ML20205T699

Responds to 860507 Requests for Addl Info Re 860314 Info on New Steam Line Rupture Detection/Isolation Sys & Temp Profiles for Equipment Qualification Program

ML20205T699
Person / Time
Site:	Fort Saint Vrain
Issue date:	06/10/1986
From:	Warembourg D PUBLIC SERVICE CO. OF COLORADO
To:	Berkow H Office of Nuclear Reactor Regulation
References
P-86417, TAC-60421, NUDOCS 8606160170
Download: ML20205T699 (15)

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June 1Y,Y6 Fort St. Vrain Unit No. 1 P-86417 Director of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555 Attn: Mr. H.N. Berkow, Director Standardization and Special Projects Directorate Docket No. 50-267

SUBJECT:

Fort St. Vrain Equipment Qualification - SLRDIS

REFERENCES:

1) NRC Letter Heitner to Walker, Dated May 7, 1986, (G-86246)

2) PSC Letter Walker to Berkow, Dated March 14, 1986, (P-86208)

3) PSC Letter Walker to Berkow, Dated June 4, 1986 (P-86227)

4) PSC Letter Warembourg to Berkow, Dated February 28, 1986 (P-86120)

5) NRC Letter Heitner to Walker, Dated April 6, 1986 (G-86181)

Dear Mr. Berkow:

Reference 2 submitted information on the new Steam Line Rupture Detection / Isolation System (SLRDIS) and the temperature profiles for the FSV EQ program.

Reference 1 was a response to the information in Reference 2 and other related documents and contained 10 requests for additional information.

0 8606160170 860610 7 DR ADOCK 0500 L l

P-86417 June 10, 1986 1

The responses to these requests are contained in Attachment 1. If i you have any further questions on this subject, please contact l Mr. M.H. Holmes at (303) 480-6960.

Very truly yours,

) IT W &

D. W. Warembourg, ger Nuclear Engineering Division i DWW/FWT:pa l Attachment l .

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. Attachment 1 to P-86417

1. Since a high energy line break will result in a defined jet of hot water or steam in a limited area, justify your assumption that the entire length of thermistor cable in the steam line rupture detection and isolation system (SLRDIS) will be at the same temperature after a high energy line break. Further, because the entire length of a 200 ft. long thermistor cable must "see" a 55 degree Fahrenheit / minute temperature change following a high energy line break in order to initiate a secondary system isolation signal, show that the SLRDIS response time to this condition is rapid enough to result in the required isolation prior to exceeding equipment qualification envelopes for essential plant shutdown equipment.

Response

The FSV EQ Program is based on the concept of a bulk building temperature following a high energy line break (HELB). The bulk temperature concept was adopted by FSV after discussions with the NRC staff which concluded that the bulk temperature concept was considered industry standard. In contrast, any break that only results in localized temperature increases would not create a common mode failure mechanism.

GA Technologies was contracted by PSC to generate the bulk temperature profiles following a multitude of HELB scenarios.

The CONTEMPT-G computer program was used as described in reference 2 to generate the profiles. This computer model is currently being reviewed by the NRC staff for 3 scenarios that were submitted in reference 4.

These temperature profiles do not conclude that the entire 200 ft. length of cable will be at exactly the same temperature.

However, the profiles do conclude that the entire cable length will see the bulk building temperature. Any limited cable lengths in the path of a water / steam jet would see temperatures much higher than the bulk building temperature relied upon. Each thermistor cable independently acts as a zone temperature sensor and provides a resistive signal that decreases exponentially with increasing temperature. Thus the trip setpoint is based upon an input resistance signal determined by the length of the sensor cable reaching high temperature.

Therefore, to determine the time in which the SLRDIS 55 degrees Fahrenheit / min trip setpoint is reached, the following methodology was used. The above mentioned temperature profiles were used to determine the rate of temperature rise of the ambient air. With this information, it was possible to calculate

. Attachment 1 to P-86417 the resulting thermistor cable temperature rate of rise based upon experimental data from the cable response time test referenced in Question 4.f. The trip setpoint of 55 degrees Fahrenheit / min is based on the cable temperature rate of rise and takes into account actual response time test data to verify that SLRDIS can adequately isolate the HELB.

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Attachment 1 to P-86417

2. -Discuss your plans to verify continued satisfactory operation of the SLRDIS after initial installation including your proposal to conduct ' periodic systematic tests of the SLRDIS in place. This discussion should include the Technical Specification modifications you plan to provide to accomplish periodic, in situ testing. Discuss how you intend to verify the SLRDIS response time assumed in the safety analyses.

Response

The response to describe the SLRDIS testing will follow within 30 days from the date of this letter. i i

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. Attachment I to P-86417

3. Discuss actions to be taken by plant operators in the event the pre-trip alarm temperature (135 degrees Fahrenheit) is reached following a high energy line break (HELB) without causing the 55 degrees Fahrenheit / min. temperature change that would result in automatic SLRDIS actuation. Show that equipment needed for plant shutdown in such an event is not damaged by the HELB.

Response

In the development of the temperature profiles described in Reference 2, various small line breaks and low energy line breaks did not trip the SLRDIS 55 degrees Fahrenheit / min setpoint. In these cases, it was assumed that the operator isolated the break approximately 12 minutes after the 135 dep ees Fahrenheit pre-trip alarm was received. The preferred philosophy is for the operator to only isolate the loop affected by the break and to reestablish shutdown cooling using unaffected equipment as soon as possible (maximum time of 1 1/2 hours). Actions taken by the operator to isolate the break would be based on instrumentation readings, observations, and operator judgement. It cannot be specified exactly what operations are performed for each postulated break since an infinite number and size of breaks can be assumed. Procedures will address in general what instruments could be used to detect and isolate major unisolated line breaks by using the SLRDIS 135 degree F alarm and continuous temperature readout. The local manual actions required by the operators following a HELB will be further addressed in a future response to Reference 5. The safe shutdown equipment is qualified to an enveloping ccmposite temperature curve utilizing these assumptions.

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Attachment 1 to P-86417 l

4. Provide the following information for our review (as noted in Attachment I to your letter P-86208, dated March 14,1986):

a. Resistance vs Temperature curve of the 9090-13 thermistor cable (200' lengths ut.ed at Fort St. Vrain) Dwg. No. 280023 Rev. A;

b. Sensor Center Conductor to Case Resistance vs Temperature -

Initial and Final Curves after Accelerated Aging and i Radiation Tests;

c. Functional Test of Alison Control After Seismic Test - dated l

11/1985;

d. Equipment qualification Package;

e. Seismic Test of Control Rack and Sensor Assemblies performed by Wyle Labs, 11/9/85;

f. Response Time Test of Thermistor Cable performed by Factor Mutual Research Corporation, 12/10/85; and

g. Qualification Test Report of 9090-13 Sensor Assembly (Doc. No. ETR101), dated 2/7/84 for Application at Davis-Besse.

Response

The above information can be found in Attachment 2 to this letter.

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Attachment !

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i l S. Provide a discussion which indicates how the unavailability goal of 0.01 4

has been attained for the portions of the SLRDIS shown in Figure 3 of Attachment 2 to your letter P-86208. If this discussion is not for the J complete SLRDIS, indicate what the unavailability is for the entire SLRDIS.

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Response

The " unavailability goal" figure stated in Attachment 2 to Reference 2 is for the entire SLRDIS system as depicted in Figure 4 of Reference 2. The Reference 2 submittal incorrectly referenced Figure 3. The SLRDIS unavailability goal of 0.01 was a specification goal based on feedback from users of this equipment and manufacturer's literature. No detailed unavailability studies have been made or are intended to be made to verify this unavailability number. The actual unavailability number is not i of importance since the operability requirements are contained in the Technical Specifications submitted in Reference 3.

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- Attachment 1 to P-86417

6. Confirm that in the event of a fire in those areas which may impact on the SLRDIS, safe shutdown of the plant is not affected.

Response

The SLRDIS Safety Evaluation forwarded in Reference 3 addresses a SLRDIS actuation due to a fire. SLRDIS can be reset and safe shutdown of the plant can be achieved within the allowable 90 minutes. The SLRDIS recovery procedures will address the reset actions required.

. Attachm:nt I to P-86417

7. Attachment 2 (Page 4.4-6c, action statement 1) to your submittal dated 12/31/85 (P-85456) discussing the SLRDIS system states:

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Power operation above 8% rated thermal power may continue provided the inoperable channel is placed in the bypassed or tripped condition--- ".

Provide justification for placing an inoperable channel in the bypassed condition.

Response

A new submittal, PSC to NRC, dated 6/4/86 (P-86227) changes the action statement referred to in the question; however the action still requires an inoperable channel to be bypassed as stated below:

"... operation at power may continue provided the inoperable channel is placed in bypass within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> or reduce power to below 2% within the next 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />."

In addition, the action statement that is applicable in the event of two inoperable channels has been changed to require that both inoperable channels be placed in bypass, and that reactor power be reduced.

These actions were changed because the SLRDIS design does not incorporate a " tripped" position for a channel. Lifting leads and placing a resistor in the circuit electrically would have been required to simulate a " tripped" channel. Placing a channel in bypass is accomplished with front panel controls only.

Justification for these action requirements is based on using a 2 out of 4 sensing channel logic to provide a trip signal to the final output relay trip logic as well as considering the consequences of SLRDIS actuation. It should be noted that an automatic system to mitigate the consequences of a harsh environment at Fort St. Vrain HTGR requires isolation of steam and water systems used to drive the helium circulators. Thus, an interruption of forced cooling (10FC) is the resultant mitigation for the harsh environment. It is highly desirable to minimize the probability of an 10FC occurring due to a system or operator malfunction. When the first inoperable channel is placed in bypass, the system functions as a 2 out of 3 sensing channel logic to provide the trip signal to the final output relay trip logic. This 2 out of 3 channel configuration satisfies the current licensing basis of the existing Plant Protective System

- Attachment I to P-86417 as defined in Criterion 20 of the FSV FSAR.

A four sensing channel system was conceived to provide additional flexibility in operation and maintenance of SLRDIS. However, a key consideration through design, operation, surveillance and administration controls of SLRDIS is to minimize inadvertent actuations. This concept is best delivered by placing an inoperable channel in bypass; thus minimizing the opportunity for noise spikes or voltage fluctuations on the remaining operable channels to increase the probability of an 10FC.

Placing a second inoperable channel in bypass is justified because this condition also requires power to be reduced to below 2% within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />, and the likelihood of a steam line break during this period is quite small. Also, the two remaining operable channels and the other SLRDIS locp provide operator alarms and are capable of SLRDIS actuation.

The actions to place inoperable channels in bypass are consistent with those required for inoperable engineered safety feature actuation systems in the Westinghouse Standard Technical Specifications (NUREG 0452). For 4 channel systems, the first inoperable channel is required to be bypassed and a second channel is pennitted to be bypassed for a short time for test purposes.

Again, consideration of reduced instrumentation available for detection must be balanced with the severe transient placed on plant systems and components due to an automatic safety system actuation. PSC considers the proposed SLRDIS Technical Specification amendment to represent that balanced approach.

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. Attachment I to P-86417

8. Will a high energy line break in some areas cause increased temperatures in both the reactor building and turbine building?

If so, show that you have accounted for this in the qualification of essential equipment.

Response

High energy line breaks will not cause harsh environments in the Turbine Building and Reactor Building simultaneously. These buildings are separated by a steel wall. It is anticipated that the escape path out of these buildings will be through the pressure relieving devices (blow-out panels, windows, etc.), and not into the other building.

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. Attachment I to P-86417

9. Is there a potential for a steam line break at power levels 59%

to be more severe than those at higher power levels because of the use of auxiliary boilers? If so, show that your analyses confirming equipment qualification has accounted for this potential.

Response

In the development of the composite profiles presented in Reference 2, various plant power levels were evaluated in different scenarios to assure that the most limiting environment would be evaluated. Temperature profiles were initially generated assuming a plant power level of <59% for the worst-case scenarios where the auxiliary boilers contributed to the break.

Subsequent analyses were performed since operating procedures allow the auxiliary boilers to be in service up to a plant power level of 65%. As further conservatism, those scenarios were also run with the plant power level assumed to be 100% and the auxiliary boilers assumed to be in-service and as such were factored into the composite temperature profiles.

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• Attachment I i to P-86417

10. Show that essential equipment required for shutdown, including instrumentation, exposed to spray from moderate energy line breaks is qualified to withstand such spray and maintain their function.

Response

Per PSC's May 2,1986 meeting with the NRC Staff the direct water spray from moderate energy line breaks is not a design basis event within the scope of 10 CFR 50.49. This conclusison was based on the fact that the direct spray from a moderate energy line break would not create a common mode failure mechanism. Thus any equipment failure associated with such spray would be very lxalized. Any flooding, temperature or humidity concerns associated with a moderate energy line break are enveloped by the high energy line break (HELB) scenarios in the FSV EO l program.

PSC has anticipated that the FSV fire suppression systems located in areas subject to harsh environments may be actuated by a HELB. The plant locations potentially subjected to this spray are limited however, any EO requirement in these areas will either be qualified for water spray or shielded from the spray.

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.. . Attachment 2 to P-86417 Response to Request 4 4a. Attached is drawing No. 280023, Rev. A; however, this drawing does not include a curve for a 200 foot long thermistor cable.

A computer printout has been included to provide this information. The tabulation is titled " Thermistor Sensor Resistance vs. Uniform Ambient Temperature", dated 5/2/86.

b. Sensor Center Conductor to Case Resistance vs. Temperature -

Initial and Final Curves after Accelerated Aging and Radiation Tests - Attached.

c. Functional Test of Alison Control After Seismic Test dated 11/85 - Attached,

d. Equipment Qualification Package -

Attached. Please be advised that this is preliminary package and has not been approved.

e. Seismic Test of Control Rack and Sensor Assemblies performed by Wyle Labs, 11/9/85 - Attached,

f. Response Time Test of Thermistor Cable performed by Factory Mutual Research Corporation - Attached.

g. Qualification Test Report of 9090-13 Sensor Assembly (Doc. No. ETR 101), dated 2/7/84 for Application at Davis-Besse.

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