ML19345A639

Safety Evaluation Supporting Proposed Change 80 to Tech Specs

ML19345A639
Person / Time
Site:	Yankee Rowe
Issue date:	04/29/1968
From:	Skovholt D US ATOMIC ENERGY COMMISSION (AEC)
To:
Shared Package
ML19345A638	List: ML19345A637 ML19345A639
References
NUDOCS 8011240399
Download: ML19345A639 (4)

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y SAFETI EVALUATIO'; BY THE DIVISION OF REACTOR LICD! SING

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YANKEE AIDMIC ELECTRIC COMPR N PROPOSED CHAZE NO. 80 TO TECNICAL SPECIFICATIONS 3

3 INTRODUCTION 1968, Yankee Atomic Electric Conpany requested approval By letter dated January 4, to substitute one electrically-operated control valve, to be used as a variable orifice, for the three fixed orifices and nunually-operated block valves in the bleed line of the Charging and Volume Centrol System of the Yankee Nuclear Pw er Station. This request has been designated Proposed Change Ib. 80.

DISCUSSION In the present system, bleed-line flow is adjusted in the range from 0 to 100 gpm by the mnual operation of valves to pemit bleed flow through the appropriate combination of three flow orifices connected in parallel. In series with this prallel co2ination of orifices, there is an isolation valve which is normlly open, but which closes autonatically if the water level in the pressurizer vessel falls below a set point. The charging pumps automtically adjust feed flow to mintain a constant water level in the pressurizer vessel.

This During operation, the pressure drop across the orifices is about 2000 psi.

high pressure drop has caused wear and has required replacement of crifices and In order to reduce maintenance, the licensee proposes to repair of block valves.

replace the parallel cocination of orifices and block valves with one control This control valve is designed to take a very high pressure dmp, and is valve.

capable of adjusting the bleed flcw continuously in the range from 6 to 100 gpm.

The control valve will be operated electrically fmm the control room.

In the design of current pressurized water reactors, the pressure reduction is accomplished in two stages, first through an orifice and then through a pressure control valve, thus reducing the pressure drop across the orifices. The licensee has evaluated a design concept similar to that presently used in me new plants, but has decided to use a single control valve of a type used in bciler feeduater Tne licensee will not renove the existing parallel bleed lines with system.

orifices until operating experience is gained with the new control valve.

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EVALUATION 7

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We have evaltated the potential hazards resulting from failure of the proposed 3

contml valve to perform its function thmugh loss of power, imdvertent mis-operation and erosion of the valve plug.

Even though the valve is designed for a large pressure dmp across the valve plug, some emsion of the valve plug might occur. Such erosion would lessen the flexibility that the control valve provides, but mkes it no less effective frem either a durability or safety standpoint than the present orifices. 'Ihere-fore, if the valve plug wem to erode, the consequences would be an operational inconvenience and possibility of plant downtire, but no hazard censiderations would be involved.

In case of loss of power, the electrically-operated control valve will remin static in its position; therefore, the situation would be the same as having the present fixed crifices in the line, which has been previously evaluated in the Final Hazards Sumary Report and found to have no hazard inplications.

Inadvertent closing of the valve would stop the flw of coolant to the purifi-cation system. As a result, the activity level in the coolant would incret_,e.

However, the purification system flow rate is so smil in carparison to the total coolant volume that the activity increase would be very gradual. We believe that the purification system f1w can be stopped for an extended period of tire (several weeks under norral operating conditions) without appreciably increasing the radio-activity level of the coolant. Any increase in mdioactivity level of the coolant would be detected by routine sa pling and analysis of the coolant. Therefore, we conclude that the inadvertent closing of the control valve would not present significant hazards considemtions.

'Ihe inadvertent opening of the control valve will increase the bleed flow to the aximum capacity of the control valve. If bleed flow exceeds feed flow, the water level in the pressurizer vessel will drop. However, when a low-water level con-dition exists in the pressurizer vessel, all bleed flow is stopped by closure of the isolation valve in the bleed line dwnstream of the orifices and the proposed contml valve. 'Ihe resulting situation is the same as that evaluated above for inadvertent closing of the valve. If the water level drops too far, alams will notify the operator to take corm ctive action. Eventt: ally, the reactor will be scra red from the pressurizer vessel 1m-water-level signal. Even if this safety circuit does not function, l w reactor pressure wottld scram the reactor thereby protecting the reactor. Therefore, we conclude that the inadvertent opening of the proposed contml valve would not present significant hazards considerations.

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Lj CO?'CLUSIO!!

We conc 1tde that the substitution of one electrically-operated control valve for the fixed orifices and trantally-operated block valves does rot present significant hazards considerations rot described or implicit in the hazards sumry report and that there is reasonable assurance that the health and safety of the public will rot be endangered by operation of the facility in accotxlance with the prgesed change.

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F Donald J. c svholt Assistant irector for Reactor Operations Division of Reactor Licensing Date:

April 29, 1968 C

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