ML26020A218
| ML26020A218 | |
| Person / Time | |
|---|---|
| Site: | Technical Specifications Task Force |
| Issue date: | 01/20/2026 |
| From: | Office of Nuclear Reactor Regulation |
| To: | Technical Specifications Task Force |
| References | |
| Download: ML26020A218 (1) | |
Text
NRC Staff Comments on Draft TSTF-606, Revise the Actions Associated with an Inoperable Rod Worth Minimizer Rod Worth Minimizer (RWM) Trip Settings Refer to Columbia Generating Station which uses RWM system at low power during startup. Its Final Safety Analysis Report (FSAR) Section 7.7.1.2.2.2, Rod Block Trip System, paragraph b.2.(e) states:
The RWM can initiate a rod insert block and a rod withdrawal block. The purpose of these functions is to reinforce procedural controls that limit the reactivity worth of control rods under lower power conditions. The rod block trip settings are based on the allowable control rod worth limits established for the design basis rod drop accident.
Adherence to prescribed control rod patterns is the normal method by which this reactivity restriction is observed.
According to the above description, the RWM system is provided with rod block and rod withdrawal trip settings established for the control rod drop accident (CRDA). In the absence of the RWM system, explain how these trips at the same trip setting in the RWM are accomplished.
Procedural Controls The RWM provides rod withdrawal and rod insertion block signals if the control rod movements ordered by the operator do not comply with the analyzed rod position sequence (BPWS NEDO-21231-A and Improved BPWS NEDO-33091-A, Rev 2). During low power operations, specific control rod sequences are designed to mitigate the consequences of CRDA.
The BPWS limits individual control rod worths so that, should a CRDA occur, the peak fuel enthalpy would remain below the specific energy design limit of 280 cal/gm. Beyond 280 cal/gm fuel rod failure is assumed to occur. For the RWM function to be bypassed or inoperable, its block function would be disabled. For startup without RWM, what are the specific procedural controls that should be implemented to prevent a Chanter 15 rod withdrawal error (RWE) event.
Reference 1-General Electric Topical Report NEDO-21231, "Banked Position Withdrawal Sequence," dated January 1977.
General Electric topical report NEDO-21231 has been recently revised to NEDO-21231-A, Revision 1. The only change in this revision is the inclusion of the NRC safety evaluation for the
-A version plus a correction of an error on page A-2 of the report. The ADAMS accession package number of the issued report is ML25248A319. Please revise Reference 1 accordingly.