Information Notice 2006-04, Design Deficiency in Pressurizer Heaters for PWRs
| ML060100450 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde, Waterford  |
| Issue date: | 02/13/2006 |
| From: | Charemagne Grimes NRC/NRR/ADRA/DPR |
| To: | |
| Omid Tabatabai | |
| References | |
| IN-06-004 | |
| Download: ML060100450 (4) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
February 13, 2006 NRC INFORMATION NOTICE 2006-04:
DESIGN DEFICIENCY IN PRESSURIZER
HEATERS FOR PRESSURIZED-WATER
REACTORS
ADDRESSEES
All holders of operating licenses for pressurized-water reactors, except those who have
permanently ceased operations and have certified that fuel has been permanently removed
from the reactor.
PURPOSE
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to inform
addressees about pressurizer heaters that failed following replacement because the heater
elements provided by the vendor did not match the licensees' design specification. 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
During the Fall 2004 refueling outage, the licensee at Palo Verde Generating Station, Unit 3, replaced all 36 pressurizer heaters with replacements supplied by Framatome that had heater
internals manufactured by Thermocoax. From December 2004 through February 2005, four of
the replaced heaters in the proportional heater banks failed. On May 23, 2005, with Palo Verde
Unit 3 in Mode 5 (cold shutdown), the licensee replaced nine Framatome/Thermocoax heaters
with General Electric (GE) heaters. During the subsequent reactor heatup, five
Framatome/Thermocoax heaters in the backup heater banks failed. As a result of the continued
heater failures, the licensee returned to Mode 5 to replace all remaining
Framatome/Thermocoax pressurizer heaters with GE heaters. When the
Framatome/Thermocoax heaters failed, all were grounded, and all but one tripped a circuit
breaker to clear a ground fault. The licensee discovered one heater grounded while
maintenance was being performed during the outage. There was no damage to any other
equipment such as power cables as a result of the heater failures.
During the Spring 2005 refueling outage, Waterford Steam Electric Station, Unit 3, replaced
29 pressurizer heaters with replacements supplied by Framatome that had the heater internals
manufactured by Thermocoax. During plant heatup but prior to reactor startup, two of the
replaced heaters experienced partial ejection of the epoxy in the receptacle area due to heat
transfer to electrical connections in the receptacle area, six experienced failure due to
grounding, and several experienced partial melting of the silicon-type material used to seal the
bottom end of the receptacles. The licensee replaced 23 Framatome/Thermocoax heaters with
Watlow heaters and abandoned the remaining 6 Framatome/Thermocoax heaters in place by
electrically disconnecting them. There was no damage to any other equipment such as power
cables as a result of the heater failures.
The vendor subsequently inspected the failed heaters from the Palo Verde and Waterford plants
and determined that the heaters had been incorrectly fabricated with a
longer heating element than the licensees' design specification. The longer heating elements
extended down into the heater sleeves and pressurizer shell thereby changing the location of
the transition joint that separates the heated and unheated portion of the heater assembly. This
resulted in a reduced ability to transfer that heat away from the heater and also allowed more
heat transfer to electrical connections in the receptacle area.
DISCUSSION
Technical specifications for PWRs specify a minimum required available capacity of pressurizer
heaters to ensure that the RCS pressure can be controlled to maintain subcooled conditions in
the RCS. Plant operation with failed pressurizer heaters can affect a facilitys ability to control
reactor pressure. Following a reactor trip, unnecessary safety injection actuations could occur
due to inability to maintain RCS system pressure above the actuation set point.
Additionally, the longer heating elements extended down into the heater sleeves and
pressurizer shell resulted the potential to exceed the allowable temperature limits by the
American Society of Mechanical Engineers Boiler and Pressure Vessel Code.
The Palo Verde and Waterford licensees had each supplied Framatome the correct design
specification regarding the location of the transition joint between the heated and unheated
portions of the heater assembly. However, Framatome supplied pressurizer heater assemblies
that did not match the design specification. The licensees did not obtain vendor specifications
and drawings that were sufficiently detailed to allow them to identify that the replacement
pressurizer heaters were not consistent with the licensees' design specification.
At Palo Verde Generating Station, Unit 3, one heater was discovered grounded while
maintenance was being performed during the outage. Sensitive ground-fault protection on low
voltage circuits such as 480 V pressurizer heater circuits, can help in the detection of a ground
fault.
Additional information on this subject is available in a Title 10 of the Code of Federal
Regulations Part 21 (10 CFR Part 21) report from Framatome dated July 28, 2005, which is
accessible using NRCs document control system (Agencywide Documents Access and
Management System (ADAMS), Accession No. ML052140277).
CONTACT
S
This information notice requires no specific action or written response. Please direct any
questions about this matter to the technical contacts listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.
/RA/
Christopher I. Grimes, Director
Division of Policy and Rulemaking
Office of Nuclear Reactor Regulation
Technical Contacts:
David N. Graves, R-IV/DRP/RPB-E
Troy W. Pruett, R-IV/DRP/RPB-D
817-860-8147
817-860-8173 E-mail: DNG@nrc.gov
E-mail: TWP@nrc.gov
Vijay K. Goel, NRR/DE/EEEB
301-415-3730
E-mail: VKG@nrc.gov
NRR Project Manager:
Omid Tabatabai, NRR/DIRS/IOEB
301-415-6616 E-mail: OTY@nrc.gov
Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under Electronic Reading Room/Document Collections.
CONTACT
S
This information notice requires no specific action or written response. Please direct any
questions about this matter to the technical contacts listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.
/RA/
Christopher I. Grimes, Director
Division of Policy and Rulemaking
Office of Nuclear Reactor Regulation
Technical Contacts:
David N. Graves, R-IV/DRP/RPB-E
Troy W. Pruett, R-IV/DRP/RPB-D
817-860-8147
817-860-8173 E-mail: DNG@nrc.gov
E-mail: TWP@nrc.gov
Vijay K. Goel, NRR/DE/EEEB
301-415-3730
E-mail: VKG@nrc.gov
NRR Project Manager:
Omid Tabatabai, NRR/DIRS/IOEB
301-415-6616 E-mail: OTY@nrc.gov
Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under Electronic Reading Room/Document Collections.
DISTRIBUTION:
IN File
ADAMS ACCESSION NO: ML060100450
OFFICE
BC: R-IV/DRP/RPB-E
BC: R-IV/DRP/RPB-D
TECH EDITOR
D:R-IV/DRP
NRR/DE/EEEB
NAME
DNGraves
TWPruett
HChang
ATHowell
VKGoel
DATE
1/24/2006
1/24/2006
1/17/2006
1/24/2006
2/13/2006 OFFICE
BC:NRR/DE/EEEB NRR/DIRS/IOEB
TL:NRR/DIRS/IOEB
LA:PGCG/DPR
PM:PGCB/DPR
NAME
RVJenkins
OTabatabai
EJBenner
CMHawes
DBeaulieu
DATE
1/23/2006
1/19/2006
1/3/2006
1/19/2006
2/13/2006 OFFICE
BC:NRR/DPR/PGCB D:NRR/DPR/PGCB
NAME
CJackson
CIGrimes
DATE
2/13/2006
2/14 /2006