ML20098D180
| ML20098D180 | |
| Person / Time | |
|---|---|
| Site: | LaSalle  |
| Issue date: | 05/19/1992 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20098D176 | List: |
| References | |
| NUDOCS 9205280078 | |
| Download: ML20098D180 (5) | |
Text
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n UNITED STATES g ~E NUCLEAR REGULATORY COMMISSION
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..e LAFETY EVALUATION BY THE QTFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 83 TO FACILITY OPERATING LICENSE NO. NPF-ll AND bMENDMENT NO. 67 TO FACILITY OPERATING LICENSE NO. NPF-18 COMMONWEAtTH EDISON COMPAfil LASALLE COUNTY STATION. UNITS 1 AND 2 D0raI NOS. 50-375 JND 50-374 1.0 INTR 0jlQQT10H By letter dated Janut.ry 21, 1992, Commonwealth Edison Company (Ceco, the licensee) requested an amendment to Facility Operating License Nos. NPF-11 and NPF-18. The proposed amendment would revise the Surveillance Requirements to Section 4.9.6 of the Technical Specifications (TS) for the refueling platform main hois.. The proposed amendment would allow the station to replace their existing refueling mast with one of a newer design while a11 ewing the". 21 maintain the existing mast as a backup.
2.0 QLSp)MigN LaSalle County Station is replacing their existing General Electric (GE) model 762E974 refueling mat with an improved design by the same manufacturer.
The newer design is the GE NF500 model.
The reason for the replacement is that the existing mast is no longer being manufactured by GE anti spare parts are obsolete and available by special order only.
Refueling and transportation of reactor components is accomplished using a gantry crane. The crane sprns across the fuel storage and the reactor vessel pools and rides on tracks emoedded in the refuel floor. A trolley system is used to lift, lower, or orient fuel bundles as required to load them into the reactor vessel or into the fuel storage pool rack.
The new refuel mast (NF500) design consists of four concentric, telescoping, solid tube sections (see Figure 1).
The mast hangs down vertically from the bottom of the trolley. The top section is fixed to the trolley and doas not move in the vertical direction. When the hoist is in the " normal up" position, only the weight of the top section of the refuel mast is transmitted diractly to the trolley. The weight of the three lower sections, plus any load on the grapple,-is supported by the hoist via the hoist cables. When the hoist is in the " normal down" position, only the weight of the lowest section of the mast, plus any load on the grapple, is supported by the huist. The other sections of the mast are directly supported by the section above it, and therefore, by the trolley.
Since the main fuel hoist is located on the trolley, the total weight of the mast and any load on it is, at all times, 9205280078 920519 PDR ADCCV 03000373 P
t supported by_the refuel platform structure via-the trolley and gantry crane.
It is only the manner in which-the load is transmitted to the structure that changes and forms-the basis for determining the setpoints for the Fuel Hoist Loaded and the Fuel Holst Overload Cutoff interlock setpoints, The existing refuel mast design (762E974) consists of four cancentric, triangular, telescoping sections.
Each section is constructed of reinforced
-tubular frame in a lattice work 'arangement (see Figure 2). -The way the mast operates and transmits the load weight to the crane sup) ort structure is similar to the'new mast. The m.
fference is that tie existing mast is 420 pounds lighter than the new mast.
' 2 weight differential is dut primarily to its open lattice c wstruction vict me solid construction of the new mast.
Therelare several advantages to the new mast design:
~ 1.
It can help in the reduction of personnel _ exposures. T_he stainless steel cylindrical construction reduces corroston and the introduction of
. activated corrosion products into the spent fuel pool or the reactor vessel.
lhe construction also allows for easier decontamination when
.the mast is removed for maintenan:e or storage.
Since the air hoses and electrical _ cable are run inside the mast cylinders, Beta radiation doses as well as airborne and fixed contamination to the console operators is reduced.
In addition, air hoses anf electrical cables-have quick conr.ect ampherol design fittings plugged to the top _of the innermost mast section. This_redut.es exposuret due to replacement of the air hoses-or electrical cable because it is no-longer necessary to remove the mast to perform _this work.
2.
The round design of the mast profuces less ripple in the water during movement of the mast, thus--improving operator visibility and reducing the probability of a fuel mispositioning event.
3.
Tna new design is more rigid and more resistant to bending or bowing.
-This results-in the mast settling more cauickly after a move, thus, improving operator control.
4.
_The-licensee will save time and high-costs by not having to special order obsolete parts on an expedited basis.
The: licensee proposes to modify the requirements in Sec ion-4.9.6 of the TS for.the Overload Cutoff and'the Fuel Hoist Loaded-interlock setpoints. The
- oxisting requirements for the 762E974 mast would remain, but would-be
~clarifled to show that they were for that mast only. New requirements would be added for_the NF500 mast which would require _different setpoints because of_
its heavier weight.- The new setpoints proposed by the licensee are 1600
+100/-0 pounds -for the Overload Cutoff setpoint and 700 +50/-0 pounds for the
- Fuel Hoist Loadec' interlock setpoint.
The.parpose of the Overload Cutoff setpoint is to prevent damage to the fuel assemblies-due to excessive lifting force. The purpose of the Fuel Hoist Loaded interlock setpoint is to provide indication to the operator that the
grapple is loaded.
In addition, the Fuel Hoist: Loaded interlock initiates a control rod' block in order to prevent withdrawing a control rod when the hoist is leaded and located-over the reactor vessel.
It also prevents lifting a load when-the platform is over the reactor vessel with a control rod withdrawn disengaging the grapple when the fuel hoist is loaded, and lifting a load when the grapple is not fully engaged.
In order for the refueling mast to function properly, the setpoints were selected as follows:
l.
A Fuel Hoist Loaded signal should not be present when the hoist is unloaded and shuuld not be present throughout the mast's entire range of travel. The highest load experienced by the cable when unloaded is 620 to 660 pounds when the mast is full up.
This is primarily the weight of the graaple and the three lower sections of the mast. When loaded, there siould be a fuel Hoist Loaded signal generated. The signal should continue to be generated throughout the entire range of travel for the mast while it is loaded. The minimum load experienced by the cable when loaded is 830 pounds (130.for the small section of the mast and 650 for the fuel assembly) when the mast is fully extended.
The licensee-has determined that a.setpoint of 700 +50/-0 pounds will be sufficient to meet this criteria since the minimum setpoint is greater than the maximum' unloaded weight on the cable and the maximum setpoint is less than the minimum-loaded weight on the cable. One setpoint is being used
.for this interlock instead of two (currently in the'TS.for the 762E974-mast) because they are both required.to be activated when a fuel bandle is grappled to the mast, so theyLare.both being set to the same value.
2.
The: Fuel Hoist Overload Cutoff signal should 'not be generated spuri-ously-due to impulse loadings csused by movement of the mast.
If the setpoint is too low, this could cause jamming of the mast.
In addition,
- the Fuel Hoist Overload Cutoff setpoint must; be low enough to prevent damage from occurring due.to excessive lifting force. The weight on the cable when the mast is loaded with a fuel assembly and fully withdrawn-is 1300 pounds.. Additional margin is required to prevent spurious trips due to normal mast moveTent.- Therefore, the-licensee has determined that-a'setpoint of 1600+100/-0 pounds is sufficient to meet this criteria and is well within the allowable-stress limits for core components such as a fuel assembly and top guide.
The new setpoint is at least 300 pounds less than the allowable lin'it of 2000 pounds to prevent damage to the core internals, fuel, and refuel equipment.
3;0 -
fyALUATION The mast replacement does _not affect the function nor the operation-of the
~ main hoist of the refueling platform.
The auxiliary hoists.of the-refueling platform will also. remain lun:: hanged.
However, since the new mast weighs more, the Fuel Hoist Loaded and Fuel Holst Overload interlocks must be revised, as these load _-limits utilized the weight of the mast in the establishment of.
their:setpoints.- Since the' existing mast will be retained as a backup, the existing setpoints will remain with the clarification that they appl,v to the 762E974 mast only.
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4 The only accident that could be potentially affected by the new refueling mast is the fuel handling accident (described in the LaSalle UFSAR, Section 15.7.4). The postulated accident is that a failure of the fuel bundle lifting mechanism could cause the occurrence of a dropped fuel bundle, grapple, and mast. The iicensee has determined that the calculated number of fuel rod failures with the new mast is 116. This is bounded by the current UFSAR calculations which are based on 124 fuel rod failures.
The new mast is similar in design and function to the old mast and exceeds all design requirements. Therefore, this new mast cannot create a new or different kind of accident.
Since the overload cutoff and the loaded interlock still perform their design function, there is no reduction in the margin of safety.
In addition, the new mast provides a safety benefit by reducing personnel exposure and minimizing the potential for a fuel mispositiening event.
Therefore, the staff finds the proposed TS change to be acceptable.
4.0 ETATE CONSULTATION In accordance with the Commission's regulations, the Illinois State official was notified of the proposed issuance of the amendments. The State official had no comments.
5.0 fNVIRONMENTAL CONSIDERATI03 The amendments change surveillance requirements.
The NRC staff has determined that the amendments involve no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendments involve no significant hazards consideration, and there has been no public comment on such finding (57 FR 9440). Accordingly, the amendments meet the eligibility criterk for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR 51.22(b), no environmental imaact statement or environmental assessment need be prepared in connection wit 1 the issuance of the amendments.
6.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that:
(1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor: R. Elliott Date:
May 19, 1992
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Existing 762E974 Refueling Mast
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