ML20212D447
| ML20212D447 | |
| Person / Time | |
|---|---|
| Site: | University of Missouri-Columbia |
| Issue date: | 09/20/1999 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20212D442 | List: |
| References | |
| NUDOCS 9909230123 | |
| Download: ML20212D447 (4) | |
Text
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% UNITED STATES
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! j NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 30086 4001
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO. 31 TO
' AMENDED FACILITY LICENSE NO R-103 THE UNIVERSITY OF MISSOURI- COLUMBIA DOCKET NO. 50-186
1.0 INTRODUCTION
By letter dated May 4,1999, as supplemented on July 23,1999, the University of Missouri - ,
Columbia (UMC or the licensee) submitted a request for amendment to the Technical Specifications (TSs),' Appendix A, of Amended Facility License No. R-103 for the University' of Missouri Research Reactor (MURR). The licensee has requested changes in the TSs to authorize the conduct of movable and unsecured experiments in the center test hole of the reactor.
2.0 EVALUATION The licensee has requested changes in TS 3.6.e to allow the conduct of movable and unsecured experiments in the center test hole of the reactor flux trap. The center test hole of the flux trap is one of the experimental facilities at the MURR. TS 1.6 defines " Flux Trap" as that portion of the reactor through the center of the core bounded by the 4.5-inch inside diameter tube and 15 inches above and below the core vertical center line. TS 1.3 defines the
" Center Test Hole" as the volume in the flux trap occupied by the removable experiment test tubes.
One of the attributes of experiments that must be closely controlled in a research reactor is the reactivity effect that experiments will have on the reactor. Adding reactivity to a critical reactor makes the reactor supercritical, which results in increased reactor power. If the reactivity of the reactor is changed during operation such that the reactor control system or the physics of the reactor's design cannot compensate for or accommodate the change, damage to the reactor fuel may result. Of particular concem is the sudden addition of a lerge amount of reactivity to a critical, operating reactor. The reactivity effect that an experiment will have in a reactor depends or .1e composition of the experiment and the location of the experiment in the reactor.
To protect the reactor from damage, research reactor TSs contain limits on the amount of reactivity that types of experiments may possess.
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The types of experiments that are defined in the TSs are movable (TS 1.11), secured (TS 1.24),
. and unsecured (TS 1.25). The definitions of these experiments are as follows:
Movable Exoeriment A movable experiment is one which is designed with the intent that it may be moved into and out of the reactor while the reactor is operating.
Secured Experiment A secured experiment is any experiment which is rigidly held in place by mechanical means with sufficient restraint to withstand any anticipated forces to which the experiment might be subjected.
Unsecured Exoeriment An unsecured experiment is any experiment which is not secured as defined in T.S.1.24, or the moving parts of secured experiments when they are in motion.
The reactivity limits for experiments are given in TS 3.1 as follows:
1 3.1 g. The reactivity worth of each secured removable experiment shall be limited to 0.006 AK.
3.1.h. The absolute value of the reactivity worth of all experiments in the center test hole shall not exceed 0.006 AK.
3.11. Each movable experiment or the movable parts of any individual experiment shall have a maximum absolute reactivity worth of 0.001 AK.
3.1 J. The magnitude of the reactivity worth of each unsecured experiment shall not exceed 0.0025 AK.
3.1 k. The sum of the magnitudes of the reactivity worths of all unsecured experiments which are in the reactor shall not exceed 0.006 AK.
One reason for these TS limits is to help ensure that if an experiment moved either intentionally
- (movable experiment) or unintentionally (movable or unsecured experiment) in the reactor during operation, the reactivity charige would not damage the reactor. Because secured experiments have the most constrairts against inadvertent movement, it has the highest I
allowed reactivity worth. Likewise, movable experiments have the smallest allowed reactivity worth because they can be placed into and removed from the reactor while it is in operation.
The experiment reactivity limits for unsecured and movable experiments are based on a step addition of reactivity and were analyzed by the licensee during initial licensing of the reactor and have been shown not to create a safety problem.
l TS 3.6 e. on experiments and the basis for the TS currently state- 1 l .
1 3.6 e. Experiments in the center test hole shall be removed or installed only with 1 the reactor shutdown and shalbe rigidly held in place during reactor l operation. '
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Bases a
3.6 e. Although the reactivity worth of experiments h the center test hole is
! restricted to less than the reactivity insertion which would cause fuel element failure, this specification eliminates a potential mechanism for uncontrolled addition of reactivity.
The licensee has proposed that this TS and bases be amended to read:
3.6 e. Only movable experiments in the center test hole shall be removed or installed with the reactor operating. All other experiments in the center test hole shall be removed or installed only with the reactor shut down. Secured experiments shall be rigidly held in place during reactor operation.
Bases -
3.6 e. Specification 3.6.e is intended to limit the experiments that can be moved in the center test hole while the reactor is operating, to those that will not introduce reactivity transients more severe than one that car $ be controlled wnhout initiating safety system action (Ref. Add. 5 to HSR).
The licensee is not requesting any changes in the definition of " flux trap," " center test hole,"
" movable," " secured" or " unsecured experiment" or the reactivity limits on experiments. The requested TS will allow the center test hole to be controlled by the same TS requirements as the rest of the experimental facilities at the MURR.
At the time of initial reactor operation in 1965, restrictions were placed on the use of the center test hole beyond those placed on the other experimental facilities. The restrictions are that experiments in the center test hole are only moved with the reactor shut down and are rigidly held in place during operation (secured experiment). This measure was imposed to prevent experiments in the center test hole from moving during operation and having a reactivity effect on the reactor.
The estimation of the reactivity worth of an experiment before it is placed in an experimental facility is based on calculations and experience with similar experiments. Because of the high neutron flux in the center test hole, errors in the estimation of the material composition of an experiment or uncertainties in the accuracy of the calculations would have a larger impact on reactivity than in the other experimental facilities. The 1965 safety analysis report for the reactor recognized that as experience was gained with the use of the center test hole,'the restrictions could be relaxed.
The ability to conduct unsecured and movable experiments in the center test hole will allow the j licensee additional flexibility in reactor utilization. The licensee has irradiated approximately 20,000 different sample cans in the center test hole with a wide variety of contents over the past 30 years.
The licensee estimates the reactivity of samples to be irradiated using a one-energy group importance function based on reactivity type and a position factor utilizing perturbation theory.
This method is based on reactor physics which allows evaluation of the effect on reactivity of i
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. small changes in the properties of an initially critical reactor. The licensee determines a position factor, which is an indication of the neutron flux the experimental sample will be exposed to, based on the location where the sample will be placed in the experimental facility and the size of the experimental sample. The type worth for the experimental sample (etiective macroscopic cross-section), which is an indication of how the sample will interact with the neutron flux, is determined from a sample reactivity measurement in the reactor or by comparison with known samples, if calculations show that a new experiment type is acceptable, the licensee can measure the reactivity effect of the experiment by looking at the difference in control rod position at low power with the experiment in and out of the experimental facility. The licensee can also conduct conservative measurements such as placing an experiment in the reactor as a secured experiment to take advantage of the higher reactivity limit to confirm that the experimental sample meets the lower requirements for a movable experiment. Where the sample type has been previously irradiated, the licensee also can refer to actual reactivity measurements. The licensee's methods for estimatirs reactivity and procedures for the conduct of experiments have resulted in a history of accurate determinations of sample reactivity worth The NRC staff asked the licensee about the accuracy of estimates of experimental reactivity worths over the last 10 years. During this period, there have been no instances in which the estimated reactivity worths have been in error such that the error resulted in exceeding the TS limits.
The staff finds that the licensee has gained sufficient experience with the irradiation of samples in the center test hole to accurately estimate their reactivity worth through calculations, measurements, and past experience. The licensee will continue to follow the existing TS on experiment definition and experiment worth. Therefore, the staff concludes that the conduct of movable and unsecured experiments in the center test hole is acceptable.
3.0 ENVIRONMENTAL CONSIDERATION
This amendment involves changes in the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 or changes in inspection and
- surveillance requirements. The staff has determined that this amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that ;
may be re! eased off site, and 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 prapared in connection with the !
issuance of this amendment.
4.0 CONCLUSION
The staff has concluded, on the basis of the considerations previously discussed that (1) because the amendment does not involve a significant increase in the probability or i consequences of accidents previously evaluated, or create the possibility of a new or different i
kind of accident from any accident previously evaluated, and does not involve a significant reduction in a margin 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.
PrincipalContributor: A. Adams,Jr.
Date: Septster 20,1999
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