ML20247P534
| ML20247P534 | |
| Person / Time | |
|---|---|
| Site: | LaSalle  |
| Issue date: | 07/26/1989 |
| From: | Morgan W COMMONWEALTH EDISON CO. |
| To: | Murley T Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20247P539 | List: |
| References | |
| NUDOCS 8908040214 | |
| Download: ML20247P534 (6) | |
Text
3 u
,[E
/
.g Comm*nwea th Edison J~.
.. 72 West Adams Street, Chicago, Illinois j1
' Address Reply 10: Post Office Box 767-V 5
. Chicago, Illinois 60690 - 0767
?i July 26, 1989 d
.c
'Dr. Thomas E.,Murley,' Director-Office of Nuclear Reactor Regulation
' U.S. Nuclear Regulatory Conaission Washington, DC 20555-
Subject:
LaSalle County Station Units.1 and 2 Proposed AmenCnent to Technical
, Specifications for Facility Operating License NPF-11 and NPF-18 NRC Docket Nos. 50-373 and 50-374 References-(a):
C.M.'. Allen letter to U.S. NRC dated July 10, 1987.
(b):
D.R. Muller letter to L.D. Butterf.is1d dated February 8, 1988.
Dr. Murley Reference (a) transmitted Commonwealth Edison's proposed Techncial Specification Amendment to allow removal of the main steam line isolation
-function from the main steam tunnel temperature and differential temperature sensors.
Reference.(b) transmitted the NRC position that the proposed amendment could not be approved on the sole basis of a risk-based evaluation alone.
'the letter. recommended that.the submittal be revised to address the Updated Final' Safety Analysis Report requirements and design basis and logic for the leak-detection system.
The following attachments provide Commonwealth Edison's revised l;
submittal. This submittal proposes to amend the Technical Specifications'to'-
allow continued plant operation for a period of 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> with the Main Steam Tunnel High Ambient Temperature and High Ventilation System Differential Temperature ' Trips Bypassed. Attachment A provides-an introduction and discussion. Attachment B provides copies of the changes to be made to the Facility Operating Licenses. Commonwealth Edison has reviewed this document and finds that no significant hazards exists. This review is documented in Attachment-C. A risk analysis evaluation is enclosed as Attachment D of which Sections 1, 2,
4, 6 and 7 and Appendix B provide support for this proposed Q
p}60402i4s9972$ADOCK 05000373 00
-0106T:5 i1
1 Dr. T.E. Murley July 26, 1989 amendment. Attachment E contains copies of applicable pages of the LaSalle Updated rical Safety Analysis Report (UFSAR).
Attachment F contains'a portion of a Sarger.t and Lundy (S&L) report in which the basis for the setpoints was investigated.
Commonwealth Edison is notifying the State of Illinois of our revised amendment request by transmitting a copy of this letter to the designated state official.
If you have any additional questions regarding this matter, please contuct this office.
I Very truly yours, I
f
> L, y
(
/
W. E.'Norgan Nuclear Licensing Administrator 1m Attachments cc:
P.C Shemanski - Project Manager, LaSalle Regional Administrator - Region III NRC Resident Inspector - LaSalle County Station Office of Nuclear Facility Safety - IDNS 0106T 6 L
.._-_._____________________.______i
1
?? t.
AITAQMMI._A A
TECHNICAL SPECIFICATION CHANGE REOUEST LASALLE COUNTY STATION UNITS 1 AND 2 j
BACKGROUND AND DISCUSSION y
BACKGROUND As part of the nuclear boiler leak detection system, the Main Steam Tunnel (MST) ambient air temperature and ventilation system dif ferential temperature sensors are used for the detection of small leaks in the MST.
The j
'. temperature sensors for these parameters are set to annunciate in the control roon whenever an air temperature increase corresponding to a 5 gpm leak is detected and to cause a Group I Primary Containment Isolation (PCIS) trip when a 25 gpm leak is detected. Since approximately 90 percent of the reactor building ventilation system (VR) air flow passes through the Units 1 and 2 main steam tunnels, detection of small leak rates requires the trip setpoints to be set very close to normal operating temperatures. Any disruption of.
reactor building ventilation flow or rapid changes in reactor building air temperature can result in a spurious Group I isolation (main steam isolation
~
valve closure)'. Disruptions in reactor building ventilation flow can be caused by surveillance testing, random ventilation system failures or by clogged ventilation filters caused by environmental factors, such as agricultural dust during the spring plowing season and by snow in the winter.
During the Spring'and Fall, rapid outside temperature decreases at night cuase the reactor building ambient temperature to drop, which in turn causes a rapid increar.e in the differential temperature between the MST ventilation intake and exhaust to a point very close to the isolation setpoint. At times the plant may be required to operate for extended periods of time under these conditions.
In July, 1987, Commonwealth Edison submitted an snendment request (Reference A) to remove the MST temperature trips for the technical specifications. This submittal was based on both qualitative arguments and a risk-based analysis. This request was denied by the NRC in February, 1988 (Reference E).
At this' time, Commonwealth Edison is proposing that the Techncial Specifications be amended to allow bypassing the MST ambient temperature and high ventilation differential temperature trips for a 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> period. This amendment will allow the needed time to perform required maintenance activities and surveillance, such as VR system filter changes and damper cycling, and secondary containment leak rate tests while reducing the i
risk of causing unnecessary challenges to reactor safety systems.
plSCUSSION The following variables are used to detect stemn leakage outside of the primary containment and to cause a Group I (MSIV) isolation:
MST high ambient temperature and high differential temperature.
Low main steamline pressure (operating condition 1 only).
High main steamline flow rate.
- Low reactor water level.
F v>
r I.:. 1 A review of UFSAR requirements was performed to determine the origin of the 5'gpm and 25 gpm limits for the MST ambient and differential temperature.
setpoints. The UFSAR in Table 5.2-8 requires that the MST monitored for high ambient temperature and differential temperature and that these variables
. provide alarms and isolation signals. Table 7.3-2 provides the temperature trip setpoints end allowableLvalues for these instruments. These trip setpoints (140*F for ambient temperature and 36*F for differential temperature) are set to detect a 25 gpm leak, which is inconsistent with UFSAR Section 7.3.2.2.3.3, which requires that the MST ambient temperature and differential temperature sensors detect leaks in the range of from 1% to 10% of rated steam flow (1% rated steam flow is approximately 282 gpm).
Section 7.3.2.2.3.3 also states that:
The main steamline space high temperature trip is set far enough above the temperature expected during operation at r ated power to avoid spurious l'solations, yet low enough to provide early indication of a j
steamline break.
I 1
The design bases for the Primary Containment Isolation System are provided in Section 7.3.2.1 of the UFSAR. Paragraphs a and d of this section state that:
a.
To limit the release of radioactive materials to the environs, the primary containment and reactor vessel isolation control system shall, with precision and reliability, initiate timely isolation of penetrations through the primary containment whenever the values of monitored variables exceed preselected operational limits.
l:
d.
To provide assurance that conditions indicative of a failure of the reactor coolant pressure boundary are detected to fulfill safety design basis a, primary containment and reactor vessel isolation l
control system inputs shall be derived from variables that are true, direct measures of operational conditions.
The Architech/ Engineer's (AE) analysis (Attachment F) of the leak detection system has shown that the ambient and differential temperature setpoints cannot be accurately established with respect to quantifying leakage because the temperatures being sensed are directly affected by outside environmental conditions.
Therefore, the MST ambient and differential temperatures cannot be considered a precise or reliable indication of MST conditions. Nor can these variables be considered to be a true and direct measure of plant operational conditions.
A review of the following documents was performed by the AE to determine the design basis ano logic for the Leak Detection System:
Regulatory Guide 1.e5 " Reactor Coolant Pressure Boundary Leak Detection Systems."
0106T 8 e-
_ _ ___ _ ____=_ ____ _--
l Standard Feview Plan 5.2.5 " Reactor Coolant Pressure Boundary Leakage."
General Electric Company's Design Specification for Leak Detection (GE Document Number 22A2870, Revision 7).
General Electric Company's Design Specification Data Sheet Number 22A2870AA, Revision 3 " Leak Detection System."
The regulatory documents do not specify quantitative requirements for the temperature monitoring systems used for detecting leakage outside of the primary containment.
Instead, it appears that they specify only requirements for the capabilities of system designe required to detect leakage within the primary containment.
In fact, the regulatory guide indicated tnat htimidity, temperature and pressure monitoring of containment atmosphere should be considered as alarms or indirect indication of leakage to the containment.
The specific requirements for the ability to detect a 5 gpm leak and cause an alarm as well as the ability to detect a 25 gpm leak and cause an isolation to occur, are contained only within the GE design specification.
There are no references to regulatory documents in the reference section of the GE design specification, and it appears that the 5 and 25 gpm values originated from the GE System Design Engineer. Within the GE specification, the words describing the use of temperature sensors to detect steam leaks appear as follows:
" Alarm should be actuated by a temperature rise corresponding to the steam leakage of 5 gpm and automatically isolate the system on 25 gpm."
A risk-based evaluation has been completed to determine the effect on plant safety of removing the ambient and dif ferential temperature trips from the Primary Containment Isolation System (PCIS) Group I isolation logic. This evaluation was sponsored by the Electric Power Research Institute (EPRI) to determine the usefulness of risk-based methodology in achieving technical specification improvements. The MST ambient and differential temperature trips were included in the report as one of the areas evaluated. Applicable portions of this report have been included in Attachment C.
The analysis concluded in section 4.9, that the reliability of the MSIVs to close in response to a steam line break outside the containment is not significantly compromised by removal of the MST temperature trip sensors as part of the trip logic. The small increase in risk to plant safety due to small steam line breaks which quickly propagate to large breaks is more than offset by the reduction in risk to plant safety posed by the challenges to plant safety systems caused by spurious MSIV closures. The report recommends retention of the MST high temperature alarm function to provide detection of small steam leaks.
0106T 9 l
- SUMMABX It is clear t'.lat given the LaSalle Station reactor building ventilation system configuration that the MST ambient and ventilation system differential temperature detectors are not the primary means of protection against a major steam leak in the HST.
These instruments provide a means for early detection of small steam leaks from the reactor pressure boundary.
Risk analysis has shown that the plant safety would not be reduced by remo;.'al of the MST Group I temperature trips. Therefore, a technical specification amendment allowing operation of the units for a 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> period with these
' instruments bypassed would not reduce the margin of safety and may in fact increase the safety margin by allowing improvements to and verification of the reliability of the reactor building ventilation system and its secondary containment isolation system dumpers.
Based on the above discussion, it is proposed that the Units 1 and 2 technical specifications be amended to allow continued plant operation for a 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> period of time with the MST high ambient temperature and high ventilation differential temperature PCIS trips bypassed. During the period of time that the temperature trips are bypassed, the MST temperatures will be monitored to ensure that the temperature limits for any environmentally
. qualified equipment in the MST is not exceeded.
I 0106T:10
- - _ _ _ _ _ _ _ _ _ _ - _.