ML19345A420
| ML19345A420 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 06/20/1969 |
| From: | Skovholt D US ATOMIC ENERGY COMMISSION (AEC) |
| To: | |
| Shared Package | |
| ML19345A417 | List: |
| References | |
| NUDOCS 8011210354 | |
| Download: ML19345A420 (4) | |
Text
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O O
t SAFETY EVALUATION BY THE DIV*ISION OF REACTOR LICENSING DOCKET No. 50-29 YANKEE ATCHIC ELECTRIC COMPANY FROPOSED CHANGE NO. 86 INTRODUCTION By letter dated May 9, 1969, Yankee Atomic Electric Company requested approval of Proposed Change No. 86 to the Technical Specifications of License No. DPR-3, to authorize the loading of Core VIII, and to continue the irradiation of four test fuel assemblies clad with Zircaloy-4 in the Yankee Atomic Power Plant.
DISCUSSION The licensee proposes to load Core VIII at the next refueling of the Core VIII will be loaded in the three-region fuel loading Yankee reactor.
The fuel loading configuration for pattern used in the previous cores.
Core VIII will be as follows:
Region A (center)
This region will contain four fuel assemblies, originally 4.947.
enriched uranium, stainless steel clad, which were irradiated in Cores VI and VII to an average exposure of approximately 20,000 MWD /MTU.
Region B (middle)
This region will contain thirty-two fuel assemblies originally 4.947. enriched uranium, stainless steel clad, which were irradiated in Core VII to an average burnup of approximately 9.300 MWD /MTU, and four test assemblies containing the zircaloy clad fuel rods, which were irradiated in Core VII to an average burnup of approximately 13,000 MWD /MTU. The test assemblies were discussed in Proposed Change No. 81.
Region C (paripheral)
This region will contain thirty-six unirradiated, stainless steel clad, 4.947. enriched fuel assemblies of the same type used in Cores VI and VII.
011210 M f 3
t t Core VIII will be operated with borated coolant, as was Core VII.
Ihe excess reactivity of Core VIII will be less than Core VII, therefore, no increase in the current authorized limit of 1700 ppm boron concentration (above 15 Hwe) is required.
EVALUATION The licensee has performed calculations which show that the hot shutdown margins will be 4.4% delta k with all rods in, and 2.1% delta k with the highest worth control rod fully withdrawn. The present minimum licente requirements are 4% delta k and 2% delta k, respectively.
In addition, boron will be added to the primary coolant to maintain the reactor at least 5% delta k subcritical during any cooldown, and 7%
delta k subcritical during refueling. Since the shutdown margin is ade-quate, we agree with the licensee's conclusion that the reactivity con-trol provided for Core VIII is satisfactory. Further, the reactivity coef ficients for Core VIII with respect to changes in power, temperature and void content are essentially the same values as for Core VII and have been determined by us te be acceptable.
The licensee has evaluated the thermal capabilities of Core VIII. The DNB ratios, heat fluxes and hot channel temperatures were analyzed as a function of rod position and power level. As in the analyses for previous core loadings, the hot channel factors were found to improve as fuel burnup progresses, xenon builds up and control rods rre withdrawn from the core.
In order to keep the Core VIII thermal conditions equal to or less severe than the values of prior cases for which accident l
analyses have been evaluated as acceptable, the licensee will limit the reactor power to 540 Mwe until control rod greaps 3, 4 and 5 are fully withdrawn from the core (control rod group 6 is withdrawn prior to crit-icality) and xenon reaches essentially its equilibrium value. The power will then be raised to 600 Mwt.
Administrative procedures are used to l
limit power and to ensure that the nuclear instrumentation scram points are adjusted for each new power level. The minimum DNB ratio specified in the Technical Specifications is 2.0 for normal operating conditions and 1.25 for abnormal conditions. Since the calculated DNB ratios for Core VIII are greater than the minimum values specified in the Technical Specifications, we agree with the licensee's conclusion that the thermal 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 VIII, we have concluded that the safety margins in Core VIII sre adequate.
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. Four zircaloy test assemblies (two Type A and two Type B) were included in Core VII to confirm the adequacy of design and predicted performance of each type. To date, none of the four test elements has exhibited any unusual conditions. The four zircaloy clad test assemblies that were irradiated in Region C during Core VII operation will be moved to Region B for Core VIII. Because of the burnup experienced by these test assemblies during Core VII operation, they will contribute less reactivity worth in Core VIII. The minisasa calculated DNB ratios for Core VIII are higher than those calculated for Core VII. On the basis of our review, we have concluded that the safe operation of the Yankee reactor will not be adversely affected by the continued irradi-ation of the four test assemblies in Core VIII.
CONCLUSION On the basis of the foregoing considerations, we have concluded that the proposed change does not present significant hazards considerations not described or implicit in the hazards summary report, and that there is reasonable assurance that the health and safety of the public will not be endangered by operation of the reactor in the manner proposed.
,,o N Donald J.
kovholt Assistant Director for Reactor Operations Division of Reactor Licensing Date: June 20, 1969 1
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