ML19345E397
| ML19345E397 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 04/02/1965 |
| From: | Boyd R US ATOMIC ENERGY COMMISSION (AEC) |
| To: | |
| Shared Package | |
| ML19345E396 | List: |
| References | |
| NUDOCS 8101160282 | |
| Download: ML19345E397 (5) | |
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SAFETY ANALYSIS 3Y THE RESEARCH AND POWER REACTOR SAFETY BRANCH DIVISION OF REACTOR LICENSING IN THE MATTER OF
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CONSUMERS POWER COMPANY BIG ROCK POINT NUCLEAR PU,NT DOCKET No. 50-155 PROPOSED CHANGE NO. 6 - SPECIAL REACTOR START-UPS Introduction Consumers Power Company, by letter dated January 13, 1965, hes requested a change in the Technical Specifications of License DPR-6 to permit a limited number of reactor start-ups when the present minimum requirement of 3 counts per second (eps) and a signal t.o-noise ratio of 3 to 1 on the out-of-core low-level neutron detectors cannot be satisfied. Additional information was presented by WX's dated ' arch 2 and March 8,1965.
A D,lscussion i
Because of the 7-8 month reactor shutdown period starting September 18, 1964, and the resultant decay of the antimony-beryllium cource strength, Consumers anticipates that until sufficient power operation has been accumulated after the initial 1965 start-up to sufficiently irradiate the antimony pins, the signals at the out-of-core detectors will be too low to permit reactor siert-up in the normal manner. Consumers 1as, therefore, proposed special reactor r
vessel " head-off" approaches to r,riticality with extra neutron detectors I' ncat;ed within the core where the neutron concentration is higher in order to moniter neutron multiplication from the initial withdrawal of control rods to criticality.
Data from the normal out-of core instruments obtained during the " head-off" approaches to criticality will be used to evaluate and control reactor start-up when the in-core neutron detectors have been withdrawn and the reactor vessel head has been sealed and bolted onto the reactor vessel in preparation for reactor power operstion. The " head-on" approach to criticality will be con-ducted with out-cf-core neutron detectors, core geometry, loadin8, temperature, control rod withdrawal sequence and rate of control rod withdrawal unchanged.
Safety Evaluation In supplements to the original January 13, 1965 request to change the Technical Specifications (WX's dated March 2 and March 8,1965) Consumers has reported that:
1.
Core power for the previous 84 fuel bundle core with all rods fully inserted was 5 x 10-9 of full power. The maximum possible rod worth was 3.47.6k.
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The 82 bundle core to be assembled during March and April 1965, in i
the fully shut down condition with all control rods inserted, will be at 1 x 10-9 of full power (i.e. 10-7. full power). The maxinum 7
possible rod worth will be 3.47. ok.
3.
The start-up accident described in the November 14, 1961 Final l
Hazards Sumary Report for the Big Rock Point plant was based on a power level of 1 x 10-11 of full power (10-9. full power).
7 Maxinum rod worth considered was 3 97.dk.
4.
If the operator were *o deviate from written procedures during start-up and withdraw control rods in an off-standard sequence to insert reactivity at the maximum rate, the period monitor or picoammeter over power trip circuits would scram the reactor before power could increase appreciably, (i.e. approximately 10-4. indicated 7
power from picoameter scram circuit if low range is not res9t).
5.
If the worst reactivity insertion accident were to occur during the initial 1965 reactor start-up with the reactor vessel head removed, the transfer of energy from the fuel to the water would not begin until af ter the neutron flux transient had been terminated by the Doppler effect. The energy produced in the fuel rods would be re-leased by rapid boiling of the water and escape of steam to the containment vessel. Since the conteinment volume is approximately 220 times larger than the reactor coolant system and because of the many potential heat absorbers, the containment temperature and pressure changes as a result of this postulated worst reactivity insertion accident would be negligible.
Consumers has stated that the shutdown reactivity, based on the most recent calculations which consider among other things the substitution of zircaloy for stainless steel fuel bundle channels, is 0.951 and that withdrawal of the single control rod which inserts the most reactivity would result in a kegg of 0.99.
Out-of-core detectors should respond, according to Consumers, before this value of k,gg is reached.
Reactor safety is to be further enhanced by restricting the weguence and rate of rod withdrawals by special written procedures.
It has been predicted by Consumers and G. E. that when the outer 16 control rods are withdrawn to notch six, kegg will be 0.98. When the eight rods in outer rows A and F are withdrawn to notch eight, k gg will be 0.99 and response on out-of-core detectors e
will be above the specified mininum. Criticality is expected when control rod rows A and F are at approximately notch nine and rows 1 and 6 are at notches six or seven.
Based on the information above Consumers concludes, and we agree, that the most severe accident with reactor vessel head on or off resulting from con-tinuous insertion of reactivity would be less severe than the accident described 1
in the 1961 Final Hazards Sumary Report.
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, Conclusion Based on (1) the results of the most severe start-up accident analysis, (2)
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the requirements for written procedures wnich are designed to prevent such accident conditions, (3) the requirement that " head-of f" tests with neutron detectors -located -temporarily in the core be performed for erch different core geometry so that out-of-core detector response characteristics are known as the Tods are withdrawn vv. timugh-the all-rods-in count rate in below the sninimum response normally required at the out-of-core neutron detectors, and considering that the predicted source level will be about 1 cps at the out-of-core low neutron level sensors, we have concluded that the changes to the Te hnical Specifiuttions outlined below do not present c
significant hazard consideretions not described or implicit in the hazards sumnary report and that-thenr is reasonable assurance that-the health and safety of the public will not be endangered. Therefore, we have concluded that the Technical Specifications may be revised as set forth in Attachment A.
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y Roger S. Boyd, Chief Research & Power Reactor Safety Branch Division of Reactor Licensing
Enclosure:
Attachment A Dates APR 2 1965 i
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r ATTACHMENT A CONSUMERS POWER COMPANY CHANGES TO TECHNICAL SPECIFICATIONS CHANGE NO. 6 1.
Section 7.3.2(d) is changed to add a new paragraph to read:
"In the event that. the antimony-beryllium source strength is insufficient to produce a count rate of 3 counts per second (cps) and a signal-to-noise ratio of 3 to 1 on the out-of-core low-level neutron detectors, the approach to criticality for the reactor start-up following the September 18, 1964 shutdown and such additional start-ups as may be necessary until sufficient power operation has been accumulated to irradiate the antimony pans to acceptable levels (but not to exceed 3 months from first start-up) shall be allowed with the count rate from the two out-of-core low-level neutron detectors less than 3 cps and the signal-to-noise ratio-less than 3 to 1 provided that the following conditions are met:
Critical approaches with the reactor vessel head-off shall be a.
performed to evaluate the out-of-vessel low-level detector response, special low-level miniature in-core detector response and the control rod withdrawal sequences. Two additions 1 low-level detectors shall be temporarily inserted in the vessel to monitor these head-of f critical approaches and these detectors aust satisfy the minimum requirement of 3 cps with a 3 to 1 signal-to-noise ratio with all rods in.
b.
The intervals between the step (notch) control rod withdraws 1s shall be restricted-to permit continuous plotting and evaluation of control rod position, k,gg and detector signals, (a minimum of three miniature in-core fission counters, two temporary in-core low neutron level detectors, and all out-of-core detectors) vs. time until criticality is -achieved and the CIC picoacceters respond.
Evaluation of instrument responses during the head-off critical approaches-shall -demonserate that-by-the eime the estimsted k gg e
of the core reaches 0.990 either (1) the low-level out-of-core start-up detectors are reading at least 3 cps with a 3 to 1 signal-to-noise ratio or (2) the two special low-level in-core miniature detectors are responding to changes in k gg and are reading at least e
10 cps.
c.
Critical approaches with the head on and without the temporary in-vessel low-level detectors in service shall be permitted pro-vided thatt (1) The instrument response requirements of b. above have been demonstrated and these requirements are also ex-pected to be met during the critical approaches with the f
head on.
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(2) The sequence of control red withdrawal is identical to the sequence of rod withdrawal analyzed to be safe and used during the previous approaches to critica11ty'with the head off.
(3) The rate of control rod withdrawal is no faster than with-drawal rates used during ' head-off' tests.
(4) Rod positions, k gg and all nuclest signals are annually e
recorded or plotted against time and evaluated against the
' head-off' performance. Deviations from expected behavior during the start-up which could cause nuclear uncertainties shall require an immediate manus 1 scram of all control rods.
d.
The procedures in a. and b. above shall be repeated in the event 4
either a core configuration change or a significant change in the control rod withdrawal sequence is employed.
j e.
A qualified reactor engineer shall be in the control room during
-l all low source level start-up operatices overseeing the start-up operations."
2.
Section 7.3.2(e) is revised in its entirety to reads
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" Critical approaches shall be monitored using low-level neutron detectors.
The start-up rate shall be restricted to demonstrate that the CIC picosameters overlap of low-level neutron detectors signals for at least one decade starting at aboat 10-5, indicated full power on the picoammeters is normal 7
and satisfactory for control and safety purposes before continuing further into the power range. Control red withdrawal sequence shall be specified and limited to those sequences shown by previous analysis or tests to preserve fuel integrity in the event of accidental reactivity insertion either while starting up or at power."
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