ML19256G243
| ML19256G243 | |
| Person / Time | |
|---|---|
| Site: | Summer  |
| Issue date: | 11/15/1979 |
| From: | Anderson T WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP. |
| To: | Stello V NRC OFFICE OF INSPECTION & ENFORCEMENT (IE) |
| Shared Package | |
| ML19256G241 | List: |
| References | |
| NS-TMA-2162, TAC-55816, TAC-55817, NUDOCS 7912280540 | |
| Download: ML19256G243 (2) | |
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Westinghouse Water Reactor esass Electric Corporat,lan Divisions PittsburghPenrcytvania 15230
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'Hovember 15, 1979 HS-TMA-2162 x,
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. Ref: NS-TMA-2063, l j)f March 30, 1979
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' 'ir. Y. Stello
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Office of Inspection and Enforcement
./.".d U. S. Nuclear Regulatory Commission 1717 H Street' Washington, D. C.
20555
Subject:
Rod Drop Analysis
Dear Mr. Stello:
This letter confirms a telephone notification by Westinghouse m November 15, 1979.
plants and 10CFR50.55e for plants under construction.
a previous notification (reference) under 10CFR50.59 was made by Westinghouse which identified the potentia On March 28, 1979 the NRC for certain classes of Westinghouse plants.
by Westinghouse at. that time to review the SAR dropped rod acci A meeting methodology and to revise Technical Specifications as required. f our was subsequently held.with the NRC on April 12 to di e
informed as to.the results of an ongoing investigation.l concern may involve ii
.. w ngoing review, we have determined that this or g naIn addition, a concern relative additional classes of Westinghouse plants.
This results from three to multiple dropped rod events has been identified.
newly identified potential problem areas.
' The assumption.of a single failure in the rod controller circuits of two an four loop plants may result in a response similar to that previo fied for three loop plants.tive High Flux Rate Trip protection system Specifications may be non-conservative.it.sertibn profiles for crop The following Negative Rate Trip Setpoints may also be non-conservative.
paragraphs further elaborate on these concerns.
1653 265 T912 80 $L}Q
Mr. V. Stello November 15, 1979 NS-TMA-2162
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b A review.'of all rod control systems was made to define failure modes with respect to postulating a single failure in the Rod Control System.
The review shows that for three loop plants, a single failure in the Pro-The two and four loop plant review shows tection System is most limiting.
that a single failure in the nuclear power auctioneering unit of the rod control system may result in more limiting DNB ratios than previously
.o Therefore, the SAR analysis may not represent the most limit-reported.
When the assumption of a ing assumption for credible single failure.
single failure in the rod control system is made, the two and four loop
..:e plant responses to dropped rods may t.e similar to the three loop con-cerns discussed in the referenced March 28 notification.
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The second concern involves a potential reduction in conservatism in the error allowances assumed in the analysis for the Power Range Neutron The value currently listed in the Technical
. Flux High Negative Rate.
This value assumed that Specifications is.S% of Rated Thermal Power.
the differentiation of the NIS power signal by the circuitry would eliminate all steady state errors in the circuit before the differen-tiation; therefore, only precision and accuracy errors after the dif-This assumption is now believed to be ferentiation were considered.
non-conservative since errors associated with precision (hysterisis, repeatability, etc.) may not be entirely eliminated by differentiator When these potential additionr1 errors are factored into the circuit.
analysis, a reactor trip may not occur in some cases previously assumed.
The thir.1 concern involves a potential reduction in conservatism in the method utilized to generate power distributions and rod worths for dropped New analyses have been performed using a more conservative rod events.
reactivity feedback model and the results indicate that certain multiple rod drops may not trip the reactor as previously assumed.
These concerns are basically a result of application of the single Past e.'
failure criteria in conjunction with conservative methodology.
experience shows that dropped rod events have always resulted in a reactor trip for a Westinghouse plant from the present Negative Flux Rate Trip logic and setpoint.
This in-The attachment-identifies the affected Westinghouse plants.
fonnation has been communicated to the utility owners of these affected Westinghouse recommends a meeting with appropriate NRC Staff plants.
i
. members (and affected utilities) to review these findings and determ ne an appropriate course of action.
If you require further information, please call-D. W. Call of my staff.
V truly you,rs, a
T. H. Anderson, Manager
/bek Nuclear Safety Department Attachment 1653 266 t
.