ML20236G879

Safety Evaluation Supporting Amend 86 to License DPR-54

ML20236G879
Person / Time
Site:	Rancho Seco
Issue date:	10/23/1987
From:	Office of Nuclear Reactor Regulation
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ML20236G854	List: ML20236G851 ML20236G861 ML20236G879
References
NUDOCS 8711030327
Download: ML20236G879 (4)

Text

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[oaeow*o UNITED STATES l' E o

, NUCLEAR REGULATORY COMMISSION

{ .$ WASHINGTON, D. C. 20555

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SAFFTY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO. 86 TO FACILITY OPERATING LICENSE NO. DPR-54 SACRAMENTO MUNICIPAL UTILITY DISTRICT R,ANCHO SEC0 NUCLEAR GENERATING STATION DOCKET NO. 50-312

1.0 INTRODUCTION

By letter dated February 20, 1987, as sup Municipal Utility District (the licensee)plemented proposedJune 2, 1987, revisions to Sacramento the Bases of Technical Specification (TS) 3.1.6, " Leakage", and TS 3.8, " Fuel Loading and Refueling" for Rancho Seco Nuclear Generating Station Unit No. 1. These pro-posed revisions reflect the replacement of the existing radiation monitors R-15001 A through E with radiation monitors R-15100 and R-15044. The Technical Specification 3.1.6 Bases are being updated to state that the particulate chan-nel of the new radiation monitor R-15100 is the only radiation-sensitive reac-tor coolant leak detection method. Prior to this proposed revision, the licensee was using both the particulate and the noble gas channels of its radiation monitors as the radiation-sensitive reactor coolant leak detection method.

2.0 DISCUSSION 10 CFR 50, Appendix A, General Design Criterion 30, Quality of Reactor Coolant Pressure Boundary, requires that "means shall be provided for detecting and, to the extent practical, identifying the location of the source of reactor coolant leakage."

Regulatory Guide 1.45, " Reactor Coolant Pressure Boundary leakage Detection Systems", states that " leakage to the primary reactor containment from uniden-tified sources should be collected and the flow rate monitored with an accuracy of one gallon per minute or better." This guide also states that at least three separate detection methods should be employed to detect this leakage.

Two of these methods should be (1) sump level and flow monitoring and (2) air-borne particulate radioactivity monitoring. The third method may be either monitoring of condensate flow rate from air coolers or monitoring of airborne gaseous radioactivity. Although not committed to Regulatory Guide 1.45, the licensee provides the first two methods of detection and substitutes a Reactor Coolant System (RCS) Inventory-based method for the third. This third detection method has been previously accepted by the NRC.

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Regulatory Guide 1.45 also states that each detection method should be "ade-quate to detect a leakage rate, or its equivalent, of one gpm in less than one hour." The licensee meets the intent of this with the particulate and sump I

level methods, by detecting a one gpm leak in 1-2 hours. The RCS Inventory method is not a continuous method but,can confirm a one gpm leak in one hour if the leak is detected by other means.

Prior to this proposed Technical Specification change, the licensee was using l both the airborne gaseous and airborne particulate channels of its radiation monitor as one of its methods for detecting reactor coolant leakage. Since the original plant design was based on the ca gaseous activity in the Reactor Building (RB)pability remainedof purging at a levelatthat power, the permit-ted detection of small amounts of reactor coolant leakage (i.e., one gpm) using the airborne gaseous channel of the radiation monitor. However, current oper- l ating philosophy at Rancho Seco does not allow purging of the RB during plant l operation. Consequently, the gaseous activity in the RB is allowed to build up i to levels that make the airborne gaseous channel of the radiation monitor inef fective in detecting one gpm of reactor coolant leakage to the RB.

1 In order to comply with the guidelines of Regulatory Guide 1.45 with respect to having a radiation-sensitive leak detection method, the licensee has replaced its existing Victoreen radiation monitors R-15001 A through E with a General Atomics (GA) Particulate, lodine and Gas radiation monitor R-15100 and a GA gas monitor R-15044. The particulate channel of GA monitor R-15100 will be used exclusively as the RB Atmosphere Leak Detection Monitor. Unlike radioactive gases, which build up in the RB during operation, the background air particu-late activity in the RB is maintained at a reduced level as a result of contin-uous filtering and plateout. Because the background air particulate activity in the RB can be maintained at a reduced level, the licensee states that the air particulate channel of its R-15100 radiction monitor will be able to detect a one gpm unidentified leak in the RB within 1-2 hours assuming less than 0.05% failed fuel. The Control Room operators will automatically be alerted if such a leak is detected and they will verify this leakage by two other means of leak detection (i.e., sump level and coolant inventory).

3.0 GALUATION The staff has evaluated the licensee's recuest to use the particulate channel of their newly installed GA radiation monitor R-15100 as the only radiation-sensitive reactor coolant leak detection method. In analyzing the leak detection capability of this monitor, the licensee calculated typical RB concentrations, sample line plateout, sample filter lifetime, monitor sensitiv-ity and setpoints, and monitor response times.

Using various RB atmosphere equilibrium levels (both calculated and measured, with various failed fuel concentrations) and different setpoints, the licensee calculated the monitor response time for detecting a one gpm unidentified leak in the RB for both the particulate and iodine channels. In each case, for failed fuel concentrations of 0.05% or less (typical values for Rancho Seco),

calculations indicated that the particulate monitor would be able to detect a one gpm unidentified leak within 62.5 minutes. These calculations assumed a

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filter age of seven days (worst case). For failed fuel concentrations of 0.1%

and 1%, the particulate channel would be unable to detect leakage due to the f act that the detector filter would become overloaded within 3.68 hours7.87037e-4 days <br />0.0189 hours <br />1.124339e-4 weeks <br />2.5874e-5 months <br /> and 21 minutes, respectively. A particulate monitor response time of 62.5 minutes will give the Control Room operators sufficient time to confirm the leak by quantitative means, such as a RCS Inventory calculation or sump level indica-tion. The alert alarm setpoint for the particulate monitor will be maintained at about three times the highest expected background level to ensure timely alarm indication to abnormal leakage without spurious alarm actuation.

Calculations performed for the fodine channel indicated that the response time cf the monitor to a one gpm unidentified leak increase in the RB would be 5.2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />. Due to this long response time, the licensee will use this channel as a secondary means of leak detection to the particulate channel.

Based on the licensee's calculations, for historical coolant concentrations (less than 0.05% failed fuel), the particulate channel should be able to detect a one gpm unidentified leak in the RB in about one hour. High background par-ticulate levels could cause detector overloading, resulting in substantially longer response times to RCS leakage. Possible causes of high RB equilibrium levels include: 1) extraordinary high failed fuel (greater than 0.1%), 2) extraordinary high identified RCS leakage, and 3) failure of the RB HVAC recir-culation fans or filters. However, daily readings of the particulate monitor strip chart recorder should ensure that the detector does not become overloaded and inoperable without the operators being aware of the situation.

In addition to the installation of radiation monitor R-15100, the licensee plans to use radiation monitor R-15044 as a dual purpose RB Stack and RB Atmo-sphere monitor. Radiation monitor R-15044 is essentially an equivalent re-placement of radiation monitors R-15001 A and B.

On the basis of the above evaluation, the staff concurs with licensee's pro-posed changes, which would revise portions of the Technical Specifications to reflect the replacement of existing radiation monitors R-15001 A through E with radiation monitors R-15100 and R-15044. The licensee's use of the R-15100 particulate channel to replace the gaseous channel as a means of detecting reactor coolant leakage is in accordance with the guidance of Regulatory Guide 1.45 and is acceptable.

During the next operating cycle, the license should closely monitor the perfor-mance of the new radiation monitors R-15100 and R-15044 to ensure that they are ,

performing as designed. After completion of the upcoming operating cycle, NRC J has requested that the licensee submit a report containing an evaluation of the  !

performance of the new radiation monitors, including the capability of the '

particulate channel of radiation monitor R-15100 to detect a one gpm unidenti-fied leak in the RB within 62.5 minutes. This report should contain data on  ;

the actual RB equilibrium levels for particulate and iodines measured during i the upcoming operating cycle. It should also describe the response of radia-tion monitor R-15100 to any known leakage increases during this time period and I compare this with the calculated response. If the setpoints for radiation 1

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monitor R-15100 are changed during this cycle, this report should include the new setpoints, describe why the setpoints were adjusted, and verify that the particulate channel of radiation monitor R-15100 is still capable of detecting a one gpm unidentified leak in the RB within 62.5 minutes.

4.0 CONTACT WITH STATE OFFICIAL The NRC staff has advised the Chief of the Radiological Health Branch, State Department of Health Service, State of California, of the proposed determina-tion of no significant hazards consideration. No comments were received.

5.0 ENVIRONMENTAL CONSIDERATION

This amendment involves changes in the installation or use of a facility compc-nent located within the restricted area as defined in 10 CFR Part 20. The staff has determined that the amendment involves 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 this amendment involves no significant hazards consideration and there has been no public comment on such finding. Accord-ingly, this amendment meets the 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 this amendment.

6.0 CONCLUSION

We have concluded, based on the considerations discussed above, that (1) there l is reasonable assurance that the health and safet endangered by operation in the proposed manner, 2) (y of the such public will activities willnot bebe conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to common defense and security or to the health and safety of the public.

Principal Contributor: Charles S. Hinson Dated: October 23, 1987

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