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007 0 7 1977 MEMORANDUM FOR: Division Directors, Office of Nuclear Reactor Regulatten FROM:
Victor Stello, Jr., Director l
Division of Operating Reactors
SUBJECT:
INFORMATION MEMORANDUM NO. 5 CONTR01. OF RADI0 ACTIVITY IN SECONDARY SYSTD4 0F PWR's The control of radioactivity in the secondary system of PWR's has been identified as a potential prchlem for plants with once-through (B&W) steam generators. The incident that identified this problem was the inadvertent urnonitored release of about 3 Cf of I-131 on January 15, 1977, to the Xeowee River from the Oconee Station.
Being a pir.nt of older design, Oconee did not have turbine building sump radiation monitors as presently required for new plants.
Contaminated water of the secondary system was discharged to the turbine-building sump during hydrotesting of the steam-generator tubes. This release from the turbine building sump during plugging of steam generator tubes exceeded the Technical Specification instantaneous release concentration and the calendar quarter Curie quantity. However, it did not exceed the yearly average limits of 10 CFR Part 20 and posed no threat to the public health ami safety.
Recirculating (U-tube) steam generators serve as a hold-up vessel for radioactivity that may be introduced to the secondary side < from steam-generator tube leakage. A blowdown system which ordinarily discharges to the environment, may be diverted to the rad-waste system if the contamination of the secondary fluid exceeds prescribed limits.
l The "once-through" steam generator does not have a discrete liquid-l vapor interface, and does not serve as a hold-up vessel for radio-activity introduced from the primary coolant. These generators are not equipped with a blowdown system; rather full flow condensate polishers are used for maintaining the desired secondary-side water chemistry. Therefore, all of the radioactivity introduced into the secondary side is either entrained in the secondary water system or collected:by the condensate polishers. This type system lends it=
self to the concentration of significant quantities of radioactivity in the secondary systan under conditions of steam generator tube leaks. It is therefore necessary that adequate controls be main-tained on the release of secondary system radioactivity to prevent inadvertent releases as experienced at Oconee.
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l Oconee relied on administrative procedures for controlling the secondary system radioactivity. However, these administrative controls did not appear to be sufficient since another unmoni-tored release occurrad on May 7, 1977.
00R ACTION 00R considers that adequate control can be established by a com-bination of administrative procedures and installed instrumentation.
We have requested the licensee to submit Technical Specification changes for the Oconee Station to:
l 1) include a turbine building sump radiation monitor with an alarm in the control room;
- 2) add a composite water sampler at the outfall of the hold-up basins which receive the water from discardod resins l
from the condensate polishers and the discharge of the turbine building sump prior to release to the Keowee River; and
- 3) add procedural requirements for two independent checks on valve alignment for discharges of radioactive spent resins from the condensate polishers to the receiving storage tank te prevent an inadvertent release of highly contaminated resins to the holdup basins. A radiation monitor interlock system was not required because the condensate polishers do not automatically backwash the spent resins as do most l
new designs.
Other plants with once-through steam generators will be reviewed for similar action by D0R on an as-needed basis (i.e., when steam generator tube leaks become a problem).
The appropriateness of upgrading the Standard Review Plan (Section
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11.5) to include additional controls on secondary side radioactivity l
should be considered. Such action may include radiation monitors l
on the condensate polisher spent resin discharge line with an inter-lock system to prevent the backwash of highly contaminated resins l
to the environment. Many of the condensate clean-up systems have i
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Div,ision Directors OCT 0 7 577 an automatic backwash system initiated on a specified pressure differential (AP) across the resin beds. During periods of steam generator tube leaks, the plant operator's attention to the radiation levels of the condensate clean-up system may be restricted and in-adequate to prevent the inadvertent discharge of highly contaminated resins to the environment.
ensass mised nr L 8*'*
Ytetor Stello, Jr., Dinactor Division of Operating Reactors D0R
Contact:
J. Blar.d, EEB, 28066 cc; E. G. Case S. Hanauer Deputy Directors, NRR Assistant Directors, NRR DOR Branch Chiefs 00R Section Leaders L. Nichols L. Higginbotham J. Collic.;
W. Kreger J. Bland DISTRIBUTION Central files EEB Rdg J. Guibert R. Cudlin SEE PREVIOUS YELLOW FOR OTHER CONCURRENCES.
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