ML19345A384
| ML19345A384 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 11/04/1970 |
| From: | Burger A US ATOMIC ENERGY COMMISSION (AEC) |
| To: | |
| Shared Package | |
| ML19345A382 | List: |
| References | |
| NUDOCS 8011210233 | |
| Download: ML19345A384 (4) | |
Text
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g UNITED STATES
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ATOMIC ENERGY COMMISSICN 4[
wAssisoros. o.c. ros4s
'rsm 5 h0V 4 19/0 File (Docket No.
-29)
, Chief, ORB-1, DRL THRU:
i N
SAFETY REVIEW OF PROPOSED CHANGE No. 95 - YANKEE AIDMIC ELECTRIC COMPA5Y -
YANKEE AIDMIC POWER STA~ LION By letter dated July 15, 1970, and supplements dated July ?2, October 9, and October 23,1970,* Yankee Atomic Electric Company submitted Proposed Change No. 95 to the Technical Specifications to License No. DPR-3 for the Yankee-Rowe reactor.
The proposed change would permit the installa-tion of a capability for long-term recirculation of reactor coolant.
The present Yankee emergency core cooling system does not include a capability for long-term removal of fission product decay heat following a loss-of-coolant accident. During the injection phase, initiated by a low reactor coolant pressure signal, borated water from the safety injection water tank will be delivered to the reactor core by automatic operation of the safety injection pumps. One high pressure pump and two low pressure pu=ps will operate in series or parallel flow, depending on the size of the break.
Even if the entire coolant inventory in the reactor vessel were displaced by blowdown of coolant following a pipe break, it would only require delivery of 40,000 gallons of the 117,000 gallons of borated water stored in the safety injection water tank to reflood the core. Yankee procedures require that af ter the core has been reflooded (in about 7.5 minutes in the worst case of complete voiding of the reactor vessel) the operator is to cut back flow of coolant from the safety injection water tank into the core; he would reduce flow to a rate necessary for making up coolant water inventory loss caused by steam leaving the reactor vessel. The continued formation and dispersal of steam from the coolant in the reactor vessel is the mechanism for removal of fission product decay heat from the fuel which is necessary for the preservation of fuel integrity. The steam which escapes from the reactor vessel through the break gives up its latent heat upon contact with the colder surface of the vapor container steel wall and the condensate runs into the vapor container sump.
Yankee does not presently have a capability fcr transferring the conden-sate from the vapor container sump into the reactor vessel. Therefore, the coolant loss due to the steam leaving the reactor vessel through the break can only be made up by operator action in the manner described above.
Even if the operator conserves the remaining water inventory in the safety injection water tank, by reducing the pumping rate to the minimum necessary, this sole source of make-up water will eventually be
- The safety review includes information contained in Nupplement No. 4 to Proposed Change No. 95 dated October 29, 1970.
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6/0 exhausted in a matter of hours. Thereafter,.because fission product decay heat can no longer be removed, the integrity of the fuel elements l
would be in jeopardy. To eliminate this potential safety problem,' Yankee proposes to install a system for recirculation of reactor coolant from the.
vapor container sump back into the reactor vessel. This system will con-tinuously replace the coolant volume escaping the reactor vessel in the form of vapor and will thus provide the necessary means for indefinitely j
removing the fission product decay heat from the fuel following a loss-j i
of-coolant accident.
l The recirculation loop would utilize existing flowpaths and valves of other i
reactor systems, including the two pumps of the reactor coolant purifica-tion system.
Coolant collected in the vapor container sump will be drawn through a new 4-inch drain line to the suction of the purification pumps and will be returned to the reactor vessel through the safety injection header.
Yankee has shown that the proposed system is capable of providing the necessary coolant flow, even with a single pump operating.and assuming i
30% of -this flow is lost through the pipe break and not available for decay heat removal. We have concluded that the proposed recirculation system will provide the. reactor coolant make-up flow rate necessary for l
Iemoving the fission product -decay heat in the fuel following a loss-of-i coolant accident.
i The available redundancy of active components ':Ln the recirculation system i
will preclude loss of function 'in the event of ' failure of a single acti te j
component. The purification pump motors and redundant motor-operated
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valves will be powered from s,parate electrical buses. -- The recirculation system will. also be' operable from on-site emergency power.
Yankee-proposes -to. install' a single recirculation header which will penetrate'the vapor container through the manhole cover; the header will.
be connected by two parallel branch lines to the suction of the recircu- '
lation pumps. Two motorized valves in' the pump suction lines.which-are located near the pumps will remain closed ~during normal reactor, operation to provide containment isolation.- The installation of a. redundant header-with isolation valves close to the. vapor container would be desirable = to preclude loss of function and to provide isolation capabilities if a poten-tial failure of.the header is considered. Yankee has explored feasible' configurations and has determined that it is not -practical-to. provide-a
. e have concluded W
redundant header; suitable for the intended purpose.
that the possible approaches: visf(l) a second header penetrating the manhole, ;(2) a second. header through a new vapor container. penetration,.
and (3) the use of an existing 3-inch carbon steel drain pipe and
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isolation valve, all within the confines of existing plant features, present serious limitations on the design and construction of a high quality redundant header capability.
We are of the opinion that the proposed design, f abrication and testing of the single header in accordance with the requirements of ASME 31.7 will provide a high quality passive system component capabic of perform-ing its intended function with a large margin of safety. The header will be protected from missiles which might be generated during the loss-of-coolant accident, by an existing concrete barrier inside the vapor container. The header will also be protected from the effects of freezing of collected water by two independent heat trace circuits and insulation on the exposed sections.
All other new pipe sections in the proposed recirculation system will also be designed, f abricated and tested in accordance with the requirements of ASMI 31.7.
All new valves will meet the requirements of the new ASME pump and valve code.
The existing purification pumps to be used for recircula-tion of reactor coolant will have more than the necessary NPSH under peak accident conditions (31.4 f t available head at pump inlet, compared to 14 ft required head at pump inlet for full flow of 200 gpm).
Yankee has proposed pre-operational check-out and testing of the recircu-lation system, including flushing and hydrostatic tests to be performed on all new pipe sections; optrational testing of valves by remote actua-tion to verify full valve stroking and remote position indication.
The penetration of the manhole cover will be tested for leak tightness.
Acceptable operation of the existing pumps used in the recirculation system is being verified during normal operation. These pre-operational tests will verify operability of the recirculation system and are acceptable.
Yankee also proposes technical specifications which define the surveil-lance requirements for the recirculation system.
These requirements I
include tests to verify header integrity, leak tightness of the header penetration at the vapor container manhole and tests to verify opera-l bility of pumps and valves. The scope and frequency of the specified i
tests will allow identification end correction of any component deficiency before it could result in loss of availability c' the recircu-i lation system. The proposed surveillance requirements are considered to be acceptable.
l Yankee will have approved operating procedures, including pump operating curves which will include detailed instructions for the operctor on when-and how to operate the recirculation system.
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Because of the potential consequences of a loss-of-coolant accident with the present lack of long-term core cooling capability, the installation of the proposed recirculation system during the next refueling outage is desirable. We are of the opinion that through implementation of the code requirements in the design, f abrication and testing of the proposed single header installation, in addition to the proposed pre-operational and surveillance tests, the continued integrity of the recirculation header will be assured.
In view of the foregoing, we have concluded that the proposed change will increase the margin of safety for operating the Yankee reactor and that there is reasonable assurance that the health and safety of the public will not be endangered by operation of the Yankee reactor with the proposed change.
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Alf red Burger Operating Reactor Branch #1 Division of Reactor Licensing cc:
D. J. Skovholt R. H. Vollmer R. J. Schemel A. Burger S. A. Teets Mary Jinks (2) b