ML19345A590
| ML19345A590 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 04/12/1968 |
| From: | Skovholt D US ATOMIC ENERGY COMMISSION (AEC) |
| To: | |
| Shared Package | |
| ML19345A588 | List: |
| References | |
| NUDOCS 8011240250 | |
| Download: ML19345A590 (4) | |
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S/EETt EVALUATION BY THE DIVISION OF REACTOR LICENSING DCCKET NO. 50-29 IN THE PATTER OF YANKEE ATDMIC ELECTRIC COMPR.'Y PROPOSED CHANGE NO. 81 INTRODUCTION By letter dated March 1,1968, Yankee Atoric Electric Company requested appmval of Proposed Change No. 81 to the Technical Specifications of License Ib. DPR-3 to authorize the loading of Core VII and the irradiation of four test fuel asserblies clad with zircaloy-4 in the Yarkee Atomic Power Plant.
DISCUSSION ihe licensee proposes to load Core VII at the next refueling of the Yankee reactor.
Core VII will be loaded in the three-region fuel loading pattem used in the previous cores. The fuel loading configuration for Core VII wil? be as follcus:
Region A (center) - This region will contain fou-fuel asse-blies, originally 4.94% enriched uranium, stainless steel clad, which were irradiated in Cores V and VI to an average exposure of approxirately 19,000 &'D/hTJ.
Region 3 (middle) - This region will contain thirty-six fuel asserblies originally 4.94% enriched uranium, stainless steel clad, which were irradiated in Core VI to an average burnup of spproxirately 9,600 E'D/MiU.
Region C (peripheral) - This region will contain thirty-two unirradiated stainless steel clad, 4.94% enriched uranium fuel assemblies, plus four preposed test asserblies containing the zircaloy clad fuel rods. The four test asserblies include two designated as Type A and two designated Type B, with rinor differences between them.
Core VII will be operated with borated coolant, as was Core VI.
The excess re-activity of Core VIl will be less than Core VI due to the large burnup of the Core VI fuel asserblies that are being recycled in Core VII. Therefore, no 5 crease in the current authorized limit of 1700 ppm boron concentration (above 15 we) is mquired.
EVALUATION The licensee has perforced calculations which show that the hot shutdown rargins will be 4.5% delta k with 111 rods in, a:xi 2.1% delta k with the highest worth centrol rod fully withdrawn. The pmsent minirum license mquirements are 4%
delta k and 2% delta k, respectively.
In addition, boron will be added to the 801124,0 N
s primry coolant to reaintain the reactor at least 5% delta k subcritical during any cooldown, and 7% delta k subcritical during refueling. Since the shutdown mrgin is adequate, we agree with the licensee's conclusion that the reactivity contml provided for Core VII is satisfactory.
The licensee has evaluated the therral capabilities of Core VII. The D?!B ratios, heat fluxes, and hot channel temperatures wem analyzed as a functicn of rod position and power level. As in the analysis for previous core loadings, the hot-channel factors were found to impreve as fuel burnup progresses, xenon builds up and ccatrol rods are withdrawn from the core.
In onder to keep the Core VII therral conditions equal to or less severe than the
,1ues of prior cores for which accident analyses have been evaluated as aceptable, the licensee will lirit the recciar power to 485 Eit until control md groups 3, 4 and 5 are fully withdrawn from the core a:d the xencn reaches near equilibrium. The power will then be raised to 600 Mwt. A -inistrative procedures are used to lirit power.
The nuclear instrumntation scram points are readjusted for each power level. The licensee has evaluated the accidental increase in power to 600 Met instead of the 485 Met when contml rod group 5 is still the contmlling gmup. This situation presents the rest severe hot-channel factors. The calculpted rinimum D??B ratio using the W-2 correlation, with the coolant terperature at 527"F, is 2.11 for the stainless steel asse-bly,1.87 for the zircaloy A test asse-bly and 1.84 for the zircaloy B test asse-bly. With the W-3 correlation, (which is now used in place of the W-2 correlaticn for pressurized water power reactors and which elirinates the discontinuity at the saturation temperature and provides a single unadigious criterion of the design rargin), the IllB ratios are 3.67, 2.18 a-1 2.17, respectively.
The rinimum D?IB ratio specified in the Technical Specifi-cations is 2.0 for norral operating conditions and 1.25 for abnomal corditions.
Since the D!!B ratios calculated by both correlations are greater than the rinimum values specified in the Technical Specifications, we concur with the licensee's conclusion that even if the lirits set on the reactor power are exceeded, and the reactor is operated at 600 Ikt with contml red group 5 controlling, ther al conditions are less severe than in previous accident analyses. Based on the previous operating experience of the Yankee reactor and the anticipated power distribution for Core VII, we believe that the safety rargins in Core VII are adequate.
Four zircaloy test assemblies (two Type A and two Type B) will be incitded in Core VII to confirm the adequacy of design and predicted performnce of each type.
The applicant has reviewed reactivity transients with respect to the circonium-clad test asserblies for Core V and has adequately considered the potential consequences of reactor operation with such test elements. Since the zircaloy test asserblies in Core VII differ only slightly from those in Core V, we agree with the conclusion reached by the licensee that the transient behavior of the core is not affected by the presence of the four zircaloy clad fuel elements.
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o A CONCLUSION On the basis of the foregoing considerations, we have concluded that the pro-posed change does not present significant hazards considerations not described or implicit in the hazards sur: mary report, and that there is reasonable assu-ance that the health ard safety of the pablic will not be endangered by operation of the reactor in the r:anner proposed.
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n Donald J.skovholt Assistant Dimetor for Reactor Operations Division of Reactor Licensing Date: April 12, 1968 n
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