ML20113E741
| ML20113E741 | |
| Person / Time | |
|---|---|
| Site: | University of Texas at Austin |
| Issue date: | 07/02/1996 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20113E740 | List: |
| References | |
| NUDOCS 9607080313 | |
| Download: ML20113E741 (4) | |
Text
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k UNITED STATES j
j NUCLEAR REGULATORY COMMISSION
'C WASHINGTON, D.C. 20555-0001
,o SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO. 1 TO FACILITY OPERATING LICENSE NO. R-129 DOCKET NO. 50-602 THE UNIVERSITY OF TEXAS AT AUSTIN
1.0 INTRODUCTION
By letter dated January 25, 1993, the University of Texas at Austin (UT or the licensee) notified NRC of a reportable event at its TRIGA research reactor, and applied for an amendment to Facility Operating License No. R-129. The licensee reported that as part of a test of an update replacement of the control system software for the reactor instrumentation and control (I&C) system it was discovered that a discrepancy existed between one requirement for control rod interlocks in the technical specifications (TSs) and the reactor control system design.
The licensee proposed to remove the discrepancy by amendment of the TSs, and enclosed a proposed revision. The licensee also committed not to operate the reactor in automatic or square-wave modes pending NRC action on the application. The licensee supplemented their request by letters dated November 11, 1995, April 16, 1996, and June 6, 1996.
2.0 EVALUATION Non-power reactors are designed to avoid or limit possible accidents or malfunctions that could lead to loss of fuel integrity or uncontrolled release of radioactive material. One such potential accident is a nuclear power excursion initiated by insertion of a large amount of reactivity in a short amount of time.
To limit such an event, many non-power reactors with multiple control rods are typically designed so that only one rod can be withdrawn at a time with the reactor in manual operating mode.
This is usually accomplished by an interlock system activated by a manual switch on each rod.
The UT reactor has three types of control rods; two shim rods, which are manually controlled; one regulating rod which may be controlled manually or by an automatic servo-controller; and one transient rod which can be used to control the reactor manually or can be used to initiate a power pulse. The reactor has four operating modes; manual where all rods are manually controlled by the operator; automatic where a servo-controller moves the l
regulating rod to maintain the reactor at a set power level; pulse mode where l
the pulse rod can be rapidly removed from the core to initiate a power pulse; l
and square wave, where reactor power is rapidly increased to a power level within the steady state power limit, held at that power for some period of I
time and then the reactor is shut down.
9607080313 960702 PDR ADOCK 05000602 P
. These I&C systems are designed so that when an automatic servo-controller is in control of the regulating rod, it may be possible to insert additional reactivity by moving a shim rod simultaneously by manually activating its individual switch.
The UT TS contained an errcr in that it considered manual mode (where simultaneous withdrawal of two rods is prohibited) to also consist of automatic mode and square wave modes instead of considering each mode separately.
This prohibited the reactor from being operated as designed.
If a shim rod were withdrawn while the reactor was operating at steady power in automatic mode, the servo-controller would react to try to compensate for the added reactivity by inserting.
If the requested reactor power level was below the actual power level, a shim rod could be manually withdrawn while the regulating rod was withdrawing until the requested power level was reached.
Most TRIGA reactors, such as the one at UT, are designed to operate in this way.
The automatic servo-controller on this reactor is also designed with a minimum reactor period limiter, so that if the reactor period were to be decreased to this limit by manual withdrawal of a shim rod, even if the actual power were well below the demand power level, the servo-controller would drive the regulating rod into the core to decrease the reactivity.
This additional feature provides further assurance that short reactor periods cannot be initiated by inadvertent manual control rod withdrawal while the reactor is operating in the automatic mode.
In addition to these instrumentation safety features, TRIGA reactors are designed to operate safely in the pulsed mode, with rapid insertions of reactivity. The UT reactor is authorized to operate in the pulse mode with reactivity insertions up to 3.145.
The UT TRIGA reactor has a General Atomics designed and supplied I&C system whose design was reviewed and approved by the NRC staff and is similar to that reviewed and approved by the staff for the General Atomics Mark I TRIGA reactor, the Armed Forces Radiobiology Research Institute TRIGA reactor, the l
Dow Chemical Company TRIGA reactor, the United States Geological Survey TRIGA reactor, and the University of Illinois TRIGA reactor.
UT TS 3.2.2 was inadvertently written to state that the control-rod interlock could prevent simultaneous withdrawal of more than one rod under all conditions, which would include when the automatic servo-controller is operating in either steady state or square wave mode. Thus, the TSs are not consistent with the reactor system, as built and operating.
Because the staff considers the safety of the reactor I&C system acceptable, as designed, correcting the TSs is an acceptable remedy.
i Changes to the TSs have been requested by the licensee to clarify the TSs and allow the TSs to accuracy reflect the existing I&C system.
The definition for shim rod, TS 1.22.1 currently reads:
A shim rod is a control rod having an electric motor drive and scram capabilities.
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4 The licensee has proposed changing this definition to read as follows to clarify ambiguities in the original definition:
A shim rod is a control rod with an electric motor drive that does not perform a special function such as automatic control or pulse control.
The shim rod shall have scram capability.
The licensee has proposed changes to the table in TS 3.2.2 including footnotes defining reactor operating modes which shows control safety system interlocks.
The changes show specifically the types of control rod for which interlocks must be functioning for each effective mode of operation.
The proposed TS clearly shows that in manual mode all four rods are interlocked to prevent simultaneous withdrawal and in automatic mode two shim rods and one transient
- rod must have their simultaneous withdrawal interlock function operable which allows simultaneous withdrawal of the regulating and one other rod. The licensee has also proposed changes to the basis for this TS to clarify the operation of the regulating rod under automatic control. This allows the TS to agree with the design of the I&C system.
The licensee has proposed changes to the table in TS 3.2.3 including footnotes defining operating modes which shows scram safety channels that shall be I
operable. The changes clearly show all effective modes to be consistent with TS 3.2.2.
The licensee also rearranged the information in the table without changing the information.
l The licensee has proposed changes to the table in TS 3.2.4 including footnotes defining operating modes which shows minimum measuring channels that shall be i
The changes clearly show all effective modes to be consistent with TS 3.2.2.
The licensee also rearranged the information in the table and added a new column to the table on instrument system function.
l The staff has determined that the proposed changes to the TS would result in no change in the actual reactor systems or operating conditions and that the proposed changes to the TS clarify the actual design and achieve consistency with the I&C system.
These operating conditions have been found acceptable on several other licensed TRIGA reactors. Thus, this license amendment would not l
change radiological risks to the operating staff, the environment, or the public and therefore, is acceptable to the staff.
In the letter dated June 6,1996, the licensee proposed an additional change to the UT TSs.
UT has changed the name of the site the reactor is located at from the Balcones Research Center to the J. J. Pickle Research Campus. The licensee proposed changing TS 5.1.1 a. to reflect this change.
This change is administrative in nature and is therefore acceptable to the staff.
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3.0 ENVIRONMENTAL CONSIDERATION
This amendment involves changes in the installation or use of facility components located within the restricted area as defined in 10 CFR Part 20 ano changes in inspection and surveillance requirements.
The staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and there is no significant increase in individual or cumulative occupational radiation exposure. Accordingly, this amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of this amendment.
This amendment also involves changes in recordkeeping, reporting, or administrative procedures or requirements. Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(10).
Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of this amendment.
4.0 CONCLUSION
The staff has concluded, based on the considerations discussed above, that:
(1) because the amendment does not involve a significant increase in the probability or consequences of accidents previously evaluated, or create the possibility of a new or different kind of accident from any accident previously evaluated, and does not involve a significant reduction in a margin l
of safety, 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 the proposed activities, and (3) such activities will 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 the health and safety of the public.
Principal Contributors:
R. E. Carter, INEL A. Adams, Jr., NRC Dated:
July 2, 1996 l