ML20040A614
| ML20040A614 | |
| Person / Time | |
|---|---|
| Site: | 05000514, 05000515 |
| Issue date: | 05/15/1978 |
| From: | Novak T Office of Nuclear Reactor Regulation |
| To: | Varga S Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML111090060 | List:
|
| References | |
| FOIA-80-515, FOIA-80-555 NUDOCS 8201210294 | |
| Download: ML20040A614 (4) | |
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s UNITED STATES y %@ pk NUCLEAR REGULATORY COMMISSION
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0 WASHINGTON, D. C. 20555 f
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Docket Nos. 50-514I515 MAY t 5 B78 MEMORANDUM FOR:
S. A. Varga, Chief, LWR Branch 4. OPM FROM:
T. M. Novak, Chief, Reactor Systems Branch, DSS I
SUBJECT:
ASLB QUESTIONS ON PEBBLE SPRINGS Enclosed is the Reactor Systems Branch response to ASLB Question Number 6.
Reference 3 of the Enclosure (letter notifying the applicant of the rhaff cold shutdown requirements) has not yet been sent.
It is requested that the LPM include the date of this letter in the table of references when available. Note that the reference. to Supple-ment 5 assumes that it will be published by the time the responses are submitted.
b l
. M. Novak, Chief l
Reactor Systems Branch, DSS
Enclosure:
As Stated t
cc:
S. Hanauer R. Mattson D. Ross D. Vassallo C. Stahle T. Novak l
G. Mazetis S. Israel i
H. Li S. Newberry
Contact:
S. Newberry, NRR i
x27341 0201210294 010403 PDR FOIA MADDEN 80-515 PDR
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ENCLOSURE n
RESPONSE TO ASLB QUESTION NUMBER 6 Decay Heat Removal System Initiation The general Design Criteria do not require a completely automatic residual heat removal system. The Pebble Springs decay heat removal system is man-ually initiated from the control room by the operator when reactor coolant system temperature is less' than 305 degrees Fahrenheit. These actions are taken as part of the normal shutdown sequence and consist primar'ily of operation of the DHRS pumps, associated suction, discharge valves and cool-er bypass valves to attain the desired cooldown rate of the reactor coolant system.
Decay Heat Removal System Single Failure The Pebble Springs decay heat removal system is capable of being operated t
from t'ie control room with either onsite, or only offsite' power available, assuming a single failure. A failure of e single valve will not compromise both trains of the system.
If one of the trains is not operable due to a single valve failure, the decay heat removal system can still cool the reactor coolant system to 212 degrees Fahrenheit in less than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
Section 7.4.1 of the Pebble Springs Safety Evaluation Report Supplement 3 expresses the staff's concern regarding the failure of the decay heat removal system to meet the single failure criterion with respect to isola-tion of system piping ruptures outside containment.
This concern was re-l solved by a system design modification which meets the single failure criterion and is discussed in Supplement 5 (Section 7.4.1) to the Safety i
Evaluation Report.
Sharing of Power and Air Sucolies With Non-Safety Grade Systems The power supplies to the safety-related components in the decay heat re-moval system are not shared with systems that are not safety grade.
The i
decay heat removal system heat exchanger bypass valves are pneumatic valves
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which Ire supplied'with non-safety grade air for motive power.
Loss of air to these valves would not prevent the system from performing its function.
A Provisions For Shutdown r
A plant cooldown from hot shutdown conditions is generally performed in two stages. The first stage involves removal of decay heat via the steam generators with makeup to the steam generators provided by the auxiliary feedwater system.
Depending on the availability of offsite power, steam
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is either routed to the main condenser or alternatively steam generator dump valves are opened to permit steam release.
Depressurization of the I
primary coolant system is controlled by spray cooling of the pressurizer steam space. This procedure is followed until the primary crolant conditions reaches the DHRS cut-in point. At this point the aecond phase i
of the cooldown begins using the DHRS.
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Section 5.5.5 of the Pebble Springs Safety Evaluation Report states that the decay heat removal system design is sufficient to cool the reactor j
coolant system from 305 degrees Fahrenheit to 140 degrees Fahrenheit in 14 hours1.62037e-4 days <br />0.00389 hours <br />2.314815e-5 weeks <br />5.327e-6 months <br />, starting 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> after shutdown.
Tne reactor coolant system must first be depressurized to approximately 400 pounds per square inch and cooled to 305 degrees Fahrenheit prior to using the, decay heat removal system. The applicant committed ir reference 1 to prov'ide information to show that the Pebble Springs plant can remain for a prolonged period in a hot shutdown condition assuming loss of offsite power with only safety-grade equipment, or that the plant can be cooled and depressuri:ed t
4 using o-ly safety-grade equipment (assuming loss of offsite power).
Until recently, the staff has not required the systems which perform the cooldown and depressurization to the decay heat removal system cut-in l
point to be safety grade. A new position on these cold shutdown require-i ments was recently published by the NRC Regulatory Requirements Review Committee and reported in reference 2.
The staff now requires that the e
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plant have the capability to be taken to cold shutdown using safety-grade
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systems, assuming only onsite or offsite power is available, and assuming a single active failure. The applicant was notified of these requirements in reference 3, and must, at a minimum, provide a commitment to meet them prior to issuance of a construction permit.
References 1.
Letter from W. J. Lindblad (PGE) to S. A. Varga (NRC) dated December 7, 1977.
2.
Memorandum from E. G. Case, Committee Chairman, to L. V. Gossick, Executive Director for Operations, dated February 16, 1978.
3.
Letter from S. Varga (NRC) to W. J. Lindblad (PGE) dated e
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