Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
SSINS No.: 6835
IN 82-13
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
May 10, 1982
Information Notice No. 82-13: FAILURES OF GENERAL ELECTRIC TYPE HFA
RELAYS
Addressees:
All holders of a nuclear power reactor operating license (OL) or
construction permit (CP).
Purpose:
This inforation notice is provided as an early notification of a potentially
significant problem pertaining to General Electric type HFA relays with
LEXAN or NYLON coil spools in safety related systems. It is expected that
addressees will review the information for applicability to their
facilities. No specific action or response is required at this time.
Description of Circumstances:
NRC IE Inforation Notice 81-01, dated January 16, 1981, alerted licensees
and holders of construction permits of LEXAN coil spool surface cracking.
General Electric Service Inforation tetter (SIL) No. 44 Supplement 2 dated
February 1981 directed to all boiling water reactor (BWR) owners and General
Electric Service Advice PSM 152.1 dated April 28, 1976 directed to all
General Electric ,(GE) customers advised them of the coil cracking problem
and recommended replacing cracked LEXAN and NYLON coil spools with new
Century Series "TEFZEL" coil spools or replacement of the entire relay with
a HFA Century Series relay.
Recently, in addition to the previously identified cracking problem, there
have been several instances of melting of LEXAN and NYLON coil spool
material. The licensee reports listed below are some reported instances, of
melting in HFA relays:
1. Monticello - Northern States Power Company reported on November 6, 1981
that during cold shutdown, a GE type 12HFA 51A49F relay pertaining to
primary containment isolation system logic circuit failed to open when
deenergized.
Follow-up investigation indicated that partial melting of the NYLON
coil spool prevented the relay from moving to the deenergized position
for several minutes after the coil was deenergized. Several switches in
series with the relay coil circuit were burned-out and had to be
replaced.
2. Millstone 1 - Northeast Nuclear Energy Company reported on February 24,
1982 that during a routine surveillance one GE type HFA relay
associated with the containment isolation logic circuit stayed in the
energized position when deenergized. As discussed below, melted LEXAN
material
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IN 82-13
May 10, 1982
Page 2 of 3
was found to be the cause. The relay deenergizes to cause main steam
isolation valve closure on main steam ine high radiation. The logic
requires one of two channels in each of two trip systems to deenergize
and cause the isolation. The other three channels were operable,
therefore, an actual high main streamline radiation level would have
resulted in valve closure.
3. Brunswick 2 - Carolina Power & Light Company reported on February 4,
1982 that during the functional performance test of the primary
containment isolation system main streamline high flow channel it was
discovered that the main streamline high-flow channel "C" logic would
not actuate. The details of this failure are somewhat different than
the failures observed at Monticello and Millstone 1. In Brunswick 2,
the armature apparently did move to the deenergized position. However,
melted insulation from the relay coil of the actuation relay GE Model
12HFA 5lA49F had coated the relay contacts, preventing electrical
contact. Like the Millstone 1 event, the remaining main streamline high
flow channels "A", "B" and "D" were operable and would have initiated
isolation upon an actual high flow condition.
During earlier surveillance and coil replacement programs, testing did not
identify a failure in the mechanism which would prevent the relay contacts
from opening. Subsequent evaluation of the Millstone l relay by GE Power
Systems Management Business Department in Philadelphia, led to the following
analysis: A piece of the spool flange fell into the gap between the open
armature and pole face. When the relay was energized the armature attempted
to close but was prevented from sealing against the pole face due to the
piece of spool flange in the air gap. At this point, the contacts could have
been just touching. This created a fixed air gap in the magnetic circuit.
The increase in the current caused by an air gap produced an excessive
temperature rise in the coil. This excessive temperature rise, thru
conduction and convection to the armature assembly and shading ring and
eventually the piece of spool flange caused the loose piece of spool flange
and remaining spool flange to soften, melt and move. As the piece of spool
flange in the gap melted, the air gap closed permitting the normally open
contacts to fully close. In addition, the closure of the gap reduced the
current to normal. This reduction in current caused a lower temperature and
melted LEXAN then hardened and created a bond between the armature and the
pole face. Thus, when the coil was deenergized the return spring force was
not enough to break this bond. Subsequent testing of the coil shows that the
coil is in normal operating condition (no shorted turns).
Although the examples cited above relate to BWRs, the. GE type HFA relays
are also commonly used in the safety system logic circuits of pressurized
water reactors (PWRs). The above information identifies means whereby the
function of a major safety-related system can be jeopardized or compromised
by relay malfunctions.
GE has notified its BWR and PWR customers of its findings and has reiterated
the need for periodic visual inspections. In addition, GE has also amplified
its earlier recommendations. In the event that cracked spools or evidence of
overheating is observed, GE recommends that either the entire
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IN 82-13
May 10, 1982
Page 3 of 3
relay be replaced with a HFA Century Series relay or that the LEXAN or NYLON
1 coil spool be replaced with Century Series TEFZEL coil spools.
If you have any questions regarding this matter, please contact the Regional
Administrator of the appropriate NRC Regional Office, or this office.
Sincerely,
Edward L. Jordan, Director
Division of Engineering and
Quality Assurance
Office of Inspection and Enforcement
Technical Contact: W. Laudan
301-492-4766
Attachment:
Recently Issued IE Information Notices
