ML19225A331
| ML19225A331 | |
| Person / Time | |
|---|---|
| Site: | University of Buffalo |
| Issue date: | 06/07/1979 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19225A328 | List: |
| References | |
| SER-790607, NUDOCS 7907180867 | |
| Download: ML19225A331 (5) | |
Text
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO.17 TO FACILITY OPERATING LICENSE NO. R-77 STATE UNIV GSITY OF NEW YORK AT BUFFALO DOCKET NO. 50-57 Introduction By letter dated July 18, 1977, as supplemented May 19, 1978, December 29, 1978, and January 9,1979, the State University of New York at Buffalo (the licensee) requested an amendment to the Technical Specifications (TS) of Facility Operating License No. R-77.
The requested change would permit:
I.
Reenabling of the automatic control system; II. Deletion of the period scram and period reversal; and III. Taking effluent monitor out of service for periods not to exceed four hours.
I.
Reenabling the Automatic Control System The licensee's P'JLSTAR reactor is equipped with an autcmatic pcwer level control system.- After the operator preselects the_ demand _ reactor power level the auto-matic power level control system driv = the shim-safety rod within acceptable limits to achieve and maintain the desired power level. This autcmatic control system is presently disabled (power level control is now performed manually) because the calculated reactivity insertion rate was in excess.
In the Hazard s Sumary the reactivity insertion rate is based on a rod speed of 8 inch / minute and the calculated rod reactivity worths.
Subsequently, the rod drives have been geared down to a sceed of 3 incn/ minute to meet another TS requirement which limits the reactivity insertion rate to 0.1 ak/k/second for all ganged rods.
In support of the request, the licensee measured the reactivity wortns of rods for a variety of core configurations that are representative of normal operations. The measured reactivity worths for all rods were more than a factor of 2 lower than the calculated values used in tne Hazards Sumnary. This comparison shows that maximum reactivity worth for the rods used in a core with the maximum allcwable leading (a worse case condition) is conservative.
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Evaluation The design basis startup accident in the Hazards Summary Report (Revision II September 23,1963) assumes that all six rods are driven out of the core at a maximum speed of 8 inch / minute and no corrective action is taken until the power reaches the high level trip point. Under such an accident scenario with the rods in core positions of maximum differential worths, the Hazards Summary states that the total reactivity insertion rate is 0.27 ak/k/sec. The peak power reached during this accident is 386 MW resulting M a total energy release of 17.6 MW-sec.
These values are well below the rorrt,1 pulse values of 2,000 MW and 40 MW-sec. which the staff found acceptable (i.e., Safety Evalsation Report June 18, 1964).
The most severe accident cowrning the malfunction of the automatic control system would be a continuous withdrawal of a single shim-safety rod.
In the eve.;t of such a malfunction with a rod speed limited to 3 inch / minute the licensee has shown the average and maximum reactivity intertion rate of the regulating control rod are less than 0.013 and 0.024% ak/k/sec respectively. The staff has evaluated these values and found them acceptable. The maximum reactivity insert;on of 0.024% ak/k/sec is more than a factor of ten below the desu;n casis startup accident discussed above (.27% ak/k/sec). This accident would therefore be
'ess severe than the design basis startup accident analyzed in the Hazards Surmary.
Based on these findings we have concluded that using the automatic control system tc control reactor power level will not significantly reduce the safety margin.
Therefore, the prorosed change is acceptable.
II. Deletion of the Period Scram and Period Reversal Discussion The period scram and the period reversal serves as protection against power pulses for-the MTR type core which was the approved core for the facility at the time of granting '. the operating license. Subsequently by Amendment No. 7 (June 14,1964),
the licensee was pennitted to operate the reactor with a PULSTAR core designed to with-stand power pulses of 2 milli-second and has routinely operated in pulse modes of approximately 5 milli-second. These operating conditiors are much more severe than the 4 second period scram and the IS second period reversal which the licensee procosed to disable from the nonnal scram circuit.
During the pulse made the period scram is T assed so that the pulse response can be monitored. For ronpulsing operation de period scram cannot be disabled wnich results in a fast scran when the reactor attains a 4 second aeriod. Tne licensee has reported that spurious activation of the pericd scram during nonpulsing operation has been causing most of the unplanned shutdowns. The period reversal has caused a decrease in operational flexibility. The North Carolina University is presently operating a similar PULSTAR reactor withcut a period scram nor a period
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Evaluation The Hazards Sumary Report for the design basis startup accident does not take any credit for the operation of the period scram nor the period reversal. The analysis however does take credit for the Coppler temperature coefficient and the high level scram setting. The high level scram is not affected by this proposed change.
The margin of safety would not be reduced by eliminating the period scram and the period reversal. This is illustrated by the tabulation below of the total reactivity insertion, which is a direct indicction of energy input, under the reactor designed pulse conditions, design basi: start accident, the 4 second period scram and the period reversal.
Total Reactivity Insertion Oceratina renditions
% ak/k Design Reactor Pulse 1.63 Design Basis Startup Accident Analysis (Rev. II, September 23,1963)
.943 Reactivity Insertion by 4 Second Period Scram
$0.40 Reactivity Insertion by a 15 Second Period Reversal s0.20 As shown above the total energy input to activate the period scram and the period reversal are much lower than the input energy of the design basis startup accident (i.e.,.243% ak/k) which is considered the lower bound of the safety margin. The design baris startup accident is also considered conservative from reactivity insertion rate point of view because the analysis is based on a rod speed of 8 inches /
minute whereas the existing rod drives are 3 inches / minute.
Furthermore, even if this lower bound of the safety margin would be reached, the Hazards Sumary shows that no fuel damage would occur. Based on the above evaluation the staff finds the licensee's proposed change acceptable.
III. Effluent Monitor Oceration Discussion The licensee has proposed a change to the TS pernitcing effluent monitors to be taken cet of ser. ice for periods not to exceed four hours in order to establish background activ10 levels curing reactor operations.
Information on these background levels is necessary to improve the accuracy of the monitor instrumentation.
Presently the licensee is obtaining background levels curing reactor shutdowns when the back-ground is lower than when the reactor is ocerating.
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4 Effluents from the reactor facility are exhausted through a roof vent and through a 160 f t. building stack. Air from the normally occupied personnel work areas is filtered and monitored by a gaseous effluent monitor before leaving the roof vent. Air drawn through the reactor facilities such as the thennal column, pneumatic cenveyor, hot cell, etc., is filtered, monitored for radioactive gaseous and particulate matter and then exhausted throggh the 160 f t. building stack. The effluent monitors located in the reactor building and the mechanical equipment area exhibits an increase in background activity when the reactor is operating. Although these monitors are adequately shielded, the shielding is not sufficient to completely eliminate the low level background activity. Additional shielding to eliminate all of the background activity or the installation of a duplicate system are economically prohibitive.and impractical.
The requested change would increase the accuracy of the monitoring instruments and the accuracy of setting of the al5nn setpoints.
Evaluation Each monitor will be isolated and bypassed during the four hour period when the low background activity level is checked. High airborne activity release could occur only in the unlikely event of a fuel failure or processing radioactive experiments.
In the 14 years of reactor operation there has never been a fuel element failure that resulted in airborne releases that activated the effluent monitor's alam system.
If a fu e 1 element failure would occur while an effluent monitor is isolated, the reactor operating personnel and the public would be adequatW protected because three area effl.uent monitors and the primary water monito. wc Id sense the high radioactivity and appropriate safety measures would be taken.
The licensee has agreed to limit the checks on the background activity level to four times a year and while such checks are in progress no unusual experiments will be condueted and no radioactive chemicals nor experiment processing will occur.
Changes to the TS reflecting these agreements are made part of this amendment.
Based on the above evaluation the staff has found this proposed cnange to the TS acceptable.
Environmental Consideration We have detemined that the amendment does not authori;:e a change in effluent types or total amounts nor an increase in power level and will not result in any significant environmental impact.
Having made this deternination, we have further concluded that the amendment involves an actior which is insicnificant from the standpoint of environmental impact and, pursuant to 10 CFR 851.5(d)(4), that an environmental impact statement, or negative declaration and environ-mental impact appraisal need not be prepared in connection with the issuance of this amencment.
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. Conclusion We have concluded, based on the considerations discussed above, that:
(1) because the amendment does not involve a significant increase in the probability or consequences of c:cidents previously considered and does not involve a significant decrease in a safety margin, the amendment does not involve a significant hazards consideration, (2) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (3) such activities wi.ll be conducted in compliance with the Commission's regulations and the issuance of this amendment will not be inimical to the common defense and security or to the health and safety of the public.
Dated: June 7, 1979
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