Bulletin 80-17: Supplement No. 3, Failure of Control Rods to Insert During a Scram at a BWR
SSINS: 6820
Accession No.:
8006190074
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
IE Bulletin No. 80-17,
Supplement No. 3
Date: August 22, 1980
Page 1 of 2
FAILURE OF CONTROL RODS TO INSERT DURING A SCRAM AT A BWR
NRC staff evaluation of a potential single failure mechanism of the control
rod drive control air system has identified the need for licensee actions in
addition to those requested by IEB 80-17 and Supplements 1 and 2.
The potential single failure was discussed in IE Information Notice 80-30,
which was issued on August 19, 1980. It involves gradual or partial loss of
control air system pressure, which could cause partial opening of scram
outlet valves without rod motion. The resultant accumulated seal leakage
could conceivably fill the scram discharge volume in a few minutes. Since
not all operating BWR's have instrumentation presently installed to
continuously indicate water level in the scram discharge volume headers and
to provide a control room alarm or scram function, the possibility exists
for the scram discharge volume to fill to a level which could prevent
reactor scram before automatic protective action or before the operators
could be warned.
In view of the possible single failure mechanism described above, the
following actions are requested in addition to those specified in IE
Bulletin 80-17, Supplements 1 and 2:
1. For those plants in which the scram discharge volume headers are
connected to the instrument volume by a 2-inch pipe, within five days
of the date of this Bulletin, provide or verify that procedures are in
effect to:
a. Require an immediate manual scram on low control rod drive air
pressure with a minimum 10 psi margin above the opening pressure of
the scram outlet valves.
b. Require an immediate manual scram in the event of:
(1) Multiple rod drift-in alarms, or
(2) A marked change in the number of control rods with high
temperature alarms.
Installation of water level instrumentation in the scram discharge
volume with level alarm and continuous level indication in the control
room, in response to Item B.1 of IEB 80-17 Supplement No. 1, may provide
a basis for relaxation of the time for initiating a manual scram.
.
IE Bulletin No. 80-17,
Supplement No. 3
Date: August 22, 1980
Page 2 of 2
2. In addition, every BWR licensee is requested within five days of the
date of this bulletin to provide and implement procedures which require
a functional test using water for the instrument volume level alarm,
rod block and scram switches after each scram event, before returning
to power. This procedure should remain in effect until modifications
in addition to Item B.1 of IEB 80-17 Supplement No. 1 are completed to
substantially increase reliability of water level indication in the
scram discharge volume(s).
Licensees of all operating BWRs shall submit a report summarizing action
taken in response to the above items within 10 days of the date of this
Bulletin Supplement. Accordingly, you are requested to provide within 10
days as specified above, written statements of the above information signed
under oath or affirmation. Reports shall be submitted to the Director of
the appropriate NRC Regional Office and a copy forwarded to the Director,
Division of Reactor Operations Inspection, NRC. Office of Inspection and
Enforcement, Washington, D.C. 20555.
Approved by GAO, B180225 (R0072); clearance expires July 31, 1980.
(Application for renewal pending before GAO.) Approval was given under a
blanket clearance specifically for identified generic problems.
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