ML20055G310
| ML20055G310 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 07/10/1990 |
| From: | Frizzle C Maine Yankee |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20055G311 | List: |
| References | |
| CDF-90-63, MN-90-69, NUDOCS 9007230032 | |
| Download: ML20055G310 (7) | |
Text
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MaineYankee Ni@MI5M"?RMf@5ME?OP2 ED! SON DRIVE
- AUGUSTA. MAINE 04336 * (207) 622 4868 July 10, 1990 MN-90-69 CDF-90-63 Proposed Change No. 155 UNITED STATES NUCLEAR REGULATORY COMMISSION Attention:
Document Control Desk Washington, DC 2005E
References:
(a)
License No. DPR-36 '5 det No. 50-309)
Subject:
Proposu hchnical Specification Change No.155 - SIAS Block Enable Gentlemen:
Maine Yankee hereby submits, pursuant to 10 CFR 50.90, this application to amend sections of the Maine Yankee Technical Specifications.
This proposed change increases the setpoint below which bypassing of the Engineered Safeguards Features (ESF) it permitted, from 1685 psig (100 psid above the SIAS setpoint) to 1760 psig (175 psid above the SIAS setpoint). The propased modification of this Specification is a result of recent analyses of safety system setpoint uncertainties which, when applied, have effectively reduced the window between the ESF bypass ::etpoint and the SIAS setpoint from the original 100 psid to 27 psid. An increase in the ESF bypass pressure specification value is necessary to restore the 100 psid window, thus reducing the potential for an inadvertent safety injection event.
The proposed amendment would modify Technical Specification 3.9, " Operational Safety Instrumentation, Control Systems, and Accident Monitoring Systems" by changing the bypass conditions for reactor coolant pressure from less than 1685 psig to less than 1760 psig.
The reason for the change is that, as a result of a recent change in the way Maine Yankee determines safety system setpoints and instrument uncertainties, the window between the ESF bypass satpoint and the SIAS pressure setpoint has been effectively reduced from 100 psid to 27 psid.
Our change in determining setpoint uncertainties is a result of comments from a recent NRC Safety System Functional Inspection.
The resulting 27 psid operating window can potentially increase the likelihood of an inadvertent safety injection LTOP event. The original ESF bypass setpoint,1685 psig, was intended to provide a 100 psid window between the SIAS trip setpoint and the bypass setpoint.
However, in order to apply the instrument uncertainties in a conservative manner, the bypass specification value should be increased such that when the instrument uncertainty is accounted for in the setpoint, the original 100 psid window will be restored.
Increasing the bypass specification value to 1760 psig will continue to provide the operators with a reasonable bypass window while assuring the plant could not operate with the ESFs in a bypassed mode, acomoon mov s PDR ADOCt 0% CO30
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MaincYankee UNITED STATES NUCLEAR REGULATORY COMMISSION MN-90-69 Attention:
Document Control Desk Page Two A description of the proposed change and a summary of the Significant Hazards l
evaluation is presented in Attachment A. As discussed in the attachment, this change does not involve a significant increase in the probability or consequences of an accident or malfunction of equipment important to safety previously analyzed.
Nor does it create the possibility of a new or different kind of accident or malfunction important to safety. Lastly, it does not cause a significant reduction in the margin of safety.
A discussion regarding the basis and justification for the proposed change is presented in Attachment B.
A revised Technical Specification Table 3.9-2 (page 3.9-6) is included as Attachment C.
This proposed change has been reviewed and approved by the Plant Operation and Review Committee.
The Nuclear Safety Audit and Review Committee has also reviewed this submittal.
A representative of the State of Maine is being informed of this request by a copy of this letter.
We request that this proposed change be made effective within 30 days of the actual setting in of the new setpoint values during the Cycle 12/13 refueling outage.
l Very truly yours, Charles D. Frizzle President WBD:SJJ Attachment c:
Mr. Thomas T. Martin Mr. Eric J. Leeds Mr. Charles S. Marschall Mr. Clough Toppan
-STATE OF MAINE Then personally appeared before me, Charles D. Frizzle, whc being duly sworn did state that he is President of Maine Yankee Atomic Power Company, that he is duly authorized to execute and file the foregoing request in the name and on behalf of Maine Yankee Atomic Power Company, and that the statements therein are true to the best of his knowledge and belief.
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Mxx Ngt'ary Public CDF9063.LTR BNy dbt$E ktY COLuSSION EXPtR!.S JUhc D,1996
L ATTACHMENT A Descriotion of Proposed Chanae This proposal increases the RCS pressure setpoint at which the Emergency Safeguards Features (ESF), specifically the Safety injection Actuation System (SIAS), the Containment Spray Actuation System (CSAS), and the Containment Isolation System (CIS), can be bypassed. Technical Specification 3.9.B (Table 3.9-2) currently allows this bypass to occur when the RCS pressure has been reduced below 1685 psig which is 100 psid above the SIAS nominal trip setpoint (1585 psig). As a result of a recent NRC Safety System Functional Inspection (SSFI), we have changed our methodology for calculating setpoint uncertainties.
When the actual setpoints are determined, accounting for instrument loop accuracy and uncertainties, the pressure window in which the bypass can be established is quite small.
This small operating window could potentially lead to.an inadvertent safety injection event during normal cooldown and depressurization operations.
In order to restore the 100 psid bypass window, this proposed change would increase the ESF bypass specification value to 1760 psig.
The intent of the original bypass setpoint (1685 psig) was to provide a reasonable value to allow operators to bypass the ESFs and prevent an inadvertent safety injection during a routine plant cooldown. The original setpoint was sufficiently low to assure that the plant could not operate at power with the ESFs in a bypassed mode (Technical Specificatien Figure 3.10-6), increasing the Technical Specification setpoint to 1760 psig will continue to provide the operators with a reasonable bypass window (about 100 psid) while assuring that the plant could not operate at power with the ESFs in a bypassed mode.
This setpoint, referred to as the Block Enable and t!ta Auto Unblock setpoints, are not utilized in any of the FSAR Chapter 14 safety analyses.
These~ features are strictly operational to allow a routine plant cooldown and to insure that reinstatement of the ESFs is not overlooked during plant startup.
Sianificant Hazards Evaluation The proposed change to Technical Specification 3.9 to increase the allowable ESF bypass specification setpoint has been_ evaluated againsi the standards of
- 10. CFR 50.92 and has been determined to not involve a significant hazards consideration. This proposed change does not:
1.
Involve a signi'Ticant increase in the probability or consequence of an accident previously analyzed. The ESF bypass setpoint has not been used in any of the FSAR Chapter 14 analyses and thus will not affect the current safety analyses.
Assuring that an adequate operational RCS pressure window exists to allow bypassing the ESFs is important to reduce the probability of an inadvertent safety injection event during a normal plant cooldown.
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k ATTACHMENT A (continued) 2.
Involve a significant increase in. the probability or consequence of a 1
malfundion of equipment important to safety.
The proposed change will e
not involve a modification to existing hardware at the plant but simply a -
resetting of the ESF bypass setpoint. In addition, no modification to the.
SIAS trip setpoint itself is proposed.
The increase. ef the bypass setpoint does slightly expand the operating spato and cchsequently the 1
time ;during which the ~ plant may be operating-with ths ESFs bypassed.
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However, the plant is only expected to operate.in this presture range for l-short periods of time during cooldown and depressurization.and only when
-the reactor is-in shutdown conditions. Thus, the probability of an event:
challenging any ESF-- setpoint in this mode of operation is negligibly increased.
3.
Create -the possibility of a new or different kind of accident or malfunction ' of equipment important to safety from any previously evaluated. Increasing the bypass setpoint does not create the possibility of a new or different kind of accident since the proposal involves neither a hardware modification nor the creation of a unique operating condition.
4.
Involve a significant reduction in the margin to safety, Increasing the 1:>
ESF bypass setpoint does not chango the results of any of the FSAR l~
Chapter 14 _ events.
Increasing the ESF bypass setpoint does slightly I
expand the operating space within which the ESFs will be bypassed.
However, the revised bypass setpoint will remain below the allowable pressure for power operation, i
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ATTACHMENT B Basis and Justification for an Increase in the Engineered Safeguards Features Bypass Setpoint
SUMMARY
Maine Yankee Technical Specification 3.9.B currently defines the required operational equipment to assure proper operation of the Engineered Safeguards Features (ESF) -the Safety Injection Actuation System (SIAS), the Containment Spray Actuation System (CSAS) and the Containment Isolation System (CIS). Table 3.9-2 currently defines the specification setpoint at which the ESFs can be bypassed as below 1685 psig which is 100 psig above the SIAS specification setpoint of 1585 psig. When establishing the actual setpoints, accounting for the newly calculated instrument loop accuracy and uncertainties, the pressure window in which the SIAS bypass can be enabled is small.
This attachment documents the basis and justification for increasing the bypass setpoint from 1685 psig (100 psid above the SIAS specification setpoint) to 1760 psig (175 psid above the SIAS specification setpoint) to restore the original 100 psid pressure window when instrument uncertainties are applied.
DISCUSSION Currently, Technical Specification 3.9.B (Table 3.9-2) permits blocking of the ESFs after the RCS pressure has been reduced below 1685 psig.
This setpoint was established to allow the operators a 100 psid window in which to bypass the ESFs during normal cooldown operations. The instrument loop accuracy and uncertainty for the Engineered Safeguards System has recently been calculated as 30.6 psig. For increasing signals, the actual setpoint equals the Technical Specification value minus the calculated uncertainty value. For decreasing signals, the actual setpoint value is equal to the Technical Specification value plus the calculated loop accuracy and uncertainty value.
Thus, for the initiation of Safety Injection, the actual setpoint is equal to 1585 psig plus 30.6 psig or 1615.6 psig. The Auto Unblock and Block-. Enable functions share the same bistable, with the Auto Unblock function 1
occurring.on an increasing pressure and the Block Enable function occurring on a
. decreasing pressure. Since it is the same bistable and both functions cannot occur simultaneously, the Block Enable function is established as the bistable trip. As a result, the Auto Unblock function occurs when the bistable resets on an increasing pressure. Thus, to calculate for the Block Enable trip function while ensuring that the Auto Unblock function will occur within the present Technical Specification requirement of <1685 ps'3, the bistable reset differential must be combined with the instrument loop accuracy and uncertainty for the Engineered Safeguards System. The reset differential of the bistable for the pickup to dropout is a nominal 1.0% of scale. With the scale being 1,200-2,400 psig, this equates to 12.0 psig. Therefore, the reset function of the bistable will occur at a nominal 12.0 psig greater than the trip.
The 12.0 psig is combined with the calculated uncertainty to determine the
- Block Enable setpoint.
The Technical Specification requirement is for the Block
- Enable to occur at less than 1685 psig.
As a result, the Block Enable setpoint calcalation will take on the form of a trip on increasing signal.
Thus, the Block Enable setpoint. is equal to 1685 psig minus (30.6 psig plus 12.0 psig) or 1642.4 psig. The Auto Unblock will occur at a nominal 12.0 psig above this value or 1654.4 psig.
The difference between the actual Block Enable setpoint and the actual SIAS CDF9063.LTR
ATTACHMENT B (continued)
Initiation setpoint represents the operating band available to the operators to bypass the SIAS Initiation feature. Establishing the above actual setpoints results in a 26.8 psid operating band in which to perform the bypass function.
Figure 1 depicts these relationships graphically.
PRESENT TS V
. PROPOSED TS VALUES t
AND ACTUAL SE AND ACTUAL SETPOINTS.
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BLOCK ENABLE TS 1760-N I,
30.6 NCU i
AUTO UNBLOCK ACTUAL 1729A -
BLOCK ENABLE ACTUAL 12.0 RESET 1.
g7j.
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Eb BLOCK ENABLE TS 1685-s 101.8 PSID BYPASS U
30.6 NCU VINDOV i
-1654.4 --
DCK ENARE ACTUAL 12.0 RESU.
1642A -
26.8 PSID BYPASS
- SIAS INIT. ACTUAL VINDOV -
SIAS INIT. ACTUAL 30.6 NCU 30.6 NCU SIAS INIT. TS SIAS INIT. TS j
FIGURE 1 - PRESENT AND PROPOSED SIAS INITIATION BYPASS ' VINDOVS NCU E NORMAL CHANNEL UNCERTAINITY CDF9063.LTR
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p ATTACHMENT B (continued)
In order to regain the operating window, an increase in the bypass specification value is proposed. Maine Yankee's proposal is to retain the 100 psi differential but apply it to the actual setpoints vice the specification values.
Using the Safety injection initiation actual setpoint of 1615.6 psig, the Block Enable specification value would be equal to 1615.6 psig plus 100 psid plus 42.6 psig (calculated unct ;ainty plus bi~ : Able reset) or 1758.2 psig (iound upward to 1760 psig - see Figure 1). A review of the Maine Yankee safety analyses indicates that there are no events whose results require the bypass setpoint to be below 1685 psig.
Increasing the ESF bypass specification setpoint does slightly expand the operating space within which the ESFs will be bypassed.
However, the revised bypass specification will remain below the allowable pressure for power operation.
CONCLUSION The proposed change to Technical Specification 3.9.B (Table 3.9-2), which would increase the setpoint below which. the ESFs can be bypassed during cooldown operations, _has been found not to significantly reduce the margin of safety which currently exists in the safety analysis.
Operation with this proposed change has been shown not to constitute an unreviewed safety question and, therefore, should be approved.
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