United States Nuclear Regulatory Commission - Protecting People and the Environment

U.S. Nuclear Regulatory Commission

Monitoring of Radioactive Release Via Storm Drains

HPPOS-007 PDR-9111210092

Title: Monitoring of Radioactive Release Via Storm Drains

See the memorandum from W. J. Dircks to Commissioner

Bradford dated August 28, 1981. This memo states that a

blanket requirement for monitoring storm drains (yard

drains) from every power reactor is unwarranted from a

safety standpoint. The information was also provided to J.

H. Joyner (and others) by L. J. Cunningham in the form of a

memorandum dated September 10, 1981.

Based on an unmonitored release of radioactive water on

July 30, 1981, at the Northern States Power Company's

Monticello Plant and similar occurrences at Millstone, Unit

1 (June 21, 1981) and at the Japanese Tsuruga plant, it was

asked if there were technical reasons for not continuously

monitoring storm drains for radioactivity.

In the Monticello Plant incident, an unreviewed and

improper action by a plant engineer resulted in radioactive

water being used in the cement solidification of

radioactive wastes at a newly-installed portable

solidification system located in the radwaste shipping

building. The building was not designed for this purpose

and did not have floor drains or curbs to prevent spilled

water from escaping. The incident occurred when the

responsible engineer improperly and inadvertently used

slightly radioactive water from the reactor's condensate

storage tank by connecting a rubber hose secured by a hose

clamp to the piping of the concrete mixing system. The

hose came loose and an estimated 2,000 gallons of

radioactive water spilled onto the concrete floor of the

radwaste storage building. The water ran down the sloping

floor, under two closed overhead garage-type doors, and

into the storm drain system.

An estimated 100 gallons of water, contaminated with

4.5x10-7 micro-Ci/ml I-131 and 1.4x10-6 micro-Ci/ml I-133,

entered the Mississippi River at the storm drain outfall.

At the point of release, the isotope concentrations were

approximately 300% of the "maximum permissible

concentration" described in 10 CFR 20 (§§20.1-20.601),

Appendix B, Table II, Column 2, but dilution and dispersion

by the Mississippi River was assumed to have resulted in

essentially instantaneous reduction to non-detectable

concentrations with essentially zero environmental

radiation-dose impact. The remainder of the water entered

the soil or was trapped in the storm drain ditches.

NRR replied that no insurmountable technical reasons

existed with regard to the monitoring of storm drains for

radioactivity. However, practical difficulties in the

automatic sampling or extraction of material for

radioactivity analysis, as well as practical problems of

volumetric measurements from the highly variable stream

flow rates would need to be resolved if the total release

were to be determined. In addition, if it is assumed that

each nuclear power plant is serviced by a single storm

drain system (also called yard drains), the initial cost of

the installation of monitoring equipment per plant would be

approximately 200 to 500 thousand dollars and that the

annual operation and maintenance costs would be 20 to 50

thousand dollars.

Because of the difficulties in monitoring radioactive

discharge into storm sewer drains, the associated costs for

installation and operation, the general knowledge of past

experiences with this particular type of unmonitored

release from reactor operations, and the small potential

effect on public health, it was the opinion of the EDO that

requirements for monitoring storm sewer drains were


Regulatory references: 10 CFR 20.201, 10 CFR 20.1501,

Technical Specifications

Subject codes: 7.3, 7.4, 9.2

Applicability: Reactors

Page Last Reviewed/Updated Thursday, March 29, 2012