ML20028F306
| ML20028F306 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 01/26/1983 |
| From: | Dircks W NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO) |
| To: | Ahearne J, Gilinsky V, Palladino N NRC COMMISSION (OCM) |
| References | |
| NUDOCS 8301310391 | |
| Download: ML20028F306 (5) | |
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[ Docket File. 50-327/3284 ?
IIRC PDR SECY JAN 2 61983 L PDR OGC PRC System OPE LB#4 RF W1Dircks, ED0
$frn JcbOLM, ON EAdensam CStahle MDuncan 11EMORAllDUM FOR: Chaiman Palladino DEisenhut/RPurple/MJambor Comissioner rGilinsky TNovak/MStine Comissioner Ahearn,e ELJordan, DEQA:IE Comissioner Roberts JMTaylor, DRP Comissioner Asselstine Attorney, OELD MDridgers, EDO FROM:
William J. Dircks, Executive Director for Operations
SUBJECT:
SEQUOYAH HYDROGEN HITIGATION SYSTEM Enclosed are the responses to Comissioner Ahearne's questions on the Sequoyah hydrogen control system. These questions were raised during the Commission meeting on December 15, 1982, and subsequently identified in a memorandum for S. J. Chilk to W. J. Dircks dated December 23, 1982.
(Signed) William L Dircks William J. Dircks, Executive Director for Operations
Enclosure:
As stated
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N RESPONSES TO COMMISSIONER AHEARNE'S QUESTIONS ON SEQUOYAH HYDRor.EN CONTROL SYSTEM Ouestion 1: Consider whether actuation of the hydrogen control systen should cccur automatically upon a safety injection signal.
Response
The staff concludes that the licensee should not be required to modify the hydrogen control systen to automatically energize the igniters upon a safety injection signal.
This conclusion is based on (1) worst-case analysis shows that the igniters are not needed until approximately thirty minutes into the accident, and (2) our guidance indicates that thirty minutes is sufficient time to allow manual actuation.
The guid-ance used is draft standard ANS 58.8/ ANSI N660, Revision 2, March 1981,
" Time Response Design Criteria for Safety Related Operator Actions."
Although this draft standard has not been approved by the standards organizations, it was used by the staff for guidance in making previous licensing decisions.
Question 2: Clarify whether the procedures require that the hydrogen control system remain activated until the unit reaches cold shutdown.
Response
The current procedures at Sequoyah instruct the operator to turn on the igniters for any reactor trip and safety injection.
1ney instruct the operator to turn the igniters off when reaching cold shutdown following a loss of reactor coolant or upon recovering from a spurious safety injection actuation.
If a situation occurred for which safety injection was needed but the plant was not taken to cold shutdown (if, for instance, repairs were made at hot shutdown), the operators would notice that the igniter switches were in the "on" position during the shift panel check.
If not they could possibly remain in the "on" position until perfornance of the weekly control check procedure.
TVA is cur-rently revising the procedures to assure igniter switches are shut off as soon as appropriate.
_0uestd'an 3: Confirm and clarify that the maximum equipment temperature calculated was substantially lower than the qualification temperature of the equipment.
Response
- TVA has calculated the surface temperature of the Barton Transmitter for 0
the hydrogen burn event.
The calculated surface temperature is 245 F.
The Barton Transmitters have been qualified to a minimum temperature of 0
9 310 F.
Thus, a margin of 65 F is achieved between the qualification temperature and the calculated surface teraperature due to a hydrogen burn event.
The staff believes that except for cables the expected margin will be close to the margin calculated for the Barton Transmitter.
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. staff's belief is based on the results of the analyses submitted for the McGuire and Grand Gulf plants for other components.
Also, it should be noted that the margin will be higher if, instead of the surface temper-ature, internal temperature is taken into consideration.
For cables TVA has dev.cnstrated the survivability based on the conservative experimental denonstration as discussed in SER Supplement No. 6.
Ouestion_4:
Provide infomation on whether scaling is a significant factor in environ-nental qualification testing.
Response
Sandia, in their report NOREG/CR-2730, has sJated that on the basis of some preliminary test results, scaling (volbme of Containment Building vs volume of test chanber) may be a significant factor in analyzing the survivability of the equipment.
However, it should be noted that this finding is based on preliminary test results only, and it is not possible to quantify the effect of the scaling on the equipment survivability at this time.
Sandia, as well as EPRI, at the Nevada Test Site are going to perfom additional tests to address the concern regarding scaling.
How-ever in the mean time, based on the available margin (discussed in response to item 3) and conservative assumptions used in the analysis, based on the full scale containment, the staff believes that even after taking the scaling ef fect into consideration, the equipment will survive the hydrogen burn environment. The results from the Sandia and EPRI's upcoming tests will be reliyJ on to confirm the staff's judgement regarding the scaling effect on the equipment survivability in the hydrogen burn environment and will also be used to verify the analytical models used by the TVA.
Question 5: With respect to survivability of essential equipment, provide informa-tion on how the staff detemined the list of sensitive equipment developed by TVA was satisfactory.
Response
TVA restricted the survivability evaluation to the equipment which is most sensitive to the temperature change.
The criteria used to determine the component sensitivity were based on low heat capacity, inclusion of heat sensitive components, or location in the containment.~ Based on these criteria. TVA has reviewed the list of the equipment (Table 22.3 in SSER No. 6 ) and selected the equipment which meets the criteria.
The exposed RTD and themocouple cable associated with the hot and cold leg temperature monitors and the core unit themocouple were chosen for detailed evaluation due to the small size and, therefore, low heat capa-bility.
The igniter power cable in conduit was also chosen because of the small size and location in the upper plenum of the ice condens::r where a omcep sunuwe) one)
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4 large number of burns may occur.
The igniter assembly, due to its loca-tion in the upper plenum, was chosen for detailed evaluation.
A trans-mitter was also picked because of its relatively small size and because heat sensitive solid-state components were used in its construction.
The staff has reviewed and accepted the criteria used by TVA in selecting the equipment for analytical and experimental investigations for equip-ment survivability.
The staff has also reviewed the list of equipment (Table 22.3 in SSER No. 6) and agrees with the TVA's selection of equip-ment based on the above criteria.
Hence, once the survivability of the items selected is shown in a reasonable manner, then those evaluations will bound all items on the list.
Question 6: Provide information on whether 31 of the 32 igniters per train are needed to maintain effective coverage throughout the containment.
Response
The technical specification on the hydrogen control system, proposed by TVA and accepted by the staff, requires that at least 31 of 32 igniters per train be operable.
Further, if two igniters are inoperable, those igniters must not serve the same region.
These requirements insure that all regions of the containment are served by at least one igniter.
It is the staff's judgement that 31 of 32 igniters per train are not absolutely necessary to maintain effective coverage depending upon the location of inoperable igniters, e.g., for regions served by more than 2 igniters, it may be acceptable to have more than one failed igniter per train.
If proposed by the licensee or in the event a non-compliance situation occurs, the staff would be prepared to consider a proposed change to or a proposed temporary exception from the' Technical Specifications to permit continued plant operation at power.
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large number of burns may occur. The igniter assepbly, due to its loca-tion in the upper plenum, was chosen for detailed evaluation.
A trans-mitter was also picked because of'its relati ly small size and because heat sensitive solid-state conponents wer ed in its construction.
The staff has reviewed and accepted the iteria used by TVA in selecting the equipment for analytical and expertmental investigations for equip-ment survivability.
The staff has afso reviewed the list of equipment (Table 22.3 in SSER No. 6) and apre,es with the TVA's selection of equip-ment based on the above criterje.
Hence, once the survivability of the items selected is shown in a reasonable manner, then those evaluations 7
will bound all items on the list.
Question 6: Provide infonnation on ether 31 of the 32 igniters per train are needed to maintain effective coverage throughout the containment.
Response
The technical s cification on the hydrogen control system, proposed by TVA and accept 6d by the staff, requires that at least 31 of 32 ignitors per train he' operable.
Further, if two igniters are inoperable, those ignitersfriust not serve the same region.
These requirements insure that all regions of the containment are served by at least one igniter.
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It is the staff's jv:gement that 31 of 32 igniters per train are not
. absolutely necessary to maintain effective coverage depending upon the
,/ location of inoperable igniters, e.g., for regions served by more than -
f 2 igniters, it may be acceptable to have more than one failed igniter per train.
If such a non-compliance situation occurs, the. staff would be prepared to consider a proposed temporary exception from or a proposed change to the Technical Specifications to pennit continued plant operation at power.
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December 23, 1982
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OF FICE OF THE SECRETARY
,Q T l(.,
MEMORANDUM FOR:
William J.
Dircks, ExecuP Ve Director i
for Operations FROM:
Samuel J. Chilk, Secret
SUBJECT:
STAFF REQUIREMENTS - DIS'CC'G3 ION AND POSSIBLE VOTE ON SEQUOYAH - HYDROGEN CONTROL, 10:00 A.M.,
WEDNESDAY, DECEMBER 15, h982, COMMISSIONERS' CONFERENCE ROOM, D.C. OFFICE -(OPEN TO PUBLIC ATTENDANCE)
The Commission
By a vote of 4-0, the Commission approved the hydrogen control system as adequate with qthe condition that four additional igniters bo installed in the upper containment.
By;a vote of 3-1 (Commissioner Roberts disapproving), the Commission approved a license condition that additional tests be performod to demonstrato that the igniters initiate combustion.
Commissioner Ahearne requested that:
1.
The staff consider whether actuation of the hydrogen control system should occur automatically upon a safety injection signal.
(NRR)
(SECY Suspense: 1/14/83) 2.
The staff clarify whether tho procedures require that the hydrogon control system remain activated until the unit reaches cold shutdown.
(NRR)
(S$CY Suspense:
1/14/83) 3.
The staff confirm and clarify that the maximum equipment temperature calculated was substantially lower than the qualification temperature of the equipment.
(NRR)
(SECY Suspense:
1/14/83)
- Commissioner Asselstinc was not present.
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The staff provide information on whether scaling is a significant factor in environmental qualification testing.'
(NRR)
(SECY Suspense:
1/14/83) 5.
With respect to survivability of essential equipment, the -
staff provide information on how it determined-the list of
- sensitive" equipment developed by TVA was satisfactory.
(NRR)
(SECY Suspense:
1/14/83) 6.
The staf f provide information on whether 31: of the 32 igniters per train is needed.to maintain an effective coverage throughout the containment.
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(NRR) cc Chairman Palladino Commissioner Gilinsky Commissioner Ahearne Commissioner Roberts Commissioner Asselstine Commission Staff Offices PDR - Advance DCS - 016 Phillips d
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