ML19309A616
| ML19309A616 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse, Oconee, Mcguire, Arkansas Nuclear, Crystal River, Rancho Seco, McGuire, Crane  |
| Issue date: | 02/03/1975 |
| From: | BABCOCK & WILCOX CO. |
| To: | |
| Shared Package | |
| ML19309A611 | List: |
| References | |
| NUDOCS 8003310504 | |
| Download: ML19309A616 (3) | |
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a REPORT ON EJECTED TJD WORTH EVALUATION This report is being made pursuant to 10 CFR 50.55 (e) on Significant Defi-ciencies to document the goneral investigation of a Significant Deficiency in the calculation of ejected rod worths and in the procedure for testing for hot zero power ejected rod worth.
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Identification of Problem AE On September 21, 1974, a zero power physics test was performed at Rancho Seco in which the ejected rod worth was measured to be 1.24% ao.
This value is in excess of the Technical Soecification limit of 1.0% as and the estimated maxi =ua ejected
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rod worth of 0.87% ap.
The test was performed with rod group 5 at the 17% with-drawn position; however, the Technical Specifications allow rod group 5 to be fully inserted at hot zero power. The ejected rod wor di is a function of the initial inserted rod worth and increases with greater Inserted worths.
~I Analysis g
e ri An investigation has revealed that the ejected rod worth for Rancho Seco (B&W's first soluble boren controlled plant to operate) was. estimated fron data and calculations made for rod-control plants.
It was not realized at that ti=e that the ejected rod worth is so greatly influenced by the initial inserted rod worth.
i f)N Rancho Seco has approximately 1.6% ao greater inserted worth in the regulating
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groups (5, 6, and 7) than the previously analyzed rod-control plants.
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The ejected rod worth measurement at Rancho Seco was performed with rod group 5 17% withdrawn rather than fully inserted as the Technical Specifications rod position limits would allow. This configuration was arrived at by a reactivity swap of the highest wnrth potential ejected rod being withdrawn and rod ;grong 5 being inserted fron'an initial position of 50% withdrawn.
The initial positAc'n of rod group 5 at 50% withdrawn was based on a very conservative consideration of shutdown margin with a stuck rod. Subsequent ceasurements were made with rod group 5 at the 50% withdrawn position and reactivity changes made by a boron swap with the potential ejected rod.
The later measurements showed a hot zero power potential ejected rod worth of 0.8% ap.
Analyses for the other B&W plants with Operating Licenses has revealed that all are within the 1.0% ao limit with the current Technical Specification rod position limits at hot zero power up to the control rod interchange.
This is supportec r-by actual measurements at each site with the regulating rod groups (5, 6, and 7)
-y fully inserted. After the centrol rod interciange, the analyses have shown the T-i rod control plants to exceed or be very close to the 1.0% ap limit with the control rods at the Technical Specification rod position limits at hot zero power.
,l The analyses have shown that, for soluble boron control plants, the BOL potential ejected rod worth is in excess of 1.0% ao (possibly as high as 1.6% ap) and that the effects of burnup are to reduce that worth. With a minimum of %50% withdrawal f
of rod group 5 at hot zero power, the 1.0% ap limit is not exceeded during the g
entire fuel cycle.
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For rod control plants, the opposite effect with burnup takes place.
The potential ejected rod worth is less than 1.0% do at BOL and increases with burnup. Af ter the control rod interchange, the ejected rod worth with all regulating rod groups inserted to the Technical Specification position limit exceeds 1.0% ao (possibly as high as 1.6% ao). With a rod index of 100% (rod group 5 at 87.5% withdrawn and rod group 6 at 12.5% withdrawn) after the control
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rod interchange, the ejected rod worth will not exceed the 1.0% ao limit.
pf Evaluation The maximum potential ejected rod worth acceptance criterion for the zero power physics test at Rancho Seco was based on an extrapolation rather than detailed calculations.
The zero power physics testing program was designed to verify the
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design, including the potential ejected rod worth.
The prc3 ram was in effect when the ejected rod worth measurement was made and, thus, met its intended function. It is conceivable, however, that an acceptable value (i.e., less thaa 1.0% op) could have been measured with rod group 5 partially withdrawn, whereas the maximum ejected rod worth at the fully inserted position (Technical Specifi-cation limit) would have been in excess of the 1.0% ao limit.
Thus, the s,afety of operations of the plant could have been affected adversely in the event of en ejected rod accident.
The ejected rod worth could have been in excess of the Technical Specification limit and the maximum value evaluated in the safety analysis.,-
There was a breakdown in B&W Quality Assurance because an additional measurement J
of ejected rod worth was made prior to notifying the B&W design organization that i
N the initial me0surement exceeded the maximum acceptance cricerion.'
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This problem is considered by B&W to represent a Significant Deficiency as defined by 10 CFR 50.55 (e).
Corrective Actions The Technical Specification rod position limits for Rancho Seco have been revised to restrict rod group 5 to a minimum withdrawal of 49% at zero power.
- Further, the Technical Specli1 cations have been revised to require that the regulating rod groups (5, 6, and 7) be placed within the Technical Specification limits subsequent to full withdrawal of the safety rod groups (1, 2, 3, and 4) and prior to deboration.
With these revisions, the ejected rod measurement procedure is nou consistent with
' the Technical Specifications.
The Technical Specifications for the other operating plants (Oconee 1, 2, and 3 THI-1, and ANO-1) will be revised as required and as verified by measurements of ejected rod worth at exposures of 100-200 EFPD at Oconee 2.
All operating B&W NSS plants have been notified that the Technical Specifications for the rod control
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plants must be revised to prevent the hot zero power ejected for worth.from exceeding the 1.0% Ao limit. The Commission was also notified by letter, James F.
Mallay to Mr. A. Giambusso, December 27, 1974.
T The plants wie.h Construction Permits will have restrictions on rod positions to
[I prevent the ejected rod worth from exceeding the Technical Specificatlin limit of 4
(T, 1.0% ao at hct zero power.
These limits will be defined prior to issuing final
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Technical Specifications.
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(V Reportability The application of 10 CFR 50, Section 55, paragraph (e) is to those plants with Construction Permits.
The interpretation of this regulation is that it applies 8
to those incidents and probicms identified,between the dates of the Construction Permit and the Operating License. Problems identified after an Operating License is obtained are reportable only under the provisions of the Technical Specifica-33 tions. It is considered that this problem represents a Significant Deficiency, but it is not reportable by any plant.
The justification fci this position is as follows:
Operating Plants (Oconee 1, Oconee 2, Oconee 3.
TMI-1, ANO-1, and SMUD):
The regulation (10 CFR 50.55 (e)) does not apply.
Plants with Construction Permits (TMI-2, Crystal River 3, Midland 1, FEdland 2, Davis-Besse 1, Bellefonte 1, Bellefonte 2, North Anna 3,
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North Anna 4, Surry 3, and Surry 4):
The Technical Specification rod position limits have not been defined.
The procedures for measuring potential ejected rod worth have not been finalized.
These plants will have the corrective action described above applied to the rod position limits and to the measurement procedures.
,s B&W is notifying each of the plants with Construction Permits and Operating Li' enses of this problem and of the B&W position relative to 10 CFR 50.55 (e).
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