ML20147C376

Safety Eval Rept in Support of Amend 40 to Oper Lic 39 & Amend 37 to Oper Lic 48

ML20147C376
Person / Time
Site:	Zion  File:ZionSolutions icon.png
Issue date:	11/30/1978
From:	Schwencer A Office of Nuclear Reactor Regulation
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Shared Package
ML20147C354	List: ML20147C348 ML20147C363 ML20147C369 ML20147C376 ML20147C380
References
NUDOCS 7812180242
Download: ML20147C376 (4)

Text

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8 4e UNITED STATES

[N . ,t NUCLEAR REGULATORY COMMISSION 3 A j WASHINGTON. D. C. 20555 M" n s,

,p SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO. 40 TO FACILITY LICENSE NO. DPR-39 l

SUPPORTING AMENDMENT NO. 37 TO FACILITY LICENSE NO. DPR 48 COMMONWEALTH EDISON COMPANY ZION STATION UNITS 1 AND 2 D

_OCKET NOS. 50-295 AND 50-304 Introduction By letter dated May 24, 1977 as supplemented September 27, 1978, Commor. wealth Edison Company (the licensee) requested a change to Technical Specifications appended to Facility Operating Licenses DPR-39 and DPR 48 for Zion Station Units 1 and 2, respectively.

The proposed amendments would allow the pressurizer boron concen-tration to be 200 ppm less than the reactor coolant loop beron concentration during plant heatup. The amendments would also cor ect two minor errors that presently exist in the Zion Technical Speci'i-cations regarding the Isolation Valve Seal Water Systems and the Penetration Pressurization Systems.

Discussion The Zion Station Technical Specifications presently require that, during plant heatup, the boron concentration in the reactor coolE:1t loops and pressurizer be sampled every 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> with a boron deviction of no greater than 50 ppa allowed between successive 4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> samples.

This has been interpreted as also limiting the difference betweer the pressurizer and reactor coolant loop boron concentration to 50 pim for the same 4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> sample period. This interpretation however, does not adequately recognize the normal dynamic swings in boron concentration in the pressurizer due to vaporization and condensation, especially during reactor heatup.

During heat up of the reactor coolant system, prior to startup, a steam bubble (vaporization) is formed in the pressurizer. causing an increased boron concentration in the remaining non-vaporized i water in the pressurizer. Conversely, when steam in the top of the pressurizer is condensed this increases the water content and the boron concentration decreases. Therefore, if during the cou se of a reactor heatup it becomes necessary to collapse and re-esta,lish i a steam bubble, the pressurizer boron concentration can be expected  !

1 7 81218 0 2 (1[ c'?

e to vary. An increase in the pressurizer boron concentration (bubb'.e formation) would have the conservative ef fect of increasing the reactivity shutdown margin of the core somewhat should the contents i

of the pressurizer mix with the reactor coolant system. A decrease in the concentration (bubble collapse) would have the opposite effect.

To gain more operating flexibility within acceptable changes in the pressurizer baron concentration the licensee has proposed to change the Zion Technical Specifications to allow a difference of up to 209 ppm between the boron concentr6 tion in the pressurizer and that of the reactor coolant loops. The Technical Specifications would continue to limit the reactor coolant loop boron concentration such that a dec ease of not more than 50 opm between successive 4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> samples would be allowed.

The licensee has also proposed two corrections to the existing Technical Specifications. The first involves the minimum requirec water level in the Isolation Valve Seal Water Tank and the second concerns the upper limit for long term uncorrected air consumption for the Penetration Pressurization Systems.

Evaluation The basis provided by the licensee for the proposed Technical Specification boron concentration change is that the pressurizer volume is small compared to the total volume of the reactor coolant system and that, therefore, the mixing of pressurizer water of lower boron concentration with the larger volume of the entire system ciuses only minor changes in the reactor coolant boron concentration and, hence, the reactivity of the core.

In the example provided by the licensee, a boron concentration of 1500 ppm is assumed in the reactor coolant flowing through the core and the 1300 ppm is assumed to be in the pressurizer which is connected t-minor reactor coolant system by a dead leg, if the pressurizer i.

also assumed to be completely filled with water at the lower concentration and then emptied into and mixed with the main reactcr coolant system flow paths, the resultant boron concentration in tne reactor coolant flowing through the core would decrease by approx.mately 22 ppm. This reduction of 22 ppn, caused by a 200 ppm difference between

the pressurizer and the main loops, is well within the variance of 50 ppm allowed for the reactor coolant system on successive 4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> samples. It would result in a small reactivity increase of about 1. 2" ak/k. The Zion Technical Specifications require a shutdown margir of at least 1". Ak/k when in a cold shutdown condition (T a less than 200*F) and between 1*, to 1.6",ak/k, depending on the reactor g olant borcn concentration, when greater than 200'F. The 0.2", ak/k change that would be experienced in the worst case (200 ppm difference in baron concentration) represents only a minor fraction of the total required shutdown mt egin of the system and therefore, no potential would exist for a significant reduction in the shutdown margin should the entire contents of the l pressurizer mix with the reactor coolant system at a time when thE main  !

reactor coolant flow boron concentration is already at its lowest allowed level. As discussed in the licensees letter of September 27, 1970 l the maximum variance of 50 ppm allowed for the reactor coolant sys*.em f on successive 4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> samples is a conservative limit that was inccrporated l during the initial plant startup. It was originally recommended as a precautionary measure by the reactor vendor for Zion Station as the first 4-loop Westinghouse plants to preclude unknown reactivity d'lutions during initial heatup due to the inadvertent addition of clean makeup water. The 50 ppm value was selected to insure that the differential measurement would be well above normal sample uncertainties and low enough to insure that subcriticality would be maintained with adet uate margin. The 50 ppm maximum allowed variance was included in the Zion Technical Specifications when the Unit 1 and 2 operating licenses were i issued in that it was conservative and constituted good operating philosophy.

The reactor vendor nb longer recommends such a limitation in its startup procedures and no other operating plant has such a requirement in its Technical Specifications. Rather than requesting a deletion of the existing requirement, the licensee has proposed to retain the max' mum allowed variance in boron concentration in the reactor coolant syttem between successive boron concentration to reflect its operating philosophy, but to gain some operating flexibility with regard to the allowed difference in boron concentration between the pressuriznr and reactor coolant system loop.

Based on our review of the licensee's proposed change we have con- luded that the licensee has properly evaluated the potential effects anu that no adverse impact on safety is involved. Based on the above we ccnclude that the proposed change is acceptable.

With regard to the proposed change to the Isolation Valve Seal Water System specifications, the present requirement to maintain a level v' at least 28" in the Seal Water Tank corresponds to a tank inventory of greater than 130 gallons of water whereas the minimum level requirement is based on a 70 gallon volume. The change would delete the level requirement and substituta the more basic 70 gallon minimum volume requirement.

We find this proposed change to be acceptable.

The other change would correct a calculational error made in Technical Specification Section 3.9.2E involving the upper limit for long term uncorrected air consumption for the penetration pressurization system.

The allowed uncorrected air consumption rate is 0.2", of containment volume per day at 47 psig. Converted to standard conditions, this amount of leakage would be 950 standard cubic feet per hour (SCFH) not 226.25 SCFH as presently contained in the Technical Specificat ans.

We find this proposed correction of a calculational error to be acceptable.

Environmental Considerations We have determined that the amendments do not authorize a change ir effluent types or total amounts or 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 551.5(d)(4), that an environmental mpact statement, or negative declaration and environmental impact appraisJ1 need not be prepared in connection with the issuance of these amencments.

CONCLUSION We have concluded, based on the considerations discussed above, th.t: (1) ,

because the amendments do not involve a significant increase in the l probability or consequences of accidents previously considered and do  :

not involve a significant decrease in a safety margin, the amendments I do not involve a significant hazards consideration, (2) there is reasonable i assurance that the health and safety of the public will not be end..ngered ,

by operation in the proposed manner, and (3) such activities will se l conducted in compliance with the Commission's regulations and the )

issuance of these amendments will not be inimical to the common defense l and security or to the health and safety of the public.

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