Information Notice 2000-08, 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
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- 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
____________________________________________________________________________________
OL = Operating License
CP = Construction Permit