ML20148Q523
| ML20148Q523 | |
| Person / Time | |
|---|---|
| Site: | Dresden, Quad Cities  |
| Issue date: | 11/13/1978 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20148Q509 | List: |
| References | |
| NUDOCS 7811300077 | |
| Download: ML20148Q523 (4) | |
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UNITED STATES O/
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DRESDEN AND QUAD CITIES NUCLEAR POWER STATIONS COMMONWEALTH EDISON COMPANY DOCKET NOS. 50-237, 50-249, 50-254 AND 50-265 Introduction _
By letters dated September 10, 1974 and May 17, 1976, as supplemented by letters dated March 21, 1977 and March 13, 1978, Commonwealth Edison (CE) proposed changes to the Technical Specifications appended to Operating Licenses DPR-19 and DPR-25 for Dresden Units 2 and 3, and Technical Spec-ifications appended to Operating Licenses DPR '9 and DPR-30 for Quad Cities Units 1 and 2.
The changes would modif) the reactor coolant system thermal and pressurization limitations to account for irradiation induced increases in reactor vessel metal nil ductility temperature (RT DT).
The N
CE submittals were based on the determination that certain changes were necessary to bring the reactor coolant system pressure-temperature limits into conformity with the requirements of Appendix G to 10 CFR Part 50.
Discussion Title 10 CFR Part 50, Appendix G " Fracture Toughness Requirements", requires that pressure-temperature limits be established for reactor coolant system heatup and cooldown operations, inservice leak and hydrostatic tests, and reactor core operation.
These limits are required to ensure that the stresses in the reactor vessel remain within acceptable limits.
They are intended to provide adequate margins of safety during any condition of normal operation, including anticipated operational occurrences.
The specific pressure-temperature limits which are initially established depend upon the metallurgical properties of the reactor vessel material and the design service conditions.
However, the metallurgical properties vary over the lifetime of the reactor vessel because of the effects of neutron irradiation.
One principal effect of the neutron irradiation is that it causes the reactor vessel nil ductility temperature (RTNDT) to increase or shif t with time.
The practical results of the RTNDT shift 1
I RT is the temperature associated with the transition from ductile to briklefracturemodeoffailure.
7811300077
. is that for any given value of reactor pressure, the reactor vessel metal temperature must be maintained at higher values during the heatup and cooldown process.
By periodically revising the pressure-temperature limits to account for neutron irradiation induced increases in RTNDT, the stresses in the reactor vessel are maintained within acceptable limits.
Evaluation The CE submittals dated September 10, 1974 and May 17, 1976 included, for the Dresden Units and Quad Cities Units, respectively, pressure-temperature limits for hydrostatic testing, mechanical heatup and cooldown and minimum temperature for Core Operation (criticality).
During our review of these submittals we determined that the radiation damage estimate curves, i.e.,
the effect of neutron fluence on RTNDT, did not appear to be as conservative as that presented in Regulatory Guide 1.99.
I In a letter dated February 15, 1978, CE stated that their radiation damage estimateswerebasedona"worsgcase" basis.
Subsequent staff calculations determined the end of life neutron fluence made on " worst case" conditions at-the one-quarter thickness (1/4T) location to be 9x1017 n/cm2,3 Branch Technical Position MTEB 5-2 " Fracture Toughness Requirements" requires that calculations be performed in regions of high stress unless the assumed RTNDT.of the beltline region is at least 50 F above the RTNDT of all higher stressed regions.
To satisfy this requirment, CE obtained stress intensities in regions of discontinuities by adjusting the results of a generic analysis made to account for differences between the design and materials of the Dresden and Quad Cities vessels and those of the reference plant.
We have reviewed the licensee's submittal and determined that this is an acceptable procedure for calculating pressure-temperature operating limits.
The operating limits for hydrostatic testing, mechanical heatup or cooldown, and minimum temperature for core operagion (criticality) were calculated by CE and submitted on March 13, 1978.
Based on the use of the previously discussed " worst case" damage estimates, an end of life neutron fluence of 9x1017 n/cm2 at the 1/4T location, and the limiting curves submitted on March 13, 1978, we conclude that these limits and damage estimates are acceptable for operation through approximately 6 effective full power years.
Accordingly, the staff added a Specification to the temperature and pressure limits to require that the figures for hydrostatic testing, mechanical heatup and cooldown, and minimum tempera-ture for core operation (criticality) will be updated to account for radia-tion damage at least 6 months prior to 6 effective full power years.
This additional requirement was discussed with and agreed to by the licensee.
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We conclude that the pressure-temperature operating limits as amended by the staff are acceptable through 6 EFPY.
For this operating period the proposed pressure-temperature operating limits are in accordance with Appendix G, 10 CFR Part 50.
Compliance with Appendix G in establishing safe operating limitations will ensure adequate safety margins during operation, testing, maintenance and postulated accident conditions and constitute an acceptable basis for satisfying the requirements of NRC General Design Criterion 31, Appendix A,10 CFR Part 50.
Environmental Consideration We have determined that the amendments do 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 amendments involve an action which is in-significant from the standpoint of environmental impact and, pursuant to 10 CFR B51.5(d)(4), that an environmental impact statement or negative declaration and environmental impact appraisal need not be prepared in connection with the issuance of these amendnents.
i Conclusion We have concluded, based on the considerations discussed above, that:
i (1) because the amendments do not involve a significant increase in the probability or consequences of accidents previously considered and do not involve a significant decrease in a safety margin, the amendments do not involve a significant hazards consideration, (2) there is reasonable assur-ance that the health and safety of the public will not be er. dangered by operation in the proposed manner, and (3) such activities will be con-ducted in compliance with the Commission's regulations and the issuance of these amendments will not be inimical to the common de7ense and security or to the health and safety of the public.
Dated:
November 13, 1978
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References 1.
Letter to Don Davis (NRC/0RB #2) from M. S. Turbak (CE); dtd February 15, 1978.
2.
i.e., the upper limit line in Regulatory Guide 1.99, Revision 1.
3.
Adjusted data from Table 2-2 of NED0-21708 per instructions in table note.
Results from this procedure yield more conservative results than those supplied by CE.
t 4.
Submitted as Figures 4, 5, and 6 in attachment to letter from M. S.
Turback (CE) to George lear (NRC/0RB #3); dtd March 13, 1978.
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