ML20203H905

Forwards Response to Generic Ltr 86-05, Implementation of TMI Action Item II.K.3.5, 'Automatic Trip of Reactor Coolant Pumps.' Util Will Address Primary Sys Void Detection & Mgt & Provide Implementation Schedule in Sept 1986

ML20203H905
Person / Time
Site:	Three Mile Island
Issue date:	07/31/1986
From:	Hukill H GENERAL PUBLIC UTILITIES CORP.
To:	Miraglia F Office of Nuclear Reactor Regulation
References
TASK-2.K.3.05, TASK-TM 5211-86-2123, GL-86-05, GL-86-5, NUDOCS 8608050128
Download: ML20203H905 (7)

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GPU Nuclear Corporation i

Nuclear o

e m es : 48o Middletown, Pennsylvania 17057 0191 717 944 7621 TELEX 84 2386 Writer's Direct Dial Nurnber:

July 31,1986 5211-86-2123 Office of Nuclear Reactor Regulation Attn: Frank J. Miraglia, Director Division of PWR Licensing-B U.S. Nuclear Regulatory Commission Washington, DC 20555

Dear Mr. Miraglia:

Three Mile Island Nuclear Station Unit 1 (TMI-1)

Operating License No. DPR-50 Docket No. 50-289 Response to Generic Letter 86-05 Implementation of THI Action Item II.K.3.5 Generic Letter 86-05 " Implementation of TMI Action Item II.K.3.5, ' Automatic Trip of Reactor Coolant Pumps'" requests licensees to provide schedules for submittal of plant specific information relative to instrumentation uncertainties, potential reactor coolant pump problems, and operator training and procedures relative to the reactor coolant pump trip on loss of subcooling margin.

Attachment 1 provides the requisite infor11ation regarding instrumentation uncertainties and potential reactor coolant pump problems. As discussed with l Mr. John Thoma (NRC) on July 3,1986, GPUN intends to address primary system l void detection and management and to provide an implementation schedule in September, 1986, i

l Sincerely, f

I l ,

4 D. Hukill Vice President and Director, TMI-l HDH/SK/pa(3637f)

Attachment 8608050128 860731 PDR ADOCK 05000289 A P PDR gdh[

GPU Nuclear Corporation is a subsidiary of the General Public Utilities Corporation l

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ATTACINENT RESPONSE TO GENERIC LETTER 86-05 IMPLEMENTATION OF TMI ACTION ITEM II.K.3.5 The following discussions provide GPUN responses to HRC requests for information presented in Generic Letter 86-05 Section IV.

Information provided in response to items A and B.1 was previously provided to the NRC staff in References 1 through 5. The reactor coolant pump trip considerations discussed in response to item A were found acceptable by the NRC staff for TMI-l in Reference 6. The containment isolation provisions discussed in response to item B.1 were found acceptable by the NRC staff in Reference 7.

A. DETERMINATION OF RCP TRIP CRITERIA

1. Identify the instrumentation to be used to determine the RCP trip setpoint, including the degree of redundancy of each parameter signal needed for the criterion chosen.

Response

TMI-l Abnormal Transient Procedure ATP 1210-10 requires that all operating reactor coolant pumps be tripped immediately if 25F*

subcooling margin is lost. The minimal margin to saturation 25F* is determined by the more conservative of the two subcooling margin monitors. ,

The saturation margin (Tsat) monitoring system is a redundant system consisting of an A and a B loop. Each loop provides a continuous control room display of the margin between the actual reactor coolant system temperature and the saturation temperature based upon the existing pressure of the reactor coolant system.

Ts at provides alarm annunciation in the control room when either loop indicates insufficient margin.

In each of the redundant loops, reactor coolant temperature and pressure inputs are brought into signal conditioning cabinets.

Signal conditioning circuits convert the RC pressure to a signal that is proportional to the saturation temperature for that pressure. The signal is compared with a signal representing the actual RC temperature, and the difference represents the temperature margin to saturation. Tsat margin monitor information is displayed on digital indicators on the control room back panel. The indicators display Tsat margin ir, fahrenheit degrees for RC Loop "A" and Loop "B". The Tsat margin monitor also provides a "B" Loop isolated output to the plant computer, and "A" and "B" Loop isolated, low Tsat margin to the annunciation system for control room alarm annunciation, should Tsat margin be less than set point. The output to the plant computer provides trending and status monitoring i nformation.

r The individual components that comprise the Tsat system are lE qualified. The system consists of the following components:

a. RTD's (TE 958, TE 960)

b. Pressure Transmitters (PT 963, PT 949)

c. Signal Conditioning Modules

d. Digital Indicators (TI-977, TI-978)

All Tsat equipment in the A loop is powered from the Al signal conditioning cabinet (Red), and the B loop from the B1 signal conditioning cabinet (Green).

Pressure transmitter PT 963 and temperature sensor TE 958 are located in the hot leg associated with OTSG A. Pressure transmitter PT 949 and temperature sensor TE 960 are located in the hot leg associated with OTSG B. The pressure input range is 0 to 2500 gsig. The digital display meter will indicate - 100F* to +400F Tsat margin.

During normal operation of the plant, the set point for alarm for each loop is whenever the Tsat margin is less than 25F*. Signal conditioning circuits for the Tsat A loop are located at elevation 338 ft. in the control tower, and for Tsat B loop at elevation 322 ft. The temperature inputs have a range of 120*F to 920*F.

2. Identify the instrumentation uncertainties for both normal and adverse containment conditions. Describe the basis for the selection of the adverse containment parameters. Address, as appropriate, local conditions such as fluid jets or pipe whip which might influence the instrumentation reliability.

Response

The following table presents the total alarm loop error for the saturation margin monitoring system under normal and adverse containment conditions.

RC Pressure Total Alarm Loop Uncertainty (psig) Normal (F*) SBLOCA (F*)

200-400 -11.12 +7.32 -5.79 +14.95 400-600 -7.85 +6.25 -4.42 +12.74 600-900 -7.32 +5.82 -4.96 +11.10 900-1300 -6.65 +5.56 -4.84 +10.24 1300-1900 -6. 71 +5.41 -4.80 +9. 72 1900-2500 -6.17 +5.37 -4.88 +10.06 The calculated errors are the difference between the indicated margin value and the true margin value. When the error is algebraically subtracted from the indicated value it gives the true value. A negative error is conservative and denotes that the indicated value is less than the true value.

r The negative error for each range was calculated by statistically combining the independent random errors and then algebraically adding the maximum negative characterizer error. The positive error was calculated in the same manner except that the maximum positive characterizer error is zero.

The GPUN loop error analysis for adverse containment conditions (SBLOCA) assumed that the worst case combination temperature, pressure and radiation errors would be bounded by containment conditions of 0 psig, 212*F and an integrated dose of 4 x 106 Rads.

Selection of the adverse containment conditions is discussed in detail in Reference 3.

3. In addressing the selection of the criterion, consideration of uncertainties associated with the BWOG or plant specific supplied analyses values must be provided. These uncertainties include both uncertainties in the computer program results and uncertainties resulting from plant specific features not representative of the BWOG generic data group.

Response

GPUN proposed in March 1983 a reduction of the minimum indicated subcooling margin setpoint for reactor coolant pump trip from 50F* to 25F* based upon analyses demonstrating that a reduced subcooling margin allows better plant control during recovery from events of interest, including small break LOCA's, steam generator tube rupture events, and overcooling transients.

Detailed analyses have demonstrated that a reduction in subcooling margin for TMI-l is supported on the grounds that the combination of instrument string errors and geometry effects are bounded.

To account for uncertainties in geometry, GDUN has evaluated the

" physical configuration factor" which is a bounding value for the difference between the indicated pressure at the hot leg pressure instrument and the actual pressure at the top of the hot leg. Our calculations showed a maximum physical configuration factor of less than 1.3F*, under all containment environmental conditions with RC pressure of 200 psig or greater. Details of the GPUN loop error analysis are provided in References 2, 3 and 4 This approach was found acceptable by NRC in Reference 6.

B. POTENTIAL REACTOR COOLANT PUMP PROBLEMS Section 5.4 of the BWOG generic report discusses the various aspects of the essential service water systems for the B&W plants in a generic fashion. Each licensee needs to identify and describe the plant specific features to:

1. Assure that containment isolation, including inadvertent isolation, will not cause problems if it occurs for non-LOCA transients and accidents.

a. Demonstrate that if water services needed for RCP operations are terminated, then they can be restored fast enough to prevent seal damage or failure once a non-LOCA situation is confirmed.

b. Confirm that containment isolation with continued pump operation will not lead to seal or pump damage or failure.

Response

As discussed in Section 2.1.1.5 and in the response to Question 24 (Supp.1 Part 1) of the TMI-l Restart Report, RC pumps seal and motor cooling are capable of being restored following containment isolation. In the event that Intermediate Closed Cooling (ICC) water to the seals is lost, makeup seal injection water provides adequate cooling for the seals. In the event that makeup seal injection water is lost, ICC provides adequate cooling for the seals. The pump can be operated indefinitely if either makeup seal injection or ICC is functioning normally. If both makeup seal injection and ICC were lost, the pump would trip automatically.

Motor cooling and ICC seal cooling are only isolated under high containment pressure (30 psig) or line break conditions. Seal injection water is not isolated on containment isolation, but can be isolated manually, if necessary to do so. Therefore, the potential for loss of RC pump services is greatly reduced from the original design in which seal and motor cooling were isolated on 4 psig containment pressure.

This position has been endorsed by NRC in Reference 7, Section C, Order Item 8, (2.1.4).

2. Identify the components required to trip the RCP's, including relays, power supplies and breakers. Assure that RCP trip, when determined to be necessary, will occur. If necessary, as a result of the location of any critical component include the effects of adverse containment conditions on RCP trip reliability. Describe the basis for the adverse containment parameters selected.

Response

Marmal trip of the four RC pumps is accomplished from the main control room console center (CC) using pump individual switches designated CS1. Each of these switches is powered from 125V DC buses in the 6.9KV switchgear. The 125V DC at the switchgear originates from 125V DC Engineered Safeguards distribution panels lE (Red) and 1F (Green) in the Control Building. CS1 interfaces directly with the trip coil in the 6.9KV switchgear. The 6.9KV switchgear is located in the Turbine Building switchgear room elevation 322. No critical components required to initiate a manual RC pump trip are located in harsh environment. A manual trip may also be initiated directly at the 6.9KV switchgear.

C. OPERATOR TRAINING AND PROCEDURES (RCP TRIP)

In response to NRC questions concerning the identification and management of primary system voids, the BWOG response identified potential changes to the AT0G procedures to incorporate proposed detection and management schemes.

Each licensee should endorse this program as described, and provide an implementation schedule for the revised AT0G.

If a licensee does not endorse the provided proposal, then a suitable alternate proposal must be provided including an implementation schedule.

Response

As discussed with Mr. John Thoma (NRC) on July 3,1986, GPUN intends to address primary system void detection and management and provide an implementation schedule in September,1986.

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References:

1. GPUN Letter 5211-83-017, H. D. Hukill to D. G. Eisenhut (NRC), "RCS Trip on 25" Subcooling Margin", March 31, 1983.

2. GPUN Letter 5211-84-2291, H. D. Hukill to J. F. Stolz (NRC), " Error Analysis - Subcooling Margin Indication", November 30, 1984.

3. GPUN Letter 5211-85-2001, H. D. Hukill to J. F. Stolz (NRC), " Error Analysis - Subcooling Margin Indication", January 16, 1985.

4. GPUN Letter 5211-85-2027, H. D. Hukill to J. F. Stolz (NRC), "Subcooling Margin Indication", February 22, 1985.

5. GPUN Letter 5211-85-2090 H. D. Hukill to J. F. Stolz (NRC), "Subcooling Margin Configuration Factor", May 9,1985.

6. SECY-85-189, "Three Mile Island (TMI-1) Restart Certification on Subcooling Instrumentation", May 28, 1985.

7. NUREG-0680 "TMI-1 Restart; Evaluation of Licensee's Compliance with the Short and Long Term Items of Section II of the NRC Order dated August 9, 1979", Supplement No. 3, April,1981.