ML19208A920
| ML19208A920 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 08/17/1979 |
| From: | Herbein J Metropolitan Edison Co |
| To: | Jay Collins NRC - TMI-2 Operations/Support Task Force |
| Shared Package | |
| ML19208A918 | List: |
| References | |
| CQL-1074, NUDOCS 7909180273 | |
| Download: ML19208A920 (3) | |
Text
LoulTOR
.a
$0 - : O Metropolitan Edison Cornpany Post Of fice Box 542 J~ Q Reading Pennsylvania 19640 215 929 3601 Writer's Direct Dia! Nurnber August 17, 19~9 GQL 107h TMI-2 Support Attn: John T. Collins, Deputy Director U.S. Nuclear Fegulatory Co==ission Washington, D. C. 20555
Dear Sir:
Three Mile Island Nuclear Station Unit 2 (D!I-2)
License No.
DPE-73 Docket th.
50-320 Natural Circulation Stability In response to your questions posed in your =eco of July 26, 1979 concerning Loss of Natural Circulation, the following reply is given:
QUESTION 1 Confirm in writing that the cyclic cooling mode, if it is to be relied upon, is safe.
The effect of rapid trans. ar of water in the Reactor Coolant System, ther=al cycling of components (OTSG, Vessel, etc. ) and Reactor Coolant System pressure control (considering solid operation) should be addressed. Further, this evaluation should consider the length of time this mode of operation vill be utilized.
EESPONSE It is expected that stable natural circulation vill continue until the A loop aT reaches 3 h degrees F
(,i.e., September - October 1979). At that time, loop operation vill be aharacterized by the following:
- a. Periodic Natural Circulation on "A" loop with a T 3-5 degrees F.
- b. Periodic " burps" of the "B" loop triggering an oscillation in the "A" loop temperatures (both Th and T ).
These oscillations may become divergent C
and may result in stopping of "A" loop flow.
If "A" loop flow stops - the following vill occur:
c.
- 1) T and TC vill be relatively constant u,g 0.,
u.
H w
- 2) Beactor Coolant System pressure vill increase
- 3) Incore thermocouple te=peratures vill increase M09s0273 90918 op jQ Metropohtan Ed: son Company is a Memoer of the General Puahc Utihties System
.o a
- Page Two d.
After some period of increasing Reactor Coolant System pressure and incore thermocouple temperature, the "A" loop vill begin to flow.
This restoration of flow will be slow compared to the present " burps" in the "B" loop It is also expected that the stagnant period vill not be very long since the cooling effect of steaming on "A" is large compared to the envirorne stal heat loss from "B" (which currently results in water movement every h to 6 days ).
It is anticipated that the period of stagnar.t operation to be on the order of hours or most likely =ay si= ply be an oscillation of flow with a T varying between 2-5 degrees F.
Based on this anticipated cyclic behavior, it is felt that the worst case of ther=al cycling of ecmponents is occurring nov during "B" loop " burps. " Furthermore, it in felt that the critical co=ponent is the OTSG. B&W has performed a conservative analysis of this condition ang has determined that the OTSG can withstand at least 10 such cycles.
Therefore, the cyclic cooling mode of operation should also be acceptable for any reasonably foreseeable future (e.g., years).
Pressure control during this mode of operation is discussed in the response to Question 3.
QUESTION 2 Outline tne = odes of cooling for long term u cay heat removal to be called upon, and at what point they vill be used to replace the cyclic Natural Circulation mode via the "A" OTSG.
Include the priority for use of these cooling modes.
RESPONSE
It is expected that by the time cyclic operations occur, TMI-2 vill have installed a mini-decay heat removal syste=.
This small sy stem vill enable heat removal from the Reactor Coolant System without the need for steaming the
'1" OTSG or Natural Circulation.
This system is the long term mode of decay heat removal and is to be operated up to and during Reactor Coolant System draining, react +
vessel head removal and defueling.
The system can.slace Natural Circulation cooling any time after it becomes oper-ational.
If the mini-decay heat removal system becones unavailable for any reason, Met-Ed reco= mends the following backup moces in the priority shown:
a.
Cyclic Natural Circulation stecning "A" Steam Generator.
b.
Cyclic Natural Circulation steaming "A" and "B" Steam Generators.
(r S1 o a.d"y ir)-
ws
~
? age Three Cyclic Natural Circulation using "3" LTC.
c.
d.
LP safety injection and pressurizer venting, if required to allow step (e).
Nor=al plant safet'y grade dect:- heat removal system.
e.
~~
QUESTION 3 Indicate a schedule for revision to those currently active emergency and standard operating procedures (such as EP-34, Loss cf Eatural Circulation and Z-39, Natural Circulation Operation) that vill be necessary as a result of the determined course of action to be followed upon loss of Natural Circulation.
RESPONSE
B&W has already completed reco== ended changes to EP-3h,
" Loss of Natural Circulaticn" and Z-39, " Natural Circulation Operation." These changes cover cyclic Natural Circulation operation.
Additionally, B&W has reco== ended recent changes to Z-63, " Solid Plant Operation." Pressure control under cyclic operation is covered under these recommended changes to EP-3h and Z-63 These 3&W changes have been incorporated into procedures and are now in the review and approval chain.
Sincerely,
'9/
t G
bb [ 7%
/# J. G. Herbein k
Vice President Nuclear Operations
/ tab e
U (.A.51Gb h [ri M'
.