ML20206U875

Forwards Responses to Request for Addl Info Re Conformance to Reg Guide 1.97

ML20206U875
Person / Time
Site:	Yankee Rowe
Issue date:	09/30/1986
From:	Papanic G YANKEE ATOMIC ELECTRIC CO.
To:	Mckenna E Office of Nuclear Reactor Regulation
References
RTR-REGGD-01.097, RTR-REGGD-1.097 DCC-86-147, FYR-86-091, FYR-86-91, NUDOCS 8610080445
Download: ML20206U875 (11)

Text

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Tc'=pho"c ('") '~'O YANKEE ATOMIC ELECTRIC COMPANY TWX 710 380 7619

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' ~ 1671 Worcester Road, Framingham, Massr.:hucetts 01701 DCC 86-147 g

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September 30, 1986 FYR 86-091 United States Nuclear Regulatory Commission Washington, DC 20555 Attention: Ms. Eileen M. McKenna Project Directorate No. 1 Division of PWR Licensing - A

References:

(a) License No. DPR-3 (Docket No. 50-29)

(b) YAEC Letter to USNRC, dated August 30, 1983 (FYR 83-81) l (c) YAEC Letter to USNRC, dated January 19, 1984 (FYR 84-08) ,

(d) YAEC Letter to USNRC, dated July 16, 1984 (FYR 84-77) '

(e) USNRC Letter to YAEC, dated August 6, 1985 (NYR 85-134)

(f) YAEC Letter to USNRC, dated October 22, 1985 (FYR 85-113)

(g) USNRC Letter to YAEC, dated ' July 28, 1985 (NYR 86-162)

Subject:

Response to Request for Additional Information - Regulatory Guide 1.97

Dear Ms. McKenna:

Enclosed are the responses to the items for which additional information or justification was requested by Reference (g). We hope that this information is satisfactory. However, if you have any further questions on our Regulatory Guide 1.97 submittals, we feel that a meeting would be the best and most expeditious format for their resolution.

Very truly yours, YANKEE A'ICMIC ELECTRIC COMPANY George apanic, Jrf Senior Project Engineer Licensing GP/kmc 1 Enclosure 8610080445 DR 860930 ADOCK 05000029 1 PDR g g i

L___.___________________.______ _

ATTI.CHMENT Additional Information Requested For Conforcance to Regulatory Guide 1.97 INEL REPORT SECTION 4: CONCLUSIONS

1. Environmental Qualification: The licensee should provide additional justification for those variables that will not be upgraded to include environmental qualification and make specific commitments to upgrade those that will (see Section 3.3.1 and Appendix A).

Yankee Response Appendix A of the INEL Report summarizes the deviations from the Regulatory Guide environmental qualification recommendations. Individual responses to each of the items of Appendix A have been prepared and are included below.

2. Neutron Flux: The licensee should provide environmentally qualified instrumentation and redundant power sources (see Section 3.3.2 and Appendix A).

Yankee Response Environmental qualification of this instrumentation is addressed in the responses to the Appendix A items.

The second area of concern is the requirement to have redundant power sources for the neutron flux instrumentation. As stated in Section 3.3.2 of the INEL Report, Yankee has two additional source range channels with a range of 1 to 100,000 counts per second. The report further states that they cannot be considered redundant to SR1 and 3R2 because they do not have the full range recommended in the Regulatory Guide. This statement is incorrect. SR1 and SR2 have the same range as the two additional source range channels, 1 to 100,000 counts per second.

Therefore, these iv.* additional source range channels are indeed redundant to SRI and SR2. Redundancy is not provided for the intermediate and power range neutron flux channels since it is not necessary, as will be shown below.

Section 3.3.2 of the INEL Report states that redundant instrumentation is required for the full range of neutron flux in the event of a loss of VBl. It further states that a loss of VB1 results in a reactor scram, and neutron flux is a key variable for detecting an uncontrolled approach to criticality and for determination that an accident has been successfully mitigated.

Following a reactor scram, the neutron flux quickly decays into the source range. Flux levels in the source range will provide verification that the accident has been mitigated. Source range neutron flux indication would then be used to detect an uncontrolled return to criticality. The operators are trained to expect source range flux levels to be continuously decreasing with time. Any time source range

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counts are increasing after a trip, operators are instructed by procedure to initiate emergency boration. Post-trip flux levels above the source range receive the same response from the operators. The range provided by the redundant source range instruments is more than adequate to provide the operator with the indication needed to detect a return to criticality. Post-trip flux level indications above the source range are not needed since the required response is undertaken before flux levels increase out of the source range.

Therefore, rodundant instrumentation for the intermediate and power range neutron flux instruments is not necessary for a loss of VBl. Operator actions dictated by emergency procedures are designed specifically to keep the neutron flux level in the source range and decreasing.

Redundant instrumentation for neutron flux outside of the source range would be useless to the operators since their actions are specifically designed to prevent this from occurring, and their response to increasing neutron flux levels would be initiated based on source range instrumentation only.

APPENDIX A - ENVIRONMENTAL QUALIFICATION

1. Reactor Coolant System (RCS) Pressure Sensors Powered by Vital Bus 2: No justification was provided by the licensee. Environmental qualification is necessary to complete the redundancy required for this Type A instrumentation.

Yankee Response As indicated in Yankee's compliance table, Pressure Transmittar MC-PT-200 is supplied by Vital Bus 2 (VB2) and is environmentally qualified. This channel therefore provides redundancy to the channels listed as supplied by Vital Bus 1 (VB1). The remarks column of the table indicated that

" isolation of primary coolant Loop 2 to minimize the consequences of a break in that loop will cause MC-PT-200 to be isolated. A subsequent failure of VB1 would render all remaining qualified channels inoperable." Contrary to the above rationale, isolation of the primary coolant loops is not used to mitigate a loss-of-coolant or high energy line break accident (i.e., not included in plant procedures). Loop isolation is only used to mitigate steam generator tube rupture. Since a steam generator tube rupture does not create a harsh environment inside containment, unqualified pressure transmitters supplied by VB2 will provide indication of primary pressure for the scenario described above.

2. Neutron Flux: The licensee states that there is no long-term environmental qualification'. The licensee states that alternate instrumentation for long-term observation of the core conditions includes control rod position, boron concentration, and RCS temperature.

The measurement of neutron flux is the key variable for detecting and directly observing an uncontrolled approach to criticality and for the determination that an accident has been successfully mitigated. Since key variables are Category 1,'and include environmental qualification, the licensee should -commit to the installation of instrumentation for this variable that is in accordance with Regulatory Guide 1.97.

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Yankee Response Section 3.3.2 of the INEL Report states that neutron flux instrumentation is a key variable for the following two functions:

1. For determination that an accident has been successfully mitigated,

( i.e., the reactor is shutdown, and

2. For detecting an uncontrolled approach to criticality.

l There are two types of accidents that result in harsh environments inside containment; primary system pipe breaks (LOCAs) and main steam or feed line breaks. For both types of accidents, a reactor scram is initiated and the reactor shut down before a harsh environment is formed.

Therefore, the neutron flux instrumentation will perform the first function, verification of accident mitigation, before a harsh environment is formed. Neutron flux is also a recorded parameter on the Safety Parameter Display System (SPDS). In the event that the operator is unable to verify reactor shutdown during an accident that resulted in a harsh environment, the SPDS recorded information would be available to verify initial reactor shutdown.

The second function for neutron flux instrumentation is to detect an uncontrolled approach to criticality. Return to criticality is not a concern for a LOCA condition since all of the safety injection water injected into the primary system is highly borated and is simply recirculated back through the reactor for long-term cooling. For main steam line breaks, a return to criticality may be a potential concern for some plants. However, this is not the case for Yankee. The DBA main steam line break accident analysis performed for Yankee has shown that shutdown margin is maintained and a re. turn to criticality is not a concern.

For any accident that results in a harsh environment inside containment, the neutron flux instrumentation performs its function prior to the environment being formed, Algor Yankee is not susceptible to accidents where return to criticality and a harsh environment acting together are a concern. Therefore, environmental qualification of neutron flux instrumentation is not required.

3. RCS Hot Leg Water Temperature: The licensee states that this variable '

can also be monitored via the core exit temperature instrumentation, and l that since cooling occurs by way of the Safety Injection System,' I environmental qualification of this instrumentation is not necessary.

We find this justification not acceptable. There are accidents and transients that would not result in a safety injection. The RCS temperature is necessary to verify that the reactor pressure vessel temperature limits are not exceeded. Therefore, the licensee would upgrade this instrumentation to include environmental qualification.

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Yankee Response 1

The use of core exit thermocouples to measure temperature in lieu of bulk coolant temperature as measured at the coolant loop hot leg (reactor outlet temperature) provides not only an adequate but a preferred means to monitor core cooling. Core exit thermocouples provide local temperature conditions for various locations just above the core. l Therefore, core exit thermocouples provide a more direct indication of coolant temperatures in the coro region (the area of heat generation) than loop hot leg resistance temperature detectors. l Multiple core exit locations are monitored by qualified thermocouple channels such that there are at least two locations monitored per core .

quadrant. Each of the two channels per quadrant is supplied ~by different vital buses. Recorders located on the main control board provide trending indication with a range of 0-700 0 F. This arrangement assures that a cross section of core exit temperature is available to monitor coolant temperature in the region above the core.

Redundant qualified reactor vessel head thermocouple channels monitor I conditions in the reactor head area. Void development under the head is therefore detectable for cooldown situations where head area coolant temperature lags behind the core coolant.

Conservative monitoring of reactor coolant inventory subcooling, particularly in the region of primary concern (the core), is provided.

The areas where coolant temperatures could be greatest (the core exit area and head area) are monitored by qualified temperature channels.

Therefore, conservative temperatures are provided for subcooling determination.

The INEL Report states that there are accidents and ' transients that would not result in a safety injection. Natural circulation through the steam generators becomes the means for coolant heat removal when the Safety Injection System does not provide the primary means of cooling. Natural circulation can be verified by monitoring the response in core exit '

temperature trend to changes in load produced by modulating the steam

-generator steam discharge. Additionally, should circulation be interrupted, the hot leg temperature could become stagnant, whereas the core exit temperature would increase. Thus, core exit temperature.is considered more effective than hot leg temperature for monitoring natural circulation heat removal.

The INEL' Report states that "the RCS temperature is necessary to verify that the reactor pressure vessel temperature limits are not exceeded."

Reactor pressure vessel temperature limits involve a concern of having main coolant temperature too low for the existing main coolant pressure.

Reactor inlet temperature derived from steam generator pressure, as discussed below under RCS cold leg water temperature, provides the means to address this concern. Therefore, hot leg water temperature is not needed to address this concern.

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4. RCS Cold Leg Water Temperature: The licensee states that this variable can also be monitored via the steam generator pressure instrumentation, and that since cooling occurs by way of the Safety Injection System, i environmental qualification of this instrumentation is not necessary.

We find this justification not acceptable. There are accidents and transients that would not result in a safety injection. The RCS temperature is necessary to verify that reactor pressure vessel temperature limits are not exceeded. Therefore, the licensee'should upgrade this instrumentation to include environmental qualification.

Yankee Response The cold leg water temperature is not required for verification of core cooling. As discussed above, under RCS hot leg water temperature, core exit temperature provides the preferred means of monitoring core cooling.

The INEL Report states that "There are accidents and transients that would not result in a safety injection." Natural circulation through the steam generators becomes the means for coolant heat removal when the  ;

Safety Injection System does not provide the primary means of cooling.

As discussed above, under RCS hot leg water temperature, natural circulation can be verified through the use of the core exit thermocouples. Loss of natural circulation will be evident from an increasing trend in core exit temperature, whereas cold leg temperature msy stagnate. Additionally, a difference between hot les and cold leg temperature alone does not assure the verification of natural circulation. Natural circulation can be assured by monitoring.the response in core exit temperature trends to steam generator load changes produced by modulating steam discharge.

The INEL Report states that "the RCS temperature is necessary to verify that reactor pressure vessel temperature limits are not exceeded." This involves a concern of having main coolant temperature too low for the existing main coolant pressure. Under natural circulation, cooler water is introduced at the reactor inlet and its temperature will correspond to the saturation temperature of steam generator pressure. Natural-circulation can be verified, as discussed above, through the use of the core exit thermocouples. Therefore, once natural circulation is occurring, cold leg temperature derived from steam generator pressure can be used for verification that reactor pressure vessel limits are not exceeded.

5. Degrees of Subcooling: The licensee states that the RCS pressure input for this variable is not environmentally qualified. This instrumentation should be environmentally qualified (see 1. above).

Yankee Response The above statement is incorrect. Yankee has not stated that the RCS pressure input for this variable are not environmentally qualified. The pressure inputs to the saturation margin monitor (MC-PT-712 and PR-PT-700) are qualified.

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6. Containment Effluent Radioactivity - (Noble Cases From Identified Release Points): The licensee states that this instrumentation is in a mild environment except for radiation. The licensee committed to address the radiation aspect. The licensee should provide the results of this study as part of their justification or provide environmentally qualified instrumentation for this variable. -

Yankee Response See Item 17.

7. Effluent Radioactivity - Noble Gases (From Buildings as Indicated): The licensee states that this instrumentation is in a mild environment except for radiation. The licensee committed to address the radiation aspect.

The licensee should provide the results of this study as part of their justification or provide environmentally qualified instrumentation for this variable.

Yankee Response See Item 17.

8. Reactor Heat Removal (RHR) System Flow: The licensee states that this instrumentation is not required to operate during or after a harsh environment. The licensee should provide a system description that verifies this justification.

Yankee Response For most plants, the RHR System perforns a safety function following a LOCA. During the recirculation phaso of Emergency Core Cooling System (ECCS) operation, water from the containment sump is cooled by the RHR System before being returned to the containment. This is the system that removes decay heat following a LOCA.

At Yankee, decay heat is removed passively by heat loss through the metal containment s' tin. During recirculation, the ECCS draws water from the containment rump and returns it to the reactor without any forced cooling, i.e., an RHR System is not needed for LOCAs.

For most plants, the RHR System also performs a similar safety function following a HELB inside containment. Decay heat is initially removed via the intact steam generators until primary temperature and steam generator pressure have been reduced to where further temperature reduction is not possible. The RHR System is then used to lower primary temperature to less than 2000F and to remove decay heat.

At Yankee, the system that performs this function is called the Shutdown Cooling (SDC) System. The SDC flow instrumentation is located outside of containment and is not subjected to a harsh environment when it is required to operate. Therefore, environmental qualification of this instrumentation is not required.

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9. RHR Heat Exchanger Outlet Temperature: The licensee states that this instrumentation is not required to operate during or after a harsh environment. The licensee should provide a system description that verifies this justification.

Yankee Response The discussion under Item No. 8 also applies to this instrumentation.

10. Accumulator Tank Level and Pressure: The licensee states that there is and no long-term environmental qualification because the system operation is

11. complete prior to harsh environmental conditions occurring. This instrumentation is not acceptable. An environmentally qualified instrument is necessary to monitor the status of these tanks. The licensee should designate either level or pressure as the key variable to directly indicate accumulator discharge and provide instrumentation for that variable that is environmentally qualified.

Yankee Response The Safety Injection (SI) System at Yankee contains one accumulator located outside containment. This accumulator is normally depressurized. Upon receiving a Safety Injection Actuation Signal (SIAS), the accumulator is pressurized with nitrogen. It discharges to the Main Coolant System (MCS) through the low pressure injection header.

Once the accumulator is discharged, the isolation valve closes, the nitrogen supply to the accumulator is isolated, and the nitrogea pressure in the accumulator is vented to atmosphere. _ These actions are performed automatically upon actuation of accumulator low level switebas and occur during the injection phase of ECCS operation.

At a prescribed level in the refueling water storage tank, the recirculation phase of ECCS operation is initiated and the injection phase terminated. As part of the switchover to recirculation, the low pressure injection header is isolated by closing one motor-operated valve inside and one outside containment.

Because the SI accumulator is located outside the containment, its level and pressure instrumentation is only subjected to radiation as a harsh -

environment, and harsh radiation levels are not reached until after the accumulator has completed its required emergency core cooling function.

j By the time the accumulator instrumentation is subjected to a harsh I

environment, the following have already occurred:

1. The accumulator has performed its safety function by discharging its contents to the MCS.

, 2. The accumulator isolation valve has closed.

3. The nitrogen supply to the accumulator has been isolated.

4. The accumulator has been depressurized by venting it to atmosphere.

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subsequently, the low pressure injection header that the accumulator discharges into is isolated from containment by closing redundant motor-operated valves, one inside and one outside containment.

Based on the design of the ECCS at Yankee, environmental qualification of the accumulator instrumentation is not necessary.

12. Accumulator Isolation Vslve Position: The licensee states that there is no long-term environmental qualification because system operation is complete prior to harsh environmental conditions occurring. The licensee should state how the operator determines the status of these valves in post-accident situations.

Yankee Response As discussed above in the response to Items 10 and 11, the Yankee SI System has one accumulator located outside containment. The accumulator  !

isolation valve closes automatically before being subjected to a harsh environment. The accumulator is also isolated from containment by closing the inside and outside containment low pressure injection header isolation valves. These valves are manually closed by the operator from the Main Control Room when initiating recirculation. The positions of these valves are verified by the operator when they are closed by valve position indication in the Control Room. If the accumulator isolation valve position indication were to fail, the operator could insure the accumulator was isolated from the MCS by verifying the low pressure injection header isolation valves were closed. Position indication for the inside containment valve is environmentally qualified.

13. Containment Atmosphere Temperature: The licensee states that since~the containment is passively cooled, environmentally qualified instrumentation for this variable is not necessary (see Section 3.3.16).

Based on this justification, we find this deviation acceptable.

Yankee Response None required.

14. Makeup Flow-In: The licensee states that this instrumentation is not required to operate during or after a harsh environment. The licensee should provide a system description that verifies this justification.

Yankee Response At Yankee, harsh environments result from LOCAs and High Energy Line Breaks (HELBs) inside containment. During a LOCA, all three charging pumps are automatically secured upon receiving a SIAS, and the Charging System is not used. Charging flow indication is therefore not needed.

Note that emergency boration is accomplished integrally through the function of the SI System.

Following a HELB inside containment, the Charging System may be used for emergency boration. The charging flow instrumentation is located outside containment, and is not subjected to a harsh environment following this 4902R l

, HELB. Therefore, environmental qualification of this instrument is not l needed.

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15. Letdown Flow-Out: The licensee states that this instrumentation is not required to operate during or after a harsh environment. The licensee should provide a system description that verifies this justification.

i l Yankee Response The letdown line contains a containment isolation valve which closes automatically on a SIAS or on a high containment pressure. As discussed above for Item 14 the Charging System is not used to mitigate a LOCA.

The Charging System may be used for emergency boration following a HELB; however, it is not necessary to drain coolant via the letdown line. The  ;

MCS can be borated simply by making up to the system for shrinkage during cooldown. The letdown line therefore remains isolated and is not used to l mitigate a LOCA or a HELB. Environmental qualification of this l instrumentation is therefore unnecessary. l

16. Volume Control Tank Level: The licensee states that this instrumentation is not required to operate during or after a harsh environment. The licensee should provide a system description that verifies this justification.

i Yankee Response Volume control tank level indication is only required when the tank is being used as a water source for the charging pumps. As discussed in the response to Item 14, the charging pumps are secured automatically during a LOCA. When they are used for a HELB inside containment, the charging pumps and the volume control tank level instrumentation are located outside of containment, and are not subjected to a harsh environment.

Therefore, the volume control tank level instrumentation does not require environmental qualification.

17. Common Plant Vent or Multipurpose Vent - Noble Gases: The licensee i states that this instrumentation is in a mild environment except for radiation. The licensee committed to address the radiation aspect. The licensee should provide the results of this study as part of their justification or provide environmentally qualified instrumentation for this variable.

Yankee Response We will review the environmental radiation levels with respect to possible equipment damage for the high-range monitor and sample pump. l The low-range channel provides monitoring capability for normal plant . i operation and will not be included in the review. The high-range monitor i can adequately monitor decreasing levels of noble gas concentrations. '

The low-range level of the monitor corresponds to the following off-site doses:

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Distance from Plant (Miles) Off-Site Dose Rate (mR/hr) 0.5 0.5 1 0.2 2 7.2 x 10-2 The manufacturer of the high-range monitor has indicated on a preliminary basis that the components of this system should be capable of operating within the postulated radiation environment for the Yankee installation.

Yankee is in the process of requesting a proposal from the manufacturer to review and document the environmental radiation exposure capability expected for this equipment.

The sample pump is common to both the high-range and low-range channels.

The sample pump and associated components will also be reviewed with respect to performance in the postulated radiation environment.

It is expected that these reviews will be completed by May 1, 1987, and a decision will be made at this time to replace, upgrade, or document the radiation capability of the equipment as is.

18. Vent from Steam Generator Safety Relief Valves or Atmospheric Dump l Valves: The licensee states that this instrumentation is not required to operate during or after a harsh environment. The licensee should provide a system description that verifles this justification. ,

Yankee Response Main steam line radiation monitors are used to monitor noble gas effluent from steam generator safety relief valves or atmospheric dump valves.

The steam generator safety valves and atmospheric dump valves are only used to vent steam to atmosphere for decay-heat removal following a

. HELB. During a LOCA, decay heat is removed by operation of the ECCS.'

The steam generators are not used for decay heat removal following a LOCA. The steam generator safety valves and atmospheric dump valves will remain closed during a LOCA. '

The steam line radiation monitors are located outdoors, there are therefore no HELBs that could subject them to a harsh environment.

Therefore, environmental qualification of this instrumentation is not required.

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