Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
SSINS No.: 6820
Accession No.:
7912190687
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
March 10, 1980
IE Bulletin No. 80-05
VACUUM CONDITION RESULTING IN DAMAGE TO CHEMICAL VOLUME CONTROL SYSTEM
(CVCS) HOLDUP TANKS (SOMETIMES CALLED "CLEAN WASTE RECEIVER TANKS")
In July 1977, IE Circular No. 77-10 identified two instances which resulted
in radioactive gaseous releases when tanks at Trojan and Rancho Seco buckled
due to partial vacuum conditions. The Circular "recommended that you examine
the systems of your reactor facility(ies) that contain low pressure process
or holdup tanks and assure that adequate measures have been taken to protect
against vacuum conditions that could result in tank inward buckling and
failure with subsequent release of radioactive material or cause other
detrimental effects with regard to overall safety of plant operations."
Despite issuance of the Circular, similar events have subsequently occurred
at Turkey Point 3 (LER's 78-17, 79-8, and 79-25) and Salem 1 (LER's 79-67
and 79-76).
The accident at TMI has re-emphasized the importance of protecting against
unexpected radioactive release paths during abnormal conditions. The CVCS
Holdup Tanks (HUT) represent such a path since normal letdown flow is
directed into the CVCS which could add radioactive water to the HUT during
abnormal conditions if fuel failures are present. It is also possible for
the same "abnormal conditions" to cause HUT damage, since there is a greater
probability of operational errors resulting from the combination of manual
and automatic maneuvers made to respond to the abnormal condition. These
errors could cause a partial vacuum to be drawn in the HUT, causing tank
rupture and a release path that bypasses the normally present reactor vessel
and containment barriers to such releases.
We note that both Turkey Point and Salem have elected to install vacuum
breakers in their CVCS-HUTS. As specified by the required Actions below, you
should consider installing vacuum protection in your plants, appropriately
designed to preclude collapse of the tanks. Any proposed or already
installed vacuum protection system must consider the necessity for
precluding adverse effects due to operation or misoperation of the system
(for example, creation of an explosive gas mixture if hydrogen gas is
present in the HUT). Any proposed or already installed system must also
include consideration of the following: (a) tanks with a cover gas must be
able to admit the cover gas fast enough to keep up with the maximum rate of
liquid removal from the tank; (b) vacuum relief valves must be covered by an
acceptable surveillance program; (c) tanks that are located outside must
have adequate freeze protection for the tank and for the vacuum relief
system.
Actions to be taken by all PWR licensees and permit holders:
1. Review the design of all systems that contain low pressure or holdup
tanks that can be valved to contain primary system water. Assure that
adequate
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IE Bulletin No. 80-05 March 10, 1980
Page 2 of 2
measures have been taken to protect against vacuum conditions that
could result in tank damage with the potential for release of
radioactive material or detrimental effects with regard to overall
safety of plant operations.
2. Provide a listing of those systems reviewed in Item 1. Describe any
measures that already exist for those systems to protect against vacuum
conditions, and either: (1) explain why those measures are adequate in
light of the events referenced above, or (2) identify corrective
actions taken or planned to provide acceptable protection, and provide
a schedule for any planned corrective actions.
Licensees of all operating power reactor facilities shall submit the
information requested within 90 days of the date of this letter. Include in
your response to this Bulletin, (a) your schedule for correcting these
items, (b) if reactor operation is to continue prior to correcting
identified deficiencies, include your justification for continued operation.
Licensees with a construction permit shall also submit the design
information requested within 90 days of the date of this letter.
Reports shall be submitted to the Director of the appropriate NRC Regional
Office and a copy forwarded to the Director, NRC Office of Inspection and
Enforcement, Washington, D.C. 20555.
Approved by GAO, B180225 (ROO72): clearance expires 7-31-80. Approval was
given under a blanket clearance specifically for identified generic
problems.
