ML20127H480

Requests Exemption from Installation of Reactor Vessel Level Instrumentation Sys to Conform to NUREG-0737,Item II.F.2 Due to Sys Cost & Lack of Corresponding Increase in Plant Safety Margin

ML20127H480
Person / Time
Site:	Rancho Seco
Issue date:	05/16/1985
From:	Reinaldo Rodriguez SACRAMENTO MUNICIPAL UTILITY DISTRICT
To:	Stolz J Office of Nuclear Reactor Regulation
References
RTR-NUREG-0737, RTR-NUREG-737, TASK-2.F.2, TASK-TM RJR-85-205, TAC-57802, NUDOCS 8505210309
Download: ML20127H480 (3)

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SACRAMENTO MUNICIPAL UTILITY DISTRICT O 6201 S Street, P.O. Box 15830, Sacramento, CA 95813; (916) 452 3211 RJR 85-205 AN ELECTRIC SYSTEM SERVING THE HEART OF CALIFORNIA May 16,1985 DIRECTOR OF NUCLEAR REACTOR REGULATION ATTENTION JOHN F STOLZ CHIEF OPERATING REACTORS BRANCH 4 U S NUCLEAR REGULATORY COMMISSION WASHINGTON D C 20555 DOCKET 50-312 RANCHO SECO NUCLEAR GENERATING STATION UNIT NO. 1 NUREG 0737 ITEM II.F.2 INADEQUATE CORE COOLING (ICC)

Your letter dated December 10, 1982, notified Sacramento Municipal Utility District that the Commission had issued an Order of Modification of License for Rancho Seco Nuclear Generating Station. The Order required that the District install an ICC instrumentation system which conforms to the design parameters specified in NUREG 0737 Item II.F.2. The intent of this Order was to increase the margin of safety for restoring coolant coverage of the core following a postulated ICC event.

Included in the ICC instrumentation system described in the order was a reactor coolant inventory system consisting of inventory measurements over the ranges of the vessel upper head to the bottom of the hot leg (vessel level) and from the top of the hot leg to the bottom of the hot leg (hot leg level).

A District letter dated April 15, 1983 identified the District's preferred method of ICC inventory monitoring as being a combination of the Combustion Engineering heated junction thermocouple system for reactor vessel level indication and a differential pressure system for hot leg level indication.

In the April 15, 1983 letter, the District questioned the benefit of the reactor vessel head level instrumentation and presented a discussion as to the system's cost and lack of corresponding increase in the plant safety margin.

Your response, dated August 24, 1983, indicated that the staff did not feel that District's discussion provided an acceptable basis to change the conclusion that the instrumentation was required.

The District believes that as a result of the recent Once Through Integral Systems (OTIS) tests conducted on the behalf of the District and Florida Power Corporation (see District letter RJR 85-109, dated April 12, 1985), an acceptable basis now exists to determine that the reactor vessel level instrument is not required. The bases for our conclusion are as follows:

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h o John f Stolz RJR 85-205 May ,1985

1. The DTIS' tests indicated that the presence of a gas bubble in the reactor-vessel head above the hot legs would have no-adverse effect on the ability to cool the core with either natural circulation or feed and bleed cooling.

2. The District ICC. procedures require opening of the hot leg high point vents when an ICC event is indicated, thus assuring that any gases formed would be vented from the hot legs and that cooling to the core can be maintained. These procedures (modified to the DTIS facility) were used during the OTIS testing.

3. Any postulated operator actions which might be taken in response to

. reactor vessel level instrument indications would already have been taken based on existing instrumentation (incore thermocouples and subcooling margin monitors) which provides an earlier warning of the approach to ICC.

As can be seen from the above discussion, the OTIS testing supports the conclusion that the reactor vessel level instrumentation does not provide an

. increase in the margin of safety for Rancho Seco.

In addition, there are several negative aspects to the installation of the

. reactor vessel level. instrumentation:

1. The central control rod would be removed and not replaced, reducing the available shut down margin.

2. . Installation will involve an estimated 10 man-rem exposure to station

. personnel.

3. Maintenance requirements will further add to station personnel radiation exposure.

4. Significant installation and maintenance costs would be involved.

'The District has installed qualified and redundant subcooling margin monitors and is installing qualified and redundant incore thermocouples and hot leg level instrumentation during the current (Cycle 7)-refueling outage. A total

! .of 16 incore thermocouples are being upgraded. The hot leg level instrumentation is redundant on each hot leg. The incere.thermocouples and hot leg level instrumentation are qualified up to the display with the display.

being; upgraded in accoidance with the Living Schedule. This instrumentation will provide early and unambiguous indication of the approach to ICC. In addition, the hot leg level instrumentation provides continuous trend of inventory depletion, indicates loss of natural circulation, indicates status of system refill and provides information for the transition from LPI to DHR

-operation during a LOCA, all of which are not provided by the reactor vessel level instrumentation.

The lack of identifiable net safety benefit coupled with the identified

adverse factors has lead the District to the conclusion that the reactor

, vessel level instrumentation should not be installed.

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John F Stolz RJR 85-205 May , - 1985 We request an expeditious review of this submittal leading to an early and permanent exemption from the installation of a reactor vessel level

. instrumentation system at Ranche Seco.

The exemption would assure subst.intial savings to the District and its customers, without detriment to the health and safety of the general public or the plant operators.

The application fee of $150.00, pursuant to 10 CFR 170.12, was previously submitted.

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Assistant Gener(l a Manager, Nuclear b

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