Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
UNITED STATES
NUCLEAR REGULATORY COMMISSION
WASHINGTON, D. C. 20555
July 31, 1981
ALL LICENSEES OF OPERATING PLANTS AND HOLDERS OF CONSTRUCTION PERMITS
Gentlemen:
SUBJECT: STEAM GENERATOR OVERFILL (GENERIC LETTER 81-28)
(Formerly Issued July 1, 1981, as Generic Letter 81-16)
In a letter dated March 28, 1980 from H.R. Denton, we informed you of the
revised criteria to be used by the staff in evaluating reactor operator
training and licensing that could be implemented under the current
regulations. We also advised you that Commission review in the area of
operator training and qualification was continuing and it could be expected
to result in additional criteria.
The NRC Office of Analysis and Evaluation of Operational Data has produced a
report entitled, "AEOD Observations and Recommendations Concerning the
Problem of Steam Generator Overfill and Combined Primary and Secondary Side
Blowdown," dated December 17, 1980, a copy of the report is enclosed. This
report documents results of studies completed to data by the Office of
Analysis and Evaluation of Operational Data with regard to the team
generator overfill problem.
This report expresses concerns in the following area: (1) increased dead
weight and potential seismic loads placed on the main steamline and its
support should this line become flooded; (2) the load placed on the main
steamlines due to the potential for rapid collapse of steam voids resulting
in water hammer; (3) the potential for secondary safety valves sticking open
following discharge of water or two-phase flow; (4) the potential for
rupture for weakened tubes in the once-through-steam-generator (OTSG) on B&W
NSSS plants due to tensile loads caused by the rapid thermal shrinkage of
the tubes relative to the generator shell.
From the examining experiences of the Operator Licensing Branch, operators
at nuclear power plants are aware of the need to avoid overfilling steam
generators and not operating steam systems with water accumulation. However,
there may be a general lack of appreciation of the potential seriousness of
situations that can arise from these events.
.
- 2 - July 1, 1981
While this issue is being studied further, we request that you determine
which scenarios are credible for your plant and that you include in your
overall training program, plant-specific information stressing the
importance of feedwater flow as well as the possible consequences of steam
generator overfill. This information should be factored into your initial
operator training programs and the operator requalification programs.
Sincerely,
Darrell G. Eisenhut, Director
Division of Licensing
Office of Nuclear Reactor Regulation
Enclosure:
As stated
