Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
UNITED STATES "REVISED PAGE"
NUCLEAR REGULATORY COMMISSION ADDRESSEE LINE
OFFICE OF NUCLEAR REACTOR REGULATION CHANGED
WASHINGTON, D.C. 20555-0001
June 27, 1997
NRC INFORMATION NOTICE 97-41: POTENTIALLY UNDERSIZED EMERGENCY DIESEL
GENERATOR (EDG) OIL COOLERS
Addresses
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to the discovery of potentially undersized EDG oil
coolers at Limerick Generating Station, Units 1 and 2. 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
Philadelphia Electric Company (PECO) Nuclear, the licensee for Limerick
Generating Station, Units 1 and 2, and its consultant Stone and Webster were
recently evaluating EDG heat exchangers in response to NRC Generic Letter (GL)
89-13. In the course of this evaluation it was determined that the Limerick
EDG lubricating oil coolers were undersized relative to the design conditions
reported on the heat exchanger data sheet. The oil coolers in question are
used to cool lubricating oil for the Coltec EDGs and were designed and
manufactured by American Standard in May 1976. The cooling water for heat
removal circulates through the tubes and the lubricating oil circulates on the
shell side. Finned tubes are used to provide additional heat transfer
surface. In the process of verifying the design adequacy of the heat
exchanger, the licensee utilized the widely used computer modeling program
ST-5, Mod 0.5-1.3, developed by Heat Transfer Research Inc. (HTRI). HTRI is
the leading association for the heat-exchanger industry; its membership
includes all major heat exchanger manufacturers and designers. The licensee
used data obtained from the design data sheet of the heat exchanger. This
data included the design geometry and design conditions, as well as the tube-
side fouling factor of 0.002 and the oil-side heat transfer rate of 83.2
BTU/(hr ft2 �F) for SAE 30 oil. The calculation indicated that the heat
exchanger was 22.8 percent undersized. The licensee informed Coltec about
this discrepancy and requested further evaluation.
Discussion
An evaluation performed by Coltec and its consultants indicates that all
design calculations performed by American Standard in 1976 for this heat
exchanger were complete and correct,
9706230171 . IN 97-41
June 27 1997
Page 2 of 3
including the proper application of the finned tubing surface area ratio to
the specified tube-side fouling factor. PECO Nuclear and its consultant
originally suspected that the 0.002 fouling factor was erroneously applied
unmodified to the outside surface in the original design of the heat
exchanger, resulting in an undersized heat transfer surface. The evaluation
demonstrated that this was not the case. Heat transfer calculations supported
by HTRI at the time of design were considered "state of the art" and the heat
exchanger design was based on the methodology that was current at that time.
The discrepancy between the newly calculated and original design heat transfer
surfaces, according to Coltec and its consultants, was caused by a revision in
the calculational methodology for designing heat exchangers implemented in
1985. Calculations based on the revised method invariably lead to a lower
heat transfer surface in comparison with the previously used calculation
procedure. Thus heat exchangers designed before 1985, if evaluated in
accordance with the revised design methods, would be considered undersized.
In 1985, after extensively testing industrial-sized heat exchangers, HTRI
modified its calculation method for cooling viscous shell side fluids. The
new calculation method is considered to be more precise in predicting actual
heat transfer and pressure drop performance. In general, the calculated
shell-side heat transfer coefficients obtained with this revised method are
lower than those obtained with the former method. In some cases, the
coefficient can be appreciably lower, depending on fluid viscosity, operating
temperatures, flow velocity, and fin geometry.
It therefore appears that heat exchangers designed before 1985 are smaller in
size for the same performance requirements than those designed after 1985.
This does not necessarily mean that they are now considered inadequate for
meeting the design requirements. It, however, does mean that they have a
lower fouling margin, possibly requiring more frequent cleaning and testing of
the heat exchangers in order to maintain operability. PECO Nuclear has
determined that for the Limerick design, sufficient margin is available given
the calculated temperatures of the emergency service water (ESW) system to
handle the post-accident loading (which is below the continuous rating). PECO
Nuclear's analysis takes into consideration the seasonal variation of ambient
temperatures and the results indicate that by scheduling of the heat exchanger
cleaning precisely, Limerick will be able to maintain EDG operability.
Evaluation of similar heat exchangers of the same vintage may yield similar
results.
. IN 97-41
June 27, 1997
Page 3 of 3
This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
one of the technical contacts listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.
signed by S.H. Weiss for
Marylee M. Slosson, Acting Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical contacts: Jai Rajan, NRR
301-415-2788
E-mail: [email protected]
John R. Tappert, NRR
301-415-1167
E-mail: [email protected]
