stainless

steel housing and the change in lubricating oil viscosity resulted in the inoperability of both LPI/DHR pumps. The changes in the bearing housing material and use of a higher viscosity oil, in combination with low cooling water temperatures (<42-F), resulted in both low pressure

injection/decay heat removal pumps operating with high bearing temperatures, which required

the pumps to be secured. From January 28 to February 5, 2000, when the cooling water

temperature was 42-F or less, both low pressure injection/decay heat removal pumps were not

operable as they could not perform their intended safety function. These design deficiencies

were not identified by post modification or surveillance testing. Testing performed by

recirculating water from the borated water storage tank did not duplicate actual operational

conditions because the pumped fluid (from the borated water storage tank) was at a much

lower temperature than the RCS.

Subsequent investigation by the ANO licensee identified other potentially susceptible equipment

in both units and took appropriate corrective actions.

At the Beaver Valley Power Station, the licensee determined that when warmer seal water is

provided to an idle pump during cold river water conditions, the warmer seal water travels down

the pump shaft and increases the shaft temperature. The pump casing is not in direct contact

with the seal water and, therefore, is not affected by the increase in seal water temperature.

This temperature differential resulted in elongation of the pump shaft, impeller contact with the

pump casing, and eventual pump binding. The same warmer seal water supplied to the pumps

when they are idle is also supplied to them when they are operating. However, the effect of

having warmer seal water supplied to an operating pump was negligible because of the

extremely large volume of pumped fluid acting as a heat sink on the small volume of seal water

passing through the pump inner column. The licensee also determined that the filtered water

system could introduce a common-mode failure to all three safety-related river water pumps.

The filtered water system was subsequently isolated as a supply source to the river water

pumps and the pumps were operated from their safety related supply.

During this operation, the licensee identified an inadequacy in the design of the safety-related

seal water supply strainers. Since original plant operation in 1976, the non-safety-related

filtered water system had been the primary supply to the river water pump seals. However, during operation of the pumps on their safety-related supply, the safety-related in line strainers

fouled during high silt conditions.

Safety-related pumps are expected to operate under a wide range of environmental conditions.

These two events highlight the importance of assessing the effects of differential temperatures

on safety-related pump operability. In addition, these events highlight the importance of having

test programs that include suitable qualification testing under the most adverse design

conditions (e.g., temperature and differential temperature), when the test program is used to

verify the adequacy of a specific design feature (e.g. seal water supply). 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.

/RA/

Ledyard B. Marsh, Chief

Events Assessment, Generic Communications

and Non-Power Reactors Branch

Division of Regulatory Improvement Programs

Office of Nuclear Reactor Regulation

Technical contacts: Charles D. Petrone, NRR Eric J. Benner, NRR

301-415-1027 301-415-1171 E-mail: cdp@nrc.gov E-mail: ejb1@nrc.gov

Attachment: List of Recently Issued NRC Information Notices 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.

/RA/

Ledyard B. Marsh, Chief

Events Assessment, Generic Communications

and Non-Power Reactors Branch

Division of Regulatory Improvement Programs

Office of Nuclear Reactor Regulation

Technical contacts: Charles D. Petrone, NRR Eric J. Benner, NRR

301-415-1027 301-415-1171 E-mail: cdp@nrc.gov E-mail: ejb1@nrc.gov

Attachment: List of Recently Issued NRC Information Notices

DISTRIBUTION:

REXB R/F

Public

• See previous concurrence ACCESSION # ML003712586 TEMPLATE # 052 To receive a copy of this document, indicate in the box C=Copy w/o attachment/enclosure E=Copy with attachment/enclosure N = No copy

OFFICE REXB:DRIP E REXB:DRIP E Tech Editor DLPM/LPD4 E

NAME C Petrone* EBenner* BCalure* MNolan*

DATE 04/11/00 04/11/00 04/10/00 5/05/00

OFFICE DLPM/LPD1 DE/EMEB E REXB:DRIP E C:REXB:DRIP E

NAME DCollins* DTerao* TKoshy* LMarsh

DATE 4/19/00 04/12/00 5/08/00 5/15/00

OFFICIAL RECORD COPY

Attachment LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

_____________________________________________________________________________________

Information Date of

Notice No. Subject Issuance Issued to

________________________________________________________________________________

2000-07 National Institute for 4/10/2000 All holders of operating licenses

Occupational Safety and for nuclear power reactors, non- Health Respirator User Notice: power reactors, and all fuel cycle

Special Precautions for Using and material licensees required to

Certain Self-Contained have an NRC-approved

Breathing Apparatus Air emergency plan

Cylinders

2000-06 Offsite Power Voltage 3/22/2000 All holders of operating licenses

Inadequacies for nuclear power reactors, except those who have

permanently ceased operations

and have certified that fuel has

been permanently removed from

the reactor

2000-05 Recent Medical 3/06/2000 All medical licensees

Misadministrations Resulting

from Inattention to Detail

2000-04 1999 Enforcement Sanctions 2/25/2000 All NRC licensees

for Deliberate Violations of

NRC Employee Protection

Requirements

2000-03 High-Efficiency Particulate Air 2/22/2000 All NRC licensed fuel-cycled

Filter Exceeds Mass Limit conversion, enrichment, and

Before Reaching Expected fabrication facilities

Differential Pressure

2000-02 Failure of Criticality Safety 2/22/2000 All NRC licensed fuel-cycled

Control to Prevent Uranium conversion, enrichment, and

Dioxide (UO2) Powder fabrication facilities

Accumulation

2000-01 Operational Issues Identified in 2/11/2000 All holders of licenses for nuclear

Boiling Water Reactor Trip and power reactors

Transient

____________________________________________________________________________________

OL = Operating License

CP = Construction Permit