ML17157B820
| ML17157B820 | |
| Person / Time | |
|---|---|
| Site: | Susquehanna  |
| Issue date: | 05/21/1992 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17157B819 | List: |
| References | |
| NUDOCS 9206030230 | |
| Download: ML17157B820 (7) | |
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UNITEDSTATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT N0.119TO FACILITY OPERATING LICENSE NO. NPF-14 AMENDMENT N0.87 TO FACILITY OPERATING LICENSE NO. NPF-22 PENNSYLVANIA POWER
& LIGHT COMPANY ALLEGHENY ELECTRIC COOPERATIVE INC.
SUS UEHANNA STEAM ELECTRIC STATION UNITS 1
AND 2 DOCKET NOS.
50-387 AND 388
1.0 INTRODUCTION
By letter dated April 18,
- 1991, as supplemented November 4,
- 1991, and December 17, 1991, the Pennsylvania Power and Light Company and Allegheny Electric Cooperative, Inc. (the licensees) submitted a request for changes to the Susquehanna Steam Electric Station, Units 1 and 2, Technical Specifications (TS).
The requested changes would make changes to the technical specifications to revise the isolation setpoint for the leak detection temperature function in the Turbine Building main steam tunnel.
The technical specifications involved are Item 3i of Table 3.3.2-2, which specifies the temperature requirements, and Section 3/4.3.2 of the Bases.
The November 4,
- 1991, and December 17, 1991, letters provided clarifying information that did not change the initial proposed no significant hazards consideration determination.
2.0 EVALUATION The turbine building main steam tunnel (TBMST) is a long, narrow, L-shaped room which is opened on the end facing the turbine-generator.
The heating, ventilating and air conditioning (HVAC) system air supply enters the tunnel at the reactor building end and is exhausted through a duct near the turbine-generator end.
The TBMST is provided with four temperature elements.
These temperature elements are located such that HVAC air flow passes the elements'efore being exhausted from the steam tunnel.
The heat load from the main steam piping is sufficient to create a temperature gradient along the length of the tunnel as great as 40'F under normal operating conditions.
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The TBHST temperature elements are part of the Primary Containment and Reactor Vessel Isolation Control System (PCRVICS),
and their operation is described in Section 7.3. 1. Ia.2.4. 1.3 of the SSfS Final Safety Analysis Report (FSAR).
The FSAR states that high temperature in the TBHST could indicate a breach in a main steam line.
The FSAR also states that automatic closure of the main steam isolation valves (HSIVs) and main steam drain valves on high TBNST temperature prevents the excessive loss of reactor coolant and the release of significant amounts of radioactive material from the reactor coolant and the release of a significant amount of radioactive material from the reactor coolant pressure boundary (RCPB).
As described in the FSAR, the TBMST high temperature trip setpoint is set high enough to avoid a spurious isolation during operation at rated
- power, but low enough to provide early indication of a steam line break, By analysis, the current isolation temperature setpoint of 117'F corresponds to an effective steam leakage rate of 25 gpm equivalent water at standard temperature and pressure.
Loss of HVAC during normal operation could result in measured temperatures higher than the current isolation setpoint being sensed at the temperature elements.
This condition would lead to spurious closure of the HSIVs and a subsequent reactor trip.
In order to determine the transient response of the TBNST temperature to a steam leak and loss of HVAC, the licensee developed a model using the Compartment Transient Temperature Analysis Program (COTTAP).
The model is limited in that only the bulk average temperature of the tunnel is modeled.
Therefore, in order to approximate the conditions at the temperature element when HVAC is in operation, the licensee applies a 20'F temperature gradient to the average temperature.
As part of a program to establish the design basis for steam leak detection, the licensee determined that a non-leak failure such as a loss of HVAC, or a small (packing sized) leak should not isolate the main steam line and cause a
full power reactor scram.'n order to meet this design requirement, the licensee used the COTTAP model to determine the increase in temperature within the tunnel following a loss of HVAC.
The licensee determined that the temperature reaches 182'F in eight hours under worst case summer conditions.
The proposed setpoint of 197'F is based on providing sufficient margin above the 182'F temperature to prevent unnecessary main steam line isolation.
The proposed setpoint corresponds to a steam leakage rate within the tunnel of 65 gpm (32,500 ibm/hr) assuming conservative design winter temperatures.
Section 10.3 of the Standard Review Plan (SRP),
NUREG-0800, provides guidance in evaluating the design capabilities of main steam supply systems.
This guidance includes a provision for review of the main steam supply system with regard to measures provided to limit blowdown of the system in the vent of a main steam line break.
The capability to detect and control system leakage and the capability to provide accidental releases to the environment are also included as elements for review under the guidance of Section 10.3 of the SRP.
Diversity in main steam line isolation signals is provided by main steam line tunnel high temperature, reactor building steam tunnel high differential temperature, high main steam line flow, low main steam pressure, and reactor vessel low low water level (Level 2).
The high flow, low pressure and low water level isolation signals are most effective for large ruptures in a main steam line.
The retention of a TBHST high temperature isolation feature sensitive to smaller breaks ensures adequate and diverse measures are provided to limit blowdown of the primary system following a main steam line break.
The 65 gpm leak detection threshold is adequate to assure early detection and isolation of a main steam line break within the TBHST.
Therefore, the proposed revision to the TBHST high temperature isolation setpoint is acceptable based on the guidance of Section 10.3 of the SRP with regard to measures provided to limit blowdown of the system in the event of a main steam line break.
, The existing TBHST temperature recorder pre-isolation alarms (single channel, non-safety-related) provide advance warning to the operators of a leak.
The alarm setpoint of 157'ill detect leaks of less than 25 gpm in the TBHST.
The alarm allows the operators to take corrective action to control leakage.
This feature is acceptable based on the guidance of Section 10.3 of the SRP with regard to the provision of a means to detect and control system leakage.
The licensee has performed analyses which have demonstrated that the radiological consequences of a 65 gpm steam leak are within the acceptance criteria of Section 15.6.4 of the SRP based on the requirements of 10 CFR Part 100 and are bounded by the steam line break analysis of the FSAR.
Based on a
conservative analysis performed by the licensee which assumes all activity immediately reaches the Turbine Building vent stack, the release rates of iodine and noble gases for a 65 gpm leak would exceed rates corresponding to 10 CFR Part 20 limits for radioactivity in effluents to unrestricted areas.
However, the steam tunnel exhaust flow is recirculated within the Turbine Building which dilutes any iodine and noble gas releases, and allows detection of the radioactivity by area radiation monitors in the Turbine Building.
In
- addition, the Turbine Building exhaust vent stack is equipped with system particulate, iodine and noble gas monitors which are set to alarm at release rates corresponding to 10 CFR Part 20 limits.
Releases exceeding 10 CFR Part 20 limits would normally be alarmed by the monitors and allow corrective action to be taken.
Based on the above. evaluation, the staff finds the proposed revision to the TBHST temperature isolation setpoint acceptable with regard to the capability to preclude accidental releases to the environment.
The proposed addition to the TS Bases adequately describes the basis for the revision to the TBHST temperature isolation setpoint.
The revised setpoint allows early detection and isolation of main steam line break. and decreases the probability of an inadvertent HSIV isolation.
Therefore, the staff finds the proposed addition to the TS Bases to be acceptable.
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The staff review revealed a deficiency in the licensee's equipment qualification (Eg) program.
Although Section 7.3. l. la.2.4. 1.3.5 of the SSES FSAR credits the main steam line tunnel temperature trip signal as a means of isolating a main steam line break, the TBMST temperature elements are not included in the licensee's Eg program.
Environmental qualification of safety-related electrical equipment relied upon to remain functional during and following design basis events to ensure the integrity of the RCPB is required by 10 CFR 50.49.
Design basis events include the entire spectrum of steam line break sizes up to the design basis steam line rupture.
While the licensee has justified exclusion of the TBMST temperature elements from the Eg program for the design basis steam line rupture event, such justification has not been established for the whole spectrum of steam line break scenarios.
Insofar as this deficiency is an existing condition and has no bearing on the action requested by the licensee, it will be referred to Region I for further
- action, as appropriate.
3.0
SUMMARY
The proposed revision to the TBMST 'temperature isolation setpoint was reviewed with respect to the guidance contained in Section 10.3 of the SRP.
The proposed revision was found to be acceptable with regard to provisions to limit system blowdown following a steam line break, provisions to detect and control main steam system leakage, and the capability to preclude accidental releases to the environment.
In addition, the proposed revision to the TBMST temperature isolation setpoint reduces the probability of an inadvertent HSIV isolation.
The addition to the TS Bases accurately describes the basis for selection of the proposed temperature setpoint.
Therefore, the proposed TS revision is acceptable.
4.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Pennsylvania State official was notified of the proposed issuance of the amendments.
The State official had no comments.
- 5. 0 ENVIRONMENTAL CONSIDERATION The amendments change a requirement with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20.
The NRC staff has determined that the amendments involve no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure.
The Commission has previously issued a proposed finding that the amendments involve no significant hazards consideration, and there has been no public comment on such finding (56 FR 22471).
Accordingly, the amendments meet eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendments.
6.0
~CONCLUSIO The Commission has concluded, based on the considerations discussed
- above, that:
(1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed
- manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributors:
S. Jones J.
Raleigh Date:
May 21, 1992
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