ML20206P393

Proposed Tech Specs,Revising 3/4.1.7, Reactivity Change W/Temp to Be Consistent W/Increased Values for Calculated Reactivity Worth of Reserve Shutdown Sys,Per Rev 4 to FSAR, Section 3.5.3.3

ML20206P393
Person / Time
Site:	Fort Saint Vrain
Issue date:	04/08/1987
From:	PUBLIC SERVICE CO. OF COLORADO
To:
Shared Package
ML20206P386	List: ML20206P381 ML20206P393
References
TAC-65241, NUDOCS 8704210174
Download: ML20206P393 (9)

Text

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e ATTACHMENT 2 PROPOSED CHANGES 8704210174 870408 PDR ADOCK 05000267 P PDR

Amandment No.

Page 3/4.1- 36.

REACTIVITY CONTROL SYSTEMS 3/4.1.'7 REACTIVITY CHANGE WITH TEMPERATURE

~ LIMITING CONDITION FOR OPERATION 3.1.7 The reactivity change due to a CORE AVERAGE TEMPERATURE increase between 220 degrees F and 1500 degrees F, shall be at .least .as negative as 0.031 delta k but no more negative than 0.065 delta k throughout the REFUELING CYCLE.

APPLICABILITY: POWER OPERATION, LOW POWER, and STARTUP ACTION: With a reactivity change outside-the range specified, the reactor shall be placed in ' SHUTDOWN within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> of determination.

SURVEILLANCE REQUIREMENTS 4.1.7 At the beginning of each REFUELING CYCLE the reactivity change as a function of CORE AVERAGE TEMPERATURE change (temperature coefficient) shall be measured and integrated to verify that the measured reactivity change is within the above limits.

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Amendment No.

Page 3/4 1- 37 BASIS FOR SPECIFICATION LCO 3.1.7/SR 4.1.7 The negative temperature coefficient is an inherent safety mechanism that tends to limit power increases during temperature excursions. It is a stabilizing element in flux tilts or oscillations due, for example, to xenon transients.

Fuel temperatures during a power excursion beginning from a high power level are well within design limits regardless of the magnitude of the negative temperature coefficient, provided protective action is initiated by a power. level signal. However, if protective action occurs much later, such as from a manual scram or activation of the Reserve Shutdown System, peak fuel temperatures will be senutive to the magnitude of the negative temperature coefficient.

Requiring a reactivity change at least as negative as 0.031 delta k for a CORE AVERAGE TEMPERATURE increase from 220 degrees F to the 1500 degree F temperatures associated with the nominal RATED THERMAL POWER value, ensures temperature coefficients at least as negative as those used in the FSAR accident analysis. All rod withdrawal transients assume a reactivity temperature defect of 0.028 delta k which when combined with an uncertainty of plus or minus 10%, yields the specified defect of 0.031 delta k.

The maximum reactivity temperature defect of 0.065 delta k (0.072 delta k minus 0.007 delta k for uncertainty) assures that there is sufficient reactivity control to ensure. reactor SHUTDOWN in the unlikely event that all control rod pairs cannot be inserted and the reserve shutdown system has been activated.

The reactivity worth of the reserve shutdown system was calculated to be 0.130 delta k in the equilibrium core (FSAR Section 3.5.3). From calculated excess reactivity data in Table 3.5-4 and Section 3.5.3 of the FSAR it is seen that the maximum excess reactivity in the equilibrium core with the CORE AVERAGE TEMPERATURE of 220 degrees F, Xe-135 decayed, Sm-149 built up, and 2 weeks Pa-233 decay, is 0.102 delta k. Assuming no control rods are inserted and the reserve shutdown system has been activated, the excess SHUTDOWN MARGIN for that excess reactivity is 0.028 delta k, (0.130 delta k minus 0.102 delta k). The calculated reactivity temperature defect for that cycle is 0.044 delta k. Therefore, if the reactivity temperature defect were as large as 0.072 delta k (0.044 delta k plus 0.028 delta k) reactor SHUTDOWN could be ensured for at least 2 weeks even for the unlikely event that all control rods failed to insert, ano the reserve shutdown system was activated.

Amendment No.

Paga 3/41- 38

.g .

The major shifts in reactivity change' as a function of core

- temperature change will occur following refueling. The specified frequency of measurement following each refueling will assure

. that the change of reactivity as a function of changes in core temperature will be measured on a timely basis to evaluate the limit provided in Specification 3.1.7.

The maximum value of reactivity. temperature defect occurs at the beginning of the cycle and slowly decreases through the cycle to a minimum value at the end of the cycle. . Since the measurement

' is made at the beginning of a cycle and the minimum value occurs at' the end of a cycle, a direct evaluation cannot be made.

However, by comparing the calculated value at the beginning of the cycle with the measured value, an evaluation for compliance can be made using the calculated value at the end of cycle.

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ATTACHMENT 3 SAFETY ANALYSIS

O Attachment 3 SAFETY ANALYSIS This Technical Specification specifies limits for the reactivity change with temperature, both a minimum limit and a maximum limit.

The minimum limit is to assure that the temperature coefficients are at least as negative as the those used in the FSAR rod withdrawal accident analyses and the maximum limit assures that there is sufficient reactivity control within the Reserve Shutdown System to ensure reactor SHUTDOWN in the unlikely event that no control rods are inserted. .

In Revision 4 to FSAR Section 3.5.3.3, the Reserve Shutdown System (RSS) calculated reactivity worth, when all 37 RSD units are inserted in the absence of any control rod pairs, was revised from 0.12 to 0.13 delta k for the equilibrium core, and from 0.13 to 0.14 delta k for the initial core. During a review of documentation in support of the Technical Specification Upgrade Program, PSC determined that the lower FSAR worths did not reflect the final reference core design.

The actual calculated RSS worths for the final core design are higher because of lighter uranium and thorium loading.

Since the maximum limit given in this specification is based directly on the calculated worth of the Reserve Shutdown System, this limit has been revised to be consistent with the updated value. The surveillance requirement to measure the reactivity change with temperature at the beginning of each refueling cycle is unchanged, and in fact still includes a 10% uncertainty for the measured value.

The basis for the proposed specification, which describes the manner in which these minimum and maximum limits were specified, has been revised to reflect the updated values.

In compliance with 10 CFR 50.59, the following questions are addressed:

1) Has the probability of occurrence or the consequences of an accident or malfunction of equipment important to safety previously evaluated in the FSAR been increased?

No. The FSAR has been reviewed and this change has no impact on the probability of any of the accidents analyzed.

Increasing the reactivity change with temperature would tend to reduce the consequences of rod withdrawal accidents analyzed, because any temperature increase resulting from the rod withdrawal would produce a greater negative reactivity addition due to temperature. The existing accident analyses, with the minimum temperature coefficients possible, are conservative. See FSAR Section 14.2.2.

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2) Has the possibility of an accident or malfunction of a different type than any evaluated previously in the FSAR been created?

N o '. The proposed specification change'does not involve any modification to plant systems, equipment, or- structures.

The only changes to procedures are to ensure compliance with the revised limit.

Ei Has the margin of safety, as defined in the basis for any 3)

Technical Specification been reduced?

No. The margin of safety that ensures' reactor shutdown capability for at least 2 weeks after.a failure of control rods to insert, allowing for 10% uncertainty in reactivities, is maintained. As noted above, the revised limit updates previously calculated values, and does not change the margin of safety as defined in the Technical Specification Basis.

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e ATTACHMENT 4 SIGNIFICANT HAZARDS CONSIDERATION t

J Attachment'4 SIGNIFICANT HAZARDS CONSIDERATION I. Evaluation From .the safety analysis provided as Attachment 3 to this Technical Specification change, it can be seen that revising the maximum limit of the allowable reactivity change with temperature does not result in an unreviewed safety question.

1. Neither the probability nor consequences of accidents previously evaluated have been affected by this proposed Technical . Specification change. The maximum limit is based directly on the calculated worth of the Reserve Shutdown System, which has been updated in Revision 4 of the FSAR.

That revision did not result from any new nuclear analysis nor changes to the analytical methods or model, but reflects.

the previously calculated value of the final core design.

2. The possibility of a new or different kind of accident from those previously evaluated has not been introduced. There is no change to the plant facility or equipment, and the only change in procedures reflects the revised maximum limit.

3. No margin of safety has been reduced. The logic in determining the maximum limit is unchanged, and the change in calculated worth of the Reserve Shutdown System, which is the basis for the limit, came directly from the calculated worth of the final core design.

II. Conclusion Based on the above evaluation, it is concluded that operation of Fort St. Vrain in accordance with the proposed changes will not (1) involve a significant increase in the probability or consequences of an accident previously evaluated, (2) create the possibility of a new or different kind of accident from any accident previously evaluated, or (3) involve a significant reduction in a margin of safety.

Therefore, this change will not create an undue risk to the health and safety of the public nor does it involve any significant hazards consideration.

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