ML19208D901
| ML19208D901 | |
| Person / Time | |
|---|---|
| Issue date: | 06/15/1978 |
| From: | NRC OFFICE OF INSPECTION & ENFORCEMENT (IE) |
| To: | |
| References | |
| IEC-78-11, NUDOCS 7910010714 | |
| Download: ML19208D901 (4) | |
Text
i UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D. C.
20555 June 15, 1978 IE Circular No. 78-11 RECIRCULATION M-G SET OVERSPEED STOPS In August 1977, personnel at the Cooper Nuclear Station reported finding the recirculation M-G set overspeed mechanical and electrical stcps at 112 percent and 120 percent of rated core flow.
The licensee had believed the set point to be 107 percent f ar these stops, although a search of Station preoperational and startup test records could not establish the actual initial set point.
Subsequent to this finding, the licensee set the mechanical stop at 102 percent of rated core flow.
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The technical specifications require that the Minimum Critical Power Ratio (MCPR) be maintained greater than 1.22 for 8 X 8 fuel.
The technical specifications further require MCPR to be above a minimum s of 1.22 times Kf whenever operating at less than rated flow.
The correction factor Kf is always greater than or equal to 1.0 and thus increases the MCPR limit when at less than rated flow. Technically, this factor increases the required MCPR thermal margin in the event a recirculation M-G set speed control failure would occur and allow the recirculation pump to overspeed.
The lower the initial core flow, the more severe is the flow transient, thus Kf increases as actual core flow is decreased. The Kf factor is read from a curve included in the technical specifications.
A family of Kf curves is given in the figure in the technical specifications.
The proper curve to use is the curve corresponding to the set point of the manual flow control overspeed stop (the M-G set mechanical stop). A lower set point of the overspeed stop results in a small Kf correction factor for a given core flow, as the flow transient on an M-G set speed control failure is less severe.
Thus, it can be seen that by using a lower curve (e.g., 107 percent curve) than that requ' red by the actual overspeed stop set point (believed to have been set at 112 percent), a ionconservative Kf correction factor was being used.
The M-G set overspeed steps were set during the preoperational test program by a General Electric Company startup engineer.
The stops were checked by a GE preoperational test procedure. This procedure did not include a requirement to specifically record the stop setting.
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f IE Circular No. 78-11 June 15, 1978 included only a requirement to verify that the stop setting had been made.
It appears likely that these same procedures, and perhaps the same engineer, were involved in the preoperational/startup test programs at several other sites.
All holders of operating licenses for Boiling Water Reactor plants employing recirculat ion M-G sets should be aware of the potenti 1 for improperly or undocuinented settings on recirculation M-G set speed stops.
It is recommended that the following be considered in your review:
1.
Facility records should be searched to determine if the actual existing set point on the recirculation M-G set overspeed mechanical stops is positively established.
2.
If the setting of the mechanical and electrical overspeed stops is in doubt, then steps should be initiated to determine the setting or additional conservatism should be included in the determination of Kf.
3.
The actual Kf being used for the process computer calculations in the determination of MCPR limits should be verified to be appropriate to (or more conservative than) the actual setting of the recirculation M-G set mechanical overspeed steps.
This circular is also issued to holders of BWR Construction Permits for information or use as appropriate to assure that steps are taken during the preoperational test program to confirm that the M-G over-speed stops are set properly and that the proper Kf will be used with the process computer.
No written response to this circular is required.
If you require additional information regarding this matter, contact the Director of the appropriate NRC Regional Office.
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IE Circular No. 78-11 June 15, 1978 LISTING OF IE CIRCULARS ISSUED IN 1978 Circular Subject Date Issued To No.
of Issue 78-01 Loss of Well Logging 4/5/78 All Holders of Source Well Logging Source Licenses 78-02 Proper Lubricating Oil 4/20/78 All Holders of for Terry Turbines Reactor OLs or cps 78-03 Packaging Greater Than 5/12/78 All Holders of Type A Quantities of Reactor OLs, cps, I
Few Specific Activity Fuel Cycle, l
Radioactive Material Priority I Mate rial for Transport and Waste Disposal Licenses 78-04 Installation Error That 5/15/78 All Holders of Could Prevent Closing of Reactor OLs or Fire Doors cps 78-05 Inadvertent Safety Injection 5/23/78 All Holders of During Cooldown Reactor OLs or cps 78-06 Potential Common Mode 5/23/78 All Holders of Flooding of ECCS Equipment Reactor OLs or Rooms at BWR Facilities cps 78-07 Damaged Components of a 5/31/78 All Holders of Bergen-Paterson Series Reactor OLs or 25000 Hydraulic Test cps Stand 78-08 Environmental Qualification 5/31/78 All Holders of of Safety Related Equipment Reactor OLs or at Nuclear Power Plants cps 78-09 Arcing of General Electric 6/5/78 All Holders of Company NEMA Size 2 Reactor OLs or Contactors cps Enclosure Page 1 of 1 1033 m3
IE Circular No. 78-11 June 15, 1978 LISTING OF IE CIRCULARS ISSUED IN 1978 Date of Issued to Circular Subject Issue No.
6/14/78 All Medical Control of Scaled Licensees in 78-10 Sources Used in Categories G Radiation Therapy and G1 I
k Enclosure Page 2 of 2 1
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