Bulletin 74-014: BWR Relief Valve Discharge to Suppression Pool
BL74014
UNITED STATES
ATOMIC ENERGY COMMISSION
WASHINGTON, D.C. 20545
NOV 13 1974
J. P. O'Reilly, Director, Region I
N. C. Moseley, Director, Region II
J. G. Keppler, Director, Region III
E. M. Howard, Director, Region IV
R. H. Engelken, Director, Region V
RO BULLETIN 74-14 - BWR RELIEF VALVE DISCHARGE TO SUPPRESSION POOL
The subject Bulletin has been revised and should be dispatched for action to
all BWR facilities with operating licenses, and for information to holders
of construction permits for BWR's by close of business on November 15, 1974.
The text of the Bulletin together with draft letters to licensees is
enclosed for this purpose.
John G. Davis, Deputy Director
for Field Operations
Directorate of Regulatory Operations
Enclosure:
As stated
cc: D. F. Knuth, RO:HQ
H. D. Thornburg, RO:HQ
J. L. Crews, RO:HQ
H. H. Brown, OGL
D. Thompson, OOE
Regional Coordinators
B. H. Grier, RO:HQ
K. R. Goller, L:HQ
L. I. Cobb, A/D, RO (3)
.
(Draft letter to holders of construction permits only for BWR's)
RO Bulletin 74-14
Gentlemen:
The enclosed RO Bulletin is forwarded to you for information, regarding
your boiling water reactor under construction. No written reply is required
of you in response to the Bulletin.
Sincerely,
Director
Enclosure:
RO Bulletin 74-14
.
(Draft letter to BWR's with operating licenses).
RO Bulletin 74-14
Gentlemen:
The enclosed RO Bulletin requests actions by you with regard to your boiling
water reactor (BWR) facility(ies) with operating license.
Should you have questions regarding this Bulletin or actions requested of
you, please contact this office.
Sincerely,
Director
Enclosure:
RO Bulletin 74-14
This request for generic information was approved by GAO under a
blanket clearance number B-180225 (R0072); this clearance expires
July 31, 1977.
.
RO Bulletin 74-14 Date: 11/14/74
BWR RELIEF VALVE DISCHARGE TO SUPPRESSION POOL
Description of Circumstances:
Various BWR licensees have in the recent past, experienced unplanned
actuation of reactor coolant system steam relief valves. These valves
typically discharge to the suppression pool, where the discharge steam is
quenched. With the suppression pool water at its normal temperature, the
steam quenching proceeds in the expected manner. Extended discharge of a
single relief valve, however, may raise the local temperature of the
receiving water to a level at which the steam quenching becomes erratic and
local pressure pulses of significant magnitude may be generated.
Past occurrences at several AEC licensed reactors have resulted in varying
degrees of damage, such as baffle displacement and piping support damage.
This damage has previously been attributed to a variety of causes; however,
based upon more recent evaluations by the nuclear steam system supplier,
General Electric Company, damage may have resulted from local pressure
pulses as described above. Since only a limited number of temperature
sensors are provided within the suppression pool, local temperature
increases and resulting pressure pulses have not been specifically
identified in past occurrences.
It appears that, during events in which relief valves cannot be closed
promptly, primary attention by the operator may be directed under current
procedures toward minimizing temperature and pressure transients in the
reactor coolant system, without sufficient attention to the effects of
extended steam discharge on the pressure suppression pool structure. This
situation is currently under review by the Regulatory staff including
consideration of whether revision to technical specifications may be
required.
Action Requested of Licensees:
1. Review your current operating procedures which are applicable to the
situation discussed above, to determine whether they are adequate or
should be modified in any of the following areas:
.
RO Bulletin 74-14 -2-
a. Limiting bulk suppression pool temperatures during normal
operation and during controllable transients.
b. Requiring reactor trip if the bulk suppression pool temperature
exceeds that established as a limit for controllable transients or
if relief valve(s) fails to reseat properly.
c. Taking prompt steps in case of inadvertent relief valve actuation
or failure to reseat, to minimize the duration of steam discharge
to the suppression pool.
d. In cases of relief valve discharge, promptly initiating
suppression pool circulation to dissipate local peaking of water
temperatures.
e. Conduct of visual internal and external inspection of suppression
pool structure for evidence of damage in instances where one or
more relief valve(s) fails to reseat properly or discharges to the
suppression pool for an extended period of time.
During this review, the various aspects of plant operations should be
considered so that procedural changes designed to minimize the effect
of steam discharge to the suppression pool do not have an adverse
effect in other areas.
2. Report to this office in writing within 20 days of receipt of this
Bulletin the results of your procedural review and any changes you have
made or plan to make in your operating procedures, including the date
when such changes were or will be completed.
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