ML19345E409
| ML19345E409 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 02/12/1965 |
| From: | Boyd R US ATOMIC ENERGY COMMISSION (AEC) |
| To: | |
| Shared Package | |
| ML19345E408 | List: |
| References | |
| NUDOCS 8101160349 | |
| Download: ML19345E409 (4) | |
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HAZARDS ANALYSIS BY THE RESEARCH AND POWER REACTOR SAFETY BRANCH l
DIVISION OF REACTOR LICENSING 1
IN THE MATTER OF
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CONSUMERS POWER CG(PANY t
DOCKET No. 50-155 IN-CORE MONITORS AND PICOAMMETER 5% LEVEL TRIP Introduction Consumers Power Company has requested by letter dated October 27, 1964, changes in-the Technical Specifications of License DPR-6.
The changes, hereafter l
identified as Proposed Change No. 3, would permit the use during power opera-tion of new developmental in-core flux monitors, and improve picosameter scram circuit reliability when these instruments are set in their most sensitive ranges by providing a low range by-pass for the low 5% level trip.
Backaround In-Core Detectors Consumers Power Company and General Elee.tric Company are engaged in a program to develop improved reactot nuclear instrumentation in order that the neutron population can'be monitored from withf.i the core over the entire range from source to full power. They have indicated that two special in-core detectors are ready for testing in the Big Rock reactor and would be installed in place of two of the eight in-core probes during the current shutdown.
One of the special in-core instruments is a,Traversina Probe composed of a miniature fission counter and a rigid stainless-steel sheathed qua.tJz-fiber insulated triaxial cable operating within a dry-well thimble.
The f*ssion counter probe will have a sensitivity of approximately 10-4 counts per 6
second/nv and a readout range will extend from 10 to 10 cps. By positioning the probe about 3 feet below the core while in the power range, and at more
. sensitive positions within the core while in the sub-power range, the probes are expected to monitor reactor power level from source level to full power.
At lower power levels axial flux profiles can be obtained by raising or lowering the probe. Readout will be provided in the control room.
i The other special in-core instrument to be inserted into the reactor during the current shutdown is identified as a Camobell chamher Assembly consis ting of a fission counter and associated cable for use with a standard current pulse amplifier and log count rate meter, a Campbell chamber and associated cable for use with a Campbell counting system, and one cable with no detector but with a suitable terminating element to withstan? reactor coolant pressure.
The Campbell chamber will be connected to an "In-Core Wide Range Monitor" similar to a picoammeter, except that wide band a-c electronics will be employed rather than the d-c circuitry in the present meters.
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. Tha Campbell chamber voltage variance method of neutron monitoring has, according to General Electric and Consumers, the advantage of being almost independent of leakage currents caused by degradation of insulation resis-tance. They anticipate that the Campbell Chamber Assembly will provide power 1evel indication from 105 nv to 1014 Readout of the Campbell Chamber and nv.
the Start-up Fission Counter will be provided in the control room. The dead-ended cabis in the assembly is installed to obtain further information on degradation of cable insulation resistance, photoconductivity of quartz fiber and S glass and the ionization effects in quartz fiber and S glass cable.
5% of Scale Piccammeter Trip With regard to the Picosameter down scale trip, Consumers has pointed out that an upscale trip due to noise in one channel while operating in sensitive ranges has been quite common.
If a second channel is reading below 5% at the same time, again quite common for the most sensitive ranges, the reactor will scram in accordance with existing Technical Specifications. Consumers reports that to date the reactor has scrammed 28 times on upscale-downscale spurious trips, and there has been no instance of picosaceter, ion chamber, or ion chamber power supply failure during operation resulting in a downscale trip.
Evaluation In-Core Detectors Consumers Power Company plans to remove two of the eight in-core probes during the current shut down, and to insert the two different developmental in-core monitors described above. The existing Technical Specifications require that 12 of the 24 sensors contained in the in-core probes be operating.
(Eech of the 8 probes contains three miniature fission counters).
Consumers stated in its final hazards summary report that the out-of-core ion chambers, because of the rela tively small core size, are capable of detecting flux perturbations within the core and scramming the reactor before exceeding design limits, and that the in-core flux monitors are not necessary to protect the core.
On this basis, it was determined that connection of the in sore instruments to the scram protection system was not necessary fro a a safety standpoint.
However, the in-core sensors are used by the operat >rs at Consumers to measure local flux at a number of positions within the core.
If oscillations are detected by these instruments or appreciable differences between predictions and measurements occur, operator corrective action can and should be taken.
Use of the in-core instruments in this. facility provides l
added assurance that local fluxes within the core will not exceed design limits.
l The number of in-core instruments in service at any one time should be adequate to insure that local heat flux' limits are not exceeded, and that core power distribution is stable. To provide greater flexibility in the use of in-core detectors without compromising reactor safety considerations, we believe that the specificatione may be changed as follows:
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p t Section 6.1.2.4 "In Core Flux Monitors" In-core flux monitors shall be used to evaluate predict'ed power distri-l butions and detect power oscillations or deviations from' expected values in time for operator corrective action to avoid exceeding local heat flux limits or viola te.g stability criteria."
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f Section 6.1.5(f) Substitute the following:
"During power operation in-core flux monitors shall be operating to insure that local heat flux limits specified in Section 5.3.1 are not exceeded."
5% of Scale Picoansneter Trip To guard against undetected failure of a picoammeter, ion chamber, or ion chamber power supply, a downscale trip circuit was provided originally on each of the picoammeter circuits. When a picoammater signal is la'as than 5%
of scale, a signal greater than 120% of scale on either of the other pico-asumeters will cause an automatic reactor scrc s.
However, at low neutron levels the inability of the safety system to discriminate against spurious noise pulses causes frequent and unnecessary scrams if one of the picoenmeters is below 5%
of scale.
The most severe startup accident considered to be credible for the Big Rock Point reactor, assumes a rod withdrawal sequence to maximize the rate of power rise. This accident has been analyzed and is described in Sections 12.7 and
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12.13.2 of the Big Rock Point Final Hazards Summary Report.
Under tt.condi-j tions postulated for this accident, even if the power excursion continued into i
the power range and was terminated by a reactor scram on 120% ove.rpower trip, core damage or center fuel temperature in excess of 19500F would not result..
Under actual startup conditions scram would occur at least six or seven decadeslowerthantge120%powerlevel,assumingthepicosameterrangeof effectiveness is 10' to 125% of full power. Thus, it can be seen that if the low 5% scale trip circuit were bypassed for the. lowest picommmeter range settings, the rer;1Lant effect on core protection would not be significant.
Consequently, to eliminate spurious scrams while approaching power,a bypass could be provided to eliminate the 5% scale low level trip until the reactor power is above the range of excessive noise, 40 x 10-5% power. The intent of the Consumers change request is satisfied in this manner without completely eliminating the 5% low scale trip.
Accordingly, we believe Section 6.1.2 may be changed by adding the following under, the Scram Setting and Tolerance column for " Protection Against 3 Pico-ammeter Circuit Failure":
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"Except that the three downscale trips are simultaneously bypassed when the picoammeter range switches are simultaneously set to operate below 40 x 10-5% power. The bypass becomes ineffective when the range for 5
any of the detectors is ~ set above 40 x 107 % power".
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4 Conclusion On the basis of our evaluation we have concluded that the ' Technical Specifi-cations of License DPR-6 inay be revised as indicated. Proposed Change No. 3, in our opinion, presents no significant hazards not described or implicit in the hazards susunary report and there is reasonable assurance that the health and safety of the public will not be endangered.
vi:jnal sgned by-Roger S. Boyd Roger S. Boyd, Chief Research & Power Reactor Safety Branch Division of Reactor Licensing Date:
FG 12 365 1
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