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NUCLEAR REGULATORY COMMISSION
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%b,,,g /a February 4, 1993 Docket Nos. 50-335 and 50-389 MEMORANDUM FOR:
Ellis W. Merschoff, Director Division of Reactor Projects Region II FROM:
Gus C. Lainas, Assistant Director for Region II Reactors Division of Reactor Projects I/II Office of Nuclear Reactor Regulation
SUBJECT:
TECHNICAL ASSISTANCE REQUEST, CONTINUOUS CORE REACTIVITY MONITORING FOR COMBUSTION ENGINEERING REACTORS - TIA 92-022 (TAC NOS. M84757 AND M84758)
By memorandum dated October 22, 1992, you requested assistance in resolving the need for and means of continuous core reactivity monitoring for St. Lucie 2 and for Combustion Engineering (CE) reactors in general. Specifically, the question of whether a technical specification (TS) change is needed to assure proper reactivity monitoring and control was raised, and if so, to initiate that l
change.
In general, CE reactors contain excore monitors which sense leakage neutron 4
levels from 10 % to 200% power. The system is divided into startup, control, and safety channels.
e monitor (SRM) channel covers i
shutdown and subpower neutron levels (10Thestartup,orsourcerang%).
4 to 10' The safety channels, or wide-rangemonitors,aredividedintologarithmicandlinearpowerchapnelsand cover the subpower levels as well as the entire power range from 2x10' to 200%.
l The control channel yields information on core neutron level when the reactor is critical and supplying heat to the reactor coolant system and covers the range from 1 to 125%. The startup and safety channels overlap by at least one decade to prevent loss of indication when one range is operating at the high end of its scale and the next range is operating at the low end of its scale.
The St. Lucie TS as well as the current and improved CE Standard Technical 3
Specifications (STS) require redundant source range monitoring capability to detect changes in the reactivity condition of the core during refueling (Hode 6). Redundant neutron monitoring is required by the Wide Range Logarithmic Neutron Flux Monitor for Modes 1 through 5, as part of the reactor protection system (RPS) instrumentation LCO. These monitors provide contir.cous indication in the control room and are relied on for the mitigation by tF.e operator of events such as an inadvertent boron dilution from shutdown canditions.
It is the Wide Range Logarithmic Power Level-High trip that protects the integrity of the fuel cladding and the reactor coolant pressure boundary in the event of an unplanned criticality from shutdown.
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.s Ellis W. Merschoff February 4, 1993 The issue of continuous core reactivity monitoring is of sufficient safety significance such that neutron flux monitoring requirements for all Modes are discussed in the Bases of the CE Improved STS (ISTS).
ISTS 3.3.I, " Reactor Protection System (RPS) Instrumentation," addresses flux / power monitoring for Modes I and 2 as part of the RPS.
ISTS 3.3.I3, "[ Logarithmic] Power Monitoring Channels," addresses Modes 3, 4, and 5.
The requirements for source range neutron flux monitoring during refueling (Mode 6) are addressed in ISTS 3.9.2,
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" Nuclear Instrumentation."
No action is required to change the St. Lucie 2 current or improved STS.
The above position has been coordinated with the Reactor Systems Branch and the Technical Specifications Branch.
(Original Signed By H. Berkow for)
Gus C. Lainas, Assistant Director for Region II Reactors Division of Reactor Projects I/II Office of Nuclear Reactor Regulation Distribution M M 98f PDII
- Reading S. Va.ya G. Lainas H. Berkow E. Tana J. Norris OGC M. Boyle M. Sinkule, Region II 0FFICE LA:PDII-2 PM:PDhi-d 0:P0hb2 WE ETana M f JNorrk
}de h ouE 02/ / /93 02/ 'T /93 02/7/93
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OFFICIAL RECORD COPY FILENAME: A:\\SL84757. TAR i
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