Radioactive Waste Systems - Liquid / Gaseous / Solid

Overview

Nuclear power plants usually have 3 types of radioactive waste treatment/handling systems for processing and storing the low-level waste that accumulates as part of normal operations. These systems treat and store:

• Liquid radioactive waste
• Gaseous radioactive waste
• Solid radioactive waste

Liquid Radwaste Systems

The Liquid Radioactive Waste systems are used to collect, process, and store liquids from:

• sumps in potentially contaminated areas as the containment, auxiliary or reactor buildings, and turbine building (if a BWR)
• systems which collect radioactive leakage
• normal discharge from the reactor cooling systems (e.g. during a startup) or other systems which may be connected to the reactor cooling system (e.g. pressurizer relief tank) or located in potentially radioactive contamination areas.

Typically, the liquids are collected in large storage tanks. The liquids are then processed using ion exchangers to remove radioactive and chemical contaminants. Water which meets chemical criteria (e,g, chlorides, fluorides) can be reused. If not, it can be reprocessed. Water which meets regulatory criteria specified in Title 10 Code of Federal Regulations Part 20 can be discharged to the environment. Chemical and radioactivity levels in the tanks and process streams are monitored by sampling. If criteria are not meet, the water may be routed through additional ion exchangers. In some plants reverse osmosis units may be used. At one time, evaporators were used to purify/process water, however, experience with these units showed they were costly to run, susceptible to heat exchanger tube leaks, and insufficiently able to process the quantities of liquids used in a power plant.

The radioactive waste liquid systems are used to provide makeup to:

• Reactor Cooling System
• Chemical & Volume Control System
• Emergency Core Cooling System(s)
• Spent Fuel Storage Pool

Gaseous Radwaste Systems

The Gaseous Radioactive Waste systems are used to collect, process, and store gases from:

• Reactor Cooling System Pressurizer Relief Tank (PWR) - usually nitrogen if pressure is higher than desired
• Chemical and Volume Control System Volume Control Tank (PWR) - usually hydrogen and potentially fission products
• Containment/Drywell (BWR) - usually nitrogen
• Air Ejector exhaust (in a BWR) - usually nitrogen with some hydrogen

The gases are typically routed to storage tanks. When appropriate, compressors may be used to regulate the pressure in the tanks. Sometimes the gaseous system may connected to the the vent header of the tanks in the liquid radwaste systems to regulate pressure to reduce the likelihood of a vacuum being drawn in large tanks.

In systems containing hydrogen, hydrogen recombiners are used to prevent hydrogen levels from building up to flammable or explosive concentrations. Hydrogen recombiners use a catalyst containing platinum and temperatures of ~ 800 to 1000 F to chemically combine the hydrogen with a regulated supply of oxygen to form water.

Solid Radwaste Systems

The Solid Radioactive Waste systems are used to collect, process, and store solids from:

• sump sludges or accumulation
• spent (exhausted) ion exchange resins (as used in waste and reactor water chemical cleanup systems)
• anti-contamination clothing that is no longer usable or can be laundered (many plants clean and reuse this clothing until no longer re-useable
• rags or other materials used in cleaning

These materials are normally stored onsite and periodically shipped to authorized low level waste storage facilities. Special containers are used for shipment of spent resins. Super-compaction is used. Incineration is only performed at authorized facilities (e.g in Tennessee).

Copyright © 1996-2004.  Joseph Gonyeau, P.E.. The Virtual Nuclear Tourist. All rights reserved. Revised: March 15, 2001.