ML20148D815

Safety Evaluation Rept Supporting Amend#26 to Facil Oper Lic#R-28 Concluding That an Increase from 1 Mw to 2 Mw in Maximum Allowed Pwr of Fnr w/10-plate Fuel Assemblies in E,W & Core Positions Is Acceptable

ML20148D815
Person / Time
Site:	University of Michigan
Issue date:	10/13/1978
From:	Office of Nuclear Reactor Regulation
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ML20148D805	List: ML20148D800 ML20148D808 ML20148D815
References
NUDOCS 7811060019
Download: ML20148D815 (3)

Text

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1. UNIT E D STATEti f #

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION _

SUPP_0RTING AMENDMENT NO. 26 TO FACILITY OPERATING LICENSE N0. R-28 UNIVERSITY OF. MICHIGAN FORD NUCLEAR REACTOR

. DOCKET NO. 50-2 Introduction By letter dated June 27, 1978, the University of Michigan (the licensee) requested an amendment to Facility Operating License No. R-28. The requested amendment would authorize the Ford Nuclear Reactor (FNR) to operate at a maximum power level of 2 Mw with 10-plate fuel assemblies, acquired from the Pennsylvania State University (PSU) Research Reactor, in the east, west and south fringe locations of the FNR core. The Commission authorized, by Amendment No. 24 to Facility License No. R-28 dated October 12, 1977, operation of FNR at power levels up to 1 megawatt (Mw) with the 10-plate PSU fuel assemblies intermixed with the normal 18-plate FNR fuel assemblies. This request is necessary to improve the FNR's utilization for experiments by allowing the power level to be increased to the normal value of 2 Mw while continuing to use the excess 10-plate fuel assemblies from PSU.

Background

In our Safety Evaluation (SE) supporting Amendment No. 24, we found that substituting the 10-plate fuel assemblies for 18-plate fuel assemblies was acceptable if the maximum reactor power level was limited to 1 Mw.

This finding was based on:

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' Reducing the maximum FNR power level from 2 Mw to 1 MW results in nearly identical thermal / hydraulic performance of 10-plate and 18-plate fuel assemblies for the forced convection cooling mode;

' Extensive operating experience which proved the design accept-ability of the 10-plate fuel assembly; and

' Ascertaining that reactivity parameters were within existing Technical Specification (TS) values by performing startup tests.

Evaluation To support the return to operating the FNR at power levels up to 2 Mw, the licensee has performed experiments to measure the thermal flux level for various core loadings of 18-plate and 10-plate fuel assemblies. The 781 M Ool

measurements were made at 1 Mw using a self-powered rhodium detector.

Since the normal 18-plate fuel assembly contains less of the fission-able uranium isotope (U-235) than the PSU 10-plate fuel assembly,140 -

grams verses 169 grams U-235, it is expected that the 10-plate fuel assembly should generate more power (increased neutron flux level) than the 18-plate fuel assembly. The experiments confirmed that operating at 1 Mw with 10-plate fuel assemblies in the center of the core results in a power generation increase of about 18 percent. However, in the fringe (outside row) of the core, the neutron flux data indicated less effect on the power generation of the 10-plate fuel assemblies. In one experiment, substituting a single 10-plate fuel assembly on the north fringe decreased the neutron flux by about 14 percent, while in another experiment with 3 adjacent 10-plate fuel assemblies on the south fringe, the neutron flux increased by about 10 percent. The results of the experiment with 3 adjacent fuel assemblies were provided in a supplement from the licensee dated September 14, 1978. Extrapolating these experimental results for a confiauration with 10-plate fuel assemblies in all locations along a fringe, we conclude the maximum flux value will occur in a mid-fringe assembly and that the overall increase will be insignificant.

The conclusion reached by the licensee is that the peak power generation of 45 Kw, corresponding to a normalized measured neutron flux of 0.045 presently authorized for 1 tb operation, will not be exceeded by the power generation of PSU 10-plate fuel assemblies located in the east, west and south fringe positions of the core with the reactor operating at 2 Mw. This conclusion was justified by the experimental data showing that the maximum power generation during 1 Mw operation, of a fringe 10-plate fuel assembly was 22 Kw and increasing the authorized reactor power level to 2 Mw will, because of the cosine shape of the neutron flux, increase the fringe assembly power generation by less than a factor of 2. Therefore, the power generation of a 10-plate fuel assembly in a fringe location will be less than 44 Kw. The licensee did not apply to load the PSU 10-plate fuel assemblies in the north fringe core positions because of the neutron flux peak shift toward the heavy water shielding tank located against the north face of the core.

We conclude that an increase from 1 Mw to 2 Mw in the maximum allowed power of the FNR with 10-plate fuel assemblies in the east, west and south core positions is acceptable. He base this conclusion on:

eAs shown above, increasing the maximum FNR power level from 1 tk to 2 Mw, results in peak power generation in 10-plate fuel assem-blies in fringe locations to be less than or equal to that gener-ated in central core locations at 1 Mw. Therefore, the thermal /

hydraulic performance of these fuel assemblies in fringe locations at 2 Mw will be nearly identical to that of fuel assemblies located ~

in the central core at 1 Mw for the forced convection cooling mode, eExperimental evidence indicates that the power generation of the 10-plate fuel . assemblies located in the fringe, operating in a core limited to power level of 2 Mw, is bounded by the power generation of these fuel assemblies operating in a central core location at a core power level of 1 Mw;

' Operating experience with the PSU 10-plate fuel assemblies that shows reactivity parameters are within existing Technical Specification values.

Environmental Consideration We have determined that the amendment does not authorize 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 determination, we have further concluded that the amendment involves an action which is insignificant from the standpoint of environmental impact and pursuant to 10 CFR 651.5(d)(4) that an environmental impact statement or negative declaration and environmental impact appraisal need not be prepared in connection with the issuance of this amendment.

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 accidents previously considered and does not involve a significant decrease in a safety margin, the amend-ment 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 will be conducted in compliance with the Commission's regu-lations and the issuance of the amendment will not be inimical to the L

common defense and security or to the health and safety of the public.

Dated: October 13, 1978 6

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